Drive Circuit and Switching Power Supply Device

Abstract

To provide a drive circuit and switching power supply device.SOLUTION: A drive circuit for driving a first switching element includes: a first diode having a cathode terminal connected with a gate terminal of the first switching element; a second switching element having a first terminal connected with an anode terminal of the first diode, a second terminal connected with the gate terminal of the first switching element, and a third terminal connected with a source terminal of the first switching element; a third switching element having a drain terminal connected with the anode terminal of the first diode, and a source terminal connected with the source terminal of the first switching element; a parallel circuit including a Zener diode and a first capacitor; and a drive transformer having one end connected with the drain terminal of the third switch through the parallel circuit, and the other end connected with a gate terminal of the third switching element, and having a winding connected with the source terminal of the third switching element through the second diode. One end of the parallel circuit is connected with one end of the winding, and a cathode terminal of the second diode is connected with the other end of the winding.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] This invention relates to a drive circuit for driving a main switch element and a switching power supply device that performs power conversion by the main switch element driven on and off at a predetermined frequency.

Background Art

[0002] As a core component of a switching power supply, a MOSFET is voltage-driven, has a high operating frequency, and has advantages such as no current tailing during turn-off, so it is widely used in DC / DC converters. With the miniaturization, modularization, and high power density in the development of switching power supplies, the requirements for efficiency have been continuously increasing. New-generation high-speed super-junction MOSFETs have also been introduced. The on-resistance is an important parameter for reducing losses and is becoming lower and lower. On the other hand, the input capacitance, which is another performance parameter of the MOSFET, increases with the increase in the power capacitance of the MOSFET. However, the increase in the input capacitance slows down the turn-off speed of the MOSFET, leading to an increase in turn-off loss. Therefore, in actual applications, power supply designers need to devise the circuit design for MOSFET turn-off.

[0003] Therefore, there is a need for the design of a highly reliable drive circuit for a main switch element with a large input capacitance. In the case of a high-output module, full-bridge and half-bridge circuit topologies are commonly used. One way to drive the upper and lower FETs is to use a dedicated driver chip. However, usually, such a chip is expensive, the design is complex, and the delay in switching on and off becomes long. Otherwise, there is a method of using a transformer-coupled method. This method has less delay, is low-cost, allows for a flexible design, and furthermore, the voltage can be adjusted at any time by the transformer ratio design. Therefore, this method is also currently relatively widely used. This invention is also a new type of drive circuit using a transformer-coupled method, but it can of course also be applied to a drive circuit equipped with a dedicated drive chip and has a wide range of applications.

[0004] For example, in Patent Document 1, as shown in FIG. 11, there is proposed a gate drive device for a MOS-FET, which is composed of a pulse transformer for performing circuit insulation, a diode for half-wave rectifying the secondary side of this pulse transformer, a resistor for determining a time constant for setting the turn-on / turn-off time of the MOS-FET connected in series with this diode, a PNP transistor having an emitter connected to the cathode side of the diode, a collector connected to the source side of the MOS-FET, and a base connected to the anode side of the diode, and a resistor for limiting the base current connected between the base and collector of the transistor. With this gate drive device, the charge accumulated in the input capacitance of the MOS-FET Q1 is rapidly discharged through this PNP transistor Q2, so that the turn-off time can be shortened and the turn-off loss can be reduced. However, in the circuit of Patent Document 1, in order to improve the turn-off speed of the MOS-FET Q1, it is necessary to increase the resistance R1 of the current-limiting resistor and decrease the resistor R2 for determining the time constant. As a result, the turn-off loss can be reduced. However, when resetting the transformer in the reverse direction, since there is no resistor for limiting the current, a large reset current flows through the PNP transistor Q2, which may even damage the PNP transistor Q2. Therefore, Patent Document 1 is only suitable for applications where the input drive signal is a unidirectional pulse, and thus has limitations in terms of applications.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in view of the above background art, and an object thereof is to provide a drive circuit for a semiconductor switch element that can rapidly discharge the charge accumulated in the input capacitance even when the input capacitance of a MOSFET increases and has little loss. Another object of the present invention is not only to drive a main switch element having a large input capacitance with high speed and high reliability, but also to reduce the power consumption of the drive circuit and to be applicable even when driven by an AC pulse. Therefore, it is also suitable for the case where a full-bridge circuit and a half-bridge circuit are driven by an isolation transformer. Further, it can be applied even when the drive signal is a positive pulse, and can also be applied to a circuit for driving a single main switch element. Therefore, the circuit of the present invention has a wider practicality.

