# Basic electronics theory (response to Layman's issues)

Discussion in 'Architecture & Engineering' started by billvon, Nov 18, 2014.

1. ### leopoldValued Senior Member

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heh, the article distinctly mentioned that it needs to be tuned to the correct frequency.
capacitors do not transfer DC layman, although they can transfer DC spikes and varying DC down to a low frequency.

3. ### LaymanTotally Internally ReflectedValued Senior Member

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OMFGLMFAO!!!!

You people are really something else. The word signal does not mean that it is AC! There is an input signal, that is commonly just a DC voltage that would then run through the inductor to ground. If it lead to the power rails of other circuits it would require DC. Radars will use this circuit, and it doesn't violate any physical laws. They will have inputs to this type of circuit that is just a voltage level.

Most of the time they don't, because they do so very slowly, but more often than not the signal will change before it can do that, so it just acts like an open circuit in this way. Eventually, a capacitor will transfer its voltage and lose its charge to ground from the other side of the input voltage.

5. ### TrippyALEA IACTA ESTStaff Member

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If they're not tuned properly you introduce beat frequencies (among other things)

7. ### leopoldValued Senior Member

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i'm beginning to wonder if you can use a VOM.

8. ### TrippyALEA IACTA ESTStaff Member

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And here's what happens when you add a DC offset voltage: Link

9. ### LaymanTotally Internally ReflectedValued Senior Member

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I changed the input voltage to DC, and it works just as well in the simulator.

10. ### TrippyALEA IACTA ESTStaff Member

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Maybe you should keep this in mind yourself eh?

Just because there's a changing voltage inducing a changing magnetic field, inducing another changing voltage doesn't mean that it's AC either.

It requires an oscillating current for that circuit to work. That oscillating current can have a DC offset, but the DC offset is reduced by thew stepdown transformer by the same ratio. If you replace the AC source with a DC one, the osilcation is provided by the LC circuit.

Not a given.

You may need to rephrase this - it makes little or no sense as it is written.

11. ### TrippyALEA IACTA ESTStaff Member

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Right - because the LC components in that loop set up a resonant circuit that generates its own AC signal from a DC input.

Something I'm fairly sure you have claimed was impossible. Note that with a DC power supply the output is AC.

12. ### LaymanTotally Internally ReflectedValued Senior Member

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"An ideal transformer (with sufficiently large inductance and sufficiently low resistance) can pass DC, but real transformers are not ideal and only work with AC. This transformer passes DC at first, but after a short time, the DC voltage fades due to resistance in the primary and the finite inductance of the transformer coils."

Curious how you will try to weasel your way out of this one.

13. ### TrippyALEA IACTA ESTStaff Member

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Don't need to. Real transformers behave in exactly the way I, and others have described - the source confirms this.

14. ### TrippyALEA IACTA ESTStaff Member

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Ideal transformers have infinite inductance, zero resistance and and perfect magnetic coupling. Because they have infinite inductance, the current in the primary takes an infinite amount of time to reach the maximum current. On the principles espoused by myself and others in this thread (IE everyone except you) then it would be expected that a perfect transformer would pass DC.

15. ### LaymanTotally Internally ReflectedValued Senior Member

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So how would I link a circuit I made with that applet?

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17. ### billvonValued Senior Member

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So you believe that capacitors and transformers pass DC?

Try this. Go to Radio Shack. Buy a capacitor, a line transformer and a meter. Connect the capacitor to a battery then read the voltage. See if you get the battery voltage - or zero volts. Next connect the primary of a transformer to a constant current source. Now measure the secondary. See if you get a voltage - or zero volts.

Once you try this experiment you'll realize why you are wrong.

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19. ### leopoldValued Senior Member

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if you are going to talk perfect transformers then you must also talk about perfect DC.
a perfect transformer WILL NOT pass perfect DC.
you cannot get transformer action with an unvarying magnetic field.
this implies either varying the primary power or introducing an outside magnetic influence.
yes, i understand it takes a finite time to "charge" the field, but this is VARYING DC, not "perfect" DC.
i believe this time is called the time constant of the circuit in question.

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Probably.

Correct.

21. ### leopoldValued Senior Member

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it seems this might be one of laymans problems.
layman,
if you have a DC voltage of 6 volts and modulate that with an AC sine wave component (say 60 hz) of 5 volts, what do you get?
ans: you get a DC component that varies from 1 to 11 volts at 60 hz.
passing this new component through a capacitor removes (blocks actually) the DC and leaves you with the original AC.
the same is true of a transformer.

the above is one of the primary reasons a well regulated supply is desirable.
the ripple that rides on an unregulated supply can be coupled along with the signal and can cause all kinds of problems from distortion to feedback

22. ### Aqueous Idflat Earth skepticValued Senior Member

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It got quiet here. Hopefully Layman didn't blow up the largest electrolytic capacitor he could find at Radio Shack or wherever.

I did this once. At a party. A wedding no less. I had built a little practice amp by placing a power amp and power supply inside a cabinet that served as a baffle for a large subwoofer. I would play my bass guitar through a foot pedal which provided the preamp. I had used it for years without any problem.

Well, the design I chose used two ports on the front which were tubes. Right at the end of the bride's dance with her father we ended with a loud crescendo, so loud it shook the capacitors in the power supply loose from their mounts. A design flaw, in retrospect. And the revelers went wild as metallic ribbon shot out of the ports like a chaff dispenser. But then the acrid smell and with a burst of panic followed by an Civil Defense type call for orderly evacuation, the room quickly emptied.

Gee I hope Layman's OK. Folks, don't try this at home without safety glasses and a fire extinguisher. And please: check with billvon before you try to prove him wrong.

23. ### TrippyALEA IACTA ESTStaff Member

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I had a friend when I was studying who, during a fault finding class put a standard red LED in a mains socket and turned it on. There was an explosion accompanied by a blinding flash of red light, and they managed to blow three levels of fuses - Room, floor, and building.

We run a 240 VAC MEN setup here - for those that know what that means.