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Measuring 140V DC on RA0 on a PIC Micro

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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?
 

MikeMl

Well-Known Member
Most Helpful Member
What are the resistor values?
 

picbits

Well-Known Member
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).
 

MikeMl

Well-Known Member
Most Helpful 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?

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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MikeMl

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The only one that counts is the 100K. Look at the blue trace on my plot:D
 

MikeMl

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MikeMl

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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?
 

Hero999

Banned
Make R2, 3k3, a standard value.
 

alec_t

Well-Known Member
Most Helpful Member
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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