Silicon carbide power switch driving circuit

Abstract

The invention provides a silicon carbide power switch driving circuit, and relates to the technical field of power electronic driving, the silicon carbide power switch driving circuit comprises a pulse generation module, an isolation transformer and a driving output module, the pulse generation module converts an input direct current voltage into an alternating pulse voltage with dead time and outputs the alternating pulse voltage to a primary winding of the isolation transformer; the driving output module comprises a charging loop, an active discharge loop and a discharge resistor assembly, the active discharge loop comprises a normally-on switch tube, the control end of the normally-on switch tube is connected with one winding section of the secondary winding, and a discharge path bypassing the secondary winding is provided for the gate-source capacitor in the dead zone time. The discharge resistor assembly comprises a first discharge resistor and a second discharge resistor which are arranged in series and located outside and inside the active discharge loop respectively. The discharge falling edge is effectively accelerated, the contradiction of mutual restriction of the discharge speed and oscillation suppression is solved, the structure is simple, and the cost is low.

Description

Technical Field

[0001] This invention relates to the field of power electronic drive technology, and more specifically to a silicon carbide power switch drive circuit. Background Technology

[0002] Existing silicon carbide power device driving solutions mainly include dedicated integrated driver chips, discrete component driver circuits, active driver circuits, and isolation transformer driver circuits. While dedicated integrated chips offer high integration and ease of use, their driving capability is fixed, making them unsuitable for high-power multi-transistor parallel applications, and they are also costly. Discrete component driver circuits offer flexible design, but they involve a large number of components, resulting in complex PCB layouts, and parasitic parameters can easily cause ringing and overshoot during high-frequency operation. Active driver circuits optimize switching performance by dynamically adjusting drive parameters through real-time monitoring of switching transients, but they require multiple control signals with different phases, making design and debugging difficult. Isolation transformer driver circuits utilize a transformer to achieve electrical isolation while simultaneously performing voltage transformation; only the number of winding turns needs to be adjusted to output the desired voltage amplitude. Their simple structure and controllable cost make them a relatively ideal technical approach at present.

[0003] The key to achieving asymmetrical drive using an isolation transformer lies in the fact that the same winding of the transformer outputs symmetrical voltages at different phases, while the silicon carbide devices require unequal positive and negative drive voltage amplitudes. To resolve this contradiction, existing solutions typically incorporate taps in the transformer's secondary winding, dividing the winding into two parts and utilizing the turns ratio of different winding segments to output voltages of varying amplitudes. By coordinating the switching on and off of diodes and MOSFETs, different charging circuits can be selected during the turn-on and turn-off phases, thereby achieving asymmetrical drive voltage output.

[0004] However, existing isolation transformer drive schemes generally face a prominent problem: the transformer windings participate in the current loop in all operating stages, and leakage inductance is unavoidable. This leakage inductance, together with the gate-source parasitic capacitance of the silicon carbide device, forms a series RLC resonant circuit. During the discharge phase following the forward voltage, the leakage inductance limits the rate of change of the discharge current, leading to a prolonged capacitor discharge time and a slower falling edge of the drive signal. Attempting to accelerate the discharge speed by reducing the discharge resistance may cause the circuit to enter an underdamped state, inducing voltage oscillations; conversely, increasing the resistance to suppress oscillations further slows down the discharge speed. Since the discharge circuit and the reverse charging circuit share the same path, adjusting the resistance affects each stage, making independent optimization impossible. This contradiction makes it difficult for existing schemes to simultaneously meet the dual requirements of rapid discharge and oscillation suppression, severely impacting the switching performance of silicon carbide power devices.

[0005] Chinese patent document CN108063542A discloses a simple, reliable, and low-cost silicon carbide power switching device drive circuit. It discloses a technical solution that uses a full-bridge push-pull circuit with a tapped isolation transformer and utilizes a depletion-type MOSFET for self-driving to achieve asymmetrical voltage output. This solution achieves the technical effects of single power supply, simple circuit, low cost, and the ability to output +15V / -5V asymmetrical drive voltage. However, it still has the problems of leakage inductance limiting the discharge speed due to the transformer winding participating in all current loops, and the shared circuit for discharge and reverse charging making it impossible to balance rapid discharge and oscillation suppression.

