CN117055674A - Bipolar pulse constant current source with high switching rate - Google Patents

Abstract

The application relates to a bipolar pulse constant current source with high switching rate, belonging to the technical field of power electronics. The bipolar pulse constant current source comprises a positive pulse constant current source and a negative pulse constant current source, wherein the positive pulse constant current source comprises a positive reference potential selection circuit, a positive constant current source circuit and a positive pulse constant current source control circuit, and the negative pulse constant current source comprises a negative reference potential selection circuit, a reverse constant current source circuit and a negative pulse constant current source control circuit. The noise filtering capacitor of the reference potential selection circuit and the filtering inductance of the constant current source circuit greatly reduce the fluctuation of the output current of the constant current source; according to the application, the MOS tube is driven by adopting a charge pump-like method while the rapid switching of the pulse current source is ensured, and the switch tube is not driven by an isolated power supply, so that the volume of the circuit is greatly reduced. The bipolar pulse constant current source has the characteristics of high switching speed, high stability, high precision, small volume, bipolar output and the like, and can meet the measurement requirement of quickly extracting various temperature-sensitive electrical parameters of the power semiconductor device under the working condition of quick change of junction temperature.

Description

A bipolar pulsed constant current source with high switching rate

Technical field

The invention belongs to the technical field of power electronics, and is specifically a bipolar pulse constant current source with high switching rate.

Background technique

Constant current sources with high precision, low temperature drift, high reliability, and high switching rate are widely used in various fields such as transient thermal characteristic testing of power semiconductor devices, temperature-sensitive electrical parameter measurement, clock circuits, oscillators, etc. These high-precision instruments and high-precision measurements have put forward non-invasive, fast response, and high-precision requirements for constant current sources. Especially in the measurement of temperature-sensitive electrical parameters of power semiconductor devices, accurate measurement of the junction temperature of power semiconductor devices is the key to real-time performance of the device. As a prerequisite for condition monitoring and reliability assessment, junction temperature extraction of power semiconductor devices plays an important role in power electronic 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 the advantages of non-invasiveness, fast response, high accuracy, and low cost. With the development of power electronics-related technologies, the accuracy requirements for junction temperature extraction technology are also increasing.

On the one hand, when extracting temperature-sensitive electrical parameters of power semiconductor devices, a constant current source is often required to assist measurement. A stable constant current source is a prerequisite for ensuring the accuracy of temperature-sensitive electrical parameter extraction. On the other hand, different temperature-sensitive electrical parameters have different requirements on the current polarity of the auxiliary constant current source. For example, when measuring the SiC MOSFET body diode voltage drop, a constant current from source to drain needs to be provided; when measuring SiC MOSFET threshold voltage needs to provide a constant current from drain to source. Therefore, a constant current source that can generate bipolar pulse current is of great significance to meet the measurement needs of different temperature-sensitive electrical parameters, reduce the complexity of measurement operations, and increase the universality of the measurement circuit. In addition, the switching delay of the constant current source is a key factor affecting the accuracy of junction temperature extraction. Especially under operating conditions where the junction temperature changes rapidly, the switching delay of the constant current source is required to be higher. In practical applications, due to the high voltage and large current of the main circuit, the constant current source needs to be able to withstand high voltage and prevent current backflow. Existing pulse constant current sources mainly have the following problems. First, most pulse constant current sources have slow switching speeds. The pulse current has an output delay of hundreds of us or even milliseconds, which cannot meet high switching requirements such as transient thermal characteristics testing. speed requirements. Second, the output current is not stable enough to meet high-precision measurement requirements. Third, the constant current source using ground resistance feedback is difficult to integrate with other circuits.

Contents of the invention

Aiming at the current measurement requirements for temperature-sensitive electrical parameters of power semiconductor devices, the present invention proposes a bipolar pulse constant current source with high switching rate. This bipolar pulse constant current source has the characteristics of fast switching rate, high stability, high precision, small size, and bipolar output. It can meet various temperature-sensitive electrical parameters of power semiconductor devices under conditions where the junction temperature changes rapidly. Quickly extract measurement needs.

In order to achieve the above objects, the technical solutions adopted by the present invention are as follows:

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

Further, the positive reference potential selection circuit includes voltage dividing resistors R1, R2 and noise filtering capacitor C1; one end of the voltage dividing resistor R1 is connected to the positive voltage source, and the other end is connected to one end of the voltage dividing resistor R2 and the noise filtering capacitor. One end of C1 is connected to the non-inverting input end of the operational amplifier U1 of the forward constant current source circuit, the voltage dividing resistor R2 and the other end of the noise filter capacitor C1 are connected to ground; or the positive reference potential selection circuit uses a DAC signal to output through the in-phase proportional operation circuit Positive reference potential.

