UCC24612: Power management forum

Pawan Bothra1

Prodigy 10 points

Part Number: UCC24612

HI ,

I am designing a high power factor 12V @ 4 amp single stage CV power supply .

The primary Mosfet is a Si device switching at variable frequency ( 45Khz to 100Khz ) .

1) Can we use 24612-2 as sec side sync rectifier controller ?? Or 24612-1 is more preferable ??

On powering up the circuit , we found that the Gate pulse of 24612-2 was at Ton min ( as described in the DS ).

On further optimising the primary Vds , we could improvement in Ton , while the wave shape is very abnormal .

2) What is the remedy for the same ?

3) What is the co relation between primary Vds ( or the clamp components) on the secondary side sensing circuit ?

over 4 years ago

0 Jaden Ning over 4 years ago

TI__Expert 7080 points

Hi Pawan,

UCC24612-1 and -2 have different turn-on delay and minimum on time . for conventional flyback we recommend UCC24612-1 since the SR current at its maximum value during turn on delay time . short turn on delay has benefit for the efficiency . But you mentioned that the SR turn on at minimum on time in your application even you have used -2 version . may I ask some questions in here :

1. What the transformer inductance Lm , and Leakage inductance Lk ?

2. Can you share some waveforms which you think is abnormal and SR turn on at minimum on time , the waveform should including primary FET Vds , SR FET Vds and Vgs , It's better to have transformer primary winding current .

Generally , primary Vds will shows a leakage reset voltage spike and followed a ringing between leakage and Coss after primary FET turn off , if the reset time plus ringing time exceed the minimum on time . it maybe premature turn off the SR gate , low clamp voltage an high leakage inductance will lead to a long reset time .

Thanks.