[0006] Chinese patent document CN108683327B discloses a silicon carbide MOSFET driving circuit, which discloses a technical solution that uses independent three power supplies combined with a P-channel MOSFET auxiliary discharge circuit and Zener diode clamping protection. This solution achieves the technical effects of accelerating turn-off speed, preventing gate overvoltage breakdown, and reducing bridge arm crosstalk. However, it still has the problems of requiring multiple isolated power supplies, which increases system complexity and cost, and oscillation suppression relying on passive clamping, which is a post-event remedy rather than a source-based solution. Summary of the Invention

[0007] The purpose of this invention is to provide a silicon carbide power switch drive circuit that can effectively accelerate the discharge falling edge, solve the problem of mutual constraint between discharge speed and oscillation suppression, and has a simple structure and low cost.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A silicon carbide power switch drive circuit includes: a pulse generation module, an isolation transformer, and a drive output module; The pulse generation module is used to convert the input DC voltage into an alternating pulse voltage with a dead time and output it to the primary winding of the isolation transformer. The secondary winding of the isolation transformer is provided with at least two taps, dividing the secondary winding into at least three winding segments; The drive output module includes a charging circuit, an active discharge circuit, and a discharge resistor assembly. The charging circuit is used to charge the gate-source capacitor of the silicon carbide power switch during the positive and negative phases of the alternating pulse voltage, respectively. The active discharge circuit includes a normally-on switch, the control terminal of which is connected to a section of the secondary winding. The normally-on switch is turned on during the dead time, providing a discharge path for the gate-source capacitor that bypasses the secondary winding. The discharge resistor assembly includes a first discharge resistor and a second discharge resistor connected in series. The first discharge resistor is located outside the active discharge circuit, and the second discharge resistor is located inside the active discharge circuit.

[0010] Furthermore: the secondary winding includes a first winding segment, a second winding segment, and a third winding segment, with a first tap between the first winding segment and the second winding segment, and a second tap between the second winding segment and the third winding segment; the end of the first winding segment is the same-name end of the secondary winding, and the end of the third winding segment is the opposite-name end of the secondary winding.

[0011] Further: The charging circuit includes a positive voltage charging branch and a negative voltage charging branch; the positive voltage charging branch includes a gate resistor and a first diode, the anode of the first diode is connected to the same-name terminal through the gate resistor, the cathode of the first diode is connected to the gate of the silicon carbide power switch, and the second tap is connected to the source of the silicon carbide power switch; the negative voltage charging branch includes a first discharge resistor, a second discharge resistor and a first normally-on switch, and the second winding segment is connected to the gate-source capacitance of the silicon carbide power switch through the conducting first normally-on switch, the first discharge resistor and the second discharge resistor.

[0012] Furthermore, the active discharge circuit further includes a second diode and a second normally-on switch; the anode of the second diode is connected to the first end of the second discharge resistor, and the cathode of the second diode is connected to the first end of the second normally-on switch; the second end of the second normally-on switch is connected to the source of the silicon carbide power switch; the second end of the second discharge resistor is connected to the gate of the silicon carbide power switch; and the control terminal of the second normally-on switch is connected to the opposite-name terminal of the third winding segment.

[0013] Furthermore: the control terminal of the first normally open switch is connected to the second tap, the first terminal of the first normally open switch is connected to the first discharge resistor, and the second terminal of the first normally open switch is connected to the first tap.

[0014] Furthermore, the normally-on switching transistor is a depletion-type N-channel MOSFET.

