KR19980012981U - SMPS to control power supply by controlling PWM IC of SMPS - Google Patents

Abstract

The present invention relates to a switching mode power supply (SMPS) for controlling a pulse width modulation IC (PWM IC) to interrupt power supply.

The SMPS according to the present invention is a SMPS including a PWM IC which is a pulse generating means and a power interrupting means switched by the PWM IC, wherein the PWM IC further comprises a switching means for stopping the driving of the PWM IC. Then, the driving of the PWM IC is stopped by the control signal generated by the switching means, so that the power transistor, which is the power interrupting means, is turned off and the supplied power is interrupted.

The switching means of the SMPS according to the present invention can use a small switch, thereby reducing the cost of the product, and also provides an effect of eliminating the obstacles of the beautiful product design due to the use of the large switch.

Description

SMPS to control power supply by controlling PWM IC of SMPS

The present invention is a SMPS including a pulse width modulation PWM (Pulse Width Modulation IC) and a power interruption means to be switched by the PWM IC, the signal generated by the switching means to control the driving of the PWM IC The present invention relates to an SMPS that interrupts a power supply.

In general, Switching Mode Power Supply (SMPS) refers to a switching power supply, by switching the DC power voltage applied to the primary winding of the transformer so that induced electromotive force according to the winding ratio is induced in the secondary winding of the transformer, It refers to a power supply device for generating a DC output voltage of a predetermined size by rectifying the induced electromotive force induced in the secondary winding of the transformer through the rectifier.

Since SMPSs are smaller, lighter and more efficient than linear power supplies, SMPSs are adopted in power supplies of most electronic products today. There is a trend of rapid development in response to demand.

1 is a circuit diagram of a general SMPS as described above, the turns ratio Transformer 110 having a, a rectifier 120 for rectifying the induced electromotive force induced in the secondary winding (NS) of the transformer 110, and a power source connected to the primary winding (NP) of the transformer 110 The SMPS includes a power transistor 130 that is an interrupting means and pulse generating means 100 that generates a pulse for turning the power transistor 130 on and off.

2 is a circuit diagram showing an internal configuration of the PWM IC 100, which is a pulse generating means for switching the power transistor 130 of the SMPS, and outputs a pulse width modulated signal to control the power transistor, which is a power interrupting means. An under voltage lock out for outputting a signal for shutting off the PWM IC 100 when the pulse width modulator 10 and the driving voltage VCC supplied to the PWM IC 100 are below the reference voltage; UVLO) circuit 20, the overcurrent protection unit 30 for protecting the power transistor from overcurrent, and the output of the lower voltage closing circuit 20 and the pulse width modulation unit 10 are inputted to the PWM IC 100. A bias blocking unit 40 for blocking a bias and the output of the pulse width modulator 10, the lower voltage closing circuit 20, and the overcurrent protection unit 30 are turned on and off. It consists of an output part 50 which outputs a signal.

Here, the pulse width modulator 10 is connected to the oscillator 11 for outputting the oscillation frequency determined by the oscillation capacitor CT connected to the CT terminal, and the CS terminal serving as a terminal for connecting the self starting capacitor CS. Comparators C1 and C2 for detecting an overload and an overvoltage, a comparator C3 for detecting an overvoltage and a PWM comparator C5 can be internally driven by receiving a signal through the FB terminal. An error amplifier C4 and a PWM comparator C5 for modulating the pulse width by receiving the output of the oscillator 11, the voltage of the CS terminal, the output of the error amplifier C4, and the DT voltage, and the overcurrent protection. The unit 30 receives an OCP (Over-Current Protection) comparator C6 that detects an over-current of a power transistor, an RS that receives an output of the PWM comparator C5 and an output of an OCP comparator C6. It consists of a flip-flop (RS-FF).

In addition, the bias blocking unit 40 is an OR gate OR1 receiving the output signals of the comparators C1 and C2 and the low voltage closed circuit 20, and an output of the OR gate OR1. It is composed of a bias cut-off circuit 41 for receiving a signal to shut down the bias of the PWM IC (100), the output unit 50 is the lower voltage closing circuit 40, the comparator (C5), RS flip A NOR gate NOR1 that calculates the output of the flop RS-FF, and a totem pole that outputs a signal for turning the power transistor on and off according to the output of the NOR1 to the output terminal OUT. It consists of output transistors TR2, TR3, TR4, and TR5 in the form of (totem-pole).

Looking at the operation of the SMPS configured as described above, when the rectified DC voltage (Vi) is applied to the input terminal of the SMPS, the DC input voltage (Vi) is removed by the capacitor C1 connected in parallel to the input terminal of the SMPS ripple (ripple) is removed Is supplied to the primary winding of Nf, and the input voltage (Vi) charges the capacitor C2 connected to the VCC terminal of the PWM IC through the starting resistor Rg. As the charge is charged, the voltage across the capacitor C2 When the starting voltage to be started is reached, the PWM IC is started by the starting voltage applied to the VCC terminal.

