Every circuit diagram of a relaxation oscillator says I have to put a 100 ohm resistor between the capacitor and the voltage source like this:


simulate this circuit – Schematic created using CircuitLab

But I think it would be better to use an 1000 ohm resistor instead of a 100 ohm resistor. This would discharge the capacitor at a slower rate and give me a lower frequency.

What do you think?


simulate this circuit

  • \$\begingroup\$ What do I think? I think you should simulate it and see if your theory is correct :) \$\endgroup\$
    – user103380
    Commented May 9, 2020 at 15:43
  • \$\begingroup\$ CircuitLab is also a simulator. Try it and see what happens. \$\endgroup\$
    – JRE
    Commented May 9, 2020 at 17:13
  • \$\begingroup\$ @JRE Does it simulate for anyone? Or do they have to sign up at CircuitLab in order to gain that feature here? \$\endgroup\$
    – jonk
    Commented May 9, 2020 at 18:05
  • \$\begingroup\$ Jelly, you will need a negative dynamic resistance region for oscillation. The zener doesn't have one. A UJT or PUJT would do, though. You can look here for a more thorough discussion. \$\endgroup\$
    – jonk
    Commented May 9, 2020 at 18:09
  • 1
    \$\begingroup\$ @SpehroPefhany Thanks. And yes, it sounds like a bit of a pain. \$\endgroup\$
    – jonk
    Commented May 9, 2020 at 19:38

1 Answer 1


I presume your "Zener" K-A is actually something like the E-(B)-C pins of an NPN BJT.

Try this out in real life (I don't think this will simulate).

I think you'll find if you increase the resistor too much, the relaxation oscillator will be very relaxed indeed and will 'stick' after the first breakdown.


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