A bipolar pulse constant current source with high switching rate

Abstract

This invention relates to a bipolar pulsed constant current source with a high switching rate, belonging to the field of power electronics technology. The bipolar pulsed constant current source includes a positive pulsed constant current source and a negative pulsed constant current source. The positive pulsed constant current source includes a positive reference potential selection circuit, a forward constant current source circuit, and a positive pulsed constant current source control circuit. The negative pulsed constant current source includes a negative reference potential selection circuit, a reverse constant current source circuit, and a negative pulsed constant current source control circuit. The noise filtering capacitor in the reference potential selection circuit and the filtering inductor in the constant current source circuit significantly reduce the fluctuation of the constant current source output current. While ensuring rapid switching of the pulsed current source, this invention uses a charge pump-like method to drive the MOSFET, eliminating the need for an isolated power supply to drive the switching transistor, thus greatly reducing the circuit size. This bipolar pulsed constant current source features fast switching rate, high stability, high precision, small size, and bipolar output capability, meeting the measurement requirements for rapid extraction of various temperature-sensitive electrical parameters of power semiconductor devices under conditions of rapid junction temperature changes.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, specifically a bipolar pulse constant current source with a high switching rate. Background Technology

[0002] High-precision, low-temperature-drift, high-reliability, and high-switching-rate constant current sources are widely used in various fields such as transient thermal characteristic testing of power semiconductor devices, temperature-sensitive electrical parameter measurement, clock circuits, and oscillators. These high-precision instruments and measurements place demands on constant current sources that are non-invasive, have a fast response, and are highly accurate. Especially in the measurement of temperature-sensitive electrical parameters of power semiconductor devices, accurately measuring the junction temperature of these devices is a prerequisite for real-time status monitoring and reliability assessment. Therefore, junction temperature extraction of power semiconductor devices plays a crucial role in power electronics systems. In practical applications, the temperature-sensitive electrical parameter method is often used to obtain the junction temperature of power semiconductor devices in real time. This method has advantages such as being non-invasive, having a fast response, high accuracy, and low cost. With the development of power electronics technologies, the accuracy requirements for junction temperature extraction technology are also increasing.

[0003] On the one hand, constant current sources are often required to assist in the measurement of temperature-sensitive electrical parameters of power semiconductor devices, and a stable constant current source is a prerequisite for ensuring the accuracy of temperature-sensitive parameter extraction. On the other hand, different temperature-sensitive electrical parameters have different requirements for the current polarity of the auxiliary constant current source. For example, when measuring the body diode voltage drop of a SiC MOSFET, a constant current from the source to the drain is required; when measuring the threshold voltage of a SiC MOSFET, a constant current from the drain to the source is required. Therefore, a constant current source capable of generating bipolar pulse current is of great significance for meeting the measurement needs of different temperature-sensitive electrical parameters, reducing the complexity of measurement operations, and increasing the universality of measurement circuits. In addition, the switching delay of the constant current source is a key factor affecting the accuracy of junction temperature extraction, especially under conditions of rapid junction temperature changes, where the requirements for the switching delay of the constant current source are even higher. In practical applications, due to the presence of high voltage and high current in the main circuit, the constant current source needs to have the ability to withstand high voltage and prevent current reverse flow. Existing pulse constant current sources mainly suffer from the following problems: First, most pulse constant current sources have slow switching rates, with pulse current output delays on the order of hundreds of microseconds or even milliseconds, which cannot meet the high switching rate requirements of transient thermal characteristic testing. Second, the output current stability is insufficient, failing to meet the requirements of high-precision measurement. Third, constant current sources using grounding resistance feedback are difficult to integrate with other circuits. Summary of the Invention

[0004] This invention addresses the current measurement requirements for temperature-sensitive electrical parameters of power semiconductor devices by proposing a bipolar pulsed constant current source with a high switching rate. This bipolar pulsed constant current source features fast switching rate, high stability, high precision, small size, and bipolar output, meeting the measurement needs for rapid extraction of various temperature-sensitive electrical parameters of power semiconductor devices under conditions of rapid junction temperature changes.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A bipolar pulse constant current source with a high switching rate includes a positive pulse constant current source and a negative pulse constant current source; characterized in that the positive pulse constant current source includes a positive reference potential selection circuit, a forward constant current source circuit, and a positive pulse constant current source control circuit; the negative pulse constant current source includes a negative reference potential selection circuit, a reverse constant current source circuit, and a negative pulse constant current source control circuit.

[0007] The positive pulse constant current source control circuit includes MOSFETs M1-M4, driving resistors R4-R8, diodes D1-D2, capacitor C2, transistor Q2, and a positive pulse current control terminal. Transistor Q2 is an NPN transistor, MOSFETs M1 and M4 are N-channel MOSFETs, and MOSFETs M2 and M3 are P-channel MOSFETs. The drain of MOSFET M1 is connected to the collector of transistor Q1 in the forward constant current source circuit. The source of MOSFET M1 is grounded. The gate of MOSFET M1 is connected to one end of driving resistor R4. The other end of driving resistor R4 and one end of driving resistor R5 are connected to the cathode of diode D1. The anode of diode D1 is connected to the other end of driving resistor R5, one end of driving resistor R6, one end of driving resistor R8, and the positive pulse constant current source control terminal. The first terminal is connected to the second terminal; the other terminal of the driving resistor R6 is connected to the gate of MOSFET M3 and MOSFET M4. The source of MOSFET M4 is connected to the negative voltage source. The drain of MOSFET M4 is connected to the drain of MOSFET M3 and one terminal of the driving resistor R7. The other terminal of the driving resistor R7 is connected to the other terminal of capacitor C2. One terminal of capacitor C2 and the source of MOSFET M2 are connected to the collector of transistor Q1 in the positive constant current source circuit. The other terminal of the driving resistor R8 is connected to the base of transistor Q2. The emitter of transistor Q2 is connected to the source of MOSFET M3 and the gate of MOSFET M2. The collector of transistor Q2 is connected to the source of MOSFET M2. The drain of MOSFET M2 is connected to the anode of diode D2. The cathode of diode D2 is the output terminal of the positive pulse constant current source.

