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| Thread ID: 56063 | 2005-03-26 06:19:00 | 13.8v regulated power supply from AT PSU? | george12 (7) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 338212 | 2005-03-28 03:35:00 | Cool, will do. Good old current limiting :). The feedback appears to be a small audio-type transformer. I need to experiment with loading up the 5v rail and see what happens to the 12v's regulation. It is just a small isolation transformer, no relation to audio types. Loading up the 5 volt rail won't do much for you either. Here's an idea, probably wouldn't work: If I load the 5v rail to the brim (well say 15a) then will it increase the pulse-width to compensate, upping the 12v rail? You are right, it wouldn't work, and you would have 75 watts of heat to dissipate. Besides, where would you get a 75 watt 0.33 ohm resistor that wouldn't want to glow in the dark? Why do you need 13.8 volts anyway, what is it going to power, and why is the voltage that critical? (Can't recall if you have posted details or not, is it to charge your batteries?) Cheers Billy 8-{) |
Billy T (70) | ||
| 338213 | 2005-03-28 05:29:00 | Yeah it's to keep the batteries charged while being safely on 24/ without overcharging. AND run the PC at the same time. Otherwise a little battery charger would be fine. Yeah, I'm gonna look at adding some turns GF. Thanks all. |
george12 (7) | ||
| 338214 | 2005-03-29 03:35:00 | In fact, the only supply in an AT PSU which is regulated is the 5V. That's the one that must be within 5%. The rest aren't critical. (ATX might regulate to 3.3V down from the 5V ... but the critical one (CPU) is adjusted on the motherboard). The others are "regulated" by the number of turns each have on the ferrite transformer. ;) If there is a trimmer potentiometer, you could probably adjust that so that the "5V" went up. The 12V will follow. But these days they probably just put fixed resistors. ;) You could check the data sheet for the regulator, and trace the circuit ... there's a voltage divider across the 5V supply, giving 1.2 or 1.3 volts to the comparator input of the chip when the 5V is right. It's a good idea to have a few amps load on the "12V", and measure across that. |
Graham L (2) | ||
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