Further, the forward constant current source circuit includes a filter inductor L1, a current adjustment resistor R3, an operational amplifier U1 and a transistor Q1. The transistor Q1 is a PNP transistor; one end of the filter inductor L1 is connected to the positive voltage source, and the other end is connected to the current adjustment One end of resistor R3 is connected, the other end of current adjustment resistor R3 is connected to the emitter of transistor Q1 and the inverting input end of operational amplifier U1, the base of transistor Q1 is connected to the output end of operational amplifier U1, and the collector of transistor Q1 is connected to The positive pulse constant current source control circuit is connected.

Further, the negative reference potential selection circuit includes voltage dividing resistors R9, R10 and noise filtering capacitor C3; one end of the voltage dividing resistor R10 is connected to the negative voltage source, and the other end is connected to one end of the voltage dividing resistor R9 and the noise filtering capacitor. One end of C3 is connected to the non-inverting input end of the operational amplifier U2 of the reverse constant current source circuit, and the other end of the voltage dividing resistor R9 and the filter capacitor C3 are connected to ground.

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

Further, when the positive pulse constant current source control terminal outputs a high level, the positive pulse constant current source current provided by the positive pulse constant current source control terminal passes through the diode D1 and the driving resistor R4, charging the gate of the MOS tube M1 so that the MOS tube M1 turns on quickly, and the positive pulse constant current source control terminal provides base current for transistor Q2, causing MOS tube M2 to disconnect. At the same time, the positive pulse constant current source current discharges the gate of MOS tube M3 and the gate of MOS tube M4 through the driving resistor R6. Charging, MOS tube M3 is disconnected, MOS tube M4 is opened, and the negative voltage source charges capacitor C2 through driving resistor R7. At this time, the positive pulse constant current source current no longer flows through MOS tube M2, but only flows through MOS tube M1. Complete 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 and discharges the gate of the MOS tube M1, causing the MOS tube to M1 is quickly disconnected, and the positive pulse constant current source control terminal no longer provides base current for transistor Q2. At the same time, the positive pulse constant current source current charges the gate of MOS tube M3 and discharges the gate of MOS tube M4 through the driving resistor R6, causing the MOS The tube M3 is turned on and the MOS tube M4 is turned off. The capacitor C2 charges the gate of the MOS tube M2 through the driving resistor R7 and the MOS tube M3, so that the MOS tube M2 is turned on. At this time, the current no longer flows through the MOS tube M1, but only flows through the MOS. Tube M2 completes 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 negative pulse constant current source control terminal passes through the diode D3 and the driving resistor R13 to charge the gate of the MOS tube M5 so that the MOS tube M5 is quickly turned on. , the negative pulse constant current source control terminal provides the base current for transistor Q4, causing MOS tube M8 to disconnect. At the same time, the negative pulse constant current source current discharges the gate of MOS tube M7 and charges the gate of MOS tube M6 through the driving resistor R14, so that MOS tube M7 is turned off, MOS tube M6 is turned on, and 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 MOS tube M8, but only flows through MOS tube M5, completing current switching. ; When the negative pulse constant current source 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 driving resistors R12 and R13, discharges the gate of the MOS tube M5, and causes the MOS tube M5 to quickly turn off. On, the negative pulse constant current source control terminal no longer provides base current for the three-stage transistor Q4. At the same time, the negative pulse constant current source current charges the gate of MOS tube M7 and discharges the gate of MOS tube M6 through the driving resistor R14, making the MOS tube M7 is turned on and MOS tube M6 is turned off. Capacitor C4 charges the gate of MOS tube M8 through drive resistor R15 and MOS tube M7, causing MOS tube M8 to turn on. At this time, the positive pulse constant current source current no longer flows through MOS tube M5. And only flows through MOS tube M8 to complete the current switching.

Compared with the existing technology, the advantages of the present invention are:

1. Under operating conditions where the junction temperature changes rapidly and monotonically, the switching delay of the constant current source is a key factor affecting the peak/valley junction temperature extraction of the power semiconductor device. Excessive switching delay will lead to a decrease in the peak/valley junction temperature. The measurement results have a large deviation from the actual value and cannot accurately reflect the working status of the power semiconductor device. Therefore, the present invention proposes a pulse 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 a power semiconductor device, the constant current value of the constant current source will affect the measurement of the electrical parameters. Since the noise filtering capacitor is added to the reference potential selection circuit and the filter inductor is added to the constant current source circuit, extremely The ground reduces the fluctuation of the output current of the constant current source. In the actual test, when the output current is set to 1mA, the current fluctuation is less than 50nA, which has extremely high current stability. Therefore, the bipolar pulse constant current source designed in the present invention has high accuracy and can be used for accurate measurement of electrical parameters of power semiconductor devices.

2. Most of the existing pulse constant current source control circuits require an isolated power supply to drive the switching tube. However, the present invention ensures that the pulse current source can be quickly switched while using a charge pump-like method to drive the MOS tube. An isolated power supply is required to drive the switching tube, which greatly reduces the size of the circuit.

