Transistor Controlling 28 volts

Discussion in 'The Projects Forum' started by Rcflyer2552, Jan 18, 2015.

  1. Rcflyer2552

    Thread Starter New Member

    Jan 18, 2015
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    Hello,
    I am trying to get a circuit where a PNP transitor will control a 28 volt Relay when the base is grounded, will the BC327bu that is pictured in this schematic work with this?
    Thank you
     
  2. Reloadron

    Active Member

    Jan 15, 2015
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    Yeah, the BC327 will work as drawn. Just keep the relay coil current below the max current the BC327 can handle (800 mA). I would look for a relay coil requiring 500 mA or less. Anyway, yes, for a PNP transistor that is what you want and when the base is at 0 volts the transistor will be On.

    Ron
     
  3. ScottWang

    Moderator

    Aug 23, 2012
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    The thing seems not that simple, if the input voltage of high is too low then you can't turn off the transistor, it also can't turn off the relay.
    How is the input voltage, high low signal, a switch switching from high to low or some others?
    I'm not sure why you want to using a low to drive the transistor when the relay is 28V, maybe you can change to NPN.
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    I see nothing wrong, just an emitter follower driving a relay.
     
  5. ronv

    AAC Fanatic!

    Nov 12, 2008
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    I see what is bothering Scott. If the input is like 0 to 5 volts it won't turn off. If it is 0 to 28 all is well.
    Guess we need to ask. What is the input signal???
     
  6. ScottWang

    Moderator

    Aug 23, 2012
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    Yes.
    And I'm trying to suggest him if the input needs to using low to drive, maybe he can using two bjts as the first is pnp and second is npn.
     
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    An NPN transistor should be used BC337 or BC338, 2N2222 etc. the BC327 is PNP and turns on when the input value is 0.6v Lowe than the emitter voltage. The PNP will not turn off in this configuration with this input.
     
  8. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Sure, but then he needs to invert his input.
     
  9. Reloadron

    Active Member

    Jan 15, 2015
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    I believe the circuit the original poster has posted came from The Relay Switch Circuit which is just a collection of basic assorted transistors turning relays on and off. The link merely shows basic circuits without regard to component values. Here is what is stated pertaining to the circuit:

    Ron
     
  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Or just use normally closed connection on the switched connections of the relay.
     
  11. ronv

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    Now there is a thought. Why didn't I think of that?:oops:
     
  12. wayneh

    Expert

    Sep 9, 2010
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    We can only speculate. :D
     
  13. Reloadron

    Active Member

    Jan 15, 2015
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    Yep, I believe that covers it well. :)

    Ron
     
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