Switching Power Supply Unit

Abstract

To provide a switching power supply device that is not affected by the Miller effect and can extend the life of a gate terminal. [Solution] In a switching power supply device 1, the emitter of a drive transistor 20 is connected to the gate terminal of a switching element 10, the cathode of a Zener diode 30 and a capacitor 40 are connected to the base terminal of the drive transistor 20, the anode of the Zener diode 30 and the other terminal of the capacitor 40 are connected to the source terminal of the switching element 10, a resistor 60 is connected between the base terminal of the drive transistor 20 and a device 50 that generates a drive signal, and a base current, a Zener current and a charging current to the capacitor 40 flow, an anode of a diode 70 is connected to the gate terminal of the switching element 10, and a cathode of the diode 70 is connected to the device 50 that generates a drive signal.

Description

[Technical field]

[0001] The present invention relates to a switching power supply device, and more particularly to the configuration of a drive circuit for a transistor, which is a switching element used inside the device. [Background technology]

[0002] Conventional capacitor-coupled circuits store electric charge in a coupling capacitor and negatively bias the gate of a switching element such as a GaN-HEMT (High Electron Mobility Transistor).

[0003] For example, in a conventional drive circuit such as that in Patent Document 1 (particularly FIG. 1, etc.), a Zener diode or a diode is connected between the gate and the ground line to clamp the gate voltage when turned on. Also, by storing charge in a capacitor, the voltage applied to the gate during steady operation is reduced, and a reverse bias is applied when the device is off. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-336694 A Summary of the Invention [Problem to be solved by the invention]

[0005] In conventional capacitor-coupled circuits, the drive voltage of the switching power supply control IC is generally 10 to 15 V, as most control ICs are made for Si MOSFETs. The gate terminal withstand voltage of Si is generally 20 to 30 V max, while the gate withstand voltage of normally-off GaN-HEMT (excluding cascode connection type) is low at around 7 V. On the other hand, the lower limit of the drive voltage needs to be 5 V or more, taking into account the on-resistance, and the drive voltage needs to be strictly controlled.

[0006] In addition, drivers for GaN-HEMTs are expensive and difficult to obtain because there are few varieties available. GaN-HEMTs have low input capacitance Ciss and can switch at high speed, but high-speed switching can cause excessive surge voltages in the secondary rectifier and large switching noise, so the gate-on speed must be slowed down.

[0007] When slowing down the gate on speed, it is common to use a resistor to determine the gate rise speed, but if it is limited by a resistor, the gate capacitance appears to have increased due to the mirror effect when turning on, and it takes longer for the gate voltage to reach its upper limit, creating an area with high on-resistance and increasing losses. Also, the variation in gate capacitance is larger than that of capacitor components such as multilayer ceramic capacitors, so the gate on speed is also prone to variation.

[0008] In the case of conventional capacitor-coupled circuits, when the capacitor is in intermittent operation such as at startup or in burst mode, no charge is stored in the capacitor, and when no charge is stored, the voltage across the resistor increases, causing the on-speed to increase and the surge voltage of the secondary rectifier to rise. When operating intermittently such as at startup or in burst mode, even in power supplies that achieve low noise through resonant operation, hard switching always occurs at first, so if the gate on-speed is fast, surges are more likely to occur.

[0009] In addition, GaN-HEMTs tend to have a shorter gate life at low temperatures, but in the case of conventional circuits, the gate voltage increases at low temperatures, further shortening the lifespan. [Means for solving the problem]

[0010] The present invention provides a switching power supply device that can solve these conventional problems.

[0011] A switching power supply according to a first aspect of the present invention comprises a normally-off switching element having a source terminal, a drain terminal and a gate terminal, a drive transistor, a Zener diode, a capacitor, a device for generating a drive signal, a resistor and a diode, the emitter of the drive transistor is connected to the gate terminal of the switching element, the cathode of the Zener diode and one terminal of the capacitor are connected to the base terminal of the drive transistor, the anode of the Zener diode and the other terminal of the capacitor are connected to the source terminal of the switching element, the resistor is connected between the base terminal of the drive transistor and the device for generating the drive signal, a base current, a Zener current and a charging current to the capacitor flow, the anode of the diode is connected to the gate terminal of the switching element, and the cathode of the diode is connected to the device for generating the drive signal.

