UC3825: About the soft-start

Alvin Lin

Part Number: UC3825

Hi, ti's team:

Good day.

There is a question when i apply the UC3825 for a flyback circuit.

I connected the SS pin to ground with a 0.1uF capacitor, but when I turned on the power supply, I still found a large overshoot.
My question is that how to apply this IC's soft start, is there a more detailed document?

Is there any other circuit to solve this problem?

Thank you very much.

over 3 years ago

0 Hong Huang over 3 years ago

TI__Guru 57825 points

Hi,

You need to probe SS, E/A OUT, and OUTA or OUTB to get their waveforms at start to check. The Vout overshoot is usually caused by control handover from SS to feedback loop. Usually you may need to tune up your feedback loop compensation to make this handover smoothly.

0 Alvin Lin over 3 years ago in reply to Hong Huang

Prodigy 110 points

Thanks for your kindly reply.

When UC3825 protection occurs, like SS is pulled low,or Ilimit triggers protection, whether IC will enter LATCH mode.
Keep the VCC constant, after removing the protection condition, will the IC restart? If it restarts, how long will it be delayed?

Thanks.

0 Hong Huang over 3 years ago in reply to Alvin Lin

TI__Guru 57825 points

Hi,

It is not in latch so after release SS the device will restart. The process of restart similar to power on.

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UC3825: About the soft-start