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Please help need to fire relay with IC

  1. Aug 11, 2014 #1
    Hi guys I'm new here and need map some help. I have built a simple circuit with a cd4017 IC. The circuit works perfectly and has led connected to it. However I want to connect much larger load to it. A relay is the obvious answer but I'm not getting enough current from the IC to fire the relay. I tried using a triac but the triac latches and I'm led to believe that this is because it's a dc load, the relay. I'm stuck now any suggestions welcome please.
  2. jcsd
  3. Aug 11, 2014 #2


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    a transistor would be a better/easier way to go unless you were switching more that say 10A


    OK I have drawn this one ... still switching a LED
    The 2N3904 transistor will switch a couple of 100 mA

    choose a transistor rated for a current and load you want to switch

    for high currents, you could replace the LED and 1k resistor with a relay ... don't forget to add a reverse biased diode (1N4001) across the relay coil, else you will kill the transistor


    Attached Files:

  4. Aug 11, 2014 #3
    More often than not you will find that you have to turn things on in stages because the control IC doesn't provide enough current to drive the switching device. Davenn's suggestion is good. I just wanted to add that the reverse biased diode he mentioned is often called a "flyback diode" and it is sometimes included inside the relay itself. Check your datasheet for your relay to see if it has a diode.
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