[0015] Further: the pulse generation module includes a PWM signal generator and a full-bridge push-pull circuit; the full-bridge push-pull circuit includes a first bridge arm and a second bridge arm, the first bridge arm is composed of a first upper transistor and a first lower transistor connected in series, and the second bridge arm is composed of a second upper transistor and a second lower transistor connected in series; the first upper transistor and the second upper transistor are enhancement-mode N-channel MOSFETs, and the first lower transistor and the second lower transistor are enhancement-mode P-channel MOSFETs; the PWM signal generator outputs two complementary PWM signals to drive the first bridge arm and the second bridge arm respectively; the midpoint of the first bridge arm and the midpoint of the second bridge arm are respectively connected to the two ends of the primary winding.

[0016] Furthermore, the isolation transformer includes two sets of secondary windings, with the corresponding terminals of the two sets of secondary windings in opposite positions, respectively used to drive the upper bridge arm silicon carbide power switch and the lower bridge arm silicon carbide power switch.

[0017] Further: the number of turns in the primary winding is n1, the number of turns in the first winding segment is n21, the number of turns in the second winding segment is n22, and the number of turns in the third winding segment is n23; the forward drive voltage V1 and the reverse drive voltage V2 satisfy:

[0018]

[0019] Where V in This is the input DC voltage.

[0020] Furthermore: the discharge circuit resistance R1 during the dead time is less than the reverse charging circuit resistance R2; the discharge circuit resistance during the dead time... for:

[0021] Reverse charging circuit resistance for:

[0022] in, The on-resistance of the normally-on switching transistor is given. R is the on-resistance of the second diode. fH1 R is the resistance value of the first discharge resistor. fH2 R2 is the resistance value of the second discharge resistor; R2 is greater than R1.

[0023] Compared with the prior art, the present invention has the following advantages: I. This invention forms a three-segment winding structure by setting a double tap on the secondary winding and constructing an active discharge circuit using a normally-on switching transistor. During the dead time, it provides a low-impedance discharge path for the gate-source capacitor that bypasses the transformer winding, avoiding the limitation of the discharge current change rate by the transformer leakage inductance and effectively accelerating the falling edge of the positive voltage.

[0024] Second, the present invention adopts a separate structure in which the first discharge resistor and the second discharge resistor are connected in series. The second discharge resistor is located inside the active discharge circuit, and the first discharge resistor is located outside the active discharge circuit, so that the discharge circuit resistance R1 is smaller than the reverse charging circuit resistance R2. While ensuring rapid discharge, the damping ratio of the reverse charging circuit is improved, which fundamentally solves the contradiction between discharge speed and oscillation suppression in the existing scheme. There is no obvious overshoot and ringing at each voltage conversion node.

[0025] Third, the overall circuit of this invention only uses basic components such as transformers, depletion-type MOSFETs, diodes and resistors. It does not require multiple isolated power supplies and additional control signals. The normally open switching transistor is automatically turned on and off by the transformer winding voltage. It has a simple structure, low cost and strong versatility. When replacing silicon carbide power switches with different parameters, only the number of winding turns and the resistance value need to be adjusted to adapt them. Attached Figure Description

[0026] Figure 1 A schematic diagram of a silicon carbide power switch drive circuit provided by the present invention; Figure 2 A schematic diagram of the main drive circuit of a silicon carbide power switch drive circuit provided by the present invention; Figure 3 A key operating waveform diagram of a silicon carbide power switch drive circuit provided by the present invention; Figure 4 Equivalent circuit diagram of process 1 for a silicon carbide power switch drive circuit provided by the present invention; Figure 5 Equivalent circuit diagram of process 2 for a silicon carbide power switch drive circuit provided by the present invention; Figure 6 The present invention provides a process equivalent circuit diagram 3 for a silicon carbide power switch drive circuit; Figure 7 The present invention provides a process equivalent circuit diagram 4 for a silicon carbide power switch drive circuit; Figure 8 A complete waveform diagram of a silicon carbide power switch drive circuit provided by the present invention; Figure 9 The positive falling edge and reverse rising edge waveforms of a silicon carbide power switch drive circuit provided by the present invention; Figure 10 The main voltage change instantaneous waveform diagram of a silicon carbide power switch drive circuit provided by the present invention. Detailed Implementation

[0027] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1 like Figure 1 As shown: This invention provides a silicon carbide power switch drive circuit, including a pulse generation module, an isolation transformer, and a drive output module.

