Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Driving relay with low current

  1. Mar 3, 2010 #1
    Hey. I am trying to use a single quick pulse of about 2.5 mA to run a latching relay. I know that this signal needs to be amplified (probably with a transistor) but am unfamiliar on how to do this.

    Thanks for the help,

  2. jcsd
  3. Mar 4, 2010 #2
    Here is a relay driver. The diode in this circuit is used to protect the transistor from high voltage that is being induced by the relay coil.

    http://www.vlearnvshare.com/home/images/articles/NPN-DRIVER1.GIF [Broken]
    Last edited by a moderator: May 4, 2017
  4. Mar 5, 2010 #3
    If the relay current is over 50 milliamps, you should use a Darlington transistor, such as the TIP120 (available at Radioshack) or equivalent. See datasheet


    The current gain at saturation is ~250. You should also have a 10k resistor from the data input to ground.

    Bob S
  5. Mar 6, 2010 #4
    Thanks for the help. I'm going to get the parts today so I'll let you know.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook