What resistors needed for 2N2222 transistor?

Robin91 said:

Hello,

I have troubles solving the correct resistor values for my transistor controlled led arrays.
After searching the web and trial and error i have got evrything working except the lights are to dim.

My setup:

PIC16F877A on 5V to control the 21 lines of leds and some other stuff.
2N2222 transistor to pass the 12V to the leds.
1 row contains of 6 leds for testing (gonna be 21).

Im using the transistor to put the - (end of the led row) on the ground / mass.
The led rows contains some 600 ohm resistors to get 20mA.
Now when i connect a 5V source to the base with a 10k resistor the leds stay very dim.

Do i need to put a resistor on the emitter instead of the base or am i missing something else?

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JimB said:

Are the LEDs connected to the emmitter or the collector of the transistor.

Post a schematic.

JimB

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Robin91 said:

Thank you, but my problem is still not solved.

Without the transistor evrything works like it should.

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Robin91 said:

The leds are not the problem, because when i leave the transistor out, they work perfect on 12V.
But the leds are normal "high brightness" leds of 20 mA / 3-3.3V i got from ebay.

* And they are white if that matters

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Robin91 said:

Oke i didnt know sorry.
So you need to calculate the dropped voltage when choosing a resisor?
But it does not matter if i put the resistor on the base or the end of the array right?

I guess ill buy some 150R resistors then.

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Robin91 said:

I accedently blew up my test resistor on the board and when i replaced it, the leds burn like they should.
Thank you very much for your help.

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carbonzit said:

Eric--have you got a link for that LED reference (so I can get the text)? Very useful info there.

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