I thought that NPN (Negative+Positive+Negative) passes Negative supply (like N-Channel FET) and PNP (Positive+Negative+Positive) passes Positive supply (like P-channel FET) when Base of it is powered. But seeing these two voltage regulator which are opposite than my understanding.
In the circuit NPN is passing positive supply and PNP is passing negative supply.
My questions are-
- how NPN passes positive and PNP passes negative supply?
- how transistors pass regulated voltage through CE if base of it is regulated? (I know emitter have 0.6V less than base voltage though).
Please tell me the operations (maybe path of current/voltage flow and working principle) of these regulators in simple words (circuit analysis). Simple words because I am just a hobbyist. Thank you!
In a BJT, when a small current flow from the base to the emitter, that allows a large current to flow from the collector to the emitter.
It may be "wrong, wrong wrong and wrong again" to you but that's not the whole story to most practicing engineers.Wrong, wrong and wrong again. The emitter-base current does not control the emitter-collector current. The base current is waste current that happens to be proportional to the current entering/leaving the collector terminal (beta). A BJT is a voltage controlled current source device, also known as a transconductance amplifier. Please ask about this or for clarification.
Thank you for that. Your post arrived while I was writing something to defend my simple transistor model.It may be "wrong, wrong wrong and wrong again" to you but that's not the whole story to most practicing engineers.
I know you enjoy educating the unwashed masses as to the physics of BJT operation but that can be overkill for the unwashed.
It may be "wrong, wrong wrong and wrong again" to you but that's not the whole story to most practicing engineers.
I know you enjoy educating the unwashed masses as to the physics of BJT operation but that can be overkill for the unwashed.
Engineers and hobbyists are mainly interested in the black box characteristics of a transistor that are useful in circuit design using the device. Thus a BJT appears to be a current operated device with the base-emitter input looking like a forward biased diode (even if that's not true on a quantum level) when using them in large signal applications such as switches, DC bias design for AC amps, and power applications, and that's the easiest way to do a large signal design with them. That's why the current gain (Beta or hfe) is given in the data sheets of all BJTs (gasp) and that's why current gain is used in the design of large signal designs.
Using gm for the design of large-signal BJT circuits is difficult and awkward (how would you even use it to determine the base drive needed to properly saturate a BJT switch?) and I doubt that any practicing designers use if for those types of designs.
The transconductance characteristics of a BJT are mainly of interest to a designer in small signal design, such as low level AC amplifiers (audio to RF) and are properly used in the design of those. But those designs are a small subset of electronic circuit design with BJTs.
So you are certainly more than welcome to continue on your pedantic, Don Quixote quest to convert us to the truth of BJT operation but, in the meantime, the rest of us will continue to view BJTs as current-operated devices in large-signal applications.
Cheers.
Thank you for that. Your post arrived while I was writing something to defend my simple transistor model.
It is interesting to note that the current gain of a transistor is quoted more often than other gains, and that the Wikipedia page that mentions the more complicated models has a warning that it is too technical for many readers.
NPN and N-Ch Enhanced are used as low side switches. PNP and P-ch enhanced are used as high side switches. Switches are always inverting from Base to collector or Gate to Drain
Emitter Followers are non inverting Current buffers.
Switches are characterized by their saturated resistance Rce or Rdson
Okay. If the only BJT you've seen as a current amplifier is with "lots of resistance in the base and emitter" then you've led a sheltered life.Well, every time I see a transistor wired up and demonstrated as a current amplifier, it is in a circuit, usually with lots of resistance in the base and emitter. So the black box you refer to is really a current amplifier circuit. Show me a "naked' transistor that acts like a current amplifier. I observe a dichotomy here. For instance, everyone agrees that a ordinary operational amplifier is a dual high gain opposite polarity voltage amplifier with a combined output. From that one device building block, one can make just about any electrical function including a current amplifier. Yet, I don't see folks insisting that it is better to think of an op amp by itself as a current amp, differentiator, integrator, etc. So, why does a true transconductance device like a BJT get referred as a current amplifier when a op amp does not? So when I say that a BJT is not a current amplifier, I mean just that. I mean the device itself without being in a circuit.
Fundamentals of the switch are what was asked "Please tell me the operations (maybe path of current/voltage flow and working principle)"Interesting, but what do those nonlinear applications have to do with whether a BJT is current or voltage responding?
Ratch
Okay. If the only BJT you've seen as a current amplifier is with "lots of resistance in the base and emitter" then you've led a sheltered life.
You put a current from a current-source into the base-emitter junction of a "naked" BJT and a voltage from a voltage source between the collector and emitter (no resistors in sight).
The collector-emitter current is then proportional (as related by the Beta) to the base-emitter current.
This device has a relatively low input impedance and a high output impedance.
How is this black box device then not a current amplifier as per the common definition of such?
(And it's not a "circuit").
A naked op amp is a voltage amplifier, no argument there.
The only "dichotomy" observed here here is one that you may see but I doubt many others do.
Your tilt.
YOur reasoning lacks the intrinsic VI characteristics are reversible. One is obtain from the other, so either may be applied to their respective models using gm or hfe. But most people use the current amplifier model.Oh yes there is. The current source is a voltage source with a relatively large resistor. Therefore, anytime you hook up a current source to the base of a BJT you are making a transistor circuit by adding the external resistor of the current source.
Yes it is a circuit due to the added resistance in the base from the current source.
So, where did I go wrong in my reasoning?
Your turn.
Ratch
Fundamentals of the switch are what was asked "Please tell me the operations (maybe path of current/voltage flow and working principle)"
It has everything to do with any application be the load linear or not. The same principles apply even for RF CLass J.)
It is fallacious to say BJT responds to voltage drive or current, since VI characteristics are intrinsic.
You can determine or drive either way from a voltage source or current source or anything in between.
THe best rule of thumb is BJT switches when saturated at rated Vce(sat) is they are current amplifers with a gain much less than hFE. Every datasheet will specify in the standard Ic:Ib = 10, 20 or 50 depending on the junction quality for saturation. Due to special doping processes)
YOur reasoning lacks the intrinsic VI characteristics are reversible. One is obtain from the other, so either may be applied to their respective models using gm or hfe. But most people use the current amplifier model.
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