[0029] The pulse generation module converts the input DC voltage into an alternating pulse voltage with a dead time and outputs it to the primary winding of the isolation transformer. The secondary winding of the isolation transformer has at least two taps, dividing the secondary winding into at least three winding segments. The drive output module includes a charging circuit, an active discharge circuit, and a discharge resistor assembly. The charging circuit charges the gate-source capacitor of the silicon carbide power switch during the forward and reverse phases of the alternating pulse voltage, respectively. The active discharge circuit includes a normally-on switch, the control terminal of which is connected to one winding segment of the secondary winding. The normally-on switch conducts during the dead time, providing a discharge path for the gate-source capacitor that bypasses the secondary winding. The discharge resistor assembly includes a first discharge resistor and a second discharge resistor connected in series. The first discharge resistor is located outside the active discharge circuit, and the second discharge resistor is located inside the active discharge circuit.

[0030] With the above structure, only the second discharge resistor participates in the discharge circuit during forward voltage discharge, resulting in low circuit impedance and fast discharge speed; during reverse charging, the first and second discharge resistors are connected in series to participate in the circuit, increasing the total impedance and improving the damping ratio, which can effectively suppress oscillation.

[0031] In one specific embodiment of this example, the secondary winding includes a first winding segment, a second winding segment, and a third winding segment. A first tap is provided between the first and second winding segments, and a second tap is provided between the second and third winding segments. The end of the first winding segment is the same-name terminal of the secondary winding, and the end of the third winding segment is the opposite-name terminal of the secondary winding. Specifically, the first and second winding segments jointly output a forward drive voltage, the second winding segment outputs a reverse drive voltage independently, and the third winding segment is used to control the on / off state of the normally-on switching transistor.

[0032] In one specific embodiment of this example, the charging circuit includes a positive voltage charging branch and a negative voltage charging branch. The positive voltage charging branch includes a gate resistor and a first diode. The anode of the first diode is connected to the same-name terminal via the gate resistor, the cathode of the first diode is connected to the gate of the silicon carbide power switch, and the second tap is connected to the source of the silicon carbide power switch. The negative voltage charging branch includes a first discharge resistor, a second discharge resistor, and a first normally-on switching transistor. The second winding segment is connected to the gate-source capacitor of the silicon carbide power switch via the conducting first normally-on switching transistor, the first discharge resistor, and the second discharge resistor. During the positive phase, current flows from the same-name terminal through the gate resistor and the first diode into the gate, charging the gate-source capacitor to a positive voltage. During the reverse phase, the first normally-on switching transistor is turned on, and the voltage of the second winding segment charges the gate-source capacitor to a negative voltage via the first and second discharge resistors. In one specific embodiment of this example, the active discharge circuit further includes a second diode and a second normally-on switch. The anode of the second diode is connected to the first terminal of the second discharge resistor, and the cathode of the second diode is connected to the first terminal of the second normally-on switch. The second terminal of the second normally-on switch is connected to the source of the silicon carbide power switch. The second terminal of the second discharge resistor is connected to the gate of the silicon carbide power switch. The control terminal of the second normally-on switch is connected to the opposite terminal of the third winding segment. During the dead time, the voltage of the third winding segment is zero, the second normally-on switch is turned on with zero bias, and the gate-source capacitance discharges to the source through the second discharge resistor, the second diode, and the second normally-on switch. This path bypasses the transformer winding, has extremely low impedance, and achieves rapid discharge.

[0033] In one specific embodiment of this example, the control terminal of the first normally-on switch is connected to the second tap, the first terminal of the first normally-on switch is connected to the first discharge resistor, and the second terminal of the first normally-on switch is connected to the first tap. During the reverse phase, the potential of the first tap is lower than that of the second tap, and the gate-source voltage of the first normally-on switch is positive, thus turning it on. During the forward phase, the potential of the first tap is higher than that of the second tap, and the gate-source voltage of the first normally-on switch is negative, thus turning it off. The switching on and off of the first normally-on switch is automatically controlled by the transformer winding voltage.

