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some-witterings · 10 months ago

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Alright, I finally vaguely understand how a BJT transistor works as an amplifier so now you fuckers have to as well... (Also known as: Man rants against conventional current, the worst thing physics and engineering has ever made)

First things first. This is not a formal scientific explanation that is guaranteed to be right or fully comprehensive. This is one man's attempt to drag others into insanity over fucking electrons and humanity's inability to put an arrow on a diagram the right fucking way.

So lets open this descent into madness with a discussion of what the fuck a BJT is. In short, it is a lump of silicon and some other elements designed to make engineers feel pain and only designed by what I can only assume is divine intervention. In terms of it's use in electronics however, it is two things. An amplifier and a switch.

These behaviours are what you think they are. A switch is just like the one on your wall. You interact with it and a thing either starts or stops happening. You then interact with it again and the inverse happens.

An amplifier takes a small signal, and makes a bigger version of it. Small wiggle to big wiggle where both wiggles are the same.

I hear some of you asking "How does a BJT work?". For those who aren't asking that question: magic. For those who are: what is wrong with you. But nevertheless I shall indulge you. First, a picture:

What, I never said you were getting a good picture

The picture shows 3 different areas. Each one of these regions is a bit of silicon with something called "dopants" in. A semiconductor can be N-doped or P-doped. An N-doped region has an excess of Electrons and thus has a bunch free to move about, a P-doped region has an excess of Holes. These are introduced by adding an atom with more than 4 outer electrons in the case of N-doping and with 3 outer electrons in the case of P-doping. For N-doping this means there is a free electron that is just allowed to float around, for P-doping this means that there is a space for an electron to be sucked into and generate a hole.

Holes are inherently confusing, but know as I explain them they are the far more reasonable alternative to cracking open a cold can of quantum mechanics. A hole can be thought of as a kinda of bizarro electrons. It has the equivalent charge to an electron, but positive instead of negative. They are also technically heavier, but that is a conversation for a different day. More to the point, they represent the absence of an electron.

So just to summarise at this point. We have two regions with lots of free electrons, sandwiching a region with a deficit of electrons (or excess of holes). Though, there is something on the diagram yet to be explained. That is the charges in circles.

When the doped regions are brought together the old saying remains true, "opposites attract". Excess holes from the P-doped border flood into the N-Doped region, and excess electrons from the N-doped region flood into the P-doped region. This includes ripping atoms of their respective holes and electrons on this border region, which means there is an imbalance of electrons to protons in the atom and thus they become ions. Otherwise known as a charged particle that cannot move.

The diagram then becomes stable once the border regions appear. Electrons in the N region cannot diffuse into the P region because of the negative barrier in the P region and holes in the P region cannot diffuse into the N region because of the positive barrier. The barriers can't be unmade either, because the excess electrons cannot diffuse close enough to the positive barrier to equalise the charge because of the negative barrier right next to it and holes cannot diffuse close enough to the negative barrier because of it's neighbouring positive barrier. This is the precarious balance that a BJT finds itself in when not connected to anything else.

this is where I need to add, for people who already know about this madness - yes there are thermal generation currents and other stuff, but for the time being I'm keeping it as simple as possible because I am in fact a weapons grade idiot.

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Okay that was a lot so I'm adding a break here. Go and get a cup of tea or preferably alcohol strong enough to strip paint off of walls. Whatever your choice of beverage, know that the logical bit is done now and to prepare yourself for arrow based madness.

Are you back with your drink now? Well then, read on whenever you are ready...

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Picking up where we left off, lets do something mad. Lets slap some batteries and labels on the fucking abomination.

Don't worry, all symbols and letters shall be explained.

The big line next to the small line is a battery, with the big line being the postive terminal and the small line being the negative terminal.

The triangles are connections to ground. Basically a place you can infinitely dump or pull electrons and holes from. A battery is a pump that sucks or pumps charge into or out of earth.

E - Emitter. Electrons come from (emitted from) here

B - Base. Middle bit and main source of confusion

C- Collector. Electrons arrive (are collected) here

With that all explained, let's dive into fuckery at the heart of a BJT. But to get there I need to take a detour to verbally assault conventional current.

When humanity first discovered electricity, we thought that electricity flowed from positive to negative. This was reasonable at the time given we hadn't discovered the electron yet. From then on everyone drew circuit diagrams with current flowing from positive to negative on a battery. For most purposes this doesn't matter, here however it does. In reality, electricity (made of negative electrons) actually flows from negative to positive. However, at no point did humanity GO BACK AND CHANGE THE FUCKING DIRECTION OF CURRENT ON CIRCUIT DIAGRAMS.

You will understand why this is such a problem in short order. So, going back to the previous diagram we can see a battery's positive terminal is attached to the base region. We can imagine this as pumping holes into the base region. As it pumps more and more holes into the base region the charge difference (voltage) across the base-emitter border region gets greater and greater, until it becomes strong enough to suck electrons from the N-doped region through the Negative Ion wall and into the P-doped region. The electrons that are sucked through from the N-doped region are replaced in that region from ground.

