At 07:01 AM 11/20/2011, Gordon Williams wrote: >Hi, > >I have to create at dual power supply from batteries: > >5V @ 500 mA >12V @ 250 mA > >I going to be using 2, 6 Volt 5Ahr sealed lead acid batteries and I'm >wondering if it is more efficient/ better to connect them in series or >parallel. Why does the 12V supply need to be regulated? If its lamps or relays=20 or motors or some such, you may be able to run the 12V load from the=20 nominal 12V that you get from your batteries connected in series. Its then easy to use an inexpensive switcher to generate the 5V from=20 your 12V rail. There are other advantages: you can easily charge your 12V SLA=20 batteries in your vehicle (needs only a low-value current-limit resistor). Bottom line: it is rare that a 12V load need to see 12.0Vdc. Its way=20 more common for a 12V load to be happy with somewhere between 11.5V -=20 14.5V, which happens to be the normal operating voltage range of 12V=20 lead-acid batteries. As far as switchers goes - I'm really partial to the National=20 Semiconductor Simple Switcher series - I still tend to use the old=20 LM257x family just because of familiarity and having good inventory=20 of the inductors that they need. That said: I regularly see really=20 low cost, tiny, board-level switchers on eBay that cost way less than=20 what the parts would cost me to purchase and assemble. I've=20 purchased some of those and they, too, use the same NS Simple=20 Switchers that I like so much. dwayne --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .