how to know the transistor is npn or pnp

This is the place for any magazine-related discussions that don't fit in any of the column discussion boards below.
Post Reply
Posts: 11
Joined: Wed Dec 21, 2005 1:01 am
Location: yuytutfg

how to know the transistor is npn or pnp

Post by newone » Wed Dec 21, 2005 9:40 am

how to know the transistor is npn or pnp

please whith full detail

User avatar
Posts: 122
Joined: Sun Apr 17, 2005 1:01 am
Location: Victoria BC

Re: how to know the transistor is npn or pnp

Post by HighFrequency » Wed Dec 21, 2005 11:44 am

ummm... read the part number off the transistor case, then google it.
There is only one correct answer, mine.

Posts: 35
Joined: Fri Jul 01, 2005 1:01 am
Location: Minnesota

Re: how to know the transistor is npn or pnp

Post by mnboy » Wed Dec 21, 2005 11:45 am

Either Google it, or do a diode test.

User avatar
Posts: 1289
Joined: Thu Jan 03, 2002 1:01 am
Location: Northern Illinois

Re: how to know the transistor is npn or pnp

Post by jollyrgr » Wed Dec 21, 2005 5:12 pm

This can be done rather simply with an Ohm meter. If the leads are labeled, you have most of the problem solved. If not, all is not lost. With standard TO-92 case devices with the flat side facing you and the leads pointed down, the pin out is E B C in most cases. But in rare cases this may not be the proper pin out. In addition to explaining the procedure for testing for the polarity, I'll explain how to find which lead is what.

Mentally identify the leads as 1, 2, and 3. Take your Ohm meter and measure the resistance between leads 1 and 2. (Use the "diode" setting or the range that will give you 200 or so Ohms on the max scale.) Reverse the meter leads and note the reading again. Do the same for leads 1 and 3, measuring with both polarities of the meter. Lastly do the same measurements on leads 2 and 3.

For two pairs of leads you should get a high Ohm reading and a low Ohm reading. For the remaining set of leads you should get two high readings. (Usually the "high" reading will be infinite or OUT OF RANGE on a digital meter; the low reading will vary from one type of transistor to another.) The two leads that give you high readings in both directions of the meter probes are the EMITTER and COLLECTOR leads. This means the remaining lead is your BASE lead. While we have not found which lead is EMITTER and which is COLLECTOR we have by process of elimination found the BASE lead. And this is what we will need to determine what the polarity is. To identify which lead is the COLLECTOR and which is the EMITTER can be done with some bipolar transistors. More will follow after we determine the polarity which is our next step.

If you are familiar with transistors you will know the bipolar style are NPN or PNP The BASE is the material that is in the "center" letter of the two types. Connect the RED meter lead to the BASE. Connect the BLACK meter lead to each of the other two terminals. If you get LOW readings on both leads this is an NPN transistor. If you get HIGH readings on both leads, reverse the meter connections and try again. This time if you get two LOW readings you have an PNP transistor.

To identify which lead is the EMITTER, take note of the two LOW readings. One of the two LOW readings will be just a bit lower than the other. The LOWER of the two low readings is the EMITTER lead. This is because the EMITTER is slightly more doped than the COLLECTOR. The EMITTER section is slightly larger as well as it must carry the BASE current in addition to the COLLECTOR EMITTER current.

(I hope I got this right and didn't mess up my polarity logic. Any faults or corrections are welcome.)
No trees were harmed in the creation of this message. But billions of electrons, photons, and electromagnetic waves were terribly inconvenienced!

Posts: 276
Joined: Tue Sep 14, 2004 1:01 am
Location: Lansing, Michigan, USA

Re: how to know the transistor is npn or pnp

Post by Enzo » Wed Dec 21, 2005 7:39 pm

EBC is for American transistors. Japanese numbers like 2SC945 have an E C B arrangement. Frankly I see more of them than I do 2N or MPS numbers. And I have never been sure which way Euro transistors are laid out.

Post Reply

Who is online

Users browsing this forum: No registered users and 19 guests