I just want to make it as simple as possible. I've tried using a potentiometer but it just wouldn't work.Welcome to AAC.
Part of the reason PWM is used is efficiency. You might as well use an incandescent bulb if you are going to waste the energy you are talking about.
LEDs, 555s, Flashers, and Light Chasers
Thank you very much! I'll start reading about PWM and hopefully I can make my own circuit.Hello,
That led probably needs 350 mA to light up.
The voltage may be between 3 and 4 Volts.
A LDR will never manage the 350 mA.
As Bill said PWM will be the correct method to dimm the led.
Bertus
Thanks a lot for the quick responses! Sorry for my ignorance, I'm a newbie to electronics and I just want to make things convenient for me. Anyway, this seems to be a great community.I'm wondering what your aversion to PWM is all about?
High-power LEDs really need a buck or buck-boost type of current regulator instead, as other methods are inefficient (such as purely resistive). You'd need a physically very large resistor, and it would make a good room heater.
Have a look at BuckPucks:
http://www.ledsupply.com/buckpuck.php?gclid=CO7Hncve-LACFU2htgod7hXzlQ
Not particularly cheap, but compact, reliable, and relatively easy to wire up.
An LM317 has a rather large dropout when used as a series current limiter (~3v), and since the LED is probably dropping ~3.2v-3.6v across itself, you're just about guaranteed to waste at least half as much power across the LM317 & resistor as you would in the LED itself.If you need help with the circuit we can help, or I can show you how to do it with a LM317 (which will get very hot, as it is the same as a resistor).
It was Bertus who mentioned 350mA, and I agree that Bertus is most likely correct.Wookie caught me out on one detail, his 350ma figure is correct.
I would really appreciate it if you could teach me how to use a current regulator. I'm using a power supply with voltages up to ~5V.If you need help with the circuit we can help, or I can show you how to do it with a LM317 (which will get very hot, as it is the same as a resistor).
Wookie caught me out on one detail, his 350ma figure is correct. I have a 3W LED.
What is the power supply voltage you are powering this with? If it is not stable (such as a car would be) we need to know.
Most of these circuits are pretty simple. Don't sweat it.
Since I brought it up automotive is not allowed. The exception is the cigarette lighter. That is never my first assumption though.
Oh, what I meant was I was only using around 5V for this project. I actually have a 15V power supply.If your power supply is only 5v, then you are just about out of luck.
That won't leave enough "headroom" for either the BuckPuck or the LM317.
If your LED drops 3.6v, you will need at least 2v more; 3.6v+2v=5.6v.
With an LM317, you would need at least 6.6v.
I tried getting the characteristics of the LED by creating a simple circuit with the LED, a resistor, and the voltage supply. The peak voltage across the LED is ~3V. The current on that circuit was ~370mA.That would work.
Where is this 5V coming from? I ask because we need to know how regulated it is.
At that low voltage a buck puck or LM317 won't work. If you could use the 15V more options open up.
I suspect I know the answer on this one, have you ever soldered electronics before?
We'll probably have to adjust our responses to your skill level.
I don't really remember the resistor getting hot. The HPLED was quite hot thought.Shoot, if the power supply is stable, like a computer PSU, you are there. I would consider 370ma close enough. Does the resistor get hot?
by Duane Benson
by Jake Hertz
by Jake Hertz