Activating a Relay with the aid of a transistor

Discussion in 'The Projects Forum' started by kneesee, Oct 1, 2010.

  1. kneesee

    Thread Starter New Member

    Oct 1, 2010
    2
    0
    I am currently working on a special application using a SICK sensor that when the beam is broken is suppose to trigger a 24vdc relay. My problem is that when the beam is broken I get the 24vdc on the wires but when I connect the wires to the relay it drops voltages to around 2vdc and relay of course does not operate. The negative is straight from the power source. The positive is what is being switched by the SICK sensor.

    -The sensor can provide a positive or negative trigger (Currently using the positive).
    -The voltage with the beam intact is .634 vdc

    I was thinking that I will need some sort of transitor to increase the current. Does this make sense?

    If there is an easier way to get this to work please let me know.

    Thanks In Advance,
    Mike
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    Do you have a datasheet of the sensor?
    This will provide more info on the possibilities.

    Bertus
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    done all the time with microprocessors that can typically only provide enough current for a transistor operation but not enough for a relay. The micro switches the transistor which energizes the relay.
     
  4. lihle

    Active Member

    Apr 12, 2009
    83
    3
    according to my knowledge . if you are using a micro controller you can turn transistor (most preferably a darlington pair) with high current gain. when the sensor detects something the transistor will be turned on and then turn the 24V Dc relay. make sure you include a protecting diode in front of the relay.

    lihle
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    A transistor will do the job.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    [​IMG]
     
    kneesee likes this.
  7. WINPINPH1

    New Member

    Sep 27, 2010
    24
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    from the data sheet the max input voltage to Vbe = 5v? so that the transistor will not fry?

    what will be the hfe? and the value of output current from the resistor that will energize the relay?

    i like to learn the computation so i will know how to design a circuit.
     
  8. kneesee

    Thread Starter New Member

    Oct 1, 2010
    2
    0
    Sorry just wanted to verify something. Looking at the drawing that Sgt Wookie provided do I need use the 24 VDC positive or the negative trigger from the SICK sensor? I would prefer to use the positive because this is how it is wired currently. I am very rusty, I used to know this stuff 20 years ago when I was in school.
     
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