Component Help

I started this thread for anyone but mostly people who are new to electronics like me and want to learn more about specific components. For example transistors either PNP or NPN and which way the power flows in both. Collector to Emitter OR Emitter to Collector. In my research I have found different explanations. One said that power flows from Collector to Emitter in both PNP and NPN and I also found where another person said that on PNP transistors power flows from Emitter to Collector. Or is it case specific and how the transistor is being used that determines which way the power is flowing? 

If this is not correct please explain?

I also have a problem with the description of what a transistor is Either a switch or power amplifier. When I look at the two different applications I can see what they are doing but where the concept breaks down for me is the idea that a transistor amplifies power as if it takes in 20V 1A and then some how defies the law of physics and out comes 40V and 2A’s. This is impossible and is essentially creating something out of nothing. What I really see is that instead of being used as a switch to turn on or off it is being used as a switch that changes path like a switch on train tracks where one path is switched to another path. So it is really just a switch either one that turns something on or off OR a switch that changes path.

If this is incorrect please tell me why? 

@john-barron John, some of the confusion may be on where the person learned electronics. Navy electronics teach flow from ground to voltage, where others teach flow from voltage to ground.

I would suggest doing a google search for “NEETS” modules and looking at the early modules on basic electricity and electronics for general info. Also talks about the usage of different electronic components.

Hello John, i think the best thing for you is to search out a really good basics electronics .pdf or actual book that explains the action of a transistor junction. It also helps to think in terms of how electric current is ‘flowing’ in any circuit. Most introduction descriptions will explain that at the virtually the atomic level we have electrons often marked a (-e) scooting around a nucleus of protons & neutrons. Electron flow occurs when some sort of force begins to act on the most outer electrons & suddenly with the force too strong to hold it in what’s called its covalent bond to the nucleus the electron leaves to travel to the ‘whatever’ that is attracting it. Enough electrons being drawn away from other atoms we have what’s called Electron Flow, negative polarity ‘bodies’ being attracted by a stronger positive force than that of the nucleus of the atom… Now in describing electric current, when the Forefathers who 1st discovered the presence of & effects of electricity immediately assumed current ‘flowed’ Positive to Negative so we tend to stay with this concept & called it Conventional Current Flow and the best way to picture that in your mind is that during Electron Flow as an electron leaves its place due to attraction, another replaces it instantly until it’s attracted away so in effect we have Holes going in the opposite direction to where the electrons are going and this flow of Holes helps us picture what is happening during Conventional Current flow…

So when thinking about a standard pnp or npn transistor a we have a 3 bodies of material sandwiched together. Think of the centre as the Base, the outers either Collector & Emitter. These pieces are often a silicon crystaline array structure at the atomic level & a special operation has been used to bond them into the order of being either p-n-p or n-p-n . Think of the n pieces having an excess of electrons , the p pieces and excess of positive holes… (It’s probably better to have a diagram to explain all this so i again suggest you go search up transistor basics .pdf notes or even videos on YouTube)….

So between the pieces of p or n or n & p material there is an electrical barrier & it is often around 0.6 volts that has to be overcome until an electron can pass through once an external voltage is applied for electron flow to begin… or for holes to begin moving the other direction as conventional current flow.

So in a real-world connection for a transistor the main circuit voltage is applied across the Collector & Emitter, the polarity being dependent upon the Collector being either P or N material & likewise the Emitter. Now the really neat stuff comes when we apply a much, much smaller voltage than that across the C & E to the Base which as long as it exceeds the 0.6V barrier the transistor goes into conduction mimicking, if you like a much larger magnitude of what are called Charge Carriers ( the Holes or Electrons) traveling via the Collector/Emitter path. If the Base has a DC voltage applied it will Saturate the junction & turn the transistor on hard (as switch) while if a changing AC signal is present (& a suitable bias DC has already been added to ensure the 0.6V is overcome) & much larger ‘mimic’ will follow in the Collector/Emitter path so we have amplification…

… Wow! APOLOGIES to everyone for the most ever wordy explanation in History! Oh and yes i am certain i have not fully explained every single thing happening but it kind of pushes along what’s happening. The other thing to note is that its not all that long since we did not have semiconductors & all this electronics stuff was achieved by heating up bit’s of metal inside vacuum contained glass envelopes & using really high voltages….

Hi, John. Give this guy a try, https://www.youtube.com/@EngineeringMindset/videos His channel is full of really interesting topics. Just search for Transistors and it will all be explained there.

Thank you for all of the replies.

How the Transistor works I am ok with and under stand electrons, atoms and the difference between convention and actual direction of electron flow as I have a degree in chemistry, The electrons are negative and what people call holes are just positive charge and positive charged atoms that want and attract electrons.

So far from the replies I have understood that Transistors ARE NOT amplifiers but just gates that ALLOW amplification such that a current and voltage being supplied to a circuit can be amplified by allowing a larger voltage or current to flow into the circuit through the collector Emitter path when a small but significant amount of energy is applied to the Base. Typically when transistors are used in pairs.

But no one has directly answered the question of direction of power flow for PNP vs NPN transistor. Which direction is the flow of power in each? Is a PNP flow from collector to Emitter OR is it from Emitter to collector? This is like asking if power flows out of a battery from negative to Positive. I understand convention that people think it is from positive to negative but in reality it is from negative to positive. The letters P and N are designators for polarity on the transistor; P=positive part and N=Negative Part. Thus a PNP is positive on the ends with Negative base. And an NPN is negative on the ends with a positive base. The flow of electrons is always from negative to positive. So in an NPN transistor the Collector and Emitter are both N type material and in a PNP transistor the Collector Emitter are both P type material.

