Protection circuit for electronic devices

Abstract

The application provides a protection circuit for protecting a power switch to improve the safety of the power switch. The protection circuit comprises a saturation voltage detection circuit, a temperature control adjustment circuit, a buffer circuit and a driving circuit. The saturation voltage detection circuit is connected to a power input terminal of the power switch and is configured to collect a first voltage of the power input terminal. The buffer circuit is connected to the saturation voltage detection circuit and is configured to convert the first voltage into a first converted voltage in a preset time when the first voltage is greater than a first threshold voltage. The temperature control adjustment circuit is connected to the buffer circuit and is configured to reduce the preset time when the temperature rises. The driving circuit is connected to the buffer circuit and is configured to output a first cutoff voltage to the power switch to control the power switch to be cut off when the first converted voltage is greater than a second threshold voltage. The application also provides a protection method of the protection circuit and an electronic device comprising the protection circuit and the power switch.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power supply, in particular to a protection method and protection circuit for protecting a power switch and an electronic device. BACKGROUND

[0002] An IGBT (Insulated Gate Bipolar Transistor) is a common electronic device in a control circuit and is commonly used in power supply circuits and power circuits. With the demand for precision and safety of power supply circuits and power circuits in electronic devices, the performance and safety requirements for IGBT devices / chips are becoming higher and higher.

[0003] However, during the operation of an IGBT, due to internal signal errors, external interference, or other circuit module abnormalities, the IGBT may be short-circuited or overvoltage, which may cause the current in the IGBT to increase sharply. At this time, the gate voltage of the IGBT needs to be turned off to avoid the IGBT from being burned out and further causing the entire system to stop running. SUMMARY

[0004] In view of the foregoing problems, the present application provides a power switch protection circuit and a protection method with better safety, and an electronic device with the foregoing power switch and protection circuit.

[0005] The first aspect of the present application provides a protection circuit for protecting a power switch, which specifically includes a saturation voltage detection circuit, a temperature control adjustment circuit, a buffer circuit, and a driving circuit. The saturation voltage detection circuit is connected to a power input end of the power switch and is configured to collect a first voltage of the power input end. The buffer circuit is connected to the saturation voltage detection circuit and is configured to convert the first voltage into a first converted voltage at a preset time when the first voltage is greater than a first threshold voltage. The temperature control adjustment circuit is connected to the buffer circuit and is configured to reduce the preset time when the temperature rises. The driving circuit is connected to the buffer circuit and is configured to output a first cutoff voltage to the power switch to control the power switch to be cut off when the first converted voltage is greater than a second threshold voltage.

[0006] When the voltage of the power input end of the power switch is large and greater than the corresponding desaturation protection threshold voltage and the temperature is high, the power switch can be quickly controlled to be cut off in time to prevent overheating and damage, that is, the protection reaction time of the power switch can be adjusted in real time according to the temperature, thereby effectively improving the safety of the power switch.

[0007] In one embodiment, the saturation voltage detection circuit includes a first resistor and a first diode connected in series between a constant voltage power supply terminal and the power input terminal. When the first voltage is less than a first threshold voltage, the first diode is forward biased, and a power supply voltage output by the constant voltage power supply terminal cooperates with the first voltage to provide a pre-charge voltage to the buffer circuit. When the first voltage is greater than the first threshold voltage, the first diode is cut off, and the power supply voltage output by the constant voltage power supply terminal is transmitted to the buffer circuit through the temperature control adjustment circuit to convert the first voltage to the first converted voltage in a preset time.

[0008] In one embodiment, the voltage detection circuit includes a second resistor and a fourth resistor. The second resistor is connected between a first node and the power input terminal, and the fourth resistor is connected between the first node and a ground terminal to convert a voltage received by the power input terminal to the first voltage and transmit the first voltage to the buffer circuit through the first node. The temperature control adjustment circuit includes a thermistor with a negative temperature coefficient. The thermistor is connected between the first node and the buffer circuit. When the temperature rises, the resistance of the thermistor decreases. When the first voltage is greater than the first threshold voltage and the temperature rises, the voltage provided by the first voltage to the buffer circuit increases, and the rising speed of the first converted voltage increases, thereby the preset time can be correspondingly reduced.

[0009] In one embodiment, the buffer circuit includes a blanking capacitor connected between the temperature control adjustment circuit and the ground terminal. When the first voltage is less than the first threshold voltage, the first voltage provides a pre-charge voltage to the blanking capacitor. When the first voltage is greater than the first threshold voltage, the blanking capacitor is charged to the first converted voltage.

[0010] In one embodiment, the protection circuit further includes a comparison circuit connected to the drive circuit. The comparison circuit is connected to the blanking capacitor and receives the first converted voltage, and compares the first converted voltage with a second threshold voltage. When the first converted voltage is greater than the second threshold voltage, a comparison signal is output to the drive circuit. The drive circuit outputs the first cut-off voltage according to the comparison signal. Through the cooperation of the comparison circuit and the drive circuit, the power switch can be cut off in time according to the voltage loaded by the power input terminal, thereby effectively preventing the power switch from being damaged.