[0034] In one specific embodiment of this example, the normally-on switching transistor is a depletion-type N-channel MOSFET. A depletion-type MOSFET is in the on state when the gate-source voltage is zero and is turned off when the gate-source voltage is negative. Self-driven control can be achieved by utilizing the polarity change of the transformer winding voltage, without the need for additional control signals.

[0035] In one specific embodiment of this example, the pulse generation module includes a PWM signal generator and a full-bridge push-pull circuit. The full-bridge push-pull circuit includes a first bridge arm and a second bridge arm. The first bridge arm is composed of a first upper transistor and a first lower transistor connected in series, and the second bridge arm is composed of a second upper transistor and a second lower transistor connected in series. The first and second upper transistors are enhancement-mode N-channel MOSFETs, and the first and second lower transistors are enhancement-mode P-channel MOSFETs. The PWM signal generator outputs two complementary PWM signals to drive the first and second bridge arms respectively. The midpoints of the first and second bridge arms are connected to the two ends of the primary winding, respectively. The full-bridge push-pull circuit converts the input DC voltage into a symmetrical pulse voltage with dead time and outputs it to the primary side of the transformer.

[0036] In one specific embodiment of this invention, the isolation transformer includes two sets of secondary windings with opposite positions of the corresponding terminals. These secondary windings are used to drive the upper and lower bridge arm silicon carbide power switches, respectively. Because the corresponding terminals are opposite, the two drive signals are complementary in phase, ensuring that the upper and lower bridge arms do not conduct simultaneously and preventing bridge arm shoot-through.

[0037] In one specific embodiment of this example, the number of turns in the primary winding is n1, the number of turns in the first winding segment is n21, the number of turns in the second winding segment is n22, and the number of turns in the third winding segment is n23. The forward drive voltage V1 and the reverse drive voltage V2 satisfy:

[0038]

[0039] Where V in By adjusting the turns ratio of each winding segment to input DC voltage, the amplitude of the positive and negative drive voltages can be flexibly set to meet the requirements of silicon carbide power switches for asymmetrical drive voltage.

[0040] In one specific embodiment of this example, the resistance of the first discharge resistor is greater than the resistance of the second discharge resistor. The discharge circuit resistance during the dead time... for:

[0041] Reverse charging circuit resistance for:

[0042] in, The on-resistance of the normally-on switching transistor is given. R is the on-resistance of the second diode. fH1 R is the resistance value of the first discharge resistor. fH2 R2 is the resistance value of the second discharge resistor; R2 is greater than R1.

[0043] Since the discharge circuit does not include the first discharge resistor, R1 is small, the discharge time constant is small, and the discharge speed is fast; the reverse charging circuit includes the first discharge resistor and the second discharge resistor, R2 is large, the damping ratio is high, and it can effectively suppress the voltage oscillation caused by the resonance of the transformer leakage inductance and the gate-source capacitance.

[0044] Example 2 This embodiment describes the detailed solution from the perspectives of circuit structure and process analysis: A silicon carbide power switch driver circuit includes: a full-bridge push-pull circuit, an isolation drive transformer, a gate positive voltage drive circuit, a gate negative voltage drive circuit, and a dead-time discharge circuit. Detailed circuit schematic is shown below. Figure 1 As shown: First, a phase-adjustable PWM wave is used to control the switching of the MOSFET, converting the input DC voltage into a high-frequency square wave. Then, a multi-winding transformer is used to achieve self-drive of the depletion-type N MOSFET, realizing dynamic path management. This results in a drive signal with complementary phase and asymmetrical amplitude.

