On the input of most (if not all?) amplifiers is a capacitor. Why? Transistors don't work on AC. The capacitor takes the AC signal and turns it into (by magic to me) a varying DC signal.
Let's imagine the flow of electrons as automobiles. In an AC signal the automobiles travel in one direction, turn around, and travel in the other. In a varying DC, the automobiles accelerate, peak, then decelerate to a trough, and so on. THE AUTOMOBILES NEVER CHANGE DIRECTION!
So?
So! So what if your signal goes from +4V to -6V! How can an automobile accelerate to 4mph and decelerate back 6mph ...all while traveling in the same direction! Impossible!
Transistors also confuse me. Maybe it's best I explain to you how I think they work. Now crystals are small, and so are junctions, so I'm going to falsely explain how a signal is amplified with a triode (vacuum tube).
Okay, 3 terminals. One in the center and two at opposing ends. Hook those two opposing ends of the tube up to a battery (amplifiers can't create power out of nowhere). Now you should have a really strong current flowing through the tube. Now take on of the wires from your input and wire it to the center tube.
Well I don't know where that other wire goes from the input signal. I'm just hoping to get across the idea that I see nothing special about a triode vacuum tube. How is that any different than wiring in a battery either in series or parallel with the signal?
(I do understand the importance of the diode in my crystal set, but you dont need to AM your signal from your receiver to your speakers, so there's no reason to extract any signal here)
Thanks!
Let's imagine the flow of electrons as automobiles. In an AC signal the automobiles travel in one direction, turn around, and travel in the other. In a varying DC, the automobiles accelerate, peak, then decelerate to a trough, and so on. THE AUTOMOBILES NEVER CHANGE DIRECTION!
So?
So! So what if your signal goes from +4V to -6V! How can an automobile accelerate to 4mph and decelerate back 6mph ...all while traveling in the same direction! Impossible!
Transistors also confuse me. Maybe it's best I explain to you how I think they work. Now crystals are small, and so are junctions, so I'm going to falsely explain how a signal is amplified with a triode (vacuum tube).
Okay, 3 terminals. One in the center and two at opposing ends. Hook those two opposing ends of the tube up to a battery (amplifiers can't create power out of nowhere). Now you should have a really strong current flowing through the tube. Now take on of the wires from your input and wire it to the center tube.
Well I don't know where that other wire goes from the input signal. I'm just hoping to get across the idea that I see nothing special about a triode vacuum tube. How is that any different than wiring in a battery either in series or parallel with the signal?
(I do understand the importance of the diode in my crystal set, but you dont need to AM your signal from your receiver to your speakers, so there's no reason to extract any signal here)
Thanks!
The input capacitor blocks Direct current it will also act as a high pass filter its frequency of operation is dependent on the capacitor value and any resistance that follows.. Ps Transistors do amplify AC. To simplify try looking at a transistor as an electronic controlled variable resistor it may help
a little
regards
a little
regards
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LOL. Well, I have a degree in electronics with 40 years of experience and I know almost NOTHING. You will spend your entire life learning electronics.
If you have not had the basic electronics classes, you really need to. The WEB is full of basic classes for free, or try and find one you can pick up as an elective whatever your major is. (We are not prejudicial of art history majors here).
I find I can explain electronics better with plumbing analogies than cars. The electrons actually DO change directions, in a simplistic sense. That is the DEFINITION of AC. What you are thinking about is an AC with a DC offset.
If you have not had the basic electronics classes, you really need to. The WEB is full of basic classes for free, or try and find one you can pick up as an elective whatever your major is. (We are not prejudicial of art history majors here).
I find I can explain electronics better with plumbing analogies than cars. The electrons actually DO change directions, in a simplistic sense. That is the DEFINITION of AC. What you are thinking about is an AC with a DC offset.
AC.
Think of a rope tied in a circle, around two pulleys (clothes line).
Pull back and forth = AC
Pull in one direction only = DC
Capacitor in this application *blocks* DC, but passes AC (magic).
Tube, transistor, etc.
It's a VALVE.
Just like a water valve.
Big pipe coming in.
Big pipe going out.
Nothing goes through until you turn the valve.
You can't stop the water with your finger, but you can use your finger (small force) to turn the valve.
The valve will adjust the flow from nothing, to something, to everything.
So, what a tube or transistor does is to permit a small force (small signal) to control the flow of a much LARGER signal.
This is called *amplification*.
The amount that the replication of the small signal - aka amplification - or "the output' is different, does not track perfectly, or varies from the small signal ("control signal"/finger on the valve) we call DISTORTION!
Now armed with this information get thee to a website or book that tells you the rest of the story.
