Simple Explanation

[Some Dude]

I just typed in electronic circuit forum to find somewhere where I could ask a question about a really simple circuit. In the last month or so I've been really into electricity and how is works so I want to make an amplifier. I've read up on transistors, capacitors, and some other things and I feel I understand it for the most part. I found this circuit:
**broken link removed**
The only thing I'd like to really know is the flow of electricity through this thing. If I'm not mistaken, audio is in AC, from negative to positive, but in this case, they are shifting the sin wave or the AC current to stay positive, or DC, right?
I'm wondering what happens when the audio signal goes positive and negative, where it the flow from the battery and signal going?
I'd really appreciate an explanation alot.

 

[MrAl]

Hi there,

It's nice to see people with an interest in this stuff.

The circuit you found isnt one of the best, in fact it's not that good at all. The speaker always has at least some DC which isnt good and may even make the sound really bad. There are much better circuits and im sure others here would be happy to share some.

Conventional current flow is from the positive of the battery, through the speaker, through the collertor of that transistor, through the transistor, and through the emitter back to the other terminal of the battery. Electron flow is the same except in the opposite direction.
The base gets a DC bias from the two 100k resistors, and the AC comes in through the 10k resistor. It modulates the base of the transistor and that changes the conductance of the collector emitter of the transistor which in turn causes more and less current flow through the speaker which is approximately the same as the input AC except at a higher power level. The speaker getting this higher signal produces sound.

 

[Some Dude]

Thank you for input!

Ok, now I'm confused though. howstuffworks said "If you connect a wire between the negative and positive terminals, the electrons will flow from the negative to the positive terminal as fast as they can..." Whats correct? When I was looking at this circuit I did think myself the transistor was backwards.

Would you be able to elaborate more on the AC current coming from the input? Basically how the flow works between both those inputs and circuit.

I found that I could understand this circuit the most but I'd be interested in other designs, preferably simple.

Thanks again.

 

[aljamri]

howstuffworks said "If you connect a wire between the negative and positive terminals, the electrons will flow from the negative to the positive terminal as fast as they can..." .

That’s correct, and called short circuit. (don't do it unless there is no load in between).

Whats correct? When I was looking at this circuit I did think myself the transistor was backwards.

probably thats because of the arrow of the transistor, it indicates the conventional way of flow, from positive to negative, but electrons will go opposite as MrAl stated.

I found that I could understand this circuit the most but I'd be interested in other designs, preferably simple.

I would rather suggest that you read about the transistor itself such as
, then go for analyzing its circuits.

 

[MrAl]

Hi again,

There's always a little confusion regarding conventional vs electron current flow. Electron flow is the usual true physical view, but conventional current flow is most often used for circuit analysis. You'll note that the transistors emitters point in the direction of conventional current flow. The electrons are considered to flow in the opposite direction through. So it depends which method you prefer here, either one will do, as long as you dont switch to another method during the analysis of a given circuit.

Electrons are said to constitute the real current flow, but holes are said to flow in the other direction, so again pick one and go with it and dont let this bug you too much. It's a little different than water flow in a hose obviously, but water is a physical entity and electrons and holes are not quite the same because after all electrons are sub atomic particles and as such they are not like anything we are used to dealing with in real life. It would be very very roughly like trying to follow every single molecule of water in that hose rather than just assuming that simply the water flows from one end to the other. It would be sort of pointless to try to do that because we are mainly concerned with what that water can do for us as a whole, so we ignore the tiny parts that make it up. Electrons flow in a complete circular path though, but the idea is basically the same.

It's also interesting that everything we deal with in real life depends on electrons, yet we never actually experience an electron directly...only it's effects. When we touch something the electrons in our fingers come close to the object we are 'touching', but the electrons never touch each other because the forces keep them apart, so we feel the forces, not the electrons themselves.

You can choose which direction of current flow you like, but it is a good idea to understand both ways just in case you read something that someone else wrote using a particular convention. It's not hard to switch, just reverse the direction you follow the circuit wires around. In any case, dont let it bug you too much, just learn both ways

 

[Some Dude]

Thank you very much for clearing up the flow of electrons and current, that makes way more sense now.

I'm just going to tell you what I think is happening then you someone can correct me.

The electrons start flowing from the negative terminal of the battery to the first emitter then go back down it and on to the first 100k resistor. The resistor drops the voltage down to 4.5. With this transistor I'm assuming its open halfway for current to flow when there is 4.5 volts at its base. Once the base takes on as many electrons as it can at 4.5 volts, the electrons flow through the second resistor then gets bumped up to 9 volts again(I read about this but didn't understand it.)

Now the electrons flow to the two collecters then through the speaker, resistor, and to the battery, making the path for current. Because the transistor is opened up by the 4.5 volts just from the battery, current can now flow through the positive terminal, through the resistor, speaker, through the transistor, which is being manipulated by the inputs flow of electrons which is either adding electrons or taking them away which changes how much current can flow through the transistor.

This is after alot of intense thought so I hope this isn't just dumb lol

I'm probably going to have quite a few more questions so please bear with me, I'm trying hard to understand how this works.

