I was given a Chinese lighting SMPS to have a look at.
It's only a small thing with a single 24v 8.3A output, coming off a 127v mains input.
It came with a blown fuse and someone had already changed the filter caps and the switching Mosfet Source resistor, and it is these values which I am wondering how best to work out.
The FET is a FQPF12N80C N-Channel with the Source resistor connecting straight to ground.
The original resistor had been replaced with two piggy-backed 0.33Ω which measures around 0.18Ω on my tester. I am still learning with SMPS's, but this seems way too low.
Do I need to calculate this resistor for the 3.0A input rating, or does it need to be able to deal with the 8.3A output current?
As for the caps, they had been replaced with 100uF 450v which were physically oversized, so sat wonky.
What calculation can I use to find a suitable value for these?
Any help would be greatly appreciated.
Attachhing some photos...
It's only a small thing with a single 24v 8.3A output, coming off a 127v mains input.
It came with a blown fuse and someone had already changed the filter caps and the switching Mosfet Source resistor, and it is these values which I am wondering how best to work out.
The FET is a FQPF12N80C N-Channel with the Source resistor connecting straight to ground.
The original resistor had been replaced with two piggy-backed 0.33Ω which measures around 0.18Ω on my tester. I am still learning with SMPS's, but this seems way too low.
Do I need to calculate this resistor for the 3.0A input rating, or does it need to be able to deal with the 8.3A output current?
As for the caps, they had been replaced with 100uF 450v which were physically oversized, so sat wonky.
What calculation can I use to find a suitable value for these?
Any help would be greatly appreciated.
Attachhing some photos...
Comment