Dimming a MR16 12V LED bulb

Hi

I am only a beginner and was wanting to make a circuit to control the brightness of a 12v MR16 4W LED bulb.

I am assuming these work on constant voltage rather than constant current? If I used a PWM to control the bulb would this still work or does this only work for Constant current LED's?

Thanks in advance for any help you can offer

A bulb like this
http://www.lightexports.com/smd-led-4w-mr16-gu5-3-bulb-ac-dc-12volt-6400k-60w-replacement/?gclid=CK3yquG578gCFYSRHwod_WoMrg
more than likely has current control built in, so you could likely get away with pulsing the 12V source to dim the brightness.
Some even say they are dimmable
[url[http://www.amazon.com/12V-Dimmable-MR16-LED-Bulb/dp/B005YVCUOE[/url]
and dimmers are available
LDK-8A 12~24 Volt DC Single Color LED Dimmer | Super Bright LEDs
Single Color LED Dimmer Switches | Controllers & Dimmers | Super Bright LEDs

Most of them just use LED's with a resistor. Those you can dim easily with PWM and a MOSFET. But there are also current driven models and then PWM may not work.

So it all depends on the model of MR16 light....

I have no experience of using this type of LED, but when I Googled "12v MR16 4W LED", a lot of the results said that that particular one was non-dimmable.

So I guess it is like septillion said, it all depends on the model of MR16.

Thanks for all the info

I guess in true arduino style I should build what I think might work and give it a try, what's the worst that can happen !!

Am I correct in thinking that if the bulb will dim using a pwm and mosfet that if I were then to power the bulb using a battery it would increase the time it would run, due to the reduced current used?

Am I correct in thinking that if the bulb will dim using a pwm and mosfet that if I were then to power the bulb using a battery it would increase the time it would run, due to the reduced current used?

Probably… PWM switches on & off, so the average voltage & current is less. But, that assumes a passive-linear (resistor like) load. It probably will consume less energy but I don’t know if it will dim properly with PWM.

These things contain a built-in power supply that’s usually designed to run from 12VAC and we can’t predict how it will react to PWM.

If you haven’t done so already, try it with regular 12VDC first, and maybe try it with 5VDC to see if it dims without flickering or otherwise acting strangely.

The MR16 LEDs I have converted had a constant current driver board inside.
Like this one.
The chip on that board (PT4115) can be converted to PWM dimming by soldering a wire to the control pin.
Datasheet is available online.
Leo..