[0012] A switching power supply according to a second aspect of the present invention comprises a normally-off switching element having a source terminal, a drain terminal and a gate terminal, a drive transistor, a Zener diode, a capacitor, a device for generating a drive signal, and a resistor, the emitter of the drive transistor is connected to the gate terminal of the switching element, the cathode of the Zener diode and one terminal of the capacitor are connected to the base terminal of the drive transistor, the anode of the Zener diode and the other terminal of the capacitor are connected to the source terminal of the switching element, the resistor is connected between the base terminal of the drive transistor and the device for generating the drive signal, a base current, a Zener current and a charging current to the capacitor flow, and the drive transistor is a bidirectional transistor.

[0013] A switching power supply according to a third aspect of the present invention comprises a normally-off switching element having a source terminal, a drain terminal and a gate terminal, a drive transistor, a Zener diode, a device for generating a drive signal, a resistor and a diode, the emitter of the drive transistor is connected to the gate terminal of the switching element, the cathode of the Zener diode is connected to the base terminal of the drive transistor, the anode of the Zener diode is connected to the source terminal of the switching element, the resistor is connected between the base terminal of the drive transistor and the device for generating the drive signal, a base current and a Zener current flow, the anode of the diode is connected to the gate terminal of the switching element, and the cathode of the diode is connected to the device for generating the drive signal.

[0014] A switching power supply according to a fourth aspect of the present invention comprises a normally-off switching element having a source terminal, a drain terminal, and a gate terminal, a drive Si-MOSFET (Metal Oxide Semiconductor Field Effect Transistor), a Zener diode, a capacitor, a device for generating a drive signal, a resistor, and a diode, the source terminal of the drive Si-MOSFET is connected to the gate terminal of the switching element, the cathode of the Zener diode and one terminal of the capacitor are connected to the gate terminal of the drive Si-MOSFET, the anode of the Zener diode and the other terminal of the capacitor are connected to the source terminal of the switching element, the resistor is connected between the gate terminal of the drive Si-MOSFET and the device for generating the drive signal, a gate terminal charging current, a Zener current, and a charging current to the capacitor flow, the anode of the diode is connected to the gate terminal of the switching element, and the cathode of the diode is connected to the device for generating the drive signal.

[0015] A switching power supply according to a fifth aspect of the present invention comprises a normally-off switching element having a source terminal, a drain terminal and a gate terminal, a drive Si-MOSFET, a Zener diode, a capacitor, a device for generating a drive signal, a resistor and a body diode of the drive Si-MOSFET, the source terminal of the drive Si-MOSFET is connected to the gate terminal of the switching element, the cathode of the Zener diode and one terminal of the capacitor are connected to the gate terminal of the drive Si-MOSFET, the anode of the Zener diode and the other terminal of the capacitor are connected to the source terminal of the switching element, the resistor is connected between the gate terminal of the drive Si-MOSFET and the device for generating the drive signal, a gate terminal charging current, a Zener current and a charging current to the capacitor flow, the anode of the body diode of the drive Si-MOSFET is connected to the gate terminal of the switching element, and the cathode of the body diode of the drive Si-MOSFET is connected to the device for generating the drive signal.

[0016] In the switching power supply device according to the present invention, the switching element may be a GaN-HEMT (High Electron Mobility Transistor).

[0017] In the switching power supply device according to the present invention, the switching element may be a Si-MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

[0018] In the switching power supply device according to the present invention, the switching element may be a SiC-MOSFET. Effect of the Invention

[0019] According to the switching power supply of the present invention, by increasing the base voltage of the drive transistor with the time constant of the resistor and capacitor, the gate of the switching element also rises with a similar gradient, making it possible to achieve a constant gate-on speed regardless of the gate capacitance of the switching element. In other words, the gradient is almost constant and not affected by the Miller effect.