3. The present invention uses MOS tubes with low switching delay and has extremely high switching rate. Compared with using a solid-state relay as a switching switch, which requires us-level or even ms-level turn-on and turn-off delays, the switching delay used in the present invention can reach ns levels, which greatly shortens the current output response time and is suitable for extremely rapid temperature changes. Acts as an auxiliary pulse constant current source in transient thermal tests.

4. Compared with the conventional current source, the current source designed in the present invention is structurally optimized. The current adjustment resistors R3 and R11 of the constant current source are connected to the power supply terminal to realize the unification of the negative current output terminal and the ground; and When designing a conventional constant current source, it is often necessary to add a feedback resistor between the negative output terminal of the current and the ground. This design method increases the complexity of the structure. When measuring, the conventional current source has a grounded feedback resistor in the calculation. existence, the current negative output terminal voltage needs to be subtracted to obtain the output voltage of the pulse constant current source. However, the present invention does not need to perform a subtraction operation. The directly measured voltage is the output voltage of the pulse constant current source, which simplifies the output voltage measurement. step.

5. The present invention is provided with a diode in the same direction as the output current at the current output end, which can prevent current from flowing back into the constant current source circuit. By replacing the MOS transistors (M2, M8) and diodes (D2, D4) used in the invention with devices that can withstand high voltages, they can be used in situations where the device under test operates at high voltages. Replace the MOS tube M2 of the positive pulse constant current source with a high voltage withstand device. The positive pulse constant current source has the ability to withstand higher negative voltage, and replace the diode M2 of the positive pulse constant current source with a high voltage withstand device. The pulse constant current source has the ability to withstand high positive voltage. In the same way, replace the MOS tube M8 of the negative pulse constant current source with a high voltage withstand device. The negative pulse constant current source has the ability to withstand higher positive voltage, and replace the diode M4 of the negative pulse constant current source with a high voltage withstand device. , the negative pulse constant current source has the ability to withstand high negative pressure. Therefore, by selecting MOS tubes and diodes with different withstand voltages, the withstand voltage level of the bipolar pulse constant current source can be improved and its scope of application can be expanded.

Description of the drawings

Figure 1 is a topological diagram of the bipolar pulse constant current source of the present invention;

Figure 2 shows the positive and negative reference potential generation circuit based on DAC;

Figure 3 shows the SiC MOSFET threshold voltage measurement circuit;

Figure 4 shows the SiC MOSFET body diode voltage drop measurement circuit.

Detailed ways

Specific embodiments will be given below in conjunction with the accompanying drawings. The specific embodiments are only used to introduce the technical solutions of the present invention in detail and do not limit the scope of protection of the present application.

The present invention proposes a bipolar pulse constant current source with high switching rate (referred to as bipolar pulse constant current source, see Figures 1-2). The bipolar pulse constant current source has high switching rate and high reliability. , high precision, small size and other characteristics, including positive pulse constant current source and negative pulse constant current source;

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; among them, the positive reference potential selection circuit includes voltage dividing resistors R1, R2 and noise filtering capacitor C1; the voltage dividing resistor One end of R1 is connected to the positive voltage source Vcc, and the other end is connected to one end of the voltage dividing resistor R2, the non-inverting input end of the operational amplifier U1 of the forward constant current source circuit, and one end of the noise filter capacitor C1 to form a connection point. Provide a positive reference potential V _{ref_I+} for the subsequent constant current source circuit; the other end of the voltage dividing resistor R2 and the noise filter capacitor C1 is connected to ground. The noise filter capacitor C1 can be selected as 1μF. The formula for calculating the positive reference potential is:

Among them, R ₁ and R ₂ are the resistance values of the voltage dividing resistors R1 and R2, and V _cc is the voltage of the positive voltage source Vcc.

In addition to using a resistor voltage dividing structure, the positive reference potential selection circuit can also use a DAC. As shown in Figure 2, the DAC signal can be generated by a specialized DAC chip or the DAC peripheral of a microcontroller. The DAC signal is connected to one end of the resistor R3. The other end of resistor R4 is connected to the non-inverting input end of the operational amplifier, one end of resistor R2 is connected to the output end of the operational amplifier, the other end of resistor R2 is connected to the inverting input end of the operational amplifier and one end of resistor R1, and the other end of resistor R1 is connected to ground. , the DAC signal is output through the in-phase proportional operation circuit to obtain the positive reference potential V _{ref_I+} .

The forward constant current source circuit includes filter inductor L1, current adjustment resistor R3, operational amplifier U1 and 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 adjustment resistor R3. The current adjustment resistor R3 The other end of the transistor Q1 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. The collector of the transistor Q1 is connected to the MOS tube of the positive pulse constant current source control circuit. The drain of M1, the source of MOS tube M2, the collector of transistor Q2 and one end of capacitor C2 are connected; among them, transistor Q1 is a PNP transistor, and the PNP transistor here can also be replaced by a P-channel MOS tube. P-channel MOS The gate, source and drain of the tube replace the base, emitter and collector of the PNP triode respectively.

The operational amplifier U1 achieves constant current by controlling the voltage difference between the positive voltage source Vcc and the other end of the current adjustment resistor R3 to be constant. The collector current of the transistor Q1 is the positive pulse output current of the bipolar pulse current source; because The current amplification factor of transistor Q1 is large, and the base current of transistor Q1 is negligible, so the collector current of transistor Q1 can be approximately equal to the emitter current; when the collector current is less than the preset positive pulse constant current source current, the emitter The current also decreases, causing the voltage difference between the positive voltage source Vcc and the other end of the current adjustment resistor R3 to decrease. At this time, the voltage at the inverting input terminal of the operational amplifier U1 is greater than the voltage at the non-inverting input terminal. Due to the effect of negative feedback, the output voltage of the operational amplifier U1 will decreases, while the diode voltage drop from the emitter to the base of transistor Q1 is almost unchanged, so the voltage at the other end of the current adjustment resistor R3 will decrease, causing the voltage difference from the positive voltage source Vcc to the other end of the current adjustment resistor R3 to increase. This causes the emitter current and collector current of transistor Q1 to increase, forming a negative feedback effect on the current, which ultimately stabilizes the output current at the preset positive pulse constant current source current. When the collector current of transistor Q1 is greater than the preset positive pulse constant current source current, the emitter current also increases, causing the voltage difference between the positive voltage source Vcc and the other end of the current adjustment resistor R3 to increase. At this time, the operational amplifier U1 reverses the direction. The voltage at the input terminal is less than the voltage at the non-inverting input terminal. Due to the effect of negative feedback, the output voltage of the operational amplifier U1 will increase, while the diode voltage drop from the emitter to the base of the transistor Q1 is almost unchanged, so the voltage at the other end of the current adjustment resistor R3 will increase. increases, causing the voltage difference between the positive voltage source Vcc and the other end of the current adjustment resistor R3 to decrease, causing the emitter circuit and collector current of the transistor Q1 to decrease, forming a negative feedback effect on the current, and ultimately stabilizing the output current at the preset value. of positive pulse constant current source current. The preset positive pulse constant current source current calculation formula is:

Among them, R ₃ is the resistance of the current adjustment resistor R3.

The positive pulse constant current source control circuit includes MOS tubes M1~M4, drive resistors R4~R8, diodes D1~D2, capacitor C2, transistor Q2 and positive pulse current control terminal I+_CTR; among them, MOS tubes M1 and M4 are N-channel channel MOS tube, MOS tube M2 and M3 are P-channel MOS tubes, and transistor Q2 is an NPN transistor; the drain of MOS tube M1 is connected to the collector of transistor Q1, the source of MOS tube M1 is grounded, and the gate of MOS tube M1 One end of the driving resistor R4 is connected to the other end of the driving resistor R4 and one end of the driving resistor R5 are connected to the cathode of the diode D1. The anode of the diode D1 is connected to the other end of the driving resistor R5, one end of the driving resistor R6 and one end of the driving resistor R8. It is connected to the positive pulse constant current source control terminal I+_CTR. The positive pulse constant current source control terminal I+_CTR is used to control the rapid switching of the positive pulse constant current source. The other end of the driving resistor R6 is connected to the gates of MOS tube M3 and MOS tube M4. poles are connected, the source of MOS tube M4 is connected to the negative voltage source Vee, the drain of MOS tube M4 is connected to the drain of MOS tube M3 and one end of the driving resistor R7, the other end of the driving resistor R7 is connected to the other end of the capacitor C2 , one end of the capacitor C2 is connected to the source of the MOS tube M2 and the collector of the transistor Q1; the other end of the driving resistor R8 is connected to the base of the transistor Q2, and the emitter of the transistor Q2 is connected to the source of the MOS tube M3 and the MOS tube M2 The gate of the transistor Q2 is connected to the source of the MOS tube M2, the drain of the MOS tube M2 is connected to the anode of the diode D2, and the cathode of the diode D2 is the output terminal of the positive pulse constant current source; the driver The positions of resistor R7 and capacitor C2 can be interchanged; NPN transistor Q2 can be replaced by an N-channel MOS transistor. The gate, source, and drain of the N-channel MOS transistor replace the base, emitter, and emitter of the NPN transistor respectively. collector.