[0008] The negative pulse constant current source control circuit includes MOSFETs M5-M8, driving resistors R12-R16, diodes D3-D4, capacitor C4, transistor Q4, and a negative pulse current control terminal. MOSFETs M7 and M8 are N-channel MOSFETs, MOSFETs M5 and M6 are P-channel MOSFETs, and transistor Q4 is a PNP transistor. The source of MOSFET M5 is grounded, the drain of MOSFET M5 is connected to the collector of transistor Q3 in the reverse constant current source circuit, the gate of MOSFET M5 is connected to one end of driving resistor R12, the other end of driving resistor R12 is connected to one end of driving resistor R13 and the anode of diode D3, and the cathode of diode D3 is connected to the other end of driving resistor R13, one end of driving resistor R14, one end of driving resistor R16, and the negative pulse current control terminal. The other end of the dynamic resistor R14 is connected to the gates of MOSFETs M6 and M7. The source of MOSFET M6 is connected to the positive voltage source. The drain of MOSFET M6 is connected to the drain of MOSFET M7 and one end of the drive resistor R15. The other end of the drive resistor R15 is connected to one end of the capacitor C4. The other end of the capacitor C4, the source of MOSFET M8, and the collector of transistor Q4 are connected to the collector of transistor Q3 in the reverse constant current source circuit. The other end of the drive resistor R16 is connected to the base of transistor Q4. The emitter of transistor Q4 is connected to the source of MOSFET M7 and the gate of MOSFET M8. The collector of transistor Q4 is connected to the source of MOSFET M8. The drain of MOSFET M8 is connected to the cathode of diode D4. The anode of diode D4 is the output terminal of the negative pulse constant current source.

[0009] Furthermore, the positive reference potential selection circuit includes voltage divider resistors R1 and R2 and noise filtering capacitor C1; one end of the voltage divider resistor R1 is connected to a positive voltage source, and the other end is connected to one end of the voltage divider resistor R2, one end of the noise filtering capacitor C1, and the non-inverting input terminal of the operational amplifier U1 of the positive constant current source circuit; the other end of the voltage divider resistor R2 and the noise filtering capacitor C1 is grounded; or the positive reference potential selection circuit uses a DAC signal to output a positive reference potential through a non-inverting proportional operational circuit.

[0010] Furthermore, the positive constant current source circuit includes a filter inductor L1, a current regulating resistor R3, an operational amplifier U1, and a transistor Q1, wherein the transistor Q1 is a PNP transistor; one end of the filter inductor L1 is connected to a positive voltage source, and the other end is connected to one end of the current regulating resistor R3. The other end of the current regulating resistor R3 is connected to the emitter of the transistor Q1 and the inverting input terminal of the operational amplifier U1. The base of the transistor Q1 is connected to the output terminal of the operational amplifier U1, and the collector of the transistor Q1 is connected to the positive pulse constant current source control circuit.

[0011] Furthermore, the negative reference potential selection circuit includes voltage divider resistors R9 and R10 and noise filtering capacitor C3; one end of voltage divider resistor R10 is connected to the negative voltage source, and the other end is connected to one end of voltage divider resistor R9, one end of noise filtering capacitor C3, and the non-inverting input terminal of operational amplifier U2 of the reverse constant current source circuit; the other end of voltage divider resistor R9 and filtering capacitor C3 is grounded.

[0012] Furthermore, the reverse constant current source circuit includes a filter inductor L2, a current regulating resistor R11, an operational amplifier U2, and a transistor Q3, wherein the transistor Q3 is an NPN transistor; one end of the filter inductor L2 is connected to a negative voltage source, and the other end is connected to one end of the current regulating resistor R11. The other end of the current regulating resistor R11 is connected to the emitter of the transistor Q3 and the inverting input terminal of the operational amplifier U2. The base of the transistor Q3 is connected to the output terminal of the operational amplifier U2, and the collector of the transistor Q3 is connected to the negative pulse constant current source control circuit.

[0013] Furthermore, when the positive pulse constant current source control terminal outputs a high level, the positive pulse constant current source current provided by the control terminal passes through diode D1 and drive resistor R4 to charge the gate of MOSFET M1, causing MOSFET M1 to turn on quickly. The positive pulse constant current source control terminal provides base current to transistor Q2, causing MOSFET M2 to turn off. Simultaneously, the positive pulse constant current source current passes through drive resistor R6 to discharge the gate of MOSFET M3 and charge the gate of MOSFET M4, causing MOSFET M3 to turn off and MOSFET M4 to turn on. The negative voltage source charges capacitor C2 through drive resistor R7. At this time, the positive pulse constant current source current no longer flows through MOSFET M2, but only through MOSFET M1, completing the current switching. When the positive pulse constant current source control terminal outputs a low level, the positive pulse constant current source current provided by the positive pulse constant current source control terminal passes through the driving resistors R4 and R5, which discharges the gate of MOSFET M1, causing MOSFET M1 to turn off quickly. The positive pulse constant current source control terminal no longer provides base current to transistor Q2. At the same time, the positive pulse constant current source current passes through the driving resistor R6 to charge the gate of MOSFET M3 and discharge the gate of MOSFET M4, causing MOSFET M3 to turn on and MOSFET M4 to turn off. Capacitor C2 passes through the driving resistor R7 and MOSFET M3 to charge the gate of MOSFET M2, causing MOSFET M2 to turn on. At this time, the current no longer flows through MOSFET M1, but only through MOSFET M2, completing the current switching.

