Hello from UK

@iceman 

Yes, "E" stood for electromotive force, IIRC.

Yep.. When I went to electronics school in the Navy back in 1965, we used E for voltage..because it was all tube theory...lol...... and, that's why I had to go back to school in 1973, after  I got out so I could learn solid state transistor theory.. solid state electronics then was fairly new as a LSI ( Large Scale Integration) was only about 600 transistors, Now they're in the millions of transistors in VLSI! Back then, J-FETs were the new kid on the block, then came mosFets, Alot has changed over the past 49 years.. but E=IR , or V=IR is still the same..not matter what symbol you use...

Posted by: @iceman

@binaryrhyme

When I learned electronics it was with tubes and voltage was abbreviated "E". It wasn't until later that it seemed to be changed to V. I was told it was changed so it wouldn't get confused with one of the elements of a new device called a transistor with element "E" for "emitter".

Really.  It is still E for me probably because it was a long long time ago when I taught myself basic electronics.  It was handy for the power formula P = IE  because it spells a word.  I don't think the concept Electric force should be conflated with its unit of measure, voltage.

So just by me asking what I thought was a simple question, "why don't they use C for current instead of I?", Has started a quite interesting discussion. 

@edlee So many rabbit holes, so little time. 🙂

@edlee, Indeed, the history of electronics in general, is fascinating,as well as edification. At any rate, we are all, at some level, learning something new and that is the main idea of of the forum. After all these years on the practical side of electrical/Instrumentation, process control, and automation, I'm still learning things I never knew, or knew little about, especially about networks and software. The OOP's use in industrial applications are fairly sophisticated and mostly proprietorial, so you only learn how to use them( program user functions, or in the case of fuzzy logic controllers, tune them) so you really never really understand how and why they work..that would take many more years of training and higher education, at least for me...lol  

As my old mentor use to say, the only stupid question is the one not asked! Different people use different means to absorb and analyze information, so what is often obvious to one, may not be obvious to another.

In electronics school, my mentor used the water analogy to help me understand how transistors worked, after that, the math and physics started to make since.. I think we all enjoy learning new things, as that's why we're here instead of fishing, hunting, or bowling...lol

Have fun, and be safe!

regards,

LouisR

Posted by: @inst-tech

As my old mentor use to say, the only stupid question is the one not asked!

Heeeeyyyy - wait a minute... I say that to all the folks I mentor. I guess I didn't make that one up. 🙂

@binaryrhyme...lol... no, that's pretty well old school..no one has a corner on that saying..so we all use it to make the point..Most of my students were already techs for 20-30 years before I got to them, so they already knew everything.right?...lol  You should have seen the looks on their faces when I had to present them with new technology that they weren't familiar with.. sour grapes and lemons...lol

Hard to teach old dogs new tricks when they are in that comfort zone..but the younger guys pretty much took to it as they had a long ways to go yet toward retirement..lol

learning is a process.. you either want to know, or you don't..

@inst-tech 

In electronics school, my mentor used the water analogy to help me understand how transistors worked,

Being self taught I never had a mentor.

Not sure what kind of analogy you would use? A water tap (faucet)?

I would see it as a constant flow regulator valve where the flow rate is determined by the base current. So the resistance in the collector circuit can vary but the actual collector current would be at some fixed value (within limits) determined by the base current.  The collector circuit would "see" a constant current source at its terminals. Is that correct?

@robotBuilder..The water analogy is that of the faucet..correct.. The handle is the base, controlling the the amount of flow threw the valve.. The base current does control the collector current and sees the collector-emitter circuit as a variable resistance.  the relationship of base to to collector is defined by the beta of that transistor Ib*Beta = Ic, and for NPN transistors, Ie= Ic+Ib... The constant current source is limited by the either the load resistance in the collector, or emitter ciruit. So, yes, your assumption is essentially correct. However, there are many ways to configure that transistor base bias to control how the the base current is controlled..Base bias, collector base feed back bias, and emitter bias are a few that come to mind. While the basic premise is simple enough to understand, unfortunately  it takes a lot of math and some physics to understand why it works as it does. lol

Of course, this has nothing to do with your ability to use know facts about how to use the devices.. and only requires minimal knowledge of the theory behind solid state devices..I know many self taught individuals  who excel at electronics,  my mentor was one of them, was only in class to receive the AS degree.. as he knew more than the instructor did, especially about vacuum tube theory and operation. 

He also had a partial photographic memory and could recite the specs of almost any vacuum tube you could hold up in front of him !    lol

regards, 

LouisR 

@inst-tech 

The water analogy is that of the faucet..correct.. The handle is the base, controlling the the amount of flow through the valve.. The base current does control the collector current and sees the collector-emitter circuit as a variable resistance.

