SR-FET not on GND - INN2904k
Hello!
i please you for your help.
Design:
Vin: 450VDC
Vout: 1x18/1A, 2x5V/100mA
A) Is it possible to place the SR-Fet on the "HighSide", red point on the screenshot?
Why i ask:
With all windings stacked, i cannot use the SR-Fet on LowSide.
B) Can i leave the SR Pin unconnected? Replacing the SR-Fet with a diode?
best regards
Walter
Comments
Hello SevenOfNine,
thank you for your answer!
Diode HighSide:
and the FWD Pin is then connected by the anode of the diode?
in the simulation i have with ringing nearly 200V on this pin, without ringing 120V.
I know INN2904k use this pin for power supply and??? I can reduce the FWD voltage with a TVS, loolk on the screenshot?
best regards
Walter
| Attachment | Size |
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| innoSecondaryDiodeHighSide.PNG (9.3 KB) | 9.3 KB |
Hi extern,
Cannot use like this configuration. The FWD_pin voltage is being compared to Vo pin with respect to GND. For better operation the diode should be on the bottom side. If you make it high side the FWD_pin voltage with respect to GND will have an offset of Vo and will not properly operate. Please also note that the FWD_pin voltage maximum rating is only 150V. You can try to add another winding for FWD_Pin and Vo sensing but this time low side. For your main power you can put the diode on high side configuration.
Best Regards,
PI-SevenofNine
Hi extern,
Thank you for using PI product on your design. Below are our answers to your inquiry.
A. You cannot put the SR-Fet on the HighSide part of your secondary. The SR-Fet source pin should be connected to the GND pin of the IC for correct drive and operation.
B. Yes, you can use a diode instead of an SR-Fet. But it is better to short the SR pin to the GND of the IC instead of no connection or floating.
Best Regards,
PI-SevenofNine