UCC256402: HV Startup

Ahmad El Hajj Hassan

Part Number: UCC256402
Other Parts Discussed in Thread: UCC256404, TL431, UCC256403

Hi,

I have two questions,

1- Verify that this is correct, or correct me if I'm wrong:
For UCC256402 or UCC256404, the datasheet doesn't specify a minimum high startup voltage (other than Vcc-startSelf = 26 V typ). So I assume if I don't use the diodes and connect DC voltage (45V) the controller will still startup normally, and after startup it doesn't consume power from HV pin anymore but it's powered from bias winding.

2- Is there an application note or help on how to implement feedback without the use of an optocoupler?

Example: output voltage --> feedback compensation circuit (with TL431 for example) --> unity amplifier --> maybe voltage to current --> feedback pin

Thanks for answering my questions

over 1 year ago

0 JCHK over 1 year ago

TI__Mastermind 47360 points

Hi Ahmad,

For question #1. The absolute maximum rating of the VCC pin on the UCC256402 is 30V with the recommended operating voltage being from 13 to 26V. If you do not need the HV startup, the UCC256403 could be an option.

For question #2, PMP10121 shows how to emulate an optocoupler for non-isolated feedback.

Also note, we now have a newer LLC the UCC25660 which might be easier to design with.

I hope this answers your questions.

0 Ahmad El Hajj Hassan over 1 year ago in reply to JCHK

Prodigy 70 points

For the first question, I mean I could apply 45 VDC with a resistor to HV pin instead of using a high voltage AC source with rectification and the controller would startup just fine.

+1 JCHK over 1 year ago in reply to Ahmad El Hajj Hassan

TI__Mastermind 47360 points

Hi Ahmad,

Sorry I misunderstood your question. If you are using the HV pin, this is fine. You just need to make divider for the BLK pin is set accordingly.

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UCC256402: HV Startup