When the positive pulse constant current source control terminal I+_CTR is at a high level, the current provided by the positive pulse constant current source control terminal passes through the diode D1 and the driving resistor R4, charging the gate of the MOS tube M1 and prompting its channel to quickly open. The control terminal of the pulse constant current source provides base current to the transistor Q2, and the current amplification effect of the transistor Q2 causes the MOS tube M2 to turn off. At the same time, the control terminal of the positive pulse constant current source provides current to the MOS tube M3 through the driving resistor R6. The gate discharge and the gate charging of MOS tube M4 cause MOS tube M3 to turn off and MOS tube M4 to turn on. The negative voltage source Vee charges the capacitor C2 through the driving resistor R7. At this time, the positive pulse constant current source current no longer flows through the MOS tube. M2, and only flows through the MOS tube M1, the pulse current successfully completes the current switching. When the control terminal of the positive pulse constant current source is low level, the control terminal of the positive pulse constant current source provides current through the driving resistors R4 and R5, which discharges the gate of the MOS tube M1 and prompts its delay channel to be pinched off. The positive pulse constant current source The control terminal no longer provides base current for transistor Q2. At the same time, the positive pulse constant current source control terminal provides current through the drive resistor R6 to charge the gate of MOS tube M3 and discharge the gate of MOS tube M4, causing MOS tube M3 to turn on. MOS tube M4 is disconnected, and capacitor C2 charges the gate of MOS tube M2 through the driving resistor R7 and MOS tube M3 to turn it on. At this time, the positive pulse constant current source current no longer flows through MOS tube M1, but only flows through MOS In tube M2, the pulse current successfully completes the current switching. It is worth noting that the driving resistors R4 and R8 need to be adjusted so that the MOS tubes M1 and M2 have a certain conduction overlap time to prevent the current of the filter inductor L1 from having no freewheeling 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; among them, the negative reference potential selection circuit includes voltage dividing resistors R9, R10 and noise filtering capacitor C3; voltage dividing One end of the resistor R10 is connected to the negative voltage source Vee, and the other end is connected to one end of the voltage dividing resistor R9, the non-inverting input end of the operational amplifier U2 and one end of the noise filter capacitor C3 to form a connection point. The connection point is the subsequent constant current source circuit. Provide a negative reference potential V _{ref_I-} ; the voltage dividing resistor R9 and the other end of the filter capacitor C3 are connected to ground. The noise filter capacitor C3 can be selected as 1μF. The negative reference potential calculation formula is:

Among them, R ₉ and R ₁₀ are the resistance values of the voltage dividing resistors R9 and R10, and V _ee is the voltage of the negative voltage source Vee.

In addition to using a resistor voltage dividing structure, the negative reference potential selection circuit can also be generated by a DAC as shown in Figure 2; the DAC signal can be generated by a specialized DAC chip or the DAC peripheral of a microcontroller. The DAC signal is connected to one end of the resistor R4, and the resistor R4 The other end is connected to the resistor R5 and the inverting input end of the operational amplifier. The other end of the resistor R5 is connected to the output end of the operational amplifier. One end of the resistor R6 is connected to the non-inverting input end of the operational amplifier and the other end is grounded. The DAC signal is output through the inverting proportional circuit to obtain the negative Reference potential V _{ref_I-} .

The reverse constant current source circuit includes filter inductor L2, current adjustment resistor R11, operational amplifier U2 and 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 adjustment resistor R11. The current adjustment resistor R11 The other end of the transistor Q3 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. The collector of the transistor Q3 is connected to the MOS tube of the negative pulse constant current source control circuit. The drain of M5, the source of MOS tube M8, the collector of transistor Q4 and one end of capacitor C4 are connected; among them, transistor Q3 is an NPN transistor. The NPN transistor here can also be replaced by an N-channel MOS tube. N-channel MOS The gate, source and drain replace the base, emitter and collector of the PNP transistor respectively.

The operational amplifier U2 achieves constant current by controlling the voltage difference between the negative voltage source Vee and the other end of the current adjustment resistor R11 to be constant. The collector current of the transistor Q3 is the negative pulse output current of the bipolar pulse current source. Since the current amplification factor of transistor Q3 is large and the base current can be ignored, 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 resulting in a negative voltage source. The voltage difference between Vee and the other end of the current adjustment resistor R11 decreases. At this time, the voltage at the inverting input terminal of the operational amplifier U2 is less than the voltage at the non-inverting input terminal. Due to the effect of negative feedback, the output voltage of the operational amplifier U2 will increase, and the emitter of the transistor Q3 The diode voltage drop to the base is almost unchanged, so the voltage at the other end of the current adjustment resistor R11 will increase, and the voltage difference from the negative voltage source Vee to the other end of the current adjustment resistor R11 will increase, causing the emitter and collector of the transistor Q3 to The current increases, forming a negative feedback effect on the current, which ultimately stabilizes the output current at the preset negative pulse constant current source current. When the collector current of transistor Q3 is greater than the preset negative pulse constant current source current, the emitter current also increases, causing the voltage difference between the negative voltage source Vee and the other end of the current adjustment resistor R11 to decrease. At this time, the operational amplifier U2 reverses The voltage at the input terminal is greater than the voltage at the non-inverting input terminal. Due to the effect of negative feedback, the output voltage of the operational amplifier U2 will decrease, while the diode voltage drop from the emitter to the base of the transistor Q3 is almost unchanged, so the voltage at the other end of the current adjustment resistor R11 will decreases, the voltage difference between the negative voltage source Vee and the other end of the current adjustment resistor R11 decreases, causing the emitter and collector current of the transistor Q3 to decrease, forming a negative feedback effect on the current, and finally stabilizing the output current at the preset negative value. Pulse constant current source current. The calculation formula of the preset negative pulse constant current source current is:

Among them, R ₁₁ is the resistance of the current adjustment resistor R11.

