Switching Circuit

Abstract

The present invention discloses a switch circuit, comprising a drive circuit, a power switch and an active clamp circuit. The drive circuit comprises an input terminal, an output terminal, a first transistor and a second transistor. The first transistor comprises a first terminal coupled to the input terminal, a second terminal coupled to a first power supply voltage and a third terminal coupled to the output terminal. The second transistor comprises a first terminal coupled to the input terminal, a second terminal and a third terminal coupled to the output terminal. The power switch comprises a first terminal coupled to the output terminal of the drive circuit, a second terminal and a third terminal. The active clamp circuit is coupled to the first terminal of the power switch, the second terminal of the power switch, the output terminal of the drive circuit and the second terminal of the second transistor.

Description

Technical Field

[0001] The present invention relates to a switch circuit, in particular to a switch circuit capable of improving system reliability. Background Art

[0002] Power semiconductor components, such as insulated gate bipolar transistors (IGBT) or metal-oxide-semiconductor field effect transistors (MOSFET), are often used in power management, such as wind power generation systems, solar power generation systems, electric vehicles, power supplies, displays, motor control, etc. Generally speaking, power semiconductor components are usually subjected to large current stress and voltage stress at the switching moment of the component on and off. At the moment when the component is turned off, the equivalent series inductance (ESL) of the copper bus and bus capacitor and the stray inductance of the component will bring greater voltage stress to the power semiconductor component and cause overvoltage, thereby damaging the component. For example, when the collector-emitter voltage of the IGBT exceeds the rated value of the collector-emitter voltage, the IGBT will be immediately damaged and the system equipment will be paralyzed and unable to operate.

[0003] In this regard, the traditional method uses active clamping to solve the problem of excessive voltage stress faced by power semiconductor components during shutdown. Figure 1A , the switch circuit 1 includes a drive circuit 10, a power switch 12, and an active clamp circuit 14. The drive circuit 10 includes transistors T1 and T2. The active clamp circuit 14 includes a transient voltage suppressor diode (TVS diode) TVS, a diode D, and resistors R1 and R2. The drive circuit 10 receives a control signal SC via an input terminal 100. When the control signal SC is at a low voltage level, the transistor T1 is turned off and the transistor T2 is turned on. The voltage at the output terminal 102 of the drive circuit 10 is pulled to the voltage level of the power supply voltage VEE (for example, -8 volts). The gate charge of the power switch 12 flows to the power supply voltage VEE through the transistor T2 under the negative drive voltage. When the gate voltage Vgate of the power switch 12 is lower than a conduction threshold voltage, the power switch 12 begins to turn off. At this time, if the closing speed is too fast, the voltage stress on the power switch 12 will be too high, that is, the collector-emitter voltage Vce of the power switch 12 will exceed the breakdown threshold voltage of the transient voltage suppressor diode TVS and form a conduction current It (or reverse breakdown current). Figure 1AAs shown, the on-current It has three shunt paths, and the on-current It includes currents I1, I2, and I3, where It=I1+I2+I3. The current I1 flows into the input terminal 100 of the driving circuit 10, thereby increasing the voltage of the input terminal 100 of the driving circuit 10. The current I2 passes through the gate resistor Rg and the transistor T2, thereby increasing the voltage of the output terminal 102 of the driving circuit 10. The current I3 directly enters the gate of the power switch 12 to provide additional charge to the gate capacitance of the power switch 12. In this way, the three paths of currents I1, I2, and I3 will slow down the turn-off time of the power switch 12, reduce the rate of change dIc / dt of the collector current, and reduce the collector-emitter voltage Vce of the power switch 12 accordingly.

