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Could I use tip31c transistors to dim LED lights of 0-5w? Answered

Like the Music to LED blinker projects. I was thinking that instead of using the LEDS to blink to the voltage which I think is the peak in voltage. I could use a pot to control the input of voltage and then the transistor could ramp it up like show in the instructable(s).

Example: as you increase the voltage with the potientometer the tip31c controls the amount of voltage that is produced.

Oh, and by the way im using slide pots, thats why I dont use a light dimmer.

If you have any other suggestions of thoughts you are free to say.

Thanks Oscar.


With heatsinks, yes, that'll work. They'd be better arranged as constant current sources/

Thanks for your comment I was wondering about heatsinks. Do you mean a LED driver as a constant current source ?
Also, if you dont mind What pot size should I use. The voltage it will handle is 0-3v

Thank you

I was going to make this circuit but I could not get the parts for it
But thanks for your suggestion

Hi again, Its not THAT critical, but I see what you mean Maplin is useless these days. :-( Try RapidOnline.com instead. They are almost what Maplin USED to be.


Thats what I use now, im ordering the parts for the circuit I was first using.
Where do you get these diagrams from? and will that one you have suggested need to be heat sink'd?


I designed 'em !
Yes, you need to heat sink, but if you do it right, they needn't be that big - just a metal plate, with the appropriate insulator kit.


Oh! I have a look in to this circuit. Do you have the the ratings of the resistors and pot?


The pot can be a 10K, if you're using darlingtons. The R under the LED depends on the voltage and current that the LED need. What's the MAXIMUM current in the LED to be ?

Oh sorry I wrote volts! the maximum current is 1amp.

Thanks for your help by the way it very much appriecated.

Alright, let the maximum voltage across R be 2V, then R= 2/1 = 2 Ohms. It will need to be a 2W resistor at least.

Play with the rest - put a 1K current limiting resistor in series with the base of the transistor and add a 1k pot (changed my mind from the 10K)

Right! I just took a trip to 'solar shed' to see my pots and ive got em' I have the 1k resistor from the diagram I was going to build. Ill keep you updated with the final result.
Thanks again for the help i'll send you a patch, sorry about the mistake.


Try it with ONE LED, and MEASURE the LED current. Check that the current stays reasonably stable with supply voltage changes if you can.

Here's another circuit: you could use your TIP transistors to good effect.
Play with it carefully. The circuit works by making the voltage across the resistor under the LED equal to the voltage on the base of the transistor. The zener diode should be arranged to equal the maximum voltage you should expect to see across the resistor, when the maximum current is flowing in the LED.

discrete current source.jpg