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Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
I got bored waiting for a new power supply, so I thought I would make a temporary one. I cheated a little, as I'm using both the -12 and +12 rail, but its still fairly impressive for a cheap SMPS. I'm not sure how long it will live under a heavy load, but it seems to do ok with a 10 ohms for now. Unfortunately something managed to die in the time it took to take the picture, and I can't turn the voltage down anymore.... It seems to hit a peak at 25v on the 12v rail, because I can still turn the pot a little more, but the voltage doesn't increase. I increased the overvoltage shutdown voltage as well, in an attempt to give it a longer life span.
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
Nicely done! I am surprised you can draw as much as 5A from the -12 rail, since it is usually not rectified with a big schottky but just a bunch of small discrete diodes. What I did with my last mod was to completely redo the 5V line, leaving the 12V alone for the controller, and rewinding the 5V winding on the transformer for more. That also works pretty well, but of course you use regulation on the modded 5V line.
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
I haven't replaced any electrolytics yet, as there are over 5 of them, and I don't have any suitable replacements. I'll replace them as they blow. I've got another SMPS lying around, so I'll try a transformer mod this time. How long has your mod survived, Joe? And what kind of voltage did you get out of it? Modding the transformer is probably alot more stable than just tricking the PWM chip...
Registered Member #78
Joined: Thu Feb 09 2006, 11:27AM
Location: Sydney, Australia
Posts: 133
wow, i hope the psu doesn't die I modded one to provide 25V once, and it died soon afterwards with transistors shorted....so make sure you have a decent load on it at all times.
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
I've put a 10ohm load inside of it for testing. I'll have to add a load in series with whatever I'm powering from now on though, because the overvoltage circuit has been tuned and may not shut the PSU down in time.
Has anyone ever tried replacing/creating their own PWM before? It would be fun to experiment with... I've thought about removing the entire secondary side, and then try to drive the primary separately. I'll use a TL494 if I can solder one off or just a pair of 555s out of phase for the PWM. Don't smps' usually run at a frequency of 20-100 khz? What should I use to run the choppers?
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50v SMPS Mod
