WO2006115223A1 - Switching power supply circuit - Google Patents

Abstract

A switching power supply circuit according to a first invention wherein a smoothing circuit includes an electromagnetic induction circuit the inductance of which is variable, a control circuit controls the electromagnetic induction circuit so that the inductance of the electromagnetic induction circuit may be a predetermined value when the amount of variation of the current is below a predetermined value and may be below the predetermined value when the amount of variation is a predetermined value or more, whereby the ripple voltage is low and the transient response to a variation of the load current is quick. A switching power supply circuit according to a second invention wherein when the variation of the current is a predetermined value or more because of a load variation and when the current increases or decreases, charge is supplied from a capacitive element to the load or absorbed by the capacitive element from the load by applying a positive or negative voltage to the capacitive element to suppress the vibratory voltage whereby a lower ripple voltage is realized and the transient response to a variation of the load current is quick.

Description

 Specification

 Switching power supply circuit

 Technical field

 TECHNICAL FIELD [0001] The present invention relates to a switching power supply circuit, and more particularly to a switching power supply circuit that supplies power according to a current flowing through a load.

 Background art

 Conventionally, a switching power supply circuit has been used as a power supply circuit for a microprocessor. As the performance of the microprocessor is improved, the load current increases and the change in the load current also increases.

 [0003] A switch-mode generation DC power computer system that provides appropriate power for fluctuations in load current flowing in a microprocessor that requires a large current is known (Patent Document 1).

 [0004] Here, when the load current does not fluctuate due to an increase in the load current, it is required to reduce the ripple voltage of the power supply output from the switching power supply circuit, and when the load current fluctuates, the high-speed transient It is required to respond.

 [0005] In order to reduce the ripple voltage, it is known to use an electromagnetic induction element having a large inductance in the smoothing circuit for smoothing the voltage. In order to respond, it is known to use an electromagnetic induction element with a small inductance in a smooth circuit.

 Patent Document 1: Special Table 2003-533754

 Disclosure of the invention

 Problems to be solved by the invention

However, there is a problem that the low ripple voltage and the high-speed transient response are contradictory performances in the electromagnetic induction element and cannot be realized at the same time.

[0007] The present invention has been made to solve the above-described problems, and provides a switching power supply circuit that has a low ripple voltage and can make a transient response to fluctuations in load current at high speed. Objective. Means for solving the problem

 [0008] In order to achieve the above object, a switching power supply circuit according to a first aspect of the present invention includes switching means for switching and outputting an input direct current voltage, an electromagnetic induction circuit whose capacitance can be changed, and a capacitive element. And a smoothing circuit that smoothes and outputs the output from the switching means, a load current fluctuation detection circuit that detects a change in current flowing through a load connected to the smoothing circuit, and the load current fluctuation detection The electromagnetic induction circuit is controlled so that the inductance of the electromagnetic induction circuit becomes a predetermined value when the fluctuation amount of the current detected by the circuit is less than the predetermined amount, and when the fluctuation amount of the current is equal to or larger than the predetermined amount. And a control circuit that controls the electromagnetic induction circuit so that the inductance of the electromagnetic induction circuit is less than the predetermined value.

 [0009] According to the switching power supply circuit of the first invention, the switching means switches and outputs the input DC voltage, and the smoothing circuit smoothes and outputs the output from the switching means. Then, the load current fluctuation detection circuit detects the fluctuation of the current flowing through the load connected to the smoothing circuit, and the control circuit detects when the fluctuation amount of the current detected by the load current fluctuation detection circuit is less than the predetermined amount. The electromagnetic induction circuit is controlled so that the inductance of the electromagnetic induction circuit becomes a predetermined value, and the electromagnetic induction circuit is controlled so that the inductance of the electromagnetic induction circuit becomes less than the predetermined value when the fluctuation amount of the current is equal to or larger than the predetermined value. To do.

 [0010] Therefore, the smooth circuit includes an electromagnetic induction circuit whose inductance can be changed, and the control circuit electromagnetically controls the electromagnetic induction circuit so that the inductance of the electromagnetic induction circuit becomes a predetermined value when the fluctuation amount of the current is less than the predetermined amount. By controlling the induction circuit and controlling the electromagnetic induction circuit so that the inductance of the electromagnetic induction circuit is less than the predetermined value when the fluctuation amount of the current is greater than or equal to the predetermined amount, the ripple current is low and the load current It is possible to make a transient response to fluctuations at high speed.

[0011] In addition, the switching power supply circuit according to the first invention can further include a holding circuit that holds the state in which the control circuit controls the inductance of the electromagnetic induction circuit to be less than a predetermined value for a predetermined time. . As a result, the holding circuit can adjust the time during which the inductance of the electromagnetic induction circuit is less than the predetermined value. [0012] In addition, the holding circuit according to the first invention can be configured by a switching element and a low-pass filter circuit.

 [0013] The switching power supply circuit according to the first aspect of the present invention is a case where the electromagnetic induction circuit is controlled by the control circuit so that the inductance of the electromagnetic induction circuit is less than a predetermined value, and the load current fluctuation detection circuit When it is detected that the current fluctuates in the increasing direction, a predetermined positive voltage is applied to the other end opposite to one end connected to the load of the capacitive element, and the electromagnetic induction circuit of the electromagnetic induction circuit is applied by the control circuit. When the electromagnetic induction circuit is controlled so that the inductance is less than the predetermined value, and the load current fluctuation detection circuit detects that the current fluctuates in the decreasing direction, A voltage application circuit for applying a predetermined negative voltage to the other end can be further included.

 [0014] According to this configuration, when the electromagnetic induction circuit is controlled by the control circuit so that the fluctuation of the current becomes a predetermined amount or more and the inductance of the electromagnetic induction circuit is less than the predetermined value, and the load current fluctuation When the detection circuit detects that the current fluctuates in an increasing direction, a predetermined positive voltage is applied to the other end opposite to the one end connected to the load of the capacitor element, and the capacitor element Supply charge to the load.

 [0015] In addition, when the electromagnetic induction circuit is controlled by the control circuit so that the fluctuation of the current becomes a predetermined amount or more and the inductance of the electromagnetic induction circuit is less than the predetermined value, and the load current fluctuation detection circuit When it is detected that the current fluctuates in the decreasing direction, a predetermined negative voltage is applied to the other end of the capacitive element to absorb the charge from the load to the capacitive element.

 [0016] Therefore, when load fluctuation occurs and the current fluctuates in the increasing direction or the decreasing direction, charge is supplied or absorbed between the capacitive element and the load to suppress the oscillating voltage. Therefore, a low ripple voltage can be realized, and a transient response can be made to the load current fluctuation at high speed.

[0017] The electromagnetic induction circuit according to the first invention is configured by connecting in parallel a first coil, a second coil, and a switch that is turned on and off by a control circuit. And a parallel circuit connected in series, and the combined inductance when the switch is off can be a predetermined value. As a result, electromagnetic induction can be achieved by turning the switch on and off. The inductance of the circuit can be controlled.

 [0018] In addition, the electromagnetic induction circuit according to the first invention is configured by connecting in series a first coil having a predetermined inductance value, a second coil, and a switch that is turned on and off by the control circuit. And a series circuit connected in parallel to one coil. As a result, the inductance of the electromagnetic induction circuit can be controlled by turning the switch on and off.

 [0019] Further, the electromagnetic induction circuit according to the first invention includes a first coil having an inductance of a predetermined value, a second coil having an inductance of less than a predetermined value, and one end connected to the output terminal of the switching means. The switch can be configured to include a switch whose other end is connected to either the first coil or the second coil by switching by the control circuit. Thus, the inductance of the electromagnetic induction circuit can be controlled by switching the switch.

 [0020] The load current fluctuation detection circuit according to the first invention includes a detection coil that induces a current corresponding to a current flowing through the load, and a resistor that is energized by the current flowing through the detection coil. be able to. As a result, the fluctuation of the current flowing through the load can be detected, and the inductance of the electromagnetic induction circuit can be controlled in accordance with the fluctuation of the current.

 [0021] In addition, the load current fluctuation detection circuit according to the first aspect of the invention includes a detection coil that induces a current corresponding to the current flowing through the load, and a force sword that is commonly connected, and one anode at one end of the detection coil. A first pair of diodes connected and having the other anode connected to the other end of the detection coil and an anode connected in common and one force sword connected to one end of the detection coil and the other force sword connected to the detection coil A second pair of diodes connected to the other end, a resistor having one end connected to the force sword of the first pair of diodes and the other end connected to the anode of the second pair of diodes. Can be configured. As a result, the fluctuation of the current flowing through the load can be detected, and the inductance of the electromagnetic induction circuit can be controlled according to the fluctuation of the current. In addition, the absolute value of current fluctuation can be detected.

[0022] The above switch includes an NMOS transistor, and the control circuit includes a non-inverting amplifier in which a voltage applied to the resistor is input to a non-inverting input terminal, and the output of the non-inverting amplifier The end can be connected to the gate of the NMOS transistor. [0023] In addition, the switching power supply circuit according to the first invention may further include a pulse width modulation circuit that switches the switching means by pulse width modulation according to the current flowing through the load. As a result, an appropriate voltage can be output according to the current flowing through the load.

 [0024] The switching power supply circuit according to the second invention comprises a switching means for switching and outputting the input DC voltage, an electromagnetic induction circuit and a capacitive element, and outputs the switching means power. A smoothing circuit for smoothing and outputting; a load current fluctuation detecting circuit for detecting fluctuations in a current flowing through a load connected to the smoothing circuit; and the current detected by the load current fluctuation detecting circuit. A determination circuit for determining whether or not a fluctuation amount of the current is greater than or equal to a predetermined amount, and when the current fluctuation is determined to be greater than or equal to a predetermined amount by the determination circuit and the load current fluctuation detection When the circuit detects that the current fluctuates in an increasing direction, a predetermined positive voltage is applied to the other end of the capacitive element opposite to the one end connected to the load, and the determination circuit Therefore, when it is determined that the current fluctuation is greater than or equal to a predetermined amount, and when the load current fluctuation detection circuit detects that the current fluctuates in a decreasing direction, A voltage application circuit that applies a predetermined negative voltage to the other end of the capacitive element.

 [0025] According to the switching power supply circuit of the second invention, the switching means switches and outputs the input DC voltage, and the smoothing circuit smooths and outputs the output from the switching means. . Then, the load current fluctuation detection circuit detects the fluctuation of the current flowing through the load connected to the smoothing circuit, and the determination circuit detects that the fluctuation amount of the current detected by the load current fluctuation detection circuit is a predetermined amount or more. Judge whether there is a certain force.

[0026] Then, when it is determined by the determination circuit that the current fluctuation is equal to or greater than the predetermined amount, and the load current fluctuation detection circuit detects that the current fluctuates in the increasing direction. Sometimes, the voltage application circuit applies a predetermined positive voltage to one end connected to the load of the capacitive element and the other end on the opposite side. In addition, when it is determined by the determination circuit that the current fluctuation is equal to or greater than the predetermined amount, and when the load current fluctuation detection circuit detects that the current is changing in the decreasing direction, Depending on the voltage application circuit, A predetermined negative voltage is applied to the other end of the quantity element.

 [0027] Therefore, when the load fluctuation occurs and the fluctuation amount of the current is greater than or equal to a predetermined amount, and the current fluctuates in the increasing direction or decreases, the positive voltage or By applying a negative voltage, charge can be supplied or absorbed between the capacitive element and the load, and the oscillation voltage can be suppressed, so that a low ripple voltage can be realized, and fluctuations in the load current can be achieved. It is possible to make a transient response at high speed.

 The invention's effect

 [0028] As described above, according to the switching power supply circuit of the first invention, the smoothing circuit includes the electromagnetic induction circuit whose inductance can be changed, and when the amount of fluctuation of the current is less than the predetermined amount by the control circuit. The electromagnetic induction circuit is controlled so that the inductance of the electromagnetic induction circuit becomes a predetermined value at a time, and the inductance of the electromagnetic induction circuit is controlled so that the inductance of the electromagnetic induction circuit becomes less than the predetermined value when the fluctuation amount of the current is equal to or larger than the predetermined value. Therefore, it has a low ripple voltage and can make a transient response to a change in load current at high speed. Further, according to the switching power supply circuit of the second invention, when the load fluctuates and the amount of fluctuation of the current is equal to or greater than the predetermined amount, the current fluctuates in the increasing direction or decreases. In this case, by applying a positive or negative voltage to the capacitive element, charge can be supplied or absorbed between the capacitive element and the load, and the oscillation voltage can be suppressed. In addition, it is possible to obtain an effect that a transient response can be made at high speed to fluctuations in the load current.

 BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, the switching power supply circuit 10 according to the first embodiment includes a DC power supply 12 that supplies a DC power supply, and a DC power supply voltage is applied to an output terminal of the DC power supply 12. One input terminal of the switching circuit 14 for switching and outputting is connected. The output terminal of the switching circuit 14 includes an electromagnetic induction circuit whose inductance can be changed, and is connected to the input terminal of the smoothing circuit 16 for smoothing and outputting the switched DC power supply voltage. The output terminal of the smoothing circuit 16 is connected to the input terminal of the load current fluctuation detection circuit 20 that detects fluctuations in the load current flowing through the microprocessor. One output terminal of the load current fluctuation detection circuit 20 is connected to an input terminal of a control circuit 26 described later, and an output terminal of the control circuit 26 is connected to an input terminal of the smoothing circuit 16. When the fluctuation amount of the load current detected by the load current fluctuation detection circuit 20 is equal to or greater than a predetermined amount, the inductance of the electromagnetic induction circuit provided in the smoothing circuit 16 is changed by the output from the control circuit 26. It has become. The other output terminal of the load current fluctuation detection circuit 20 is connected to a load (not shown) via the power supply output terminal 18, and is connected to, for example, a microphone port processor.

 [0031] The power supply output terminal 18 performs pulse width modulation in accordance with the current flowing from the switching power supply circuit 10 to the load, and outputs a signal indicating the modulated pulse width. The input terminal of the pulse width modulation circuit 22 The output terminal of the pulse width modulation circuit 22 is connected to the input terminal of the drive circuit 24 that switches the switching circuit 14 based on the signal from the pulse width modulation circuit 22. The output terminal of the drive circuit 24 is connected to the other input terminal of the switching circuit 14.

 [0032] Here, according to the relationship between the inductance of the electromagnetic induction circuit of the smoothing circuit in the switching power supply circuit and the response characteristic of the output voltage to the fluctuation of the load current, when the inductance of the electromagnetic induction circuit is large, The period of transient response to load current fluctuation is long and the ripple voltage is low. On the other hand, when the inductance is small, the period of transient response to load current fluctuation is short and the ripple voltage is high.

 Next, the circuit configuration of the switching power supply circuit 10 according to the first embodiment of the present invention will be described with reference to FIG.

[0034] One of the DC power supplies 12 is grounded, and the other is connected to the input terminal of the switching circuit 14, and outputs a DC power supply voltage of, for example, 5V. The switching circuit 14 includes a PMOS transistor 30 and an NMOS transistor 32. The drain (D in FIG. 2) of the PMOS transistor 30 is connected to one input terminal of the switching circuit 14, and the PMOS transistor 30 The source (S in FIG. 2) is connected to the output terminal of the switching circuit 14, and the gate of the PMOS transistor 30 (G in FIG. 2) is connected to the other input terminal of the switching circuit 14. The source of the NMOS transistor 32 is grounded, the drain of the NMOS transistor 32 is connected to the output terminal of the switching circuit 14, and the NMOS transistor The gate of the transistor 32 is connected to the other input terminal of the switching circuit 14. Note that one input terminal of the switching circuit 14 is connected to the DC power source 12, and the other input terminal is connected to the output terminal of the drive circuit 24.

 Further, the smoothing circuit 16 includes an electromagnetic induction circuit 34 and a capacitor 36, and the electromagnetic induction circuit 34 has a relatively small inductance (for example, 1 ^ = 100 11) and the first coil 38 and The parallel circuit 40 is connected in series, and the parallel circuit 40 has a relatively large inductance (for example, L = 900 H), and the second coil 42 and the MOS switch 44 including the NMOS transistor are connected in parallel. Connected to and configured. One end of the first coil 38 is connected to one input terminal of the smoothing circuit 16, and the gate of the MOS switch 44 is connected to the other input terminal of the smoothing circuit 16. One input terminal of the smoothing circuit 16 is connected to the output terminal of the switching circuit 14, and the other input terminal is connected to the output terminal of the control circuit 26.

