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Topic: Dimming 1w leds with transistor and walwart issues (Read 3 times) previous topic - next topic

nkd5025

fungus,

I did know this already and have a constant current driver that will supply voltage to one or all of the leds, that was actually the first ting I tried to dim them with before the 5v source.  Since it didn't work as I did not provide the common ground I just assumed that the constant current driver just pumped out more current to compensate for the dimming and keep the led at its max.

I just hook up the circuit with the constant current driver and it is all working as it should, thank you very much!
If you know of  place off the top of your head, is their a website that provides basic electrical knowledge and covers a wide basis of topics?

Nick D.

nkd5025

I noticed that when I keep the led at 350mA, which I tested with a meter, the 2n2222 transistor gets very hot very quickly.  So since this is too much current for the npn's can I use a TIP120 Power Darlington Transistor from adafruit for the job?

fungus

Try a smaller resistor on the transistor base, maybe 330 or 220 ohms. 1K might be too high to fully open the transistor.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

nkd5025

with a 220 ohm it still get too hot to touch very quickly.

dhenry

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the 2n2222 transistor gets very hot very quickly. 


That's the issue with a small device like that.

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So since this is too much current for the npn's can I use a TIP120 Power Darlington Transistor from adafruit for the job?


It will help with cooling but not with power dissipation: the darlington will have considerably higher voltage drop than the 2n2222.

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with a 220 ohm it still get too hot to touch very quickly.


That's fundamentally an issue with such a linear solution.

I would go with a larger npn (not a darlington), or a mosfet (irf510 for example), with a heatsink (or to put it in the tank).

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