controllerledsignal
I need to control 12V/10W led brightness by a pwm signal. I know I can do it with an arduino and some TIP120 or another power transistor, but the question is, is there another method to generate a 95% PWM pulse without the need of an Arduino? And maybe regulate the duty cycle with a rheostat?
I'm doing this because of the big ammount heat dissipated by the led
Thanks everybody
If you are flexible, use an Arduino Lenoardo, it has a high resolution timer that can drive 3 pins. 32U4, page 130, 10-bit High Speed Timer/Counter4 EDIT: it seems like analogWrite() doesn't support it
You can mimic 10/12 bit timers with an 8-Bit timer, by skipping cycles. I wouldn't know of a way to do this with the Arduino PWM library (analogWrite()), but if you are willing to handle timer interrupts, it becomes feasible.
There are, I think, a number of issues. Try this:
Reduce C2 to .01 uF, and increase R47 to 10k. You don't list your pot value, but I'm assuming 1k. Increase this to 100k, and put a 1k in series with it. As you've got it now, the pot value gets way too low for the circuit to operate properly.
Then, you need to do a major change on your transistor output. Try something like
simulate this circuit – Schematic created using CircuitLab
Note that there are 2 LED outputs. Divide your LEDs into 2 equal groups and drive each group with one output. This will keep the PNP current levels within spec (3906s are only rated for 100 mA).
Alternatively, get rid of the transistor and R48/49 completely. The output current for a 555 is rated at 200 mA, that's about what your LEDs will draw. R48 and R49 are so low that you're drawing near that anyways.
Finally, I'd suggest reducing your base resistors (R17 - R32) to about 1k to 2k, just to make sure the transistors are driven hard on.
Best Answer
Running the LED with pulses instead of DC won't reduce the heat the LED generates at the same brightness. In fact, it will make that a little worse.
You can run the LED dimmer than full brightness using pulses, and have the LED dissipate less power than at full brightness. However, just switching between 1/2 on and 1/2 off will give you close to 50% brightness, but will cause the LED to dissipate a little more power than if it were run steadily at 50% current. That is because the voltage drop across the LED is a bit higher at full current than at half current.
To actually do the switching controlled by a digital logic signal, the easiest is to use a "logic FET" low side switch. Something like the IRLML2502 can be driven directly from a 3.3 V or 5 V logic signal on its gate. Ground the source, and connect the LED between 12 V power and the drain.