[0011] In one embodiment, the power switch is an insulated gate bipolar transistor or a metal oxide semiconductor field effect transistor, and the collector of the insulated gate bipolar transistor or the source or the drain of the metal oxide semiconductor field effect transistor is the power input terminal.

[0012] The second aspect of the present application provides an electronic device comprising the above-mentioned protection circuit and a power supply circuit, wherein the power supply circuit is connected to the power input terminal and is configured to provide a power supply signal to the power switch. Since the power switch can be turned off in time when the input voltage is too high, the electronic device can be effectively protected from damage, and the safety of the electronic device is improved.

[0013] In one embodiment, the electronic device can be an alternating current motor, a frequency converter, a switching power supply, a lighting device or a power converter.

[0014] The second aspect of the present application provides a protection method for protecting a power switch, comprising the steps of:

[0015] collecting a first voltage of a power input terminal of the power switch;

[0016] converting the first voltage to a first converted voltage at a preset time when the first voltage is greater than a first threshold voltage;

[0017] decreasing the preset time when the temperature is increased;

[0018] outputting a first cutoff voltage to the power switch to turn off the power switch when the first converted voltage is greater than a second threshold voltage.

[0019] When the voltage of the power input terminal of the power switch is large and greater than the corresponding desaturation protection threshold voltage and the temperature is high, the power switch can be turned off in time to prevent overheating and damage, that is, the protection reaction time of the power switch can be adjusted in real time according to the temperature, and the safety of the power switch is improved.

[0020] In one embodiment, a saturation voltage detection circuit is connected to a power input of the power switch to collect a first voltage from the power input of the power switch. A buffer circuit connected to the saturation voltage detection circuit converts the first voltage to a first converted voltage in a preset time when the first voltage is greater than a first threshold voltage. A temperature control adjustment circuit connected to the buffer circuit decreases the preset time when the temperature increases. A driving circuit connected to the buffer circuit outputs the first cutoff voltage when the first converted voltage is reached. The saturation voltage detection circuit includes a first resistor and a first diode connected in series between a constant voltage power supply and the power input. When the first voltage is less than the first threshold voltage, the first diode is forward biased, and a power voltage output from the constant voltage power supply cooperates with the first voltage to provide a pre-charge voltage for the buffer circuit. When the first voltage is greater than the first threshold voltage, the first diode is cut off, and the power voltage output from the constant voltage power supply is transmitted to the buffer circuit through the temperature control adjustment circuit to convert the first voltage to the first converted voltage in the preset time. The temperature control adjustment circuit includes a thermistor with a negative temperature coefficient connected between the constant voltage power supply and the buffer circuit. When the temperature increases, the resistance value of the thermistor decreases, and when the first voltage is greater than the first threshold voltage and the temperature increases, the voltage provided by the power voltage to the buffer circuit increases, and the rising speed of the first converted voltage increases, so as to decrease the preset time.

[0021] In one embodiment, the voltage detection circuit includes a second resistor and a fourth resistor. The second resistor is connected between a first node and the power input, and the fourth resistor is connected between the first node and a ground terminal, so as to convert a voltage received by the power input to a first voltage and transmit the first voltage to the buffer circuit through the first node. The temperature control adjustment circuit includes a thermistor with a negative temperature coefficient connected between the first node and the buffer circuit. When the temperature increases, the resistance value of the thermistor decreases, and when the first voltage is greater than the first threshold voltage and the temperature increases, the voltage provided by the first voltage to the buffer circuit increases, and the rising speed of the first converted voltage increases, so as to decrease the preset time.

[0022] In one embodiment, the buffer circuit includes a blanking capacitor connected between the temperature control adjustment circuit and the ground terminal. When the first voltage is less than the first threshold voltage, the first voltage provides a pre-charge voltage for the blanking capacitor. When the first voltage is greater than the first threshold voltage, the blanking capacitor is charged to the first converted voltage.

[0023] In one embodiment, the first conversion voltage is received by a comparator circuit connected to the blanking capacitor. The comparator circuit compares the first conversion voltage with the second threshold voltage. When the first conversion voltage is greater than the second threshold voltage, a comparison signal is output to the driving circuit, thereby controlling the driving circuit to output the first cutoff voltage according to the comparison signal.

[0024] In one embodiment, the power switch is an insulated-gate bipolar transistor or a metal-oxide-semiconductor field-effect transistor, wherein the collector of the insulated-gate bipolar transistor is used as the power input terminal, or the source or drain of the metal-oxide-semiconductor field-effect transistor is used as the power input terminal. Attached Figure Description

[0025] Figure 1 This is a circuit block diagram of a frequency converter in one embodiment of this application;

[0026] Figure 2 for Figure 1 The circuit diagram of the inverter unit shown is shown.

[0027] Figure 3 For example Figure 2 A schematic diagram of the circuit structure of any IGBT in the inverter unit shown.

[0028] Figure 4 As described in the first embodiment of this application Figure 3 The circuit block diagram of the protection circuit for the IGBT transistor is shown below.

[0029] Figure 5 For example Figure 4 A schematic diagram of the specific circuit structure of the protection circuit shown.

