Admit your Brain lock

[tggzzz]

Ooooh! Politics!

10, 9, 8, ...

[pcprogrammer]

Ooooh! Politics!

10, 9, 8, ...

Nah Philosophy. 

[tggzzz]

Ooooh! Politics!

10, 9, 8, ...

Nah Philosophy. 

7, ...

[Smokey]

My brainlock is not about technical stuff but why people do bad things to others and/or themselves.

https://www.amazon.com/Thinking-Fast-Slow-Daniel-Kahneman/dp/0374533555/

https://www.amazon.com/Righteous-Mind-Divided-Politics-Religion/dp/0307455777/

[temperance]

On my Transistor issue:

Here it is cause it just happened again with an NPN. Does the transistor "START" to conduct with the .7v on its base or is it fully on with .7? I think my brain lock is the voltage range at which it amplifies and isn't just a switch?

If a transistor has 0.7 V across it's base emitter junction indicates that the BE diode is forward biased if the base more positif than the emitter in an NPN transistor. That's often enough to know if a circuit works or not. But it doesn't say anything about the state the transistor is in. If a transistor is biased into the linear region or saturated depends on the collector emitter voltage.

Why doesn't the BE voltage doesn't mean anything? To understand that you must understand a concept called dynamic resistance. For a forward biased diode, the dynamic resistance is the variation in forward voltage / variation in forward current. In a textbook ideal diode this resistance is zero. For a real diode it can be something 10...70 Ohm.

Although the BE voltage varies with changing base current it is the base current which translates onto a collector current. The collector current is Hfe x base current. The base emitter voltage depends on the circuit configuration and is simply calculated with ohm's law.

A second concept to you have to understand is current sources and current sinks. If that concept is not understood, you will have a very hard time understanding transistors.

I found this for you:
Dave explaining voltage and current sources


w2aew explaining transistor biasing


If you understand the current sink concept explained here you will be good to go. (that is, the collector current doesn't change when changing the collector resistor within the limits of the circuit)

[temperance]

Can't wrap my brain around that. How stupid can you be?

Think about the mathematical concept called average and now translate what that means to a populations IQ.

Edit: break checking someone is stupid but taking advantage of that fact that you have a webcam to prove that someone was break checking you is equally stupid in many ways.

[switchabl]

Unless you have actually failed to understand/retain relevant theories of distributive justice (like Rawls'), rather than just disagreed with them, this seems like a bad example.

There is a difference between fair sharing based on income and wealth while paying taxes during your life, and taking a, sometimes big, slice of the pie that is often intended to make the life of loved ones better.

How is it fair that frugal people are penalized to cater for the willy nilly behavior of people that can't balance their checkbook, the government included for that matter.

And just like fourfathom, though I can wrap my brain around it somewhat dislike philosophy.

I really don't want to argue one side or the other here. Just that "I can't get how taxes are fair" doesn't seem to be in the same category as "I can't get how transistors work". At least assuming that the first one is mainly an expression of opinion rather than saying you repeatedly tried to study the concept of fairness and couldn't make sense of it.

Actually, the latter has definitely happened to me with some philosophy texts. Sometimes because I really couldn't figure out what they were trying to say (mostly 19th century stuff) and sometimes because they were very complicated and abstract and I didn't have the motivation to really dig in (mostly analytic philosophy). But others have really helped me structure my thoughts better. As well as provide some perspective and humility because usually the best arguments I can come up with have already been made (and criticised) a long time ago, in a much clearer and more detailed way.

[unseenninja]

As I get older, I feel I have a limited capacity to learn new things, and have to be selective. It's like my brain is filling up. I feel that if I try to learn too much new stuff, my brain is probably going to erase old stuff to make room.

It does, trust me. For every new thing I learn, something gets forgotten.

My block is that I just can't get my head around joins (plain, inner and outer) in SQL.

