Overcurrent protection circuit and switching circuit

Abstract

The overcurrent protection circuit includes: a first transistor having an emitter connected to a control voltage; and a second transistor having a base connected to the collector of the first transistor, a collector connected to the base of the first transistor and pulled up to a predetermined voltage, and an emitter grounded. When the control voltage exceeds a predetermined first threshold voltage, the overcurrent protection circuit initiates the following protection operation: the first and second transistors are turned on, the pull-up voltage decreases, causing the control voltage to decrease, thereby disconnecting the switching element. The overcurrent protection circuit also includes: a first diode connected between the control voltage and the emitter of the first transistor; and a component circuit connected between the emitter and base of the first transistor. The component circuit is any one of the second diode, the first resistor, and a parallel circuit of the second diode and the first resistor.

Description

Technical Field

[0001] This invention relates to overcurrent protection circuits and switching circuits incorporating such overcurrent protection circuits. The switching circuits include, for example, boost chopper circuits, half-bridge inverter circuits, and full-bridge inverter circuits. Background Technology

[0002] Semiconductor devices typically have short-circuit withstand capabilities; if a current exceeding these capabilities flows through them, it can potentially cause damage. Overcurrent protection for semiconductor devices can be achieved by rapidly detecting overcurrent flowing through them due to a short circuit and stopping the current flow.

[0003] For example, Patent Document 1 provides an overcurrent protection device for a power conversion device, which can change the set level of the collector short-circuit detection voltage at any time when the DC voltage is high, low, or constant, and can reliably protect the voltage drive element from the influence of overcurrent.

[0004] The overcurrent protection device disclosed in Patent Document 1 includes: a power conversion device having a voltage-driven power switching element; an overcurrent detection unit that detects the voltage at the input side main terminal of the power switching element and provides a disconnect signal to the power switching element when the voltage exceeds a predetermined value; and an overcurrent setting unit configured to be connected in parallel with the overcurrent detection unit at any time and to change the predetermined value.

[0005] GaN devices are semiconductor devices that utilize gallium nitride (GaN). Compared to existing semiconductor devices such as insulated gate bipolar transistors (IGBTs) and SiC devices, they have the characteristic of being able to be driven at high frequencies.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2006-14402

[0007] However, compared to existing semiconductor devices, GaN devices have weak overcurrent resistance; for example, an overcurrent of around 100 nanoseconds can sometimes cause damage. Therefore, existing overcurrent protection technologies such as the DESAT (Desaturation Protection) function, CT (Current Transformer) detection, or the technology in Patent Document 1, which detect the unsaturated (overcurrent) state between the collector and emitter of the IGBT element and automatically cut off the gate, cannot adequately protect GaN devices. Summary of the Invention

[0008] The purpose of this invention is to solve the above problems and provide an overcurrent protection circuit and a switching circuit with the overcurrent protection circuit, which can protect semiconductor switches from the effects of overcurrent at high speed compared with the prior art.

[0009] The overcurrent protection circuit of the present invention is used for a switching element that is controlled to be switched on and off according to a control voltage, and includes:

[0010] The first transistor is a PNP bipolar transistor, having an emitter connected to the control voltage; and

[0011] The second transistor is an NPN bipolar transistor, having a base connected to the collector of the first transistor, a collector connected to the base of the first transistor and pulled up to a specified pull-up voltage, and an emitter grounded.

[0012] When the control voltage exceeds a predetermined first threshold voltage, the overcurrent protection circuit initiates the following protection operation: the first and second transistors are turned on, and the pull-up voltage is reduced, causing the control voltage to decrease, thereby disconnecting the switching element.

[0013] The overcurrent protection circuit includes:

[0014] A first diode has an anode connected to the control voltage and a cathode connected to the emitter of the first transistor; and

[0015] The component circuit is connected between the emitter and base of the first transistor.

[0016] The component circuit is any one of the following:

[0017] (1) A second diode having a cathode connected to the emitter of the first transistor and an anode connected to the base of the first transistor;

[0018] (2) First resistor;

[0019] (3) The parallel circuit of the second diode and the first resistor.

[0020] Therefore, the overcurrent protection circuit and the like according to the present invention can protect semiconductor devices from the effects of overcurrent at a high speed compared with the prior art. Attached Figure Description

[0021] Figure 1 This is a block diagram illustrating an example configuration of the boost chopper circuit 101 involved in the comparative example.

[0022] Figure 2 It means Figure 1 A block diagram illustrating the detailed configuration of the current-driven switching circuit 110.

[0023] Figure 3A It means Figure 2Timing diagram of the operating waveforms of signals, etc. in the current-driven switching circuit 110.

[0024] Figure 3B yes Figure 3A A magnified view of the base-emitter voltage Vbe of transistor Q1.

[0025] Figure 4 This is a block diagram illustrating an example configuration of the boost chopper circuit 1 according to Embodiment 1.

[0026] Figure 5 It means Figure 4 A block diagram illustrating a detailed configuration example of a current-driven switching circuit 10.

[0027] Figure 6 It means Figure 5 Timing diagram of the operating waveforms of signals, etc. in the current-driven switching circuit 10.