Go to your library (ur in college, right?) and get a copy of The Art Of Electronics, by Horowitz and Hill. That give nice plain language explanations of all of this.
_-_-
Think of a rope tied in a circle, around two pulleys (clothes line).
Pull back and forth = AC
Pull in one direction only = DC
Capacitor in this application *blocks* DC, but passes AC (magic).
Tube, transistor, etc.
It's a VALVE.
Just like a water valve.
Big pipe coming in.
Big pipe going out.
Nothing goes through until you turn the valve.
You can't stop the water with your finger, but you can use your finger (small force) to turn the valve.
The valve will adjust the flow from nothing, to something, to everything.
So, what a tube or transistor does is to permit a small force (small signal) to control the flow of a much LARGER signal.
This is called *amplification*.
The amount that the replication of the small signal - aka amplification - or "the output' is different, does not track perfectly, or varies from the small signal ("control signal"/finger on the valve) we call DISTORTION!
Now armed with this information get thee to a website or book that tells you the rest of the story.
Go to your library (ur in college, right?) and get a copy of The Art Of Electronics, by Horowitz and Hill. That give nice plain language explanations of all of this.
_-_-
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I have been doing it 36 years. Mostly software and electronic design.
I recently got into class d amplifiers and LLC SMPS and realised I knew very little ! I started to get into the realm of high frequencies and that's when things change radically. PCB layout and decoupling becomes vital.
I also got into SMPS transformers and it turns out to be very complicated.
My major is EE, but I have nothing but math under me. Circuit Analysis isn't until next semester.
I'm under the impression that transistors can only amplify DC signals, because transistors themselves are powered with DC sources.
But according to Lenz, when you speak into a mic, you'll get an AC signal. So how are you supposed to amplify an AC signal when transistors will only amplify DC signals?
You can cheat and wire a capacitor in series at the input to get a DC offset. It may be DC, but it's still AC in nature.
See it all works out.
^I understand this is incorrect, but I'm just showing you where my logic is at.
I'm under the impression that transistors can only amplify DC signals, because transistors themselves are powered with DC sources.
But according to Lenz, when you speak into a mic, you'll get an AC signal. So how are you supposed to amplify an AC signal when transistors will only amplify DC signals?
You can cheat and wire a capacitor in series at the input to get a DC offset. It may be DC, but it's still AC in nature.
See it all works out.
^I understand this is incorrect, but I'm just showing you where my logic is at.
Lesson learned: it's a bad analogy.
You're looking at my analogy and thinking this is how I understand AC.
That is incorrect. That analogy explains my understanding of DC offset. That is, a signal with electrons flowing in one direction only, but vary in amplitude over time. And if the signal is varying in amplitude over time, then the signal is AC in nature, regardless of electron flow.
Get this book - Malvino Electronic Principles - Albert Paul Malvino - Google Books
You can find used older copies for less than the price of a cheap 6-pack. It is one of the more pragmatic treatments of basic electronics I've seen, and still useful as a basic reference for old dogs. There is just enough math for basic understanding, not so much as to overwhelm.
You can find used older copies for less than the price of a cheap 6-pack. It is one of the more pragmatic treatments of basic electronics I've seen, and still useful as a basic reference for old dogs. There is just enough math for basic understanding, not so much as to overwhelm.
...Thales and his discoveries with amber. The lodestone. Letter of Petrus Perigrinus. Gilbert. Hauksbee and his glowing electrostatic machines. Gray's Charterhouse experiments. Kleist. Musscenbroek and the leiden jar. Franklins experiments that he never really conducted. Volta VS Galvani. Cavendish and the torpedo fish. Sturgeon and his electromagnets. Joseph Henry. Transatlantic cable (fail). George Ohm. Faraday's invisible lines of force. Maxwell. Hertz. Oliver Lodge and his iron filings. Branly coherer. Bose's semiconducting crystals. Geissler's glowing tubes. Flemings valves. Marconi. Sarnoff. Priest....
I have been taking baby steps since early September. I have most of the history down ...at least up until the discovery of the transistor at Bell Labs (Europeans had a better one in early 48
). I'm ready to understand theory.
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Try this one....Think of a transistor as a roller-coaster, voltage going up & down on a large structure "above ground" Ha, ha, ha. Now, picture the 'hills' of another roller-coaster above the ground & the other half, the valleys, dug into the ground.....(Weird looking roller-coaster)............The transistor is the 'conventional' type roller-coaster & we extracted the AC component to make the half & half strange looking type roller-coaster. The capacitor has removed the "supporting structure" (DC) of the coaster, evening out the Ups & Downs, (AC).
___________________________________________________Rick..........
___________________________________________________Rick..........
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Minne, you didn't bother to read my post??
Understand the rope analogy to DC?