 [0036] The output terminal of the parallel circuit 40 is connected to the output terminal of the smoothing circuit 16 and one end of the capacitor 36, and the other end of the capacitor 36 is grounded.

 [0037] The load current fluctuation detection circuit 20 includes a transformer 46. One end of the primary side coil 46A of the transformer 46 is connected to the input end of the load current fluctuation detection circuit 20, and the primary side coil The other end of 46A is connected to one output end of the load current fluctuation detection circuit 20. One output terminal of the load current fluctuation detection circuit 20 is connected to the power supply output terminal 18.

[0038] Also, a first pair of diodes 48 and 50 are connected to the secondary side coil 46B of the transformer 46 as a detection coil for inducing a current according to the current flowing through the load, and the secondary side The anode of the diode 48 is connected to one end of the coil 46B, the anode of the diode 50 is connected to the other end, and the force swords of the diodes 48 and 50 are connected in common. Further, a second pair of diodes 52 and 54 are connected to the secondary coil 46B, a force sword of the diode 52 is connected to one end of the secondary coil 46B, and a diode is connected to the other end. The power swords of the diodes 54 and 54 are connected, and the anodes of the diodes 52 and 54 are connected in common. In addition, one end force of the resistor 56 is connected to the force sword of the first pair of diodes 48 and 50, and is connected to the other output end of the load current fluctuation detecting circuit 20, and the other end of the resistor 56 is connected to the first end of the resistor 56. Connected to the anode of two pairs of diodes 52, 54 and grounded Yes.

 The control circuit 26 constitutes a non-inverting amplifier using the operational amplifier 58. The non-inverting input terminal of the operational amplifier 58 is connected to the input terminal of the control circuit 26, and the resistance 56 of the load current fluctuation detection circuit 20 is connected. The applied voltage is input to the non-inverting input terminal. Further, the output terminal of the operational amplifier 58 is connected to the output terminal of the control circuit 26, and is connected to the gate of the MOS switch 44. The amplification factor of the control circuit 26, which is a non-inverting amplifier, is such that the output voltage from the operational amplifier 58 becomes a voltage that turns on the MOS switch 44 when the fluctuation amount of the load current exceeds a predetermined amount. The resistance values of the resistor 60 and the resistor 62 are determined so as to obtain this amplification factor.

 [0040] Next, the operation of the present embodiment will be described. An example will be described in which the load connected to the switching power supply circuit 10 fluctuates, the current lout flowing to the load fluctuates from OmA to 100 mA, and fluctuates from 100 mA to OmA.

 [0041] First, the DC power source voltage force output from the DC power source 12 is switched by the switching circuit 14, the output of the switching circuit 14 force is smoothed by the smoothing circuit 16, and the load current from the power source output terminal 18 Flows to the load connected to the power supply output 18. At this time, if the load current lout is OmA and there is no fluctuation in the load current, the current flowing in the primary side coil 46A of the load current fluctuation detection circuit 20 does not change, so the secondary side coil 46B is not inducted. The voltage output from the load current fluctuation detection circuit 20 is 0, no voltage is output from the control circuit 26 to the gate of the MOS switch 44 of the electromagnetic induction circuit 34, and the inductance of the electromagnetic induction circuit 34 is This is the combined inductance of the inductance of the coil 38 and the inductance of the second coil 42. Therefore, the inductance of the electromagnetic induction circuit 34 of the smoothing circuit 16 increases and the ripple voltage decreases.

[0042] Next, when the load connected to the power supply output terminal 18 becomes small and the load current lout fluctuates to 100mA, the current flowing through the primary side coil 46A of the load current fluctuation detection circuit 20 fluctuates, and the secondary current As shown in Fig. 3A, current flows in the order of diode 48, resistor 56, diode 52, and secondary coil 46B, and the current is detected from the load current fluctuation detection circuit 20 as shown in Fig. 3A. Is output. This predetermined voltage is input to the operational amplifier 58, and the amplified voltage (Vcont in FIG. 2) is transferred from the control circuit 26 to the electromagnetic induction circuit 34. When the MOS switch 44 is input to the gate and a predetermined voltage is input to the gate, the drain and source of the MOS switch 44 are energized and turned on, so the inductance of the electromagnetic induction circuit 34 is It is equal to the inductance of coil 38. Therefore, the inductance of the electromagnetic induction circuit 34 of the smoothing circuit 16 becomes small.

 Then, the pulse width modulation circuit 22 narrows the switching pulse width of the switching circuit 14 via the drive circuit 24 based on the changed load current. When the output with the narrowed pulse width is smoothed by the smoothing circuit 16, the inductance of the electromagnetic induction circuit 34 is small, so that it responds transiently to fluctuations in the load current, Reduce the voltage of the current flowing through the load (Vout in Figure 2).

 [0044] When the load connected to the power supply output terminal 18 becomes large and the load current lout fluctuates to 100 mA force OmA, the current flowing through the primary coil 46A of the load current fluctuation detection circuit 20 fluctuates. As shown in Fig. 3B, the secondary coil 46B is inducted and current flows in the order of the diode 50, resistor 56, diode 54, and secondary coil 46B. Is output. This predetermined voltage is input to the operational amplifier 58, the amplified voltage Vcont is input from the control circuit 26 to the gate of the MOS switch 44 of the electromagnetic induction circuit 34, and the drain and source of the MOS switch 44 are energized. Therefore, the inductance of the electromagnetic induction circuit 34 is equal to the inductance of the first coil 38, and the inductance of the electromagnetic induction circuit 34 of the smoothing circuit 16 is small.

[0045] Then, the pulse width modulation circuit 22 widens the switching pulse width of the switching circuit 14 via the drive circuit 24 based on the changed load current. When the output with a wide pulse width is smoothed by the smoothing circuit 16, the inductance of the electromagnetic induction circuit 34 is small, so that it responds transiently to fluctuations in the load current, Increase the voltage Vout of the current flowing through the load.

Next, simulation results of changes in the voltage Vcont output from the control circuit 26 when the load current fluctuates will be described with reference to FIGS. 4A and 4B. As shown in Fig. 4A, when the voltage fluctuates discretely from OmA to 100 mA, the voltage Vcont also fluctuates almost discretely. circuit High-speed transient response with 16 outputs is realized. In addition, as shown in FIG. 4B, when the voltage gradually changes from OmA to 10 OmA, the voltage Vcont also changes gradually. This reduces the inductance of the electromagnetic induction circuit 34, thereby reducing the smoothness. A fast transient response of the output of circuit 16 is realized.

 Next, the simulation result of the response characteristic of the voltage output from the switching power supply circuit 10 when the load current fluctuates will be described with reference to FIG. When the inductance L of the electromagnetic induction circuit 34 is 100 μΗ, the load current fluctuates and the force response time (the time it takes for the load current fluctuation force voltage fluctuation to converge within the ripple voltage) is 1 45 ms, when the inductance L of the electromagnetic induction circuit 34 is ImH 2. 45 ms. On the other hand, in the switching power supply circuit 10 according to this embodiment, the load current fluctuation is detected by the load current fluctuation detection circuit 20, the MOS switch 44 is turned on by the control circuit 26, and the inductance of the electromagnetic induction circuit 34 is changed. When 100 / z H, the load current fluctuates and the response time of force is 1.54 ms, which is as short as when the inductance is fixedly small, ensuring a transient response time. .

 [0048] Simulation results of the ripple voltage characteristics of the voltage output from the switching power supply circuit 10 will be described with reference to FIG. When the inductance L of the electromagnetic induction circuit 34 is ImH, the ripple voltage is 0.94 mVpp (mV peak—to—peak: voltage from the minimum to the maximum in the voltage waveform), and the ripple is when the inductance L is 100 μΗ. The voltage is 3.2mVpp. On the other hand, in the switching power supply circuit 10 which is effective in the present embodiment, when the MOS switch 44 is turned off by the control circuit 26 in which the load current does not fluctuate and the combined inductance of the electromagnetic induction circuit 34 becomes ImH, The ripple voltage is 2.8 mVpp, and the ripple voltage can be made lower than when the inductance is fixedly large.

