> OK, here I go, biting off more than I probably can chew again, for a one > off home project... > > I want to build a high current PC power supply, but it has to run from > an automotive electrical system. The board I am am going to use has a > hard drive connector on it, so I don't have to make a negative supply > (thank goodness) but I want it capable of supplying at least 5A at both > 5 and 12 volts. This is a repost of a message from Steve Smith. Will give you some good ideas. RM ________________________________ From: "Steve Smith" To: Sent: Tuesday, February 17, 2004 9:04 AM Subject: Re: [PICLIST] [EE]: Boost & Buck regulator in one? > I have used this circuit for years 3843 fed from the output with a > bootstrap startup circuit its input voltage span is from 4v to just > under 400v gives 24v output at about 30W the only thing you have to > remember is that the fet carries both the primary and secondary current > so must be sized for high Vds and a very low on resistance so it doesn't > get too hot when its stepping up from 4-5v. basic circuit (very poor > ascii art > > ------------L1------------C1-----D1>|------- Vout > | | | > D L2 | > G | | > S | C2 > | | | > R1 | | > | | | > --------------------------------------------- 0v > > L1=L2 can be almost any value we use 680uh ETD25 3f3 core > FET IRF740 AFI > R1 0r33 > C1 mkp22 0.22 / 400v > D1 D4L40U > C2 220/35 LXFVB > > Input cap (not shown 47/400 and .22 mkp22 > Set the 3843 to operate at about 100khz and feed it from the output > (look up UC38xx there are 4 versions there is a low voltage start (8v) > and a higher voltage one (12v) and use the one that works with your > output voltage if there is a very high voltage input >150 the start > circuit needs special attention chip needs about 1mA to get it going > then it self powers from the output > > Regards Steve... -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu