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filtering circuit for automotive pic supply

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kpatz

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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...
 

Thunderchild

New Member
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...
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
 

3v0

Coop Build Coordinator
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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
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
 
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Thunderchild

New Member
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
 
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