[0049] As described above, according to the switching power supply circuit according to the first embodiment of the present invention, the smoothing circuit includes the electromagnetic induction circuit whose inductance can be changed, and the load is controlled by the control circuit. The electromagnetic induction circuit is controlled so that the inductance of the electromagnetic induction circuit is increased when the fluctuation amount of the current is less than the predetermined amount, and the electromagnetic induction circuit is reduced so that the inductance of the electromagnetic induction circuit is reduced when the fluctuation amount of the current is the predetermined amount or more. By controlling the induction circuit, It is a pull-up voltage and can make a transient response at high speed to fluctuations in load current.

 [0050] Inductance of the electromagnetic induction circuit can be controlled by turning on and off the MOS switch of the electromagnetic induction circuit.

[0051] Further, the load current fluctuation detection circuit can detect the fluctuation of the current flowing through the load, and can control the inductance of the electromagnetic induction circuit according to the fluctuation of the current.

[0052] Further, the pulse width modulation circuit can output an appropriate voltage according to the current flowing through the load.

 [0053] Next, a second embodiment of the present invention will be described. Note that portions similar to those in the first embodiment are denoted by the same reference numerals and description thereof is omitted. In the second embodiment, the circuit configuration of the electromagnetic induction circuit of the smoothing circuit is different from that of the first embodiment. As shown in FIG. 7, the electromagnetic induction circuit 134 provided in the smoothing circuit 116 of the switching power supply circuit 110 according to the second embodiment has a relatively large inductance (for example, the inductance is lmH). One coil 138 and a series circuit 140 are connected in parallel. The series circuit 140 is configured by connecting a second coil 142 and a MOS switch 144 composed of an NMOS transistor in series, and the drain of the MOS switch 144 is connected to one input terminal of the electromagnetic induction circuit 134. The source is connected to one end of the second coil 142. The gate is connected to the output terminal of the load current fluctuation detection circuit 20 via the other input terminal of the electromagnetic induction circuit 134. Since other configurations are the same as those in the first embodiment, description thereof is omitted.

 Next, the operation of the second embodiment will be described. First, when the load current lout force is OmA and the load current does not fluctuate, the voltage output from the load current fluctuation detection circuit 20 becomes 0, and the control circuit 26 applies the voltage to the gate of the MOS switch 144 of the electromagnetic induction circuit 134. No voltage is output, the MOS switch 144 is turned off, and the inductance of the electromagnetic induction circuit 134 is equal to the inductance of the first coil 138. Therefore, the inductance of the electromagnetic induction circuit 134 of the smoothing circuit 116 increases and the ripple voltage decreases.

[0055] Next, when the load connected to the power supply output terminal 18 decreases and the load current lout fluctuates to 100 mA, a predetermined voltage is output from the load current fluctuation detection circuit 20 and the amplified voltage Vcont is controlled. Circuit 26 force is also input to the gate of MOS switch 144 of electromagnetic induction circuit 134 Since the drain and source of the MOS switch 144 are energized and turned on, assuming that the inductance of the first coil 138 is Ll and the inductance of the second coil 142 is L2, the inductance of the electromagnetic induction circuit 134 is Is obtained by the following equation.

 L = 1 / (1 / L1 + 1 / L2)

 Therefore, the inductance of the electromagnetic induction circuit 134 of the smoothing circuit 116 is reduced.

 [0056] Then, the pulse width modulation circuit 22 narrows the switching pulse width of the switching circuit 14 via the drive circuit 24 based on the changed load current. When the output with the narrowed pulse width is smoothed by the smoothing circuit 16, the inductance of the electromagnetic induction circuit 134 is reduced, so that the transient response at high speed to the fluctuation of the load current Reduce the voltage Vout of the current flowing through the load.

 [0057] Next, when the load connected to the power output terminal 18 becomes large and the load current lout fluctuates to 100 mA, the load current fluctuation detection circuit 20 outputs a predetermined voltage, and the amplified voltage Since Vcont is input from the control circuit 26 to the gate of the MOS switch 144 of the electromagnetic induction circuit 134 and the drain and source of the MOS switch 144 are energized and turned on, the inductance of the electromagnetic induction circuit 34 is calculated by the above equation. Therefore, the inductance of the electromagnetic induction circuit 134 of the smoothing circuit 116 becomes small.

 [0058] Then, in the pulse width modulation circuit 22, the switching pulse width of the switching circuit 14 is widened via the drive circuit 24 based on the changed load current! Then, since the inductance of the electromagnetic induction circuit 134 is small, a transient response is quickly made to the fluctuation of the load current, and the voltage Vout of the current flowing through the load is lowered.

[0059] As described above, according to the switching power supply circuit according to the second embodiment, the smooth circuit includes the electromagnetic induction circuit whose inductance can be changed, and the amount of change in the load current is controlled by the control circuit. The electromagnetic induction circuit is controlled so that the inductance of the electromagnetic induction circuit is increased when the current is less than the predetermined amount, and the electromagnetic induction is controlled so that the inductance of the electromagnetic induction circuit is decreased when the current fluctuation amount is the predetermined amount or more. By doing so, the ripple voltage is low and a transient response can be made to the load current fluctuation at high speed.

Next, a third embodiment of the present invention will be described. The same as the first embodiment About the same part, the same code | symbol is attached | subjected and description is abbreviate | omitted. In the third embodiment, the circuit configuration of the electromagnetic induction circuit of the smoothing circuit is different from that of the first embodiment. As shown in FIG. 8, the electromagnetic induction circuit 234 provided in the smoothing circuit 216 of the switching power supply circuit 210 according to the third embodiment has a relatively small inductance (for example, an inductance) L = 100H) and the first coil 244 and the second coil 248 having an inductance larger than the inductance of the first coil 244 (for example, inductance L = lmH). The switching switch 238 includes an NMOS transistor 242 and a PMOS transistor 246. The drains of the NMOS transistor 242 and the PMOS transistor 246 are connected to one input terminal of the electromagnetic induction circuit 234, and the NMOS transistor 242 Is connected to the first coil 244, and the source of the PMOS transistor 246 is connected to the second coil 248. The gates of the NMOS transistor 242 and the PMOS transistor 246 are connected to the output terminal of the load current fluctuation detection circuit 20 through the other input terminal of the electromagnetic induction circuit 234. Since other configurations are the same as those in the first embodiment, description thereof is omitted.

 Next, the operation of the third exemplary embodiment will be described. First, when the load current lout force is OmA and the load current does not fluctuate, the voltage output from the load current fluctuation detection circuit 20 becomes 0, and the NMOS transistor 242 and P MOS of the electromagnetic induction circuit 234 from the control circuit 26 Since no voltage is output to the gate of the transistor 246, only the drain and source of the PMOS transistor 246 are energized, the PMOS transistor 246 is turned on, and the NMOS transistor 242 is turned off, so that the electromagnetic induction circuit 234 The inductance is equal to the inductance of the second coil 244. Therefore, the inductance of the electromagnetic induction circuit 234 of the smoothing circuit 216 increases and the ripple voltage decreases.

[0062] Next, when the load connected to the power supply output terminal 18 becomes small and the load current lout fluctuates to 100 mA, a predetermined voltage is output from the load current fluctuation detection circuit 20 and the amplified voltage Vcont is controlled. Circuit 26 force Input to the gate of NMOS transistor 242 and PMOS transistor 246 of electromagnetic induction circuit 234, and only the drain and source of NMOS transistor 242 are energized, NMOS transistor 242 is turned on, and PMOS transistor 246 is turned off Therefore, the inductance of the electromagnetic induction circuit 234 is the inductance of the first coil 244. Equal to cactance. Accordingly, the inductance of the electromagnetic induction circuit 234 of the smoothing circuit 216 is reduced.

 Then, the pulse width modulation circuit 22 narrows the switching pulse width of the switching circuit 14 via the drive circuit 24 based on the changed load current. When the output with the narrowed pulse width is smoothed by the smoothing circuit 216, the inductance of the electromagnetic induction circuit 234 is small, so that the transient response to the load current fluctuation is fast. Reduce the voltage Vout of the current flowing through the load.

 [0064] Next, when the load connected to the power supply output terminal 18 increases and the load current lout fluctuates to 100 mA, the load current fluctuation detection circuit 20 outputs a predetermined voltage, and the amplified voltage Vcont is input from the control circuit 26 to the gates of the NMOS transistor 24 2 and the PMOS transistor 246 of the electromagnetic induction circuit 234, and only the drain-source of the NMOS transistor 242 is energized to turn on, and the drain-source of the PMOS transistor 246 Since the coil is turned off without being energized, the inductance of the electromagnetic induction circuit 234 is equal to the inductance of the first coil 244. Accordingly, the inductance of the electromagnetic induction circuit 234 of the smoothing circuit 216 is reduced.