[0004] However, in Figure 1A In the switch circuit 1, the resistor R2 of the active clamp circuit 14 is coupled to the input terminal 100 of the driving circuit 10, so that the current I1 flows into the input terminal 100 of the driving circuit 10 to pull up the voltage of the input terminal 100, and then increases the gate voltage of the power switch 12 through the driving circuit 10. In this case, since the signal transmission path is too long, the gate response time of the power switch 12 will be too long, so that the suppression effect on the collector-emitter voltage Vce of the power switch 12 is not good, and the transmission time delay leads to a phase lag, which will also inject a disturbance signal into the power main loop to cause an oscillation problem. Furthermore, when the transient voltage suppressor diode TVS is broken down by the external bias, the reverse conduction voltage will increase with the increase of the reverse current. Since the resistance of the resistor R1 and the gate resistor Rg is small, the current I2 will flow from the transistor T2 to the voltage source VEE (for example, the voltage source VEE is -8 volts), and the collector-emitter voltage Vce of the power switch 12 will increase with the increase of the conduction current It, resulting in exceeding the rated value of the collector-emitter voltage. Figure 1B As shown in the characteristic curve, when the collector-emitter voltage of the power switch 12 increases with the increase of the on-current It, it cannot be clamped at the clamping voltage VC near the breakdown threshold voltage VR as expected. This will affect the reliability of the overall system.

[0005] In addition, due to the bypass current I2 that continuously passes through the transistor T2, the current It that flows through the transient voltage suppression diode TVS will continue to exist and will increase with the increase of the collector-emitter voltage of the power switch 12, causing the clamping voltage of the transient voltage suppression diode TVS to increase accordingly, and ultimately resulting in a significant increase in the power consumption of the transient voltage suppression diode TVS. Therefore, the prior art needs to be improved. Summary of the invention

[0006] (I) Purpose of the invention

[0007] The main purpose of the present invention is to provide a switch circuit that can improve system reliability to improve the above problems.

[0008] (II) Technical solution

[0009] The present invention provides a switching circuit, comprising: a driving circuit, comprising: an input end; an output end; a first transistor, comprising a first end coupled to the input end, a second end coupled to a first power supply voltage and a third end coupled to the output end; and a second transistor, comprising a first end coupled to the input end, a second end and a third end coupled to the output end; a power switch, comprising a first end, a second end and a third end, the first end of the power switch being coupled to the output end of the driving circuit; and an active clamping circuit, coupled to the first end of the power switch, the second end of the power switch, the output end of the driving circuit and the second end of the second transistor. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1A is a schematic diagram of a conventional switch circuit with a source clamp circuit;

[0011] Figure 1B is a schematic diagram of a characteristic curve of a transient voltage suppression diode;

[0012] Figure 2 is a schematic diagram of an embodiment of a switch circuit according to an embodiment of the present invention;

[0013] Figure 3 for Figure 2 A schematic diagram of a variation of the embodiment of the power switch;

[0014] Figure 4 FIG. 2 is a schematic diagram of a modified embodiment of the driving circuit in FIG. 2;

[0015] Figure 5 FIG. 2 is a schematic diagram of a variation of an operating power supply of the active clamping circuit.

[0016] Reference numerals:

[0017] 2: switch circuit; 20: drive circuit; 200: input end; 202: output end; 22: power switch; 24: active clamping circuit; 240: first protection circuit; 242: second protection circuit; D: diode; I1, I2, I3: current; It: on-current; R1, R2, R3: resistance; Rg: gate resistance; SC: control signal; T1, T2, T3, T4: transistor; TVS: transient voltage suppression diode; VCC, VEE: power supply voltage; Vce: collector-emitter voltage; Vgate: gate voltage. DETAILED DESCRIPTION

[0018] Certain words are used in the specification and subsequent patent applications to refer to specific components. Those with ordinary knowledge in the field should understand that hardware manufacturers may use different terms to refer to the same component. This specification and subsequent patent applications do not use differences in names as a way to distinguish components, but use differences in the functions of components as the criteria for distinction. The word "including" mentioned throughout the specification and subsequent patent applications is an open term and should be interpreted as "including but not limited to". In addition, the word "coupled" here includes any direct and indirect electrical connection means. Therefore, if the text describes a first device coupled to a second device, it means that the first device can be directly electrically connected to the second device, or indirectly electrically connected to the second device through other devices or connection means.