[0045] Drive circuit structure: Figure 1 This is the circuit schematic of the present invention. T is a pulse transformer, n1 is the number of turns in the primary winding of the transformer, and n2 and n3 are secondary windings with two center taps, respectively. n2 consists of three winding segments with turns n21, n22, and n23; n3 consists of three winding segments with turns n31, n32, and n33. To the left of the transformer is a full-bridge push-pull circuit. Q1 and Q3 are enhancement-mode N-MOS transistors, Q2 and Q4 are enhancement-mode P-MOS transistors, and R1, R2, R3, and R4 are their gate drive resistors. The PWM / PFM generator outputs a compliant PWM wave. Vcc is the input DC voltage. The circuit on the left generates a symmetrical pulse voltage with a certain dead time, with positive and negative amplitudes equal to Vcc.

[0046] The circuit on the right side of the transformer is the main drive circuit design, and the circuit diagram is as follows: Figure 2 As shown: It is a depletion-type N MOSFET. The gate drive resistor of the SiC MOSFET. The gate-source resistance of the SiC MOSFET. For discharge resistor, D is the gate drive resistor for a depletion-type N-MOSFET. 1H D 2H D 1L D 2L For reverse current blocking diodes, S H ,S L Example of a driven SiC MOSFET.

[0047] Work process: Since the two secondary windings are symmetrical in structure, only with opposite polarities, the following analysis takes the n2 winding as an example. Figure 3 The waveform shows the transformer output voltage. Based on the waveform, the operating state within one cycle can be divided into four processes, and the output voltage waveforms of the two channels of this drive circuit for each process are as follows: Figure 3 As shown.

[0048] Process 1 (t0-t1) [ Figure 4 At this time, the transformer input voltage is positive, and the current on the secondary side of the transformer flows out from the same-name terminal. The gate-source voltages of the depletion-type N MOSFETs QfH and QrH are negative, and they are in the off state. Diode D 1H In forward conduction, the output voltage of the first and second winding sections (with turns n21 and n22 respectively) of the transformer secondary winding passes through the gate resistor R. gHCharging the gate-source capacitance of the SiC MOSFET, due to the gate-source resistance R gsH >>R gH Almost all the voltage is applied to the gate and source of the SiC MOSFET, at which point the voltage across it is... (1) Process 2 (t1-t2) Figure 5 To prevent the symmetrical SiC MOSFETs from conducting simultaneously, this is the dead time of the pulse input, and the output voltage across the transformer is zero. The depletion-type N MOSFET Q... fH Q rH The gate-source voltage is zero, and the device is in the ON state. The gate-source capacitance of the SiC MOSFET begins to discharge, and the discharge resistor R... fH2 and forward-conducting diode D 2H This provides a discharge circuit with very low impedance to the capacitor, allowing the voltage across the capacitor to drop to zero in a very short time.

[0049] The left half of the dashed line in the circuit can be considered as being short-circuited by the MOSFET and diode, and the discharge resistor can be considered as... (2) Among them, R ds (on) is Q rH The on-resistance, For diode D 2H The on-resistance.

[0050] Process 3 (t2-t3) [Figure]: At this time, the transformer output voltage is negative, and the depletion-type N MOSFET Q... fH Q rH The gate-source voltage is positive, and the diode is in the on state. 1H D 2H When in reverse cutoff state, current flows in from the same-name terminal of the transformer, passes through the discharge resistor R fH1 ,R fH2 and depletion-type N MOSFET Q fH Due to gate-source resistance >>(R) fH1 +R fH2 The voltage is almost entirely applied to the gate and source of the SiC MOSFET, at which point the voltage... (3) Resistance in the circuit: (4) Among them, R ds (on) is Q fH The on-resistance.

[0051] Process 4 (t3-t4) Figure 7 [This is the dead time before the next cycle; the transformer output voltage is zero, and the depletion-type N MOSFET Q...] fH Q rH When the gate-source voltage is zero, the diode is in the on state. 2H In reverse cutoff state, diode D 1H Forward conduction. Gate-source capacitance C gsH Discharge begins with two discharge circuits: one passing through transformer winding n22 and discharge resistor R. fH1 ,R fH2 and depletion-type N MOSFET Q fH A line passing through transformer windings n21 and n22, and the gate resistor and diode D 2H .

