Dimming 12VAC LED bulbs with arduino via MOSFET

As I was wiring up the lighting for my new studio I was thinking it would be cool to have everything controllable via iPhone app with arduino and Bluetooth LE.
I've got 3 x RGB LED strips and 6 x 12v LED globes in total.

Each color channel of each strip and each bulb has it's own separate wiring (15 channels)

I'd started making up a board with MOSFETS for RGB strips and was about to do the same for the bulbs until I realised they are AC not DC.

So question is can I still use this approach for the 12VAC bulbs? Would I have to use 2 mosfets for each bulb to switch both legs together?

Keep in mind these are only 5W bulbs so each line only needs to handle about 500ma.

OK after doing some more searching, most bulbs of this type seem to be rated AC/DC and sure enough they work fine on a 12V DC supply.

Does this mean I can use the same Mosfet driven PWM dimming approach as the LED Strips to control them?

for me sir i think much better to use Two MOSFET because they have different power source. just in my thoughts.

Filament lamps are just resistors that get hot. PWM should not be a problem.

I would run them on 2 MOFETS as they will require different amounts of power for LEDs and lamps.

LEDs will glow at say 10% while the lamps will feel warm with no light output.


In the original post, does globe==bulb ?

Depending on what the globe/bulb is, it is likely to work very badly in your installation. There will be an AC to DC converter inside the bulb and it will be able to keep the LED at constant brightness with different power inputs. Whatever PWM you try to do will be defeated by the bulb.

Send us a link, preferably to something that has a datasheet.

12 volt AC bulb is unlikely to have any electronics inside.


You've got some unknowns. We don't know if those LED bulbs are dimmable, and we don't know if they'll run on DC... The odds are neither. I don't even know if they make 12V dimmable LED "bulbs".

Dimmable LED lighting normally uses a dimmable constant current (controlled current) power supply. (example). These require a 0-10VDC dimming signal, or some work with 10V PWM signal. (That's just a low-current control-signal, not the actual power.) That's the industry standard way of doing it, but it would require replacing your lighting system, because your 12V (constant voltage) LEDs won't work with this kind of power supply.

I really think the best solution would be to start-over with this kind of industry-standard type of dimmable LED lighting.

You can also get a constant-current LED power supply that's dimmable from a standard phase controlled AC dimmer.

Normally, low-voltage household lighting (such as halogens) is dimmed with a regular AC dimmer on the high-voltage side of the transformer. But, that requires a phase-controlled dimmer synchronized to the AC power line. And, we don't know if that would work with your lighting.

Some experiments you could do -

  • Try connecting one of your 12V LED bulbs to a 12V DC power supply. It would probably be a good idea to put a fuse in series to protect the power supply (and maybe the bulb). If it lights-up with 12VDC try 5VDC to see if it lights up more dimly.

  • Try a [u]6VAC transformer[/u] to see if lights-up dimly.

  • Try a regular 'ol [u]light dimmer[/u] on the AC side of your 12V lighting setup.

Ok I finally got some time to sort this. I ditched the bulbs I had as they obviously had some sort of regulator or other electronics that was inhibiting PWM control.

I knew that with the strips working, and LEDs being DC in their raw form, this had to work if I found MR16 globes with no additional electronics.
Problem when searching is most say AC/DC and either dimmable or not. But are they AC/DC because they have a regulator? Are they dimmable because we can send PWM, or because they have voltage controlled PWM built in?

Only way to find out was to order a heap of different types and see. Luckily I figured cheapest was probably best in this situation as they're likely to not have extra stuff and they're only $2 each from china!

Out of all the types that I received, only one worked, but they work a treat! A nice diffuse warm white, PWM dimming works perfects; and I can feel no heat from the globe after being on for an hour.

These are the ones you want.


Not too bright at 3W, but it means I can run a heap of them from low gauge wire and have dimming control for each bulb.
Right now I have 8 of them running over 2 cat5e cables.
Plenty of light with all of them on, super low power consumption, and individual dimming control of each bulb via arduino.

$2.37 * 8 = $18.96 for bulbs
$5 roll of ethernet cable from seconds yard
$8 arduino clone
$5 11x FQP30N06L MOSFET.
$4 Ethernet LAN Network Module
$20 10A 12VDC supply.

$60.96 AU for fully automatable light with max total 24W consumption. Super easy and tidy cabling and no dangerous mains to deal with. I'm calling it a win!

The first 8 mosfets are for the white bulbs, the last 3 for RGB channels for the strip that i'll hook up aswell.
I need to upgrade to a Mega or use softPWM to get enough PWM pins to put everything online.

Controllable via custom OSX app over USB right now but working on the ethernet control for web server control + custom iPhone app.