BC337 not working - darlington???

[DanPBP]

First, thanks for you answers!

And one more question, could this darlington transistor work?

MPSA14 http://www.onsemi.com/pub/Collateral/MPSA13-D.PDF

Daniel.

[T.Jackson]

My first bit of advice would be to learn OHM's law. If you have a collector resistor of 100 ohm, and VC (voltage collector) is 7.2V, the most amount of current you'll squeeze out is: VC - (0.6 + 3.2) / 100 = ~34mA The 0.6 is the emitter drop on the transistor while the 3.2 is the drop on the LEDs.

[Acetronics2]

Hi, Trent ...

There are TWO leds in series ...

7.2 - 3.2 - 3.2 - .6 = ... .2v

.2 v / 100 ohms = ... 2 mA

and the light was ... NOT !!!

Alain

[T.Jackson]

Must be those new white LEDs. Never used them.

[Acetronics2]

Hi, Trent

Buuuuuut,

you forgot the BC 337 base is @ 5v level !!!

so, Emitter is @ 4.4v !

4.4 - 3.2 -3.2 = - 2v !!! LOL

The leds NEVER give any light !!! ...

Alain

[T.Jackson]

It's an NPN transistor, meaning the base must be at 0.6V greater than the emitter in order for it to turn on. I too fail to see how it would ever switch on if those LEDs are in fact 3.2V types.

[DanPBP]

Hi Guys,

The circuit as I posted works fine with more than 5 volts on the base of the transistor, fully bright LEDs.

Yesterday, I did a new PCB with the BC337 placed between cathodes and ground and now they work just fine with the PIC.

Thanks for your help! Btw, I'm a software guy, sometimes electronics beats me.

Daniel.