Automated switch for converting a positive voltage to negative

Discussion in 'The Projects Forum' started by Raghav0211, Apr 6, 2012.

  1. Raghav0211

    Thread Starter New Member

    Apr 6, 2012
    Hi Guys,

    I need to turn a motor in a clockwise as well as an anti-clockwise manner however lab-view can only output a positive voltage. Therefore i tried this circuit out with the motor connected to both the collector of the npn and pnp transistor. It still doesn't work. Please advise.

    Many thanks.
  2. chrisw1990

    Active Member

    Oct 22, 2011
    whats wrong with an h-bridge?
    why use a +/- power supply?

    see here forexample..
  3. John P

    AAC Fanatic!

    Oct 14, 2008
    If you have the negative supply available, that circuit should (almost) work. But running a motor off a 9V battery, if that's what powers it, will run down the battery very fast.

    The circuit can't work because the diodes are facing the wrong way. And there ought to be pullup/pulldown resistors from the base to the emitter on both transistors. And are you really truly sure that the two transistors can never be on at the same time?