How a transistor works!

a transistor amplifies current, for example a little current in the base of a transistor can control a large current of the collector. also it can be used as a switch. all ordinary transistors have 3 pins, they are known as base (B), collector (C) and emitter (E),

a picture of an ordinary low power transistor

ciruit symbols of transistors

internal diagram of transistor maybe imagined as connecting two diodes, this picture will help you when you test a transistor. Test it as you testing a diode!

Some Tips

a transistor may be damaged if an excessive voltage is passed into it, or wrong pin connection may also be a problem. if you are building a circuit using transistors, make sure you have used all the pins correctly and used in correct voltage as mentioned in its datasheet and have chosen a correct value resistor for its base pin. The resistor in the base pin of a transistor must be chosen as the value of input voltage,for example if you choose a very low value resistor for base pin of a transistor but the transistor needs a high value resistor in its base pin, then the transistor which you use in your circuit will be overheated and will be destroyed within a few of seconds. Here are some advices to help you while using a transistor

never exceed voltage in a transistor more than its recommended valtage.

always download datasheets of transistors and see the manufacturer’s notes and other parameters.

datasheets are available in internet for free, so just enter the part number of the transistor you have got in the search box of your browser so you can find its datasheet.

Never replace power transistors with low power transistors.

the base pin of a transistor is its key to turn it on, so a correct value resistor must be used in base pin of a transistor

don’t place your hot soldering iron on the pins of a transistor for a long time when soldering, which may cause to be overheat the transistor and maybe damageed.

Testing a transistor

as i said earlier, a transistor damages only if a large voltage and current passed into it, however the “only” does’t mean “Never”, because some will damage as it is getting old or by some physical activity, and too much hot while soldering it to the pcb may also be a problem.


testing will be very easy if you have some basic skills of using a multimeter.

if you got a transistor and you don’t know whether it’s a PNP or NPN you can make a search in the google and find all its details and may even download its datasheet if neccessery. Then select your Digital multimeter’s diode test function or continuity testing(usually both functions are in same position)

PNP transistor testing using a DMM(DIGITAL MULTIMETER)

to test a pnp place your meter’s black probe in the base of the transistor and place the red probe in the collector and emitter pins, you should get a reading about “700” (reading may vary for different transistors) in both pins, and place the probes in both collector and emitter then it should’t read anything, and place the red probe in base and black probe in both Collector and emitter it should’t read anything. If these results are what you get then the transistor which you test is good. If it’s all in opposite than mentioned above then the transistor is damaged!

Testing NPN using DMM

place your multimeter’s red probe in the base pin of the transistor and place the black probe on collector and emitter, you should get a reading around “700”, and place the red probe on collector and emitter, now you should’t get any reading, place the black probe on base and red probe on both emitter and collector, it will not read anything. If these results are what you get when testing an NPN transistor, then it is good, If not the transistor is damaged!.

Some pictures

Power transistor: power transistor can handle more current so they can be used in high current circuits.

RF power transistors: used only in RF circuits

Different kinds of transistors in drawings

world’s first working transistor invented at bell labs on december 23,1947! Amazing! Is not it?

Note: this page covers only a very little informations about transistors, for advanced learning about transistors these links will help you



About Ztronn

hellooo i'm lsid ,i am a DIY (do it yourself) stuff loving kinda guy, i mean i love to build things and posting it on my blogs for the world to see. i love reading about technology and innovation. i love the nature,mysteries of space and of course God. no aliens. kindly let me know what you think about my simple innovations in the comments.
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