[0020] According to the switching power supply device of the present invention, the gate voltage can be clamped to any voltage below the drive signal by the Zener diode and the drive transistor.

[0021] According to the switching power supply of the present invention, for example, a 5 to 6 V Zener diode has a positive temperature characteristic, and the base-emitter voltage VBE of the drive transistor has a negative temperature characteristic, so that the gate voltage of the switching element drops at low temperatures, enabling the gate terminal to be designed to have a longer life.

[0022] According to the switching power supply device of the present invention, it is possible to control the voltage level shift and gate on speed with a small number of discrete components, without using a driver IC dedicated to switching elements such as GaN.

[0023] According to the switching power supply of the present invention, the capacitor voltage is reset for each switching operation, so that the on-speed can be kept constant during intermittent operation such as start-up or burst mode operation, just like during steady operation. Other objects, features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a circuit diagram of a switching power supply device according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a circuit diagram of a switching power supply according to a second embodiment of the present invention. [Diagram 3]FIG. 3 is a circuit diagram of a switching power supply according to a third embodiment of the present invention. [Figure 4] FIG. 4 is a circuit diagram of a switching power supply according to a fourth embodiment of the present invention. [Diagram 5] FIG. 5 is a circuit diagram of a switching power supply according to a fifth embodiment of the present invention. [Figure 6] FIG. 6 is a diagram showing the operation of the switching power supply device according to the present invention. [Figure 7] FIG. 7 is a diagram showing a comparison between a conventional switching power supply using capacitor coupling and a switching power supply according to the present invention. [Figure 8] FIG. 8 is a diagram showing an example of a conventional capacitor-coupled circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0025] FIG. 1 is a circuit diagram of a switching power supply device according to a first embodiment of the present invention. A switching power supply device 1 according to a first aspect of the present invention comprises a normally-off switching element 10 having a source terminal, a drain terminal and a gate terminal, a drive transistor 20, a Zener diode 30, a capacitor 40, a device 50 for generating a drive signal, a resistor 60 and a diode 70.

[0026] In the switching power supply device 1 according to the first aspect of the present invention, the emitter of the drive transistor 20 is connected to the gate terminal of the switching element 10. The cathode of the Zener diode 30 and one terminal of the capacitor 40 are connected to the base terminal of the drive transistor 20. The anode of the Zener diode 30 and the other terminal of the capacitor 40 are connected to the source terminal of the switching element 10. The resistor 60 is connected between the base terminal of the drive transistor 20 and the device 50 that generates a drive signal. A base current, a Zener current, and a charging current to the capacitor 40 flow through the resistor 60. The anode of the diode 70 is connected to the gate terminal of the switching element 10. The cathode of the diode 70 is connected to the device 50 that generates a drive signal.

[0027] By adopting the configuration of the first aspect, the gate voltage increases at a constant rate, so that the on-resistance can be effectively reached at a low level quickly.

[0028] The switching element 10 has a source terminal, a drain terminal, and a gate terminal. The switching element 10 is preferably a normally-off switching element. The switching element 10 may be a GaN-HEMT (High Electron Mobility Transistor). The switching element 10 may be a Si-MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The switching element 10 may be a SiC-MOSFET.

[0029] The emitter of the drive transistor 20 is connected to the gate terminal of the switching element 10 .

[0030] The cathode of the Zener diode 30 is connected to the base terminal of the drive transistor 20. The anode of the Zener diode 30 is connected to the source terminal of the switching element .

[0031] The capacitor 40 is connected to the base terminal of the drive transistor 20. The other terminal of the capacitor 40 is connected to the source terminal of the switching element 10.

[0032] A resistor 60 is connected between the device 50 for generating a drive signal and the base terminal of the drive transistor 20 .

[0033] A resistor 60 is connected between the base terminal of the drive transistor 20 and an apparatus 50 for generating a drive signal.

[0034] The anode of the diode 70 is connected to the gate terminal of the switching element 10. The cathode of the diode 70 is connected to the device 50 which generates a drive signal.

