NPN vs. PNP Transistors as Common-Emitter Switches

NPN and PNP transistors are two complementary types of bipolar junction transistors (BJTs). They both work the same way: when current flows thru the Base-Emmitter junction, the transistor "turns on", and creates a current path through the Collector-Emmitter junction. The amount of current that will flow through the C-E junction (our "Load" current), is determined by the amount of current flowing thru the B-E junction (our "Control" current). (The C-E current is typically larger than the B-E current, and it's equal to the B-E current multiplied by some value, called "hFE" or "common emitter current gain".)
The only significant difference between an NPN and a PNP transistor is that to turn on an NPN transistor, current flows IN to the Base and OUT of the Emitter; we accomplish this by applying a positive voltage to the Base relative to the Emitter. To turn on a PNP transistor, current must flow IN to the Emitter and OUT of the Base (the opposite direction of NPN), and to accomplish this we a apply a negative voltage to the Base RELATIVE TO the Emitter. That is why you see things like "-5V" in a datasheet for PNP. Usually the Emitter is "common" and thus a voltage reference for the Base.
Bipolar transistors are often used as simple switches in a "common emitter" configuration. For NPN transistors, we tie the Emitter to ground and turn the transistor on by applying a voltage to the base that is higher than ground; the Collector provides a "switched ground" output (either "open" or tied to ground).
For PNP transistors, we tie the Emitter to our positive power supply rail, and turn the transistor on by applying a voltage to the base that is lower than the positive power supply rail; the Collector provides a "switched positive" output (either open or tied to the positive power supply rail).

[@HellaFunnyShorts]

One of the best, simplest, and most straight-to-the-point demonstrations I've seen. Obviously excluding the backwards battery

[@kevpatt]

Thanks!

[@BrianSeklecki]

Perfect 👌! 100+ introduction-to-transistors videos on KZbin in 2025 , this is the only one that makes sense ! 25 years after I first learned electrical circuits, finally I understand how Transistors work.

[@tonyrebeiro]

Except for the battery symbol being flipped, the explanation is Very clear and easily understood.

[@kevpatt]

Thanks!

[@luvradios]

As an Electronics technician for the last 25 years, my job primarily has been to troubleshoot why something isn’t working, having a basic understanding of electronics principles and experience with tons of failure scenarios has served me well. Scrolling through the videos on here today I found yours to be the only one that brilliantly and simply explained transistors, I loved the imaginary jumper explanation of how the transistor works as a switch. When troubleshooting any electronic device the first rule is simplicity! Example - if your receivers FM band isn’t working doubtful you’ll find the problem in the amp section. Well done sir!

[@PhilJonesIII]

Five vids in and you are the one that nailed it. One guy even showed how to wire an NPN when he was in fact using a PNP......confusing as hell. I was following along on my breadboard. Nice video, clear explanation. Keep it up.

[@kevpatt]

Thanks! Glad it was helpful!

[@markybogbrushify]

agreed! video eeds more votes!!

[@DupczacyBawol]

Theres 80% of idiots who pretend to know and understand and 15% of those who intentionally upload the Internet with false information and knowledge.

[@MarkWarbington]

Watched ten transistor videos before this one. Yours was the best. Excellent job!

[@kevpatt]

+Mark Warbington Thanks!

[@radostar7139]

Agree

[@wakefieldyorkshire]

Yup I second that.

[@rayhantec4833]

I agree too

[@electronicstuff6355]

Me fourth

[@mikecatlapp5775]

That was the best description of NPN vs PNP I have seen

[@kevpatt]

+Mike Catlapp Awesome, glad it could be of help!

[@BillAnt]

Not sure if it was mentioned, that PNP transistors are commonly used in audio power amplifiers as a complementary pair on the output end, working in a push/pull configuration of the signal.

[@maxwarfield6699]

Finally! NPN transistors and PNP explained, in a COMPREHENSIBLE manner, for complete NOOBS like me. Been looking all over the web and all I came across was a bunch of FAST talking know-it-alls preaching to the already converted. Kudos and THANK YOU good sir, for this great video. Cheers!

[@kevpatt]

You're welcome! Glad it was helpful.

[@MrMac5150]

Nobody but you, made it easy to understand, I could never understand, the shunt effect. good video, I hope you have one on Mosfets. Thanks.

[@kevpatt]

MrMac5150 Thanks! Yes, I will be posting more videos on mosfets and other components.

[@MrMac5150]

Kevin Patterson You have got my attention on your channel, it is excellent.

[@kevpatt]

Glad to have you. Thanks!

[@BobSmith-bv9ep]

Finally. Not even nine minutes long and I can actually get it . Why can't they all be this simple? I was seriously becoming convinced that an easy explanation was not out there. Subscribed.

[@kevpatt]

Thanks! Glad it was helpful!

[@mingdeli8124]

Perfectly explained the difference between PNP and NPN !! I have searched more than 10 videos and no one is better than this one !!! Thank you!

[@kevpatt]

Awesome, thanks!

[@marko5472]

This really helped me understand transistors better than any other videos I have seen. When the teacher is good, also difficult things are easier to grasp.

[@paulb8264]

Even with the battery symbol slip (didn't notice till I read some comments) the walk through of the concept was extremely useful and well explained. Thank you very much for this video.

[@jimedgar6789]

Years I have tried to grasp this. Wow... thanks.

[@captbullsnort]

The very best explanation and video I have ever seen on transistors. They have always been confusing to me. I never thought anyone could explain these silly little devices in a clear and simple way. YOU DID AND YOU NAILED IT.

[@SpeakerBuilder]

This is the best and clearest description of the switching function of transistors I have seen, very well explained, thanks.

[@kevpatt]

Awesome, glad you found it helpful!

[@GreatWhiteNiko]

Not sure that you realize - by this time (May 2019) your video is the best on KZbin explaining how a PNP transistor works. You don't explain how the electrons flow inside the PNP transistor but providing that one knows how the electrons flow inside a NPN transistor (plenty of videos about that on KZbin) and from all the other details that you clarify it becomes obvious how the flow of electricity from Emitter to Base allows the PNP transistor depletion zones to open up for higher current flow. Thank you very much!

[@captainprototype187]

@GreatWhiteNiko. You know about this stuff. Does the base need current or just voltage? I am trying to make my first pulse motor which is like the HOLY GRALE for me.. The base gets its jolt from spinnin the rotor (with magnets attached) near a coil. The NPN opens and lets trough a big puls of current to magnitise the coil. This pulse of magnetism pushes the rotor along. I think I got the theory down but in practice.....

[@GreatWhiteNiko]

@@captainprototype187 Oh no, don't get me wrong. I am just starting to learn electronics. So far I'm at the level of "how it works" but literally nothing practical. You need to ask someone else. Your question makes me wonder too - does the base need amps and voltage or just some so-so voltage?

[@captainprototype187]

@GreatWhitwNiko. Lol, you sure sounded like an expert! I think I got the answer now. The npn has 2 circuits built in. The first, trigger, circuit activates the bigger circuit. So you put the positive lead on the base and the negative goes to ground. That makes the first circuit. And every circuit draws a current. Furthermore, every vid calls the transistor a current drawing device. I found this vid that helped me a lot. kzbin.info/www/bejne/oX-5knynorCIpas

[@GreatWhiteNiko]

@@captainprototype187 Well, today I asked a friend of mine that is an electronics guru about the very basics of transistor use. What he told me was unexpected for me. See if you learn something practical too: 1. Bipolar (PNP and NPN) are used to REGULATE current. Used to control motor speed for example. 2. FETs (MOSFET) are used as switches - just turn on/off the current. Not sure in what applications they are used most. I see them in TV circuit boards all the time. If they are used as switches it'd make sense to assume that FETs are used in computer chips but I apparently speculate here. Also: 1. Bipolar - the gate uses CURRENT - From 0 up to 0.7A. You vary the current (Amps) of the gate and the big current from Emmiter (Source) to Collector (Drain) varies with it. 2. FETs (MOSFETs) the gate use VOLTAGE. Because what you want is to "pressure" up the area that creates the magnetic field which "opens" the flow of current from Emitter to Collector. And FETs basically work like that - you supply voltage and they do nothing. You increase the voltage and they still do nothing. Then at some point they let all the current flow. So that's a "digital" type of operation - 0 or 1 - closed or open. That's why they are used as switches. My friend also said that all the details about electrons/holes, and depletion zones are not needed at all when you actually work with electronics. The movement of electrons etc are good to know and cool to know but once you start practically using the components that goes way way in the background. But to me it is about feeling confident about my knowledge so I like to learn stuff like that. Good luck.

[@captainprototype187]

Thanks. some new info here. I will concentrate only on npns. Making a working circuit is hard you will find. It is for me, anyway.

[@JamesKelly89]

What really blew my mind about this video is that I never thought of transistors as actually being two different circuits. I think I understand them far better than ever before now!

[@kevpatt]

Glad it was helpful!

[@wtfucrazy]

Simple, to the point and not losing yourself in details. Good job.

[@boshboshish]

I swear, you have explained the transistor basics more and way better than when I took it back in school.

[@enriquesalgadoaceves9017]

dude, I went through at least 50 vids trying to understand, I got a basic idea, but you my friend, youuuu, your voice is clear, its smooth and easy to.listen to, its sound is just right, your pauses are perfect while explaining, the mellowness helps, and within all that the overall explanation of the how hard it is for us noobs, you make it sooooo much easier my friend, you get unlimited lifetime likes and promoted to my diy buddies thank you GB..

[@enriquesalgadoaceves9017]

having said that I'm still learning on how to.make it work with my project, I'm trying to make a solar lamp, I'm using a 3.7v lithium ion battery , 2400mah. I have my light dependant resistor which I think its around 15ohms, and my load (LEDs) will vary, my problem is to find an easy formula to calculate what resistor will I need to work with each individual led or small 6v hylogen lamps, if you can point me in the right direction I would appreciate it

[@SergeyRyabenko]

Thank you Kevin! This is the most concise yet probably the best explanation I've seen about the topic.

[@taneliharkonen2463]

This was THE best explanation of the npn/pnp transistors! Subscribed! :D

[@kevpatt]

Thanks!

[@moegasim]

The clearest explanation found...thanks for sharing

[@ElTurbandito]

it is so sad I am paying for university but have to go to youtube to get a professor who doesn't just spew formulae and actually explains the concepts. Thanks for the concise explanation.

[@kevpatt]

You're welcome! Hopefully things will become clearer as you get a handle on the basics. Good luck!

[@PeterFiroozi]

Hands on one of the best explanations available on transistors! Keep up the good work!

[@yoramalon5273]

I subscribe to this channel , because this man has a unique gift. He explains things in the most easiest way to understand, in the most easiest conotation, in the most simple way. He does it slowly and explicitly. This is the best teacher i have seen on youtube.

[@khordad1216]

This is by far the Best, easiest to undrestand and most awesome explanation (atleast for me) that I found In 24 hours of my study on transistors even in 2021. THANK YOU!

[@jolid9373]

At long last, a video that explains how transistors work in a circuit, thank you.

[@steveo7052]

Best transistor explanation ive seen thus far!

[@kevpatt]

Thanks!

[@844pm2]

Thanks Kevin, I've see through many videos about the transistor, their explanation are complicated but you're making it easier for people to understand

[@kevpatt]

+Forever Joy Thanks!

[@zanecook4402]

This is the best explanation of PNP vs NPN transistors I have come across.

[@stevetrout1275]

The best explanation of these transistors that I've EVER seen! Keep up your good work.

[@kevpatt]

Thanks!

[@nickbungus]

Thank you, thank you. Finally, an explanation on how to use transistors and not how they work internally.

[@kevpatt]

+Nick James Thanks, and you're welcome!

[@prakashq2020]

I have watched so many videos, I name it BY-FAR THE BEST.

[@IBullsHit]

I was struggling to understand the difference between npn & pnp.Your last statement clarified everything for me : control signal has to be lower than 5v to turn on a pnp and control signal has to be higher than 0v to turn on npn. Thank you!

[@chapinoable]

Of all videos I've watched about transistors, your video made understand it better. Thank You

[@madamerotten]

I don't want to seem negative, but I am positive that your battery symbol is reversed.

[@kevpatt]

+madamerotten yup... a sketch drawn in haste and then turned around... I will apparently never live this one down. :(

[@laggeroomaepiclagger2454]

3 GUARD

[@nick54thegreat]

Doe!

[@stormshockin]

I actually disagree.. since power seems to actually work from neg to positive. And not from pos to neg. I think it is more accurate this way.

[@nick54thegreat]

he has the Positive terminal of the battery connected to the ground symbol, and has labelled it negative, while the negative terminal of the battery is labelled positive.

[@tinkmarshino]

Well Kevin.. at 66 years dumber I get it! I am trying to tech myself a new trick... so much to learn so little time to learn it... thanks Kev.,...

[@kevpatt]

You're welcome! Glad it was useful!

[@erichfeit7779]

Yes, I agree . Your battery symbols are reversed. But the rest of your teaching is excellent. 75 year old electrical teacher here.

[@jasongreen5360]

Best video. After 2 years, I finally understand the difference

[@kevpatt]

+Jason Green Awesome, thanks!

[@464340]

+Jason Green .you are lucky. it takes 4yrs for me.

[@nikosadie]

best explanation yet. Now I start to understand the basis of transistor use in amplification.

[@hambernat6444]

I also watched eleven or twenty transistors videos before this one. Yours was the best. Excellent job!

[@davebalz4039]

Excellent. Clear. Understandable. No frills. Great teacher.

[@jimc52]

Ii love your elegant and simple illustrations and explanations. This was very well done.

[@kevpatt]

Thanks!

[@thenet0120002]

Great video on the basics of transistors clearly goes over the current flow and the function of transistors theory.

[@mcmx88]

Absolutely fantastic. Best explanation I've seen. I finally understand. Thank you!

[@MrRanmaedu]

Good video my good sir. The inverted symbol of your power source is in fact inverted but you are aware of it. Thank you for your video

[@kevpatt]

+MrRanmaedu Thanks for the kind remarks.

[@lucysluckyday]

OK, I had my doubts when it started going by the battery symbol, but I actually watched out of curiosity and this is really good!

[@alexanderjustinkonga6447]

For a first time i can make my Simple circut of a Transistor. So i say Thank you Sir. -from Tanzania East Africa

[@xpress021hundred]

Thank you, good sir, transistor basics are a lot clearer to me now! Keep up the good work! I would absolutely love to hear more of your own spin on electronic tutorials in the future! For instance; radio frequency/communication systems explained easy.

[@kevpatt]

+qdnguyenbp I will certainly be making more videos as I have the time. Thanks for the encouragement!

[@AB1Vampire]

Appreciated the explanation of difference between PNP & NPN at the end of video.

[@monkporfyrius97]

You made it simple for me , i've watched many videos about transistors and everybody is trying to be so coplicated ( you see coplicated is more kickass than simple).

[@tigerseye73]

As a welder, I learned long ago that DC voltage flows from negative to positive. You can weld with the electrode set up at either polarity, but electrode negative results in a deeper puddle ( more heat into the work piece ), and cooler running feed wire. Reverse the set up and you have just the opposite outcome. Just saying. Your presentation is very well done and thank you for sharing.

[@kevpatt]

Yes, conventional current flow (as used on schematics), is the opposite of electron current flow. Still no excuse for drawing the battery symbol upside down! :( Thanks for the kind remarks!

[@jimmychen119]

Amazing! As an outsider, I learned a lot from this video!!

[@kevpatt]

Awesome!

[@umbratherios5614]

FINALLY! A video I can understand and actually learn how transistors work! Thanks man :)

[@GamersMedia2723]

thanks kevin petterson this is the best tutorial i have seen yet

[@kevpatt]

Aashu Malik You're welcome!

[@Marc_Miller]

Thumbs up for hand sharpened pencil and nice drawings. And great explanation of NPN and PNP.

[@nkacarova4000]

You are the best man! So simple you give us light with how it works! So many videos here in youtube for this topic, but this is the best one!

[@kurtlittlebridge]

I watched this many time before I finally got it and even though I'm still not sure. However, I feel I have enough of a grasp to implement it in my circuits. Thank you!

[@kevpatt]

+PS Awesome, keep at it. I started learning electronics when I was just a kid, and it's amazing when I look back and realize how little I actually understood and all the misconceptions I had. However, perseverance and study will get you there. Sometimes experimentation is the fastest way to learn. :)

[@3deeguy]

Excellent tutorial. The BJT is a "current multiplier". The PNP emitter faces power, the NPN emitter faces ground.

[@7999rahul]

Simplest and best video I found. Great explanation. Many thanks.

[@kevpatt]

You're welcome!

[@marcusventer8609]

The Best Explanation Of NPN/PNP If Seen. Just the right type of Vid for a beginner like me

[@kevpatt]

Glad you found it useful!

[@tonyvtech25]

Awesome video super understandable LOL. Finally i understand how transistors work and the difference between PNP and NPN. Thank you very much kevin.

[@kevpatt]

You're welcome!

[@michaelhiggins7365]

What a fantastic video. Thank you.

[@kevpatt]

You're welcome!

[@Michealfarmer]

Thanks for the great video. Finally learnt something useful about PNP transistors! Cheers!

[@kevpatt]

You're welcome!

[@radioscout]

Finally an easy to understand explanation

[@davidpeters7447]

Nice explanation. Easy to understand and no confusion.

[@PLMHero]

I've been watching lots of video about transistor. But yours is my favorite. It answers my questions.