Well I first imagined it that way at first but it is misleading. The faucet handle, unlike the base current, does not control the flow it controls the resistance.  You would need a human monitoring a water flow meter and adjusting the handle to maintain a fixed value to mimic transistor operation.

He also had a partial photographic memory and could recite the specs of almost any vacuum tube you could hold up in front of him !

I believe that is hereditary. I know someone who as a child could remember how a word was spelt by viewing it once. He can remember names after hearing them once. And so on. Memory however is not always accompanied by understanding. It is one thing to remember a formula and how to use it and another to understand how it was derived and why it works.

@robotBuilder..Indeed, The base current does control the resistance, and in the case of the faucet handle, the water flow is "restricted" by closing off the channel the water has to flow through.. Hyrdo-dynamics are similar to electron current flow.. and yes, a human would have to manipulate the handle of the faucet just as an external current force would manipulate the base current. The principle of what the base is doing is the same as what the handle on the valve is doing.. so the analogy is a good fit.. of course, knowing how the chemistry and physic work makes it plain that there is much more going on at an atomic level...lol

I used this method to teach others that had little electrical or electronic background.. it mostly works.. but what ever works for you, that's the way you should proceed..As I was the SME (subject Matter expert) at my plant for over 20 years, in Control Valve technology, and having an understanding of  how liquid flow mediums through a control valve was analogous to electron flow, made it easier to teach others how control valves worked internally, and why it was important to know how to size and select one properly..

At any rate, enjoyed the conversation with you.. and glad you have a good understanding of how they work..

kind regards,

LouisR

@inst-tech 

@robotBuilder..Indeed, The base current does control the resistance...

But that isn't what I was saying although it is written in tutorials.

The base current controls the collector current not the collector to emitter resistance.

In the example below using an ideal transistor with a beta of 500 it is the collector resistance that is controlling the collector to emitter resistance not the base current.

If the base current is constant then the collector current is constant.

If I am wrong then please correct me. I just remember it was a confusion for me when it was stated that the base current determined the collector to emitter resistance as that wasn't what I saw happening.

To enlarge image, right click image and choose open link in new window.

Hi @robotbuilder & @inst-tech 

 I think if you look at what you are saying, maybe there is a 'degree of truth' in both your views.

For the common emitter circuit (as per diagram above), to get a 'feeling' of how it will respond, it is often convenient to consider the collector-to-emitter as a resistance whose value is controlled by the current being fed into the base.

i.e. increasing the base current will increase the collector current, implying the collector-to-emitter resistance has decreased. This simplified conceptual model 'works' because the collector resistor usually has a fixed resistance value. This looks like the base current is controlling the effective collector-emitter resistance, since the collector resistance is constant, but the collector current is varying.

If you change the rules, and say the collector resistance is variable, but the base current is constant, then the collector current will remain the same, inspite of the collector resistance value changes (over a limited range of values and to a reasonable approximation). To keep the collector current constant, with a fixed voltage supply (12V), the following equation must be true.

Collector Resistor value + Effective Collector-Emitter resistance = constant

Thus. if the Collector Resistor value is decreased, the effective collector-to-emitter resistance must increase by the same amount

Clearly this looks like the collector resistance is determing the effective collector-emitter resistance.

In summary, even the humble transistor (or triode tube/valve 😀 ) has fairly complex characteristics.  Its 'apparent resistance from collector-to-emitter' is not a simple value or even a simple equation. To make sense of larger circuits without getting bogged down in precise calculations, etc. we tend to use oversimplified models - which is an astute thing to do, providing we remember that there is a lot more detail to consider when we really need it.

If you have a circuit such a transistor amplifier whose characteristics are not obvious, I recommend playing with a simulator like LTspice (free) ... it will not be 100% accurate (generally), but it may give you some useful insight.

Hope this helps .... Best wishes to all. Dave

When analyzing the use of an NPN transistor as an amplifier (where the junctions are not full saturated, and thus fluctuations in the voltage applied to the base functions to scale the conductivity of the BE junction, and therefore the CE current as well), you can model it as a current multiplier or a resistance modifier - it's all just equations, after all - but it is typical to model the current ratio in spec sheets - our beloved Beta.

Of course, once the junction saturates, it's just a constant 0.7V drop, regardless of what is upstream or downstream (just like a diode).

Am I missing the point of confusion? A pretty decent walkthrough is here:

NPN Transistor Tutorial - The Bipolar NPN Transistor (electronics-tutorials.ws)