The basic argument arises from two separate issues:
1. Some people believe that DC means 'all the current/voltage goes in the same direction' - this is what is often taught in elementary courses/textbooks. Others believe, more correctly in my view, that DC means 'frequency=0Hz' - this is what people usually believe after they have encountered Fourier theory. In either case it is an argument about words rather than substance. Whether we call the output from a poorly smoothed supply 'DC with ripple' or 'DC plus AC' has no effect on how the electronics works, and such arguments are often a sign that people know just enough to confuse themselves and annoy others.
2. Most electronic components have a voltage rating and this is usually DC. Some components have an AC voltage rating (such as mains filter capacitors) while others are said to be intended for 'audio'. This does not mean that a DC-rated component cannot be used for AC, and it does not mean that components not 'intended' for audio will somehow ruin an audio signal. The AC voltage rating on some capacitors is a safety issue: it means that the capacitor is designed to cope with continuous high voltage stress and fail safely. The 'audio' rating on some components usually means nothing at all.
1. Some people believe that DC means 'all the current/voltage goes in the same direction' - this is what is often taught in elementary courses/textbooks. Others believe, more correctly in my view, that DC means 'frequency=0Hz' - this is what people usually believe after they have encountered Fourier theory. In either case it is an argument about words rather than substance. Whether we call the output from a poorly smoothed supply 'DC with ripple' or 'DC plus AC' has no effect on how the electronics works, and such arguments are often a sign that people know just enough to confuse themselves and annoy others.
2. Most electronic components have a voltage rating and this is usually DC. Some components have an AC voltage rating (such as mains filter capacitors) while others are said to be intended for 'audio'. This does not mean that a DC-rated component cannot be used for AC, and it does not mean that components not 'intended' for audio will somehow ruin an audio signal. The AC voltage rating on some capacitors is a safety issue: it means that the capacitor is designed to cope with continuous high voltage stress and fail safely. The 'audio' rating on some components usually means nothing at all.
A full bridge rectifier should make AC to DC, but the only difference is that the signal do not change polarity, one lead is always positive and one negative.
If AC has to change polarity to be called AC, you could just bias it until it do not change polarity and it's DC. On the other hand, if you have a rail to rail DC +/-20V, you could call it AC if you choose to make i.e. an circuit turn a pentameter both ways, alternatively.
Sorry to be confused now🙂
If AC has to change polarity to be called AC, you could just bias it until it do not change polarity and it's DC. On the other hand, if you have a rail to rail DC +/-20V, you could call it AC if you choose to make i.e. an circuit turn a pentameter both ways, alternatively.
Sorry to be confused now🙂
"AC" is electrical slang for any non-zero frequency, any disturbance. In air, the average atmospheric pressure is the "DC component". "Sound" generally means a disturbance in the constant air pressure and therefore "sound" is "AC".
An amplifier requires active components, which could be described as electrical valves. And they amplify/multiply a signal by modulating a DC current, creating an AC component, ie transistors only operate in one polarity. So transistors require a DC bias be added to the input to operate and that DC has to be removed at the output to a speaker. Modern amplifiers usually use NPN or N-channel and PNP or P-channel transistors types who's DC bias cancel each other leaving only the audio AC.
An amplifier requires active components, which could be described as electrical valves. And they amplify/multiply a signal by modulating a DC current, creating an AC component, ie transistors only operate in one polarity. So transistors require a DC bias be added to the input to operate and that DC has to be removed at the output to a speaker. Modern amplifiers usually use NPN or N-channel and PNP or P-channel transistors types who's DC bias cancel each other leaving only the audio AC.
Okay now I think I get it, so a non changing voltage, except when the battery is getting empty or your turn down the voltage, is DC while anything else is AC. So a voltage that is going trough a rectifier that do not have a constant voltage, can still not be called real DC.
If I am right thanks, or else please say so. 🙂
The whole "problem" did arrive when I tried to make a zero droop peak detector. And then got the strange thought, can this contraption be used as a zero ripple power supply?
I know that the circuit contains some errors but do not know how to solve them.
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It all comes back to the same play on words. If you apply AC to a diode rectifier you get half wave pulses at the other side.
Text books tell you that it has converted AC to DC.
One printed definition of DC is that the current flow is always in the same direction although the amplitude may vary. The current never swings the other way or reverses. Is that an official definition though? I don't know.
Wikipedia shows a graph of DC current (that meets my definition of it) and AC current (that also meets my definition of it), however it then shows the equivalent of our 'ripple on a rail' and calls that 'pulsating' and then shows what would be our 'audio voltage in our amplifier' as 'variable'.
Those last two names are new ones on me 🙂
(and where do all those negative half cycles end up, all those we don't use in simple half wave rectifiers. There must be a big room full of them somewhere 😉)
Direct current - Wikipedia
Text books tell you that it has converted AC to DC.
One printed definition of DC is that the current flow is always in the same direction although the amplitude may vary. The current never swings the other way or reverses. Is that an official definition though? I don't know.
Wikipedia shows a graph of DC current (that meets my definition of it) and AC current (that also meets my definition of it), however it then shows the equivalent of our 'ripple on a rail' and calls that 'pulsating' and then shows what would be our 'audio voltage in our amplifier' as 'variable'.
Those last two names are new ones on me 🙂
(and where do all those negative half cycles end up, all those we don't use in simple half wave rectifiers. There must be a big room full of them somewhere 😉)
Direct current - Wikipedia
DC means a constant voltage. So, the electron flow is in ONLY ONE direction. However, since voltages are a kind of forces, they can be superposed on each other. So, a DC voltage can have an AC voltage superposed, and even other DC voltages.
AC voltages can also superpose on each other. An AC voltage/signal that is a pure sine wave of the form V*sin(2*3.142*f*t) is a mathematically pure tone. This means, there are no other frequency components in it. When an AC signal is not a perfect sine wave, it is said to contain signals that are multiples of its frequency. These are known as harmonics and are always multiples of the base frequency. The latter is known as the fundamental frequency. For example, a square wave is the result of an infinite number of harmonics with the fundamental frequency equal to the square wave's frequency.
Electrons within metals repel each other. This makes them collectively behave like a spring. If you disturb the electrons at one end of a metal bar, the disturbance travels to the entire length of the bar back and forth until its energy is dissipated.
AC voltages can also superpose on each other. An AC voltage/signal that is a pure sine wave of the form V*sin(2*3.142*f*t) is a mathematically pure tone. This means, there are no other frequency components in it. When an AC signal is not a perfect sine wave, it is said to contain signals that are multiples of its frequency. These are known as harmonics and are always multiples of the base frequency. The latter is known as the fundamental frequency. For example, a square wave is the result of an infinite number of harmonics with the fundamental frequency equal to the square wave's frequency.
Electrons within metals repel each other. This makes them collectively behave like a spring. If you disturb the electrons at one end of a metal bar, the disturbance travels to the entire length of the bar back and forth until its energy is dissipated.
No. The "zero droop" output is not very strong, and is derived from a Regulated power rail.
It IS a clever idea, for signal processing (not Power). Agree that plan isn't 100% yet.
http://application-notes.digchip.com/003/3-4081.pdf
Thanks I am learning a lot from all of you!🙂
So is this statement correct?
That's why audio is neither pure AC nor DC... Pure AC is a alternating direction current (crossing zero) with a non changing frequency. While DC is a non alternating current containing a non changing voltage.
When we are talking about signals it can change in both voltage, current and frequency. Everything from DC, AC to "chaos"?
Thanks, great link, It does, to my eyes, look a bit like the one I have copied.
But it sounds like a bit of a dead end, if it can not act as a minimal ripple power supply. I was hoping to make a SMPS that shall deliver 5VDC to a <1GHz differential probe. The problem is that it does not work like it should, just using a standard wall USB charger. As I understand it, lower noise and ripple, gives better probe data. Both the probe circuit and the SMPS have to "live" in the same box but can easily be about 4-6 inches apart with shielding between. Even that, I would really love to have a small but great SMPS to avoid degradation in the probes signal. 🙂
Loosely, yes it is DC, but actually its a sum of frequencies including zero Hertz, ie DC. And the peak amplitude of the AC components does not exceed the DC component value. A full wave rectifier output is the sum of a zero Hertz component (DC), a 120Hz component (2x) and many other harmonic frequencies.
