current controlled current source

Discussion in 'General Electronics Chat' started by talhaali, Jun 13, 2012.

  1. talhaali

    Thread Starter New Member

    Nov 24, 2011
    19
    0
    i need a circuit for current controlled current source , actually i have 2 operate relays through the pic microcontroller bt its current is to small as compared to the required current drawn by rellay , so i thought to make a curnt controlled current source that cud help, please tell me if this culd be done by some other way to, i,l b oblidged
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
    971
    A VERY common way to power relays or other devices that require more current than a micros outputs can supply is to drive a transistor with the micro pin and use that to switch on a secondary power source like shown in the attached pdf
    http://www.arduino.cc/playground/uploads/Main/relays.pdf
     
    talhaali likes this.
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,395
    1,607
    A switched voltage source may work better. Relays typically have a defined coil resistance so all you need do is give them their rated voltage and they control their own current. So all you would need is a transistor and a catch diode. Lots of references for those around.

    Your micro drives the transistor base thru a resistor, and the transistor switches the relay. This way the relay can run off a different voltage (higher or lower) then the micro does.
     
    talhaali likes this.
Loading...