 Then, the pulse width modulation circuit 22 expands the switching pulse width of the switching circuit 14 via the drive circuit 24 based on the fluctuating load current, and the smoothing circuit 216 Since the inductance of the electromagnetic induction circuit 234 is small, the voltage Vout of the current flowing through the load is reduced by making a transient response to the load current fluctuation at high speed.

[0066] As described above, according to the switching power supply circuit according to the third embodiment, the smooth circuit includes the electromagnetic induction circuit whose inductance can be changed, and the amount of change in the load current is controlled by the control circuit. The electromagnetic induction circuit is controlled so that the inductance of the electromagnetic induction circuit increases when the current is less than the predetermined amount, and the electromagnetic induction circuit is reduced so that the inductance of the electromagnetic induction circuit decreases when the amount of current fluctuation is equal to or greater than the predetermined amount. By controlling it, it has a low ripple voltage and can respond to transients of load current at high speed.

Further, the inductance of the electromagnetic induction circuit can be changed by turning on and off the PMOS transistor and the NMOS transistor of the electromagnetic induction circuit. [0068] Next, a fourth embodiment will be described. Note that parts similar to those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

 [0069] The fourth embodiment is different from the first embodiment in that the MOS switch has an on-time adjusted so as to continue for a predetermined time.

 As shown in FIG. 9, a holding circuit 328 is provided between the control circuit 326 and the smoothing circuit 16 of the switching power supply circuit 310 according to the fourth embodiment. The holding circuit 328 includes an NMOS transistor 370 as a switch element, a DC power source 372, a low-pass filter circuit 378 including a capacitor 374 and a resistor 376.

 The gate of the NMOS transistor 370 is connected to the output terminal of the operational amplifier 58, the drain is connected to the DC power supply 372, and the source is connected to one end of the capacitor 374. One end of the capacitor 374 is connected to the gate of the MOS switch 44, and the other end is grounded. One end of the resistor 376 is connected to the gate of the MOS switch 44 and one end of the capacitor 374, and the other end is grounded.

 Next, the operation of the fourth embodiment will be described. First, when the load connected to the power supply output 18 becomes small and the load current lout changes from OmA to 100mA, the current flowing through the primary coil 46A of the load current fluctuation detection circuit 20 fluctuates. The side coil 46B is inducted to generate a current, and a predetermined voltage is output from the load current fluctuation detection circuit 20, and this predetermined voltage is input to the operational amplifier 58 and amplified. The amplified voltage is input from the operational amplifier 58 to the gate of the NMOS transistor 370, and when a predetermined voltage is input to the gate, the drain and source of the NMOS transistor 370 is energized. A predetermined voltage is applied to the capacitor 374, and the capacitor 374 is charged.

 [0073] The voltage of the electric charge stored in the capacitor 374 (Vcont in FIG. 9) is output to the gate of the MOS switch 44 of the electromagnetic induction circuit 34, and the predetermined voltage is input to the gate. Then, since the drain and source of the MOS switch 44 are energized and turned on, the inductance of the electromagnetic induction circuit 34 becomes equal to the inductance of the first coil 38 and the electromagnetic induction of the smoothing circuit 16 The inductance of circuit 34 is reduced.

Then, the electric charge stored in capacitor 374 is discharged to resistor 376 and capacitor 374 When the voltage Vcont of the electric charge stored in the capacitor becomes less than the predetermined voltage, the drain-source of the MOS switch 44 is turned off and no current flows.Therefore, the inductance of the electromagnetic induction circuit 34 is the inductance of the first coil 38. And the inductance of the second coil 42, and the inductance of the electromagnetic induction circuit 34 of the smoothing circuit 16 increases. Therefore, the holding circuit 328 holds the state where the drain-source of the MOS switch 44 is turned on for a predetermined time.

 Next, simulation results of response characteristics of the voltage Vcont output from the holding circuit 328 and the voltage output from the switching power supply circuit 310 when the load current fluctuates will be described with reference to FIG. As shown in Fig. 10, when the load current varies discretely from OmA to 100mA, the control voltage Vcont also varies almost discretely, and then the voltage Vcont gradually decreases. As a result, the state where the inductance of the electromagnetic induction circuit 34 is reduced is held for a predetermined time. Note that the holding time can be adjusted by adjusting the slope when the voltage Vcont gradually decreases by the capacitance C of the capacitor 374 and the resistance value R of the resistor 376.

 [0076] In addition, the response time (the time it takes for the voltage fluctuation to converge within the ripple voltage from the fluctuation in the load current) due to the fluctuation in the load current is the inductance L of the electromagnetic induction circuit. When the load current fluctuates, the oscillating voltage when the load current fluctuates is almost the same as when the inductance L is fixed (eg 100 H). ) Is getting smaller.

 Specifically, as shown in FIG. 11A, when the inductance L of the electromagnetic induction circuit 34 is 100 H, the load current fluctuates and the force response time is 2. Oms. In the switching power supply circuit 310 according to the embodiment, the load current fluctuation is detected by the load current fluctuation detection circuit 20, the MOS switch 44 is turned on by the control circuit 326 and the holding circuit 328, and the inductance of the electromagnetic induction circuit 34 is, for example, 3 H In this case, as shown in Fig. 11B, the load current fluctuates and the force response time is 1.20 ms, and the inductance is fixed, ensuring a shorter transient response time. And

[0078] When the inductance L of the electromagnetic induction circuit is fixedly 100 H, the oscillating voltage when the load current changes is 40 mV. On the other hand, the switching power applied to this embodiment is In the source circuit 310, the load current fluctuation is detected by the load current fluctuation detection circuit 20, the MOS switch 44 is turned on by the control circuit 326 and the holding circuit 328, and the inductance of the electromagnetic induction circuit 34 becomes, for example, 3 μΗ. The oscillating voltage is 23 mV, and the oscillating voltage can be made lower than when the inductance is fixed.

 [0079] Simulation results of the ripple voltage characteristics in the voltage output from switching power supply circuit 310 will be described with reference to FIG. When the inductance L of the electromagnetic induction circuit 34 is 100 H, the ripple voltage is 0.9 mVpp, and when the inductance L is, the ripple voltage is 4.7 mVpp. On the other hand, in the switching power supply circuit 310 that is effective in this embodiment, the control circuit 326 and the holding circuit 328 in which the load current does not fluctuate, thereby turning off the MOS switch 44, and the combined inductance of the electromagnetic induction circuit 34 is reduced. When it reaches 100 H, the ripple voltage is 1.2 mVpp, and the ripple voltage can be lowered as in the case where the inductance is fixedly large.

 [0080] As described above, according to the switching power supply circuit according to the fourth embodiment, the holding circuit maintains the state of controlling the inductance of the electromagnetic induction circuit to be low for a predetermined time. Therefore, the time during which the inductance of the electromagnetic induction circuit is lowered can be adjusted.

 [0081] In the above-described embodiment, the inductance that is variable in inductance using the force MEMS technology described as an example in which the inductance is changed by combining a plurality of coils is used for the switching power supply circuit, and the inductance is reduced. Let's change it.

 Next, a fifth embodiment will be described. Note that parts having the same configurations as those of the first embodiment are denoted by the same reference numerals and description thereof is omitted.

 In the fifth embodiment, the first point is that a predetermined voltage is applied to the capacitor of the smoothing circuit in accordance with the fluctuation of the current detected by the load current fluctuation detection circuit. It differs from the embodiment.

The power supply circuit for a microprocessor has a demand for low ripple (stability) due to an increase in load current and a demand for high-speed response due to an increase in load current fluctuation. In particular, when the load fluctuates, high-speed response is the first requirement, but low ripple is also required. Because of these requirements, low ripple during load fluctuations, which was difficult with conventional circuits, is achieved. The method will be described in the present embodiment.

 As shown in FIG. 13, in the switching power supply circuit 410 according to the fifth embodiment, one of the three output terminals of the load current fluctuation detection circuit 420 is connected to the input terminal of the voltage application circuit 428 described later. The other output terminal of the load current fluctuation detection circuit 420 is connected to the input terminal of the control circuit 426 as a judgment circuit, and the output terminal of the control circuit 426 is connected to one input terminal of the voltage application circuit 428. It has been.

