Post by thread:[EE]: 12V Vehicle to 5V

Hello, I'm building a simple circuit that will be used in a (12 v) car. I'm planning to use a simple 7805 regulator. I have only read about the spikes that gets generated when the alternator starts up or shuts down. I thought of TVS, supression chips or MOVs, but have no experience with them. Has anybody done similar projects? Regards, Robert Francisco . -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> Hello, > > I'm building a simple circuit that will be used in a (12 v) car. I'm > planning to use a simple 7805 regulator. I have only read about the > spikes that gets generated when the alternator starts up or shuts down. > I thought of TVS, supression chips or MOVs, but have no experience with > them. Has anybody done similar projects? > > Regards, > > Robert Francisco I have here a circuit for a DGPS project. +12 goes thru a 1N4002 diode, 1/2A SB fuse, 1000uH choke to a 220uF 35V cap to ground and a P6KE20 transorb. That then goes to a LP2950ACZ-5.0 regulator which I think is designed for automotive use. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use spam_OUTlistservTakeThisOuTmitvma.mit.edu?body=SET%20PICList%20DIGEST

You just need a big enough filtering system to slow down / absorb all the electronic noise. Start with a big inductor - about 100 turns of insulated, solid wire around a bit of steel, all wrapped in insulation tape to hold it together; this will block and reflect most of the fast signals. Then add a BIG capacitor and a small capacitor; these can absorb slow signal and pass back to ground fast signals. Next a big fat diode to protect against reversed connections and a 10W low value resistor to set the maximum current into your whole circuit. Followed by a suitably rated zener to hold the input voltage steady around 9V. Follow these components with a conventional power supply regulation stage and you'll be safe. Of course these 6 components add considerably to the cost of your circuit. Some builders would leave various pieces out, but if you are a hobby builder then you'll probably want them in for the peace of mind. Bye. {Original Message removed}