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Measuring 140V DC on RA0 on a PIC Micro

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gavo4444

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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?
 
What are the resistor values?
 
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).
 
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?

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).

Like this:

OpAmp has to be capable of pulling its output pin close to 5V rail. You must use a "rail-to-rail" OpAmp.
 

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The only one that counts is the 100K. Look at the blue trace on my plot:D
 
do you know of any voltage regulator to operate at that voltage as well down to around +12V?

Do you want to convert 140VDC to 12VDC?
 
Make R2, 3k3, a standard value.
 
My resistors are getting very hot (100W resistors)
47K R1 and 1K for R2
If those really are 100W rated resistors (wow!) then you have something wired incorrectly.
 
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