forget it. the 7812 is a linear regulator. you can compare this to a resistor based voltage control, where the voltage above 12v is converted to heat. it's almost the same, but regulated. if you neet 24v, you will need a switch mode psu, or to get it easier, take a dc/dc converter. tino Tim ODriscoll Gesendet von: pic microcontroller discussion list 15.08.2003 13:11 Bitte antworten an pic microcontroller discussion list An: PICLIST@MITVMA.MIT.EDU Kopie: Thema: [EE:] 24vdc from a 15vdc psu Hi Everyone, I've got an awkward device that needs 24vdc in a 12vdc environment. I'm planning on using an unregulated 15v psu and then an lm7812 for the 12v side. Reason being that unregulated 15v psu's seem to be cheaper than their regulated 12v counterparts. Is there a cunning way I can rig up (say) 2x lm7812's from the same 15v supply to give me a regulated 24v? I was thinking of using a -12v regulator to feed the ground pin of the +12v regulator (whose input would be +15v).. Or would I just see a flash and lots of magic smoke escaping? I know it's a bad idea to use regulators in parallel, but I've not found any notes on hooking them up in series... Cheers, Tim -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads