Mechanical switches suffer from vibration when the contact position changes. For push buttons this means that we need to wait for a while before we read the final value of the button. There are different techniques to do this.

Now lets come to mechanical switch being used as On/Off switch. This could be a slide switch that has a lever or a push down switch that latches its state. In both cases there will be vibration. This brings me to my questions:

  1. Do the power mechanical switches need to be filtered in some way since their output will cause the voltage regulators to see a vibrating input when the switch changes state?
  2. If (1) is true, how should this oscillation be minimized or completely mitigated?


Used as on/off switch for FPGA/CPLD/MCU board that contains multiple voltage rails generated by switching and linear regulators. Maximum current 1A. Input range is 12-18V. Several rails are generated from this 5V, 3.3V, 2.5V, 1.8V.

  • \$\begingroup\$ Used as on/off switch for what? Voltage and amps being switched are important, and the type of load as well. \$\endgroup\$
    – Justme
    Jul 1, 2023 at 21:36

1 Answer 1

  1. Usually no. I don't think I've ever seen any FPGA/CPLD/MCU or other dev boards or consumer products implemeting any filtering due to power switch contact bounce. Not on their low-voltage DC input.

Some products switch the power directly with the switch.

Some products switch a control signal which turns on a transistor or regulator to power up the device.

  1. No special measures need to be taken, if the switch is rated to make, break, and pass the rated current at the rated voltages, including any inrush surge currents to charge capacitors when making a connection, and kickback voltage caused by breaking current of an inductive load.
  • \$\begingroup\$ I saw a few schematics and found nothing as well. Some of the schematics for FPGA/CPLD boards had no switch on the PCB. Others did have one. However, I found nothing to apply any filtering affect as such. This is confusing because I know that mechanical switch does bounce and an oscillating input into any electronic component is not a good thing. \$\endgroup\$
    – quantum231
    Jul 1, 2023 at 22:33
  • 1
    \$\begingroup\$ Not entirely correct. The regulator input itself would not care about contact bounce much, and similarly, the FPGA or MCU input circuitry would usually not care much about bouncy signal either. What matters is what the signal is used for in the FPGA logic, for example, you can't count how many times user has pushed the button if the signal bounces. Sure the regulator output would bounce too, but any chip or board should handle slight glitches during power-on, as these generally have a power-on reset circuitry built-in or external monitor chip which releases chip reset when supplies are stable. \$\endgroup\$
    – Justme
    Jul 1, 2023 at 22:58

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