 

[tytower]

Hi again,
There's always a little confusion regarding conventional vs electron current flow. Electron flow is the usual true physical view, but conventional current flow is most often used for circuit analysis. You'll note that the transistors emitters point in the direction of conventional current flow. The electrons are considered to flow in the opposite direction through. So it depends which method you prefer here, either one will do, as long as you dont switch to another method during the analysis of a given circuit.
Electrons are said to constitute the real current flow, but holes are said to flow in the other direction, so again pick one and go with it and dont let this bug you too much. It's a little different than water flow in a hose obviously, but water is a physical entity and electrons and holes are not quite the same because after all electrons are sub atomic particles and as such they are not like anything we are used to dealing with in real life. It would be very very roughly like trying to follow every single molecule of water in that hose rather than just assuming that simply the water flows from one end to the other. It would be sort of pointless to try to do that because we are mainly concerned with what that water can do for us as a whole, so we ignore the tiny parts that make it up. Electrons flow in a complete circular path though, but the idea is basically the same.
)

A Proffessor in the States created the holes bit to satisfy earlier teachings which were wrong !
There are no holes and only a fool allows himself to believe something which is wrong.
Forget the hole confusion and concentrate on electron flow is my advice. Water flow is an ideal way to view it.
Then you must take into account that all the arrows are wrong but that will eventually change when enough people have forgotten about conventional flow .

A bit like law -the courts accept a given law , say gray is in fact black and apply it to many many cases . New argument is presented to show grey is actually different , and then the court says that was always the case and the previous decisions were right but new decisions will follow the new interpretation. They won't admit they were wrong.

By the way the defenders will swarm in now but the above stands and they will fade away

 

[carbonzit]

I like simple explanations too, and I think you deserve one.

So I added the current flows to your little circuit here:

**broken link removed**

Notice that I chose the direction of "conventional current flow", even though it's the opposite of the actual, physical flow of electrons. That usually makes things a whole lot easier to comprehend.

So there are 3 main pathways of current here:

1. The green flow is the input current through the base of the first transistor. (You realize, of course, that your "transistor" is actually two transistors mashed together in what's called a "Darlington pair", named for some dude Darlington, I guess.) This is the smallest current here.

2. The red flow is through the collector-emitter of the first transistor, into the base of the second transistor. This is larger than the first flow (that is, the transistor has amplified the input current).

3. The third and largest flow is the purple line through the 50Ω resistor, the speaker, and the 2nd transistor. This is the output of the "power amplifier" that drives the speaker.

This all is somewhat of an oversimplification, but as they say, it'll do as a first-order explanation.

 

[carbonzit]

There are no holes and only a fool allows himself to believe something which is wrong.

So are you calling me a fool?

But seriously, yes, there are holes: it's just that you can't see them. They're only a conceptual construct, but they're certainly real, as there's both electron flow and "hole" flow (which is really just reverse electron flow). So I guess I really don't see what your problem with them is. But hey, let's not drag this thread out into an argument over this, OK?

 

[tytower]

That's fine but like all disagreements please let me respond . Can you in any way demonstrate the existence of holes ? Not a big post just a URL or something small.

Edit . It is obvious he can't even give any reference material so make your own mind up about that

 

[carbonzit]

That's fine but like all disagreements please let me respond . Can you in any way demonstrate the existence of holes ? Not a big post just a URL or something small.

Sorry, this discussion is over (at least on my end). Somewhere else, perhaps.

 

[Some Dude]

Awesome little explanation cabonzit! That was really helpful for real.

Would you be able to show the electron flow aswell?

Now the red and purple can both function at the same time because they would have to correct?

So how come the current will not travel through those resistors at all?

 

[carbonzit]

Current flows through every part of the circuit, including all the resistors. Otherwise, why would we put them there?

But I only showed the main pathways and left out several. At your level of understanding you needn't bother with every path in the circuit. Wait for a while on that. (For instance, there's a small current, known as "bias current", that flows up from the battery through the resistor and speaker, around to the 100K resistor and into the 1st transistor's base.)

You want electron flow? Just reverse the arrows. Electrons flow from negative to positive.

Not sure what you're asking about the red and purple functioning at the same time. If you look at the wire in the middle, from the top line down to both transistor collectors, both the red and purple currents flow through it at the same time. One is smaller (red). They split at the connection to the first transistor's collector. (Now we're getting into what's known as "network analysis".)

 

[aljamri]

So how come the current will not travel through those resistors at all?

I think It is the time you realy need to read the transistor basices such as

 

[Mr RB]

How did they come up with "1 Watt"??

Even with a perfect drive waveform and changing to a FET the most current you could get through the 8 ohm speaker is 9v / 58 = 155mA which would be a instantaneous peak speaker power of 192mW with the RMS audio power significantly less than that.

 

[Some Dude]

I already did read up on how and what transistors do but I don't see what the relation of them was with the resistors I was talking about.

I should probably invest in a book and start reading up legitimately if I want to get this though.

Thanks for the help though guys, much appreciated.