The negative pulse constant current source control circuit includes MOS tubes M5~M8, drive resistors R12~R16, diodes D3~D4, capacitor C4, transistor Q4 and negative pulse current control terminal; among them, MOS tubes M7 and M8 are N-channel MOS tubes , MOS transistors M5 and M6 are P-channel MOS transistors, and transistor Q4 is a PNP transistor; the source of MOS transistor M5 is connected to ground, the drain of MOS transistor M5 is connected to the collector of transistor Q3, and the gate of MOS transistor M5 is connected to the driving resistor. One end of R12 is connected, the other end of the driving resistor R12 is connected to one end of the driving resistor R13 and the anode of the diode D3, the cathode of the diode D3 is connected to the other end of the driving resistor R13, one end of the driving resistor R14, one end of the driving resistor R16 and the negative pulse The current control terminal is connected, and the negative pulse current control terminal is used to control the rapid switching of the negative pulse constant current source; the other end of the driving resistor R14 is connected to the gates of MOS tube M6 and MOS tube M7, and the source of MOS tube M6 is connected to the positive voltage source. Vcc is connected, the drain of MOS tube M6 is connected to the drain of MOS tube M7 and one end of driving resistor R15, the other end of driving resistor R15 is connected to one end of capacitor C4, the other end of capacitor C4 is connected to the source of MOS tube M8 and The collector of transistor Q4 is connected; the other end of the driving resistor R16 is connected to the base of transistor Q4, the emitter of transistor Q4 is connected to the source of MOS tube M7 and the gate of MOS tube M8, and the collector of transistor Q4 is connected to the MOS tube. The source of M8 is connected, and the drain of MOS tube 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 driving resistor R15 and capacitor C4 can be interchanged; PNP transistor Q2 can Replaced by a P-channel MOS transistor, the gate, source, and drain of the P-channel MOS transistor replace the base, emitter, and collector of the PNP transistor respectively.

When the negative pulse constant current source control terminal I-_CTR is low level, the negative pulse constant current source control terminal provides current through the diode D3 and the driving resistor R13 to charge the gate of the MOS tube M5 and prompt its channel to quickly open. The negative pulse The constant current source control terminal provides base current for transistor Q4, and through the current amplification effect of transistor Q4, the MOS tube M8 is turned off. At the same time, the negative pulse constant current source control terminal provides current through the driving resistor R14 for the gate of MOS tube M7. The positive voltage source Vcc charges the capacitor C4 through the driving resistor R15. At this time, the negative pulse constant current source current no longer flows through the MOS tube M8. , and only flows through the MOS tube M5, the pulse current successfully completes the current switching. When the negative pulse constant current source control terminal I+_CTR is high level, the negative pulse constant current source control terminal provides current through the drive resistors R12 and R13, which discharges the gate of MOS tube M5 and prompts its delay channel to be pinched off, and the negative pulse The constant current source control terminal no longer provides base current for the three-stage transistor Q4. At the same time, the negative pulse constant current source control terminal provides current through the drive resistor R14 to charge the gate of the MOS tube M7 and discharge the gate of the MOS tube M6, so that MOS tube M7 is turned on and MOS tube M6 is turned off. Capacitor C4 charges the gate of MOS tube M8 through the driving resistor R15 and MOS tube M7 to turn it on. At this time, the positive pulse constant current source current no longer flows through MOS tube M5. And only flowing through MOS tube M8, the pulse current successfully completes the current switching. It is worth noting that the driving resistors R4 and R8 need to be adjusted so that the MOS tubes M5 and M8 have a certain conduction overlap time to prevent the current of the filter inductor L2 from having no freewheeling circuit.

Figures 3 and 4 are the SiC MOSFET threshold voltage measurement circuit and the body diode voltage drop measurement circuit respectively. When measuring the threshold voltage, the gate and drain of the SiC MOSFET need to be short-circuited, and the positive pulse constant current source is controlled through the positive pulse current control terminal I+_CTR of the above-mentioned bipolar pulse constant current source. When the positive pulse constant current source When outputting a constant current, the terminal voltage between the drain and source of the SiC MOSFET is the threshold voltage. When measuring the body diode voltage drop, it is necessary to apply negative voltage to the gate and source of the SiC MOSFET, and control the negative pulse constant current source through the negative pulse current control terminal I-_CTR of the above-mentioned bipolar pulse constant current source. When the negative pulse When the constant current source outputs a constant current, the terminal voltage between the drain and source of the SiC MOSFET is the body diode voltage drop.

The parts not described in the present invention are applicable to the existing technology.