Means for Solving the Problems

[0007] The present invention is a drive circuit for driving a first switch element, including a first diode having a cathode terminal connected to a gate terminal of the first switch element, a second switch element having an anode terminal of the first diode connected to a first terminal, a gate terminal of the first switch element connected to a second terminal, and a source terminal of the first switch element connected to a third terminal, a third switch element having an anode terminal of the first diode connected to a drain terminal and a source terminal of the first switch element connected to a source terminal, a parallel circuit having one end connected to a cathode terminal of a Zener diode and one end of a first capacitor and the other end connected to an anode terminal of the Zener diode and the other end of the first capacitor, and a drive transformer having a winding with one end connected to the drain terminal of the third switch through the parallel circuit, the other end connected to the gate terminal of the third switch element, and connected to the source terminal of the third switch element through a second diode, wherein one end of the parallel circuit is connected to one end of the winding, a cathode terminal of the second diode is connected to the other end of the winding, and at least one of the connection between the second terminal and the gate terminal of the first switch element and the connection between the third terminal and the source terminal of the first switch element is connected through a resistance element.

[0008] According to the drive circuit of the present invention, even if the input capacitance between the gate and source of the main switch element of the switching power supply device increases, the charge accumulated in the input capacitance can be rapidly discharged, and the loss of the semiconductor switch element can be reduced.

[0009] In addition, in the drive circuit of the present invention, the second switch element is a PNP bipolar transistor, the first terminal is a base terminal, the third terminal is a collector terminal, and the second terminal is an emitter terminal. Thereby, an inexpensive PNP bipolar transistor can be used, and the cost of the drive circuit can be reduced.

[0010] In addition, in the drive circuit of the present invention, the second switch element is a P-chFET, the first terminal is a gate terminal, the third terminal is a drain terminal, and the second terminal is a source terminal. Thereby, a highly reliable and small-sized P-chFET can be used, and the drive circuit can be made compact and highly reliable.

[0011] In addition, in the drive circuit of the present invention, a first resistor element is connected between the gate terminal of the first switch element and the second terminal of the second switch element. This first resistor element can adjust the discharge speed of the charge accumulated in the input capacitance of the first switch element and has an excellent effect of stabilizing the operating point of the second switch element.

[0012] In addition, in the drive circuit of the present invention, a second resistor element is connected between the source terminal of the first switch element and the third terminal of the second switch element. This second resistor element has an excellent effect of being able to adjust the discharge speed of the charge accumulated in the input capacitance of the first switch element.

[0013] Further, in the drive circuit of the present invention, a third resistor element is connected between the gate terminal of the third switch element and the other end of the winding. This third resistor element has an excellent effect of being able to adjust the voltage rise speed between the gate and source of the third switch element.

[0014] Further, in the drive circuit of the present invention, a fourth resistor element is connected between the gate terminal and the source terminal of the third switch element. This fourth resistor element has an excellent effect of discharging the voltage between the gate and source of the third switch element or suppressing the surge voltage, thereby protecting the third switch element.

[0015] Further, in the drive circuit of the present invention, preferably, a second capacitor is connected between the gate terminal and the source terminal of the third switch element. This second capacitor has an excellent effect of increasing noise suppression.

[0016] Further, in the drive circuit of the present invention, a fifth resistor element is connected between the gate terminal and the source terminal of the first switch element. This fifth resistor element has an excellent effect of being able to protect between the gate and source of the first switch element.

[0017] Further, in the drive circuit of the present invention, a sixth resistor element is connected between one end of the parallel circuit and one end of the winding. This sixth resistor element has an excellent effect of being able to adjust the voltage rise speed between the gate and source of the first switch element.