[@cuttyflam6136]

best explanation I've seen anywhere, thanks so much

[@kevpatt]

+Cutty Flam You're welcome!

[@denzelnolet]

Pity you never made more videos. You have such a way at explaining these concepts.

[@PreludeSon]

Very good explanation, easy to understand and the drawing helps a lot.(battery symbol is flipped)

[@kevpatt]

+InfinityOrchid Thanks! Yeah I drew the sketch and turned it around, forgot about the symbol. Quite embarrassing. :(

[@tomasfranco4870]

Perfect video mate. Still helping people in 2021. Thanks

[@1yyymmmddd]

Never seen such a clear explanation. Excellent! It might be also useful to show some practical examples, i.e. say we have 5V battery, 2K base resistor, which provides xx mA to the base and that results in yy mA current through the LED.

[@kevpatt]

+1yyymmmddd Thanks for the kudos. I do have another video that shows the circuit in action (in a simulator), and I think it shows some numbers too. Check it out: kzbin.info/www/bejne/f5-kna1ro5yHmLc

[@impulsivez4825]

This is best explanation by far thank you. Was so confused on how to set it up.

[@jasonmurawski5877]

Thank you for this video, i was having a very hard time understanding the difference between the two with what i read on google, watched this video and instantly understood it.

[@mpl868]

Why don't you come to my university as my lecturer? Nice presentation for npn and pnp transistor!! I could save a few weeks if I find this video early!

[@blockeduser5769]

Great Explanation NPN feeds a ( - ) to the load PNP feeds a ( + ) to the load.

[@Rising_Pho3nix_23]

Struggling to learn this stuff, I took a screen cap at 7:39 and printed it off. This helps a lot thank you!

[@kevpatt]

brandon day You're welcome! Keep studying, the learning pays off!

[@michituurbentaler1378]

Great! exactly that explanation i was looking for! Thank you.

[@kevpatt]

+michi tuurbentaler You're welcome!

[@haloomar2906]

finally i understand how transistor work as a switch i watched many videos but yours is the best

[@Traderhood]

Best explanation ever, and I have been through bunch of tutorials on youtube. Thank you.

[@SABIRALI-gf3fv]

Thank you Mr. Kevin Patterson ,Nice video & Explanation.

[@kevpatt]

Thanks!

[@griefbacon222]

Thank you! This is by far the best explanation.

[@kevpatt]

You're welcome!

[@HenriqueMarquesFernandes]

Just awesome video! cheers from Brazil!

[@kevpatt]

+Henrique Marques Fernandes Glad you liked it. Cheers!

[@hooverzavala8071]

Best explanation ever. Finally i get the idea about PNP trans. Too bad you dont have hundreds videos regarding electronics

[@raghavvsrinivasan9645]

Seriously, I have seen like about ten videos and none of them had such a simple and easy circuit. Great video, great explanation. Eager to see your next videos. Do something with LDRs. I also subscribed ;)

[@kevpatt]

Thanks!. Do you mean LDOs (Low Dropout [Voltage] Regulators)?

[@mattserone3381]

That was a very good precise informative video..thanks pal keep producing great vids

[@kevpatt]

Thanks!

[@atelesia]

Best explanation.Simple and easy to understand.Thanks :)

[@kevpatt]

+atelesia Thanks!

[@NeonblueIndustries]

Yes BRILLIANTLY explained! Thank you man! Great Video!

[@kevpatt]

Thanks for the kind words. You're welcome!

[@abhimanyu7274]

This is the first time I understood. Thanx

[@kevpatt]

You're welcome!

[@orvillellewellyn9525]

Your lesson was well done and easily understood.

[@michaelgronlund1854]

Very nice job explaining the difference!!

[@james66872]

This the best tutorial so far.

[@kevpatt]

Thanks!

[@464340]

Simply superb.very easy to understood. thanks a lot.

[@kevpatt]

You're welcome!

[@arturocespedes6630]

Best explanation I heard !! Thanks for sharing!!

[@HilltopComputing]

Nicely done. Thanks for the clear explanation!

[@kevpatt]

+Hilltop You're welcome!

[@warsymphony]

FINALLY a good explanation of transistors!!!

[@kevpatt]

Joshua Foster Thanks!

[@ashlingbuyandsell]

Thanks for the great video, helped me nail this at last.

[@kevpatt]

You're welcome!

[@jawadazam9707]

nice explanation sir . you made it really easy to understand . hats off .

[@kevpatt]

Thank you!