[0030] Figure 6 For example Figure 5 The diagram shows the steps involved in the operation of the protection circuit.

[0031] Figure 7 For example Figure 5 The diagram shows the operation of the protection circuit when the IGBT is in normal working condition.

[0032] Figure 8 For example Figure 5 The diagram shows the operation of the protection circuit when the IGBT is in a desaturation state.

[0033] Figure 9 As in the second embodiment of this application Figure 4 A schematic diagram of the specific circuit structure of the protection circuit 10 shown;

[0034] Figure 10 As in the third embodiment of this application Figure 4A schematic diagram of the specific circuit structure of the protection circuit shown.

[0035] Figure 11 For example Figure 10 The diagram shows the working process of the protection circuit. Detailed Implementation

[0036] The specific technical solutions of this application will be described below with reference to specific embodiments.

[0037] Please see Figure 1 , Figure 1 This is a circuit block diagram of a frequency converter in one embodiment of this application. The frequency converter 100 is used to provide power to the load for driving the load to operate normally. In this embodiment, the load may be a motor.

[0038] Specifically, the frequency converter 100 includes an inverter unit 110 and a control unit 120. The inverter unit 110 is a full-bridge inverter unit. The control unit 120 is connected to the inverter unit 110 and is used to control the operating state of the inverter unit 110, specifically, to control the inverter unit 110's response to the input DC power supply Vin. Figure 2 The inverter converts the DC power supply to AC power and controls the voltage, current, and frequency of the output AC power. The DC power supply Vin is provided by a DC power supply circuit. The full-bridge inverter unit 110 can be a three-phase full-bridge inverter unit or a single-phase full-bridge inverter unit. This embodiment uses a three-phase full-bridge inverter unit (UVW) for illustration.

[0039] It should be noted that the connections between circuit units or electronic components described in the embodiments of this application are all electrical connections, that is, the circuit units or electronic components can transmit current and voltage through the connection.

[0040] Please see Figure 2 , Figure 2 for Figure 1 The circuit diagram of the inverter unit 110 shown is as follows. Figure 2 As shown, the inverter unit 110 includes a drive circuit (not shown) containing six power switches, which constitute a three-phase (UVW) bridge converter circuit. In this embodiment, the power semiconductor switches can be insulated-gate bipolar transistors (IGBTs). In other embodiments of this application, the power switches can also be metal-oxide-semiconductor field-effect transistors (MOSFETs).

[0041] In this embodiment, the power semiconductor switch is taken as an N-type IGBT tube as an example for illustration. It can be understood that the working principle and connection mode of the MOS tube are similar to those of the IGBT tube, and the present embodiment will not be described again.

[0042] Specifically, the six IGBT tubes are respectively denoted as a first IGBT tube VT1, a second IGBT tube VT2, a third IGBT tube VT3, a fourth IGBT tube VT4, a fifth IGBT tube VT5 and a sixth IGBT tube VT6.

[0043] The first IGBT tube VT1, the third IGBT tube VT3 and the fifth IGBT tube VT5 are respectively an upper bridge arm IGBT tube of a U phase, an upper bridge arm IGBT tube of a V phase and an upper bridge arm IGBT tube of a W phase.

[0044] The second IGBT tube VT2, the fourth IGBT tube VT4 and the sixth IGBT tube VT6 are respectively a lower bridge arm IGBT tube of the U phase, a lower bridge arm IGBT tube of the V phase and a lower bridge arm IGBT tube of the W phase.

[0045] The gate of each of the IGBT tubes VT1-VT6 is connected with the control unit 120. The collector of the first IGBT tube VT1, the collector of the third IGBT tube VT3 and the collector of the fifth IGBT tube VT5 are connected with a positive pole V+ of a bus (not shown), the emitter of the first IGBT tube VT1 is connected with the collector of the second IGBT tube VT2, the emitter of the third IGBT tube VT3 is connected with the collector of the fourth IGBT tube VT4, the emitter of the fifth IGBT tube VT5 is connected with the collector of the sixth IGBT tube VT6, and the emitter of the second IGBT tube VT2, the emitter of the fourth IGBT tube VT4 and the emitter of the sixth IGBT tube VT6 are connected with a negative pole V- of the bus; the node at which the emitter of the first IGBT tube VT1 is connected with the collector of the second IGBT tube VT2, the node at which the emitter of the third IGBT tube VT3 is connected with the collector of the fourth IGBT tube VT4, and the node at which the emitter of the fifth IGBT tube VT5 is connected with the collector of the sixth IGBT tube VT6 are respectively three output nodes (not shown) of a three-phase inverter, and are connected with a load (not shown).

[0046] The control unit 120 outputs corresponding control drive signals to the gates of IGBTs VT1 to VT6 to control the on and off states of IGBTs VT1 to VT6. By adjusting the duty cycle and frequency of the control drive signals, the on and off times of IGBTs VT1 to VT6 can be adjusted, thereby adjusting the voltage and current of the three-phase AC power output by the inverter unit 110. In this embodiment, each of the first IGBT VT1, the second IGBT VT2, the third IGBT VT3, the fourth IGBT VT4, the fifth IGBT VT5, and the sixth IGBT VT6 can be individually fabricated as an integrated circuit (IGBT chip).