[TimFox]

On my Transistor issue:

Here it is cause it just happened again with an NPN. Does the transistor "START" to conduct with the .7v on its base or is it fully on with .7? I think my brain lock is the voltage range at which it amplifies and isn't just a switch?

Start with a NPN transistor with, say, +5V connected from the emitter to the collector through a current meter.
If you carefully and slowly increase the BE voltage from 0 to roughly 0.7 V, the collector current increases exponentially, reaching a “typical” current value for Vbe approximately 0.7 V.
The current increases rapidly, but not discontinuously.

[pcprogrammer]

Can't wrap my brain around that. How stupid can you be?

Think about the mathematical concept called average and now translate what that means to a populations IQ.

Everyone, despite it's level of intelligence can do stupid things for sure. But based on your average you would expect more people to act "normal" but it seems like people are getting more and more stupid every day. Can be biased of course on one sided input of information, and being on the higher end of the scale based on several tests in the past it is sometimes hard to grasp that "normal" is not more normal across the population. Maybe it is that "normal" is just on a sliding scale.

This is inline with nctnico and not understanding why the human race acts like it acts. For instance a while back on the news it was about AI and robots and the question was if in the future one AI should be allowed to marry another AI.    Who comes up with such, in my eyes, nonsense. 

Edit: break checking someone is stupid but taking advantage of that fact that you have a webcam to prove that someone was break checking you is equally stupid in many ways.

And I agree that if you have a web cam and then purposely rear end someone who break checks you is, well not really stupid but, criminal. Taking physics into account some just won't have enough time and space to avoid it. And that might also be possible to extract from the footage. Calculating if indeed it could not have been avoided.

[tggzzz]

On my Transistor issue:

Here it is cause it just happened again with an NPN. Does the transistor "START" to conduct with the .7v on its base or is it fully on with .7? I think my brain lock is the voltage range at which it amplifies and isn't just a switch?

BJTs are current devices, not voltage devices. There is no simple easy relationship between a BJT's "input" and "output" voltage, so if you start there you are bound to be perplexed.

There is a single simple relationship between "input" current and "output" current; I_C=h_FEI_B

So, start by working out the input (base) current, that will give you the output (collector) current. That current flowing through the load will determine the output voltage.

[Zero999]

On my Transistor issue:

Here it is cause it just happened again with an NPN. Does the transistor "START" to conduct with the .7v on its base or is it fully on with .7? I think my brain lock is the voltage range at which it amplifies and isn't just a switch?

BJTs are current devices, not voltage devices. There is no simple easy relationship between a BJT's "input" and "output" voltage, so if you start there you are bound to be perplexed.

There is a single simple relationship between "input" current and "output" current; I_C=h_FEI_B

So, start by working out the input (base) current, that will give you the output (collector) current. That current flowing through the load will determine the output voltage.

Let's not start that.

In applications where the BJT is being used as a linear amplifier, it's always right to consider it to be a voltage controlled device, with I_C being dependant on V_BE.

Current control only makes sense when dealing with a saturated switch, but even then, in order to ensure a fast turn-off time, it's necessary to take the base voltage below the normal 0.6V diode drop, preferably even negative.

[tggzzz]

On my Transistor issue:

Here it is cause it just happened again with an NPN. Does the transistor "START" to conduct with the .7v on its base or is it fully on with .7? I think my brain lock is the voltage range at which it amplifies and isn't just a switch?

BJTs are current devices, not voltage devices. There is no simple easy relationship between a BJT's "input" and "output" voltage, so if you start there you are bound to be perplexed.

There is a single simple relationship between "input" current and "output" current; I_C=h_FEI_B

So, start by working out the input (base) current, that will give you the output (collector) current. That current flowing through the load will determine the output voltage.

Let's not start that.

In applications where the BJT is being used as a linear amplifier, it's always right to consider it to be a voltage controlled device, with I_C being dependant on V_BE.

Current control only makes sense when dealing with a saturated switch, but even then, in order to ensure a fast turn-off time, it's necessary to take the base voltage below the normal 0.6V diode drop, preferably even negative.