[0019] Please refer to Figure 2 The switch circuit 2 includes a drive circuit 20, a power switch 22, an active clamp circuit 24 and a gate resistor Rg. The drive circuit 20 includes an input terminal 200, transistors T1, T2 and an output terminal 202. The drive circuit 20 can be a push-pull output circuit. The transistor T1 and the transistor T2 are coupled between the input terminal 200 and the output terminal 202. Figure 2 As shown, the transistor T1 and the transistor T2 are connected in series in a totem pole form. The transistor T1 and the transistor T2 may be bipolar junction transistors (BJT). The base of the transistor T1 is coupled to the input terminal 200, the collector of the transistor T1 is coupled to a power supply voltage VCC (e.g., +15 volts), and the emitter of the transistor T1 is coupled to the output terminal 202. The base of the transistor T2 is coupled to the input terminal 200, the collector of the transistor T2 is coupled to the active clamp circuit 24, and the emitter of the transistor T2 is coupled to the output terminal 202. In addition, the transistor T1 and the transistor T2 may also be metal-oxide-semiconductor field effect transistors (MOSFET). For example, the transistor T1 may be an N-type metal-oxide-semiconductor field effect transistor, and the transistor T2 may be a P-type metal-oxide-semiconductor field effect transistor, but it is not limited thereto.

[0020] A first terminal of the gate resistor Rg is coupled to the output terminal 202 of the driving circuit 20. The power switch 22 may be an insulated gate bipolar transistor (IGBT) or a metal oxide semiconductor field effect transistor. Figure 2As shown, the power switch 22 is an insulated gate bipolar transistor. The gate of the power switch 22 is coupled to the second end of the gate resistor Rg and the active clamp circuit 24 , and the collector of the power switch 22 is coupled to the active clamp circuit 24 .

[0021] The active clamp circuit 24 is coupled to the gate of the power switch 22, the collector of the power switch 22, and the collector of the transistor T2 of the driving circuit 20. The active clamp circuit 24 includes a first protection circuit 240 and a second protection circuit 242. The first protection circuit 240 is coupled to the gate of the power switch 22, the collector of the power switch 22, and the second end of the gate resistor Rg. The first protection circuit 240 generates a conduction current IT according to the voltage of the collector of the power switch 22. The first protection circuit 240 includes a transient voltage suppressor diode (TVS diode) TVS, a diode D, and a resistor R1. The cathode of the transient voltage suppressor diode TVS is coupled to the collector of the power switch 22. The anode of the diode D is coupled to the anode of the transient voltage suppressor diode TVS, and the cathode of the diode D is coupled to the resistor R1 and the second protection circuit 242. A first end of the resistor R1 is coupled to the cathode of the diode D and the second protection circuit 242 , and a second end of the resistor R1 is coupled to the gate of the power switch 22 and the second end of the gate resistor Rg.

[0022] The second protection circuit 242 is coupled to the first protection circuit 240 and the collector of the transistor T2. The second protection circuit 242 includes a resistor R2, a resistor R3, a transistor T3, and a transistor T4. A first end of the resistor R2 is coupled to the cathode of the diode D and the first end of the resistor R1, and a second end of the resistor R2 is coupled to the transistor T4. The transistor T3 and the transistor T4 can be bipolar junction transistors (BJT) or metal oxide semi-conductor field effect transistors. For example, Figure 2 As shown, transistor T3 and transistor T4 are bipolar junction transistors. The base of transistor T4 is coupled to the second end of resistor R2, the collector of transistor T4 is coupled to resistor R3 and transistor T3, and the emitter of transistor T4 is coupled to a power supply voltage VEE. A first end of resistor R3 is coupled to power supply voltage VCC, and a second end of resistor R3 is coupled to transistor T3 and the collector of transistor T4. The base of transistor T3 is coupled to the second end of resistor R3 and the collector of transistor T4, the collector of transistor T3 is coupled to the collector of transistor T2, and the emitter of transistor T3 is coupled to power supply voltage VEE (e.g., -8 volts).

