#336 Comparator-based Relaxation Oscillator

Test a classic comparator-based relaxation oscillator, modified for single-supply LM358 OpAmp.

Notes

The comparator-based relaxation oscillator is similar to the astable opamp oscillator - see LEAP#039 - but is a more straight-forward and symmetrical circuit, one that is easy to intuit.

Rather than use dual (+/-) supply, I’m using a voltage divider and buffer to provide a half-supply reference.

The theoretical frequency f = 1/(2ln(3)RC)

I tried a few combinations, and performance was remarkably close to the theory:

Here’s the 100kΩ/100nF combo on the scope. Channels connected per the schematic, clearly showing the hysteresis of the capacitor charging curve as it battles the positive feedback.

Construction

Credits and References

• Comparator–based relaxation oscillator - wikipedia
• LEAP#039 AstableOpamp - astable opamp oscillator
• LM358N Datasheet
• ..as mentioned on my blog