[0018] Another object of the present invention is to provide a switching power supply device including any one of the above drive circuits.

Advantages of the Invention

[0019] According to the drive circuit and the switching power supply device of the present invention, when the secondary-side voltage of the drive transformer is reversed, by turning on the third switch element, the charge accumulated in the input capacitance of the first switch element can be rapidly discharged via the second switch element, thereby realizing a high-speed turn-off and reducing the turn-off loss. Further, all of the turn-off current flows through the second and third switch elements, and no current flows through the isolation transformer and the drive IC, so the power consumption and temperature rise of the drive IC and the transformer can be significantly reduced. At the same time, by designing the parameters of the first resistor element and the second resistor element, high-speed and highly reliable turn-off of MOSFETs with different input capacitances can be realized, and the design becomes simple.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0021] Hereinafter, the switching power supply device 1 according to an embodiment of this invention will be described with reference to the drawings.

[0022] FIG. 1 is a circuit diagram of a switching power supply device according to an embodiment. The switching power supply device 1 includes a full-bridge circuit in each of the primary-side circuit 10 and the secondary-side circuit 20, and is coupled by an isolation transformer (transformer) 120. The transformer has a primary-side coil and a secondary-side coil.

[0023] The primary-side circuit 10 includes a primary-side bridge circuit B1, an input capacitor Cin connected to the primary-side bridge circuit B1, and an inductor Lr.

[0024] The secondary-side circuit 20 includes a secondary-side bridge circuit B2, an inductor Lf and a smoothing capacitor Co connected to the secondary-side bridge circuit B2.

[0025] The primary-side bridge circuit B1 includes a first switch element Q101, a second switch element Q103, a third switch element Q102, and a fourth switch element Q104. The primary-side bridge circuit B1 has a first leg 50 and a second leg 60. The first leg 50 includes the first switch element Q101 and the second switch element Q103. A first connection point A between the first switch element Q101 and the second switch element Q103 is connected to one end of the primary-side coil of the transformer 120 via the inductor Lr. The second leg 60 includes the third switch element Q102 and the fourth switch element Q104. A second connection point B between the third switch element Q102 and the fourth switch element Q104 is connected to the other end of the primary-side coil of the transformer 120.

[0026] The secondary bridge circuit B2 includes a fifth switch element Q201, a sixth switch element Q203, a seventh switch element Q202, and an eighth switch element Q204. The secondary bridge circuit B2 has a third leg 70 and a fourth leg 80. The third leg 70 includes the fifth switch element Q201 and the sixth switch element Q203. A third connection point C between the fifth switch element Q201 and the sixth switch element Q203 is connected to one end of the secondary coil of the transformer 120. The fourth leg 80 includes the seventh switch element Q202 and the eighth switch element Q204. A fourth connection point D between the seventh switch element Q202 and the eighth switch element Q204 is connected to the other end of the secondary coil of the transformer 120. In the present embodiment, each of the switch elements Q101 to Q104, Q201 to Q204 is constituted by a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), but may be constituted by other switch elements, for example, an IGBT (Insulated Gate Bipolar Transistor).

[0027] FIG. 2 is a circuit diagram of a drive circuit for a main switch element of the switching power supply device according to the present embodiment. As shown in FIG. 2, the drive circuit 100 includes a series circuit of a primary winding T1-p of a drive transformer T1 and an input resistor R0 connected to a signal source (such as a drive IC) that generates an AC pulse signal Vg on the primary side of the drive transformer T1.

[0028] On the secondary side of the drive transformer T1, drive units 100-1 and 100-2 of main switch elements Q101 and Q103 are connected to secondary windings T1-S1a and T1-S1b respectively, and their outputs are connected between the gate-source terminals of main switch elements Q101 and Q103 respectively. The secondary windings T1-S1a and T1-S1b have the same number of turns, and the drive units 100-1 and 100-2 of main switch elements Q101 and Q103 have the same circuit configuration, but are connected such that the polarities of the secondary windings T1-S1a and T1-S1b are different (here, the polarities of T1-p and T1-S1a are the same). Also, since the drive circuits of main switch elements Q102 and Q104 are the same, the description here is omitted.

