I'm thinking of making a high powered par can type thing and I'm not sure what all I should use. I was thinking of using a 30 watt rgb led with 3 constant current drivers (one for each channel) and 3 power mosfets with pwm control off of an arduino. This seems like a pretty easy way to get it up and running but I'm not sure what mosfets or heat sinks I should use because theres so many of them.I would like to use a mosfet that has 3 actual mosfets in one case so that I could just use one monster heat sink rather than three smaller ones. I'll post links to the led and drivers below. Also if anyone has suggestions for heat sinks that would be good, I've been looking for a long time and theres soooo many its crazy. For the LED I was thinking probably a forced air sink with a thermal resistance of about .5 C/W and I'm not sure what I would need for the mosfets. Thanks in advance
You cannot PWM these constant current driver circuits with the expectation that they would dim an LED. LED brightness is based on current; these drivers are "constant" current meaning they'll output only one quantity of current no matter what kind of power you feed them. You need to look for a driver that explicitly allows dimming.
Sorry that is wrong, you PWM the constant current so that it is either on at a constant level or off altogether. It is exactly the same technique but applied to the current control circuit.
By the way what is a LED par can? I have not come across those words.
Yeah my plan was to PWM the current from the constant current driver to the LED so it should work fine. I'm going with that driver because its so cheap and I'm on a really small budget. Par stands for parabolic aluminized reflector, its a type of light usually used in DMX systems that has a cylindrical body and a reflector in the front-
They often have non-LED light sources but the ones that do can be controlled much easier without gels and of course use less power. I'm planning on putting it up in my room, probably mounted on a store bought mounting bar so that I can add to it in the future. And considering that my room isn't huge I think that 30 watts is more than enough to light it up
Thanks,
I did a lot of stage lighting in the late 60s early 70s but I have not come across that term. I suspect it has been introduced since I stopped doing it. They had only just got on to solid state dimmers when I left. Before that it was 2 foot long variable resistor sliders, if you wanted to dim more than two at the same time without an assistant you used a large stick to pull several down at once.
Any suggestions on a good general purpose high power mosfet that could handle the high speed, high power (led drives at 350 mA, like 30 V for each channel) and relatively low power coming from the arduino to turn it completely on. I've actually never used a mosfet before so I don't have a frame of referance. I've only used transistors and I've not been super happy with the whole voltage drop and massize amounts of heat being created. I think I found a pretty cheap fan assisted heatsink that will work for the led
Well 350mA is not a high current for a FET so most will do. You have to make sure they are logic level FETs (it should say in the data sheet). However just switching is not the biggest problem but maintaining the current at 350mA is. This calls for a constant current supply and there are lots of modules and ICs that will perform this function. You can not just use a resistor to limit the current. The next problem is getting rid of the heat from the LED, some LEDs have built in heat sinks others you have to add your own.
Have a look at these old threads:- http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1234273497 http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1258412419
and also follow the links off these threads.
Ok thanks. Like I said I am going to be using constant current drivers which I think were meant for these LEDs so that shouldn't be a problem. And I found a good heat sink for the LED im using. How much heat will the mosfets make?