 [0086] The output terminal of the voltage application circuit 428 is connected to one input terminal of the smoothing circuit 416, and the voltage application circuit according to the fluctuation of the load current detected by the load current fluctuation detection circuit 420 A predetermined voltage is applied to a capacitor provided in the smoothing circuit 416 from 428.

 Next, the circuit configuration of the switching power supply circuit 410 according to the fifth embodiment of the present invention will be described with reference to FIG.

 The smoothing circuit 416 includes an electromagnetic induction circuit 434 and a capacitor 436, and the electromagnetic induction circuit 434 includes a coil 438. One end of the coil 438 is connected to one end of the capacitor 436 and one input terminal of the smoothing circuit 416, and the other end of the coil 438 is connected to the output terminal of the smoothing circuit 416. Further, the other input end of the smoothing circuit 416 is connected to the other end of the capacitor 436.

 In addition, the control circuit 426 is configured by a non-inverting amplifier using the operational amplifier 58, and the non-inverting input terminal of the operational amplifier 58 is connected to one input terminal of the voltage application circuit 428 to detect the load current fluctuation. The voltage applied to the resistor 56 of the circuit 420 is input to the non-inverting input terminal, and the output terminal of the operational amplifier 58 is connected to one input terminal of the voltage application circuit 428.

The voltage application circuit 428 includes a non-inverting amplifier using the operational amplifier 470 and an inverter 472. The non-inverting input terminal force of the operational amplifier 470 is connected to the load current via one input terminal of the voltage application circuit 428. It is connected to one end of the secondary coil 46B of the fluctuation detection circuit 420, and the voltage at one end of the secondary coil 46B when a current is generated in the secondary coil 46B is the non-inverting input terminal. To be input. The output terminal of operational amplifier 470 is connected to one input terminal of inverter 472, and the output terminal of operational amplifier 58 is connected to inverter. Connected to the other input terminal of the 472.

The output terminal of the inverter 472 is connected to the non-inverting input terminal of the operational amplifier 474 and is connected to the other end of the capacitor 436 of the output terminal force smoothing circuit 416 of the operational amplifier 474.

 Note that the amplification factor of the operational amplifier 58 is determined by the resistance values of the resistors 60 and 62, and the amplification factor of the operational amplifier 470 is determined by the resistance values of the resistors 476 and 478.

 Next, the operation of the switching power supply circuit 410 according to the fifth embodiment will be described. First, when the load connected to the power supply output terminal 18 becomes small and the load current lout changes to OmA force of 100mA, the output voltage Vout oscillates greatly. At this time, the current flowing through the primary side coil 46A of the load current fluctuation detection circuit 20 fluctuates, the secondary side coil 46B is dielectrically generated, and a current is generated, and a positive voltage is input to the non-inverting input terminal of the operational amplifier 470. Then, a positive voltage is amplified from the operational amplifier 470 and output to the inverter 472.

 In addition, a predetermined voltage is output from the load current fluctuation detection circuit 420 to the control circuit 426, and the predetermined voltage is input to the operational amplifier 58, amplified, and input to the inverter 472.

 As shown in FIG. 15, the inverter 472 applies a positive voltage to one end of the capacitor 436 via the operational amplifier 474 in accordance with the fluctuation in the increasing direction of the current.

 At this time, as shown in FIG. 16A, by increasing the voltage at one end of the capacitor 436, the charge stored in the capacitor 436 is supplied to the load due to the relationship of Q = CV, and the voltage at the load is Reduce drop.

 Next, when the load connected to the power supply output terminal 18 becomes large and the load current lout fluctuates to 100 mA, the output voltage Vout greatly oscillates. At this time, the current flowing through the primary side coil 46A of the load current fluctuation detection circuit 20 fluctuates, the secondary side coil 46B is dielectrically generated, and a current is generated. A negative voltage is input to the non-inverting input terminal of the operational amplifier 470. The negative voltage is amplified from op amp 470 and output to inverter 472.

In addition, a predetermined voltage is output from the load current fluctuation detection circuit 420 to the control circuit 426, and the predetermined voltage is input to the operational amplifier 58, amplified, and input to the inverter 472. The

 Then, as shown in FIG. 17, the inverter 472 applies a negative voltage to one end of the capacitor 436 via the operational amplifier 474 in accordance with the fluctuation in the current decreasing direction.

 [0100] At this time, as shown in FIG. 16B, by lowering the voltage at one end of the capacitor 436, the charge accumulated in the load is absorbed by the capacitor 436 due to the relationship of Q = CV. Reduce the voltage drop.

 [0101] With the above-described operation, it is possible to suppress a change in the amount of charge in the load and reduce the oscillation voltage, that is, the ripple voltage when the load changes. Here, simulation results of changes in the voltage Vr applied to one end of the capacitor 436 and the output voltage Vout when the load current lout fluctuates in the increasing direction will be described with reference to FIG.

 [0102] When the load current lout changes from OA to 500mA and no voltage is applied to the capacitor, the oscillating voltage is 253mV. On the other hand, when the voltage at one end of the capacitor 436 is raised to 0 V force, 0.4, the oscillating voltage is 180 mV. Thus, it can be seen that when the voltage at one end of the capacitor 436 is increased, the oscillation voltage becomes smaller. In particular, the output voltage Vout immediately after a load change decreases to 2.3 IV when no voltage is applied to the capacitor, whereas 2.3 V and 40 mV when the voltage at one end of the capacitor 436 is increased. It turns out that it becomes high.

 [0103] Further, simulation results of changes in the voltage Vr and the output voltage Vout applied to the capacitor 436 when the load current lout fluctuates in the decreasing direction will be described with reference to FIG.

 [0104] When the load current lout changes to 500mA force OA, and no voltage is applied to the capacitor, the oscillation voltage is 256mV. On the other hand, when the voltage at one end of the capacitor 436 is lowered from 0 V to −0. IV, the oscillation voltage is 180 mV. Thus, it can be seen that the oscillation voltage decreases when the voltage at one end of the capacitor 436 is lowered. In particular, the output voltage Vout immediately after a load change rises to 2.69 V when no voltage is applied to the capacitor, whereas when the voltage at one end of the capacitor 436 is lowered, it is 2.64 V and 50 mV. It turns out that it becomes low.

As described above, according to the switching power supply circuit according to the fifth embodiment, the negative When the load fluctuates and the current fluctuates greatly in the increasing direction or greatly decreases, the positive or negative voltage is applied to the capacitor to raise or lower the voltage at one end of the capacitor. By doing so, charge can be supplied or absorbed between the capacitor and the load, and fluctuations in the amount of charge at the load can be suppressed to suppress the oscillation voltage, so that a low ripple voltage can be realized. .

 In the above-described embodiment, the switching power supply circuit uses a capacitor having a variable capacitance using force MEMS technology described as an example in which a voltage is applied to the capacitor when the load current fluctuates. Try to supply and absorb the charge from the load.

 [0107] Next, a sixth embodiment will be described. Note that the same components as those in the first embodiment, the fourth embodiment, and the fifth embodiment are denoted by the same reference numerals, and description thereof is omitted.

 [0108] In the sixth embodiment, the MOS switch is turned on so that the ON state is maintained for a predetermined time, and the electromagnetic induction circuit includes a coil and a coil with a switch. The fifth embodiment is different from the fifth embodiment in that it is connected in series.

 As shown in FIG. 20, in the switching power supply circuit 510 according to the sixth embodiment, a holding circuit 328 is provided between the control circuit 526 and the smoothing circuit 516, and the load One of the three output terminals of the current fluctuation detection circuit 420 is connected to the input terminal of the voltage application circuit 428, and the other output terminal of the load current fluctuation detection circuit 420 is connected to the input terminal of the control circuit 526. ing.

 [0110] Other configurations are the same as those of the first embodiment, the fourth embodiment, and the fifth embodiment, and thus description thereof is omitted.

 Next, the operation of the switching power supply circuit 510 according to the sixth embodiment will be described. First, when the load connected to the power supply output terminal 18 is reduced and the load current lout changes to OmA force of 100 mA, the secondary coil 46B of the load current fluctuation detection circuit 420 is dielectrically induced, and a positive voltage is output from the operational amplifier 470. Amplified and output to inverter 472. In addition, a predetermined voltage is output from the load current fluctuation detection circuit 420 to the control circuit 526, and the predetermined voltage is input to the operational amplifier 58, amplified, and input to the inverter 472.