Please understand that "AC" and "DC" are used loosely. If the speakers says a signal is DC then they probably means the value never crosses zero. If the speaker says the signal is AC then they probably mean it is capacitor or transformer coupled which means it will have and average value of zero. If the signal has a DC offset but does cross zero, then neither would be exactly correct, but many digital signals which would be called DC actually overshoot the zero state due to signal termination problems.
So in short, AC and DC is a bit of a gray-zone when we go into details, but the standard AC do cross zero and DC does not, it the nearest it is normally thought of? 🙂
A pure AC signal is a SINE wave. When a signal's waveform departs from that it is no longer pure, which simply implies, there are other signals superposed.
Regarding the output from a rectifier, this has a strong DC component. So, it is described as DC. The oscillating shape implies there is still a strong signal that is twice the rectified frequency. Together with that, there are other harmonics.
To better understand this, I suggest you read a basic introduction to Fourier Analysis.
The Fourier Theorem:
Fourier theorem states that a periodic function f(x) which is reasonably continuous may be expressed as the sum of a series of sine or cosine terms (called the Fourier series), each of which has specific amplitude and phase coefficients known as Fourier coefficients.
What is an Audio Signal:
Audio signals like music signals and voice signals, are a complex ever changing mixture of different frequencies. The amplitudes of these temporary frequencies also change in time; human voice is a particular example. So, an audio signal does not have a particular shape, unless it is from a note from a musical instrument.
Regarding the output from a rectifier, this has a strong DC component. So, it is described as DC. The oscillating shape implies there is still a strong signal that is twice the rectified frequency. Together with that, there are other harmonics.
To better understand this, I suggest you read a basic introduction to Fourier Analysis.
The Fourier Theorem:
Fourier theorem states that a periodic function f(x) which is reasonably continuous may be expressed as the sum of a series of sine or cosine terms (called the Fourier series), each of which has specific amplitude and phase coefficients known as Fourier coefficients.
What is an Audio Signal:
Audio signals like music signals and voice signals, are a complex ever changing mixture of different frequencies. The amplitudes of these temporary frequencies also change in time; human voice is a particular example. So, an audio signal does not have a particular shape, unless it is from a note from a musical instrument.
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Good answer 😉
It's up to you (it's 'your' thread) although it probably would be best if you want to get heavily into a new topic.
SMPS and very small UHF instrumentation circuitry doesn't sound like a great mix tbh, at least not on a diy basis.
There are things called 'charge pumps' that can be used to double or invert voltages and so provide negative rails. They have much less energy flying and radiating around the circuit and are based on capacitor storage.
Be aware of who you are talking to. An electrician does not think as mathematically as a ~DSP engineer, so their use of "AC" and "DC" is a bit different.
And have a read about Fourier Transforms and the theory behind it.
Fourier transform - Wikipedia
The signal imposes its characteristics on the propagation medium. The excitation process has considerable complexity, but is very well understood. It is not included in the Fourier theory.
You should not believe what you believe. Again, mathematical entities (0 Hz, phase delay, the sinusoidal waveform...) have no physical meaning and make no sense outside of a particular mathematical model. Why don't you try to look beyond your superficial knowledge?
On the other hand, I would agree that diyAudio is the wrong forum to discuss this. Maybe it is better to treat things on a superficial level and leave some (nevertheless repeatedly arising) questions unanswered.
You are right, this subject has developed in a way that may not belong here, but my start was about if components saw audio signals as AC or DC🙂
I didn’t mean it that way. I was partially referring to previous discussions of that issue. You did pose a legitimate question.
Signal characteristics are not specifiable in terms of AC or DC, fixed polarity or periodically changing polarity are not signal attributes. Inhomogeneities and irregular changes in intensity, frequency, polarity... are required.
Zero (or infinite) Hz does not imply a change thus a physical existence in the first place. It is not possible to express a change or events mathematically. The Fourier theorem does not represent anything physical.
It would have been so simple to just stick to what DC and AC stand for: Direct Current, Alternating Current. But that's too late now ...
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