Minimum switch current

Discussion in 'General Electronics Chat' started by jpanhalt, Feb 22, 2008.

  1. jpanhalt

    Thread Starter Expert

    Jan 18, 2008
    Is there a minimum switch current to ensure reliable switching for toggle and push button switches?

    I am thinking of using a switch in a delay circuit with a comparator. The more current I design for, the bigger the capacitor I will need. Since the target delay is 0.5 to 1 sec. the capacitor size is not trivial on an SMD PCB with a 1 mA current. Put another way, any opinions on whether a 100 uA current is too low for a mechanical switch.

    Some relay specifications give a minimum current, but I could not find such a specification for the toggle switches (CK, E-Switch, Tyco) I reviewed. My thinking is that switches have a different mechanical action that might lead to much lower minimum currents.

    Thanks. John
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    There is no minimum current that has to flow through the contacts on a switch. The significant figure is the contact resistance, typically in milliohms. If there is a difference in potential, current will pass through the switch.
  3. Audioguru


    Dec 20, 2007
    A low current or no current switch has gold-plated contacts. They have a max power rating of about 2W. They are called a DRY contact. they cost the same or slightly more than silver plated contacts. I use them as audio switches.

    Silver contacts tarnish and don't work at low or no currents. They rely on a high power spark to burn away the tarnish.
  4. jpanhalt

    Thread Starter Expert

    Jan 18, 2008
    Thanks for the great advice. I will use a switch with gold contacts. What gave me pause was the datasheet for some Tyco relays:

    Contact Data
    Arrangements: 1 Form A (SPST-NO) Wiring Diagram Code 1, 2,3.
    2 Form A (DPST-NO) Wiring Diagram Code 5.
    1 Form C (SPDT) Wiring Diagram Code 1, 2, 3.
    2 Form C (DPDT) Wiring Diagram Code 5.
    Material: Silver-nickel 90/10.
    Minimum Load: 12V/100mA.
    Expected Mechanical Life: 10 million operations.
    Initial Contact Resistance: 100 milliohms max @ 1A 12VDC.

    When I saw that minimum load, I thought I would never be able to match that. So, it started me wondering if there was a similar minimum for switches.

    A 100K resistor at 12V into 10 uF will do just fine and still have some current. John
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    Some switches have a wiping action which prevents build-up of oxidation. Have a look at this blurb from Carling. Search for "wiping".