[0052] As described above, this scheme utilizes the dynamic management of transformer windings and circuits to achieve adjustable positive and negative voltage outputs, i.e., formulas (1) and (3). The specific values ​​can be controlled by changing the number of winding turns as required, thereby achieving an asymmetrical pulse voltage output.

[0053] During the discharge period (process 2) and the reverse charging period (process 3), the circuits do not completely overlap. During the discharge period, it can be regarded as a first-order circuit with zero input response and only one capacitor, with a time constant. (5) To accelerate the discharge rate, the time constant needs to be reduced; however, since the capacitor is a fixed value in the circuit, the circuit resistance needs to be reduced. .

[0054] During reverse charging, due to the leakage inductance of the transformer, resonance will occur with the capacitor, which is equivalent to a second-order RLC circuit in series, with a damping ratio of... (6) To prevent resonance, the circuit needs to be controlled in a critically damped or overdamped response state, i.e., the damping ratio. Since the inductance L and capacitance C in the circuit are basically fixed values, it is necessary to appropriately increase the circuit resistance. .

[0055] The resistance R can be adjusted fH1 and R fH2 , making the circuit resistance ,exist While relatively small With a larger discharge rate, fast discharge speed can be achieved and reverse charging can be performed without spikes or oscillations.

[0056] Experimental results: When R is taken fH1For 10 ohms, R fH2 The transformer has a capacitance of 3.9 ohms, and the turns ratio of each winding segment is n1:n21:n22:n23 = 15:13:5:5 (where n1 is the number of turns in the primary winding, and n21, n22, and n23 are the number of turns in the first, second, and third winding segments of the secondary winding, respectively). With an input voltage of 15V and a PWM frequency of 40kHz, a 10nF capacitor is used to simulate the charging and discharging of a SiC MOSFET. The measured waveform on the oscilloscope is as follows: Figure 8 As shown: The blue and yellow lines represent the two complementary secondary windings of this drive circuit and the drive waveforms generated by the circuit, respectively. The blue line represents the voltage waveform of channel 1, and the yellow line represents the voltage waveform of channel 2. Figure 8 The measurement parameters are: F = 40kHz, Vgs (5V / div), t (200ns / div). It can be seen that the amplitude, frequency, symmetry, and the slow-on / fast-off characteristics required for silicon carbide switching devices have been largely achieved. Figure 9 The forward voltage discharge time of channel one (process 2) and the reverse voltage discharge time of channel two (process 4) are defined as follows. Figure 9 The measured parameters are: Vgs (5V / div) and t (200ns / div). It can be seen that the discharge time is stable and reliable, and there is almost no voltage overshoot or ringing, which meets the engineering requirements. Furthermore, the discharge time can be further shortened by replacing the resistor with a smaller one. Figure 10 The measured waveforms for the entire reverse charge and discharge process are shown below: Figure 10 The measured parameters are: Vgs (2V / div) and t (200ns / div). It can be seen that the voltage changes that are more likely to cause voltage overshoot and ringing are only very small and can be ignored. It can ensure good switching characteristics even when driving a large parasitic capacitance switching transistor.

[0057] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A silicon carbide power switch drive circuit, characterized in that, include: Pulse generation module, isolation transformer, and drive output module; The pulse generation module is used to convert the input DC voltage into an alternating pulse voltage with a dead time and output it to the primary winding of the isolation transformer. The secondary winding of the isolation transformer is provided with at least two taps, dividing the secondary winding into at least three winding segments; The drive output module includes a charging circuit, an active discharge circuit, and a discharge resistor assembly. The charging circuit is used to charge the gate-source capacitor of the silicon carbide power switch during the positive and negative phases of the alternating pulse voltage, respectively. The active discharge circuit includes a normally-on switch, the control terminal of which is connected to a section of the secondary winding. The normally-on switch is turned on during the dead time, providing a discharge path for the gate-source capacitor that bypasses the secondary winding. The discharge resistor assembly includes a first discharge resistor and a second discharge resistor connected in series. The first discharge resistor is located outside the active discharge circuit, and the second discharge resistor is located inside the active discharge circuit.