[0023] The driving circuit 20 receives a control signal SC via the input terminal 200. For example, the control signal SC may be a pulse width modulation signal, but is not limited thereto. When the control signal SC is in a low level state (e.g., a low voltage level), the transistor T1 is closed (cut off) and the transistor T2 is turned on. The power supply voltage VEE draws the gate charge of the power switch 22, and the gate charge of the power switch 22 flows to the power supply voltage VEE through the transistor T2 under the negative driving voltage operation. A gate voltage Vgate of the power switch 22 is pulled low. When the gate voltage Vgate of the power switch 22 is lower than a conduction threshold voltage, the power switch 22 starts the shutdown (cut-off) procedure. When a collector-emitter voltage Vce of the power switch 22 reaches or exceeds a breakdown critical voltage (or breakdown voltage) of the transient voltage suppression diode TVS, the transient voltage suppression diode TVS is turned on and generates a conduction current It (or reverse breakdown current). As Figure 2 As shown, the on-current It has three shunt paths, and the on-current It includes currents I1, I2, and I3. Among them, the current I1 turns on the transistor T4 through the resistor R2. The current I1 turns on the transistor T4 through the resistor R2. When the transistor T4 is turned on, the current I1 flows through the resistor R2 and the transistor T4. When the transistor T2 and the transistor T3 are turned on, the current I2 flows through the transistor T2 and the transistor T3. The current I2 changes linearly according to the current size of the current I1. The current I3 flows directly into the gate of the power switch 22 to provide additional charge to the gate of the power switch 22, thereby slowing down the falling slope of the rate of change of the gate voltage Vgate (i.e., dVgate / dt), and reducing the rate of change of the collector current of the power switch 22 (i.e., dIc / dt), so that the collector-emitter voltage Vce of the power switch 22 is suppressed. Among them, the on-current It and the currents I1, I2, and I3 can be expressed as follows:

[0024] It=I1+I2+I3 (1)

[0025] Among them, It represents the on-current It, I1 represents the current I1, I2 represents the current I2, and I3 represents the current I3.

[0026] In addition, the base current of transistor T3, the collector current of transistor T4 and the current I2 can be expressed as follows:

[0027]

[0028] Among them, IT4_C represents the collector current of transistor T4, βT4 represents the common emitter current gain (also known as the amplification factor) of transistor T4, I1 represents the current I1, IT3_B represents the base current of transistor T3, VCC represents the power supply voltage VCC, VEE represents the power supply voltage VEE, VT3_BE represents the base-emitter voltage of transistor T3, R3 represents the resistance value of resistor R3, I2 represents the current I2, and βT3 represents the common emitter current gain of transistor T3.

[0029] According to formula (2), the linear relationship between current I1 and current I2 can be expressed as follows:

[0030]

[0031] From formula (3) and Figure 2 It can be seen that the current I1 and the current I2 form a negative feedback loop. When the current I1 increases, the current I2 decreases, and the current I2 changes linearly according to the current size of the current I1. When the current I1 increases, the current I2 will decay linearly with a two-stage amplification factor until the transistor T4 works in a saturated conduction state and the transistor T3 works in a cut-off state, thereby cutting off the power supply voltage VEE path and making the current I2 zero. In other words, when the on-current It is turned on, the current I1 will increase and the transistor T4 will be turned on, and the current I1 will flow through the resistor R4 and the transistor T4. Then, the current I2 will decay linearly and the transistor T3 will be turned off.

[0032] Further, according to Figure 2 The current path of the current I2 in the power switch 22, the relationship between the current I2 and the collector-emitter voltage Vce of the power switch 22 can be expressed as follows:

[0033]

[0034] Wherein, Vce represents the collector-emitter voltage Vce of the power switch 22, VR_TVS represents the reverse bias voltage of the transient voltage suppression diode TVS, VF_D represents the forward bias voltage of the diode D, Vb represents the voltage value of the output terminal 202 of the driving circuit 20, R1 represents the resistance value of the resistor R1, and Rg represents the resistance value of the resistor Rg.

