H Bridge Design Critique

Discussion in 'The Projects Forum' started by xXGiuseppeXx, Jul 31, 2012.

  1. xXGiuseppeXx

    Thread Starter New Member

    Jul 30, 2012
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    Hello all, I have always used this site for quick reference for information or learning new info but didn't know how nice the forums are!

    Anyway, I recently became an electrical engineering intern and been assigned a design task. Basically, there was an H bridge designed prior to my employment and it really doesn't work so they asked me to redesign it. The attached pdf is what I came up with. I used the MC33886 H bridge for a quick solution. The specs they gave me was that the control inputs are from an MCU (0 =ground, 1 =5V) and the load that it will be controlling through the bridge will need 10VDC. The load is also 8Ω so that is 1.25A. Also, the main input voltage to their system this bridge is going in is 24VDC.

    I decided that a voltage regulator would be fine for this (attached is also the regulator I chose to use, it has 4% tolerance), one that could source 1.5A. I am not sure if I need a heat sink but I probably will use one anyway.

    I guess what I need is a quick sanity check on my design. Also, I know I need those diodes (in the pdf schematic) but I do not know yet which ones are good for inductive loads.
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    From 24V to 10V @1.25A is a lot of power the chip needs to dissipate. Does the load not support 24V? If it does just decrease the PWM pulse width, so that it gives the same mean value.

    If it doesn't, well you will need a big heatsink. You may be better of with a step-down converter so you wouldn't waste so much power...
     
  3. xXGiuseppeXx

    Thread Starter New Member

    Jul 30, 2012
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    Unfortunately, the load can only see 10V. Yeah I thinking it would get hot from that big voltage drop. Are step down converters expensive?
     
  4. xXGiuseppeXx

    Thread Starter New Member

    Jul 30, 2012
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    Also, I was under the impression by the IC I chose that PWM is optional. The load will not be PWM'd, just straight voltage. Is this a bad thing?

    I think what my supervisor is looking for is a quick, dirty, and cheap solution. Judiging by the last H bridge I saw, there was no PWM involved.
     
  5. mcasale

    Member

    Jul 18, 2011
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    Is the load a DC motor, or a stepper motor?

    If it's a stepper motor, you can use an Allegro drive chip like the A3979, which does all the PWM chopping and current limiting you need. I have used this chip successfully in a previous design. You still have to be careful with grounding and parasitics.

    Why is there a 10v limit on this load?
     
  6. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Yes, they are expensive. example: http://www.digikey.com/product-detail/en/APXW003A0X3-SRZ/555-1245-1-ND/2640013

    You can build yourself buying a few components but it will also cost a few dollars.

    I didn't know that the signal isn't PWM... So yes you will have to bring down the voltage.

    The load coil needs to be driven in both directions, is that right?
     
  7. xXGiuseppeXx

    Thread Starter New Member

    Jul 30, 2012
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    Not sure on the 10V limit, I was told that I could not go over (by much) this voltage for their "shutter coils"; I need to ask more info on this.
     
    Last edited: Jul 31, 2012
  8. xXGiuseppeXx

    Thread Starter New Member

    Jul 30, 2012
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    Yes, I will be driving it in both directions.
     
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