2. The silicon carbide power switch drive circuit according to claim 1, characterized in that: The secondary winding includes a first winding segment, a second winding segment, and a third winding segment. A first tap is provided between the first winding segment and the second winding segment, and a second tap is provided between the second winding segment and the third winding segment. The end of the first winding segment is the same-name end of the secondary winding, and the end of the third winding segment is the opposite-name end of the secondary winding.

3. The silicon carbide power switch drive circuit according to claim 2, characterized in that: The charging circuit includes a positive voltage charging branch and a negative voltage charging branch; the positive voltage charging branch includes a gate resistor and a first diode, the anode of the first diode is connected to the same terminal via the gate resistor, the cathode of the first diode is connected to the gate of the silicon carbide power switch, and the second tap is connected to the source of the silicon carbide power switch; the negative voltage charging branch includes a first discharge resistor, a second discharge resistor, and a first normally-on switch, and the second winding segment is connected to the gate-source capacitance of the silicon carbide power switch via the conducting first normally-on switch, the first discharge resistor, and the second discharge resistor.

4. The silicon carbide power switch drive circuit according to claim 3, characterized in that: The active discharge circuit further includes a second diode and a second normally-on switch; the anode of the second diode is connected to the first end of the second discharge resistor, and the cathode of the second diode is connected to the first end of the second normally-on switch; the second end of the second normally-on switch is connected to the source of the silicon carbide power switch; the second end of the second discharge resistor is connected to the gate of the silicon carbide power switch; and the control terminal of the second normally-on switch is connected to the opposite-name terminal of the third winding segment.

5. A silicon carbide power switch drive circuit according to claim 4, characterized in that: The control terminal of the first normally open switch is connected to the second tap, the first terminal of the first normally open switch is connected to the first discharge resistor, and the second terminal of the first normally open switch is connected to the first tap.

6. A silicon carbide power switch drive circuit according to any one of claims 3-5, characterized in that: The normally-on switching transistor is a depletion-type N-channel MOSFET.

7. A silicon carbide power switch drive circuit according to claim 1, characterized in that: The pulse generation module includes a PWM signal generator and a full-bridge push-pull circuit. The full-bridge push-pull circuit includes a first bridge arm and a second bridge arm. The first bridge arm is composed of a first upper transistor and a first lower transistor connected in series, and the second bridge arm is composed of a second upper transistor and a second lower transistor connected in series. The first upper transistor and the second upper transistor are enhancement-mode N-channel MOSFETs, and the first lower transistor and the second lower transistor are enhancement-mode P-channel MOSFETs. The PWM signal generator outputs two complementary PWM signals to drive the first bridge arm and the second bridge arm respectively. The midpoint of the first bridge arm and the midpoint of the second bridge arm are respectively connected to the two ends of the primary winding.

8. A silicon carbide power switch drive circuit according to claim 1, characterized in that: The isolation transformer includes two sets of secondary windings, with the corresponding terminals of the two sets of secondary windings in opposite positions, respectively used to drive the upper arm silicon carbide power switch and the lower arm silicon carbide power switch.

9. A silicon carbide power switch drive circuit according to claim 4, characterized in that: The primary winding has n1 turns, the first winding segment has n21 turns, the second winding segment has n22 turns, and the third winding segment has n23 turns; the forward drive voltage V1 and the reverse drive voltage V2 satisfy: Where V in This is the input DC voltage.

10. A silicon carbide power switch drive circuit according to claim 9, characterized in that: Dead time discharge circuit resistance Less than the reverse charging circuit resistance The discharge circuit resistance during the dead time for: Reverse charging circuit resistance for: in, The on-resistance of the normally-on switching transistor is given. R is the on-resistance of the second diode. fH1 R is the resistance value of the first discharge resistor. fH2 R2 is the resistance value of the second discharge resistor; R2 is greater than R1.

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