Hmmm. IIRC, 78xx series regulators have a 3V or so Dropout voltage; You cannot use one to regulate 14V to 12V. (Also do want to watch the upper voltage limit!) If you put a carefully picked power resistor from car power, to a small local (motorcycle or gel cell) battery, then regulate down off that with an LM2941 or other fairly Low Dropout regulator, most any battery problems become sort of irrelevant (Can anyone tell I have quite a few gel cells here? ) A diode in series with that is a GOOD idea, unless you cart the whole deal off when not using it (You don't want to drain the small cell when starting the car.) The small battery will charge on high car power system voltages, acting like one heck of a power Zener diode, pick the series resistor to have a 1 volt drop or so at the desired load current into the camera. (BGMicro sells 4500mAh Gel Cells for $6.95, might have 17000mAh cells for the same price still.) Learn about Gel Cell charging first, of course, if you use one For safety: fuse the battery, close to the + terminal as you can manage that - Under the 1/4" terminal if you can manage it. Duct tape the lot for safety, afterwards. (Digikey sells polyswitches, made by RayChem, 86 cents or so, pp 536-537 in their current catalog. I'm migrating to those from regular fuses.) If you expect to recharge that battery harder than the fuse will like, parallel a power diode across the polyswitch, it'll at least charge slowly then while the polyswitch is open. Maybe use a Schottky, due to lower voltage drop ) If you want to get "fancy", a switcher is probably a "better" answer, so long as you somehow handle the possibility of power supply disconnection - that's why I tend to use a battery. I've done some field research where we drove around with 8 or so devices, all sucking power off the 12V accessory power socket. We found the power connector'd fall part way out quite regularly, thus the battery - AND, the electrical tape we used to get it down to just falling out every few days, not daily Or, just use a "spare" small deep-cycle battery, recharge it as needed etc. So many "good", working answers... Mark Larry G. Nelson Sr. wrote: > If you are just using the battery then no problem. If the car is running > when you are using this it is another story entirely. The specs allow for > some surges that are very bad news. I bought a cheap inverter and get 110 > VAC which I then feed to the standard wall supply brick. Works for > computers and saves expense of buying power supplies or the hassle of > building something. > If you really want to build something you want to block, swamp, and absorb > spikes and surges to protect your equipment. A 7812 will NOT reliably do > the job for you. > > At 12:53 AM 3/15/00 -0500, you wrote: > >Of course it is, you just need to know the camera current consume at > >12V, so it will be easy to calculate the 12V regulator. If you can > >ensure the battery will be at least 13V (1V above the 12), then it is > >easy to produce a transistor series regulator. If the battery will stay > >around 14V constantly, then probably 3 "robust current" diodes in series > >will drop the voltage to the camera to aprox 12.1V... you just need to > >know the camera current consume. > > > >Wagner > > > >Tony Nixon wrote: > >> > >> Hi all, > >> > >> Does anyone know if it's possible to regulate a car battery supply > >> (usually 14V) to 12V. The video camera I am using expects a 12V 5% > >> supply, but I need to regulate the power to it from a car battery which > >> will be fully charged when used. > >> > >> -- > >> Best regards > >> > >> Tony > >> > >> http://www.picnpoke.com > >> mailto:sales@picnpoke.com > > > > > Larry G. Nelson Sr. > mailto:L.Nelson@ieee.org > http://www.ultranet.com/~nr -- I re-ship for small US & overseas businesses, world-wide. (For private individuals at cost; ask.)