[0035] Then, substituting equation (4) into equation (3), we can obtain the following result:

[0036]

[0037] As can be seen from equation (5), the collector-emitter voltage Vce of the power switch 22 includes the following components: the voltage drop formed by the current I2, the forward conduction voltage drop of the diode D, the reverse conduction voltage drop of the transient voltage suppressor diode TVS, and the voltage of the output terminal 202 of the driving circuit 20. The forward conduction voltage drop of the diode D and the reverse conduction voltage drop of the transient voltage suppressor diode TVS are monotonically increasing functions. Therefore, when the collector-emitter voltage Vce of the power switch 22 increases and exceeds the breakdown threshold voltage (or breakdown voltage) of the transient voltage suppressor diode TVS, the negative feedback loop of the active clamping circuit 24 is activated, the current I1 increases and the current I2 decreases significantly, and the voltage value of the output terminal 202 of the driving circuit 20 decreases slowly, so that the rising slope of the collector-emitter voltage Vce can be effectively suppressed.

[0038] Furthermore, referring to equation (1), it can be seen that due to the decrease of current I2, the conduction current It through the transient voltage suppression diode TVS will be reduced accordingly. Figure 1B It can be seen from the characteristic curve of the transient voltage suppressor diode shown that when the on-current It decreases, the reverse bias voltage (e.g., breakdown threshold voltage or collapse voltage) of the transient voltage suppressor diode TVS will decrease accordingly. In this case, according to formula (5), the collector-emitter voltage Vce of the power switch 22 will decrease and be clamped near the breakdown threshold voltage of the transient voltage suppressor diode TVS, and the reduction of the on-current It will significantly reduce the loss of the transient voltage suppressor diode TVS.

[0039] On the other hand, the power switch 22 may be an insulated gate bipolar transistor, a metal oxide semiconductor field effect transistor or other power semiconductor elements. Figure 2 As shown, the power switch 22 may be an insulated gate bipolar transistor. Figure 3 As shown, the power switch 22 may be a MOSFET. In addition, the transistor T3 and the transistor T4 may be bipolar junction transistors or MOSFETs. In one embodiment, Figure 2 As shown, transistor T3 and transistor T4 are bipolar junction transistors. In a variant embodiment, at least one of transistor T3 and transistor T4 is a metal oxide semi-conductor field effect transistor. For example, Figure 4 As shown, transistor T3 is a metal oxide semi-conductor field effect transistor, and transistor T4 is a bipolar junction transistor. The control power supply of the active clamp circuit 24 can adopt the power supply voltage provided by the switch circuit 2 or the power supply voltage provided by an external power supply. In one embodiment, as Figure 2 As shown, the resistor R3 of the active clamp circuit 24 is coupled to the power supply voltage VCC (eg, +15 volts) of the switch circuit 2 to receive power for operation. Figure 5As shown, the resistor R3 of the active clamp circuit 24 is coupled to a power voltage Vext provided by an external power source to receive power for operation.

[0040] In addition, when the power switch 22 is in a normal working state, that is, the collector-emitter voltage Vce of the power switch 22 is not in an overvoltage state, the current value of the current I1 is zero, the transistor T4 is turned off (that is, it works in the cut-off state) and the transistor T3 is turned on (that is, it works in the saturated conduction state). In this case, the negative feedback active clamping circuit 24 has little effect on the driving power supply of the power switch 22.