[0035] FIG. 2 is a circuit diagram of a switching power supply according to a second embodiment of the present invention. In the switching power supply 1 according to the second aspect of the present invention, the drive transistor 20 is a bidirectional transistor. A "bidirectional transistor" is a transistor that allows current to flow in both directions, such as an NPN transistor. The switching power supply device 1 according to the second embodiment of the present invention is different from the switching power supply device 1 according to the first embodiment of FIG. 1 in that the switching power supply device 1 according to the second embodiment of the present invention does not include a diode 70.

[0036] In a switching power supply device 1 according to a second aspect of the present invention, the emitter of the drive transistor 20 is connected to the gate terminal of the switching element 10. The cathode of the Zener diode 30 and the capacitor 40 are connected to the base terminal of the drive transistor 20. The anode of the Zener diode 30 and the other terminal of the capacitor 40 are connected to the source terminal of the switching element 10. A resistor 60 is connected between the base terminal of the drive transistor 20 and a device 50 that generates a drive signal. A base current, a Zener current, and a charging current to the capacitor 40 flow. In the switching power supply device 1 according to the second aspect of the present invention, the drive transistor 20 is composed of a bidirectional transistor.

[0037] By adopting the configuration of the second aspect, it is possible to obtain an effect that it is possible to eliminate the diode 70 for increasing the off speed when the switching element is turned off.

[0038] FIG. 3 is a circuit diagram of a switching power supply according to a third embodiment of the present invention. The switching power supply 1 according to the third aspect of the present invention does not have the capacitor 40 of the switching power supply 1 according to the first aspect of FIG. 1, but instead uses only the junction capacitance of the Zener diode 30 and the drive transistor 20 in place of the capacitor. The switching power supply 1 according to the third aspect of the present invention comprises a normally-off switching element 10 having a source terminal, a drain terminal and a gate terminal, a drive transistor 20, a Zener diode 30, a device 50 for generating a drive signal, a resistor 60 and a diode 70. The difference from the switching power supply 1 according to the first aspect of FIG. 1 is that it does not have the capacitor 40.

[0039] In a switching power supply device 1 according to a third embodiment of the present invention, the emitter of a drive transistor 20 is connected to the gate terminal of a switching element 10. The cathode of a Zener diode 30 is connected to the base terminal of the drive transistor 20. The anode of the Zener diode 30 is connected to the source terminal of the switching element 10. A resistor 60 is connected between the base terminal of the drive transistor 20 and a device 50 that generates a drive signal. A base current and a Zener current flow through the diode 70, and the anode of the diode 70 is connected to the gate terminal of the switching element 10. The cathode of the diode 70 is connected to the device 50 that generates a drive signal.

[0040] By adopting a configuration such as that of the third aspect, it is possible to reduce the number of parts.

[0041] FIG. 4 is a circuit diagram of a switching power supply according to a fourth embodiment of the present invention. The switching power supply 1 according to the fourth embodiment of the present invention is configured with a Si-MOSFET 80 instead of the drive transistor 20 of the switching power supply 1 according to the first embodiment of FIG. A switching power supply device 1 according to a fourth aspect of the present invention includes a normally-off switching element 10 having a source terminal, a drain terminal and a gate terminal, a drive Si-MOSFET 80, a Zener diode 30, a capacitor 40, a device 50 for generating a drive signal, a resistor 60 and a diode 70.

[0042] In a switching power supply device 1 according to a fourth aspect of the present invention, the source terminal of the drive Si-MOSFET 80 is connected to the gate terminal of the switching element 10. The cathode of the Zener diode 30 and one terminal of the capacitor 40 are connected to the gate terminal of the drive Si-MOSFET 80. The anode of the Zener diode 30 and the other terminal of the capacitor 40 are connected to the source terminal of the switching element 10. The resistor 60 is connected between the gate terminal of the drive Si-MOSFET 80 and the device 50 that generates a drive signal. A gate terminal charging current, a Zener current, and a charging current to the capacitor flow. The anode of the diode 70 is connected to the gate terminal of the switching element 10, and the cathode of the diode 70 is connected to the device 50 that generates a drive signal.