[0028] Figure 7A It is used for in Figure 5 In the current-driven switching circuit 10, diodes D11 and D12 are added to prevent overvoltage. Figure 6 A magnified view of the base-emitter voltage Vbe.

[0029] Figure 7B Is Figure 5 In the current-driven switching circuit 10, when the protection function is activated... Figure 6 A magnified view of the base-emitter voltage Vbe of transistor Q1.

[0030] Figure 7C Is Figure 5 In the current-driven switching circuit 10, when switching to the protection operation holding state... Figure 6 A magnified view of the base-emitter voltage Vbe and the detection voltage Vocp of transistor Q1.

[0031] Figure 7D It is used for in Figure 5 The current-driven switching circuit 10 describes the adjustment of the time from the protection operation holding state to automatic recovery. Figure 6 A magnified view of the base-emitter voltage Vbe and the detection voltage Vocp of transistor Q1.

[0032] Figure 8 This is a block diagram illustrating a detailed configuration example of the current-driven switching circuit 10A according to Embodiment 2.

[0033] Figure 9A It is used for in Figure 8The waveform of the base-emitter voltage Vbe of transistor Q1 is described by adding diode D11 and resistor R11 to the current-driven switching circuit 10A to prevent overvoltage.

[0034] Figure 9B Is Figure 8 In the current-driven switching circuit 10A, the waveform of the base-emitter voltage Vbe of transistor Q1 when the protection function is working is shown.

[0035] Figure 9C It is used for in Figure 8 The waveforms of the base-emitter voltage Vbe and the detection voltage Vocp of transistor Q1 are shown in the current-driven switching circuit 10A, which describes the time from the protection function holding state to automatic recovery.

[0036] Figure 10 This is a block diagram illustrating a detailed configuration example of the current-driven switching circuit 10B according to Embodiment 3.

[0037] Figure 11A It is used for in Figure 10 The waveform of the base-emitter voltage Vbe of transistor Q1 is shown in the current-driven switching circuit 10B, in which diodes D11 and D12 and resistor R11 are added to prevent overvoltage.

[0038] Figure 11B It is used for in Figure 10 The waveform of the base-emitter voltage Vbe of transistor Q1 in the current-driven switching circuit 10B, which describes the timing of overcurrent occurrence, is shown.

[0039] Figure 12A This is a block diagram illustrating a detailed configuration example of the current-driven switching circuit 10C according to Embodiment 4.

[0040] Figure 12B It means Figure 12A Timing diagram of the operating waveforms of signals, etc. in the current-driven switching circuit 10C.

[0041] Figure 13 This is a block diagram illustrating a detailed configuration example of the current-driven switching circuit 10D according to Embodiment 5.

[0042] Figure 14 This is a block diagram illustrating a detailed configuration example of the current-driven switching circuit 10E according to Embodiment 6.

[0043] Figure 15 This is a block diagram illustrating a detailed configuration example of the current-driven switching circuit 10F according to Embodiment 7.

[0044] Figure 16 This is a block diagram illustrating a detailed configuration example of the current-driven switching circuit 10G according to Embodiment 8.

[0045] Figure 17 This is a block diagram illustrating an example of the configuration of the half-bridge inverter circuit 1A involved in Modification Example 1.

[0046] Figure 18 This is a block diagram illustrating an example configuration of the full-bridge inverter circuit 1B involved in Modification Example 2. Detailed Implementation

[0047] The embodiments of the present invention will now be described with reference to the accompanying drawings. However, the embodiments described below are merely illustrative in all respects. Various modifications or variations can be made without departing from the scope of the invention. That is, specific configurations corresponding to the embodiments may be appropriately adopted when implementing the present invention.

[0048] Below, after describing the circuit configuration and operation of the comparative example and the problems involved therein, the implementation methods and variations for solving the problems will be described.

[0049] (Comparative Example)

[0050] Figure 1 This is a block diagram illustrating an example configuration of the boost chopper circuit 101 involved in the comparative example. Figure 1 In the boost chopper circuit 101, there are a current-driven switching circuit 110, an inductor L1, a diode D1 and a capacitor C1. The current-driven switching circuit 110 has a semiconductor switch 14 as a switching element.

[0051] exist Figure 1 In this circuit, the input voltage Vi is applied via inductor L1 to the junction of the anode of diode D1 and the drain of semiconductor switch 14. The source of semiconductor switch 14 is grounded. The cathode of diode D1 is connected to one end of capacitor C1, which outputs the voltage Vo, and the other end is grounded.

[0052] In the boost chopper circuit 101 configured as described above, inductor L1 generates an electromotive force (EMF) in the direction that hinders current changes. Therefore, when semiconductor switch 14 switches from on to off according to the control voltage applied to the gate of its control terminal, inductor L1 generates an EMF in the same direction as the input voltage Vi to prevent current reduction due to the resistance of diode D1. This generates a voltage higher than the input voltage Vi, which is smoothed by capacitor C1 and converted into an output voltage Vo. Thus, by periodically and selectively switching semiconductor switch 14 on and off, boost chopper circuit 101 converts the input voltage Vi into a DC output voltage Vo that is higher than the input voltage Vi and outputs it.

