Where this peak of 200mA comming from. A 5 volt driven siren?
In car application where, at least, alternator inject a huge amount of noise in the 12Volt line, i would suggest a rc or LC filter. But even 1000 uF and up should work great... plus the 10uF tantalum + 0.1 uF.
Some use 47Uf electrolytic but they're far to be as efficient as tantalum are.
....the car battery is going straight to the regulator, can this damage the regulator?
No this is why they're made for. But my biggest concern will be about the quiescent current of your regulator. The one you suggest need 5-6 ma all the time. It's not too bad but be sure your PIC is most of the time in sleep mode and your external hardware don't add too much in the current need.
10mA is still fair for a car battery, but you really should reduce it. 78L05 will need less quiescent current BUT is really limited in current drive.
There's some other linear regulator who need less quiescent current but can drive more mA. LP2960 is a great one, widely use by myself, seems to be great as now.
Tell us more about your circuit and we will come up with a better solution.
Last edited by mister_e; - 20th May 2006 at 17:17.
Steve
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