Low voltage H bridge

Discussion in 'General Electronics Chat' started by Navarr0, Feb 24, 2015.

  1. Navarr0

    Thread Starter New Member

    Oct 10, 2013
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    Hello, please, I need help. I have MCU with LED display, both powered from two AA batteries with DC 5V converter. Now I need control little DC motor (1.5-3V and current max 500mA). So I wanna build H bridge controled with 5V voltage from MCU. Can you tell me, if this circuit will work? http://www.electro-tech-online.com/i.../3304-idea.JPG. H bridge must be powered directly from two AA (cca 3.2V when new). I wanna use four n-channel mosfet TSM2302CX with Vgs(th)=0.95V. For low side nfet there is Vgs=5V without problem. But for high side nfet there is 5V-3.2V when open =1.8V, so it's still good? Thanks for response.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    No. Use low-threshold NFETs for the bottom pair, and low-threshold PFETs for the top pair.
     
  3. Navarr0

    Thread Starter New Member

    Oct 10, 2013
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    Thank you. Mosfets with the lowest threshold voltage what I can get are NFET TSM2302CX with Vth=1.2V(max) and PFET TSM2301CX with Vth=0.95V(max). Do you think that't enough?
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I would write your program so as to use four port pins to control the four FETS. A high turns on the NFETS. A low turns on the PFETs. Put a delay so that you write a low to the opposite PFET after you write a high to the NFET. Put a delay so that you write a high to the PFET before you write a low to the NFET.
     
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  5. Navarr0

    Thread Starter New Member

    Oct 10, 2013
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    Ok that's clear, thank you very much :).
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I should have added:

    The resting state (motor freewheeling or not running) is two lows to the NFETs; two highs to the PFETS.

    To brake the motor, both NFETs high, both PFETs high.

    But never turn on both the NFET and PFET on either side of the h-Bridge at the same time!
     
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