A 40 Amp LED dimmer - where to start

Discussion in 'The Projects Forum' started by badbaud, Mar 6, 2009.

  1. badbaud

    Thread Starter Member

    Mar 5, 2009
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    A local club is building a wall of those 12VDC LED lamp clusters. Calculated DC Amps is a little less then 40 Amps after measuring one lamp hooked to a power supply and measuring the DC current.

    Any suggestions on how to proceed with this project? Parallel MOSFET's? One really big IGBT? Really big bipolar power transistors?

    Figured I would use a 555 for timing and drive the gate(s)? base? through a high speed optoisolator.
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    One MOSFET can do the job if you use PWM. Use a 555 to create a PWM signal and then use a BJT to drive the MOSFET as to turn it on faster.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    But it will need to mount on a really big heat sink.
     
  4. mik3

    Senior Member

    Feb 4, 2008
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    Of course, this the drawback of power electronic devices. Dissipating heat quickly and efficiently costs money.
     
  5. badbaud

    Thread Starter Member

    Mar 5, 2009
    26
    0
    Got a whole box of large heatsinks. Have had custom ones extruded in the past (www.aldor.net) .
    Am going to order a handful of Fairchild FDP3205 MOSFETS (55V 115A) and some MIC502 PWM motor control chips. The MIC502 has a temperature sense input which I may be able to use to monitor the MOSFET for heat. If that doesn't work I will digress to the 555 solution.
    My only concern is some kind of current monitor on the output so if the DC current exceeds 50 Amps the circuit gets shut down before the MOSFET lets out it's smoke.
    Anybody know of a IC that can accomplish this?
     
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,173
    397
    Use a one milli ohm resistor in return line. Detect current with a comparator.Lead from power supply to equipment shoulr give enough drop to work with.
     
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