filtering circuit for automotive pic supply

One upside of PICs is they will run on as low as 2V, so LDO isn't really all that important unlike protection from transients/surges. Even if your car battery drops way low and the PIC receives 4V instead of 5 it'll still run. Now other circuits tied to the PIC that rely on a stable voltage would be affected...

kpatz said:

One upside of PICs is they will run on as low as 2V, so LDO isn't really all that important unlike protection from transients/surges. Even if your car battery drops way low and the PIC receives 4V instead of 5 it'll still run. Now other circuits tied to the PIC that rely on a stable voltage would be affected...

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the problem there is that if its a 78L05 5 V reg and the voltage gets to 7 then you will get an output of 7 ! also i use the supply as a ADC reference

Thunderchild said:

the problem there is that if its a 78L05 5 V reg and the voltage gets to 7 then you will get an output of 7 ! also i use the supply as a ADC reference

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A regulator's dropout voltage determines the lowest usable supply voltage. The datasheet for the 78L05 show a dropout of 1.7V. As long as the input voltage is above 6.7V the output will be a regulated 5V.

So at 7V you would have regulated 5V on Vout.

I confused the issue by talking about tracking regulators. They will be of no use if you need a Vref based on the regulator. If you could use a Vref of about 1/2 of the regulator Vout (maybe a zener or a dedicated ref chip) then a tracking regulator would allow circuit operation below the regulated voltage.

3v0

well thats all very ingenious and useful but aparantly the battery will not go below 6 V anyway and if it does its knackered, but its an interesting possibility