[0053] Figure 2 It means Figure 1 A block diagram illustrating the detailed configuration of a current-driven switching circuit 110. Figure 2 In this circuit, the current-driven switching circuit 110 includes an overcurrent protection circuit 111, a control unit 12, a drive unit 13, a semiconductor switch 14, and a resistor R1. The overcurrent protection circuit 111 includes transistors Q1 and Q2, a pull-up resistor R2, and a voltage detection circuit 15.

[0054] exist Figure 2 In this process, the control unit 12 uses a pulse signal, namely the drive signal Sdrv, to control the drive unit 13. In addition, the control unit 12 monitors the signal representing the detection voltage Vocp applied from the voltage detection circuit 15 of the overcurrent protection circuit 111 to the base of the transistor Q1. When the detection voltage Vocp is lower than a predetermined threshold, the abnormal detection flag Fh is set to a high level, the drive signal Sdrv is fixed to a low level, and the drive unit 13 is stopped.

[0055] The driving unit 13 applies a gate-source voltage Vgs to the gate of the semiconductor switch 14 via a resistor R1 based on the driving signal Sdrv from the control unit 12, thereby controlling the on / off state of the semiconductor switch 14. The semiconductor switch 14 is, for example, a switching element such as a GaN device, and the driving unit 13 selectively switches whether the drain current Id is conducted by controlling its on / off state. It should be noted that the gate-source voltage Vgs is an example of the "control voltage" of this invention.

[0056] In the overcurrent protection circuit 111, transistor Q1 is, for example, a PNP bipolar transistor. Additionally, transistor Q2 is, for example, an NPN bipolar transistor, having a base connected to the collector of transistor Q1, a collector connected to the base of transistor Q1, and an emitter grounded. Furthermore, the collector of transistor Q2 is pulled up to a threshold voltage VTH via a pull-up resistor R2. The threshold voltage VTH is an example of the "pull-up voltage" of this invention.

[0057] During the period when transistor Q1 is off (insulated), no current flows through the base of transistor Q2. When transistor Q1 is turned on, current flows through the base-emitter junction of transistor Q2 because the emitter-collector junction is conductive. Therefore, when transistor Q1 is turned on, transistor Q2 is also turned on. The voltage detection circuit 15 detects the collector-emitter voltage of transistor Q2, i.e., the detection voltage Vocp, and outputs a signal representing the detection voltage Vocp to the control unit 12. It should be noted that the voltage detection circuit 15 is an example of the "voltage detection unit" of the present invention, and the signal representing the detection voltage Vocp is an example of the "first control signal" of the present invention.

[0058] Figure 3AIt means Figure 2 Timing diagram of the operating waveforms of signals, etc., in the current-driven switching circuit 110. Figure 3B yes Figure 3A A magnified view of the base-emitter voltage Vbe of transistor Q1.

[0059] exist Figure 3A In this process, the current-driven switching circuit 110 starts working at time t1, the semiconductor switch 14 experiences a short circuit at time t2 and begins protection operation, and the control unit 12 detects the short circuit at time t3. Furthermore, the abnormal state is eliminated at time t4, and stable operation resumes at time t5. The period from time t1 to t2 is referred to as the stable operation period 201, the period from time t2 to t3 is referred to as the protection operation period 202, and the period from time t3 to t5 is referred to as the Vgs signal disconnection period (or stop period) 204.

[0060] During the stable operation period 201, except for the overshoot period of the detection voltage Vocp, no current flows through the pull-up resistor R2, so the detection voltage Vocp is the threshold voltage VTH. This threshold voltage VTH is set higher than the gate-source voltage Vgs supplied by the drive unit 13 when the drive signal Sdrv is high, so during the stable operation period 201, both transistors Q1 and Q2 are always disconnected.

[0061] Typically, when an overcurrent flows through a semiconductor device, the gate-source voltage of the semiconductor switches included in the semiconductor device overshoots (instantaneously rises). In this comparative example, at time t2 in Figure 3, the drain current Id flowing through semiconductor switch 14 also rises excessively, and the gate-source voltage Vgs of semiconductor switch 14 rises sharply, becoming a value higher than the threshold voltage VTH. As a result, transistor Q1 turns on, and therefore transistor Q2 also turns on.

[0062] Here, after transistors Q1 and Q2 are both turned on, the gate of semiconductor switch 14 is grounded through transistors Q1 and Q2. Therefore, the gate-source voltage Vgs drops rapidly to 0V. Consequently, semiconductor switch 14 is turned off, thus stopping the overcurrent flowing through it, and the overcurrent protection circuit 111 begins its protective operation. The time from the occurrence of the short circuit at time t2 to the start of protection operation by the overcurrent protection circuit 111 includes the switching delay of transistors Q1 and Q2, which is, for example, as short as approximately 20-100 nanoseconds.

[0063] Furthermore, when transistor Q2 is turned on, the detection voltage Vocp drops rapidly to 0V. Specifically, when resistor R1 is smaller than pull-up resistor R2, the gate-source voltage Vgs drops faster than the detection voltage Vocp. Therefore, even if the gate-source voltage Vgs decreases, transistor Q1 can remain on. Subsequently, when the drive signal Sdrv of the control unit goes low, the drive unit 13 stops, and the gate-source voltage Vgs drops to 0V. Therefore, transistors Q1 and Q2 turn off sequentially, and the detection voltage Vocp rises again to the threshold voltage VTH, ending the protection operation.