Once the PWM IC is activated, the oscillator 11 inside the PWM IC generates a triangular wave by repeatedly charging and discharging the capacitor CT connected between the CT terminal and the ground, and the generated triangular wave is the amount of the PWM comparator C5. It is input to the input terminal of (+).

At this time, the capacitor CS connected to the CS terminal is supplied with electric current through the constant current source 12 to charge the charge, and the voltage of the rising CS terminal causes the PWM IC 100 to soft start. The clamp is clamped to a constant voltage by a Zener diode Zn built in the PWM IC 100.

In addition, the voltage of the CS terminal is input to one negative input terminal of the three of the PWM comparator C5, and the output voltage of the error amplifier C4 is applied to the other negative input terminal of the PWM comparator C5. DT voltage is input to another negative input terminal.

As such, when each signal voltage is input to four input terminals of the PWM comparator C5, the PWM comparator C5 outputs three negative voltages of the output voltage of the oscillator 11 input to the positive input terminal. The output terminal outputs a high level signal only when the output voltage of the oscillator 11 is higher than the lowest voltage among the CS terminal voltage, the output voltage of the error amplifier C4, and the DT voltage compared to the signal voltage input to the input terminal. When the output voltage of the oscillator 11 is lower than the lowest voltage among the input terminal signal voltages at the negative input terminal, a low level signal is output to the output terminal.

By repeating such an operation, the PWM comparator C5 outputs a signal having a variable pulse width to the output terminal, and the signal output from the PWM comparator C5 is inverted by the NOR gate NOR1 of the output unit 50 and output. It is output to the output terminal OUT of the PWM IC 100 through the transistors TR2 to TR5.

The pulse width modulated signal output from the output terminal OUT of the PWM IC 100 is switched on and off by turning the power transistor 130 on, and thus the primary winding of the transformer 110 to which the power transistor 130 is connected. The DC power supply voltage applied to the NP is cut off, and thus induced electromotive force is induced in the secondary winding NS of the transformer 110.

In this way, the induced electromotive force VS induced in the secondary winding NS is rectified to a DC voltage by the rectifying diode D2 and the capacitor C3 of the rectifier 120 to generate an output power supply voltage VO at the output terminal of the SMPS.

In addition, the winding 110 as well as the winding Nf is wound around the primary side of the transformer 110, and as the power transistor 130 switches, the winding ratio from the secondary winding NS to the primary winding Nf is changed. Induced electromotive force Vf is induced and is induced in the primary winding Nf. The driving voltage VCC is supplied so that the PWM IC 100 started with the supplied starting voltage VCC may continue to operate.

3A illustrates a power supply of a laser beam printer as an example of an electronic product to which an SMPS as described above is applied.

As described above, the SMPS-applied power supply has good efficiency and enables free voltage, but as shown, the power supply to the SMPS is interrupted by a power switch connected to the power input side of the SMPS.

Since the laser beam printer has a large amount of current flowing through the power switch 160, sparks may be generated due to mechanical interruption at the contact point when the switch is turned on or off, and thus the power switch 160 may malfunction. When the 150 is driven, the inrush current also increases, so that the switch is broken or easily aged and the reliability is lowered.

As a result, such a large-capacity switch is used for such a power switch, which increases the manufacturing cost, and the large size of the switch also impedes the design of a beautiful product design.

FIG. 3B is a power supply device for a laser beam printer configured by connecting the power switch 160 to the power input terminal of the SMPS in which the heating lamp unit 150 and the SMPS 140 branch to improve the above-described problem.

While the inrush current flowing through the illustrated power switch 160 is relatively reduced by the current entering into the heat generating lamp unit 150, the current flowing into the SMPS 140 acts on the power switch 160 as it is, and thus a small power source. There was a limit to the use of switches.

Accordingly, an object of the present invention is to provide an SMPS capable of intermittent power supply by controlling a PWM IC using a switching means in which a small switch is used in view of such a conventional problem.

1 is a circuit diagram of a typical SMPS,

2 is a circuit diagram showing an internal configuration of a PWM IC;

3 is a block diagram schematically showing a power supply device of a laser beam printer to which SMPS is applied;

Figure 4 is a circuit diagram of the SMPS to control the PWM IC of the SMPS according to the present invention to control the power supply.

Explanation of symbols for main parts of drawings

10: pulse width modulator, 11: oscillator, 12: constant current source, 20: low voltage closed circuit, 30: overcurrent protection, 40: bias cutoff, 41: bias cutoff circuit, 50: output, 100: SMPS, 110: transformer, 120: rectifier, 130: power transistor, C1 to C3, CS, CT: capacitor, R1, Rg, Re: resistor, D1, D2: diode, TR1 to TR5: transistor, C1 to C6: comparator, Vref1 To Vref5: reference voltage.

The present invention for achieving the object as described above further comprises a switching means for stopping the operation of the PWM IC in the SMPS comprising a PWM IC which is a pulse generating means, and a power interrupting means switched by the PWM IC. As it is configured to include, when described with reference to the accompanying drawings, preferred embodiments as follows.

