How to Make a Very Simple NPN Transistor Tester


Introduction: How to Make a Very Simple NPN Transistor Tester

in this instructable i will show you how to make a very simple NPN transistor tester.

Step 1: You Will Need:

a NPN transistor (to test) 
a 10K OHM resistor
a 470 OHM resistor
a on/off switch
and a 9V battery (5-12V)

Step 2: Making It.

here are the schematics. and a picture of my finished product.



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    Thanks for the upload ,pls may i know . how do i test a transistor using a PIC microcontroller? im ean what mechanisms or theory will the PIC employ while testing the transistor

    No transistor socket on the PC board, no they still such an animal anymore? Of course you can always check a transistor for basic functionality with an ohm meter no shorts or opens it should work to a degree.

    In my science book we have a super basic section of electronics and its kinda sad... But in later years when I actually go to school for electronics I'll learn about it. Maybe my dad dose know maybe he doesn't, he gave me all of his NEETS modules from the Navy and they have EVERYTHING about electronics!

    1 reply

    In regards to NEETS. NEETS can be read online, while connected the to the internet. Because I couldn't find a place where can download the individual modules as I did years ago I'm in the process of uploading the modules to www.archive org I see that the ones I have already upload are being downloaded. Also I see they are being converted to the format the Kindle can use.

    I have no idea what all of those numbers and symbols are and what not but very smart! Electronics are almost always fun (not when they dont work)! I cant wait till I'm 17 because theres a guy that works at EATON that wants to hire me! He gives me all kinds of electronics thats they dont need worth $1000's so I sell it on eBay! I LOVE IT!!!!

    maybe you could made something to reverse the polarity so you dont need one battery.

    Nice! I'm subscribing to you! I'll look @ what ever you make!! =D

    1 reply

    Soo...Hate to sound stupid but I am tryin to grasp the concept of how all of this works. I understand for the most part what NPN and PNP mean (NPN- Power applied to "B" will allow power to pass through "C" and "E", PNP is opposite). I also understand that to run a LED you need a resistor to create the proper power for the bulb. But...why the resistor on the tester line? Why cant you just run straight power from the 9v to "B"?

    Also I see the one comment below recommends changing the 10k to 100k and the 470k to 330k, how does that change it "that much"?

    3 replies

    without the resistors you'll blow the led and transistor and i dont know, all it does it light up the led if there is a working transistor.

    I guess I had assumed that once the power from the test leads hits B it is simply redirected out of E back to the power source. I just thought it treated the transistor like an on/off switch and never touched the LED. Also how much power can the resistor take? I have seen some that say they can handle 60v. Sorry I am new to this and trying to learn from all sources.

    the 470ohm resistor is for the LED and the 10k resistor is for the transistor, and you are right it does acts like a switch and the power goes through the LED to show you the transistors working properly, and not all transistors can handle 60V, the one in the picture (c945) can but this is "universal." I made this when i was pretty new to electronics, i'll be glad to help anytime.

    I have 3 questions: 1: how can I tell which lead of the transistor is which (and can't find the data-sheet online)? 2: I have a component that looks and acts like a transistor, in that it needs a small current current through one of the leads to connect the other two, except it stays on after that base current is shut off. What is it and is it useful? 3: is there any way to determine it's frequency or max current? Thanks!

    2 replies

    when you hook it up the only leads that will make the light come on are the base and emitter or vice versa,and the datasheets, use this website, and could you put up a picture of your thing and i might know what it is (also give me all the markings on it)

    Never mind. I think it's this or one of these, "Silicon Controlled Rectifiers".

    Apparently it's ". . . designed and tested for repetitive peak operation required for CD ignition, fuel
    ignitors, flash circuits, motor controls and low-power switching applications." -could be useful.