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Kaan AYDIN
Kaan AYDIN
Associate
November 7, 2017
Question

SCT30N120 Intrinsic Body Diode

  • November 7, 2017
  • 1 reply
  • 1069 views
Posted on November 07, 2017 at 12:32

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 ? What will be the disadvantages of that.

External SiC SBD's are expensive 

#sic-mosfet #sbd #sct30n120
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1 reply

Luigi Abbatelli_O
Luigi Abbatelli_O
Visitor II
November 24, 2017
Posted on November 24, 2017 at 16:02

The intrinsic diode can handle the same current as the MOSFET, nevertheless the diode has a very high voltage drop compared to the drop due to the Rds(on), hence ST recommends to minimize the use of the intrinsic diode to reduce the losses. With regard to inverters it is suggested to use the intrinsic diode only during the dead time and exploiting the 3rd quadrant operation during free-wheeling phase (so please drive the MOSFET with 18V also when the current flows from source to drain except for the dead time obviously). Using an external diode is possible but it is needed to use SiC SBDs especially at high frequency in order to maintain low switching losses, adding an SBD is more expensive and even less efficient than using the SiC MOSFET in the third quadrant.

Kaan AYDIN
Kaan AYDINAuthor
Associate
November 28, 2017
Posted on November 28, 2017 at 15:02

Thank you for your reply, I know intrinsic body diode has more losses due to the voltage drop but I am a little bit confused according to your reply, You're saying that ' 

ST recommends to minimize the use of the intrinsic diode to reduce the losses ' and also ' 

adding an SBD is more expensive and even LESS EFFICIENT than using the SiC MOSFET in the third quadrant.'  we are planning to make a prototype of 30-50kW inverter of statcom.

and Also I did not get what you were saying here ' 

With regard to inverters it is suggested to use the intrinsic diode only during the dead time and exploiting the 3rd quadrant operation during free-wheeling phase (so please drive the MOSFET with 18V also when the current flows from source to drain except for the dead time obviously).

 ' 

what do you mean with 18V operation ? should I apply it during the free wheeling phase ? 

Can you explain that clearly ? I really need the right answer.

Thank you.

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