[0043] By adopting a configuration like the fourth aspect, the temperature characteristic of the Vth of a Si-MOSFET is more positive than that of an NPN transistor, so that a design that lowers the gate voltage at low temperatures is possible.

[0044] FIG. 5 is a circuit diagram of a switching power supply according to a fifth embodiment of the present invention. A switching power supply 1 according to a fifth embodiment of the present invention is configured such that the diode 70 of the switching power supply 1 according to the first embodiment of FIG. 1 is replaced with a body diode of a drive Si-MOSFET. A switching power supply according to a fifth aspect of the present invention comprises a normally-off switching element 10 having a source terminal, a drain terminal and a gate terminal, a drive Si-MOSFET 80, a Zener diode 30, a capacitor 40, a device 50 for generating a drive signal, a resistor 60 and a body diode 90 of the drive Si-MOSFET.

[0045] In a switching power supply device 1 according to a fifth aspect of the present invention, the source terminal of the drive Si-MOSFET 80 is connected to the gate terminal of the switching element 10. The cathode of the Zener diode 30 and one terminal of the capacitor 40 are connected to the gate terminal of the drive Si-MOSFET 80. The anode of the Zener diode 30 and the other terminal of the capacitor 40 are connected to the source terminal of the switching element 10. The resistor 60 is connected between the gate terminal of the drive Si-MOSFET 80 and the device 50 that generates a drive signal. A gate terminal charging current, a Zener current, and a charging current to the capacitor flow. The anode of the body diode 90 of the drive Si-MOSFET is connected to the gate terminal of the switching element 10, and the cathode of the body diode 90 of the drive Si-MOSFET is connected to the device 50 that generates a drive signal.

[0046] By adopting the configuration of the fifth aspect, it is possible to obtain an effect that it is possible to eliminate the diode 70 for increasing the off speed when the switching element is turned off.

[0047] FIG. 6 is a diagram showing the operation of the switching power supply device according to the present invention. In Fig. 6, the slope of the Vc10 voltage is determined by the DRV voltage, the capacitance of resistor R60, and capacitor C40. That is, the slope (dv / dt) of the Vc10 voltage in Fig. 6 is determined by the constants of resistor R60 and capacitor C40 and the drive voltage, and the upper limit of the Vgs voltage is determined by the Zener voltage of Zener diode ZD30 and Vbe of transistor TR20. Vgs is Vgs=Vc10-Vbe. Since the Vth of GaN is about 2V, for example, in the case of a drive voltage of 10 to 12V, GaN is turned on in the nearly linear region of the RC time constant, so the variation in on-time and on-speed due to the variation in Vth is small. Here, the on-speed is the dv / dt of Vgs when passing through Vth. Since the speed at which Vc10 rises does not depend on the input capacitance of GaN, the speed at which Vgs rises does not change due to the Miller effect that occurs when GaN is turned on. Since the gate voltage slope of Vgs is independent of the input capacitance, the time it takes to reach 5V or higher (the voltage at which the device is completely turned on) is shortened.

[0048] FIG. 7 is a diagram showing a comparison between a conventional switching power supply using capacitor coupling and the switching power supply according to the embodiment of FIG. 6 of the present invention. Fig. 7(a) is a graph showing the change in the slope of Vgs in the switching power supply device with the conventional capacitor coupling of Fig. 8. Fig. 7(b) is a graph showing the change in the slope of Vgs in the switching power supply device 1 according to the embodiment of the present invention of Fig. 6. The vertical axis of Fig. 7(a) and (b) represents voltage, and the horizontal axis represents time. In the conventional switching power supply with capacitor coupling shown in Fig. 7(a), the gate resistor R65 is 220Ω, Ciss is 50pF, and the time constant is 11.0ns. In the switching power supply 1 according to the first embodiment of the present invention shown in Fig. 7(b), the gate resistor, i.e., resistor R60, is 10,000Ω, capacitor C40 is 22pF, and the time constant is 220.0ns.