[0064] The voltage detection circuit 15 outputs a signal representing the detected voltage Vocp to the control unit 12. The control unit 12 monitors the value of the detected voltage Vocp. When the detected voltage Vocp is lower than a predetermined threshold, it determines that protection operation has been performed, sets the abnormal detection flag Fh to a high level, and stops the output of the drive signal Sdrv (at time t3). During the period after time t3 when the Vgs signal is disconnected (the stop period) 203, the drive signal Sdrv remains at a low level, and the semiconductor switch 14 remains open.

[0065] Specifically, when the response of the control unit 12 is slow, at time t3, before the output of the drive signal Sdrv stops, the drive signal Sdrv can become high again. At this time, as... Figure 3A As shown, an overcurrent flows through the semiconductor switch 14 again, and the overcurrent protection circuit 111 starts its protection operation again.

[0066] As described above, the overcurrent protection circuit 111 involved in the comparative example includes a pull-up resistor R2, a PNP transistor Q1, an NPN transistor Q2, and a voltage detection circuit 15. When the gate-source voltage Vgs of the semiconductor switch 14 exceeds the threshold voltage VTH, transistors Q1 and Q2 are sequentially turned on. As a result, the overcurrent protection circuit 111 reduces the gate-source voltage Vgs to 0, initiating the protection operation of disconnecting the semiconductor switch. Furthermore, the control unit 12 monitors the detection voltage Vocp detected by the voltage detection circuit 15. When the detection voltage Vocp is lower than a predetermined threshold voltage, the drive unit 13 stops, thus disconnecting the semiconductor switch 14. Therefore, according to this embodiment, compared to the prior art, it is possible to stop the overcurrent flowing through the semiconductor switch 14 at a high speed, protecting the semiconductor switch 14.

[0067] (The topic of comparison)

[0068] As described above, in the overcurrent protection circuit 111 of the comparative example, the gate voltage Vgs of the current-driven semiconductor switch 14 is monitored by using transistors Q1, Q2 and the detection voltage Vocp, thereby realizing the overcurrent protection function.

[0069] However, the following issues exist in this configuration: Figure 3B When the semiconductor switch 14 shown is turned off, the gate-source undervoltage 120, or when a negative gate bias voltage is applied to the semiconductor switch 14, the base-emitter voltage Vbe of the transistor Q1 may be overvoltage 120.

[0070] (Implementation Method 1)

[0071] Figure 4 This is a block diagram illustrating an example configuration of the boost chopper circuit 1 according to Embodiment 1. Figure 5 It means Figure 4 A block diagram illustrating the detailed configuration of a current-driven switching circuit 10. Figure 4 In the middle, the boost chopper circuit 1 has the same characteristics as... Figure 1 The boost chopper circuit 101 has the same circuit configuration, but is similar to... Figure 2 Compared to the switch drive circuit 110, Figure 5 The current-driven switching circuit 10 has the following differences in order to solve the problem in the comparative example.

[0072] (1) An overcurrent protection circuit 11 is provided instead of an overcurrent protection circuit 111. Specifically:

[0073] (2) A diode D11 is inserted between the gate of the semiconductor switch 14 and the emitter of the transistor Q1. The anode of the diode D11 is connected to the gate of the semiconductor switch 14, and the cathode of the diode D11 is connected to the emitter of the transistor Q1.

[0074] (3) A diode D12 is inserted between the emitter and base of transistor Q1. The anode of diode D12 is connected to the base of transistor Q1, and the cathode of diode D12 is connected to the emitter of transistor Q1. Here, diode D12 is an example of the component circuit of the present invention.

[0075] Figure 6 It means Figure 5 Timing diagram of the operating waveforms of signals, etc., in the current-driven switching circuit 10. Figures 7A-7D It is used for in Figure 5 In the current-driven switching circuit 10, diodes D11 and D12 are added to prevent overvoltage. Figure 6 Enlarged view of the base-emitter voltage Vbe and the detection voltage Vocp.

[0076] In implementation method 1, by means of... Figure 5 As shown, an additional diode D12 is inserted, such as Figure 7AAs shown, the charge Vbe between the base and emitter of transistor Q1 is discharged to the emitter side of transistor Q1 via diode D12. Additionally, diode D11 is subjected to a voltage equal to the detection voltage Vocp + Vds (the drain-source voltage of semiconductor switch 14). This provides the characteristic of preventing overvoltage of the base-emitter voltage Vbe of transistor Q1.

[0077] When an overcurrent is generated in semiconductor switch 14, such as Figure 7B As shown, the overshoot (Vocp-Vgs) of the gate-source voltage Vgs is applied between the base and emitter of transistor Q1. If transistor Q1 is turned on, the protection function is activated.

[0078] In addition, after the protection work, such as Figure 7C As shown, through transistors Q1 and Q2, the detection voltage Vocp, which is a threshold voltage, is discharged and reduced, and the system switches to the protection operation holding state.

[0079] Furthermore, since the gate signal to semiconductor switch 14 is stopped, the protection operation hold state is automatically restored. For example... Figure 7D As shown, the time until recovery can be set by adjusting the rise time of the detection voltage Vocp using resistor R2 (or impedance).