[0047] Please see Figure 3 , its is like Figure 2 The circuit structure diagram of any IGBT in the inverter unit 110 shown is as follows: Figure 3 The IGBT 20 shown includes an emitter (E) 21, a collector (C) 22, and a gate (G) 23, which are led out from the doped regions of three semiconductor substrates.

[0048] In this IGBT 20, a first voltage Vce exists between the emitter 21 and collector 22, and a second voltage Vge exists between the gate 23 and emitter 21. When the second voltage Vge is greater than the threshold voltage Vth, the IGBT 20 is turned on, and a collector current Ic is formed from the collector 22 to the emitter 21. In other words, the IGBT 20 receives the operating collector current Ic from its collector 22. Conversely, the collector 22 serves as the power input terminal of the IGBT 20, and the power signal formed by the voltage and current received at the power input terminal provides power to other power circuits.

[0049] During operation, the IGBT 20 can be in the cutoff region, saturation region, and amplification region.

[0050] When the second voltage Vge is less than the threshold voltage Vth, the IGBT 20 is turned off, that is, the IGBT 20 is in the cutoff region, and no current flows in the IGBT 20 at this time.

[0051] When the second voltage Vge is greater than the threshold voltage Vth, the IGBT 20 is turned on, and a collector current Ic flows through the collector 22. The voltage between the emitter 21 and the collector 22 increases linearly with the increase of the collector current Ic. At this time, the IGBT 20 is in the saturation region.

[0052] When the current Ic of collector 22 increases to the critical point and then stops increasing, while the voltage between emitter 21 and collector 22 increases rapidly, IGBT 20 is operating in the amplification region.

[0053] When the IGBT tube 20 exits from the saturation region and works in the amplification region, the collector current Ic stops increasing, and if the first voltage Vce continues to increase and is greater than the desaturation protection threshold voltage Vdesa at this time, the IGBT tube 20 is in the desaturation state. If the IGBT tube is not turned off in time at this time, that is, if the second voltage Vge between the gate 23 and the emitter 21 of the IGBT tube 20 is still greater than the threshold voltage Vth, the IGBT tube 20 will generate more heat due to the large current, and thus overheat to cause permanent damage.

[0054] The higher the ambient temperature of the IGBT tube 20 at this time, the smaller the maximum dissipation power allowed by the IGBT tube 20, that is, the shorter the time that the IGBT tube 20 can withstand the desaturation protection threshold voltage Vdesa, and thus the more rapid protection is required at this time. There is a problem that the response of the protection is too long at high temperature, and the IGBT tube cannot be turned off in time, resulting in failure of the tube.

[0055] Therefore, the application provides a protection circuit to quickly and timely control the IGBT tube 20 to be turned off and cut off when the IGBT tube 20 exits from the saturation region and works in the amplification region, the first voltage Vce continues to increase and is greater than the desaturation protection threshold voltage Vdesa, and the ambient temperature is high, so as to prevent the IGBT tube 20 from being damaged due to overheating.

[0056] It should be noted that although Figures 1-3 The IGBT tube 20 is taken as an example for description of the application to the frequency converter as a power switch, but it is obvious that the IGBT tube 20 can also be applied to electronic devices such as an alternating current motor, a switching power supply, a lighting device, or a power converter as a power switch.

[0057] Please refer to Figure 4 which is a circuit principle block diagram of the protection circuit of the IGBT tube 20 shown in the first embodiment of the application. Figure 3

[0058] The protection circuit 10 is connected to the IGBT tube 20, and is used to timely and quickly control the IGBT tube 20 to be in the cut-off state when the IGBT tube 20 is in the desaturation state and the first voltage Vce continues to increase to be greater than the desaturation protection threshold voltage Vdesa, so as to prevent the IGBT tube 20 from being damaged due to overheating.

[0059] The protection circuit 10 includes a saturation voltage detection circuit 11, a temperature control adjustment circuit 12, a buffer circuit 13, a driving circuit 14, and a comparison circuit 15.

[0060] ​The saturation voltage detection circuit 11 is connected to the collector 22 of the IGBT tube 20, i.e. connected to the power input end of the IGBT tube 20, for detecting the voltage of the collector 22 of the IGBT tube 20. In the embodiment, since the emitter 21 of the IGBT tube 20 is connected to the ground end GND, the saturation voltage detection circuit 11 is equivalent to detecting the first voltage Vce between the emitter 21 and the collector 22 of the IGBT tube 20, so as to determine whether the first voltage Vce in the IGBT tube 20 is greater than the first threshold voltage Vf1 corresponding to the desaturation protection threshold voltage Vdesa.

[0061] In other embodiments of the present application, the emitter 21 of the IGBT tube 20 can also be connected to a reference voltage end (not shown), as long as the voltage difference between the gate 23 and the emitter 21 is related to the threshold voltage Vth, so as to drive the IGBT tube 20 to be turned on or turned off correspondingly.

[0062] The buffer circuit 13 is connected to the saturation voltage detection circuit 11, for converting the first voltage Vce into a first converted voltage Vs1 in a preset time when the first voltage Vce is greater than the first threshold voltage Vf1.