[0014] When the negative pulse constant current source control terminal outputs a low level, the negative pulse constant current source current provided by the control terminal passes through diode D3 and drive resistor R13, charging the gate of MOSFET M5 and causing MOSFET M5 to turn on quickly. The negative pulse constant current source control terminal provides base current to transistor Q4, causing MOSFET M8 to turn off. At the same time, the negative pulse constant current source current passes through drive resistor R14 to discharge the gate of MOSFET M7 and charge the gate of MOSFET M6, causing MOSFET M7 to turn off and MOSFET M6 to turn on. The positive voltage source charges capacitor C4 through drive resistor R15. At this time, the negative pulse constant current source current no longer flows through MOSFET M8, but only through MOSFET M5, completing the current switching. When the negative pulse constant current source... When the control terminal outputs a high level, the negative pulse constant current source current provided by the negative pulse constant current source control terminal passes through the drive resistors R12 and R13, which discharges the gate of MOSFET M5, causing MOSFET M5 to turn off quickly. The negative pulse constant current source control terminal no longer provides base current to transistor Q4. At the same time, the negative pulse constant current source current passes through the drive resistor R14 to charge the gate of MOSFET M7 and discharge the gate of MOSFET M6, causing MOSFET M7 to turn on and MOSFET M6 to turn off. Capacitor C4 passes through the drive resistor R15 and MOSFET M7, which charges the gate of MOSFET M8, causing MOSFET M8 to turn on. At this time, the positive pulse constant current source current no longer flows through MOSFET M5, but only through MOSFET M8, completing the current switching.

[0015] Compared with existing technologies, the advantages of this invention are:

[0016] 1. Under conditions of rapid and monotonic junction temperature changes, the switching delay of the constant current source is a key factor affecting the extraction of peak / valley junction temperatures in power semiconductor devices. Excessive switching delay leads to significant deviations between the measured peak / valley junction temperatures and the actual values, failing to accurately reflect the operating state of the power semiconductor device. Therefore, this invention proposes a pulsed constant current source with a high switching rate to assist in the extraction of temperature-sensitive electrical parameters of power semiconductor devices. When measuring the electrical parameters of power semiconductor devices, the constant current value of the constant current source affects the measurement. By adding a noise-filtering capacitor to the reference potential selection circuit and a filter inductor to the constant current source circuit, the fluctuation of the constant current source output current is greatly reduced. In actual testing, when the output current is set to 1mA, the current fluctuation is less than 50nA, exhibiting extremely high current stability. Therefore, the bipolar pulsed constant current source designed in this invention has high accuracy and can be used for the precise measurement of electrical parameters of power semiconductor devices.

[0017] 2. Most existing pulse constant current source control circuits require an isolated power supply to drive the switching transistor. However, this invention ensures that the pulse current source can switch quickly while using a charge pump-like method to drive the MOS transistor, eliminating the need for an isolated power supply to drive the switching transistor and greatly reducing the size of the circuit.

[0018] 3. This invention uses a MOSFET with low switching delay, resulting in an extremely high switching rate. Compared to using a solid-state relay as a switching switch, which requires turn-on and turn-off delays in the microsecond (µs) or even millisecond (ms) range, the switching delay used in this invention can reach the nanosecond (ns) range. This significantly shortens the current output response time, making it suitable as an auxiliary pulse constant current source in transient thermal testing where temperature changes are extremely rapid.

[0019] 4. Compared with conventional current sources, the current source designed in this invention has an optimized structure. The current adjustment resistors R3 and R11 of the constant current source are connected to the power supply terminal, realizing the unification of the negative current output terminal and ground. Conventional constant current sources often require the addition of a feedback resistor between the negative current output terminal and ground during design. This design method increases the complexity of the structure. When measuring, conventional current sources require subtracting the voltage of the negative current output terminal to obtain the output voltage of the pulse constant current source because of the grounded feedback resistor. However, this invention does not require the subtraction operation. The voltage obtained by direct measurement is the output voltage of the pulse constant current source, simplifying the output voltage measurement steps.

[0020] 5. This invention incorporates a diode at the current output terminal that operates in the same direction as the output current, preventing backflow of current into the constant current source circuit. Replacing the MOSFETs (M2, M8) and diodes (D2, D4) used in this invention with devices capable of withstanding high voltage allows it to be used in applications where the device under test operates at high voltage. Replacing the MOSFET M2 in the positive pulse constant current source with a high-voltage-resistant device enables the positive pulse constant current source to withstand higher negative voltages, while replacing the diode M2 ​​in the positive pulse constant current source with a high-voltage-resistant device enables the positive pulse constant current source to withstand high positive voltages. Similarly, replacing the MOSFET M8 in the negative pulse constant current source with a high-voltage-resistant device enables the negative pulse constant current source to withstand higher positive voltages, while replacing the diode M4 in the negative pulse constant current source with a high-voltage-resistant device enables the negative pulse constant current source to withstand high negative voltages. Therefore, by selecting MOSFETs and diodes with different voltage ratings, the voltage withstand level of this bipolar pulse constant current source can be improved, expanding its application range. Attached Figure Description

[0021] Figure 1 This is a topology diagram of the bipolar pulse constant current source of the present invention;

[0022] Figure 2 This is a circuit for generating positive and negative reference potentials based on a DAC.

