I've done a lot of work in electrical circuits, but thanks to you, today I found out (basically) how an air-conditioner works! Very simply explained. Thanks!
Very, very helpful! I'm a vacuum tube guy trying to understand transistors, be them a BJT, FET, JFET, MOSFET... and the others. I've never heard BJTs described this way before. It's a lot of food for thought. Thank you!
The conventional viewpoint has bugged me for years, so it's nice to see someone articulating what I'd thought all along and caused me a lot of self-doubt. Nice summary.
Another terrific explanation, Bob! Yet, if I may offer a different point of view, the way I always understood it, is that the base-emitter (input) current directly controls the collector-emitter (output) current. Thanks to Ohm's law, increasing base voltage causes a rise in base current, which in turn, raises collector current far higher. Finally, thanks again to Ohm's law, this rise in collector current causes a substantial drop in collector voltage. And, conversely, dropping base voltage would have the opposite effect on collector voltage! (P.S. - I should point out that this explanation applies specifically to common- emitter circuits!)
As Bob so astutely pointed out, in order to get any measure of linearity from the input voltage variation, it must indeed be restricted to a very small operating range. This, combined with the highly linear relationship between base and collector currents, is quite probably why "they" say that BJT's amplify current, rather than voltage . Yet, I have always felt that this highly restricted input voltage range is the VERY REASON they are so useful as amplifiers, since this is PRECISELY what devices such as dynamic microphones, magnetic pickups and phonograph cartridges provide! After all, if they REQUIRED a much wider input range, something more on par with the output voltage range, then their gain would be rather insignificant, and thus, their usefulness as amplifiers would be greatly diminished!
Will the current always be limited to the power source? Let's say (hypothetically) you had a 12v battery, but for some reason it was limited to picoamps, could a transistor, like the one you describe amplify such a low current up to something more useful even though the power source itself isn't capable?
Short answer: Because that's how they work. There is always a relationship between voltage and current, and the operation of a BJT is best characterized by the current relationship.
This is probably a oversimplification but here goes. The collector has a voltage applied to it. The emitter in the video example is tied to ground. The collector to emitter basically looks like a infinite resistance with no base voltage. Applying a small voltage to the base allows current to flow through the collector to emitter. The higher the base voltage the higher the collector to emitter current. So in a nutshell, the small variable base voltage controls a large collector to emitter current. Mike KC3OSD
Not to get into the whole "Conventional current vs. Electron flow" debate, but the truth of the matter, is that electrons flow from negative to positive. So, with an NPN type transistor, as shown in the example, electrons actually flow IN to the emitter. From there, due to the atomic structure of the semiconductor layers, approximately 5% of those electrons flow OUT of the base, while the remaining 95% flow OUT of the collector. This proportion is maintained regardless of how many electrons (thus, how much "current") are actually flowing at any given time. As a result, a small change in the base current creates a much larger change in collector current, thereby amplifying the current.
Brilliant 👏 👏 👏 👏 , I finally get it !!!!!
Thank you.
That gave me more confidence than a year of therapy !!
Worth waiting for
Sir! I want to repeat this everyday: You are the best Electronics teacher in the whole world. Thank You very much!
I've done a lot of work in electrical circuits, but thanks to you, today I found out (basically) how an air-conditioner works! Very simply explained. Thanks!
Very, very helpful!
I'm a vacuum tube guy trying to understand transistors, be them a BJT, FET, JFET, MOSFET... and the others.
I've never heard BJTs described this way before. It's a lot of food for thought.
Thank you!
The conventional viewpoint has bugged me for years, so it's nice to see someone articulating what I'd thought all along and caused me a lot of self-doubt. Nice summary.
Thanks for this latest refresher! You are a teacher of great talent 👍
Another terrific explanation, Bob!
Yet, if I may offer a different point of view, the way I always understood it, is that the base-emitter (input) current directly controls the collector-emitter (output) current. Thanks to Ohm's law, increasing base voltage causes a rise in base current, which in turn, raises collector current far higher. Finally, thanks again to Ohm's law, this rise in collector current causes a substantial drop in collector voltage. And, conversely, dropping base voltage would have the opposite effect on collector voltage!
(P.S. - I should point out that this explanation applies specifically to common- emitter circuits!)
My teacher told me that if I can imagine the BJT is a current controlled current source and MOSFET is a Voltage controlled resistor.
Thanks, really informative, clear and educative video.
Thank u sir for great explaination keep up the good job and godbless
A very informative video - Thanks Sir
Do you have video for an rf npn amplifier (eg BFQ19) where a choke is used in the supply to the collector? How does this effect things? Thanks M
As Bob so astutely pointed out, in order to get any measure of linearity from the input voltage variation, it must indeed be restricted to a very small operating range. This, combined with the highly linear relationship between base and collector currents, is quite probably why "they" say that BJT's amplify current, rather than voltage .
Yet, I have always felt that this highly restricted input voltage range is the VERY REASON they are so useful as amplifiers, since this is PRECISELY what devices such as dynamic microphones, magnetic pickups and phonograph cartridges provide!
After all, if they REQUIRED a much wider input range, something more on par with the output voltage range, then their gain would be rather insignificant, and thus, their usefulness as amplifiers would be greatly diminished!
Very nice sir
Very very very Good explanation! 👽👍👍👍
Thank you sir! Really nice expanation
Wow thank u teacher to remind me the relation between current and voltage on bjt
In the world we should value and look for linear relationship. What i learned from transistor
Great video. Thanks
Thank you very much for this explanation! 👋🏻 😄
Will the current always be limited to the power source? Let's say (hypothetically) you had a 12v battery, but for some reason it was limited to picoamps, could a transistor, like the one you describe amplify such a low current up to something more useful even though the power source itself isn't capable?
Wait..so in actuality the VBE voltage is the one that controls the current ......
Short answer: Because that's how they work. There is always a relationship between voltage and current, and the operation of a BJT is best characterized by the current relationship.
How does it actually amplify the current? Maybe you can use the hybrid pi model to explain ?
This is probably a oversimplification but here goes. The collector has a voltage applied to it. The emitter in the video example is tied to ground. The collector to emitter basically looks like a infinite resistance with no base voltage. Applying a small voltage to the base allows current to flow through the collector to emitter. The higher the base voltage the higher the collector to emitter current. So in a nutshell, the small variable base voltage controls a large collector to emitter current. Mike KC3OSD
Not to get into the whole "Conventional current vs. Electron flow" debate, but the truth of the matter, is that electrons flow from negative to positive.
So, with an NPN type transistor, as shown in the example, electrons actually flow IN
to the emitter. From there, due to the atomic structure of the semiconductor layers, approximately 5% of those electrons flow OUT of the base, while the remaining 95%
flow OUT of the collector.
This proportion is maintained regardless of how many electrons (thus, how much "current") are actually flowing at any given time. As a result, a small change in the base current creates a much larger change in collector current, thereby amplifying the current.