[0029] The main switch element drive unit 100-1 includes a first diode D1a with its cathode terminal connected to the gate terminal of the main switch element Q101 (the first switch element), a PNP bipolar transistor (the second switch element) Q2a with its base terminal (the first terminal) connected to the anode terminal of the first diode D1a, its emitter terminal (the second terminal) connected to the gate terminal of the main switch element Q101, and its collector terminal (the third terminal) connected to the source terminal of the main switch element Q101, a third switch element Q1a with its drain terminal connected to the anode terminal of the first diode D1a and its source terminal connected to the source terminal of the main switch element Q101, a parallel circuit 11 with one end connected to the cathode terminal of the Zener diode ZD1a and one end of the capacitor C1a, and the other end connected to the anode terminal of the Zener diode ZD1a and the other end of the capacitor C1a, a winding T1-S1a with one end connected to the drain terminal of the third switch Q1a via the parallel circuit 11, the other end connected to the gate terminal of the third switch element Q1a, and also connected to the source terminal of the third switch element Q1a via the second diode D2a. One end of the parallel circuit 11 is connected to one end of the winding T1-S1a, and the cathode terminal of the second diode D2a is connected to the other end of the winding T1-S1a.

[0030] Also, although the second switch element Q2a has been described as a PNP bipolar transistor, a P-chFET may be used. When the second switch element is used as a P-chFET, the first terminal is the gate terminal, the third terminal is the drain terminal, and the second terminal is the source terminal.

[0031] Also, a first resistor R4a may be connected between the gate terminal of the main switch element Q101 and the second terminal of the second switch element Q2a. Also, a second resistor R5a may be connected between the source terminal of the main switch element Q101 and the third terminal of the second switch element Q2a. The first resistor R4a and the second resistor R5a have an excellent effect of being able to adjust the discharge speed of the charge accumulated in the input capacitance of the main switch element Q101 and stabilizing the operating point of the second switch element Q2a.

[0032] Also, a third resistor R2a may be connected between the gate terminal of the third switch element Q1a and the other end of the winding T1-S1a. Also, a sixth resistor R1a may be connected between one end of the parallel circuit and one end of the winding T1-S1a. The third resistor R2a and the sixth resistor R1a have an excellent effect of being able to adjust the voltage rise speed between the gate and source of the main switch element Q101 and the third switch element Q1a.

[0033] Also, a fourth resistor R3a may be connected between the gate terminal and the source terminal of the third switch element Q1a. Also, a fifth resistor R6a may be connected between the gate terminal and the source terminal of the main switch element Q101. The fourth resistor R3a and the fifth resistor R6a have an excellent effect of discharging or suppressing the surge voltage between the gate and source of the main switch element Q101 and the third switch element Q1a, and protecting the third switch element.

[0034] The diode D1a is connected in a direction such that it conducts when one end of the secondary winding T1-s1 becomes high potential due to the voltage of the AC pulse signal Vg being at a high level (positive cycle), and sets the gate voltage Vgs of the main switch element Q101 to a high level.

[0035] The third switch element Q1a is turned on by a voltage at which the other end of the secondary winding T1-s1 becomes high potential during the period (negative cycle) when the voltage of the AC pulse signal Vg is at the inversion level, and the potential of the base terminal of the PNP bipolar transistor Q2a is lowered from the gate voltage of the main switch element Q101. Thereby, the PNP bipolar transistor Q2a is turned on, and an operation of lowering the gate voltage Vgs of the main switch element Q101 is performed. Optionally, short-circuit removal of the resistor R1a for adjusting the voltage rise speed between the gate and source of the main switch element Q101 and open-circuit removal of the R6a for protecting the voltage between the gate and source of the main switch element may be performed.