FIG. 4 is a circuit diagram of an SMPS for controlling power supply by controlling a PWM IC according to the present invention, and connecting a switch SW between a grounded CS terminal connected to a self-starting capacitor CS of the PWM IC 100 and ground. The switching means constituted are shown.

Hereinafter, the operation of the SMPS in which the power supply is interrupted by the switching means as described above will be described with reference to FIGS. 2 and 4.

The input power supply voltage Vi is applied to the primary winding NP of the transformer 110 through the input terminal of the SMPS, and the PWM IC 100 is driven to generate a pulse width modulation signal to turn on / off the power transistor 130. When turned off, the induced voltage VS is induced in the secondary winding NS of the transformer while the power supply voltage applied to the primary winding NP of the transformer 100 is switched, and the induced electromotive force VS is rectified by the rectifier and output to the output terminal of the SMPS. .

At this time, when the switch SW connected to the CS terminal is closed to close the CS terminal, the comparator C1 inside the PWM IC 100 is connected to the CS terminal input to the negative input terminal. The ground voltage is compared with the reference voltage Vref1 input to the positive input terminal, and the comparator C1 is because the CS terminal voltage of the negative input terminal is lower than the reference voltage Vref1 of the positive input terminal. The high signal H is generated at the output terminal.

The high signal H generated at the output terminal of the comparator C1 is applied to the bias blocking circuit 41 to block the bias supplied to the PWM IC 100 to stop driving of the PWM IC 100.

Accordingly, since the pulse width modulation signal for switching the power transistor 130 is not generated at the output terminal OUT of the PWM IC 100, the power transistor 130 is turned off and the primary side of the transformer 110 is turned off. Since the input power supply voltage is not applied to the winding NP, the power supply state is cut off. Accordingly, the output voltage is not generated at the output terminal VO of the SMPS.

When the switch SW of the CS terminal of the PWM IC 100 is opened in such a power-off state, the capacitor of the CS terminal is again caused by the starting voltage VCC supplied from the starting resistor Rg to the VCC terminal of the PWM IC. The current is supplied to the CS to charge the charge, and accordingly, the voltage of the CS terminal rises so that a voltage higher than the reference voltage Vref1 is input to the negative input terminal of the comparator C1, and the output terminal of the comparator C1 is input. Becomes the low state (L).

When the output of the comparator C1 becomes the low state L, the bias voltage is applied again to each part of the PWM IC 100 that was interrupted by the bias blocking circuit 41, and accordingly, the PWM IC 100 operates normally. To output the pulse width modulated signal to the output terminal OUT.

In response to the pulse width modulation signal output from the output terminal OUT of the PWM IC, the power transistor 130 performs a switching operation so that the power supply voltage Vi applied to the primary winding NP of the transformer 110 is interrupted. Therefore, the output power supply voltage VO is output to the output terminal of the SMPS by the induced electromotive force VS induced by the secondary winding NS.

Since only a few hundred μA of current flows through the switch used in such a switching means, breakage and aging of the switch are prevented, and a small one can be used as such a power switch.

The present invention described above can be considered another embodiment according to the spirit of the present invention as one embodiment.

In the internal block diagram of the PWM IC of FIG. 2, when a low level (L) signal approximating 0 V is input to the negative input terminal of the PWM comparator C5, the output terminal OUT of the PWM IC 100 is input. It can be seen that a low level signal L is generated for turning off the power transistor.

Therefore, as in the above-described embodiment, a switch is connected between the FB terminal and the ground of the PWM IC 100 directly connected to the negative input terminal of the PWM comparator C5, and the switch is closed to 0 at the FB terminal. When a ground voltage of V is applied, a signal for turning off the power transistor 130 is generated at the output terminal OUT of the PWM IC 100 to interrupt the power supply.

Since the PWM IC for switching the power transistor includes an IS terminal, which is an input terminal of an OCP comparator for internal overcurrent protection, and an IN terminal, which is an input terminal of an error amplifier, the operation of the PWM IC is driven to such an input terminal. When the control signal is generated through the switching means such that the stopping condition is satisfied, the driving of the PWM IC is stopped or the output signal for turning on the power transistor is not generated at the output terminal, thereby interrupting the supplied power.

As described in detail above, according to the present invention, by controlling the PWM IC to stop driving by using a switching means that can use a small switch, and accordingly to interrupt the power supplied to the SMPS, a large size for the conventional power supply The switch can be removed, thereby reducing the cost of the product due to the use of the small switch, and also eliminating the obstacles of the beautiful product design design due to the use of the large switch.

Claims (2)

A SMPS comprising a PWM IC which is a pulse generating means and a power interrupting means switched by the PWM IC, the power supply being controlled by a PWM IC further comprising switching means for stopping the driving of the PWM IC. SMPS to regulate supply. The SMPS according to claim 1, wherein said switching means is connected between a terminal to which a self-start capacitor (CS) is connected and ground.