A novel driver circuit of SiC MOSFET for suppressing crosstalk voltage in bridge circuit

Due to the presence of crosstalk voltage in the circuit, SiC MOSFET devices can be damaged or misled. Suppressing crosstalk voltage makes it an important step for the circuit to function properly. This article first delves into the causes of crosstalk voltage generation. The main research object is synchronous Buck converters, and the reasons for the crosstalk voltage of SiC MOSFETs are analyzed. Afterwards, a novel drive circuit was designed to suppress crosstalk voltage, and the working principle of this drive circuit was analyzed. Finally, simulation was conducted using LTspice software to study and analyze the simulation results, proving the feasibility of this novel drive circuit for suppressing crosstalk voltage, and demonstrating the advantages and disadvantages of this novel drive circuit for suppressing crosstalk voltage.


Introduction
Nowadays, Power semiconductor devices are widely used in various fields such as motor drive systems, and electric vehicle charging systems [1].Due to the high-frequency characteristics of SiC MOSFETs being affected by parasitic parameters within the device, the use of SiC MOSFETs in the circuit can lead to electromagnetic interference in the power main circuit being introduced into the gate drive circuit, which is known as the phenomenon of crosstalk voltage.Crosstalk voltage can cause a sudden increase in the gate source voltage or excessive negative pressure of power devices, further causing gate source breakdown or misleading phenomenon of the device, ultimately causing circuit short circuits and converter operation faults.Therefore, suppressing crosstalk voltage is an important step.Because the parasitic parameters of the device itself cannot be eliminated, and the generation of crosstalk voltage is also difficult to suppress, the suppression of crosstalk voltage needs to be suppressed through its propagation path [2][3][4].
At present, domestic and foreign researchers have conducted extensive research on methods to suppress crosstalk voltage in circuits, and have designed many driving circuit strategies to suppress crosstalk voltage.The main method is to suppress the influence of crosstalk voltage by adding a suppression voltage circuit to the gate drive circuit of SiC MOSFET, thereby ensuring the normal operation of power devices.
Firstly, a closed-loop feedback quantity is introduced as a method to suppress crosstalk voltage [5,6], detecting the quantities that have a significant impact on crosstalk voltage during the switching process of SiC MOSFETs, such as di/dt and dv/dt.Then, feedback quantities of equal magnitude in opposite directions are added to the gate drive circuit to cancel the crosstalk voltage.Power devices such as SiC MOSFETs have made some progress in this research and development, but this method requires high accuracy, and many active devices have been added.This method is generally less commonly used.
Secondly, change the driving voltage level to suppress it.RCD (resistor capacitor diode) voltage level converter [7], which can convert the forward voltage of the gate to negative pressure without the need for additional control signals.The negative pressure generated will be utilized by the converter, which can effectively suppress the forward crosstalk voltage.This design has a good suppression effect on forward crosstalk voltage, but it also increases the burden on negative crosstalk voltage.The intelligent three-level active driving circuit, where the input of the voltage comparator is obtained from the voltage delayed through the RC series circuit, and the zero potential auxiliary circuit is controlled through the output [8].
Finally, change the impedance of the gate drive circuit to suppress crosstalk voltage.Add a passive Miller clamp suppression circuit to the driving circuit of SiC MOSFET to suppress crosstalk voltage [9].When Miller current flows through the gate drive circuit, a low impedance flow path of Miller current is provided by the conduction of the auxiliary transistor.Based on traditional RCD voltage converters, the circuit can be further improved by combining a passive Miller clamp suppression circuit with an RCD circuit [10], and comparing the proposed circuit with various other circuits demonstrates its advantages in suppression performance.

