LM311N comparator switching

Discussion in 'The Projects Forum' started by cpfc, May 9, 2015.

  1. cpfc

    Thread Starter New Member

    Jul 19, 2013
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    Hello, I have made a simple circuit using the LM311N comparator to switch a single cell lithium battery from being charged by a solar cell charge controller to powering the load. I have set the hysteresis thresholds for the comparator between 3.4V and 4V and the switch used is a P channel MOSFET. Would this circuit work?
    LM311N comparator.jpg
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Should work; but simulation shows you get closer to your 3.4V and 4V targets if R2=2k7 and R3=6k8.
     
  3. cpfc

    Thread Starter New Member

    Jul 19, 2013
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    Thank you. For the MOSFET selection would something like the IRFP9140N be suitable? Maximum load current for the design is ~8A.
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    The trip points are ratiometric to the 6V supply. How stable is it?
     
  5. cpfc

    Thread Starter New Member

    Jul 19, 2013
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    From testing it seems stable, the supply is from the REGN pin of the BQ24650 charge controller IC.

     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I wouldn't use that one; its Rds(on) is rather high (0.117Ω), so it would dissipate > 7W at 8A load current, requiring a large heatsink.
     
  7. cpfc

    Thread Starter New Member

    Jul 19, 2013
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    Ok it looks like the FDS6575 is a better option with an Rds(on) of 13mΩ
     
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