[0049] As shown in Fig. 7, when the Vgs slope changes at the on-timing, it takes time for the on-resistance to decrease. Compared to a conventional switching power supply device using capacitor coupling, the switching power supply device 1 according to the embodiment of the present invention shown in Fig. 6 has the advantage that the gate voltage increases at a constant slope, so that the on-resistance quickly reaches a low point.

[0050] As described above, according to the configuration of the switching power supply 1 of the present invention, a constant gate on-speed can be achieved regardless of the gate capacitance of the switching element, a nearly constant slope can be achieved without being affected by the Miller effect, the gate voltage can be clamped by the Zener diode and drive transistor, the gate voltage drops at low temperatures and the gate terminal life can be extended, and it is possible to control the voltage level shift and gate on-speed with a small number of discrete components without using a driver IC dedicated to switching elements such as GaN, and a constant on-speed can be achieved even during intermittent operation such as at startup or in burst mode operation, just like during steady operation. Although the above description has been given with reference to the embodiment, it is apparent to those skilled in the art that the present invention is not limited thereto, and that various changes and modifications can be made within the scope of the principles of the present invention and the appended claims. [Explanation of symbols]

[0051] 1 Switching power supply 10 Switching element 20 Drive transistor 30 Zener Diode 40 Capacitor 50 Device for generating drive signal 60 Resistance 70 Diode 80 Drive Si-MOSFET 90 Body diode of Si-MOSFET for drive

Claims

1. A normally-off switching element (10) having a source terminal, a drain terminal, and a gate terminal; A drive transistor (20); A Zener diode (30); A capacitor (40); A device (50) for generating a drive signal; A resistor (60); Diode (70) Equipped with The emitter of the drive transistor (20) is connected to the gate terminal of the switching element (10); a cathode of the Zener diode (30) and one terminal of the capacitor (40) are connected to a base terminal of the drive transistor (20); The anode of the Zener diode (30) and the other terminal of the capacitor (40) are connected to the source terminal of the switching element (10); the resistor (60) is connected between the base terminal of the drive transistor (20) and a device (50) for generating the drive signal; The base current, the Zener current, and the charging current to the capacitor (40) flow. an anode of a diode (70) connected to a gate terminal of the switching element (10), and a cathode of the diode (70) connected to a device (50) for generating the drive signal; A switching power supply (1) characterized in that a device (50) for generating the drive signal is connected to the collector of the drive transistor (20).

2. A normally-off switching element (10) having a source terminal, a drain terminal, and a gate terminal; A drive transistor (20); A Zener diode (30); A capacitor (40); A device (50) for generating a drive signal; A resistor (60); Equipped with The emitter of the drive transistor (20) is connected to the gate terminal of the switching element (10); a cathode of the Zener diode (30) and one terminal of the capacitor (40) are connected to a base terminal of the drive transistor (20); The anode of the Zener diode (30) and the other terminal of the capacitor (40) are connected to the source terminal of the switching element (10); the resistor (60) is connected between the base terminal of the drive transistor (20) and a device generating the drive signal (50); The base current, the Zener current, and the charging current to the capacitor (40) flow. A switching power supply (1) characterized in that a device (50) for generating the drive signal is connected to the collector of the drive transistor (20).

3. A normally-off switching element (10) having a source terminal, a drain terminal, and a gate terminal; A drive transistor (20); A Zener diode (30); A device (50) for generating a drive signal; A resistor (60); Diode (70) Equipped with The emitter of the drive transistor (20) is connected to the gate terminal of the switching element (10); The cathode of the Zener diode (30) is connected to the base terminal of the drive transistor (20); The anode of the Zener diode (30) is connected to the source terminal of the switching element (10); the resistor (60) is connected between the base terminal of the drive transistor (20) and a device (50) for generating the drive signal; Base current and Zener current flow, an anode of a diode (70) connected to a gate terminal of the switching element (10), and a cathode of the diode (70) connected to a device (50) for generating the drive signal; A switching power supply (1) characterized in that a device (50) for generating the drive signal is connected to the collector of the drive transistor (20).

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