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zoobyshoe
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Today I learned how to tell if a transistor is NPN or PNP:
zoobyshoe said:Today I learned how to tell if a transistor is NPN or PNP:
zoobyshoe said:Today I learned how to tell if a transistor is NPN or PNP:
The setting he says to use is "diode". As far as I know, that's a setting only available on digital meters. At least, the old Radio Shack analog meter I have has no such setting.jim hardy said:be sure you know for certain, by actual test, that the red lead indeed applies positive when ohms is selected.
zoobyshoe said:Today I learned how to tell if a transistor is NPN or PNP:
Good to know, and it's the first time I've ever heard this. Everyone seems to say the middle lead is the base. But this may explain why one of the transistors I tested seemed to be "broken." Unfortunately, I tossed it out and can't recheck it.collinsmark said:Also, the author of the video seems to make the potentially grave assumption that the base of the transistor is the middle lead. I can assure you with certainty that this is not always the case.
Also very good to know, and it means I can use either meter. What's a convenient way of testing which lead is positive?But you could use the Ohm reading on most multi-meters. But like @jim hardy brings up, if you use the Ohms reading, you might want to verify which multimeter input is which.
Good, thanks!Once you determine the base lead and find out if it's an NPN or PNP, finding out which is the emitter and which is collector is a different story. It's difficult to do with with 100% reliability without testing it in a real circuit. But usually the connection with the higher voltage drop (in reference to the base -- comparing the two diode candidates) corresponds to the emitter.
zoobyshoe said:The setting he says to use is "diode". As far as I know, that's a setting only available on digital meters. At least, the old Radio Shack analog meter I have has no such setting.
In addition to that meter, I do also have a digital meter with the "diode" setting, and that's what I used to test some unknown transistors I'd pulled off some random board.
Anyway, it seems you're saying they can also be tested by setting the meter to test resistance (provided you're sure you know which lead applies positive voltage)?
AMEN ! That is a real challenge.collinsmark said:Once you determine the base lead and find out if it's an NPN or PNP, finding out which is the emitter and which is collector is a different story. It's difficult to do with with 100% reliability without testing it in a real circuit. But usually the connection with the higher [forward] voltage drop (in reference to the base -- comparing the two diode candidates) corresponds to the emitter.
Thanks, Jim! I think I'll try to remember to stick to the digital meter diode setting, since I'm likely to forget which ohms order of magnitude won't damage the transistor.jim hardy said:Yes they can be tested on an ohms setting.
On better analog meters that have a RX1 scale, one should use the RX10 setting NOT the RX1 scale.
That's because analog meters can apply substantial current when selected to RX1, like ~150 milliamps, which can wreck a small signal transistor.
A good junction will give about 2/3 scale deflection
a shorted junction will of course give full scale deflection , zero ohms
a Darlington transistor's E-B will give about 1/3 scale deflection because it's two junctions in series.
One should avoid the highest resistance scale, RX10k on the Simpson pictured, because most analog meters when selected to that scale apply in excess of 6 volts which exceeds the reverse E-B limit for most transistors.
View attachment 93199
We've had threads about how analog ohm-meters work in EE forum.
One can extract a lot more information fromhis meter if he understands its inner workings.
if there's interest , re-open or start another one ?old jim
It strikes me as odd they never adopted some conventional markings to identify whether it was PNP or NPN, or to identify the base, collector, and emitter.jim hardy said:AMEN ! That is a real challenge.
Here's what i do-
take advantage of the fact that a transistor will operate with E-C swapped but not very well, it has at lower gain than with E-C connected properly.
So - i think of the mystery transistor's three leads as Base, Unknowns U1 and U2
I hook one ohm-meter lead to Base, other meter lead to transistor's U1 with polarity so B-U1 junction doesn't conduct. That means junction is reverse biased as a B-C junction should be,.
Next I moisten a fingertip and touch it to B-U1 leads. That injects a small current into B through my fingertip. I observe how much the meter needle rises.
Then i move meter lead from U1 to U2 and repeat moist finger check, and note which gives bigger needle rise - U1 or U2. Repeat until I'm sure.
Knowing that the transistor works better when correctly biased, i surmise that whichever U gives bigger needle rise is the collector.
Hasn't missed yet for me though sometimes i have to use RX100 scale...
old jim
zoobyshoe said:It strikes me as odd they never adopted some conventional markings to identify whether it was PNP or NPN, or to identify the base, collector, and emitter.
Perhaps some insight might come from the fact that these same packages are also used for things that are not even similar to BJTs. And not just other transistor technologies like J-FETs and MOSFETS, but also complete integrated circuits. Voltage regulators come to mind; they also have three leads and use the same package types as transistors. Modern day transistors are really, really tiny, and on an integrated circuit you could easily fit thousands (even tens of thousands) of them in that tiny package, as long as the complete circuit itself only required three external leads. So the packaging is used for more things than just BJT transistors.zoobyshoe said:It strikes me as odd they never adopted some conventional markings to identify whether it was PNP or NPN, or to identify the base, collector, and emitter.
Yes, that makes a great trivia question. And, by extension, makes a great post in the spirit of this particular thread.OmCheeto said:"Conventional"? In the EE field? Ah! Hahahahaha!
http://web.engr.oregonstate.edu/~traylor/ece112/lectures/elect_flow_vs_conv_I.pdfAnd there are still arguments about it.