[0023] Figure 3 This is a SiC MOSFET threshold voltage measurement circuit.

[0024] Figure 4 This is a circuit for measuring the body diode voltage drop of a SiC MOSFET. Detailed Implementation

[0025] Specific embodiments will be given below with reference to the accompanying drawings. These specific embodiments are only used to describe the technical solution of the present invention in detail, and are not intended to limit the scope of protection of this application.

[0026] This invention proposes a bipolar pulse constant current source with high switching rate (hereinafter referred to as bipolar pulse constant current source, see [link]). Figures 1-2 This bipolar pulse constant current source features high switching rate, high reliability, high precision, and small size, and includes both positive pulse constant current sources and negative pulse constant current sources.

[0027] The positive pulse constant current source includes a positive reference potential selection circuit, a forward constant current source circuit, and a positive pulse constant current source control circuit. The positive reference potential selection circuit includes voltage divider resistors R1 and R2 and a noise filtering capacitor C1. One end of the voltage divider resistor R1 is connected to the positive voltage source Vcc, and the other end is connected to one end of the voltage divider resistor R2, the non-inverting input of the operational amplifier U1 in the forward constant current source circuit, and one end of the noise filtering capacitor C1, forming a connection point. This connection point provides the positive reference potential Vcc to the subsequent constant current source circuit. ref_I+ The other end of the voltage divider resistor R2 and the noise filtering capacitor C1 is grounded. The noise filtering capacitor C1 can be selected as 1μF. The formula for calculating the positive reference potential is:

[0028]

[0029] Where R1 and R2 are the resistance values ​​of the voltage divider resistors R1 and R2, V cc This is the voltage of the positive voltage source Vcc.

[0030] Besides using a resistor divider structure, the positive reference potential selection circuit can also be achieved through a DAC; for example... Figure 2 As shown, the DAC signal can be generated by a dedicated DAC chip or a microcontroller's DAC peripheral. The DAC signal is connected to one end of resistor R3, the other end of resistor R4 is connected to the non-inverting input of the operational amplifier, one end of resistor R2 is connected to the output of the operational amplifier, the other end of resistor R2 is connected to the inverting input of the operational amplifier and one end of resistor R1, and the other end of resistor R1 is grounded. The DAC signal is output as a positive reference potential V after passing through the non-inverting proportional operational circuit. ref_I+ .

[0031] The forward constant current source circuit includes a filter inductor L1, a current regulating resistor R3, an operational amplifier U1, and a transistor Q1. One end of the filter inductor L1 is connected to the positive voltage source Vcc, and the other end is connected to one end of the current regulating resistor R3. The other end of the current regulating resistor R3 is connected to the emitter of transistor Q1 and the inverting input terminal of operational amplifier U1. The base of transistor Q1 is connected to the output terminal of operational amplifier U1. The collector of transistor Q1 is connected to the drain of MOSFET M1, the source of MOSFET M2, the collector of transistor Q2, and one end of capacitor C2 in the positive pulse constant current source control circuit. Here, transistor Q1 is a PNP transistor. The PNP transistor can also be replaced by a P-channel MOSFET, with the gate, source, and drain of the P-channel MOSFET replacing the base, emitter, and collector of the PNP transistor, respectively.

[0032] Operational amplifier U1 achieves constant current by controlling the voltage difference between the positive voltage source Vcc and the other end of the current regulating resistor R3. The collector current of transistor Q1 is the positive pulse output current of this bipolar pulse current source. Since transistor Q1 has a large current amplification factor and its base current is negligible, the collector current of transistor Q1 can be approximately equal to its emitter current. When the collector current is less than the preset positive pulse constant current source current, the emitter current also decreases, causing the voltage difference between the positive voltage source Vcc and the other end of the current regulating resistor R3 to decrease. As the voltage difference decreases, the voltage at the inverting input of operational amplifier U1 is greater than the voltage at the non-inverting input. Due to the negative feedback, the output voltage of operational amplifier U1 will decrease, while the diode voltage drop from the emitter to the base of transistor Q1 remains almost unchanged. Therefore, the voltage at the other end of the current regulating resistor R3 will decrease, which increases the voltage difference from the positive voltage source Vcc to the other end of the current regulating resistor R3. This leads to an increase in the emitter current and collector current of transistor Q1, forming a negative feedback effect on the current, and ultimately stabilizing the output current at the preset positive pulse constant current source current. When the collector current of transistor Q1 exceeds the preset positive pulse constant current source current, the emitter current also increases, leading to an increase in the voltage difference between the positive voltage source Vcc and the other end of the current regulating resistor R3. At this time, the voltage at the inverting input of operational amplifier U1 is less than the voltage at the non-inverting input. Due to the negative feedback, the output voltage of operational amplifier U1 increases, while the diode voltage drop between the emitter and base of transistor Q1 remains almost unchanged. Therefore, the voltage at the other end of the current regulating resistor R3 increases, causing the voltage difference between the positive voltage source Vcc and the other end of the current regulating resistor R3 to decrease. This results in a decrease in the emitter and collector currents of transistor Q1, forming a negative current feedback effect, ultimately stabilizing the output current at the preset positive pulse constant current source current. The formula for calculating the preset positive pulse constant current source current is:

[0033]

[0034] Where R3 is the resistance value of the current regulating resistor R3.