[0080] As described above, according to Embodiment 1, compared with the comparative example, by adding insertion diodes D11 and D12, overvoltage of the base-emitter voltage Vbe of transistor Q1 can be prevented.

[0081] (Implementation Method 2)

[0082] Figure 8 This is a block diagram illustrating a detailed configuration example of the current-driven switching circuit 10A according to Embodiment 2. (and) Figure 5 Compared to the current-driven switching circuit 10, Figure 8 The current-driven switching circuit 10A has the following differences.

[0083] (1) An overcurrent protection circuit 11A is provided to replace the overcurrent protection circuit 11. Details are as follows:

[0084] (2) Insert resistor R11 to replace diode D12. Here, resistor R11 is an example of the component circuit of the present invention.

[0085] The differences will be explained below.

[0086] exist Figure 8 In the middle, an additional insertion resistor R11 is added to replace it. Figure 5The diode D12 discharges the charge between the base and emitter of transistor Q1 to the emitter side of transistor Q1 via resistor R11. Furthermore, similar to Embodiment 1, by making diode D11 bear the detection voltage Vocp+Vds, overvoltage between the base and emitter of transistor Q1 can be prevented (see Figure 1). Figure 9A ).

[0087] For example, when an overcurrent is generated in semiconductor switch 14, such as Figure 9B As shown, the current Iocp caused by the overshoot of the gate-source voltage Vgs flows from the gate of semiconductor switch 14 through diode D11 and resistor R11. If the potential difference (=Iocp×R11) exceeds the threshold voltage between the base and emitter of transistor Q1, transistor Q1 turns on, and the protection function is activated. It should be noted that the maintenance of the protection state and the automatic recovery to the stable state in Embodiment 2 work in the same way as in Embodiment 1 (refer to...). Figure 9C ).

[0088] As described above, according to Embodiment 2, compared with the comparative example, by adding a diode D11 and a resistor R11, it is possible to prevent overvoltage of the base-emitter voltage Vbe of transistor Q1.

[0089] (Implementation Method 3)

[0090] Figure 10 This is a block diagram illustrating a detailed configuration example of the current-driven switching circuit 10B according to Embodiment 3. Figure 5 Compared to the current-driven switching circuit 10, Figure 10 The current-driven switching circuit 10B has the following differences.

[0091] (1) An overcurrent protection circuit 11B is provided to replace the overcurrent protection circuit 11. The details are as follows:

[0092] (2) Connect resistor R11 and Figure 8 The diodes D12 and R11 are connected in parallel. This parallel circuit of diode D12 and resistor R11 is an example of the component circuitry in this invention.

[0093] The differences will be explained below.

[0094] In the current-driven switching circuit 10B constructed as described above, such as Figure 11A As shown, the basic operation is the same as that in Implementation Method 2.

[0095] In addition, such as Figure 11BAs shown, for example, when an overcurrent is generated in the semiconductor switch 14, the potential difference caused by the detection voltage Vocp can be adjusted using the resistance value of resistor R11. Thus, by changing the values ​​of the combination of the detection voltage Vocp (which is a threshold voltage) and the resistance value of resistor R11, the operation of the semiconductor switch 14 can be optimized according to the driving conditions of the semiconductor switch 14.

[0096] As described above, according to Embodiment 3, compared with the comparative example, by adding a parallel circuit of inserted diode D11 and diode D12 and resistor R11, overvoltage of the base-emitter voltage Vbe of transistor Q1 can be prevented.

[0097] (Implementation Method 4)

[0098] exist Figure 1 In the comparative example, when the gate-source voltage Vgs of semiconductor switch 14 rises, as... Figure 3A As shown, the detection voltage Vocp overshoots. This causes the detection voltage Vocp to decrease more slowly, delaying the start of protection operation. Furthermore, as mentioned above, after the overcurrent protection of Ps during the short circuit, when the response speed of the control unit 12 is slow, overcurrent repeatedly flows through the semiconductor switch 14, which is undesirable. To solve this problem, the configuration described in Embodiment 4 is proposed below.

[0099] Figure 12A This is a block diagram illustrating a detailed configuration example of the current-driven switching circuit 10C according to Embodiment 4. Additionally, Figure 12B It means Figure 12A The timing diagram of the operating waveforms of signals, etc., in the current-driven switching circuit 10C. Figure 12A In, with Figure 10 Compared to the current-driven switching circuit 10B, the current-driven switching circuit 10C according to Embodiment 4 differs in the following aspects.

[0100] (1) An overcurrent protection circuit 11BA is provided to replace the overcurrent protection circuit 11B. Details are as follows:

[0101] (2) It also has a capacitor Ca connected to the collector and emitter of transistor Q2.

[0102] (3) The power supply of the threshold voltage VTH charges the capacitor Ca to the threshold voltage VTH through the pull-up resistor R2.

[0103] In embodiment 4 with the above configuration, when a short circuit occurs in the semiconductor switch 14 and the gate-source voltage Vgs rises sharply, the detection voltage Vocp overshoots due to the rise in the gate-source voltage Vgs, but this change is mitigated by the capacitor Ca (see reference). Figure 12BDuring the protection operation period (202). Therefore, it is possible to suppress the delay in the start of the protection operation.

