LED strip driver with unusual transistors is not working

Discussion in 'The Projects Forum' started by Cliquot22, Nov 14, 2017.

  1. Cliquot22

    Thread Starter New Member

    Jul 21, 2016
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    I am making a driver for a RGB LED strip with some parts I have on hand. I'm using IRG4PC50W transistors for the color switches (because they are left over from a different project) but they are not working correctly. This is an insulated gate bipolar transistor. Do I have my transistor hooked up incorrectly? It doesn't matter what I give the gate (0V - 3.3V), it doesn't do anything. The collector is always around 5-7V (emitter connected to ground).

    pic2.jpg pic1.jpg
     
  2. dl324

    AAC Fanatic!

    Mar 30, 2015
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    1,163
    Welcome to AAC!

    Luckily for you the circuit isn't working or you would have likely fried the LEDs.

    Understand that you're using parts on hand, but it's still a poor choice. Overkill for driving LEDs and not compatible with the logic levels of the driving circuit.

    The datasheet says Vge is 3-6V for a collector current of 250uA. Since it's a power device, the graph doesn't show what Vge is required for the current you desire (from a typical device):
    upload_2017-11-14_8-7-56.png

    What are the drive characteristics of your controller and what other transistors do you have available?
     
  3. Cliquot22

    Thread Starter New Member

    Jul 21, 2016
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    Thanks. Now I understand better what that specification means. I'll buy some n-MOSFET parts (IRLB8721) as suggested in several tutorials.
    Sometimes trying to save a few bucks isn't worth the frustration.
     
  4. dl324

    AAC Fanatic!

    Mar 30, 2015
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    That MOSFET is still overkill for driving a few LEDs.

    Another option is to use P MOSFETs and high side switch the LEDs. To do that, you need to know how much current can be forced into the driver outputs safely.

    You should also note that you need a current limiting resistor for each chain of LEDs.
     
  5. Cliquot22

    Thread Starter New Member

    Jul 21, 2016
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    0
    This is a driver for a LED strip light so I'm a bit limited in my options. The strip uses a common 12V supply. And for a 5M strip, I expect about 1.2A per color so the MOSFET should be a good choice.
     
  6. dl324

    AAC Fanatic!

    Mar 30, 2015
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    More/better information will give yield more relevant suggestions.

    I'd hardly say that using a MOSFET rated for approximately 100X the expected current is a good choice. Derating by 50% is usually considered very conservative.
     
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