Simple H bridge with PWM Question

Discussion in 'General Electronics Chat' started by maz719, Apr 1, 2009.

  1. maz719

    Thread Starter New Member

    Feb 23, 2009
    Hey all,

    I've made a lot of progress on my project but I'm hung up on the last part needed. Basically I have to control the current direction through a magnetic torque coil (just a flat plate with copper wire wrapped around it a few times - this creates a small torque against the earths magnetic field) and after looking through a few options it seems the H-Bridge was the best option for this.

    Attached is a diagram of what I initially used, but after turning the circuit on I got some funky readings from the inputs and now I'm not sure what else to do. Below is information about the circuit.

    PWM: 0 to 3.3V, at 0 to 160mA.
    Top transistors: PNP 2n2907
    Bottom transistors: NPN 2n2222

    I am looking to get reasonable current through the inputs, but being able to change the direction is the most important. If anyone has any suggestions as to why it is not working or even insight into a better design, please let me know. Anything will be greatly appreciated.
  2. nanovate

    Distinguished Member

    May 7, 2007
    You might want to add some resistors in series with the bases of the transistors