Circuit to dim 40A/12V LED chain with PWM (Arduino output)

arduinodriverledmosfetpwm

We have about 170 feet of LEDs (12VDC, 2.88W/foot) wired up in one chain. Currently they are driven by two switching power supplies (12V/27A).

We'd like to control the whole chunk of them together, dim them via an Arduino's PWM output.

Most dimming / extensions boards out there are very limiting in their load. See Sparkfun Mosfet board 10256 – it has a Mosfet ready for up to 30A, but PCB tracing and components limit it to a usage of 4A. Or this 4-channel Mosfet board – each channel can sustain 10A, but the power input terminal can only sustain 16A.

Is there even a way to wire the whole current for all LEDs through one channel (=one Mosfet?), or is this impossible due to component limitations? Could i use for example several of these smaller boards and then simply add their outputs together and feed the whole LED chain with one input? Or are there any hardware devices out there that are build to sustain higher currents (like wall dimmer switches, those seems quite sturdy…)?

Best Answer

That 4-channel board looks so cheap it would be worth customizing it for higher current. Add a beefier input connector, and maybe solder some solid copper wire to the traces that route power or ground to the output connectors. The web page you linked even suggested replacing the power connector for higher-current use.

That 170 foot antenna you're using should be good for broadcasting radio station "PWM Arduino" to the neighborhood :-)

Related Solutions

Electronic – how to control constant current led driver output with pwm

please help me

I have some concerns about the current limit circuit (based around the BC337 / R2) and its ability to work with PWM - every time the pulse goes high from U3 (initiating a current flow through the MOSFET), the voltage developed across R2 will activate the BC337 and clamp the drive voltage to the MOSFET. This means the MOSFET will get quite warm because it is operating as a current limit device.

Added to this you are trying to control the LED current via PWM BUT the BC337 circuit is also trying to limit the current. It doesn't look like it should work as you expect.

When you say the LED starts blinking, what is your PWM frequency?

Given the circuit you have I also have concerns about possible high voltages from the LED string being capacitively coupled (through the MOSFET) back to an IO pin on your MCU. Maybe protection diodes would help.

Electronic – can NPN transistor be used when sinking current

You do not need transistors on both rows and columns because, as @Milliways explained, you will not light all the rows and columns simultaneously. Since you already have a bunch of N-channel MOSFETs, and these are good for sinking current, you will put them on the columns (negative side of the LEDs). Now you can light a whole column at a time without worrying about current limitations. You do not need transistors on the rows, because at most one LED will be lit per row at any given time.

Your circuit will look like this:

P1 ───────*─────────*────…
          │         │
P2 ───────*─────────*────…
          |         |
         ├┘        ├┘
       ┌→│       ┌→│
       │ ├┐      │ ├┐
       │  │      │  │
      N1  GND   N2  GND

And your code like this:

initialize all Ns and Ps to LOW
output on P1, P2... Pn whatever you want to see on the first column (HIGH to turn the LED on, LOW to keep it off)
set N1 to HIGH, this will turn the MOSFET on and light the LEDs
wait for a few ms
set N1 to LOW, this will turn off the whole column
output on P1, P2... Pn whatever you want to see on the second column
set N2 to HIGH
wait for a few ms
set N2 to LOW
and so on if you have more columns...

Best Answer

Related Solutions

Electronic – how to control constant current led driver output with pwm

Electronic – can NPN transistor be used when sinking current

Related Topic