The third generation of power electronics semiconductors: SiC MOSFET learning notes (V) research on driving power supply

3.1 Drive power
SiC MOSFET Voltage ratio on Si IGBT low , But only the driving voltage reaches 18V～20V It can only be fully opened when ;

Si IGBT and SiC MOSFET Vgs contrast

Cree Single tube in the product manual MOSFET The manual recommends gate source voltage -4/15V; What the module gives is -5/20V Recommended driving voltage , In the actual research process, the modules use -4/20V; be based on Cree It is recommended to turn on the voltage of the third generation chip module 17_{20V, Achieve lower conduction loss , Off voltage -5V}-2V Between .

Cree Single tube MOSFET Manual recommendation Vgs

Cree Industrial grade SiC MOSFET Module recommendation Vgs

Rhom The module is actually used Vgs：-2/+20V,△Vgs=22V, In order to achieve lower conduction loss , Therefore, the gate source voltage should be set higher .

Rhom SiC MOSFET Module recommendation Vgs

Star suppliers provide information, they use Cree Chip , modular Vgs Recommended -4/15V,Rhom Chip , modular Vgs Recommended -2/15V.

Star SiC MOSFET recommend Vgs

3.2 Drive resistance
The driving resistance has a great influence on the switching speed , If the driving resistance is small, the grid capacitor will charge and discharge quickly , Switching devices have fast switching speed , Low switching loss , However, if the driving resistance is too small, the driving voltage is easy to oscillate in the switching process , It may cause false triggering of the device , In serious cases, it may even damage switching devices and power electronic equipment ; If the drive resistance Rg The value is too large , The response of the driver will be slow , This will reduce the switching speed of the device , Increase the switching loss of the device .
SiC MOSFET The driver consists of two parts , Part is inside the pipe , This part of the resistance is related to the thin layer impedance of the gate electrode material and the size of the chip ; The other part is the external grid resistance . It can also be seen from the data of the switch tube , With the increase of external driving resistance, the switching loss of the switch increases gradually , The opening time and closing time also gradually increase .
The driving resistance shall be selected so that the driving voltage will not oscillate , At the same time, maintain the fast response speed of the system , That is to reduce the driving resistance as much as possible while ensuring reliable operation . During the design, the on resistance and off resistance can be designed separately , In this way, the opening and closing speeds can be controlled more flexibly . The selection of driving resistance refers to the data manual and has been tested experimentally , Comprehensively consider the switching time 、 Switching loss 、 Oscillation and spike problems .

3.3 Driving current
SiC MOSFET For the special requirements of the driving circuit, we know that , The driving chip needs to provide sufficient driving current . Insufficient driving current will delay the switching process of the device , Thus, the loss of switching process is increased . therefore , Calculate the average driving current required in the opening process according to the following formula Ig by ：

among ：Qc Charge the grid ,td(on) Delay time for opening ,tr Rise time . Combined with the parameter values in the data book , The average driving current required in the opening process is obtained Ig by 2A. So from the isolation mode 、 The driving current is considered in two aspects , Final choice ACPL- W346 Driver chip . This optocoupler is isolated and drives the transient output current 2.5A, On delay and off delay are respectively 120ns and 30ns, Transmission delay is small , It can meet the requirements of this article SiC MOSFET The switching frequency is set to 100kHz The need for .