[0063] The temperature control adjustment circuit 12 is connected to the buffer circuit, for reducing the preset time when the temperature rises. In the embodiment, the temperature can be the ambient temperature of the IGBT tube 20 and the temperature of the temperature control adjustment circuit 12 itself.

[0064] The comparison circuit 15 is connected to the buffer circuit 13, for comparing the first converted voltage Vs1 with a second threshold voltage Vf2, and outputting a corresponding comparison result. Specifically, when the first converted voltage Vs1 is greater than the second threshold voltage Vf2, a comparison signal with a first potential is outputted, and when the first converted voltage Vs1 is less than the second threshold voltage Vf2, a comparison signal with a second potential is outputted. In the embodiment, the first potential is a high level, and the second potential is a low level. Corresponding to the P-type IGBT tube 20, the first potential is a low level, and the second potential is a high level. It can be understood that the second threshold voltage Vf2 is also a reference voltage corresponding to the desaturation protection threshold voltage Vdesa.

[0065] The drive circuit 14 is connected to the comparison circuit 15 and the gate 23 and the emitter 21 of the IGBT tube 20, and outputs a first turn-off voltage to the gate 23 of the IGBT tube 20 when receiving the comparison signal representing that the first converted voltage Vs1 is greater than the second threshold voltage Vf2, so as to control the IGBT tube to be turned off.

[0066] More specifically, please refer to Figure 5 , which is a specific circuit structure diagram of the protection circuit 10 as shown in Figure 4 . As shown in Figure 5As shown, the saturation voltage detection circuit 11 includes a first resistor R1 and a first diode D1. The first resistor R1 and the first diode D1 are connected in series between the collector 22 of the IGBT tube 20 and the temperature control adjustment circuit 12, more specifically, the first resistor R1 and the first diode D1 are connected in series between the first node N1 and the collector 22 of the IGBT tube 20, the anode of the first diode D1 is connected to the first resistor R1, and the cathode of the first diode D1 is connected to the collector 22, wherein the first node N1 is connected to the temperature control adjustment circuit 12 and the buffer circuit 13, and the first node N1 receives the supply voltage Vcc provided by the constant voltage power supply end VDD through the temperature control adjustment circuit 12.

[0067] The temperature control adjustment circuit 12 includes a negative temperature coefficient thermistor Rw connected between the constant voltage power supply end VDD and the buffer circuit 13, more specifically, the negative temperature coefficient thermistor Rw is connected between the constant voltage power supply end VDD and the first node N1. In this embodiment, the negative temperature coefficient thermistor Rw is a resistor with a negative temperature coefficient Negative Temperature Coefficient (NTC). Specifically, when the first voltage Vce is greater than the first threshold voltage Vf1 and the temperature rises, the voltage of the supply voltage Vcc output by the constant voltage power supply end VDD provided to the buffer circuit 13 is increased and the rising speed of the first conversion voltage Vs1 is increased, thereby reducing the preset time.

[0068] The negative temperature coefficient thermistor Rw is a semiconductor resistor with temperature sensitivity, and its resistance value decreases as the temperature rises. The material of the negative temperature coefficient thermistor Rw includes metal oxides such as manganese, manganese, cobalt, nickel, and copper, which have semiconductor properties. When the temperature is low, the number of carriers (electrons and holes) of the metal oxide material decreases, so that the resistance value of the thermistor Rw is high; as the temperature rises, the number of carriers increases, and the resistance value of the thermistor Rw decreases.

[0069] The buffer circuit 13 includes a blanking capacitor C1, wherein the blanking capacitor C1 is connected between the thermistor Rw and the ground end GND, more specifically, the blanking capacitor C1 is connected between the first node N1 and the ground end GND. The blanking capacitor C1 is connected between the temperature control adjustment circuit 12 and the ground end GND, when the first voltage Vce is less than the first threshold voltage Vf1, the first voltage Vce provides part of the pre-charge voltage for the blanking capacitor C1, when the first voltage Vce is greater than the first threshold voltage Vf1, the blanking capacitor C1 is directly charged to the first conversion voltage Vs1 by the supply voltage Vcc through the thermistor Rw.

[0070] The comparison circuit 15 is connected to the blanking capacitor C1 and receives the first converted voltage Vs1, and compares the first converted voltage Vs1 with the second threshold voltage Vf2, and outputs a corresponding comparison signal to the driving circuit 14 when the first converted voltage Vs1 is greater than the second threshold voltage Vf2.

[0071] The driving circuit 14 outputs a first cutoff voltage according to the comparison signal. Specifically, the first cutoff voltage is less than the threshold voltage Vth, and the driving circuit 14 is connected between the gate 23 and the emitter 21 of the IGBT tube 20. When the driving circuit 14 provides the gate 23 and the emitter 21 of the IGBT tube 20 with a first cutoff voltage less than the threshold voltage Vth, the IGBT tube 20 is immediately in a cutoff state.

[0072] Please refer to Figure 6 , which is a schematic diagram of the working steps of the protection circuit as shown in Figure 5 . Now the working principle and process of the protection circuit will be specifically explained in combination with Figure 5 , Figure 6 .

