JP7300364B2 - Driving device for switching element - Google Patents

Description

TECHNICAL FIELD The present invention relates to a drive device that turns on and off a switching element according to an externally input drive signal.

Conventionally, a driving device 100 shown in FIG. 5 is known as a driving device that turns switching elements on and off according to drive signals (see, for example, Non-Patent Document 1). In this drive device 100, when the primary side switching element _Q1 connected to the primary winding T1 of the transformer T is turned on and off in accordance with the drive signal PWM, the switching voltage generated in the secondary winding _T2 of the transformer T _causes The secondary side switching element _Q2 to be driven is configured to turn on and off. According to this drive device 100, the power required to drive the secondary side switching element _Q2 can be transmitted from the primary side to the secondary side while insulating the drive signal PWM. In the example shown in FIG. 5, the secondary side switching element _Q2 is a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor).

Tamotsu Inaba, "Fundamentals and Practical Use of Power MOS FETs", CQ Publishing, November 2004, p. 77-78

By the way, in order to sufficiently turn on the secondary side switching element Q ₂ , the voltage input between the gate and source of the secondary side switching element Q ₂ , that is, the drive voltage V _Pb ( ₌ The potential of point _Pb ) must be greater than a predetermined minimum voltage value _VLow . However, in the conventional drive device 100, as the ON duty of the drive signal PWM increases, the switching voltage V _Pa (=the potential at the point P _a based on the point P ₀ ) decreases, and accordingly the drive voltage V _Pb Therefore, the minimum voltage value _VLow cannot be ensured, and the secondary side switching element _Q2 cannot be sufficiently turned on in some cases (see FIGS. 6 and 7).

SUMMARY OF THE INVENTION It is an object of the present invention to provide a driving device capable of reliably turning on and off a switching element even when the ON duty of a driving signal varies over a wide range. do.

In order to solve the above-mentioned problems, a driving device according to the present invention turns a primary-side switching element connected to the primary winding of a transformer on and off in accordance with a drive signal to generate a switching voltage in the secondary winding of the transformer. and a driving device for turning on and off a secondary side switching element using a switching voltage, the doubling circuit generating a doubled voltage by doubling the switching voltage, and a predetermined regulated voltage by stepping down the doubled voltage. wherein the secondary side switching element is turned on and off by the higher one of the switching voltage and the regulated voltage, and the regulated voltage is switched when the ON duty of the drive signal reaches the maximum value. It is characterized by being between the voltage and the voltage double and higher than the voltage required to turn on the secondary side switching element.

According to this configuration, even if the ON duty of the drive signal increases and the switching voltage drops to such an extent that the secondary side switching element cannot be turned on, the doubling circuit and the regulator circuit generate the switching voltage based on the switching voltage. The regulator voltage (=voltage higher than the voltage required to turn on the secondary side switching element) can reliably turn on and off the secondary side switching element.

The doubling circuit of the drive may, for example, comprise a capacitor with one end connected to one end of the secondary winding and a capacitor with an anode connected to the other end of the secondary winding and a cathode connected to the other end of the capacitor. A first diode and a second diode having an anode connected to the cathode of the first diode and a cathode connected to the input of the regulator circuit may be included.

In order to more reliably turn off the secondary side switching element, the drive device receives a stop circuit that stops the operation of the regulator circuit when the switching voltage becomes zero, or a stop signal that indicates that the drive signal has stopped. It is preferable to further include a stop circuit for stopping the operation of the regulator circuit.

According to the present invention, it is possible to provide a drive device that can reliably turn on and off a switching element even when the ON duty of a drive signal varies over a wide range.

1 is a circuit diagram of a driving device according to a first embodiment of the present invention; FIG. 2 is a diagram showing the relationship between the ON duty of a drive signal and the voltage of each part in the drive device shown in FIG. 1; FIG. FIG. 2 is a voltage waveform diagram of each part of the drive device shown in FIG. 1, where (A) is a waveform diagram when the ON duty of the drive signal is 20%, and (B) is a waveform when the ON duty is 80%; It is a diagram. FIG. 4 is a circuit diagram of a driving device according to a second embodiment of the present invention; 1 is a circuit diagram of a conventional driving device; FIG. 6 is a diagram showing the relationship between the ON duty of the drive signal and the voltage of each part in the conventional drive device shown in FIG. 5. FIG. FIG. 6 is a voltage waveform diagram of each part of the conventional drive device shown in FIG. 5, (A) is a waveform diagram when the ON duty of the drive signal is 20%, and (B) is a waveform diagram when the ON duty is 80%. is a waveform diagram of.

Hereinafter, embodiments of the driving device according to the present invention will be described with reference to the drawings.

[First embodiment]
FIG. 1 shows a driving device 10A according to a first embodiment of the invention. As shown in the figure, the driving device 10A is composed of a primary side circuit including the primary winding _T1 of the transformer T and a secondary side circuit including the secondary winding _T2 of the transformer T. As shown in FIG.