Reasons for crosstalk voltage generation in SiC MOSFETs
The equivalent circuit of the synchronous Buck converter is shown in Figure 1.Among them, QL, as the disturbed object, is in a shutdown state throughout the entire process.Among them, Lg, Ld, and Ls are the parasitic inductance of the gate, drain, and source of SiC MOSFET, respectively.Cgs, Cgd, and Cds are the gate source capacitance, gate drain capacitance, and drain source capacitance of SiC MOSFET, respectively.Lloop is the stray inductance of the power circuit, and Rg_ Ex, Rg_ In is the gate resistance and internal resistance of the device.The subscript "L" is used to mark the main parameters of the synchronous pipe QL, and the subscript "H" is used to mark the main parameters of the control pipe QH.C0, R0, and L0 are the filtering capacitors, load resistors, and load inductors of the synchronous Buck converter, respectively.In the analysis of the following article, QL has been set to the cut-off state.The main waveform during the QH switching process of the upper transistor in the synchronous Buck converter is shown in Figure 2, where the entire duration of the crosstalk maintenance phase is represented by ts.During the dead time of the gate voltage, if the forward crosstalk voltage is greater than the threshold voltage of the device, it will cause conduction between the upper and lower circuits, leading to power converter failure.When the magnitude of the negative crosstalk voltage is greater than the negative limiting voltage value of the device, which leads to the destruction of the device, it disrupts the safety and stability of the entire power system operation.

Design principle of driver circuit for suppressing crosstalk voltage
The novel drive circuit for suppressing crosstalk voltage is shown in Figure 3.It can be seen that the novel drive circuit for suppressing crosstalk voltage controls the flow path of Miller current through SiC MOSFET to suppress crosstalk voltage.This novel drive circuit for suppressing crosstalk voltage uses four main devices: auxiliary resistor Rclp, auxiliary capacitor Cclp, clamp diode Dclp, and power switching device Sclp.A reasonable dead time is set for the switches of devices in the circuit.During this period, during the rise of the drain source voltage VdsL of the lower tube QL, Miller current will pass through the internal driving resistor RgL_in.Before and after the conduction of the upper tube QH, a gate drive signal is applied to the SiC MOSFET in the lower tube drive circuit to make it conduction, and the conduction process needs to be maintained for a period of time.At this point, an auxiliary circuit composed of SiC MOSFETs and a series connected capacitor Cclp provides a flow path for Miller current as shown in Figure 4(a).When the crosstalk voltage is positive, it will be effectively suppressed.At the moment when the upper tube QH is turned off, the drain source voltage VdsL of the lower tube QL is in a decreasing process.The auxiliary circuit composed of the auxiliary capacitor Cclp and the diode Dclp in series provides a flow path for Miller current, as shown in Figure 4(b).After the instantaneous completion of the device's switching, the energy stored on the capacitor Cclp will be released using the resistor Rclp, making it difficult to change the device's switching rate.Due to the need for additional control signals to be applied to the SiC MOSFET in the gate drive circuit of the lower transistor QL in this novel drive circuit for suppressing crosstalk voltage, it will increase some difficulty in designing the circuit.However, it accurately suppresses the forward crosstalk caused by the upper tube QH, and the effect of suppressing crosstalk voltage is very obvious.
When the gate source voltage VdsL is a linear function, solving the above equation can obtain the crosstalk voltage VCgsL: The coefficients in Equation ( 2) are as follows: ( By simplifying Equation ( 1), the maximum value of crosstalk voltage VCgsL is obtained: By analyzing Equation ( 4), it can be concluded that the magnitude of crosstalk voltage is closely related to the switching speed k of power devices, internal parasitic parameters in SiC MOSFETs, and the duration of crosstalk voltage ts.The size of the auxiliary capacitor Cclp in the driving circuit will also have a certain impact on the maximum value of crosstalk voltage.The SiC MOSFET used in this article is the SiC MOSFET produced by CREE company (C2M0080120D).Since the maximum gate drain parasitic capacitance of SiC MOSFET is 70 pF when Vds is greater than 10V, the size of the gate drain parasitic capacitance is taken as 70 pF in the following analysis.Due to the influence of bus voltage VDC on the maximum value of crosstalk voltage, when the value of auxiliary capacitor Cclp exceeds 10 nF, the maximum value of crosstalk voltage VCgsL can be lower than 2 V.In order to provide an ideal design space for simulation experiments, the size of capacitor Cclp can be set to 100 nF.
The design principles of auxiliary resistor Rclp and driving resistor RgL_ex are analyzed below.When there is no anti-crosstalk circuit in the driving circuit, SiC MOSFET can be regarded as an RLC series circuit.To quickly release the disturbance voltage on the parasitic capacitance VgsL between the gate and source electrodes of SiC MOSFET, the RLC circuit of the driving circuit of SiC MOSFET needs to be in an overdamped state.The size setting of the driving resistor needs to meet Equation (5):

