High Side Switch TIP120

Discussion in 'General Electronics Chat' started by binsky3333, Nov 13, 2012.

  1. binsky3333

    Thread Starter New Member

    Oct 2, 2012
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  2. tshuck

    Well-Known Member

    Oct 18, 2012
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    Both of these are NPN transistors, the TIP125/126/127 are the PNP complements to the TIP120/121/122 series, respectively.....
     
  3. binsky3333

    Thread Starter New Member

    Oct 2, 2012
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    So i used a tip120(NPN) would those circuits work? Im pretty sure the second one wont work. My input to the base is only 5V. I believe the first should work. Ill be using 5V on the base and 12v on the collector.
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The first circuit is a low side switch, not a high side switch.
    The second circuit is an emitter-follower, not a switch. When the input to the NPN 2N3565 is +5.0V then the emitter is +4.3V. If you use an NPN darlington TIP120 then the emitter is only +3.7V. The high collector voltage does not affect the emitter voltage of an emitter follower.
     
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