H-Bridge with 1 PWM and 1 Output

Discussion in 'General Electronics Chat' started by Slaxx, Mar 16, 2015.

  1. Slaxx

    Thread Starter New Member

    Mar 16, 2015
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    I'm looking for a solution to control the direction of a powerful DC Motor (http://micro-motor-warehouse.com/collections/all/products/cl-0820-17). I came up with the idea to use a H-Bridge. Since the motor uses up to 3.2A the amount of possible H-Bridges is quite limited. The supply voltage on my quad is 3.7V. Since my outputs are limited I want to control the position using only one Digital Output. Which does work in one direction if set to 0 and other direction if set to 1. The PWM output should control the velocity. Is that even possible? I found this one http://www.newark.com/texas-instrum...r-h-bridge-8a-vqfn/dp/36X2964?ost=DRV8850RGYR but I have absoultely no clue if this one can be controlled only with 2 inputs per motor (1 PWM , 1Digital Output).

    Thx for your help
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,524
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    Factory lifetime rating: 5-6 Hrs?
    Is this a DC or BLDC motor?
    Max.
     
  3. Slaxx

    Thread Starter New Member

    Mar 16, 2015
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    I don't know about the lifetime rating, but that may be right. But the motors are much easier to exchange than a H-Bridge that is soldered onto a PCB... It is a DC motor with brush.
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I have built several big DC motor reversing drives using only two port-pins from an Arduino or PIC. I use one port-pin to drive a DPDT relay, where the contacts of the relay are wired as an H-Bridge to reverse the current through the motor. The other port-pin generates PWM to the Gate of a large (heatsinked) NFET, which is connected in-series with the 0V side of the H-bridge.

    The code in the controlling micro takes care of accelerating the motor, de-accelerating it, dead-time to allow it to coast to a stop before reversing it, etc. via the PWM. I never switch the relay while I think the motor may be moving... Actually, I can measure the motor current using an A/D input to the micro, so I can tell what the motor is doing...

    Send me a PM if you want the schematic of my project, from which you can see how to wire the relay and the PWM NFET.
     
    Last edited: Mar 16, 2015
  5. crutschow

    Expert

    Mar 14, 2008
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    3,229
    Here is the data sheet for the DRV8850RGYR
    That will tell you everything you need to know about the chip.
    The chip has 4 inputs, one for each of the 4 transistors in the bridge.
    You can drive the chip with a PMW signal to turn on the diagonal MOSFETs for the motor direction you want. The other diagonal MOSFETs in the bridge must both be OFF.
    Two AND gates (such as a CD4081), one for each opposite pair of MOSFETs) and one inverter (CD4049) for the direction signal, will generate the proper signals so it will operate with one PWM signal and one direction signal as you want. (Make sure you tie all unused gate inputs to ground).
    The maximum PWM frequency is 50kHz.
    (Make sure you get the chip with through hole pins (DIP) unless you want surface-mount).
     
  6. Slaxx

    Thread Starter New Member

    Mar 16, 2015
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    I found the data sheet as well. But what you wrote about the AND gates and inverter was what I was looking for, since I was not sure how to adapt it.
     
  7. crutschow

    Expert

    Mar 14, 2008
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    Here's a simulation of the logic that should do what you want.
    Power and ground connections are not shown and must be added.
    Tie all unused inputs (not outputs) to ground.

    DRV8850RGYR Control.gif
     
  8. Slaxx

    Thread Starter New Member

    Mar 16, 2015
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    thank you very much for the simulation. What program did you use? Or what do I need to open that .asc file?
     
  9. crutschow

    Expert

    Mar 14, 2008
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    3,229
    I used the free LTspice program from Linear Technology.
    Note that you have to add the CD4000 models from the Yahoo LTspice users group to run my file.
     
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