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Electronics => Repair => Topic started by: Huram Arvit on April 21, 2024, 10:30:45 pm

Title: Secondary side controller SMPS don't turn on by itself.
Post by: Huram Arvit on April 21, 2024, 10:30:45 pm

I'm having trouble with a SMPS. When I use a bench power supply only to start it's controller circuit, it works fine adjusting the PWM and keeping output voltage at 12v, however it doesn't start by itself. I've already checked and replaced the pulse capacitor at the primary, but the problem persists. The circuit uses a 494 as PWM generator.

Title: Re: Secondary side controller SMPS don't turn on by itself.
Post by: tbegal on April 22, 2024, 09:51:06 am

How is the Modulation controlled? POT or Digital?

Title: Re: Secondary side controller SMPS don't turn on by itself.
Post by: Huram Arvit on April 23, 2024, 01:45:17 pm

It uses a voltage divider and the 5v ref and the error amp from the IC to adjust it.

Title: Re: Secondary side controller SMPS don't turn on by itself.
Post by: wraper on April 23, 2024, 01:54:39 pm

Check components around power transistor bases, especially small electrolytic capacitors.