Electronics Principles V11

Clive W. Humphris

OP-AMP APPLICATIONS: Voltage Oscillator.  

In this circuit we show the Op-Amp connected as an oscillator. In a practical circuit it would produce a continuous output waveform. R4 provides a feedback path to the inverted input and R5 to the non-inverted input. C1 begins to charge via R4, the (+) input has a fixed potential of 4V due to the potential divider R1 and R2 in parallel R3.

As the voltage across C1 rises (producing the upward part of the triangular wave shape) above 4V the Op-Amp output falls due to the phase inversion. A triangular waveshape is really a small part (straighter bit at the beginning) of an exponential waveform which is then amplified.

This discharges C1 (producing the downward part of the triangular waveform) via R4, towards this now lower potential at the Op-Amp output. Also the voltage on the (+) input falls as it now has three 100kohm resistors connected in parallel across its input.

This forces the Op-Amp to conduct for longer by maintaining the potential difference between the inputs as the (-) falls due to C1 discharging. Note: the phase inversion between the input and output waveforms.

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