Ah, let's get back to basics: does the current through a resistor causes the voltage across it, or the voltage across a resistor causes the current through it. Answer: mu.

Realise that the OP is not considering BJTs on their own, he is trying to understand how they work (i.e. design equations) for typical simple amplifiers.

If you look at most simple amplifiers, linear or saturated, the input voltages is much more than V_BE. That enables design patterns which more-or-less remove the variation in V_BE from that equations defining the amplifier's operation. The current relationships, however, remain.

For common collector amplifier, consult TAoE section 2.2.2-2.2.5; for common emitter, 2.2.8-2.2.9. Any other introductory textbook ought to be similar.

For more comprehensive analysis, consult TAoE chapter 2x, but the OP won't be interested in that.

[nctnico]

On my Transistor issue:

Here it is cause it just happened again with an NPN. Does the transistor "START" to conduct with the .7v on its base or is it fully on with .7? I think my brain lock is the voltage range at which it amplifies and isn't just a switch?

BJTs are current devices, not voltage devices. There is no simple easy relationship between a BJT's "input" and "output" voltage, so if you start there you are bound to be perplexed.

There is a single simple relationship between "input" current and "output" current; I_C=h_FEI_B

So, start by working out the input (base) current, that will give you the output (collector) current. That current flowing through the load will determine the output voltage.

Let's not start that.

In applications where the BJT is being used as a linear amplifier, it's always right to consider it to be a voltage controlled device, with I_C being dependant on V_BE.

No. Absolutely not. You are writing about a common-emitter amplifier with a resistor in the emitter to turn a transistor into a voltage to current converter. But this is a circuit, not the basic operating mode of the transistor itself.

[Siwastaja]

Ah, the good old "bipolar transistor is current controlled" "no it's voltage controlled" "no it's current controlled". This is a variation of "it's current that kills" "no it's the voltage" "no it's the current". In reality, both are correct: in say NPN bipolar transistor, Vbe and Ib are interlocked. You control current, and measured voltage changes. You control voltage, and measured current changes. There is a simple relationship between each other, a simple function, which you can plot on a 2D plane. Now because this function happens to be quite exponential (or logarithmic, depends on which way you look at it), applying a voltage e.g. from a lab supply, and hoping to get a transistor to a specific level of conduction is quite finicky, even small changes of voltage make a big difference. This is why it's tempting - and useful - to say that a BJT is current controlled, but saying it's voltage controlled isn't wrong per se.

[tggzzz]

This is why it's tempting - and useful - to say that a BJT is current controlled, but saying it's voltage controlled isn't wrong per se.

Precisely.

IMHO for simple introductory purposes, the current version is easier to understand and analyse. OTOH, the more complex linearisations and translinearisations are fascinating.

[nctnico]

This is why it's tempting - and useful - to say that a BJT is current controlled, but saying it's voltage controlled isn't wrong per se.

Precisely.

IMHO for simple introductory purposes, the current version is easier to understand and analyse. OTOH, the more complex linearisations and translinearisations are fascinating.

But those are only somewhat usefull when the transistors are next to eachother on the same die. Otherwise process and temperature variations will introduce errors quickly. IC designers have to use quite a few tricks to match transistors used to build a good opamp. And even then the opamps on the same die don't behave exactly the same. Just look at the metalisation pictures in datasheets for some of the older opamps to see how complex some structures are to achieve good as possible symmetry.

[tggzzz]

This is why it's tempting - and useful - to say that a BJT is current controlled, but saying it's voltage controlled isn't wrong per se.

Precisely.

IMHO for simple introductory purposes, the current version is easier to understand and analyse. OTOH, the more complex linearisations and translinearisations are fascinating.

But those are only somewhat usefull when the transistors are next to eachother on the same die. Otherwise process and temperature variations will introduce errors quickly. IC designers have to use quite a few tricks to match transistors used to build a good opamp. And even then the opamps on the same die don't behave exactly the same. Just look at the metalisation pictures in datasheets for some of the older opamps to see how complex some structures are to achieve good as possible symmetry.

I'm not sure what you mean by "those".

There are many circuits where is is not necessary to have semiconductors on the same substrate.
There are many circuits where it is necessary to have resistors on the same substrate.
There are many circuits where it is sufficient to thermally couple semiconductors that weren't made on the same die.
The issue is of adequacy and fitness for purpose.
All models are false, but some are useful.

And all those are irrelevant to someone struggling to understand basic BJT circuit behaviour.

[nctnico]

You missed the point that where transistor voltage control is actually useful (like current mirrors and other translinear circuits like multipliers), the transistors need to be matched closely where it comes to temperature and process to a point where that is only possible with the transistors being on the same die. So not really applicable to common transistor circuits where you'll need some form of feedback to cancel process and temperature variations in order to make a circuit behave. And in those circuits, using Hfe or Beta (current gain ) is a much more sensible approach.

[Zero999]

This is why it's tempting - and useful - to say that a BJT is current controlled, but saying it's voltage controlled isn't wrong per se.

Precisely.

IMHO for simple introductory purposes, the current version is easier to understand and analyse. OTOH, the more complex linearisations and translinearisations are fascinating.

The voltage controlled version is more applicable to linear amplifiers.

How do your explain a current mirror only considering the current model?

Now consider a current mirror with transistors of different h_FEs, yet everything else being equal.

Lets be lazy and put it in SPICE.
How do you explain the current mirror still working, if the BJTs are current controlled?



Current mirror hFE.asc

EDIT: Wrong quote.

The answer is the h_FE is irrelevant to most BJT linear amplifier designs. I_C vs V_BE is what's important.

[tggzzz]

You missed the point that where transistor voltage control is actually useful (like current mirrors and other translinear circuits like multipliers), the transistors need to be matched closely where it comes to temperature and process to a point where that is only possible with the transistors being on the same die. So not really applicable to common transistor circuits where you'll need some form of feedback to cancel process and temperature variations in order to make a circuit behave. And in those circuits, using Hfe or Beta (current gain ) is a much more sensible approach.

I hadn't missed it; I developed my first translinear circuit in 1979!

Obviously there are some circuits that depend on V_BE - but most strive to avoid dependence on that, or on h_FE/beta for that matter.

Since the context is someone who is having difficulties with understanding basic transistor operation, I think it is inappropriate and unhelpfui to introduce "advanced" topics.

That leads to your final sentence, which think is more likely to help this beginner. There we are in full agreement.

[soldar]

Perhaps because I learnt bipolar transistors at a very young age for me they are absolutely intuitive and obvious.

On the other hand magnetics and electro-mechanical motors are something I never learned deeply and so I am like a permanent beginner.

[SiliconWizard]

This is why it's tempting - and useful - to say that a BJT is current controlled, but saying it's voltage controlled isn't wrong per se.

Precisely.

IMHO for simple introductory purposes, the current version is easier to understand and analyse. OTOH, the more complex linearisations and translinearisations are fascinating.

Yes. And this is why even active engineers (not students), apart from a few, also usually find BJTs much easier to work with than MOSFETs (except for basic switching purposes).
That's always a matter of models. Like, what is DC?

[Red Squirrel]

Math, especially once the big formulas come out. I understand the concept, but I just don't know how to start when it comes to applying it.  I tend to get hung up on what each variable represents, and what unit to use as often it's not really specified. Ex: if looking at a data sheet.

[Zero999]

Math, especially once the big formulas come out. I understand the concept, but I just don't know how to start when it comes to applying it.  I tend to get hung up on what each variable represents, and what unit to use as often it's not really specified. Ex: if looking at a data sheet.

I have a similar problem. Especially when there are formulae with variables in lower and upper case, and Greek characters, which look similar to Latin ones. My hand wring is hard to read and slow, which doesn't help. I just about scraped through mathematics at college.