[0036] Next, the operation of the drive circuit 100 will be described. During the period (positive cycle) when the voltage of the AC pulse signal Vg is at the high level, the secondary winding T1-s1 induces a positive voltage. Then, this voltage is applied to the gate terminal of the main switch element Q101 via the resistor R1a, the capacitor C1a, and the diode D1a, and the main switch element Q101 is turned on. Since the drive voltage is a positive-direction voltage, the second switch element Q2a and the third switch element Q1a are turned off and do not participate in the above operation.

[0037] Next, when the voltage of the AC pulse signal Vg is inverted and enters the low level period (negative cycle), the negative voltage generated in the secondary winding T1-S1a turns on the third switch element Q1a, and the base terminal of the PNP bipolar transistor Q2a becomes low level. As a result, since the potential of the base terminal of the PNP bipolar transistor Q2a becomes lower than the potential of the gate terminal of the main switch element Q101, a current flows between the emitter and base of the PNP bipolar transistor Q2a, the emitter-collector becomes on, the gate level of the main switch element Q101 is rapidly lowered, and the main switch element Q101 is surely turned off. Optionally, the resistors R1a and R4a can be short-circuited separately or simultaneously, and the resistor R6a can be open-circuited.

[0038] As a result, the charge accumulated in the input capacitance (between the gate and the source) of the main switch element Q101 can be rapidly discharged through the PNP bipolar transistor Q2a and the resistors R4a and R5a. Then, instead of a resistor element (a resistor for base current limitation), by controlling the on / off of the second switch element Q2a with the third switch Q1a, a drive circuit for a semiconductor switch element with low losses can be provided.

[0039] Next, the discharge effect of the input capacitance of the main switch element Q101 by the drive circuit 100 will be described. FIG. 3 is an example of an operation waveform diagram of the drive circuit shown in FIG. 2, and is a diagram showing the voltage Vgs of the input capacitance (between the gate and the source) of the main switch element Q101 due to the generated voltage VT1-p of the primary side winding T1-p of the drive transformer T1. FIG. 4 is an enlarged view of the portion surrounded by the frame near the center of the waveform diagram of FIG. 3. As can be seen from FIGS. 3 and 4, the period from when the voltage Vgs of the input capacitance (between the gate and the source) of the main switch element Q101 starts to drop until it becomes 0V is within about 40 ns.

[0040] FIG. 5 is a circuit diagram of a drive circuit 100A for the main switch element of a switching power supply device according to a comparative example. The drive circuit 100A according to the comparative example has only the sixth resistor element R1a and the fifth resistor element R6a left on the secondary side compared to the drive circuit 100 according to the present embodiment. FIG. 6 is an example of an operation waveform diagram of the drive circuit shown in FIG. 5, and is a diagram showing the voltage Vgs' of the input capacitance (between the gate and the source) of the main switch element Q101 driven by the drive circuit 100A of the comparative example. FIG. 7 is an enlarged view of the portion surrounded by the frame near the center of the waveform diagram of FIG. 6. As can be seen from FIGS. 6 and 7, the period from when the voltage Vgs' of the input capacitance (between the gate and the source) of the main switch element Q101 in the comparative example starts to drop until it becomes 0V is 100 ns or more.

[0041] Therefore, according to the drive circuit of the present invention, even if the input capacitance between the gate and source of the main switch element of the switching power supply device increases, the charge accumulated in the input capacitance can be rapidly discharged, and the excellent effect of reducing the loss of the semiconductor switch element can be achieved. In the drive circuit of the present invention, by turning off at high speed and with high reliability, the set value of the minimum dead time required for the upper and lower main switch elements can be further reduced, so that the loss of the duty cycle can be reduced.

[0042] FIG. 8 is a circuit diagram of Modification 1 of the drive circuit of the main switch element (first switch element) of the switching power supply device according to the present embodiment. This Modification 1 is different from the drive circuit shown in FIG. 2 in that capacitors C2a (C2b) are connected in parallel across both ends of the fourth resistor R3a (R3b), and the noise suppression effect can be enhanced by the capacitors C2a (C2b).

