SiC intrinsic body diode vs external body diode

Hi everyone,
I am planning to use sic mosfets in inverter application(2 level or 3 level) and I searched some manufacturer and prices, I saw sct30n120 and ST says ' Very fast and robust intrinsic body diode (no need for external freewheeling diode, thus more compact systems)' , does intrinsic body diode can handle the current as much as the mosfet ? lets say 25A current , or should I use external body diode ?

If I use external body diode; can I use fast recovery diode instead of SiC SBD ? What will be the disadvantages of that. Reverse recovery ?

does intrinsic body diode can handle the current as much as the mosfet ?

Click to expand...

Yes. After all, it is in the same package, isn't it ?

Hi,

I say it depends:

If you just see the current, then it can handle the same as the mosfet.. at least for a short time.

How long .. depends on the power dissipation. If we speak about the same current, then dissipated power depends on voltage drop.
Often the voltage drop across the diode is higher than across DS of the mosfet, then the maximum DC current across the diode will be smaller than the DC current across the mosfet.

If you use external schottky diodes, then the internal diode usually never becomes conductive and thus disspates no power.

Klaus

KlausST said:

Hi,

I say it depends:

If you just see the current, then it can handle the same as the mosfet.. at least for a short time.

How long .. depends on the power dissipation. If we speak about the same current, then dissipated power depends on voltage drop.
Often the voltage drop across the diode is higher than across DS of the mosfet, then the maximum DC current across the diode will be smaller than the DC current across the mosfet.

If you use external schottky diodes, then the internal diode usually never becomes conductive and thus disspates no power.

Klaus

Click to expand...

Yes you're right. The voltage across the diode is higher than Vdson of mosfet ,then current should be small for diode than mosfet.
What about the UltraFast recovery diode instead of SiC schootky diode ?UltrafastDiode has more loss than SiC schottky diode,I know that but how much will effect the overall performance ?

The freewhelling Ultrafast recovery diode ( or schottky diode) also will effect the mosfet performance of course.

Lets say in SCT30N120 and current will be 30A

Hi,

now we need to go into detail.

Especially waveform of current through the diode.
--> can you show a scope picture?
or draw a picture of the estimated current waveform - with current magnitude and timing.
or show the schematic of the load circuit... and give the current values and timing.

Each diode has
* conduction loss
* reverse recovery time
* Q of recovery

Klaus

The body diode is going to be pretty high Vf I expect.
But the same is pretty much true of SiC Schottkies and
other WBG diodes. So while the diode (if so rated) "can"
take the current, it doesn't mean that's your best play
for efficiency.

Design of the body diode to prevent current crowding /
debiasing, to keep lifetime down so that there's no
punch-out when the drain swings back up against a
still-lit body diode (enabling bipolar conduction and
burnout, potentially) would probably be needed to get
that kind of asserted ruggedness. Diode forward
conduction may be naturally diffuse (more or less)
but reverse, you can't count on at all.

KlausST said:

Hi,

now we need to go into detail.

Especially waveform of current through the diode.
--> can you show a scope picture?
or draw a picture of the estimated current waveform - with current magnitude and timing.
or show the schematic of the load circuit... and give the current values and timing.

Each diode has
* conduction loss
* reverse recovery time
* Q of recovery

Klaus

Click to expand...

Hi,
Just think about ordinary 2 level inverter with 500hz(I choose because of speed of simulation) modulation frequency under inductive load,Vdc link =350V(such as), 2 level full bridge, 8mH+20ohm load.




Actually, I talked with an field application engineer from ROHM, and he told me there will be no problem to using intrinsic body diode, just it has more Vf than external SBD,thats why conduction losses will be higher at intrinsic body diode actually.
He sent me some documents,I will share,

https://docdro.id/FTx6Hs6


Hi dick_freebird ,
I did not get what you said in second paragraph, can you explain it again please ? maybe with an example ?

Thank you

Btw, Gate driver using bootstrap topology, dont pay attention the voltage drop of driving. Its cause of %100 duty.

Put another sic diode in antiparallel and it will share current with the internal one.....being sic it is better for reverse recovery