# Optimal method for multiple MOSFETs for LED driving with a shared power rail

I have three LEDs (RGB), with the following forward voltages and current:

• red 2.25 V @ 0.35 A
• green 3.3 V @ 0.35 A
• blue 3.1V @ 0.35 A

I plan on using three (3) RFP30N06LE MOSFETs in parallel @ 0.35 A each using independent TTL-based PWM dimming from the PWM pins of an Arduino, each MOSFET connected in parallel to a shared 9V - 12V @ 1 A power rail fed with a wall wart supply.

What would the optimal method be to wire these MOSFETs in parallel and use the same shared power rail?

Just like that, in parallel:

simulate this circuit – Schematic created using CircuitLab

However, if all three LEDs can be on at once, you might want a bigger power supply. The maximum current to power the LEDs is:

$$0.35A + 0.35A + 0.35A = 1.05A$$

This is 5% more than your power supply's rating already, plus you need to allow for some current to power control circuitry probably, and probably you want to allow some margin for reliable operation.

• So are each of the resistors different values to current limit each MOSFET to 0.35 A? I had previously tried a variant on this schematic (without resistors unfortunately) and somehow ended up destroying the LEDs, just at 0.35 A total output on the bench supply. Jun 23, 2013 at 22:57
• @user1316349 you need resistors, or some other current-limiting element, to power an LED, unless these are LED packages with the limiting already built in. But, if you managed to destroy one with only 0.35A from your supply, perhaps your specifications are wrong. If there was 0.35A from the supply, there couldn't have been more than that in the LED, unless you had a buck converter or some other non-linear power converter. Jun 23, 2013 at 23:09
• @user1316349 and yes, each resistor is a different value, because each LED has a different forward voltage. There are hundreds of questions here about that, and millions of thing on the internet at large, but maybe start here: electronics.stackexchange.com/questions/55823/… Jun 23, 2013 at 23:11
• Thanks, I will try that next. Sorry I can't upvote yet, I don't have 15+ feedback. Jun 24, 2013 at 1:38
• 350ma is rather a lot for most leds, are you sure it's not 35ma ? Jun 24, 2013 at 13:41