[0104] Additionally, during the protection operation after a short circuit occurs, 202 ( Figure 12B When transistors Q1 and Q2 are turned on, capacitor Ca is grounded via transistor Q2, and capacitor Ca discharges to zero potential. Then, the drive signal Sdrv goes low, transistors Q1 and Q2 turn off, and the detection voltage Vocp begins to rise. Here, the threshold voltage VTH charges capacitor Ca. Therefore, the time required for the detection voltage Vocp to rise to the threshold voltage VTH is longer than that in the comparative example and embodiment 3. By appropriately selecting capacitor Ca, it is possible to make the time required for the detection voltage Vocp to rise to the threshold voltage VTH longer than the time until the drive signal Sdrv goes high again. Thus, even if the control signal goes high again, transistors Q1 and Q2 will turn on before the gate-source voltage Vgs reaches the threshold voltage VTH, protecting semiconductor switch 14.

[0105] As described above, in addition to the overcurrent protection circuit 11B, the overcurrent protection circuit 11BA according to Embodiment 4 also includes a capacitor Ca. Therefore, the time from the start of protection operation to recovery after the overcurrent protection circuit 11BA performs protection is longer than that of the overcurrent protection circuit 111 according to the comparative example, preventing repeated overcurrent flow in the semiconductor switch 14. Furthermore, the overshoot of the detection voltage Vocp caused by the rise of the gate-source voltage Vgs is less than that of the overcurrent protection circuit 111, resulting in a lower delay in the start of protection operation compared to the overcurrent protection circuit 111.

[0106] It should be noted that although the overcurrent protection circuit 11BA involved in Embodiment 4 includes a parallel circuit of diode D12 and resistor R11, the present invention is not limited to this, and the parallel circuit may be replaced by only diode D12 or only resistor R11.

[0107] (Implementation Method 5)

[0108] Figure 13 This is a block diagram illustrating an example configuration of the current-driven switching circuit 10D according to Embodiment 5. Figure 13 In, with Figure 12A Compared to the current-driven switching circuit 10BA, the current-driven switching circuit 10D according to Embodiment 5 differs in the following aspects.

[0109] (1) An overcurrent protection circuit 11BB is provided to replace the overcurrent protection circuit 11BA. Details are as follows:

[0110] (2) It also has a time constant circuit 18 including resistor R3 and capacitor Cb.

[0111] (3) The time constant circuit 18 is connected in parallel with the collector and emitter of transistor Q2.

[0112] In the overcurrent protection circuit 11BB configured as described above, the time constant for charging the capacitor Ca, which has been discharged to zero potential, to the threshold voltage VTH is adjusted, and the time from protection activation to recovery in the overcurrent protection circuit 11BB is longer than that in the overcurrent protection circuit 11BA. It should be noted that the same effect can also be obtained by inserting a time constant circuit 18 in the current-driven switching circuits 10, 10A, and 10B of embodiments 1-3.

[0113] As described above, the current-driven switching circuit 10BB according to Embodiment 5 also includes a time constant circuit 18 comprising a resistor R3 and a capacitor Cb. The time from protection operation to recovery of the overcurrent protection circuit 11BB is adjusted by appropriately selecting the resistor R3 and the capacitor Cb.

[0114] It should be noted that although the overcurrent protection circuit 11BB involved in Embodiment 5 includes a parallel circuit of diode D12 and resistor R11, the present invention is not limited to this, and the parallel circuit may be replaced by only diode D12 or only resistor R11.

[0115] (Implementation Method 6)

[0116] Figure 14 This is a block diagram illustrating an example configuration of the current-driven switching circuit 10E according to Embodiment 6. Figure 14 In, with Figure 13 Compared to the current-driven switching circuit 10D, the current-driven switching circuit 10E differs in the following aspects.

[0117] (1) An overcurrent protection circuit 11BC is provided to replace the overcurrent protection circuit 11BB. Details are as follows:

[0118] (2) The overcurrent protection circuit 11BC also has a diode D2, whose anode is connected to one end of the low potential side of resistor R3 and whose cathode is connected to the other end of resistor R3.

[0119] The current-driven switching circuit 10E according to Embodiment 6, as described above, also includes a diode D2. Therefore, compared to the overcurrent protection circuit 11B, the influence of noise such as the gate-source voltage Vgs on the overcurrent protection circuit 11BC is suppressed.

[0120] It should be noted that although the overcurrent protection circuit 11BC involved in Embodiment 6 includes a parallel circuit of diode D12 and resistor R11, the present invention is not limited to this, and the parallel circuit may be replaced by only diode D12 or only resistor R11.

[0121] (Implementation Method 7)

[0122] Figure 15 This is a block diagram illustrating an example configuration of the current-driven switching circuit 10F according to Embodiment 7. Figure 15 In, with Figure 14 Compared to the current-driven switching circuit 10E, the current-driven switching circuit 10F differs in the following aspects.

[0123] (1) An overcurrent protection circuit 11BD is provided to replace the overcurrent protection circuit 11BC. Details are as follows:

[0124] (2) The current-driven switching circuit 10F also has a MOS driving section 16.

[0125] (3) Replace resistor R3 with MOSFET17.

