Measuring 140V DC on RA0 on a PIC Micro

G

gavo4444

New Member
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).
 

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).
Click to expand...

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
 
gavo4444 said:
do you know of any voltage regulator to operate at that voltage as well down to around +12V?
Click to expand...

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