Claims (6)

1. A bipolar pulse constant current source with high switching rate comprises a positive pulse constant current source and a negative pulse constant current source; the positive pulse constant current source comprises a positive reference potential selection circuit, a positive constant current source circuit and a positive pulse constant current source control circuit; the negative pulse constant current source comprises 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 comprises MOS tubes M1-M4, driving resistors R4-R8, diodes D1-D2, a capacitor C2, a triode Q2 and a positive pulse current control end; the triode Q2 is an NPN triode, the MOS transistors M1 and M4 are N-channel MOS transistors, and the MOS transistors M2 and M3 are P-channel MOS transistors; the drain electrode of the MOS tube M1 is connected with the collector electrode of the triode Q1 of the forward constant current source circuit, the source electrode of the MOS tube M1 is grounded, the grid electrode of the MOS tube M1 is connected with one end of the driving resistor R4, the other end of the driving resistor R4 and one end of the driving resistor R5 are connected with the cathode of the diode D1, and the anode of the diode D1 is connected with the other end of the driving resistor R5, one end of the driving resistor R6, one end of the driving resistor R8 and the positive pulse constant current source control end; the other end of the driving resistor R6 is connected with the grid electrodes of the MOS tube M3 and the MOS tube M4, the source electrode of the MOS tube M4 is connected with a negative voltage source, the drain electrode of the MOS tube M4 is connected with the drain electrode of the MOS tube M3 and one end of the driving resistor R7, the other end of the driving resistor R7 is connected with the other end of the capacitor C2, one end of the capacitor C2 and the source electrode of the MOS tube M2 are connected with the collector electrode of the triode Q1 of the forward constant current source circuit; the other end of the driving resistor R8 is connected with the base electrode of the triode Q2, the emitter electrode of the triode Q2 is connected with the source electrode of the MOS tube M3 and the grid electrode of the MOS tube M2, the collector electrode of the triode Q2 is connected with the source electrode of the MOS tube M2, the drain electrode of the MOS tube M2 is connected with the anode electrode of the diode D2, and the cathode electrode of the diode D2 is the output end of a positive pulse constant current source;

the negative pulse constant current source control circuit comprises MOS tubes M5-M8, driving resistors R12-R16, diodes D3-D4, a capacitor C4, a triode Q4 and a negative pulse current control end; the MOS transistors M7 and M8 are N-channel MOS transistors, the MOS transistors M5 and M6 are P-channel MOS transistors, and the triode Q4 is a PNP triode; the source electrode of the MOS tube M5 is grounded, the drain electrode of the MOS tube M5 is connected with the collector electrode of the triode Q3 of the reverse constant current source circuit, the grid electrode of the MOS tube M5 is connected with one end of the driving resistor R12, the other end of the driving resistor R12 is connected with one end of the driving resistor R13 and the anode of the diode D3, and the cathode of the diode D3 is connected with the other end of the driving resistor R13, one end of the driving resistor R14, one end of the driving resistor R16 and the negative pulse current control end; the other end of the driving resistor R14 is connected with the grid electrodes of the MOS tube M6 and the MOS tube M7, the source electrode of the MOS tube M6 is connected with a positive voltage source, the drain electrode of the MOS tube M6 is connected with the drain electrode of the MOS tube M7 and one end of the driving resistor R15, the other end of the driving resistor R15 is connected with one end of a capacitor C4, and the other end of the capacitor C4, the source electrode of the MOS tube M8 and the collector electrode of the triode Q4 are connected with the collector electrode of the triode Q3 of the reverse constant current source circuit; the other end of the driving resistor R16 is connected with the base electrode of the triode Q4, the emitter electrode of the triode Q4 is connected with the source electrode of the MOS tube M7 and the grid electrode of the MOS tube M8, the collector electrode of the triode Q4 is connected with the source electrode of the MOS tube M8, the drain electrode of the MOS tube M8 is connected with the cathode of the diode D4, and the anode of the diode D4 is the output end of the negative pulse constant current source.

2. The bipolar pulse constant current source with high switching rate according to claim 1, wherein the positive reference potential selecting circuit comprises voltage dividing resistors R1, R2 and a noise filtering capacitor C1; one end of the voltage dividing resistor R1 is connected with a positive voltage source, the other end of the voltage dividing resistor R2 is connected with one end of the noise filtering capacitor C1 and the non-inverting input end of the operational amplifier U1 of the forward constant current source circuit, and the other ends of the voltage dividing resistor R2 and the noise filtering capacitor C1 are grounded; or the positive reference potential selecting circuit adopts DAC signals to output positive reference potential through the in-phase proportional operation circuit.