[0126] exist Figure 15 In this circuit, the MOS drive unit 16 is controlled by the control unit 12, outputting a MOS drive signal Sm to control the on / off state of the MOSFET 17. The MOSFET 17 is controlled by the MOS drive signal Sm, blocking (disconnecting) the threshold voltage VTH during the period when the MOS drive signal Sm is at a low level.

[0127] That is, the current-driven switching circuit 10F starts operating ( Figure 6 Before time t1, during a preparation period, control unit 12 turns on MOSFET 17 via MOS drive unit 16. After capacitor Ca is charged to the threshold voltage VTH, control unit 12 turns off MOSFET 17 via MOS drive unit 16. Afterwards, Figure 6 After the normal operation of the stable operation period 201 at times t1-t2, protection begins during the protection operation period 202 following a short circuit, and capacitor Ca discharges to zero potential. In embodiments 1-6, during the subsequent protection operation period 202 at times t2-t3, the drive signal Sdrv goes low, transistors Q1 and Q2 are turned off, and capacitor Ca is recharged. However, in this embodiment, since MOSFET 17 is turned off, capacitor Ca is not charged, and the overcurrent protection circuit 11BD remains in operation. Afterwards, when the detected voltage Vocp falls below a predetermined threshold voltage, the control unit 12 sets the abnormal detection flag Fh high and stops the output of the drive signal Sdrv (at time t3).

[0128] Next, during the Vgs signal disconnection period 203 (t3-t5), the user of the boost chopper circuit 1 can repair the short circuit and eliminate it. Afterwards, for example, the upper-level control circuit detects the short circuit elimination and controls the control unit 12, or the user directly operates the control unit 12, causing the abnormality detection flag Fh of the control unit 12 to go low. The control unit 12 detects the abnormality detection flag Fh going low and turns on MOSFET 17 to recharge capacitor Ca. Then, similar to the previous preparation period, during the second preparation period, the MOS drive signal Sm is high, and capacitor Ca is charged to the threshold voltage VTH.

[0129] Due to the full charging of capacitor Ca during the second preparation period, the overcurrent protection circuit 11BD recovers from protection operation. Then, the current-driven switching circuit 10F returns to its original steady-state operation period 201 and resumes normal stable operation.

[0130] As described above, the current-driven switching circuit 10F according to Embodiment 7 includes a MOS driving section 16 and a MOSFET 17. Therefore, the MOSFET 17 is controlled by the control section 12 via the MOS driving section 16 to control the on / off state of the threshold voltage VTH. Since the detection voltage Vocp does not rise during the period when the MOSFET 17 is off, recovery from protection operation can be achieved at any time regardless of whether the response of the control section 12 is delayed. It should be noted that when the MOSFET 17 includes a parasitic diode, similar to the current-driven switching circuit 10E according to Embodiment 6, noise suppression can be achieved.

[0131] It should be noted that the MOSFET 17 involved in this embodiment can be similarly inserted into any one of the current-driven switching circuits 10, 10A-10E in embodiments 1-6, and the same effect can be obtained. In addition, the MOSFET 17 involved in this embodiment is an example of "another switching element" of the present invention.

[0132] (Implementation Method 8)

[0133] Figure 16 This is a block diagram illustrating an example configuration of the current-driven switching circuit 10G according to Embodiment 8. Figure 16 In, with Figure 15 Compared to the current-driven switching circuit 10F, the current-driven switching circuit 10G differs in the following aspects.

[0134] (1) An overcurrent protection circuit 11BE is provided to replace the overcurrent protection circuit 11BD. Details are as follows:

[0135] (2) It has a transistor 17a instead of MOSFET 17.

[0136] (3) A transistor driving section 16a is provided instead of a MOS driving section 16.

[0137] The control unit 12 controls the base current Itr of the transistor 17a via the transistor drive unit 16a, thereby controlling the on / off state of the transistor 17a. This achieves the same effect as in embodiment 7.

[0138] It should be noted that the transistor 17a involved in this embodiment can be similarly inserted into any one of the current-driven switching circuits 10, 10A-10E in embodiments 1-6, and the same effect can be obtained. In addition, the transistor 17a involved in this embodiment is an example of "another switching element" of the present invention.

[0139] (Modified Example)

[0140] The embodiments of the present invention have been described in detail above, but the above description is merely illustrative in all respects. Various modifications or variations can be made without departing from the scope of the present invention. For example, the following changes can be made. It should be noted that the same reference numerals are used below for the same constituent elements as in the above embodiments, and descriptions of aspects identical to those in the above embodiments are appropriately omitted. The following variations can be appropriately combined.

[0141] In embodiments 1-8, the boost chopper circuit 1 was described as a semiconductor device incorporating the current-driven switching circuits 10, 10A-10G according to the present invention. However, the present invention is not limited thereto, and can be applied to circuits and devices that control current switching via semiconductor switches.

[0142] For example, Figure 17 This is a block diagram illustrating an example configuration of the half-bridge inverter circuit 1A involved in Modification Example 1. Figure 17 In the circuit, the half-bridge inverter circuit 1A includes an inductor L2, two current-driven switching circuits 10, and a capacitor C2.

