Actually, I got the answer I was looking for. It was in the NEETS module all along. Just didn't notice it in the picture. I try to attach it. notice the output signal.
Thanks for everyones patients. I appreciate all the help
Thanks for everyones patients. I appreciate all the help
An externally hosted image should be here but it was not working when we last tested it.
no. but everything is relative. reverse as compaired to what. you have time constant and voltage. voltage swings as time moves. take your pot example again..lets make it more complacated. add a bulb. pot in middle say 10 candle power pot down 20 candle power all up bulb off. you can swing from brighter to dimmer without having to go negative candle power. it alternated, it went from bright to dim. think of your triode as a pot the swiper is the grid set the swiper in the middle (bias) as the in put swings the triode allows more or less based on your point of refrance. no it didnt conduct backwards through the tube but you still got a +/- swing or sinewave within a set time....ac.
it did go backwards if your point of refrence is over 0v...right? im not sure if that would be considerd reverse or not?
it did go backwards if your point of refrence is over 0v...right? im not sure if that would be considerd reverse or not?
sakellog
Neets - Naval Electrical Engineering Training Series
These are the U.S. Navy electronics and electricity courses. This is the main source of study material that I have been using. It would be easier if you read over the section on Alternating Current (module 2). I think that I have done a poor job of trying to explain things. I don't want to misquote anything. If you check them out you might have a better idea of my confusion. I think it does a great job of explaining how and why electrons flow the way they do in AC circuits. For DC have a look at module one.
Thanks for the posts. They are thought provoking and ultimately help me find the answers I was looking for.
Neets - Naval Electrical Engineering Training Series
These are the U.S. Navy electronics and electricity courses. This is the main source of study material that I have been using. It would be easier if you read over the section on Alternating Current (module 2). I think that I have done a poor job of trying to explain things. I don't want to misquote anything. If you check them out you might have a better idea of my confusion. I think it does a great job of explaining how and why electrons flow the way they do in AC circuits. For DC have a look at module one.
Thanks for the posts. They are thought provoking and ultimately help me find the answers I was looking for.
100K is a large value for a plate resistor, and represents a slightly imperfect constant
current source... So, how do we have AC (alternating current) when the plate current
of the triode is held more or less constant?
I submit that alternating Voltage often shares the label AC. It creates an alternating
current in the load, even if the load is just a meter... So not entirely inaccurate.
current source... So, how do we have AC (alternating current) when the plate current
of the triode is held more or less constant?
I submit that alternating Voltage often shares the label AC. It creates an alternating
current in the load, even if the load is just a meter... So not entirely inaccurate.
jow,
I can't believe you don't understand this after so many folks have tried to explain it to you. I think you are trying to pull their leg.
Rick
I can't believe you don't understand this after so many folks have tried to explain it to you. I think you are trying to pull their leg.
Rick
Just drop all those current-centric definitions. It's all much easier to understand with a voltage centric approach.
AC voltage is defined by a voltage switching polarity periodically. Obviously, you need to switch polarity around a reference, otherwise this definition is meaningless.
Let's say you have a signal generator, whose reference is 0V and it generates an AC signal going alternatively 10V positive and 10V negative. Now, you have a wire nearby sitting at a pure 10V DC. Tie a 10K resistor in between that wire and your signal generator. What current will you get through your resistor ?
First, a DC component: 1mA. Then a varying current induced by your AC signal: from -1ma to +1ma. This current will add itself to the DC current. Result: there is from 0 to 2ma through the resistor, following exactly the sine wave of the AC voltage generated by the signal generator. The current never changes direction, still there is definetly an AC signal going through that resistor. It cannot be otherwise since it is subjected to a AC voltage.
AC voltage is defined by a voltage switching polarity periodically. Obviously, you need to switch polarity around a reference, otherwise this definition is meaningless.
Let's say you have a signal generator, whose reference is 0V and it generates an AC signal going alternatively 10V positive and 10V negative. Now, you have a wire nearby sitting at a pure 10V DC. Tie a 10K resistor in between that wire and your signal generator. What current will you get through your resistor ?
First, a DC component: 1mA. Then a varying current induced by your AC signal: from -1ma to +1ma. This current will add itself to the DC current. Result: there is from 0 to 2ma through the resistor, following exactly the sine wave of the AC voltage generated by the signal generator. The current never changes direction, still there is definetly an AC signal going through that resistor. It cannot be otherwise since it is subjected to a AC voltage.
Oh, I got it finally! The right answer that will satisfy everyone!
Anode voltage is neither constant nor alternating: it is constant with ripples! 😀
Anode voltage is neither constant nor alternating: it is constant with ripples! 😀
🙄😀
Point about the drawing in post 41. Notice the voltage on the plate changes with time from +150V to +300V. The voltage is always positive if you measure from ground, the cathode. But, if you measure from the no signal bias voltage on the plate, which is +200V, you would measure the AC at +/-100Vp from that +200V reference.
The current in the tube is always flowing in the same direction because there is always a DC bias across the tube, electrons (or EMF), flow from the cathode to the anode. (however, current is typically referred to as flowing from positive to negative and the math formulas are written to assume as such. Same as in solid state circuit design.) BUT the amount of current varies with the AC signal. So when there is no input signal, 300Vbb - 200Vb bias leaves 100V/100K = 1mA of DC flowing in the tube. At the positive peak, (one single point in time,) of the AC output signal, Vb is 250V so there is only 50V/100K = 0.5mA flowing through the tube. When the output signal is at the negative peak, 150V is applied across the anode resistor, so 150V/100K = 1.5mA. The current is always flowing the same way in the tube, just less or more depending on the signal magnitude. Since the anode resistor is a fixed value, this behavior (using Ohms law) dictates that the resistance (AKA conductance) of the tube is in fact changing with the AC signal. Moving the grid more positive from the cathode reduces the resistance of the tube. This is why you see a 180 degree phase shift. When the grid is lifted positive by the input signal, the tube resistance reduces, drawing more current through the fixed resistor and creating more voltage signal across the 100K anode resistor, resulting in the negative peak. Lowering the voltage of the grid causes less current to flow in the tube and the anode resistor so the output tracks more toward the positive rail, Vbb.
The reason a capacitor conducts AC current but not DC and thus can be used to remove the DC voltage level from the signal, the 200V part of the expression Vout = 200Vdc + Sin(wt), is because the 'resistance' of the capacitor is expressed as 'R' = 1/(2*pi*f). DC is also considered an AC signal of 0Hz. Now you can see the denominator in the equation determining the resistance of the capacitor is zero. 1 divided by zero is infinity, so there is infinite resistance to DC signals, thus the DC component is removed.
IMHO, it is critical to understand the math relating to electronics, otherwise it will be almost impossible to really understand the electronics, what's going on in the circuit and how it will relate to the rest of the circuit, and to the physical world.😉
EDIT> BTW, Wikapedia is OK for explanations of simple things. When it comes to specific technicalities, they are a detriment because disseminating incorrect knowledge is worse than no knowledge at all. This kind of stuff has led to many entertaining discussions on this forum, some good some bad. But around here it usually gets smoothed out.🙂
Point about the drawing in post 41. Notice the voltage on the plate changes with time from +150V to +300V. The voltage is always positive if you measure from ground, the cathode. But, if you measure from the no signal bias voltage on the plate, which is +200V, you would measure the AC at +/-100Vp from that +200V reference.
The current in the tube is always flowing in the same direction because there is always a DC bias across the tube, electrons (or EMF), flow from the cathode to the anode. (however, current is typically referred to as flowing from positive to negative and the math formulas are written to assume as such. Same as in solid state circuit design.) BUT the amount of current varies with the AC signal. So when there is no input signal, 300Vbb - 200Vb bias leaves 100V/100K = 1mA of DC flowing in the tube. At the positive peak, (one single point in time,) of the AC output signal, Vb is 250V so there is only 50V/100K = 0.5mA flowing through the tube. When the output signal is at the negative peak, 150V is applied across the anode resistor, so 150V/100K = 1.5mA. The current is always flowing the same way in the tube, just less or more depending on the signal magnitude. Since the anode resistor is a fixed value, this behavior (using Ohms law) dictates that the resistance (AKA conductance) of the tube is in fact changing with the AC signal. Moving the grid more positive from the cathode reduces the resistance of the tube. This is why you see a 180 degree phase shift. When the grid is lifted positive by the input signal, the tube resistance reduces, drawing more current through the fixed resistor and creating more voltage signal across the 100K anode resistor, resulting in the negative peak. Lowering the voltage of the grid causes less current to flow in the tube and the anode resistor so the output tracks more toward the positive rail, Vbb.
The reason a capacitor conducts AC current but not DC and thus can be used to remove the DC voltage level from the signal, the 200V part of the expression Vout = 200Vdc + Sin(wt), is because the 'resistance' of the capacitor is expressed as 'R' = 1/(2*pi*f). DC is also considered an AC signal of 0Hz. Now you can see the denominator in the equation determining the resistance of the capacitor is zero. 1 divided by zero is infinity, so there is infinite resistance to DC signals, thus the DC component is removed.
IMHO, it is critical to understand the math relating to electronics, otherwise it will be almost impossible to really understand the electronics, what's going on in the circuit and how it will relate to the rest of the circuit, and to the physical world.😉
EDIT> BTW, Wikapedia is OK for explanations of simple things. When it comes to specific technicalities, they are a detriment because disseminating incorrect knowledge is worse than no knowledge at all. This kind of stuff has led to many entertaining discussions on this forum, some good some bad. But around here it usually gets smoothed out.🙂
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I agree with this except for your use of AC.
Lets looks at the definition of Alternating Current and Direct Current (I have provided a number sources not just wikipedia).
"All of your study thus far has been with direct current (dc), that is, current which does not change direction. However, as you saw in module 1 and will see later in this module, a coil rotating in a magnetic field actually generates a current which regularly changes direction. This current is called ALTERNATING CURRENT or ac." NEETS module 2.
The NEETS module contiues
"Alternating current is current which constantly changes in amplitude, and which reverses direction at regular intervals. You learned previously that direct current flows only in one direction, and that the amplitude of current is determined by the number of electrons flowing past a point in a circuit in one second. If, for example, a coulomb of electrons moves past a point in a wire in one second and all of the electrons are moving in the same direction, the amplitude of direct current in the wire is one ampere. Similarly, if half a coulomb of electrons moves in one direction past a point in the wire in half a second, then reverses direction and moves past the same point in the opposite direction during the next half-second, a total of one coulomb of electrons passes the point in one second. The amplitude of the alternating current is one ampere."
Now if you consider my original question on how current flows through a triode you can begin to understand the difference of view points.
Notice that the definition of direct current is NOT current that stays constant. Just as alternating current is not defined as voltage that continually changes. They are defined sole on the direction of current flow.
If your view is that AC is any current that has a fluctuating voltage then consider this. Imagine a circuit consisting of a battery and a resister. I would consider this to be a DC series circuit. Keep in mind that the actual voltage is not truly constant. Factors such as temperature and others will cause the voltage in the circuit to change over time. If AC is defined as a circuit with fluctuating voltage, then the circuit I described could only be AC. We could take it a step further, It is impossible to produce a current that remains constant indefinitely. Because it is impossible for a voltage to remain constant indefinitely we can conclude (from the definition used by many here) that DC can't exist!
Anyone with common sense can see that this isn't the case. The reason is AC is more than just a fluctuating voltage.
Sigh. You don't seem to grok the concept that "All A are B" is not the same thing as "All B are A."
One more time: ANY voltage (or current) can be expressed as a sum of a time invariant part (DC) and a time varying part (AC). Including the examples you reprinted from your book.
THE AC IS THE TIME VARYING PART OF THAT SUM. Continually mis-stating this simple concept as "AC is any current that has a fluctuating voltage" will not help your nor anyone else's understanding.
One more time: ANY voltage (or current) can be expressed as a sum of a time invariant part (DC) and a time varying part (AC). Including the examples you reprinted from your book.
THE AC IS THE TIME VARYING PART OF THAT SUM. Continually mis-stating this simple concept as "AC is any current that has a fluctuating voltage" will not help your nor anyone else's understanding.
Basic superposition.
You have AC+DC on the plate. It "passes through" a capacitor, stripping out the DC, and you are left with the wiki definition of AC.
AC always existed at the plate, however; it just didn't fit the limited definition proposed by wiki.
You have AC+DC on the plate. It "passes through" a capacitor, stripping out the DC, and you are left with the wiki definition of AC.
AC always existed at the plate, however; it just didn't fit the limited definition proposed by wiki.
A much more elegant way to express what I said in an earlier post. 😀
Wikis by definition aren't necessarily the full story.. And the comments about current flowing only in one direction... 😱
I think the many posts on this thread have covered it well.
Now let's review a solid state stage... If you take a common-emitter stage with resistive load in collector: electrons and holes travel in opposite directions, so current that flows through transistor is real AC! 😀
Probably that's why SS sounds better? 😉
Probably that's why SS sounds better? 😉
I'm confused now. Someone pops up and asks about AC and DC. We tell him. Then he starts quoting basic textbooks (with their usual simplifications and glossing over, so as not to confuse newbies), and appears to be saying that we are wrong. No wonder he is confused!
Never take what a textbook says as being 100% true. Usually, when introducing a new concept, a textbook will feed you half-truths. It does this because, at your current level of understanding, a simple half-truth is more helpful than the necessarily more complex full truth. You need to understand the simple, slightly inaccurate stuff, before you can grasp the whole truth. Don't try quoting the half-truths back at people who know enough to write the textbook!
End of rant.
Never take what a textbook says as being 100% true. Usually, when introducing a new concept, a textbook will feed you half-truths. It does this because, at your current level of understanding, a simple half-truth is more helpful than the necessarily more complex full truth. You need to understand the simple, slightly inaccurate stuff, before you can grasp the whole truth. Don't try quoting the half-truths back at people who know enough to write the textbook!
End of rant.
You crack me up, hehehe..😀
Let's open new Wiki page: Semi - conductors, that conduct semi-positive, semi-negative, that means, full wave of real AC! 😀
Hmmm.... Even simpler than my example with jumping on different levels in respect to the zero level that means ocean level? I'm confused...
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The problem seems to be that the OP is brandishing a textbook which defines AC as something which necessarily changes sign. If you then define DC as something which doesn't change sign then almost all amplifiers are handling DC only - no AC in there at all!
If you define DC as something constant and unchanging, then amplifiers are not handling AC (as it does not change sign) and not handling DC (as it is not constant). No AC, no DC - so what are our amplifiers doing all day?
If you define DC as something constant and unchanging, then amplifiers are not handling AC (as it does not change sign) and not handling DC (as it is not constant). No AC, no DC - so what are our amplifiers doing all day?
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