[0035] The positive pulse constant current source control circuit includes MOSFETs M1-M4, driving resistors R4-R8, diodes D1-D2, capacitor C2, transistor Q2, and a positive pulse current control terminal I+_CTR. MOSFETs M1 and M4 are N-channel MOSFETs, MOSFETs M2 and M3 are P-channel MOSFETs, and transistor Q2 is an NPN transistor. The drain of MOSFET M1 is connected to the collector of transistor Q1, the source of MOSFET M1 is grounded, and the gate of MOSFET M1 is connected to one end of driving resistor R4. The other end of driving resistor R4 and one end of driving resistor R5 are connected to the cathode of diode D1. The anode of diode D1 is connected to the other end of driving resistor R5, one end of driving resistor R6, one end of driving resistor R8, and the positive pulse constant current source control terminal I+_CTR, which controls the rapid switching of the positive pulse constant current source. The other end of driving resistor R6 is connected to MOSFET M3... The gate of MOSFET M4 is connected to the gate of MOSFET M4. The source of MOSFET M4 is connected to the negative voltage source Vee. The drain of MOSFET M4 is connected to the drain of MOSFET M3 and one end of the drive resistor R7. The other end of the drive resistor R7 is connected to the other end of the capacitor C2. One end of the capacitor C2 is connected to the source of MOSFET M2 and the collector of transistor Q1. The other end of the drive resistor R8 is connected to the base of transistor Q2. The emitter of transistor Q2 is connected to the source of MOSFET M3 and the gate of MOSFET M2. The collector of transistor Q2 is connected to the source of MOSFET M2. The drain of MOSFET M2 is connected to the anode of diode D2. The cathode of diode D2 is the output terminal of the positive pulse constant current source. The positions of drive resistor R7 and capacitor C2 can be interchanged. NPN transistor Q2 can be replaced by N-channel MOSFET. The gate, source, and drain of the N-channel MOSFET replace the base, emitter, and collector of the NPN transistor, respectively.

[0036] When the positive pulse constant current source control terminal I+_CTR is high, the current provided by the positive pulse constant current source control terminal passes through diode D1 and drive resistor R4 to charge the gate of MOSFET M1, causing its channel to turn on quickly. The positive pulse constant current source control terminal provides base current to transistor Q2, and through the current amplification effect of transistor Q2, it causes MOSFET M2 to turn off. At the same time, the current provided by the positive pulse constant current source control terminal passes through drive resistor R6 to discharge the gate of MOSFET M3 and charge the gate of MOSFET M4, causing MOSFET M3 to turn off and MOSFET M4 to turn on. The negative voltage source Vee charges capacitor C2 through drive resistor R7. At this time, the positive pulse constant current source current no longer flows through MOSFET M2, but only through MOSFET M1. The pulse current successfully completes the current switching. When the positive pulse constant current source control terminal is low, the current supplied by the positive pulse constant current source control terminal flows through drive resistors R4 and R5, discharging the gate of MOSFET M1 and causing its delayed channel pinch-off. The positive pulse constant current source control terminal no longer supplies base current to transistor Q2. At the same time, the current supplied by the positive pulse constant current source control terminal flows through drive resistor R6 to charge the gate of MOSFET M3 and discharge the gate of MOSFET M4, causing MOSFET M3 to turn on and MOSFET M4 to turn off. Capacitor C2, through drive resistor R7 and MOSFET M3, charges the gate of MOSFET M2, turning it on. At this time, the positive pulse constant current source current no longer flows through MOSFET M1, but only through MOSFET M2, and the pulse current successfully completes the current switching. It is worth noting that drive resistors R4 and R8 need to be adjusted to give MOSFETs M1 and M2 a certain conduction overlap time to prevent the current in filter inductor L1 from having no freewheeling path.

[0037] The negative pulse constant current source includes a negative reference potential selection circuit, an inverting constant current source circuit, and a negative pulse constant current source control circuit. The negative reference potential selection circuit includes voltage divider resistors R9 and R10 and a noise filtering capacitor C3. One end of the voltage divider resistor R10 is connected to the negative voltage source Vee, and the other end is connected to one end of the voltage divider resistor R9, the non-inverting input of operational amplifier U2, and one end of the noise filtering capacitor C3 to form a connection point. This connection point provides the negative reference potential V to the subsequent constant current source circuit. ref_I- The voltage divider resistor R9 and the other end of the noise filtering capacitor C3 are grounded. The noise filtering capacitor C3 can be selected as 1μF. The formula for calculating the negative reference potential is:

[0038]

[0039] Among them, R9, R 10 The resistance values ​​of voltage divider resistors R9 and R10 are V. ee The voltage of the negative voltage source Vee.

[0040] In addition to using a resistor divider structure, negative reference potential selection circuits can also generate values ​​such as those obtained through a DAC. Figure 2 As shown; the DAC signal can be generated by a dedicated DAC chip or a microcontroller's DAC peripheral. The DAC signal is connected to one end of resistor R4, the other end of resistor R4 is connected to resistor R5 and the inverting input of the operational amplifier, the other end of resistor R5 is connected to the output of the operational amplifier, one end of resistor R6 is connected to the non-inverting input of the operational amplifier and the other end is grounded. The DAC signal is output as a negative reference potential V after passing through the inverting amplifier circuit. ref_I- .

