Wednesday, 22 March 2017

current - Reasons for a voltage follower introducing voltage gain?


I'm using a 3130 op-amp as a voltage follower (unity gain buffer amplifier). However it is introducing voltage gain.


It is wired the following way:


Circuit Schematic


This is then just fed into a simple low pass RC circuit (R= 2k-10kΩ, C=0.5 μF).


With +Vcc @ +12V and -Vcc @ -12V, I get the following:


Vin ~ -0.4 VDC, Vout ~ 8 VDC


With +Vcc @ +5V and -Vcc @ -5V, I get the following:


Vin ~ -0.4 VDC, Vout ~ 3 VDC


What can cause voltage gain when using an op-amp as a voltage follower?



------------Edit 17-7-15---------------------


I tried a 741 op amp wired the same as above which is unity gain stable and I am still noticing a small voltage gain when supply voltage is +/-5V. input is -0.41V and output is +1.04V. However when supply voltage is +/- 12V there is no voltage gain. I dont see how this can occur, as the 741 op amp is supposed to be unity gain stable.



Answer



The amplifier CA3130 is NOT unity gain stable. That means: For 100% feedback the unit will oscillate - mostly with amplitudes reachning the power rails. Follow the data sheet recommendations and use a compensation capacitor (>47 pF).


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