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Old 11-05-2021, 08:39 PM   #40
Badcaps Veteran
Join Date: Dec 2010
City & State: Alberta
My Country: Canada
Posts: 2,474
Default Re: I need a charger schematic YLT6722000

The charger is pretty much at the max. for low cost architecture using a flyback converter for 135W. At this power level, the design has to be well done but this one is basic and low cost.

Under heavy load charging a battery, the transformer gets max duty cycle so both secondary windings will see the ringing and spikes at their worst.

The low voltage rail with D3 FR207 would get hot if the diode is slow and trying to switch off when the waveform is ringing, the diode will turn on and off many times during one pulse. When the diode is stuck on, slowwwwly turning off it will allow a -ve spike to flow through the 100uF 35V cap. LM358 can run to 36V but not handle -ve spikes. There's no other reason I think for it to heat up, how could it see a few A otherwise.

Main rectifier MUR1060 has R31//R32 4R7's with C7, as a snubber but R31 looks like dark splotch. If R31 is burnt, then this confirms the PSU has some design issues causing extra stress to the rectifiers. You would have to poke around with a scope to see if my guess is good.

R21 (27?) and R23 by U3 LM358 also look cooked, but maybe it's flux?

It could also be an the primary RCD snubber, as I see the usual 100V film cap there and they usually undersize the big resistor or use a crappy FR107 there.
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