UCC28780: High line start up

Ray Cheung

Part Number: UCC28780

Dear Sir,

My unit startup with <150Vac is properly and after startup, and then startup the PFC, also function well.

Lm:120uH

But if i use high input voltage such as 150Vac, my unit can't startup properly and I can see the CS was hit 0.6V (on duty is suddenly go from <3us to >5us)

If I use 180Vac or above, there will have no any switching. I don't know why the RUN is not enable when using High input line

Attached waveform with below setting (90Vac, 120Vac, 180Vac)

90VAC

120Vac

180VAC

Channel 1 Yellow Pin VCC

Channel 2 Blue Pin SWS

Channel 3 Pink PWML

For the one 150Vac

Channel 2 Blue Pin -CS

Channel 3 Pink PWML

Would you please advise what signal or parameter that I can adjust to resolve it?

Thanks

RAY

over 3 years ago

0 Jaden Ning over 3 years ago

TI__Expert 7080 points

Hi Ray,

Could you please share the schematic and PCB layout for reviewing?

When you capture the waveform , could you probe low side FET VDS , transformer primary winding current and VDD voltage with high resolution so we can see the first to third pulse .

Thanks.

0 Ray Cheung over 3 years ago in reply to Jaden Ning

Prodigy 30 points

Dear Jaden,

Schematic sent to your email

Thanks for your help

Ray

+1 Jaden Ning over 3 years ago in reply to Ray Cheung

TI__Expert 7080 points

Hi Ray,

Let's move to E-mail support, I'll close this thread.

Thanks.

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UCC28780: High line start up