You didn't go to the library and get a look at the book??
It's a modern book that will serve you well.
AC is merely the variation in level of a DC flow.
That's what the valve does.
If ur a EE, this ought to be blatantly clear and obvious.
If you don't vary the DC flow except to the states of OFF and ON, then you
call it "digital".
If you vary the number of pulses of DC of a given amplitude within a unit time and then integrate those pulses, you have a PDM modulator/amplifier. Pulse Density Modulator
If you change the width of those DC pulses (you know clock pulses) you get what is known as a PWM. Pulse Width Modulation.
In both of the two latter cases an AC signal has been derived from amplitude invariant signals (the pulses).
So AC is merely the variation of DC level WRT time.
This variation can be accomplished by various means.
The most usual is to use the valve as a "linear device".
That means it changes the level of the OUTPUT (electrons flowing through) is in a fixed ratio to the much smaller level of the input signal (the controlling signal).
A small controlling signal causes a corresponding larger output/throughput to occur. Ok?
How does that happen at an atomic level?
Read the ******* book kid.
In my view it is more or less magic.
_-_-bear
Understand the rope analogy to DC?
You didn't go to the library and get a look at the book??
It's a modern book that will serve you well.
AC is merely the variation in level of a DC flow.
That's what the valve does.
If ur a EE, this ought to be blatantly clear and obvious.
If you don't vary the DC flow except to the states of OFF and ON, then you
call it "digital".
If you vary the number of pulses of DC of a given amplitude within a unit time and then integrate those pulses, you have a PDM modulator/amplifier. Pulse Density Modulator
If you change the width of those DC pulses (you know clock pulses) you get what is known as a PWM. Pulse Width Modulation.
In both of the two latter cases an AC signal has been derived from amplitude invariant signals (the pulses).
So AC is merely the variation of DC level WRT time.
This variation can be accomplished by various means.
The most usual is to use the valve as a "linear device".
That means it changes the level of the OUTPUT (electrons flowing through) is in a fixed ratio to the much smaller level of the input signal (the controlling signal).
A small controlling signal causes a corresponding larger output/throughput to occur. Ok?
How does that happen at an atomic level?
Read the ******* book kid.
In my view it is more or less magic.
_-_-bear
Disrespectful post removed. All members are due a minimum level of respect per forum rules.These statements are wrong.
Direct Current (DC) is Current Flowing in one Direction.
Alternating Current (AC) is Current Flowing in Alternating directions.
That difference is fundamental !!!!
It's also important to understand that AC and DC voltages can be (and often are) superposed. Any voltage can be broken into a sum of a time invariant and a time dependent term, or if you like, an AC plus a DC term.
So drop analogies of cars or ropes or whatever- it's much simpler if you think of electricity as electricity. Under limited circumstances, you can think of fluids in pipes, but that analogy is limited as well.
If you want to actually understand HOW semiconductors work, you need a fair grounding in basic quantum mechanics. If you're content (as most are) to know how to MAKE them work, how to use them, you just need to understand the Ebers-Moll and a few other basic equations.
So drop analogies of cars or ropes or whatever- it's much simpler if you think of electricity as electricity. Under limited circumstances, you can think of fluids in pipes, but that analogy is limited as well.
If you want to actually understand HOW semiconductors work, you need a fair grounding in basic quantum mechanics. If you're content (as most are) to know how to MAKE them work, how to use them, you just need to understand the Ebers-Moll and a few other basic equations.
Andrew, per the confusion of the OP.
In a single ended amplifier, how, pray tell, does AC flow in "alternating directions" - assuming a single supply, of course.
It does not.
The AC is the result of a bias - a fixed level of DC flow - that is then varied to be greater or less.
You can see the same effect in an artificial river/stream of water, if you never reverse the flow of water, but increase it and then decrease it, repeat, you get what? Waves. AC.
Thanks Andrew.
_-_-
Pick any single ended amplifier with a single polarity supply.
That fits your DC bias situation.
Now measure the Current Flow after the Output Capacitor that prevents the DC bias burning out your load.
The currents reverses at the load !!!!!! it is alternating current at the load.
The same applies to a DC blocked input. On one side you have actual flow reversing current = AC. On the other side you have variable DC, i.e. DC with an imposed variation.
The two sides of the blocking capacitor are different. They are not both DC. They are not both AC.
That fits your DC bias situation.
Now measure the Current Flow after the Output Capacitor that prevents the DC bias burning out your load.
The currents reverses at the load !!!!!! it is alternating current at the load.
The same applies to a DC blocked input. On one side you have actual flow reversing current = AC. On the other side you have variable DC, i.e. DC with an imposed variation.
The two sides of the blocking capacitor are different. They are not both DC. They are not both AC.
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