# Checking 2N2222 Transistors



## rzw0wr (Aug 28, 2013)

I am building PC boards for OR gates and AND gates.
I am using 2N2222 transistors for the switches.

I bought a pack of 100 from E-Bay.
I have installed 6 so far and had to replace 2 of them.

Is there a way to check this transistor before I install it?

I have Hfe on my meter but, if I understand it correctly that checks gain.
If I have gain on a transistor is the transistor good and can be used as a switch?

Also, should there be a minimum gain to show a good transistor?


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## fcwilt (Sep 27, 2013)

Simply check the spec sheet for the transistor and see what the allowed range for hFE is and use your meter to determine if the transistor is in spec.


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## rzw0wr (Aug 28, 2013)

Thank you fcwilt.
The problem is that I don't rightly know how to interpret the datasheet.
It has:
Hfe(1) Vce = 10v ,Ic= 150ma. 100
Hfe(2) Vce = 10v ,Ic= 0.1ma 40
Hfe(3) Vce = 10v ,Ic= 500ma 42

I am not real sure what the numbers mean, I am assuming it is a gain number.
I don't have a clue as to which one to use or to use all 3 as a range.

The ones I checked before my last card build were all 200 or higher.

EDIT:
Down at the bottom of the page, hiding from me, is the Hfe ranges.
Low is 100-200 and high is 200-300.

I will assume that anything from 100 - 300 is good. That in the 200 - 300 range is better.


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## fcwilt (Sep 27, 2013)

I'm assuming what you are looking at is something like the attached.

What is shows is hFE values for different currents flowing through the transistor.

You will notice that only one row includes min and max values. This is the range you would use.


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## rzw0wr (Aug 28, 2013)

fcwilt, yes I am looking at that.
Also down at the bottom of my sheet is "Classification of Hfe(1)"
Low is 100-200 and high is 200-300.
These match the min-max from Hfe(1).

This is the sheet I have.

View attachment 2083851067_cEZQsfrg_2SC945.pdf



Thanks greatly for your help and making me work a little to understand.hwell:


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## fcwilt (Sep 27, 2013)

Does your testing device allow any control over the conditions (Ic and Vce) used while measuring hFE?

As you can see from the chart I referenced the "optimum" Ic is 10mA, which is the value used for the min/max ratings.

Above and below this Ic current the hFE begins to drop off.


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## rzw0wr (Aug 28, 2013)

fcwilt, I don't think it does.
My meter is a Radio Shack meter.
The instructions do not mention being able to set or adjust anything.


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## T-Man (May 16, 2008)

I have a simple transistor flash set up on a breadboard. I test them there.

Ebay has an inexpensive meter that had plug spots to test both npn and pnp transistors.


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## gunrunnerjohn (Nov 10, 2010)

Why not mock up a very simple circuit on a proto board and plug them in and see if they work. All you need is a light bulb for a load, a base resistor to limit the current, and a DC power supply.


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## rzw0wr (Aug 28, 2013)

Good idea John.
I think the problem was I was using too much heat and was burning them up.
Turned down the soldering iron and the problem went away.


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## gunrunnerjohn (Nov 10, 2010)

The 2n2222A is a pretty rugged transistor, I've used them for many years. Excess heat will adversely affect them, not to mention most other electronics.


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## rzw0wr (Aug 28, 2013)

Yeah I found that out.
When a transistor gets hot enough to burn your finger you most likely ruined it.


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## fcwilt (Sep 27, 2013)

rzw0wr said:


> Yeah I found that out.
> When a transistor gets hot enough to burn your finger you most likely ruined it.


The spec' sheet should provide the working range of temperatures.

There should also be information about allowed power dissipation. 

Heat sinks can be added if needed to keep the temperature under control.


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## gunrunnerjohn (Nov 10, 2010)

When you have the imprint of the transistor on your finger in red, the part is probably toast!


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