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Push-Pull Output not working?

karthick balu
Prodigy 210 points

Hi all,

I am working for push-pull output. my rated current is 200mA..
i design the circuit as shown in below....





  • ]when my control input is low(0 volt) i want to sink...
  • when my control input is high(3.3 volt) i want to source...



But it does not work properly....

when my control input low, both pnp and npn transistor On , so the circuit gets damaged...

but for my control input high, the only pnp transistor gets On, and source properly to get my requierd output...
please give ideas to solve my problem.. or any working push pull output stage......

  • 0
    TI__Guru**** 173126 points

    Karthick,

    If the input is binary, the circuit can be simplified greatly.

    Make Q5 NPN and Q6 PNP, this is opposite of the schematic.
    Remove R7 and R8, short R8 and R9.

    With 0V input, the output will be about 29V and will source current (from VCC).
    WIth 3.3V input the output will be about 1V and will sink current (to ground)

    You can invert the logic input to get your desired result.

    Regards,
    Ron Michallick