# Voltage Divider help

Discussion in 'General Electronics Discussion' started by Abidethedude, Sep 10, 2012.

1. ### Abidethedude

7
0
Aug 31, 2012
Hi guys, I'm trying to have a 2V DC coming from a 5V supply using a simple voltage divider to feed into a summing op amp.

However, I'm not getting the results. I thought essentially the following pictures were ideally the same:

http://i.imgur.com/SbOR1.png (Voltage Divider with 2V output)

http://i.imgur.com/qfDOd.png (DC Power Source of 2V)

When I hook up with the voltage divider into the op amp, this is the result:

http://i.imgur.com/ytpbH.png

Basically, I just want to feed 2V DC into the op amp.

For those who are wondering, the "IN" pin has an AC Signal going through

Any response will be greatly appreciated!

2. ### Laplace

1,252
184
Apr 4, 2010
Maybe it would be instructive to consider why meter XMM3 is reading 1.539 volts in the third circuit. The 'In' terminal has an AC voltage source applied but for purposes of DC biasing the 'In' terminal is at DC ground. So R2 and R5 together form a 20K resistance in parallel with R8. (10K || 20K = 6.667K)

The voltage divider with R12 gives 5x(6.667/(6.667+15))=1.539 volts. If you want to feed 2V into the op amp then you could either decrease R12 or else buffer the R12/R8 voltage divider with a voltage follower.