UCC24612: flyback SR FET control application for 200kHz switching frequency

Hello Yunsheng,

Thanks for your kind help on this case :)

Best regards,

Ann Lien

Hi, Ann Lien

If I answered your question, please help to close this thread.

thanks.

Yunsheng

Hello Yunsheng,

I will send you a mail for the test waveform. It seems like UCC24612 cannot be used in CCM mode flyback. Thanks a lot!

Best regards,

Ann Lien

Hi, Ann

please close this thread if you'd like to proceed in eamil.

Yunsheng

Hello Yunsheng,

Seems the UCC24612-1 still can’t operate in CCM mode due to too slow the VG turns off time(spec=16ns~35ns)

The converter is in shoot-through during the 18ns.

CH2:PRIMARY SIDE MOSSFET Vds

CH3:SECONDARY SIDE SYNCHROUS MOSFET Vds

CH4:UCC24612-1 VG

In DCM mode, the UCC24612-1 operates perfectly.

 CH2:PRIMARY SIDE MOSSFET Vds

CH3:SECONDARY SIDE SYNCHROUS MOSFET Vds

CH4:UCC24612-1 VG

Best regards,

Ann Lien

Hello Yunsheng,

May I know if you have update on it? Thanks a lot!

Best regards,

Ann Lien

Hi, Ann

I  think you are right, the typical turn off propagation delay of UCC24612-1 is 16ns, there is overlap between primary MOSFET and SR MOSFET, this the normal operation with CCM Flyback and it can see voltage spike on SR MOSFET. 

Also the reverse recovery characteristic is very critical, it need SR MOSFET with fast reverse recovery characteristics.

BR,

Yunsheng 

Hello Yunsheng,

Thanks for your reply :)

May we know if we have faster SR driving solution could suggest to customer? Or we don't have suitable solution to meet CCM design fly-back for SR controller? Thanks a lot!!

Best regards,

Ann Lien