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Created | April 07, 2016 |
Last modified | April 08, 2016 |
Tags | astable-multivibrator op-amp oscillator relaxation-oscillator |
A simple op-amp circuit for generating square(-ish) waves
Also known as a "relaxation oscillator" and/or "astable multivibrator."
R1 & R2 together make a kind of Schmitt Trigger (https://www.circuitlab.com/circuit/6yu89x/schmitt-trigger/) for flip-flopping the output. These in conjunction with R & C set the timescale for the charging & discharging which in turn sets the period of the oscillation.
This period is T = 2RC ln( (1+a)/(1-a) ), where a = R1/(R1+R2)
Interesting choices:
R1 = R2 means a = 1/2 and thus T = 2 RC ln(3). And ln(3) = 1.098..which is close to 1, so T = approx 2RC.
2*ln((1+a)/(1-a)) = 1, which gives a = (sqrt(e)-1)/(sqrt(e)+1) = about 0.24. So choose R1 to be roughly R2/3. Then T = approx RC.
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