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why 1K resistor

Discussion in 'General Electronics Discussion' started by garlitos, Jun 7, 2013.

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  1. garlitos

    garlitos

    3
    0
    Jun 7, 2013
    i have the current hbidge and it works fine. i need to know the function of those 1K resistors in the circuit. anyone know why?
     

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  2. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    They limit the base current to a safe value.
     
  3. BobK

    BobK

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    Jan 5, 2010
    The base to emitter of a bipolar transistor acts like a diode. If you have no resistor there, and connect a voltage above about 1V, it will draw unlimited current without the resistor.

    Bob
     
  4. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    This is not a good design. Operating half of the bridge as an Emitter Follower (Common Collector) is going to run those transistors very hot because they can't be saturated.

    Chris

    Edit: Since these transistors are Darlington's the problem is magnified.
     
    Last edited: Jun 7, 2013
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    I agree, that's not a very good design. It's also incomplete; you should show the circuit that provides the base drive signals.

    Nowadays, H-bridges are normally made using MOSFETs. They draw relatively little bias current, and can have extremely low ON-resistances, so they waste almost NO power and provide the maximum voltage swing to the load.

    There are also many H-bridge ICs that include the output devices internally. They also have dead-time control, fault detection and other logic that makes it very easy to implement an H-bridge. Here is a summary of some H-bridge ICs that I wrote up for another user: https://www.electronicspoint.com/high-power-dual-h-bridge-t259810.html#post1548333
     
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