[0112] Then, in accordance with the fluctuation in the increasing direction of the load current, the inverter 472 includes an operational amplifier 4 A positive voltage is applied to one end of capacitor 436 via 74.

[0113] Further, when the amplified voltage is input from the operational amplifier 58 to the gate of the NMOS transistor 370 and the drain and source of the NMOS transistor 370 are energized, the predetermined voltage Vcont is also electromagnetically applied to the output terminal force of the holding circuit 328. Input to the gate of MOS switch 44 of induction circuit 34, MOS switch 44 is turned on, and the inductance of electromagnetic induction circuit 34 becomes equal to the inductance of first coil 38, and electromagnetic induction circuit 34 of smoothing circuit 516 The inductance of this becomes smaller.

 [0114] When the charge stored in the capacitor 374 is discharged to the resistor 376 and the voltage Vcont of the charge stored in the capacitor 374 becomes less than a predetermined voltage, the drain-source between the MOS switch 44 is turned off. As a result, no current is applied, and the inductance of the electromagnetic induction circuit 34 of the smoothing circuit 516 is increased.

 [0115] When the load connected to the power supply output terminal 18 increases and the load current lout fluctuates to 100 mA force OmA, the secondary coil 46B of the load current fluctuation detection circuit 20 is inducted, and the operational amplifier 470 A negative voltage is input to the non-inverting input terminal, and the negative voltage is amplified from the operational amplifier 470 and output to the inverter 472.

 [0116] Also, a predetermined voltage is output from the load current fluctuation detection circuit 420 to the control circuit 426, and this predetermined voltage is input to the operational amplifier 58 and amplified, and then input to the inverter 472 to decrease the current. The inverter 472 applies a negative voltage to one end of the capacitor 436 via the operational amplifier 474.

 [0117] Further, when the amplified voltage is input from the operational amplifier 58 to the gate of the NMOS transistor 370 and the drain and source of the NMOS transistor 370 are energized, the predetermined voltage Vcont is also applied to the output terminal force of the holding circuit 328. Input to the gate of MOS switch 44 of electromagnetic induction circuit 34, MOS switch 44 is turned on, the inductance of electromagnetic induction circuit 34 is equal to the inductance of first coil 38, and electromagnetic induction circuit of smoothing circuit 516 The inductance of 34 is reduced.

[0118] Then, when the electric charge stored in the capacitor 374 is discharged to the resistor 376 and the voltage Vcont of the electric charge stored in the capacitor 374 becomes less than a predetermined voltage, the drain-source between the MOS switch 44 is turned off. When the current is turned off, the smoothing circuit 516 electromagnetic induction circuit 34 The conductance increases.

 Next, simulation results of response characteristics of the voltage output from the switching power supply circuit 510 when the load current fluctuates in the increasing direction will be described with reference to FIG. When the inductance L of the electromagnetic induction circuit 34 is 30 H, the load current fluctuates and the response time of force is 2.4 ms. When the inductance L of the electromagnetic induction circuit 34 is 0.5 H, 0.5 ms is there. On the other hand, in the switching power supply circuit 510 which is effective in this embodiment, the load current fluctuation is detected by the load current fluctuation detection circuit 420, and the MOS switch 44 is turned on by the control circuit 526 and the holding circuit 328, and the electromagnetic induction circuit. When the inductance of 34 is 1.5 H and the voltage of the capacitor 436 is raised by the voltage application circuit 428, the response time after the load current fluctuates is 2 ms, and the inductance is fixedly large. Ensure a transient response time that is shorter than the case.

 [0120] Further, the simulation result of the ripple voltage characteristic in the voltage output from the switching power supply circuit 510 will be described with reference to FIG. When the inductance L of the electromagnetic induction circuit 34 is 30 H, the ripple voltage is 1.8 mVpp, and when the inductance L is 0, the ripple voltage is 7 mVpp. On the other hand, in the switching power supply circuit 510 which is effective in the present embodiment, the control circuit 526 and the holding circuit 328 in which the load current does not fluctuate, so that the MOS switch 44 power is turned off, and the combined inductance of the electromagnetic induction circuit 34 is reduced. When it reaches 30 H, the ripple voltage is 0.6 mVpp, and the ripple voltage can be made lower than when the inductance is fixedly large.

Next, a simulation result of the response characteristic of the voltage output from the switching power supply circuit 510 when the load current fluctuates in the decreasing direction will be described with reference to FIG. When the inductance L of the electromagnetic induction circuit 34 is 30 H, the load current fluctuates and the response time of force is 2.6 ms, and when the inductance L of the electromagnetic induction circuit 34 is 0.5 11, it is 0.5 ms. is there. On the other hand, in the switching power supply circuit 510 which is effective in this embodiment, the load current fluctuation is detected by the load current fluctuation detection circuit 420, and the MOS switch 44 is turned on by the control circuit 526 and the holding circuit 328, and the electromagnetic induction circuit. When the inductance of 34 is 0.5 H and the voltage of the capacitor 436 is lowered by the voltage application circuit 428, the response time after the load current fluctuates is 2.2 ms, and the inductance is fixed. Larger and shorter than the case, ensure a transient response time.

 [0122] The simulation result of the ripple voltage characteristics in the voltage output from the switching power supply circuit 510 will be described with reference to FIG. When the inductance L of the electromagnetic induction circuit 34 is 30 H, the ripple voltage is 0.7 mVpp, and when the inductance L is 0.5 H, the ripple voltage is 8 mVpp. On the other hand, in the switching power supply circuit 510 which is effective in the present embodiment, the control circuit 526 and the holding circuit 328 in which the load current does not fluctuate, so that the MOS switch 44 power is turned off, and the combined inductance of the electromagnetic induction circuit 34 is reduced. When it reaches 30 H, the ripple voltage is 0.5 mVpp, and the ripple voltage can be made lower than when the inductance is fixedly large.

 [0123] As described above, according to the switching power supply circuit according to the sixth embodiment, when the load fluctuates and the current greatly fluctuates in the increasing direction or greatly fluctuates in the decreasing direction. By raising or lowering the voltage at one end of the capacitor, charge can be supplied or absorbed between the capacitor and the load, and the oscillation voltage can be suppressed, thus realizing a low ripple voltage. be able to.

 [0124] Furthermore, since the holding circuit can hold the state of controlling the inductance of the electromagnetic induction circuit to be low for a predetermined time, the time for which the inductance of the electromagnetic induction circuit is low can be adjusted.

 [0125] In the above embodiment, the case where the inductance is changed by combining a plurality of coils and the voltage is applied to the capacitor when the load current fluctuates has been described as an example. However, MEMS technology is used. An inductor with variable inductance and a capacitor with variable capacitance using MEMS technology may be used in the switching power supply circuit to change the inductance and supply and absorb the charge from the load.

 Industrial applicability

[0126] By applying to a power supply device for a microprocessor, the power supply device for the microprocessor can be controlled.

 Brief Description of Drawings

FIG. 1 is a schematic diagram showing a configuration of a switching power supply circuit according to a first embodiment of the present invention. 2] A circuit diagram showing the configuration of the switching power supply circuit according to the first embodiment of the present invention.

圆 3A] Load current is increased! 2 is a circuit diagram showing the operation of the load current fluctuation detection circuit and the control circuit according to the first embodiment of the present invention.

[3B] FIG. 3B is a circuit diagram showing operations of the load current fluctuation detection circuit and the control circuit according to the first embodiment of the present invention when the load current decreases.

4A] is a graph showing a simulation result of the load current fluctuation detection circuit according to the first embodiment of the present invention when the load current fluctuates discretely.

4B] is a graph showing a simulation result of the load current fluctuation detection circuit according to the first embodiment of the present invention when the load current fluctuates gradually.

[5] A graph showing response characteristics of the switching power supply circuit according to the first embodiment of the present invention.

6] A graph showing ripple voltage characteristics of the switching power supply circuit according to the first embodiment of the present invention.

7] A circuit diagram showing a configuration of a switching power supply circuit according to a second embodiment of the present invention.

[8] FIG. 8 is a circuit diagram showing a configuration of a switching power supply circuit according to a third embodiment of the present invention.

