Measuring 140V DC on RA0 on a PIC Micro

gavo4444 said:

Hi All, i am currently using a voltage divider to bring the voltage down from 140V DC to +5V on the pin of RA0 in a pic micro. My resistors are getting very hot (100W resistors). Is there perhaps another way of measuring 140V DC on a the pin of the micro?

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picbits said:

Use a high resistance voltage divider then use an opamp follower to buffer it to an impedance the PIC A2D likes (around 2k load on opamp output).

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gavo4444 said:

Hi Mike

Many Thanks what would be the divider resistor wattages?

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gavo4444 said:

i will then put both a 5W then it should run cool

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gavo4444 said:

do you know of any voltage regulator to operate at that voltage as well down to around +12V?

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Bob Thomas said:

Use R1 180k and R2 1.2 k. Add 220k series resistor at A/D input.

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Microchip Datasheet said:

The
maximum recommended impedance for analog
sources is 2.5 kΩ.

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My resistors are getting very hot (100W resistors)

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47K R1 and 1K for R2

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