[0043] Furthermore, even when the drive circuit of the present invention is modified such that the input drive signal is a one-way pulse, the drive circuit of the present invention is also applicable (only by adding the capacitor C0). Therefore, the drive circuit of the present invention is not only suitable for applications of AC pulses, but also suitable for one-way positive pulse drive. In addition, it is suitable not only for driving the upper and lower main switch elements of a full-bridge or half-bridge circuit, but also for driving the main switches of other circuit topologies such as buck, forward, and flyback.

[0044] FIG. 9 is a circuit diagram of Modification 2 of the drive circuit of the main switch element (first switch element) of the switching power supply device according to the present embodiment. The drive circuit of Modification 2 is a drive circuit with a positive pulse input. By connecting the capacitor C0 and the input resistor R0 in series, the drive circuit of Modification 2 can be applied to a positive pulse signal.

[0045] FIG. 10 is a circuit diagram of Modification Example 3 of the drive circuit of the main switch element (first switch element) of the switching power supply device according to the present embodiment. The difference between the drive circuit of Modification Example 3 and the drive circuit of Modification Example 2 is that the drive unit 100-2 is omitted. Thus, the drive circuit of Modification Example 3 can be applied to circuit topologies other than the bridge type.

[0046] Note that the drive circuit and the switching power supply device according to the present invention are not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

Description of Reference Numerals

[0047] 1 Switching power supply device 10 Primary side circuit 20 Secondary side circuit 50 First leg 60 Second leg 70 Third leg 80 Fourth leg 100, 100A Drive circuit 100-1, 100-2 Drive unit 120 Insulation transformer (transformer)

Claims

1. A drive circuit for driving a first switch element, comprising: a first diode having a cathode terminal connected to a gate terminal of the first switch element; a second switch element having an anode terminal of the first diode connected to a first terminal, a gate terminal of the first switch element connected to a second terminal, and a source terminal of the first switch element connected to a third terminal; a third switch element having an anode terminal of the first diode connected to a drain terminal and a source terminal of the first switch element connected to a source terminal; a parallel circuit having one end connected to a cathode terminal of a Zener diode and one end of a first capacitor, and the other end connected to an anode terminal of the Zener diode and the other end of the first capacitor; a drive transformer having one end connected to a drain terminal of the third switch element via the parallel circuit, the other end connected to a gate terminal of the third switch element, and having a winding connected to a source terminal of the third switch element via a second diode; one end of the parallel circuit is connected to one end of the winding, and a cathode terminal of the second diode is connected to the other end of the winding; at least one of the connection between the second terminal and the gate terminal of the first switch element and the connection between the third terminal and the source terminal of the first switch element is connected via a resistance element; The drive circuit is characterized in that the first switch element is turned on when the voltage of the winding is at a high level, and the third switch element is turned on when the voltage of the winding is at a low level.

2. The drive circuit according to claim 1, wherein the second switch element is a PNP bipolar transistor, the first terminal is a base terminal, the third terminal is a collector terminal, and the second terminal is an emitter terminal.

3. The drive circuit according to claim 1, wherein the second switch element is a P-ch FET, the first terminal is a gate terminal, the third terminal is a drain terminal, and the second terminal is a source terminal.

4. The drive circuit according to claim 1, wherein a first resistance element is connected between a gate terminal of the first switch element and the second terminal of the second switch element.

5. The drive circuit according to claim 1, wherein a second resistance element is connected between a source terminal of the first switch element and the third terminal of the second switch element.

6. The drive circuit according to claim 1, wherein a third resistor element is connected between the gate terminal of the third switch element and the other end of the winding.

7. The drive circuit according to claim 1, wherein a fourth resistor element is connected between the gate terminal and the source terminal of the third switch element.

8. The drive circuit according to claim 1, wherein a second capacitor is connected between the gate terminal and the source terminal of the third switch element.

9. The drive circuit according to claim 1, wherein a fifth resistor element is connected between the gate terminal and the source terminal of the first switch element.

10. The drive circuit according to claim 1, wherein a sixth resistor element is connected between one end of the parallel circuit and one end of the winding.

11. A switching power supply device comprising the drive circuit according to any one of claims 1 to 10.

Images