How Transistors Work - The Learning Circuit

Previously, we’ve talked about how diodes work. Silicon diodes have a p-n junction. Bipolar junction transistors or BJTs are bipolar because they have two p-n junctions. BJTs are essentially two diodes in a single package. The two main types are NPN and PNP transistors. NPN transistors have two n-type regions on either side of one p-type region, while PNP transistors have two p-type regions, on either side of one n-type region. Bipolar transistors have 3 leads, one going to each region. Typically, the middle layer is the base. P-type in an NPN, and n-type in a PNP. One of the other layers form the emitter and the third, the collector. These are labelled B, E, and C. On the circuit symbol, the arrow is always on the emitter, so we can tell which lead is the emitter and which is the collector by seeing which one has the arrow. The NPN transistor symbol has an arrow on the emitter pointing out, while the PNP transistor symbol has an arrow on the emitter pointing in. Transistors act as an electronic switch, conducting current across the collector-emitter path when a voltage is applied to the base. The switch is off if there is no base voltage present. When base voltage is present, the switch is on. We know from our diodes lesson, that diodes require a forward voltage of 0.7V before they are turned "on" allowing current to flow. In a standard NPN transistor, when 0.7V is applied between the base and the emitter, the transistor “turns ON”, allowing current to flow from the collector to the emitter. With an NPN transistor, we normally bias the device so that the collector voltage is positive with respect to the emitter. The voltage across these two points is referred to as the Collector-Emitter Voltage or VCE. If you connect the base to be positive with respect to the emitter, the voltage is referred to as the Base-Emitter voltage, or VBE. For a PNP transistor, rather than needing a minimum of 0.7V on the base of the transistor, there needs to be a minimum difference of 0.7V between the VCE, collector-emitter voltage, and VBE, base-emitter voltage. If the circuit power supply is a 9V battery, the base-emitter voltage would need to be no more than 8.3V for the transistor to turn “on” and allow current to flow between the collector and emitter. If the base-emitter voltage is 8.6V, a difference of 0.4V, the transistor would be off and no current would flow. If the base-emitter voltage is 7V, the difference of 2V is greater than 0.7V so the transistor would be “on”, allowing current to flow between the emitter and collector.

[UWB]

This is an AWESOME lesson. You pulled back the veil that has shrouded this in mystery to me for years.

[AndreasA.S.]

PNP = Points iN Permanently
NPN = Never Points iN
this may help with reading schematics.

[johnvictor]

I think this is the first time I've ever been able to wrap my head around this.

[entidade]

I swear to god I just spent 15 minutes reading about how transistors work but 3 minutes into this video I feel a lot more enlightened. The article never even mentioned why it’s called a transistor.

[davidcohen]

Excellent video.
Easy to understand. Logically ordered.
Very professional.
Like listening to a talented engineering expert.

[yoramalon]

Thank you for this video. Well explained and easy to understand.
You are the personal teacher of so many people that acess youtube.
You give joy, and self fullfilment to so many people. I cherish you in my mind.

[Calmcatfish]

Great refresher. I used to dabble with semi conductors as a kid, but didn't really understand how they worked. This video brought it all back for me...thanks!

[Utubeasiangirls]

Thanks to your simple explanation i think i finally understand PNP transistors which seemed more complex than NPN :D

[ericglover]

Without really knowing much of anything about electronics I could still get the idea of how this works. Fantastic....must resist temptation to binge watch entire series now....

[ishaanj]

Thanks, professionally made and good for reviewing the fundamentals.

[MaestroCipher]

Comprehensive, easy to understand explanation. Thank you.

[allis]

This is the most amazing explanation of transistors that I have ever run across! Thank you!

[aaronramsden]

Thanks, this is the only video that makes it super simple to understand without the presenters stroking their ego by trying to sound smart by overcomplicating things.

[THK_]

Thanks so much .. this is a great video to understanding npn and pnp transistors .. really thank you 😊

[dkryptonut]

OMG, thank you lot easier to understand than some of the stuff I've read!

[Blacksheepishot]

we owe everything to these transistors. I was working as a tube tech when these devices started to hit the market. like in all things the new replaces the old. as for npn and pnp it depends on the circuit I design. thus, a super stable low frequency tunable osc requires a small load transistor in a reverse polarity configuration.

[timornellas]

I am a new learner and found this video very useful and informative. The pace was perfect for me.

[Uvisir]

i finally felt i understood the transistor basics now. wow that took some years to grip but this video confirmed everything ive understood and by watching this i now got it, thanks

[naveenchandra]

very good and detailed explanations, cleared so many doubts which i had about transistors. thanks for making this video.

[RajendraChhimpa]

Sincere effort to explain the smallest monster of the electronics.
Also elaborate with equations.
Have a nice day