[0041] The reverse constant current source circuit includes a filter inductor L2, a current regulating resistor R11, an operational amplifier U2, and a transistor Q3. One end of the filter inductor L2 is connected to the negative voltage source Vee, and the other end is connected to one end of the current regulating resistor R11. The other end of the current regulating resistor R11 is connected to the emitter of transistor Q3 and the inverting input terminal of operational amplifier U2. The base of transistor Q3 is connected to the output terminal of operational amplifier U2. The collector of transistor Q3 is connected to the drain of MOSFET M5, the source of MOSFET M8, the collector of transistor Q4, and one end of capacitor C4 in the negative pulse constant current source control circuit. Here, transistor Q3 is an NPN transistor. The NPN transistor here can also be replaced by an N-channel MOSFET. The gate, source, and drain of the N-channel MOSFET replace the base, emitter, and collector of the PNP transistor, respectively.

[0042] Operational amplifier U2 achieves constant current by controlling the voltage difference between the negative voltage source Vee and the other end of the current regulating resistor R11 to maintain a constant value. The collector current of transistor Q3 is the negative pulse output current of this bipolar pulse current source. Since the current amplification factor of transistor Q3 is large and the base current is negligible, the collector current can be approximately equal to the emitter current. When the collector current is less than the preset constant current source current, the emitter current also decreases, causing the voltage difference between the negative voltage source Vee and the other end of the current regulating resistor R11 to decrease. At this time, the voltage at the inverting input terminal of operational amplifier U2 is less than the voltage at the non-inverting input terminal. Due to the negative feedback, the output voltage of operational amplifier U2 will increase, while the diode voltage drop between the emitter and base of transistor Q3 remains almost unchanged. Therefore, the voltage at the other end of the current regulating resistor R11 will increase, and the voltage difference between the negative voltage source Vee and the other end of the current regulating resistor R11 will increase, leading to an increase in the emitter and collector currents of transistor Q3, forming a negative current feedback effect, and ultimately stabilizing the output current at the preset negative pulse constant current source current. When the collector current of transistor Q3 exceeds the preset negative pulse constant current source current, the emitter current also increases, causing a decrease in the voltage difference between the negative voltage source Vee and the other end of the current regulating resistor R11. At this time, the voltage at the inverting input of operational amplifier U2 is greater than the voltage at the non-inverting input. Due to the negative feedback, the output voltage of operational amplifier U2 decreases, while the diode voltage drop between the emitter and base of transistor Q3 remains almost unchanged. Therefore, the voltage at the other end of the current regulating resistor R11 decreases, and the voltage difference between the negative voltage source Vee and the other end of the current regulating resistor R11 decreases, leading to a decrease in the emitter and collector currents of transistor Q3. This forms a negative current feedback effect, ultimately stabilizing the output current at the preset negative pulse constant current source current. The formula for calculating the preset negative pulse constant current source current is:

[0043]

[0044] Among them, R 11 The resistance value of the current regulating resistor R11.

[0045] The negative pulse constant current source control circuit includes MOSFETs M5-M8, driving resistors R12-R16, diodes D3-D4, capacitor C4, transistor Q4, and a negative pulse current control terminal. MOSFETs M7 and M8 are N-channel MOSFETs, MOSFETs M5 and M6 are P-channel MOSFETs, and transistor Q4 is a PNP transistor. The source of MOSFET M5 is grounded, the drain of MOSFET M5 is connected to the collector of transistor Q3, and the gate of MOSFET M5 is connected to one end of driving resistor R12. The other end of driving resistor R12 is connected to one end of driving resistor R13 and the anode of diode D3. The cathode of diode D3 is connected to the other end of driving resistor R13, one end of driving resistor R14, one end of driving resistor R16, and the negative pulse current control terminal, which controls the rapid switching of the negative pulse constant current source. The other end of driving resistor R14 is connected to the gate of MOSFETs M6 and M7. The sources of MOSFET M6 are connected to the positive voltage source Vcc. The drain of MOSFET M6 is connected to the drain of MOSFET M7 and one end of the drive resistor R15. The other end of the drive resistor R15 is connected to one end of the capacitor C4. The other end of the capacitor C4 is connected to the source of MOSFET M8 and the collector of transistor Q4. The other end of the drive resistor R16 is connected to the base of transistor Q4. The emitter of transistor Q4 is connected to the source of MOSFET M7 and the gate of MOSFET M8. The collector of transistor Q4 is connected to the source of MOSFET M8. The drain of MOSFET M8 is connected to the cathode of diode D4. The anode of diode D4 is the output terminal of the negative pulse constant current source. The positions of drive resistor R15 and capacitor C4 can be interchanged. PNP transistor Q2 can be replaced by a P-channel MOSFET. The gate, source, and drain of the P-channel MOSFET replace the base, emitter, and collector of the PNP transistor, respectively.

[0046] When the negative pulse constant current source control terminal I-_CTR is low, the current supplied by the negative pulse constant current source control terminal passes through diode D3 and drive resistor R13 to charge the gate of MOSFET M5, causing its channel to turn on quickly. The negative pulse constant current source control terminal provides base current to transistor Q4, and through the current amplification effect of transistor Q4, it causes MOSFET M8 to turn off. At the same time, the current supplied by the negative pulse constant current source control terminal passes through drive resistor R14 to discharge the gate of MOSFET M7 and charge the gate of MOSFET M6, causing MOSFET M7 to turn off and MOSFET M6 to turn on. The positive voltage source Vcc charges capacitor C4 through drive resistor R15. At this time, the negative pulse constant current source current no longer flows through MOSFET M8, but only through MOSFET M5, and the pulse current successfully completes the current switching. When the negative pulse constant current source control terminal I+_CTR is high, the current supplied by the negative pulse constant current source control terminal flows through drive resistors R12 and R13, discharging the gate of MOSFET M5 and causing its delayed channel pinch-off. The negative pulse constant current source control terminal no longer supplies base current to transistor Q4. Simultaneously, the current supplied by the negative pulse constant current source control terminal flows through drive resistor R14 to charge the gate of MOSFET M7 and discharge the gate of MOSFET M6, causing MOSFET M7 to turn on and MOSFET M6 to turn off. Capacitor C4, through drive resistor R15 and MOSFET M7, charges the gate of MOSFET M8, turning it on. At this time, the positive pulse constant current source current no longer flows through MOSFET M5, but only through MOSFET M8, and the pulse current successfully completes the current switching. It is worth noting that drive resistors R4 and R8 need to be adjusted to give MOSFETs M5 and M8 a certain conduction overlap time to prevent the current in filter inductor L2 from having no freewheeling path.