3. The bipolar pulse constant current source with high switching rate according to claim 1 or 2, wherein the forward constant current source circuit comprises a filter inductance L1, a current adjusting resistor R3, an operational amplifier U1 and a triode Q1, the triode Q1 being a PNP triode; one end of the filter inductor L1 is connected with a positive voltage source, the other end of the filter inductor L1 is connected with one end of the current regulating resistor R3, the other end of the current regulating resistor R3 is connected with an emitter of the triode Q1 and an inverting input end of the operational amplifier U1, a base electrode of the triode Q1 is connected with an output end of the operational amplifier U1, and a collector electrode of the triode Q1 is connected with a positive pulse constant current source control circuit.

4. The bipolar pulse constant current source with high switching rate according to claim 1, wherein the negative reference potential selecting circuit comprises voltage dividing resistors R9, R10 and a noise filtering capacitor C3; one end of the voltage dividing resistor R10 is connected with a negative voltage source, and the other end of the voltage dividing resistor R9 is connected with one end of the noise filtering capacitor C3 and the non-inverting input end of the operational amplifier U2 of the reverse constant current source circuit, and the other ends of the voltage dividing resistor R9 and the filtering capacitor C3 are grounded.

5. The bipolar pulse constant current source with high switching rate according to claim 1 or 4, wherein the reverse constant current source circuit comprises a filter inductance L2, a current adjusting resistor R11, an operational amplifier U2 and a triode Q3, and the triode Q3 is an NPN triode; one end of the filter inductor L2 is connected with a negative voltage source, the other end of the filter inductor L2 is connected with one end of the current regulating resistor R11, the other end of the current regulating resistor R11 is connected with an emitter of the triode Q3 and an inverting input end of the operational amplifier U2, a base electrode of the triode Q3 is connected with an output end of the operational amplifier U2, and a collector electrode of the triode Q3 is connected with a negative pulse constant current source control circuit.

6. The bipolar pulse constant current source with high switching rate according to claim 1, wherein when the positive pulse constant current source control end outputs high level, the positive pulse constant current source current provided by the positive pulse constant current source control end passes through the diode D1 and the driving resistor R4 to charge the grid electrode of the MOS transistor M1 so as to rapidly turn on the MOS transistor M1, the positive pulse constant current source control end provides base current for the triode Q2 so as to disconnect the MOS transistor M2, meanwhile, the positive pulse constant current source current passes through the driving resistor R6 to discharge the grid electrode of the MOS transistor M3 and charge the grid electrode of the MOS transistor M4 so as to disconnect the MOS transistor M3 and turn on the MOS transistor M4, and the negative voltage source passes through the driving resistor R7 to charge the capacitor C2, so that the positive pulse constant current source current does not flow through the MOS transistor M2 but only flows through the MOS transistor M1, and current switching is completed; when the positive pulse constant current source control end outputs a low level, the positive pulse constant current source current provided by the positive pulse constant current source control end passes through the driving resistors R4 and R5 to rapidly disconnect the MOS tube M1 for grid discharge of the MOS tube M1, the positive pulse constant current source control end does not provide base current for the triode Q2 any more, meanwhile, the positive pulse constant current source current charges the grid of the MOS tube M3 and discharges the grid of the MOS tube M4 through the driving resistor R6 to open the MOS tube M3, the MOS tube M4 is disconnected, the capacitor C2 charges the grid of the MOS tube M2 through the driving resistor R7 and the MOS tube M3 to open the MOS tube M2, and at the moment, the current does not flow through the MOS tube M1 any more but only flows through the MOS tube M2 to finish current switching;

when the negative pulse constant current source control end outputs a low level, the negative pulse constant current source current provided by the negative pulse constant current source control end passes through the diode D3 and the driving resistor R13 to charge the grid electrode of the MOS tube M5 so as to enable the MOS tube M5 to be rapidly opened, the negative pulse constant current source control end provides base current for the triode Q4 so as to enable the MOS tube M8 to be disconnected, meanwhile, the negative pulse constant current source current passes through the driving resistor R14 to discharge the grid electrode of the MOS tube M7 and charge the grid electrode of the MOS tube M6 so as to enable the MOS tube M7 to be disconnected, the MOS tube M6 is opened, the positive voltage source charges the capacitor C4 through the driving resistor R15, and at the moment, the negative pulse constant current source current does not flow through the MOS tube M8 but only flows through the MOS tube M5, and current switching is completed; when the negative pulse constant current source control end outputs a high level, the negative pulse constant current source current provided by the negative pulse constant current source control end passes through the driving resistors R12 and R13 to rapidly disconnect the MOS tube M5 for grid discharge of the MOS tube M5, the negative pulse constant current source control end does not provide base current for the transistor Q4 any more, meanwhile, the negative pulse constant current source current charges the grid of the MOS tube M7 and discharges the grid of the MOS tube M6 through the driving resistor R14, the MOS tube M7 is opened, the MOS tube M6 is disconnected, the capacitor C4 charges the grid of the MOS tube M8 through the driving resistor R15 and the MOS tube M7, and the MOS tube M8 is opened, at the moment, the positive pulse constant current source current does not flow through the MOS tube M5 any more and only flows through the MOS tube M8, and current switching is completed.