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Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Recently I built this as an adjustable power supply for myself.
It works, but doesn't work.
I modified the schematic a bit and used a UCC3722x pair to drive a 1:1 gate drive transformer with a DC blocking cap.
The output of the KA7500 is a high duty cycle square wave, and adjusting the potentiometer doesn't change the output voltage at all. I used a 25 ohm 50 watt resistor as a load, and it gave out 31 volts with 170 v DC input. Not bad, but I wish it was adjustable. I AM using current limiting with three 60 watt light bulbs in parallel each with it's own switch... I noticed that when switching each one on, the voltage increased on the load. Is that normal? Does it need to not have current limiting to work properly? With no load, it stays at around 161 volts.
Any idea what I'm doing wrong? I couldn't figure out what inductor value to choose, so I went with a 100 uH inductor.
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
so you're using two drivers on one transistor? how come? powering the 555 off of the output via a resistor and zener seems weird when you've got a separate 15v supply already. you could try 'not' modifying the circuit lol
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Uh. I meant, without the stuff he used...
And it's because it needs a high side gate driver, which I don't have, but I do have 1:1 GDT's, so I used one of those instead. Basically, get rid of everything on the schematic, except the TL494, and the output stuff, and replace it with a UCC37221 and UCC37222 (inverting and non inverting input gate drivers) feeding a 1:1 GDT with a DC block cap.
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Buck Converter issues
