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Computer driven relays

  1. Sep 1, 2010 #1
    I need to drive some switches which require 28V and sink about 200ma of current. What's my cheapest option? build something or buy some dac?
  2. jcsd
  3. Sep 1, 2010 #2
    You could use npn open collector transistors with a Vceo rating > 30 volts (reverse diode protected) and a current rating of >500 milliamps. 2N2222A (MPS2222A) will work, or TIP120 (Darlington) in TO-220 pkg. You can drive these with any 5-volt voltage source.

    Bob S
  4. Sep 1, 2010 #3


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    Science Advisor

    You would need something like this:

    [PLAIN]http://dl.dropbox.com/u/4222062/relay%20driver.JPG [Broken]

    R is a resistor which limits the current into the base of a small power transistor. You supply a control voltage at the left of this resistor.

    This switches a suitable relay. These are available in different coil voltage and contact ratings.

    The diode shown across the relay coil is to avoid damage to the transistor when the relay coil is switched on and off.
    Last edited by a moderator: May 4, 2017
  5. Sep 2, 2010 #4
    thanks guys!
  6. Sep 2, 2010 #5
    simplest option turned out to be just one 2N2222A - works great!

    thanks Bob.
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