The primary circuit consists of the aforementioned primary winding _T1 , a diode _D1 whose cathode is connected to one end (● side) of the primary winding _T1 , and a collector which is connected to the other end of the primary winding _T1 . It includes an NPN type primary side switching element _Q1 and a resistor _R1 having one end connected to the base of the primary side switching element _Q1 . The anode of the diode _D1 , the emitter of the primary side switching element _Q1 and the other end of the resistor _R1 are grounded. A drive signal PWM output by a higher control circuit (not shown) is input to the base of the primary side switching element _Q1 , and the power supply voltage VCC is input to the intermediate tap of the primary winding _T1 . ing.

The secondary side circuit consists of the above-mentioned secondary winding _T2 , diodes _D2 and _D3 whose anodes are connected to one end (● side) of the secondary winding _T2 , and one end connected to the cathode of the diode _D2 . connected resistor _R3 , resistor _R4 with one end connected to the other end of resistor _R3 , and PNP type with the emitter connected to the cathode of diode _D2 and the base connected to the cathode of diode _D3 . and a resistor _R2 having one end connected to the base _of switching element _Q3 . The collector of switching element _Q3 and the other ends of resistors _R2 and _R4 are connected to the other end of secondary winding _T2 .

The other end of the resistor _R3 (one end of the resistor _R4 ) is also connected to the gate of the secondary side switching element _Q2 to be driven. The other end of the secondary winding _T2 is also connected to the source of the secondary side switching element _Q2 . Incidentally, in this embodiment, the secondary side switching element _Q2 is a MOSFET.

The secondary side circuitry further includes a doubling circuit 11, a regulator circuit 12A and a diode _D6 .

The doubling circuit 11 includes a capacitor _C1 having one end connected to one end of the secondary winding _T2 , and an anode connected to the other end of the secondary winding _T2 and a cathode connected to the other end of the capacitor _C1 . and a diode _D5 having its anode connected to the cathode of diode _D4 and _its cathode connected to the input of regulator circuit 12A. Diode _D4 corresponds to the "first diode" of the present invention. Also, the diode _D5 corresponds to the "second diode" of the present invention.

Diode _D6 has an anode connected to the output of regulator circuit 12A and a cathode connected to the cathode of diode _D2 .

In the following description, the potential at point _P1 with reference to point _P0 is referred to as switching voltage _VP1 , the potential at point _P2 with reference to point _{P0 is referred to as double voltage VP2} , and point _P0 as reference _. The potential at the point _P3 with the point _{P0 as the reference is called the regulated voltage Vp3} , and the potential at the point _P4 with the point _P0 as the reference is called the drive voltage _Vp4 .

When the drive signal PWM changes rectangularly, the switching voltage V _P1 , the voltage doubler V _P2 , the regulated voltage V _P3 and the drive voltage V _P4 change rectangularly in phase with the drive signal PWM. That is, when the drive signal PWM changes from L level to H level, the voltages V _P1 , V _P2 , V _P3 and V _P4 also change from L level to H level, and when the drive signal PWM changes from H level to L level, Voltages V _P1 , V _P2 , V _P3 and V _P4 also change from H level to L level. Further, when the voltage input between the gate and source of the secondary side switching element Q ₂ exceeds a predetermined minimum voltage value V _Low due to changes in the drive voltage V _P4 , the secondary side switching element Q ₂ is turned on and When the voltage drops below _VLow , the secondary switching element _Q2 is turned off.

As shown in FIG. 2, the H level of the switching voltage V _P1 decreases as the ON duty of the drive signal PWM increases. In this embodiment, when the ON duty of the drive signal PWM exceeds 65%, the H level of the switching voltage V _P1 falls below the lowest voltage value V _Low .

The doubled voltage _VP2 is generated by the doubling circuit 11 by doubling the switching voltage _VP1 . As with the H level of the switching voltage _VP1 , the H level of the double voltage _VP2 also decreases as the ON duty of the drive signal PWM increases. However, the H level of the double voltage V _P2 does not fall below the minimum voltage value V _Low even if the ON duty of the drive signal PWM changes between the minimum value of 20% and the maximum value of 80%. . On the other hand, when the ON duty of the driving signal PWM becomes small, the H level of the double voltage V _P2 exceeds the predetermined maximum voltage value V _High which is the upper limit value of the voltage between the gate and the source of the secondary side switching element Q _{2 .} There is

The regulated voltage _VP3 is generated by the regulator circuit 12A by stepping down the doubled voltage _VP2 . The H level of the regulated voltage V _P3 has a voltage value V _Reg . The voltage value V _Reg is higher than the lowest voltage value V _Low and is set between the value of the switching voltage V _P1 and the value of the double voltage V _P2 when the ON duty of the drive signal PWM is 80%. . As _described above, the H level of the doubled voltage _VP2 may exceed the highest voltage value _{VHigh .} A voltage exceeding V _High is never applied between the gate and source of the secondary side switching element Q ₂ .

The higher one of the regulated voltage _VP3 and the switching voltage _VP1 becomes the drive voltage _VP4 indicated by the thick line. That is, in this embodiment, when the ON duty of the drive signal PWM is less than 50%, the switching voltage _VP1 becomes the drive voltage _VP4 , and when the ON duty of the drive signal PWM is 50% or more, the regulated voltage V _P3 becomes the drive voltage _VP4 .

The operation of the driving device 10A according to the present embodiment will be summarized with reference to FIG. When the ON duty of the drive signal PWM is 20%, the H level of the switching voltage V _P1 is higher than the H level (=voltage value V _Reg ) of the regulated voltage V _P3 and higher than the minimum voltage value V _Low . Therefore, the switching voltage V _P1 as the drive voltage V _P4 turns on and off the secondary side switching element Q ₂ (see (A) in the figure). On the other hand, when the ON duty of _the drive signal PWM is 80%, the H level of the switching voltage _VP1 is lower than the H level of the regulated voltage _{VP3 .} The secondary switching element _Q2 is turned on and off (see (B) in the figure).

As described above, according to the drive device 10A of the present embodiment, even if the ON duty of the drive signal PWM varies in a wide range, the higher one of the switching voltage V _P1 and the regulated voltage V _P3 is the drive voltage V. It becomes _P4 , and the secondary side switching element _Q2 can be turned on and off reliably.

[Second embodiment]
FIG. 4 shows a driving device 10B according to a second embodiment of the invention. As shown in the figure, the driving device 10B is the second in that the secondary side circuit further includes a stop circuit 13 and the secondary side circuit includes a regulator circuit 12B instead of the regulator circuit 12A. Although it differs from the driving device 10A according to the first embodiment, it is common to the driving device 10A in other respects.

The stop circuit 13 includes a diode _D7 whose anode is connected to one end of the secondary winding _T2 , a resistor _R5 whose one end is connected to the cathode of the diode _D7 , and an emitter connected to the regulator circuit 12B. and a PNP type switching element _Q4 with its base connected to the cathode of diode _D7 . The collector of switching element _Q4 and the other end of resistor _R5 are connected to the other end of secondary winding _T2 .

A switching voltage V _P1 is input to the base of the switching element Q ₄ through a diode D ₇ . When the switching voltage _VP1 is at H level, the switching element _Q4 is turned off. At this time, the switching element _Q4 has no effect on the regulator circuit 12B. On the other hand, when the switching voltage _VP1 is at L level, the switching element _Q4 is turned on. At this time, the regulator circuit 12B, from which the current is drawn by the switching element _Q4 , cannot operate and stops outputting the regulated voltage _VP3 (the regulated voltage _VP3 becomes zero).

When the on/off operation of the secondary side switching element _Q2 is finished, the upper control circuit changes the drive signal PWM to L level, and changes the switching voltage V _P1 and the drive voltage V _P4 to L level. At this time, in the driving device 10A according to the first embodiment, which does not include the stop circuit 13, the charge accumulated in the capacitor _C1 activates the regulator circuit 12A, completely turning off the secondary side switching element _Q2 . may not be possible. In this regard, in the drive device 10B according to the present embodiment, the stop circuit 13 stops the operation of the regulator circuit 12B when the switching voltage V _P1 becomes L level (zero), so that the secondary side switching element Q ₂ is reliably turned off. can be made

[Modification]
Although the first and second embodiments of the driving device according to the present invention have been described above, the configuration of the driving device according to the present invention is not limited to these.

For example, the doubling circuit of the present invention may be any circuit that produces a doubled voltage by doubling a switching voltage.

Further, the stop circuit of the present invention may be any circuit that stops the operation of the regulator circuit when the switching voltage becomes zero. It may be a circuit that stops the operation of the regulator circuit when the signal is received through.

10A, 10B drive device 11 doubling circuit 12A, 12B regulator circuit 13 stop circuit Q ₁ primary side switching element Q ₂ secondary side switching element T transformer T ₁ primary winding T ₂ secondary winding

Claims (4)

A primary side switching element connected to the primary winding of the transformer is turned on and off in accordance with a drive signal to generate a switching voltage in the secondary winding of the transformer, and the switching voltage is used to operate the secondary side switching element. A driving device for on-off operation,
a doubling circuit that generates a doubled voltage by doubling the switching voltage;
a regulator circuit that generates a predetermined regulated voltage by stepping down the doubled voltage;
with
the secondary switching element is turned on and off by the higher one of the switching voltage and the regulated voltage;
The regulated voltage is between the switching voltage when the ON duty of the drive signal reaches a maximum value and the doubled voltage, and is higher than the voltage required to turn on the secondary side switching element. A driving device characterized by: The doubling circuit comprises a capacitor having one end connected to one end of the secondary winding and a first capacitor having an anode connected to the other end of the secondary winding and a cathode connected to the other end of the capacitor. 2. A driving device according to claim 1, comprising a diode and a second diode having an anode connected to the cathode of said first diode and a cathode connected to an input of said regulator circuit. 3. The drive device according to claim 2, further comprising a stop circuit for stopping the operation of the regulator circuit when the switching voltage becomes zero. 3. The drive device according to claim 2, further comprising a stop circuit for stopping the operation of the regulator circuit upon receiving a stop signal indicating that the drive signal has stopped.

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