[0047] Figure 3 , 4 These are circuits for measuring the threshold voltage and body diode voltage drop of a SiC MOSFET. To measure the threshold voltage, the gate and drain of the SiC MOSFET are shorted. The positive pulse current source is controlled by the positive pulse current control terminal I+_CTR. When the positive pulse current source outputs a constant current, the voltage between the drain and source of the SiC MOSFET is the threshold voltage. To measure the body diode voltage drop, a negative voltage is applied to the gate and source of the SiC MOSFET. The negative pulse current source is controlled by the negative pulse current control terminal I-_CTR. When the negative pulse current source outputs a constant current, the voltage between the drain and source of the SiC MOSFET is the body diode voltage drop.

[0048] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A bipolar pulse constant current source with a high switching rate, comprising a positive pulse constant current source and a negative pulse constant current source; characterized in that, The positive pulse constant current source includes a positive reference potential selection circuit, a forward constant current source circuit, and a positive pulse constant current source control circuit; the negative pulse constant current source includes a negative reference potential selection circuit, a reverse constant current source circuit, and a negative pulse constant current source control circuit. The positive pulse constant current source control circuit includes MOSFETs M1-M4, driving resistors R4-R8, diodes D1-D2, capacitor C2, transistor Q2, and a positive pulse current control terminal. Transistor Q2 is an NPN transistor, MOSFETs M1 and M4 are N-channel MOSFETs, and MOSFETs M2 and M3 are P-channel MOSFETs. The drain of MOSFET M1 is connected to the collector of transistor Q1 in the forward constant current source circuit. The source of MOSFET M1 is grounded. The gate of MOSFET M1 is connected to one end of driving resistor R4. The other end of driving resistor R4 and one end of driving resistor R5 are connected to the cathode of diode D1. The anode of diode D1 is connected to the other end of driving resistor R5, one end of driving resistor R6, one end of driving resistor R8, and the positive pulse constant current source control terminal. The first terminal is connected to the second terminal; the other terminal of the driving resistor R6 is connected to the gate of MOSFET M3 and MOSFET M4. The source of MOSFET M4 is connected to the negative voltage source. The drain of MOSFET M4 is connected to the drain of MOSFET M3 and one terminal of the driving resistor R7. The other terminal of the driving resistor R7 is connected to the other terminal of capacitor C2. One terminal of capacitor C2 and the source of MOSFET M2 are connected to the collector of transistor Q1 in the positive constant current source circuit. The other terminal of the driving resistor R8 is connected to the base of transistor Q2. The emitter of transistor Q2 is connected to the source of MOSFET M3 and the gate of MOSFET M2. The collector of transistor Q2 is connected to the source of MOSFET M2. The drain of MOSFET M2 is connected to the anode of diode D2. The cathode of diode D2 is the output terminal of the positive pulse constant current source. The negative pulse constant current source control circuit includes MOSFETs M5-M8, driving resistors R12-R16, diodes D3-D4, capacitor C4, transistor Q4, and a negative pulse current control terminal. MOSFETs M7 and M8 are N-channel MOSFETs, MOSFETs M5 and M6 are P-channel MOSFETs, and transistor Q4 is a PNP transistor. The source of MOSFET M5 is grounded, the drain of MOSFET M5 is connected to the collector of transistor Q3 in the reverse constant current source circuit, the gate of MOSFET M5 is connected to one end of driving resistor R12, the other end of driving resistor R12 is connected to one end of driving resistor R13 and the anode of diode D3, and the cathode of diode D3 is connected to the other end of driving resistor R13, one end of driving resistor R14, one end of driving resistor R16, and the negative pulse current control terminal. The other end of the dynamic resistor R14 is connected to the gates of MOSFETs M6 and M7. The source of MOSFET M6 is connected to the positive voltage source. The drain of MOSFET M6 is connected to the drain of MOSFET M7 and one end of the drive resistor R15. The other end of the drive resistor R15 is connected to one end of the capacitor C4. The other end of the capacitor C4, the source of MOSFET M8, and the collector of transistor Q4 are connected to the collector of transistor Q3 in the reverse constant current source circuit. The other end of the drive resistor R16 is connected to the base of transistor Q4. The emitter of transistor Q4 is connected to the source of MOSFET M7 and the gate of MOSFET M8. The collector of transistor Q4 is connected to the source of MOSFET M8. The drain of MOSFET M8 is connected to the cathode of diode D4. The anode of diode D4 is the output terminal of the negative pulse constant current source.

