Why i am killing my tip120 ?

Hi all,

I am new in electronics and encounter a problem with a tip120 transistor. I wire it this way:

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.

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?

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

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

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.

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

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.

cjdelphi:
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 ?

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

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

Yes, and the led is still light

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…

confusion.png

ah yes, my amazing circuit design skills :smiley:

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.

Sorry but i don't understand your schematics :astonished:

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

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 ?

What, where's the voltage in (5v supply directly from USB) pin? i see 2 2v pins, surely not 1 is Vin? :fearful:

different LED’s require different voltages, Red being the brightest with the least (something to do with the band gap, wavelengths and things I never understood)

White for example will light dimly from a 3v cell coin, but a Red will shine really brightly… so if you used a white led, combine it with a voltage drop 3.3v, you’re at the limit’s a 5v would be better that’s all.

Are you certain that is a TIP120 (NPN), and not a TIP125 (PNP)? Under these conditions, the TIP125 would keep the LED lit no matter the voltage on the base. Look at the polarity of the collector-emitter diode in the product schematic. Left is NPN, right is PNP.

Just checking...

Oh crap! they are labeled TIP 135 :astonished: But i ordered some TIP120!! The box is labeled TIP120!

That is the problem. It is being lit by the collector-emitter diode. That is why you are seeing 0,5v collector-emitter.