[0073] In step S100, the second voltage Vce at the power input end of the power switch is collected.

[0074] Specifically, please refer to Figure 7 , when the IGBT tube 20 is in normal operation, the second voltage Vce between the collector 22 and the emitter 21 of the IGBT tube 20 is collected by the saturation voltage detection circuit 11. Among them Figure 7 is a schematic diagram of the working process of the protection circuit 10 when the IGBT tube 20 is in normal operation as shown in Figure 5 .

[0075] Specifically, as shown in Figure 7 , when the IGBT tube 20 is saturated and turned on, along the dotted line shown, for the constant voltage power supply end VDD through the heating resistor Rw, the first resistor R1, the first diode D1 and the conduction path of the IGBT tube 20, since the first voltage Vce is less than the first threshold voltage Vf1 at this time, the first diode D1 in the detection circuit 11 is forward biased, and the power supply voltage Vcc provided by the constant voltage power supply end VDD cooperates with the first voltage Vce to provide a pre-charge voltage for the blanking capacitor C1. Among them, the voltage output by the saturation voltage detection circuit 11 to the blanking capacitor C1 can be expressed as: Vc1=(Vcc-Vce-Vd1)*R1 / (R1+Rw). At this time, the voltage Vc1 output by the saturation voltage detection circuit 11 to the blanking capacitor C1 is the voltage of the constant voltage power supply end VDD cooperating with the collector 22 of the IGBT tube 20, which provides a pre-charge voltage for the blanking capacitor C1.

[0076] Wherein, Vc1 represents the voltage applied to the blanking capacitor C1, which is also the first conversion voltage Vs1 output by the buffer circuit 13; Vcc represents the power supply voltage received from the outside and transmitted to the temperature control adjustment circuit 12 by the constant voltage power supply terminal VDD; Vce represents the first voltage between the collector 22 and the emitter 21 in the IGBT 20; Vd1 represents the voltage applied to the first diode D1; R1 represents the resistance value of the first resistor R1; and Rw represents the resistance value of the thermistor Rw.

[0077] Step S200: When the second voltage Vce is greater than the first threshold voltage Vf1, the first voltage Vce is converted into the first conversion voltage Vs1 within a preset time.

[0078] When IGBT 20 experiences desaturation, such as Figure 8 As shown, when the second voltage Vce increases to exceed the preset voltage, the first diode D1 is reverse-biased due to the cathode voltage being greater than the anode voltage. The constant voltage power supply terminal VDD is disconnected from the IGBT 20's conductive path. Therefore, along the dotted line in the figure, the constant voltage power supply terminal VDD directly forms a conductive path through the thermistor Rw, the blanking capacitor C1, and the ground terminal GND. The constant current source voltage terminal Vcc directly charges the blanking capacitor C1, causing the blanking capacitor C1 voltage to gradually increase, i.e., the first conversion voltage Vs1 gradually increases until it exceeds the second threshold voltage Vf2, which triggers the desaturation threshold voltage Vdesat. When Vc1 changes from (Vcc-Vce-Vd1)*R1 / (R1+Rw) to the second threshold voltage Vf2, the blanking capacitor C1 is charged to exceed the second threshold voltage Vf2, requiring a response time t = Rw*C1. Figure 8 For example Figure 5 The diagram shows the operation of the protection circuit 10 when the IGBT 20 is in a desaturation state.

[0079] It can be seen that the smaller the resistance value of the thermistor Rw, the smaller the response time t. Therefore, when the ambient temperature of the IGBT 20 is high, the resistance value of the thermistor Rw decreases, which can more quickly identify the state of the second voltage Vce between the collector 22 and the emitter 21.

[0080] In step S300, when the first conversion voltage Vs1 is greater than the second threshold voltage Vf2, the first cutoff voltage is output between the gate 23 and the emitter 21 of the IGBT 20 to control the IGBT 20 to be cut off.

[0081] When the ambient temperature of the IGBT tube 20 is high, the resistance value of the thermistor Rw decreases, and the state of the second voltage Vce between the collector 22 and the emitter 21 can be recognized more quickly to be greater than the desaturation threshold voltage Vdesat, so that the IGBT tube 20 is controlled to be turned off more quickly, thereby preventing the power input end voltage of the IGBT tube 20 from continuously increasing to cause overheating and damage.

[0082] Referring to Figure 9 , it is a specific circuit structure diagram of the protection circuit 10 as shown in the second embodiment of the present application. Figure 4 As shown in Figure 9 , the specific circuit structure of the protection circuit 10 in the present embodiment is basically the same as the circuit structure and working principle of the protection circuit as shown in Figure 5 , and the only difference is the connection position of the thermistor Rw in the temperature control adjustment circuit 12.

[0083] Specifically, as shown in Figure 9 , the temperature control adjustment circuit 12 includes a thermistor Rw with a negative temperature coefficient, and the thermistor Rw is connected between the first node N1 and the blanking capacitor C1 of the buffer circuit 13. At the same time, the constant voltage power supply end VDD is directly connected to the first resistor R1 through the first node N1.