2. The bipolar pulse constant current source with high switching rate according to claim 1, characterized in that, The positive reference potential selection circuit includes voltage divider resistors R1 and R2 and noise filtering capacitor C1; one end of voltage divider resistor R1 is connected to a positive voltage source, and the other end is connected to one end of voltage divider resistor R2, one end of noise filtering capacitor C1, and the non-inverting input terminal of operational amplifier U1 of the positive constant current source circuit; the other end of voltage divider resistor R2 and noise filtering capacitor C1 is grounded; or the positive reference potential selection circuit uses a DAC signal to output a positive reference potential through a non-inverting proportional operational circuit.

3. The bipolar pulse constant current source with high switching rate according to claim 1 or 2, characterized in that, The positive constant current source circuit includes a filter inductor L1, a current regulating resistor R3, an operational amplifier U1, and a transistor Q1, which is a PNP transistor. One end of the filter inductor L1 is connected to a positive voltage source, and the other end is connected to one end of the current regulating resistor R3. The other end of the current regulating resistor R3 is connected to the emitter of the transistor Q1 and the inverting input terminal of the operational amplifier U1. The base of the transistor Q1 is connected to the output terminal of the operational amplifier U1, and the collector of the transistor Q1 is connected to the positive pulse constant current source control circuit.

4. The bipolar pulse constant current source with high switching rate according to claim 1, characterized in that, The negative reference potential selection circuit includes voltage divider resistors R9 and R10 and noise filtering capacitor C3; one end of voltage divider resistor R10 is connected to the negative voltage source, and the other end is connected to one end of voltage divider resistor R9, one end of noise filtering capacitor C3 and the non-inverting input terminal of operational amplifier U2 of the reverse constant current source circuit; the other end of voltage divider resistor R9 and filtering capacitor C3 is grounded.

5. The bipolar pulse constant current source with high switching rate according to claim 1 or 4, characterized in that, The reverse constant current source circuit includes a filter inductor L2, a current regulating resistor R11, an operational amplifier U2, and a transistor Q3, which is an NPN transistor. One end of the filter inductor L2 is connected to a negative voltage source, and the other end is connected to one end of the current regulating resistor R11. The other end of the current regulating resistor R11 is connected to the emitter of the transistor Q3 and the inverting input terminal of the operational amplifier U2. The base of the transistor Q3 is connected to the output terminal of the operational amplifier U2, and the collector of the transistor Q3 is connected to the negative pulse constant current source control circuit.

6. The bipolar pulse constant current source with high switching rate according to claim 1, characterized in that, When the positive pulse constant current source control terminal outputs a high level, the positive pulse constant current source current provided by the control terminal passes through diode D1 and drive resistor R4, charging the gate of MOSFET M1 and causing MOSFET M1 to turn on quickly. The positive pulse constant current source control terminal provides base current to transistor Q2, causing MOSFET M2 to turn off. At the same time, the positive pulse constant current source current passes through drive resistor R6 to discharge the gate of MOSFET M3 and charge the gate of MOSFET M4, causing MOSFET M3 to turn off and MOSFET M4 to turn on. The negative voltage source charges capacitor C2 through drive resistor R7. At this time, the positive pulse constant current source current no longer flows through MOSFET M2, but only through MOSFET M1, completing the current switching; when the positive pulse constant current source outputs a high level, the positive pulse constant current source current no longer flows through MOSFET M2, but only through MOSFET M1, completing the current switching. When the pulse constant current source control terminal outputs a low level, the positive pulse constant current source current provided by the positive pulse constant current source control terminal passes through the driving resistors R4 and R5, which discharges the gate of MOSFET M1, causing MOSFET M1 to turn off quickly. The positive pulse constant current source control terminal no longer provides base current to transistor Q2. At the same time, the positive pulse constant current source current passes through the driving resistor R6 to charge the gate of MOSFET M3 and discharge the gate of MOSFET M4, causing MOSFET M3 to turn on and MOSFET M4 to turn off. Capacitor C2, through the driving resistor R7 and MOSFET M3, charges the gate of MOSFET M2, causing MOSFET M2 to turn on. At this time, the current no longer flows through MOSFET M1, but only through MOSFET M2, completing the current switching. When the negative pulse constant current source control terminal outputs a low level, the negative pulse constant current source current provided by the control terminal passes through diode D3 and drive resistor R13, charging the gate of MOSFET M5 and causing MOSFET M5 to turn on quickly. The negative pulse constant current source control terminal provides base current to transistor Q4, causing MOSFET M8 to turn off. At the same time, the negative pulse constant current source current passes through drive resistor R14 to discharge the gate of MOSFET M7 and charge the gate of MOSFET M6, causing MOSFET M7 to turn off and MOSFET M6 to turn on. The positive voltage source charges capacitor C4 through drive resistor R15. At this time, the negative pulse constant current source current no longer flows through MOSFET M8, but only through MOSFET M5, completing the current switching. When the negative pulse constant current source... When the control terminal outputs a high level, the negative pulse constant current source current provided by the negative pulse constant current source control terminal passes through the drive resistors R12 and R13, which discharges the gate of MOSFET M5, causing MOSFET M5 to turn off quickly. The negative pulse constant current source control terminal no longer provides base current to transistor Q4. At the same time, the negative pulse constant current source current passes through the drive resistor R14 to charge the gate of MOSFET M7 and discharge the gate of MOSFET M6, causing MOSFET M7 to turn on and MOSFET M6 to turn off. Capacitor C4 passes through the drive resistor R15 and MOSFET M7, which charges the gate of MOSFET M8, causing MOSFET M8 to turn on. At this time, the positive pulse constant current source current no longer flows through MOSFET M5, but only through MOSFET M8, completing the current switching.

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