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  1. #1
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    driving p channel mosfet

    Thread started here -> https://www.edaboard.com/viewtopic.p...8727b99f06faf6 (see the last few posts)

    I am happy to report, the IRF9520 can drive 48 LEDs and not a problem at all. (no heat sink required)

    However now, I think it is all my crappy brick powersupply, which is junk. All 3 of them I have tried say 5V 2A, 2.5A, 3A... Yea right! When I have all RGB on, voltage dropped to 3.4V!! And to my surprise the current is only about 340mA!

    I think I need a "REAL" powersupply can can do steady 5V. Maybe I will hook up to my PC powersupply and do some test.

    Now my question is how much voltage drop am I suppose to expect from the MOSFET?

    When I did my simple test with 8 LEDs, the voltage drop from Source to Drain is less than 0.1V. So I said hey this is cool. But after I hook up 48 LEDs, the voltage drop between S & D seems to be larger, if I recall it was about 0.3-0.4V.. Is this normal?

    BTW the MOSFET is not even warm. Which I guess that's good.

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  2. #2
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    mosfet driving

    The IRF9520 is an "ordinary" Mosfet that needs 10V from source to gate to fully turn on. It is spec'd with a max threshold voltage of 4.0V when its current is a minimum of only 0.25mA.
    Some of them have a threshold voltage of 2.0V.

    If your gate voltage is only 5V then use a "logic level" Mosfet.



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  3. #3
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    48 channel rgb led

    Hi Audioguru.

    I am not 100% sure what you mean by "logic level" MOSFET. I did some google last night but not much useful info was found. I did re-read the spec sheets for IRF9520 and I don't see anywhere (or I misunderstood the graphs) about "10V from source to gate to fully turn on"

    I have the circuit build on breadboard already, and I really need to start putting the circuit onto a circuitboard ASAP. As I will need this LED lighting by this Sat. For what I have now, it is pretty bright, but not as bright as it suppose to be (i.e. not 20mA for each LED)

    I don't know if it is as simple as just "swapping out" the IF9520 with another p-ch MOSFET. If so, wonder if you have any suggestion on P/N.

    Here are some numbers

    Vsource = 5V
    Vgate = 0-5V
    Idrain = 48 x 20mA (planned to drive 48LEDs @ 20mA each)

    The current limit resistor I have, (drain -> resistor -> LED -> Gnd) is based on 5V @ drain.

    I hope it is just as simple as replacing the MOSFET instead of re-do 144 resistors.

    Thanks



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  4. #4
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    p mosfet rgb

    The IRF9520 is an "ordinary" P-channel Mosfet. Its RDS(on) is spec'd only when its gate-to-source voltage is 10V. Most barely turn on when the gate-to-source voltage is only 5V.

    You need a 'logic-level" Mosfet. They completely turn on and are spec'd when the gaste-to-source voltage is only 4.5V.

    I have used logic-level N-channel Mosfets but never a P-channel one. There are many available. Select one with a voltage rating less than 100V and it will turn on better.



  5. #5
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    mosfet rgb

    Quote Originally Posted by Audioguru
    The IRF9520 is an "ordinary" P-channel Mosfet. Its RDS(on) is spec'd only when its gate-to-source voltage is 10V. Most barely turn on when the gate-to-source voltage is only 5V.

    You need a 'logic-level" Mosfet. They completely turn on and are spec'd when the gaste-to-source voltage is only 4.5V.

    I have used logic-level N-channel Mosfets but never a P-channel one. There are many available. Select one with a voltage rating less than 100V and it will turn on better.
    Do you have any suggestion on Part Number?



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