Research On Gate Drive Circuit For SiC MOSFET In High Temperature Application

In this paper,a SiC MOSFET driving circuit and its protection circuit applied to high temperature environment are designed by using commercial off-the-shelf?COTS?discrete components.The main driving circuit plays the role of raising the value of the input control signal to the level of SiC MOSFET drive voltage.The control circuit is separated from the power circuit by the way of transformer isolation to prevent the power circuit from disturbing the control circuit in the high speed switching process.The level shifting function is realized through the series structure of PNP bipolar transistor and NPN bipolar transistor,and the output drive voltage is 19V/-5V.The structure solves the contradiction between the BJT switch speed in the traditional level shift circuit and power dissipation of collector resistance,and greatly reduces the rising time and the falling time of the output voltage of driving circuit.This can provides a higher frequency driving signal for SiC MOSFET and make the high speed switch performance of SiC MOSFET be excavated.The protection circuit includes undervoltage detection circuit,overcurrent detection circuit and protection execution circuit.In the undervoltage detection circuit,reference voltage value is set through a voltage regulator tube to detect whether the power supply voltage of the driving circuit is smaller than the reference voltage,and if an undervoltage signal is generated,the undervoltage signal is transmitted to the protection execution circuit.The undervoltage detection circuit designed in this paper is simple in structure,not only reduces the manufacturing cost of the circuit,but also improves the reliability of the function of the detection circuit.In particular,the simple circuit structure in high temperature environment can effectively reduce the possibility of circuit failure.It also involves a new type of overcurrent detection circuit.according to the principle that the conduction voltage drop of the SiC MOSFET overflows with the current rising,the reference voltage is set in the overcurrent detection circuit by the regulator tube.The overvoltage fault of SiC MOSFET is judged by comparing the detected drain voltage with the reference voltage value.the overcurrent detection circuit also has the characteristics of simple circuit structure.Only one PNP bipolar transistor is used to realize the function of overcurrent detection,and a delay circuit is set up in the circuit to judge the overcurrent fault and reduce the probability of misoperation of the detection circuit.So that the anti-interference ability of the circuit is improved.A protective execution circuit is designed.The function of this circuit is to process the detected fault signals,including undervoltage fault and overcurrent fault.The protection execution circuit is provided with an initialization circuit module,a latch over current fault module and a V_GS anti jump circuit.the initialization circuit plays the role of clearing the undervoltage fault signal and the overcurrent fault signal instantaneously in the protection circuit.The function of overcurrent fault latch circuit is to lock the detected overcurrent fault signal.The function of anti-jump circuit is to inhibit the jump of gate-source voltage after the two-step protection scheme.On the basis of these functions,the number of components used is reduced compared with the same type of circuits.In summary,the whole drive protection circuit can simplify the protection circuit structure,reduce the cost and improve the reliability of the circuit,based on the realization of the basic protection function.Finally,the designed driving circuit is tested.Compared with the output performance of the same type of driving circuit,the rising and falling time of the output voltage of the driving circuit are reduced.with the increase of temperature,the rise time of driving voltage decreases slightly and the fall time increases.the influence of temperature on the output performance of the circuit is acceptable.