So I found this Geiger counter at https://mightyohm.com/blog/products/geiger-counter/. You can also find the detailed electronic schematics there. I tried to figure out how this apparatus works, but I'm stuck with the boost converter and the timer to create the PWM signal. Can someone explain?

enter image description here

Because it's not the typical 555 timer setup for an astable multivibrator. I don't get how the frequency and duty cycle of the PWM signal is setup. It boost up 3 V input to 400 V output.

Thank you!

  • 3
    \$\begingroup\$ It's not a great circuit - it won't have great stabilization on the output voltage because it relies on the load current to be constant. Don't use it is my opinion. Off-load it could be a thousand volts. \$\endgroup\$
    – Andy aka
    Aug 5, 2020 at 8:44

1 Answer 1


how it works:

current builds up in the inductor until it's enough to turn Q3 on this activate the 555's ~RESET turning off the 555 out and turning off Q1, the 555 discharge pin is used to turn the Q1 off rapidly, this helps produce the hiogh voltage.

C3 now discharges through R3 until the voltage on TRIG is low enough to turn the 555 output back on.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.