OP-AMP pwm splitter

Discussion in 'The Projects Forum' started by dpeterson3, Jun 22, 2012.

  1. dpeterson3

    Thread Starter New Member

    Oct 9, 2009
    19
    0
    I've been working off and on for a while on designing a brushless motor controller just because I want to understand how to design one (I know I can buy them cheap). Of the designs I have studied, they all seem to have a single PWM output channel on a micro, and then use AND gates to drive the motor control transistors. I was trying to mimic this using comparators since they are very easy to get and already included in eagle and LTSpice (I figured simulate first). I'm having trouble in the simulator getting the op-amps to pull the transistors all the way on and off. Can I actually do this, or will I have to go to AND gates. I'll post a schematic if this arrangement doesn't make sense.Thanks.
     
  2. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    A lot of opamps can't output all the way to zero volts. Maybe giving them a simulated negative supply voltage will fix the problem, or, specify a different opamp. So many people come here after trying to use 741 opamps and expecting them to work.
     
  3. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    Yes please. What components were you using for your simulation (including power transistors)?
     
  4. dpeterson3

    Thread Starter New Member

    Oct 9, 2009
    19
    0
    I have attached a screen shot of my LT-spice model (or at least I think it attached). The power mosfets are IRF7309's. I probably won't use those in production, but I will use something very similar. I was trying to avoid logic level gates. The op-amps are LM324's, even though it doesn't say that on the schematic. All the small 5V sources are to simulate micro controller outputs, and the 10V source is the PWM channel. Thanks for your help.
     
  5. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    I'm not very good at this but I think I see a P-channel mosfet with a positive voltage on its drain.

    PS, it's good to attach datasheets for each device in question
    I provided them to make easier work for the other helpers.
     
    Last edited: Jun 23, 2012
  6. dpeterson3

    Thread Starter New Member

    Oct 9, 2009
    19
    0
    You're right. I put all three in upside down. I do that every time thinking the symbol is drawn the way I think it should be rather than the way it actually is (if that makes sense).
     
Loading...