In 1752, prior to electricity being identified with the electron, Ben Franklin chose a convention regarding the direction of current flow. Franklin assumed that electrons (being assumed positive) flow from positive to negative terminals. We now know this is incorrect.
Hornbein said:He also used to route lightning strikes through the interior of his home.
In vacuum tubes electrons actually do leave the cathode and arrive at the anode , aka plate.collinsmark said:Franklin's choice does confuse students. I agree there. Students initially want to imagine current as something tangible moving around. But Franklin's convention is not really wrong. Separating electron flow from a more abstract idea of "current" sometimes has conceptual advantages, which students learn later down the line.
My high school textbook was the 1962 edition of the GE transistor manual. Found it online hereHere the emitter emits electrons, the collector collects electrons and the base controls the flow of electrons by controlling the charge concentration in the base region, so in the broadest sense, the function of the three elements in the triode tube and the transistor are similar..."
Good possibility I wouldn't be a member here today if this wasn't part of my upbringing.jim hardy said:... 'Slide rules and electron current got us to ...
OmCheeto said:"Conventional"? In the EE field? Ah! Hahahahaha!
http://web.engr.oregonstate.edu/~traylor/ece112/lectures/elect_flow_vs_conv_I.pdfAnd there are still arguments about it.
In 1752, prior to electricity being identified with the electron, Ben Franklin chose a convention regarding the direction of current flow. Franklin assumed that electrons (being assumed positive) flow from positive to negative terminals. We now know this is incorrect.
Use a diode or a known transistor as reference, or use a second multimeter.zoobyshoe said:Also very good to know, and it means I can use either meter. What's a convenient way of testing which lead is positive?
Despite "conventional current," think of all the things in electricity and electronics that are successfully identified by conventional markings. The first one that comes to mind is resistors. Next is batteries. The positive and negative terminals are physically different in shape on most batteries, and if they're not (as with a car battery) they're clearly marked + or -. Diodes are clearly marked. LED's have the positive lead physically longer than the negative. Electrolytic capacitors have the positive and negative sides clearly marked. Speakers, microphones, and motors nearly always have a red wire soldered to the positive terminal. You don't have to get a meter out and laboriously measure any of these components: they're marked one way or another.OmCheeto said:"Conventional"? In the EE field? Ah! Hahahahaha!
There are many unconventional batteries, phone batteries for example, but that doesn't make it impossible to mark conventional batteries.collinsmark said:Perhaps some insight might come from the fact that these same packages are also used for things that are not even similar to BJTs.
Of these three, I think diode wins.mfb said:Use a diode or a known transistor as reference, or use a second multimeter.
I don't follow.To make things worse, some multimeters use very low voltages to test resistances, if the voltage is too low it might read high resistances in both cases.
This thread survived a 5 page excursion into a peculiar property of factorials unscathed. Things will normalize. Don't worry.I think we should make a separate thread out of that discussion as it is beyond the scope of "today I learned".
If you apply a voltage of 0.2 V (multimeter in an unfortunate resistance mode), it will be hard to see conductance in any direction.zoobyshoe said:I don't follow.
Oh, you mean because the needle will hardly deflect.mfb said:If you apply a voltage of 0.2 V (multimeter in an unfortunate resistance mode), it will be hard to see conductance in any direction.
The digital meter should have the "diode" setting, so you can use that, as per the video.mfb said:More thinking about digital multimeters here, but the measured resistance value will be high if you are below the threshold voltage.
I think he's saying that the voltage must be at least 0.7v, otherwise current will not flow in either direction.zoobyshoe said:The digital meter should have the "diode" setting, so you can use that, as per the video.
The pins on a transistor are typically labeled as Emitter (E), Base (B), and Collector (C). The Emitter is the heavily doped region of the transistor, the Base is the lightly doped region, and the Collector is the moderately doped region. These labels can also be identified by looking at the physical structure of the transistor, as the Emitter and Collector are typically larger than the Base.
The main difference between NPN and PNP transistors is the direction of the flow of current. In an NPN transistor, current flows from the Collector to the Emitter, while in a PNP transistor, current flows from the Emitter to the Collector. Additionally, the majority charge carriers in an NPN transistor are electrons, while in a PNP transistor, they are holes.
The easiest way to determine if a transistor is NPN or PNP is by looking at the orientation of the pins. In an NPN transistor, the Emitter will be on the left side, the Base in the middle, and the Collector on the right. In a PNP transistor, the Emitter will be on the right side, the Base in the middle, and the Collector on the left.
The Base in a transistor acts as a control switch for the flow of current between the Emitter and Collector. When a small current is applied to the Base, it can control a larger current flowing through the transistor, making it useful for amplifying or switching electronic signals.
Yes, a multimeter can be used to determine if a transistor is NPN or PNP. By setting the multimeter to the diode test mode and placing the positive lead on the Base and the negative lead on the Emitter, a reading of approximately 0.6V indicates an NPN transistor, while a reading of approximately -0.6V indicates a PNP transistor. This method may not work for all types of transistors, so it is best to consult the datasheet for the specific transistor in question.