transistor AND-ing switch

Discussion in 'The Projects Forum' started by masa6614, Feb 14, 2009.

  1. masa6614

    Thread Starter Active Member

    Nov 9, 2008
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    Hi,
    Attached is a drawing of what i'm wondering will work. I'd like to make a AND gate to control a switching transistor to close and open a relay. Now my Vcc is too high and i dont want to scale it down in size and provide the smaller supply power for a real logic AND gate to control a transistor. I'm not sure if the first transistor, 'Q1' needs a highside driver or if it will work fine the way it is? Thanks

    ( and sorry i realize i put it in the wrong forum and cant figure out how to move or delete it from here )
     
    Last edited: Feb 14, 2009
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    If you provide both with vcc and most importantly keep the zeners, then it should work. Cmos NAND gate uses the same topology for the AND part I think.
    But anyway, what voltage are you talking about? I don´t think this is suitable for high voltage. And also some gate resistors wouldn´t hurt, without them the zener might burn, or oscillation can occur.
     
  3. masa6614

    Thread Starter Active Member

    Nov 9, 2008
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    Okay, thanks, yeah the Vcc is 24V, but what i didnt show in the diagram was the signals are opamp outputs with a series 10k to get the gate voltages to ~12V and limit the zener current.
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    If you don´t require fast switching, then it should be ok. What voltage are the zeners? I would use 15V for mosfets with 20V Vgsmax.
     
  5. masa6614

    Thread Starter Active Member

    Nov 9, 2008
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    Yeah, switching fastly isnt important, and thanks for the advice, i'll be using some 15V zeners
     
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