// Disclaimer: I am acutely aware that what I am trying to achieve can be had in a smaller and safer package for under 10 €. That, however, does not include any learned experience, nor does it reduce my hoard of power supplies (nor does it include lethal danger, but for now, let us pretend that I'm suicidal). Thank you for attention.
With that said, the situation: I am trying to coerce an ATX power supply into outputting a higher voltage. Given that it's a typical DBL494 affair, the textbook method of duty cycle adjustment has already been applied - adjusting the voltage divider at pin 1, and 4.7 kΩ pulldown from pin 4 to ground for minimum deadtime to disable OVP. (I tried to modify it for higher voltage first. Spent the better part of a day tracing out what connected to the deadtime pin, before getting lost in the circuit jungle. Still didn't find a connection to any of the voltage rails) This works, but at 16 V the supply starts emitting a noticeable chirping sound, which I guess I should take as a no. Alright, onto the transformer. I desoldered it to bet a better look and realised that Ihave no idea how the secondaries are wired. Until then, I was under the impression that 12V is a regular centre-tapped winding (judging by the two-diode rectification) and 5V/3.3V are something more exotic (judging by the PCB). What's visible with XFMR off the board seems to suggest otherwise - the fat 0V wire coming out the top consosts of 8 strands. Unfortunately, I can't properly figure out what is between them and XFMR's secondary pins due to the low DC resistance - a DMM can't tell if it's an actual short or a winding. Thus I can't tell, whether it might be possible to, say, connect the 5V and 12V windings in series, or where do I put extra windings if that's a better way.
Even if this is impossible without blowing up parts on the secodary side (I've upgraded the electrolytics to higher voltage rated ones, but nothing else) I'd still be grateful for an answer on how that transformer is laid out - for curiosity, if nothing else. Or a method for finding that out - I was thinking a signal generator with a resistor in series, then watch the voltage drop over the resistor - sensible? No?
Oh, and the target voltage is 17-19V, for powering a laptop motherboard. Tried giving it 12V through the battery inputs, wouldn't take. Since the original battery is long gone, I assume it would be pretty hard to simulate battery's responses with a microcontroller.
With that said, the situation: I am trying to coerce an ATX power supply into outputting a higher voltage. Given that it's a typical DBL494 affair, the textbook method of duty cycle adjustment has already been applied - adjusting the voltage divider at pin 1, and 4.7 kΩ pulldown from pin 4 to ground for minimum deadtime to disable OVP. (I tried to modify it for higher voltage first. Spent the better part of a day tracing out what connected to the deadtime pin, before getting lost in the circuit jungle. Still didn't find a connection to any of the voltage rails) This works, but at 16 V the supply starts emitting a noticeable chirping sound, which I guess I should take as a no. Alright, onto the transformer. I desoldered it to bet a better look and realised that Ihave no idea how the secondaries are wired. Until then, I was under the impression that 12V is a regular centre-tapped winding (judging by the two-diode rectification) and 5V/3.3V are something more exotic (judging by the PCB). What's visible with XFMR off the board seems to suggest otherwise - the fat 0V wire coming out the top consosts of 8 strands. Unfortunately, I can't properly figure out what is between them and XFMR's secondary pins due to the low DC resistance - a DMM can't tell if it's an actual short or a winding. Thus I can't tell, whether it might be possible to, say, connect the 5V and 12V windings in series, or where do I put extra windings if that's a better way.
Even if this is impossible without blowing up parts on the secodary side (I've upgraded the electrolytics to higher voltage rated ones, but nothing else) I'd still be grateful for an answer on how that transformer is laid out - for curiosity, if nothing else. Or a method for finding that out - I was thinking a signal generator with a resistor in series, then watch the voltage drop over the resistor - sensible? No?
Oh, and the target voltage is 17-19V, for powering a laptop motherboard. Tried giving it 12V through the battery inputs, wouldn't take. Since the original battery is long gone, I assume it would be pretty hard to simulate battery's responses with a microcontroller.
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