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Old 02-07-2019, 06:11 AM   #1550
kevin!
recapping PCB.
 
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Join Date: Jul 2013
City & State: Gerona
My Country: Espaņa
Line Voltage: 230VAC 49Hz, 2 Ph
I'm a: Hobbyist Tech
Posts: 135
Default Re: the gutless, bloated, and fried power supply hall of shame

Quote:
Originally Posted by momaka View Post
I don't know about that.
Maybe I am too conservative... but considering the 5V rail rectifier is only good for 20 Amps and the 12V "rectifier" (3 Amp diodes on a bracket) might do 4 Amps with a bit of overheating... that's 148 Watts total on the main rails. I don't count the 3.3V rail, because it's linearly-regulated from the 5V rail. So any current that the 3.3V rail uses will be current that has to go through the 5V rectifier as well.

Now if we add the minor rails... that's 12W from the -12V rail (probably top at 1 Amp) and 10W from the 5VSB (2 Amps, if even that). This brings the total to 170 Watts.

On the other hand, it's good that this PSU has a wimpy secondary side. At least then an output rectifier can short and make the PSU shut down "gracefully" rather than have the primary side blow up and take out who knows what.


Eh. Not that terrible. For 1 Amp output, it's actually OK. It's got an offline switch IC (something considered a commodity among cheapo no-name power adapters), a proper Y2-class cap between primary and secondary (most cheap units use a regular 1kV ceramic ), a FULL BRIDGE RECTIFIER! (who else here is an Electroboom fan? ), and a CM input choke.
With good caps, that PSU will do its rated output power all day just fine. Maybe even good for 1.5 Amps with bigger output caps.


That's not a PFC winding. That's a common-mode choke to reduce EMI/RFI going into and out of the adapter.
Thanks for the correction, I will try to improve the PSU.
I will add the missing zener diode, the missing polyester capacitors in the AC input, and replace the capacitors.
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