[0041] In summary, compared with the traditional active clamping method, the active clamping circuit 24 of the present embodiment realizes the purpose of active clamping by detecting the branch current I1 of the It current to linearly close the current I2 of the voltage power supply branch. The active clamping circuit 24 of the present embodiment is completely decoupled from the driving path of the power switch 22 and does not need to raise the gate voltage Vgate through the driving path. In this way, the adverse effects of the driving circuit on the main power circuit can be effectively avoided and the reliability of the system can be improved. On the other hand, the present embodiment uses the negative feedback loop of the active clamping circuit 24 to linearly close the branch current I2 to effectively clamp the collector-emitter voltage Vce of the power switch 22 near the breakdown critical voltage of the transient voltage suppression diode TVS, thereby significantly reducing the loss of the transient voltage suppression diode TVS and improving the reliability of the system.

[0042] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A switching circuit, characterized in that: Contains: A driving circuit comprising: an input terminal; an output terminal; a first transistor comprising a first terminal coupled to the input terminal, a second terminal coupled to a first power supply voltage, and a third terminal coupled to the output terminal; and a second transistor comprising a first terminal coupled to the input terminal, a second terminal, and a third terminal coupled to the output terminal; a power switch comprising a first terminal, a second terminal and a third terminal, wherein the first terminal of the power switch is coupled to the output terminal of the driving circuit; and an active clamp circuit coupled to the first terminal of the power switch, the second terminal of the power switch, the output terminal of the driving circuit, and the second terminal of the second transistor; The active clamping circuit comprises: a first protection circuit coupled to the first end of the power switch, the second end of the power switch, and the output end of the drive circuit, the first protection circuit generating a conduction current according to a voltage at the second end of the power switch; and a second protection circuit coupled to the first protection circuit and the second end of the second transistor; Wherein, the on-current includes a first current and a second current, the first current flows to the second protection circuit through a coupling path between the first protection circuit and the second protection circuit, the second current flows to the second protection circuit through the output end of the drive circuit and the second end of the second transistor, and the second protection circuit is used to linearly shut down the second current based on the first current.

2. The switch circuit according to claim 1, characterized in that: The first protection circuit comprises: a transient voltage suppression diode, a cathode of the transient voltage suppression diode is coupled to the second end of the power switch; a diode, an anode of the diode being coupled to an anode of the transient voltage suppression diode, and a cathode of the diode being coupled to the second protection circuit; as well as A first resistor, a first end of which is coupled to the cathode of the diode and the second protection circuit, and a second end of which is coupled to the first end of the power switch and the output end of the driving circuit.

3. The switch circuit according to claim 2, characterized in that: The second protection circuit comprises: a second resistor, a first end of the second resistor being coupled to the cathode of the diode and the first end of the first resistor; a third resistor; a third transistor comprising a first terminal coupled to a first terminal of the third resistor, a second terminal coupled to the second terminal of the second transistor, and a third terminal coupled to a second power supply voltage; as well as A fourth transistor includes a first end coupled to a second end of the second resistor, a second end coupled to the first end of the third resistor and the first end of the third transistor, and a third end coupled to the second power voltage.

4. The switch circuit according to claim 3, characterized in that: When the voltage at the second end of the power switch is greater than a threshold value, the transient voltage suppression diode generates the conduction current, wherein the conduction current also includes a third current, when the fourth transistor is turned on, the first current flows through the second resistor and the fourth transistor, when the second transistor and the third transistor are turned on, the second current flows through the second transistor and the third transistor, and the third current flows to the first end of the power switch.

5. The switch circuit according to claim 4, characterized in that: After the fourth transistor is turned on and the first current flows through the second resistor and the fourth transistor, the third transistor is switched to a cut-off state.

6. The switch circuit according to claim 3, characterized in that: A second end of the third resistor is coupled to the first power voltage or a power voltage provided by an external power source.

7. The switch circuit according to claim 3, characterized in that: At least one of the third transistor and the fourth transistor is a bipolar junction transistor or a metal oxide semi-conductor field effect transistor.

8. The switch circuit according to claim 1, characterized in that: The power switch is an insulated gate bipolar transistor or a metal oxide semi-conductor field effect transistor.

9. The switch circuit according to claim 1, characterized in that: Also includes: A gate resistor has a first end coupled to the output end of the driving circuit, and a second end coupled to the first end of the power switch and the active clamping circuit.

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