- #1
dustinthewind
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I am currently trying to measure an 80pF capacitor using 2 voltage follower op amps. I have them both powered by a set of 2 1.25V rechargable batteries. They are op amp type LMP7721 link: http://www.ti.com/product/lmp7721 .
Each op amp is configured such that the voltage out terminal [end of the triangle] is connected by wire directly to the negative in therminal [voltage follower configuration]. The positive in terminal on each LMP7721 is connected respectively to 1 plate of the capacitor.
A keithly 182 volt meter is conected across each output terminal on the op amp to measure the difference in voltage.
As a test to see if they measure voltage correctly I put a battery across the plates in which I have already measured the voltage to be 1.25V. However only -0.98 shows one way and 1.02 volts shows the other way.
any idea why I am not measuring the 1.25V difference in voltage between the outputs of the op amps? No resistors are involved.
[I have also noticed when I test each voltage follower using a variable voltage (adjustable resistor) they seem to follow the voltage fine. However they will only drop to a minimal voltage of 9mV and 16mV respectively.]
I am also wondering why the voltage followers won't drop to zero volts individually wen I test them to see if they follow voltage.
Each op amp is configured such that the voltage out terminal [end of the triangle] is connected by wire directly to the negative in therminal [voltage follower configuration]. The positive in terminal on each LMP7721 is connected respectively to 1 plate of the capacitor.
A keithly 182 volt meter is conected across each output terminal on the op amp to measure the difference in voltage.
As a test to see if they measure voltage correctly I put a battery across the plates in which I have already measured the voltage to be 1.25V. However only -0.98 shows one way and 1.02 volts shows the other way.
any idea why I am not measuring the 1.25V difference in voltage between the outputs of the op amps? No resistors are involved.
[I have also noticed when I test each voltage follower using a variable voltage (adjustable resistor) they seem to follow the voltage fine. However they will only drop to a minimal voltage of 9mV and 16mV respectively.]
I am also wondering why the voltage followers won't drop to zero volts individually wen I test them to see if they follow voltage.