This is basic diode action and now a standard current. Electrons are sucked from ground, through the N-doped region, through the Negative Ion wall, and through to the positive terminal of the battery and then back to ground. Making a full circuit.

However, here we have neglected an important third of out BJT. Our collector. This has even more electron suction power on it, or rather hole injection, power. This means that whilst some electrons enter into the base and then recombine with the holes (or rather are sucked out to the battery), a majority of them are near instantly sucked out of the base and into the collector by the massive electron suction and the positive wall in the collector.

As an aside, current is normally marked like this:

Which makes zero fucking sense as why would electrons be going from the base to the emitter and what the fuck is going on at the collector. This is a minor issue solved by flipping the arrows, but is a far bigger problem when you start putting BJTs in circuits as you can't just flip the arrows there.

To try and summarise this. Electrons are providing just enough suction to be pulled from the emitter to the base, they are then instantly subjected to a far bigger suck and pulled into the collector. This is because holes are constantly being shoved into the base which electrons want to recombine with. However, in the collector there is a massive number of holes being injected so a massive number of electrons are needed to replace the ones that are vanishing in the collector and thus are pulled from the base.

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Alright, second break. Are you still sane? Comprehending the madness of the electron's world? Questioning why you are reading the mental breakdown of an already mad man?

Because you should only be doing the latter. If you are doing either of the first two I fear for you.

Go and refill your beverage of choice and come back...

All good? Well it shouldn't be. But I shall restart anyway.

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So, let's take this all a step further. First, lets use one as a simple switch. This doesn't even need a diagram. Simply take the previous diagram and imagine connecting and disconnecting the battery on the base. When it isn't connected electrons don't have enough suck to be pulled into the base so they simply don't conduct through to the collector. This is called "turning a switch off". Stick the battery back in and electrons flow again, otherwise known as "turning the switch on".

This ability to act as an electricity controlled switch is why computers are a thing. There are literal billions, if not more, transistors in the device you are reading this on right now doing this exact thing to represent 1s and 0s in your computer and then tumblr happens. Your ability to read Yaoi is predicated on the laws of physics declared by God herself and enough mad fucking engineers to make her infinite cosmos into a hyper efficient engine to make virtual men kiss each other for your amusement. This is the reason humanity are the dominant fucking species.

The next use is going to need a little more explanation.

Enter in, a simplified version of the common emitter amplifier:

Everything shall be explained so don't worry:

VB - a battery that applies enough voltage to the base-emitter connection to make it conduct

Signal Source - the origin of our wiggle that we are going to make into a bigger wiggle. The wiggle is the amount of current flowing getting bigger and smaller.

Load - this is where we view our output. The current flowing through it is our output (or the voltage across is if you wanna get Ohmically freaky)

IC, IB and IE are all our current from before.

On the right is a larger version of the symbol for a transistor with C being the collector, B being the base and E being the emitter.

Let me ask you dear reader a simply philosophical question. How can a signal be amplified by something after it in the circuit. Because according to the current, it flows through the Load and then into the BJT despite the BJT supposedly doing the amplifying. So how then is the BJT amplifying the current going through the Load. This question has driven me FUCKING INSANE. It is only resolved by remembering that the conventional current arrows are WRONG and the Load is AFTER the BJT for the electrons. I. Hate. Conventional. Fucking. Current.

With that little qualm aside. Let us return to the idea of amplification. How does a wiggle on the base, make a bigger wiggle out of the collector and across the load.

It's simple with the background you have now. As you increase the current on the base, more holes are injected into the base, hence more electrons are sucked out of the emitter and finally more are sucked into the collector and thrown out of it. As you wiggle the base current up and down, the amount of electrons flowing into the base and thus out the collector increases and decrease correspondingly. Remember, the emitter is getting it's electrons from ground which has an infinite number of them so it can throw through as many as it wants to.

Yes, injecting more holes into the base does mean more electrons recombine with electrons in the base. But the suction is such that the relationship is vaguely linear for the most part. I.e. the ratio of recombinations to electrons sucked through to the collector remains basically the same.

This all results in the idea that the more voltage there is on the collector, the more holes are put into the collector and the higher total suction on the electrons in the base. If the amount of holes isn't that high then there won't be that much suction and more electrons will recombine in the base.

In summary for amplification: Small wiggle on base introduces a corresponding wiggle of electron demand from earth via the emitter. However the base is then scammed because a majority of those electrons are sucked into the collector. Meaning that the wiggle of electrons is replicated with the bigger number of electrons in the collector.

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It's done. You now vaguely understand semiconductor chemistry and electronics. Why did you do this to yourself. I can only conclude that you, like me, are mad. Driven to insanity by the promises of science.

People fear eldritch gods because of their mind warping and their gifts of insanity. I say to them, you need not hunt for an elder god when what makes up your flesh and bones is so much stranger...

Go now, dear pupil, you have much more to learn. And deeper truths to madden yourself with...

#science side of tumblr #sciblr #electronic #chemistry #explanation #long #FUCK CONVENTIONAL CURRENT #ISO PLEASE FIX #FOR FUCKS SAKE WE ARE ENGINEERS #FIX IT #electrons #Transistors #BJT #Amplifiers #Switches #Fuck

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