Transistor is passing electricity from collector to emitter wrong

Thread Starter

__Bogdan

Joined Oct 15, 2021
11
I have a npn 2n2222 TO92 30V maximum transistor. I connected the + of a 12 V DC power source to a led, the led 2nd input to the collector, the base is unplugged and the emitter is connected to the minus of the source. I sketched this in a free app online(sorry if it looks like a 5 year old kid drawing). In the left is the circuit using conventional symbols, in th right is the same thing drawn with real life situation:
2021_10_15_10e_Kleki.png
My question is why is the led lit, when the base is unplugged? It shouldnt allow electricity to flow from collector to emitter if the base unplugged, correct? It looks like it allows and that completes the circuit and lit the led.
 

MrChips

Joined Oct 2, 2009
24,609
Welcome to AAC!

My first suggestion would be to double check the pinout of your transistor. There are two styles of 2N2222.

What is the actual part number of your transistor?
 

Thread Starter

__Bogdan

Joined Oct 15, 2021
11
It is 2n2222 TO92 from a brand called Arduino Clone, is it the same with Arduino? Anyway this it it:
1634324807566.png
It looks like it is a 331 after 2n2222
It has on the top a flat side with the writing and a round side. I assumed that I place it with the flat side to me and the first is Emitter, 2nd Base and 3rd Collector, thats what I saw online.
 

MrChips

Joined Oct 2, 2009
24,609
331 is too much of a coincident and could indicate a fake.

Test the leads with a DMM in diode mode. If you don’t know how to do that just ask for directions.
 

Thread Starter

__Bogdan

Joined Oct 15, 2021
11
Test the leads with a DMM in diode mode.
I have no idea what that means. I am a very beginner. The idea is that I am from a small country in Europe and I bought from an online market which native to my country. It is like the ebay of my country.
 

Thread Starter

__Bogdan

Joined Oct 15, 2021
11
I have something that looks like a screwdriver and lights if it detects electricity, without needing to complete the circuit it can detects just the + of DC or just the - of DC
 

MrChips

Joined Oct 2, 2009
24,609
A transistor has three legs. Number them as 1-2-3.

Use a meter in resistance mode or diode mode.
Measure the resistance in both directions, for example,
(1F) Red lead to 1, black lead to 2
(1R) Red lead to 2, black lead to 1

Do this for 6 possible combinations and directions.

1-2, 2-1
2-3, 3-2
1-3, 3-1

1634326440900.png



1634326405069.png
 

Thread Starter

__Bogdan

Joined Oct 15, 2021
11
I can't photograph it because I am on a PC now. This is the image of it from the website I bought it:
1634326500376.png
It is a very cheap one 10$. The product code is: V20D-Green
 

dl324

Joined Mar 30, 2015
13,505
If you reversed the collector and emitter terminals, you broke down the base-emitter junction and the current gain of any affected resistors will be damaged.
 

MrChips

Joined Oct 2, 2009
24,609
Thanks for the photo.
No, that will not work. If you have no alternative we can make it do what we want to do.

If you ever plan on pursuing electronics as a hobby or career then having a digital multimeter DMM is sound investment.
If you have limited funds, even a low cost analog meter might be better than nothing.

Let us know how you would like to proceed.
 

Thread Starter

__Bogdan

Joined Oct 15, 2021
11
I will buy the tools I need. I think this test will work: I risked a transistors and my DC adapter, but i found this:
I will note 1 2 3 the transistor legs:
I tried + to 1 - to 2 I got a short circuit
i tried - to 1 + to 2 I got a short circuit
I tried + to 2 - to 3 I got a short circuit
I tried - to 2 + to 3 I got a short circuit
I tried+ to 1 - to 3 I got a short circuit
I tried - to 1 + to 3 i got a short circuit
There is no possible combination that the transistor stops the current to flow
 

MrChips

Joined Oct 2, 2009
24,609
I will buy the tools I need. I think this test will work: I risked a transistors and my DC adapter, but i found this:
I will note 1 2 3 the transistor legs:
I tried + to 1 - to 2 I got a short circuit
i tried - to 1 + to 2 I got a short circuit
I tried + to 2 - to 3 I got a short circuit
I tried - to 2 + to 3 I got a short circuit
I tried+ to 1 - to 3 I got a short circuit
I tried - to 1 + to 3 i got a short circuit
There is no possible combination that the transistor stops the current to flow
I don't know what you did but I am going to bet that you killed the transistor.

Do not use your 12VDC adapter (or any adapter or battery) to test your transistor. You are going to kill the transistor every time.
Do you have any resistors at hand?
If so, what values do you have? We are looking anything in the 1k to 100kΩ range.
Do you have a plain red LED? (not the 12V LED that you are experimenting with).
 

dl324

Joined Mar 30, 2015
13,505
I think this test will work: I risked a transistors and my DC adapter
What is the voltage and current rating for your adapter? What do you mean by you measured shorts? I suspect that you destroyed every transistor you checked.

This is a picture of the continuity tester that can be used to test transistor junctions and many LEDs and diodes:
1634327637549.png
A tube that holds 2 AA batteries, a bulb that contacts one end of the batteries and a clip on the other.
 

MrChips

Joined Oct 2, 2009
24,609
We want to be able to create a circuit similar to this:


1634327804720.png


1634327841629.png



You must use a resistor. This is not an option. The value of the resistor is important. Without the resistor you will destroy the LED and your transistor.
We will select the resistance value depending on the voltage source you have available.
 
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