Astable OP amp

239

03:59:29

The OP amp output charges the capacitor, but when it reaches the reference voltage it changes polarity and discharges it until it reaches the new voltage reference. A transistor uses this signal to switch on and off a bulb.

published 10 years ago

MattFerrie

10 years ago

How do you calculate frequency and duty cycle for this?

Victor805

10 years ago

To calculate the frequency you just calculate the time it takes for the voltage at the output to fill the capacitor with a current limited by the resistor connected in series with it. You can modify it by changing the reversal voltage changing the values at the voltage divider or just by changing the resistor or capacitor at the top. The more it takes for the capacitor to charge up the lower the frequency will be. The duty cycle seems to be 50% at all times unless you change the input voltages, I guess you could use a pair of diodes and a potentiometer to use it to generate a PWM signal by changing the rate at which the capacitor gets charged depending on the polarity ot the output voltage.

hurz

10 years ago

With this symmetric configuration the formula is f=0.455/RC ; R=10kOhm C=100nF. RC=1ms. Hope this helps

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