[0084] Referring to Figure 10 , it is a specific circuit structure diagram of the protection circuit 10 as shown in the third embodiment of the present application. Figure 4

[0085] As shown in Figure 10 , the saturation voltage detection circuit 11 includes a second resistor R2, a third resistor R3 and a fourth resistor R4.

[0086] The second resistor R2, the third resistor R3 and the fourth resistor R4 are connected in series between the ground end GND and the emitter 21 of the IGBT tube 20.

[0087] The temperature control adjustment circuit 12 includes a thermistor Rw with a negative temperature coefficient, and the thermistor Rw is connected between the first node N1 and the buffer circuit 13. In the present embodiment, the first node N1 is any node between the third resistor R3 and the fourth resistor R4. In addition, the thermistor Rw is a resistance with a negative temperature coefficient. The thermistor Rw with a negative temperature coefficient is a semiconductor resistance with temperature sensitivity, and its resistance value decreases with the increase of temperature.

[0088] The buffer circuit 13 includes a blanking capacitor C1, and the blanking capacitor C1 is connected between the thermistor Rw and the ground end GND.

[0089] ​The comparison circuit 15 is connected to the blanking capacitor C1 and receives the first conversion voltage Vs1, and compares the first conversion voltage Vs1 with a second threshold voltage Vf2, and outputs a first control signal to the drive circuit 14 when the first conversion voltage Vs1 is greater than the second threshold voltage Vf2.

[0090] The drive circuit 14 outputs a first cutoff voltage according to the first control signal. Specifically, the drive circuit 14 is connected between the gate 23 and the collector 22 of the IGBT tube 20, and is used to output a drive voltage to control the IGBT tube 20 to be turned on or turned off.

[0091] It should be noted that in other embodiments of the present application, the number of resistors included in the saturation voltage detection circuit 11 can be adjusted according to actual needs, and is not limited to the number of resistors included in the saturation voltage detection circuit 11 in the embodiment shown. For example, the number of resistors included in the saturation voltage detection circuit 11 can be two, four, etc. When the number of resistors included in the saturation voltage detection circuit 11 is two, the two resistors can be the second resistor R2 and the fourth resistor R4 or the third resistor R3 and the fourth resistor R4, that is, the second resistor R2 and the third resistor R3 can be combined into one resistor. Figure 10

[0092] The working principle and process of the protection circuit 10 will be specifically described with reference to the Figure 6 , Figure 10 embodiment shown in the accompanying drawings.

[0093] In step S100, the second voltage Vce at the power input end of the power switch is collected.

[0094] Specifically, please refer to Figure 11 When the IGBT tube 20 is in normal operation, the second voltage Vce between the collector 22 and the emitter 21 of the IGBT tube 20 is collected by the saturation voltage detection circuit 11. Among them Figure 11 is the working process diagram of the protection circuit 10 as shown in Figure 10 .

[0095] Specifically, as shown in Figure 11 ​As shown, when the IGBT tube 20 is saturated and turned on, along the dotted line, the collector 22 as the power input end passes through the second resistor R2, the third resistor R3, the fourth resistor R4 and the ground end GND to form a conductive path, in which the second resistor R2, the third resistor R3 and the fourth resistor R4 are connected in series between the ground end GND and the collector 22, and the voltage of the first node N1 is the voltage taken by the fourth resistor R4, and the detection circuit 11 outputs the corresponding second voltage Vce, that is, the voltage (Vn1) of the first node N1, which can be expressed as: Vn1=Vce*R4 / (R2+R3+R4). Wherein, Vn1 represents the first conversion voltage Vs1 of the second voltage Vce output by the detection circuit 11, and R2-R4 represent the resistance values of the second resistor R2, the third resistor R3 and the fourth resistor R4, respectively.

[0096] In step S200, when the second voltage Vce is greater than the first threshold voltage Vf1, the first voltage Vce is converted into the first conversion voltage Vs1 within a preset time.

[0097] When the IGBT tube 20 occurs desaturation, the second voltage Vce voltage rises, and the first conversion voltage Vs1 directly passes through the thermistor Rw, the blanking capacitor C1 and the ground end GND to form a conductive path, and the first conversion voltage Vs1 directly charges the blanking capacitor C1, and the voltage of the blanking capacitor C1 gradually rises, that is, the first conversion voltage Vs1 gradually rises until it is greater than the desaturation threshold voltage Vdesat, that is, the desaturation threshold voltage Vdesat is triggered, wherein, Vc1 is converted from Vce*R3 / (R1+R2+R3) to the second threshold voltage Vf2, at this time, the second threshold voltage is the desaturation threshold voltage Vdesat, and the response time t=Rw*C1 is required.

[0098] It can be seen that the smaller the resistance value of the thermistor Rw, the smaller the response time t, and thus when the ambient temperature of the IGBT tube 20 is high, the resistance value of the thermistor Rw is reduced, and the state of the second voltage Vce between the collector 22 and the emitter 21 can be recognized more quickly.

[0099] In step S300, when the first conversion voltage Vs1 is greater than the second threshold voltage Vf2, the first cutoff voltage is output to the gate 23 and the emitter 21 of the IGBT tube 20 to control the IGBT tube 20 to be cut off.

