Calculation of reverse conduction loss for SiC MOSFET

Jani

Can you give some idea about the calculation of reverse conduction losses in the case of synchronous buck converter application?

jshao

Hi Jani,

Thanks for your question. Can you explain what is "reverse conduction losses" you referred in the question? Is it conduction loss, or reverse recovery loss due to body diode?

Best,

Jianwen

Jani

Hi,

As per my understanding, SiC MOSFETs have reverse conduction capabilities. So in the typical inverter application, the current is share between switch and body diode. I want to know how to calculate the losses of the switch in that condition. I think it will be a part of conduction losses.

Thanks in advance

jshao

Hi Jani,

Now I understand. We usually call it third quadrant conduction or synchronous rectification. Under that condition, all the current will go through the channel of the switch since the voltage drop is lower than body diode Vf. So the conduction loss is the Rdson loss. The Rdson is very similar to the Rdson at 1st quadrant conduction. So the power loss=Rdson*Irms^2.

Thanks,

Jianwen

Jani

Hi Jianwen,

Thanks for the explanation.

As diode forward voltage drop in the third Quadrant is greater than the channel drop, does it mean there will be no conduction drop in the body diode (i.e. only switch is conducting all the time)?

It will be vey helpful if you can provide some reference on which condition body diode will conduct.

jshao

Hi Jani,

Correct. Body diode will only conduct current during deadtime when the device is off.

Jianwen

Jani

Hi Jianwen,

Thanks for your help!