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[on:]

Hi all,

I am new in electronics and encounter a problem with a tip120 transistor. I wire it this way:
http://floran.morel.free.fr/Divers/versys_bb.jpg

The problem is, the led is always ON, and when i am testing the transistor with a multimeter in diode mode, i find 0,5v between the collector and emmiter. So i kill it and i don't know why  

I need some help to understand where is my mistake.

[Reply #1 on:]

I cannot find a datasheet on that TIP220 transistor. Can you post a link to it? Are you sure it is a TIP220 and not a TIPXXX in a TO-220 case?
 

[Reply #2 on:]

My mistake, it is a TIP120 in a TO220 as you said

here is a ilnk to the datasheet:
http://www.produktinfo.conrad.com/datenblaetter/150000-174999/150872-da-01-en-Transistor_TIP_120.pdf

[Reply #3 on:]

It's a Darlington, Collector, Base Emitter.


- not a mosfet as your circuit would describe.

you're not blowing them, they work still no doubt, collect D3 of Arduino to the Base Pin (middle/2 pin), Emitter to GND, Collector to your LED's GND (short lead) and the Anode + side goes straight to your 5v rail.

[Reply #4 on:]

But, add a 1 - 10k resistor on base or it could damage the arduino pin.

[Reply #5 on:]

Try connecting the wire connected to the Arduino D3 pin to ground instead of the Arduino pin. Does the LED still light?

@cjdelphi: That is not what the datasheet shows. Pin 1 is the base.

[Reply #6 on:]

you're not blowing them, they work still no doubt, collect D3 of Arduino to the Base Pin (middle/2 pin), Emitter to GND, Collector to your LED's GND (short lead) and the Anode + side goes straight to your 5v rail.

According to the datasheet, the base pin is the pin 1, right ?

[Reply #7 on:]

Pin 1 is the base. Did you try the test?

[Reply #8 on:]

Pin 1 is the base. Did you try the test?

Yes, and the led is still light

[Reply #9 on:]

ah yes sorry my bad, I looked at the Darlington first, then i went back to a similar datasheet i had open and looked, then i went back and realized.

take a look at the attachment....

[Reply #10 on:]

ah yes, my amazing circuit design skills

[Reply #11 on:]

fair enough, so what resistors you using? to connect the transistor? i'd use a 1k for the base, and then 300 ohms to limit the LED current, also while you're at it, move it from 3v to 5v, it's possible if you're not
using a red led, it will be dimly lit, even less so with the voltage drop through the transistor.

[Reply #12 on:]

Sorry but i don't understand your schematics 

[Reply #13 on:]

^^ so just swap to a 5v source and let us know the resistor values.

[Reply #14 on:]

I put a 1K resistor between D3 and the base pin, also put a 200 ohms resistor for the led

Why do i need to change the voltage to 5v ?  3,3v is not correct ?