DC Driver

Discussion in 'The Projects Forum' started by morgenstern, Feb 28, 2013.

  1. morgenstern

    Thread Starter New Member

    Feb 28, 2013
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    Hi!
    i want to make a driver for a DC motor 24 volt, 11 ampere that i want to control it with atmega32 and IRF540N mosfet.
    And now the question is how can i connect micro to mosfet, Do i have need optocoupler or drivers like as IR2110 and what i must do for protecting mosfet?
     
    Last edited: Feb 28, 2013
  2. mcgyvr

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    Oct 15, 2009
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  3. ScottWang

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    Aug 23, 2012
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    if you can buy IRL540 as mcgyvr mentioned is good, otherwise, if you want to use IRF540N then you need a stage of NPN transistor to be the input and drive IRF540N. (I prefer to use the b. fig of the circuits to be the input as below)

    [​IMG]

    The Rds(on) of IRL540 is 77mΩ, and the Rds(on) of IRF540N is 40mΩ, so the heat dissipation of IRF540N is better then IRL540.
     
    Last edited: Feb 28, 2013
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  4. mcgyvr

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    ^^ and you will be dissipating nearly 10 Watts with the IRL.. and as such requires a decent heatsink.
    A mosfet with a lower Rds(on) can make a world of difference.

    mosfet dissipation is just I^2R for full on..
    With a junction-ambient resistance of 62 deg C/W without a heatsink its temperature rise would be approx 620deg C (it will have died/burnt up long before it gets there)

    junction to case is 1 deg C and you will need a heatsink with a sink-ambient resistance of 8 deg C/w or less to keep it in a reasonable..still hot range.(lower the better..5degC/w or less is what I would shoot for).. (max temp of the IRL540 is 175 deg C) but it should never be allowed near that.
     
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  5. John P

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    If you have a box of those MOSFETs available, you can combine them in parallel and reduce the heat output.

    But there are much better transistors available. How about the Infineon IPP042N03L G? Digi-Key has them for $1.27 (IPP042N03LGIN-ND); they turn fully on with a logic-level input and they have an on-state resistance of 4.2 milliohms. At 11 Amps, that gives you a power loss of half a watt. Why fool around with heatsinks when it's so easy not to?
     
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  6. morgenstern

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    Feb 28, 2013
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    What type and model of elements are used in figures?
     
  7. ScottWang

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    Aug 23, 2012
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    You can use the small signal bjts, the Vceo>= 40V.
    PNP : 2N3906,2SA733,etc...
    NPN : 2N3904,2SC945,etc...

    If you want to using some more better, those are 2SC1384(PNP),2SA684(PNP)
     
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  8. morgenstern

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    Feb 28, 2013
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    what can i do to protect the circuit againt the di/dt or spike voltage?
     
  9. ScottWang

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    1. di/dt - where,Voltage ?
    2. spike voltage - where, the reverse voltage of Relay?
     
  10. morgenstern

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    Feb 28, 2013
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    when the mosfet switch off the reverse voltage can damage the mosfet, isn't it?
    I think a snubber circuit or a protection system is need.
     
  11. ScottWang

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    Aug 23, 2012
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    You can use Diode in parallel with motor, normally using 1N4007, but consider the 11A current, maybe you should choose some others.

    (+)-----Motor -+- D-Mosfet-S --- GND
    (+)-----|<|-----'


    You can search on digikey for rectifier diode 20A, or some more.
     
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