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[SOLVED] Op-Amp voltage follower as a buffer

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Manie Serrao

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I have built a standard voltage follower as a buffer between a triangle wave generator and PWModulator all built using the basic 741 chips and sharing a common single 12v supply. I have aways believed that an op-amp with neg. feedback, terminal 2 (Inv), irrespective of the voltage applied to terminall 3 (non-inv) will always tend to take up the voltage of terminal 3.
My problem is that the input signal to V Follower is 5.3V p-p (+0.7v to +6v) but the output swings between +2v and +6v, perfectly in phase and peaking at 6v simultaneously, irrespective if I connect or disconnect its output from the PWM's input.
Help please,what am I missing here....I would expect there to be a small differential input voltage between terminals 2 & 3 but not 1.3v at its extremes during the 1st and last part of each 4 second cycle
 

You may check the max. output swing vs (Vcc - Vss), for examples, you cannot get an output of +6V if your +ve supply is +6V; have a look on the datasheet of the OPAMP.
 

Hi, Thanks for the help but the supply is 12v, how come at the beginning of each cycle a differential input voltage about 1.3v exists then there is 0 differential voltage during the middle part of the cycle and appears again at the end of the cycle
 

Read the the LM741 datasheet thoroughly, particularly about input voltage range. You'll need a negative suppply voltage for an input voltage range downto 0.7 V, or an OP type suited for single supply operation, e.g. LM324.
 
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