[0100] When the ambient temperature of the IGBT tube 20 is high, the resistance value of the thermistor Rw is reduced, and the state of the second voltage Vce between the collector 22 and the emitter 21 can be recognized more quickly, so that the IGBT tube 20 is controlled to be cut off more quickly, thereby preventing the power input end voltage of the IGBT tube 20 from continuously increasing to cause overheating and damage.

[0101] In the above embodiments, the description of each embodiment is focused on, and the part not described in detail in a certain embodiment can be referred to the relevant description of other embodiments.

[0102] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the system, device and module described above can refer to the corresponding process in the foregoing method embodiments, which will not be described here.

[0103] The above describes the technical solutions provided by the present application in detail, and the principles and implementation manners of the present application are described by applying specific examples. The above embodiment description is only used to help understand the method and its core idea of the present application; meanwhile, for those skilled in the art, according to the idea of the present application, the specific implementation manner and application range will be changed, and the above description should not be understood as a limitation of the present application.

Claims

1. A protection circuit for protecting a power switch, characterized by, The protection circuit comprises a saturation voltage detection circuit, a temperature control adjustment circuit, a buffer circuit and a driving circuit, The saturation voltage detection circuit is connected to a power input terminal of the power switch and is configured to collect a first voltage of the power input terminal when the power switch is working, and the first voltage is used to determine whether the power switch is in a desaturation state; The buffer circuit is connected to the saturation voltage detection circuit and is configured to convert the first voltage into a first converted voltage at a preset time when the first voltage is greater than a first threshold voltage, and the first converted voltage is used to control whether the power switch is cut off; The temperature control adjustment circuit is connected to the buffer circuit and is configured to reduce the preset time when the temperature rises; The driving circuit is connected to the buffer circuit and outputs a first cut-off voltage to the power switch to control the power switch to be cut off when the first converted voltage is greater than a second threshold voltage.

2. The protection circuit of claim 1, wherein The saturation voltage detection circuit comprises a first resistor and a first diode, and the first resistor and the first diode are connected in series between a constant voltage power supply terminal and the power input terminal, When the first voltage is less than the first threshold voltage, the first diode is forward biased, and a power supply voltage output by the constant voltage power supply terminal cooperates with the first voltage to provide a pre-charge voltage for the buffer circuit; When the first voltage is greater than the first threshold voltage, the first diode is cut off, and the power supply voltage output by the constant voltage power supply terminal is transmitted to the buffer circuit through the temperature control adjustment circuit to convert the first voltage into the first converted voltage at the preset time.

3. The protection circuit of claim 2, wherein The temperature control adjustment circuit comprises a thermistor with a negative temperature coefficient, and the thermistor is connected between the constant voltage power supply terminal and the buffer circuit, and the resistance value of the thermistor decreases when the temperature rises, and when the first voltage is greater than the first threshold voltage and the temperature rises, the voltage provided by the power supply voltage to the buffer circuit is increased and the rising speed of the first converted voltage is increased to reduce the preset time.

4. The protection circuit of claim 1, wherein The voltage detection circuit comprises a second resistor and a fourth resistor, the second resistor is connected to a first node and the power input terminal, and the fourth resistor is connected to the first node and a ground terminal to convert the voltage received by the power input terminal into the first voltage and transmit the first voltage to the buffer circuit through the first node.

5. The protection circuit of claim 4, wherein The temperature control adjustment circuit comprises a thermistor with a negative temperature coefficient, and the thermistor is connected between the first node and the buffer circuit, and the resistance value of the thermistor decreases when the temperature rises, and when the first voltage is greater than the first threshold voltage and the temperature rises, the voltage provided by the first voltage to the buffer circuit is increased and the rising speed of the first converted voltage is increased to reduce the preset time.

6. The protection circuit of any one of claims 2-5, wherein The buffer circuit comprises a blanking capacitor connected between the temperature control adjustment circuit and a ground terminal, wherein the first voltage provides a pre-charge voltage for the blanking capacitor when the first voltage is less than a first threshold voltage, and the blanking capacitor is charged to the first conversion voltage when the first voltage is greater than the first threshold voltage.

7. The protection circuit of claim 6, wherein, The protection circuit further comprises a comparison circuit connected to the drive circuit, the comparison circuit being connected to the blanking capacitor and receiving the first conversion voltage, and comparing the first conversion voltage with a second threshold voltage, and outputting a comparison signal to the drive circuit when the first conversion voltage is greater than the second threshold voltage. The drive circuit outputs the first cut-off voltage according to the comparison signal.

8. The protection circuit of claim 6, wherein, The power switch is an insulated gate bipolar transistor or a metal oxide semiconductor field effect transistor, and a collector of the insulated gate bipolar transistor or a source or a drain of the metal oxide semiconductor field effect transistor is the power input terminal.

9. An electronic device, comprising: A power supply circuit is connected to the power input terminal, and the power supply circuit is configured to provide a power signal for the power switch.

10. The electronic device of claim 9, wherein, The electronic device is an alternating current motor, a frequency converter, a switching power supply, a lighting device, or a power converter.

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