Simulation of a novel voltage driver circuit for suppressing crosstalk
In order to verify the crosstalk suppression effect of the drive circuit for suppressing crosstalk voltage, the simulation suppression results of the two circuits were compared and analyzed using LTspice software.The simulation experimental platform for the synchronous Buck converter is shown in Figure 5.The model selection of the diode is 1N4148.SiC MOSFET has chosen C2M0080120D produced by CREE company.The values of the main parameters in the simulation experiment of the drive circuit for suppressing crosstalk voltage are shown in Table 1.The cut-off voltage of SiC MOSFET in the nonsuppressed crosstalk circuit is set to 0 V, and the turn-on voltage is set to 18 V.The comparison of the suppression results of disturbances during the device switching process is shown in Figure 6. Figure 6(a) shows the waveform affected by crosstalk when there is no crosstalk suppression circuit in the driving circuit.Through analysis, it can be seen that the maximum negative disturbance voltage of the device is -5.74 V, and the maximum positive disturbance voltage is 6.24 V. Figure 6(b) shows the waveform affected by crosstalk when the driving circuit is the novel drive circuit for suppressing crosstalk voltage.Through analysis, it can be concluded that the maximum negative disturbance voltage of the device is -1.01 V, and the maximum positive disturbance voltage is 1.30 V. Through comparison, it can be seen that the suppression effect of the novel drive circuit for suppressing crosstalk voltage is obvious.The peak values of forward crosstalk voltage and negative crosstalk voltage are much smaller compared to the passive Miller clamp suppression circuit, and the electromagnetic interference phenomenon is alleviated.

Conclusion
This article first takes the synchronous Buck converter as an example to illustrate the switching process of the device.Afterwards, the reasons for the generation of disturbance voltage during the switching process of the device were studied.Afterwards, a novel drive circuit for suppressing crosstalk voltage was proposed from the perspective of the propagation path of SiC MOSFET crosstalk voltage, its suppression principle was analyzed, and the parameters in the circuit were reasonably selected.Finally, a simulation experiment was conducted to compare the novel crosstalk suppression voltage driving circuit with the non-drive circuit for suppressing crosstalk voltage, verifying its effectiveness in suppressing crosstalk voltage.

Figure 1 .
Figure 1.Equivalent circuit diagram of synchronous buck converter.Firstly, the switching process of devices in synchronous Buck converters is studied.From Figure 1, it can be seen that QH caused crosstalk issues with QL.Analyze the crosstalk of QH based on the three parts during activation and the two parts during shutdown.The following is a research explanation for each section.The first stage (t0~t1): The gate source voltage VCgsH of the upper tube QH continuously increases to Miller voltage.The drain source voltage of the lower tube QL has not yet increased.The body diode current idL keeps decreasing to 0 A. Due to the generation of parasitic inductance LsL in the connection of the circuit, a rapid change in the body diode freewheeling current idL will cause the parasitic inductance LsL to generate an induced voltage.The induced voltage will cause the gate source parasitic

Figure 2 .
Figure 2. Waveform diagram of main parameters during QH switching process.

Figure 3 .
Figure 3.A Novel Voltage Driver Circuit for Suppressing Crosstalk.

Figure 4 .
Figure 4. Working principle of suppressing crosstalk voltage.The application of KVL law to the novel drive circuit for suppressing crosstalk voltage can obtain Equation (1):