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Adjusting output voltage of DELL brick
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elektrinis:
So I have a "slim" 130W 19.5V DELL brick that I want to adjust to 24V.
I have identified a feedback circuit and a resistor divider which sets the voltage. It is very primitive and should work... However I am unable to go past 21V - it switches off after a split second if higher voltage is specified.
I had a deeper look and could not find anything else on secondary, so there must be some kind of protection on primary side?
Looking for some advice from those who had some experience... Thanks.
amyk:
The output caps are probably rated for 25V, and 24V is a bit too close for comfort.

You'll need to post some more details about the circuit (e.g. type of IC used, partial schematic, etc.) if you want more information.
Hydron:
If it's using a flyback topology then it's possible to determine the output voltage from the primary side by measuring the waveform on the transformer/inductor. The supply is probably doing this for over voltage protection in addition to the secondary side sending.
wraper:
There might be an auxiliary winding used for powering SMPS controller. There is no simple mod in that case.
elektrinis:
Here are some photos.





Primary driver is LTA804N.
On a closer look (after blobs were removed), I have also inspected an SO8 chip LTA806N, which I could not identify. Initially I thought it is a device ID chip and did not consider it, just disconnected it's power. That, however, did not do anything. It is connected to an extra secondary winding and so far I can't find a link to feedback circuit or how it could do what it's doing.
Need your input on this... Thanks.

P.S. Yes, caps are 25V. I want to push my luck on this one.
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