From this conception I can only deduce that since collector and emitter are both same type material that the flow of power can be in either direction depending on which side has the higher potential. Yet when I search on line I get conflicting information like that of NPN transistors power flow is always from collector to emitter. With some saying that is true for NPN but for PNP it is reverse that power flow is from emitter to collector. THIS IS WHAT I WOULD LIKE EXPLAINED. Is there anyone who has a degree in Electrical engineering that can explain this in simple terms so an idiot like me can understand? No I am not an idiot but if explanations are designed to educate idiots then everyone can understand. That comes from one of the other degrees I hold an M.S.T Masters in Science in Teaching.

@peteb2 Thank you for the explanation but could you elaborate more on this portion of your explanation. “ If the Base has a DC voltage applied it will Saturate the junction & turn the transistor on hard (as switch) while if a changing AC signal is present (& a suitable bias DC has already been added to ensure the 0.6V is overcome) & much larger ‘mimic’ will follow in the Collector/Emitter path so we have amplification…”

I don’t understand what you mean by “mimic” and how can there be both AC and DC present ?

Does this determine which direction power flow is? and since both collector and emitter are both of the same type material in both NPN and PNP what determines the direction from either C to E; or E to C ?

@john-barron Hi, regarding what “peteb2” said about the AC and DC components existing at the same path well, he was referring to a “theoretical example” of an amplification stage where at the base we are indeed pushing a DC component that is formed by the voltage divider needed to properly bias the transistor’s Base and an AC component that is ” in fact” our small audio signal that we want to amplify. As we all know, an audio signal is indeed an AC component. Now. So, as you can see AC and DC can coexist (at the same time) on the Base of a transistor. Further on, what “peteb2” also meant by the word “mimic” is that the collector-emitter flow “rate/intensity” is somewhat directly proportional to the flow “rate/intensity of our audio signal. In other words, in this case, you can replace the word “mimic” with the word “proportion” or perhaps the word “swing”. Now as a side note, the maximum amount of “voltage swing/amplification” that can be obtained in the Collector-Emitor path is highly dependant of the Transistor’s amplification factor (Beta) and also the limiting factor is the supply rail voltage. So you can only amplify a signal as high as the voltage rail. Keep in mind that my explanation strictly refers to the existence of AC and DC at the same time and the way an amplification process happens. So it still doesn’t answer your question in which direction the current flows in regards to the C-E path.

@john-barron the 1st thing to revisit is the that when i quoted AC it refers to the low level (peak to peak) audio signal, in the context of amplification. This may be arriving from example a microphone, a turntable tone arm cartridge, a low level test tone from a signal test generator. This kind of signal will pass through a capacitor which DC will not. Applying it to the base of a transistor be it pnp or npn & with the correct magnitude of bias voltage to overcome the transistor’s forward biased barrier voltage of roughly 0.6V that exist between the base to the collector & base to the emitter then the transistor will go into conduction collector to emitter for npn, (opposite for pnp) & this current will be mimicking the low level AC signal one applied the base but be of a magnitude considerably larger peak to peak. Thus amplification is occurring. The output can be made to appear at the collector & the emitter using the corrector value resistor for the supply voltage in the leg to teh collector & from the emitter to ground. …. I think also that Ovi4 is explaining the the basic theory in a more real world example. Another idea to see what is truly happening with a bipolar transistor is to watch MLC’s video #13 & even follow along with experiment… (assuming you have access to a ‘scope & some breadboard & a few parts). I have even used MLC’s approach to verify a certain device i wanted to use as an equivalent replacement. link: https://www.youtube.com/watch?v=DxVPfc9gDq4&t=121s

@peteb2 OK this is making more sense now that Ovi4 clarified the issue of AC – DC and your new explanation of what is going on. One last question about what you said about “transistors going into conduction at collector to emitter for npn, (opposite for pnp)”. Does this mean that for NPN power flows from C to E, and for PNP power flows from E to C ?

This would answer my other question of power flow. I only ask this because in one of the circuits I’m working on it shows a pair of PNP transistors where it looks like power is coming in on the emitters and going out on the collectors and that made no sense to me.

@john-barron Perhaps it would be a good idea to pinpoint the exact circuit (IE: the name of the equipment you’re referring to) or small schematic snippets showing that (IMGUR picture service or sharing some pictures via Google Drive) would be of great help. And someone here would “surely” come up with a particular clarification. 

PS: current/voltage flow ” Direction” in a particular circuit is highly dependent not only on the type of transistors used but also on the architecture of that schematic. (The chosen technical solution to achieve certain specs)

@ovi4 https://drive.google.com/file/d/1LK84HCUZzhGdTNkb-IOjApZU_tEV-dYM/view?usp=sharing

Here is a link to the schematic I am working with. Look at the power amp board 030 in the lower right corner. There you will see two PNP transistors Q1 and Q3. My question is I am getting – 48V coming out of pins 14 and 29. But I should have +48V going into pins 14 and 29. I have the wires disconnected from pins 14 and 29 coming from board 052 power supply board because if I connect them I get a short and the dim bulb lights up bright. So i am thinking that there is a problem with the transistors and that it could be Q1 and Q3 but I don’t know if the power is coming in on the collector or coming in on the emitter. To me it looks like I should have +35V coming in on the emitter and power out on the collectors. I just don’t understand how else I could be getting -48V coming out of pins 14 and 29 when I should have +48V going in.

@john-barron It seems that the link you’ve posted cannot be viewed without your “express approval”. Approval request sent…

@ovi4 That is a problem with Google drive, folks need to give it permission for others can see and that is why I do not use Google anymore for pictures.

@larry_n7luf What do you use and how do you use it?