[0143] exist Figure 17 In this circuit, the semiconductor switches 14 of the two current-driven switching circuits 10 are controlled to periodically and alternately conduct. As a result, the input voltage Vi is switched, smoothed by capacitor C2, and transformed into an AC output voltage Vo. Consequently, the half-bridge inverter circuit 1A switches the DC input voltage Vi, transforming it into an AC output voltage Vo. The two current-driven switching circuits 10 can also be replaced by any one of the current-driven switching circuits 10A-10G.

[0144] in addition, Figure 18 This is a block diagram illustrating an example configuration of the full-bridge inverter circuit 1B involved in Modification Example 2. Figure 18 In the full-bridge inverter circuit 1B, there is a capacitor C3, four current-driven switching circuits 10, and inductors L3 and L4.

[0145] exist Figure 18 In this circuit, four current-driven switching circuits 10 are controlled such that the first and fourth current-driven switching circuits 10 (top left and bottom right in the figure) are turned on, while the second and third current-driven switching circuits 10 (bottom left and top right in the figure) are turned off, and the period during which their on / off states are reversed alternates periodically. Thus, the input voltage Vi is switched, and the switched input voltage Vi is smoothed by capacitor C3 and inductors L3 and L4. Therefore, the full-bridge inverter circuit 1B switches the DC input voltage Vi, converting it into an AC output voltage Vo. The four current-driven switching circuits 10 can also be replaced by any one of the current-driven switching circuits 10A-10G.

[0146] Thus, the current-driven switching circuit and overcurrent protection circuit involved in this invention can be applied to circuits and devices that control the switching of current through semiconductor devices.

[0147] Furthermore, in embodiments 1-8, a pull-up resistor R2 is used as a unit to limit the current from the power supply of the threshold voltage VTH. However, the present invention is not limited to this, and a diode or the like may be used instead of the pull-up resistor R2.

[0148] Furthermore, in embodiments 1-8, current-driven switching circuits 10, 10A-10G are used as switching circuits. However, the present invention is not limited thereto, and voltage-driven switching circuits can also be used instead of current-driven switching circuits.

[0149] Explanation of reference numerals in the attached figures

[0150] 1. 101: Boost chopper circuit;

[0151] 1A: Half-bridge inverter circuit

[0152] 1B: Full-bridge inverter circuit

[0153] 10, 10A-10G, 110: Current-driven switching circuits

[0154] 11, 11A-11B, 11BA, 11BB, 11BC, 11BD, 11BE, 111: Overcurrent protection circuit

[0155] 12: Control Department

[0156] 13: Drive Unit

[0157] 14: Semiconductor switch

[0158] 15: Voltage detection circuit

[0159] 16: MOS Driver Section

[0160] 16a: Transistor driver section

[0161] 17: MOSFET

[0162] 17a: Transistor

[0163] 18: Time constant circuit

[0164] D1, D11, D12: Diodes

[0165] Q1, Q2: Transistors

[0166] R1, R2, R11: Resistors.

Claims

1. An overcurrent protection circuit for a switching element that is controlled to be switched on and off according to a control voltage, the overcurrent protection circuit comprising: The first transistor is a PNP bipolar transistor, having an emitter connected to the control voltage; and The second transistor is an NPN bipolar transistor, having a base connected to the collector of the first transistor, a collector connected to the base of the first transistor and pulled up to a specified pull-up voltage, and an emitter grounded. When the control voltage exceeds a predetermined first threshold voltage, the overcurrent protection circuit initiates the following protection operation: the first and second transistors are turned on, and the pull-up voltage is reduced, causing the control voltage to decrease, thereby disconnecting the switching element. The overcurrent protection circuit includes: The first diode has an anode connected to the control voltage and a cathode connected to the emitter of the first transistor; The component circuit is connected between the emitter and the base of the first transistor; The control unit generates the control voltage; as well as The voltage detection unit detects the pull-up voltage and outputs the detected voltage as a first control signal to the control unit for disconnecting the switching element. The circuit is a parallel circuit of a second diode and a first resistor. The second diode has a cathode connected to the emitter of the first transistor and an anode connected to the base of the first transistor. The first resistor is connected in parallel with the second diode. For the overvoltage caused by the undershoot of the control voltage generated when the switching element is turned off, the first diode bears the overvoltage, and the element circuit discharges the charge between the base and emitter of the first transistor to the emitter side of the first transistor, thereby preventing self-destruction caused by the overvoltage between the base and emitter of the first transistor.

2. The overcurrent protection circuit according to claim 1 further comprises: The first capacitor, which is connected to the collector and emitter of the second transistor, reduces the change in the pull-up voltage when the control voltage rises.

3. The overcurrent protection circuit according to claim 1 or 2 further comprises: A time constant circuit, which is connected in parallel with the collector and emitter of the second transistor, includes a second resistor and a second capacitor, and adjusts the time from the start to the end of the protection operation by changing the time constant.

4. The overcurrent protection circuit according to claim 3 further comprises: The third diode is connected in parallel with the second resistor.

5. The overcurrent protection circuit according to claim 1 further comprises: Another switching element, when the overcurrent protection circuit recovers from the protection operation, causes the pull-up voltage to change from open to open according to a second control signal from the control unit.

6. A switching circuit, comprising: The overcurrent protection circuit as described in claim 1 or 2; and The switching element.

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