The toggle circuit below works well, but I noticed that there will be current spike when the switch is closed, i.e., when switch is closed, the two caps will charge each other without resistor in between, the energy is small, but current will spike.

Is it necessary to add a 1k resistor between the 0.01uF cap and the ground?

Or is the 0.01uF cap redundant and can be removed? (I assumed it is added to ensure the toggle is on OFF state when power on, but seems not really needed).

enter image description here


  • \$\begingroup\$ That 0.01uF capacitor is probably for decoupling purposes. \$\endgroup\$
    – user103380
    Jul 3, 2017 at 4:46
  • \$\begingroup\$ Where are you detecting the current spike and how are you measuring it? \$\endgroup\$
    – Transistor
    Jul 3, 2017 at 7:19
  • \$\begingroup\$ Good question, I can only measure the the voltage step change across the cap (0.01uF), just theoretically assume Ohm's law still applies in this case. \$\endgroup\$
    – starx
    Jul 3, 2017 at 13:03

1 Answer 1


Just add a small resistor like 82 or 100 ohms in series with the switch. The small resistor will limit the current flow spike that would occur when the switch is initially closed. Select the resistor size do the current surge is controlled but at the same time not having much effect on the normal behavior of the circuit.

  • 3
    \$\begingroup\$ Hi @Michael can you also explain how you arrived at this logical deduction so that it will be useful for other members as well. \$\endgroup\$
    – Mayank
    Jul 3, 2017 at 5:05

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.