9] A circuit diagram showing the configuration of the switching power supply circuit according to the fourth embodiment of the present invention.

10] A graph showing changes in load current, control voltage, and output voltage of the switching power supply circuit according to the fourth embodiment of the present invention.

[11A] This is a graph showing the response characteristics of the conventional circuit.

11B] A graph showing the response characteristics of the switching power supply circuit according to the fourth embodiment of the present invention.

12] A graph showing a ripple voltage characteristic of the switching power supply circuit according to the fourth embodiment of the present invention.

圆 13] Schematic showing the configuration of the switching power supply circuit according to the fifth embodiment of the present invention It is.

14] A circuit diagram showing a configuration of a switching power supply circuit according to a fifth embodiment of the present invention.

15] A graph showing a simulation result of the voltage application circuit according to the fifth embodiment of the present invention.

16A] A circuit diagram showing the operation of the voltage application circuit and the capacitor according to the fifth embodiment of the present invention when the load current fluctuates in the increasing direction.

FIG. 16B is a circuit diagram showing the operation of the voltage application circuit and the capacitor according to the fifth embodiment of the present invention when the load current fluctuates in the decreasing direction.

17] A graph showing a simulation result of the voltage application circuit according to the fifth embodiment of the present invention.

18] A graph showing load current fluctuation, control voltage, and output voltage change when the load current fluctuates in the increasing direction in the switching power supply circuit according to the fifth embodiment of the present invention.

19] A graph showing changes in load current fluctuation, control voltage, and output voltage when the load current fluctuates in the decreasing direction in the switching power supply circuit according to the fifth embodiment of the present invention.

FIG. 20 is a circuit diagram showing a configuration of a switching power supply circuit according to a sixth embodiment of the present invention.

圆 21] In the switching power supply circuit according to the sixth embodiment of the present invention, it is a graph showing the load current fluctuation and the output voltage change when the load current fluctuates in the increasing direction. 圆 22] 6 is a graph showing ripple voltage characteristics when the load current fluctuates in the increasing direction in the switching power supply circuit according to the embodiment.

圆 23] In the switching power supply circuit according to the sixth embodiment of the present invention, it is a graph showing the load current fluctuation and the change of the output voltage when the load current fluctuates in the decreasing direction. 圆 24] In the switching power supply circuit according to the embodiment, the load current It is a graph which shows the ripple voltage characteristic when fluctuates in the decreasing direction.

10, 110, 210, 310, 410, 510 Switching power supply circuit

12 DC power supply

14 Switching circuit

16, 116, 216, 416, 516 Smooth circuit

20, 420 Load current fluctuation detection circuit

22 Pulse width modulation circuit

24 drive circuit

26, 326, 426, 526 Control circuit

30 PMOS transistor

32 NMOS transistor

34, 134, 234, 434 Electromagnetic induction circuit

36, 436 capacitors

38, 138, 244 1st coinore

 0 Parallel circuit

 2, 142, 248 Second coil

 4, 144 MOS switch

 6 transformer

 6 A Primary coil

 6B Secondary coil

 8, 50, 52, 54 Diode

 6 Resistance

 8 operational amplifier

 40 series circuit

 38 selector switch

 42 NMOS transistor

46 PMOS transistor 328 Holding circuit

 370 NMOS transistor

372 DC power supply

 374 capacitors

 376 resistance

 378 Low-pass filter circuit 428 Voltage application circuit 470 Operational amplifier

472 Inverter

Claims

The scope of the claims  [1] switching means for switching and outputting the input DC voltage;  A smoothing circuit comprising an electromagnetic induction circuit and a capacitive element, the inductance of which can be changed, and smoothing and outputting the output of the switching means force;  A load current fluctuation detection circuit for detecting fluctuations in the current flowing in the load connected to the smoothing circuit;  When the fluctuation amount of the current detected by the load current fluctuation detection circuit is less than a predetermined amount, the electromagnetic induction circuit is controlled so that the inductance of the electromagnetic induction circuit becomes a predetermined value. A control circuit that controls the electromagnetic induction circuit so that the inductance of the electromagnetic induction circuit is less than the predetermined value when the electromagnetic induction circuit is greater than or equal to a predetermined amount;  Including switching power supply circuit. [2] The switching power supply circuit according to [1], further including a holding circuit that holds a state in which the control circuit controls the inductance of the electromagnetic induction circuit to be less than the predetermined value for a predetermined time.  3. The switching power supply circuit according to claim 2, wherein the holding circuit includes a switching element and a low-pass filter circuit.  [4] When the electromagnetic induction circuit is controlled by the control circuit so that the inductance of the electromagnetic induction circuit is less than the predetermined value, and the load current fluctuation detection circuit increases the current. A predetermined positive voltage is applied to the other end opposite to the one end connected to the load of the capacitive element, and the inductance of the electromagnetic induction circuit is controlled by the control circuit. When the electromagnetic induction circuit is controlled to be less than the predetermined value, and when the load current fluctuation detecting circuit detects that the current fluctuates in the decreasing direction, The switching power supply circuit according to any one of claims 1 to 3, further comprising a voltage application circuit that applies a predetermined negative voltage to the other end of the capacitive element. [5] A parallel circuit in which the electromagnetic induction circuit is configured by connecting in parallel a first coil, a second coil, and a switch that is turned on and off by the control circuit, and is connected in series to the first coil. And the combined inductance when the switch is off is the 5. The switching power supply circuit according to claim 1, wherein the switching power supply circuit is set to a predetermined value.  [6] The electromagnetic induction circuit is configured by connecting in series a first coil having an inductance value of the predetermined value, a second coil, and a switch that is turned on / off by the control circuit, and the first coil. The switching power supply circuit according to any one of claims 1 to 4, comprising a series circuit connected in parallel with each other.  [7] The electromagnetic induction circuit is connected to the first coil having an inductance of the predetermined value, the second coil having an inductance of less than the predetermined value, one end connected to the output terminal of the switching means, and the control circuit The switching power supply circuit according to any one of claims 1 to 4, further comprising a switch whose other end is connected to either the first coil or the second coil by switching according to the above.  [8] Claims 1 to 3, wherein the load current fluctuation detection circuit includes a detection coil that induces a current corresponding to a current that flows through the load, and a resistor that is energized by the current that flows through the detection coil. The switching power supply circuit according to claim 7.  [9] The load current fluctuation detection circuit is connected in common to a detection coil that induces a current corresponding to the current flowing through the load, and a force sword, and one anode is connected to one end of the detection coil, and the other A first pair of diodes whose anode is connected to the other end of the detection coil, an anode is commonly connected, one force sword is connected to one end of the detection coil, and the other force sword is connected to the detection coil. A second pair of diodes connected to the other end, a resistor having one end connected to the force sword of the first pair of diodes and the other end connected to an anode of the second pair of diodes; The switching power supply circuit according to claim 1, wherein the switching power supply circuit includes any one of claims 1 to 8.  [10] The switch includes an NMOS transistor, and  10. The control circuit is configured by a non-inverting amplifier in which a voltage applied to the resistor is input to a non-inverting input terminal, and an output terminal of the non-inverting amplifier is connected to a gate of an NMOS transistor. The switching power supply circuit described. [11] The pulse width modulation circuit according to any one of claims 1 to 10, further comprising a pulse width modulation circuit that switches the switching means by pulse width modulation according to a current flowing through the load. Switching power supply circuit. [12] switching means for switching and outputting the input DC voltage;  A smoothing circuit comprising an electromagnetic induction circuit and a capacitive element, and smoothing and outputting the output from the switching means;  A load current fluctuation detection circuit for detecting fluctuations in the current flowing in the load connected to the smoothing circuit;  A determination circuit for determining whether or not a fluctuation amount of the current detected by the load current fluctuation detection circuit is equal to or greater than a predetermined amount;  When it is determined by the determination circuit that the fluctuation of the current is greater than or equal to a predetermined amount, and when the load current fluctuation detection circuit detects that the current fluctuates in an increasing direction A predetermined positive voltage is applied to the other end opposite to the one end connected to the load of the capacitive element,  When the determination circuit determines that the current fluctuation is greater than or equal to a predetermined amount, and the load current fluctuation detection circuit detects that the current fluctuates in a decreasing direction. A voltage application circuit for applying a predetermined negative voltage to the other end of the capacitive element;  Including switching power supply circuit.