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I am trying to control multiple 24V RGBWW (6-vein) ledstrips with my raspberry pi 3b+. The ledstrip is 2 meter (24W p/m) long, and will be cut into 3 pieces. I want to control each piece (~67cm) separately.

Doing my research i found that MOSFETs can be used to do this. Does this mean i need a MOSFET for each color? (Red, Blue, Green, Warm white, Cold white) and for each piece. So 15 MOSFETs in total. Or is there a better way to do this?

I saw a IRLZ34N being used, but i dont know if this will be just enough or close to overkill. I will use a seperate 24V 80W power supply.

TIA!

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  • It's not like there's only one MOSFET possible in each application. If IRLZ34N does its job, use it, unless you have a reason to use a different one.
    – Dmitry Grigoryev
    Jan 20, 2022 at 7:07
  • Thanks for your reply. My question was more intended like: what would be a reason not to buy a certain MOSFET. I do not understand what ranges i have to play with, or what is overkill. Maybe its too complicated to do this in a single comment, if so, just say so 😄 Or maybe someone can provide a useful source.
    – vlreinier
    Jan 20, 2022 at 7:56
  • Going through dozens of parameters for hundreds of MOSFETs in the attempt to pick the optimal device is a full-time job. It only makes sense if you're going to produce a million devices and want them be as cheap as possible. For a hobby project, using a part that is known to work is often the best solution, even if some of its parameters are an overkill.
    – Dmitry Grigoryev
    Jan 20, 2022 at 10:20

1 Answer 1

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Since you did state if all the colors were in one strip I will assume one LED strip for each color. There are many choices for the MOSFET. Since I do not know your resources or skill set I can only give you some guidelines to purchase them. The simplest interface would be to switch the LEDs (Low Side) with a N-Channel MOSFET. You need to connect the Drain to the LEDs and the source of each MOSFET to ground including the Raspberry Pi. Since the LEDs use 24W per meter that is 1 amp at 24V so 2 meters is 2 amps per strip. The Pi gives you ~3.3V on the GPIO When on. you need to add a pull down resistor in the 10K range from the GPIO pin to ground. Then connect the GPIO pin to the gate with a resistor about 25 ohms. Putting the pull down resistor on the gate forms a voltage divider reducing the drive voltage to the MOSFET hence the GPIO pin. The IRLZ34N should work OK, and it is in a TO220 package allowing the addition of a heat sink. The part will not be fully on until it is driven with about 8V. With a 3.5 drive it will switch about 10 Amps, enough for each LED color. It is rated at 55V Vdss, giving you enough headroom for 24 volts. It is avalanche protected allowing it to be used with inductive loads as well. "besides using max 3.3 VGS" is not correct, the part you mentioned is rated at Plus/Minus 16V, exceeding that will destroy the MOSFET. It starts to turn on at about 1.3V (interpolated) depending on junction temperature. A MOSFET is needed for each channel you have so in your case 5.

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  • Thanks for your explanation. Its a RGBWW ledstrip which means that all colors are in one ledstrip but if i understand correctly this should not matter for the number or type of MOSFETs (only for the power wiring). If i wanted to control 3 seperate ledstrips, would i need 3×5 MOSFETs or is there an easier, cheaper way?
    – vlreinier
    Jan 20, 2022 at 7:04
  • About the 3.3V VGS, I read that you need max 3.3V Gate Treshold Voltage or the leds will not brighten enough.
    – vlreinier
    Jan 20, 2022 at 7:12
  • The MOSFET is primarily a digital device optimized for on/off operation. It was not designed to operate in between. Change your max to min and it would be correct, that is measuring from source to gate. You can connect each of the colors together then you only need 5 MOSFETs.
    – Gil
    Jan 20, 2022 at 22:01

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