Is there any difference between AC and sinusoidal waveform ?
Sine wave is AC, AC means only sine or what ???
Is quassi square waveform AC ?

UPS/inverter genrally give Quassi-square waveform o/p .
To get Sine, we use Ott Filter.
But, can quassi square wave be called as AC.

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AC just means 'Alternating Current', it can be any shape at all, not just sine wave. A square wave is an AC waveform, as is a triangle wave, or a voice pattern - basically anything which will pass through a capacitor or a transformer is AC.

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Just for clarity, DC will pass through a transformer. And pulsed DC will even pass across a transformer. The direction of current flow needn't change.

I know what you meant, Nigel, it just struck me as odd :wink: .

j.

 

John, could you clarify that? I'm assuming you mean that a fluctuating DC (equal to AC with a DC offset) will pass through a transformer.

 

pulsed DC is NOT as far as a XFMR is concerned DC anymore IT IS AC!!!

XFMR's are AC components. If you provide it with a step DC the initial step will get through the XFMR since a step has infinite harmonic content. However, if the DC is still provided the XFMR's core will very quickly saturate

 

Even if that was the case, then yes the AC content of the DC waveform (ie the ripple) would get through, however the DC content would still saturate the XFMR

 

Pulsed DC is still AC, and as you say will happily pass through a transformer (or a capacitor for that matter). The only difference between pulsed DC and 'AC' is the reference point used. If you feed the pulsed DC through a capacitor it even gives you the 'proper' AC reference (going positive and negative about zero volts.

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I thought about that, but it isn't necessarily true. Consider an air core transormer.

 

DC can pass through a transformer!

and it doesnt need to be pulsed DC. first lets look at what happens when an AC voltage is applied to a transformer. when the voltage starts to increase in the first half cycle so does the magnetic field intensity. therefore the flux through the core increases. but at some point the flux will stop to change. but in AC that point isnt reached. before that the AC reverses direction and the magnetic field intensity goes negative and so does the flux. thats how the hysteresis loop is formed.

now lets apply a DC voltage to a transformer. the magnetic field intensity H will start to increase and so does the magnetic flux increase. but with DC the transformer gets saturated and the flux ceases to change. this time the field doesnt reverse because DC doesnt change like AC. but if we interchange the input terminals and the output terminals then we could simulate the hysteresis loop of AC with a core without even needing AC. it isnt fluctuating DC niether it is AC but still transformer action is happening.

now about the method to change the terminals. well you could mechanically change the +ive and -ive terminals by a motor or something. but you could also use a better non-mechanical alternative. for more info refer to the book "Switchmode Power Supply Handbook" by Kieth Billings

 

that is a load of crap.

XFMR's are AC devices. DCC converters or SMPS that incorperate XFMR isolation just PWM DC onto the XFMR thus teh XFMR sees and AC signal .

YOU CANNOT PASS A DC LEVEL THROUGH A XFMR>

If that was the case my IGBT's gate drivers would be soo much simpler!!!!

 

Definition of alternating current:

An electric current that periodically reverses its direction.

Pulsed DC does not reverse its direction of flow (the electrons are always going the same way. The don't flow one way, then the other. They flow: then they don't: then they flow: then they don't).

Of course, I wasn't suggesting you could put a DC current through a transformer and get DC out of the secondary.

But, what originally caught my attention was that you said DC won't flow through a transformer, but of course it will, just not across the transformer.

Didn't mean to cause everyone's fur to get ruffled. Geez Styx, settle down :shock:

j.

 

Everyone is digressing from main point, whats AC and DC.
The discusion is getting centered around Transformer and its properties,
also AC and DC properties/behaviour.

now Lets think logically,
1) AC: Alternating Current
2) DC: Direct Current (Directional/ Unidirectional Current)

DC can be obtained by rectifying AC. Rectifier does not give DC voltage,
it makes Alternating Current to flow in Unidirection to give Direct Current,
to flow thru load , which in turn gives DC voltage ( more precisely: develops DC voltage in load.)

Pulsating DC is just Pulse in one direction and it has to be DC.
Pulsating DC is in the form of pulses and its not continuous, thats all!!!
One can't say pulsating DC to be AC and....lalalala

Whats need of taking Transformer View etc.. ?
Thats confsing, and more confusing coz every1 is talkin at different wavelength, i.e. , every1 has different concepts and definitions.
May be every1 is thinking same, but putting it in different (may be even wrong) manner.

So what i think is that, if u wanna talk abt properties of AC,DC,XFMR, etc.. 1'st state ur definitions precisely, it will not only help u, but also the ones who r reading it.

regards.

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except the harmonic content of a square wave will have a fundemental AC component as well as other harmonics (to produce the sharp leading/falling edge and flat periods)

 

True 'nuf.

Peace?

j.

 

:lol: lolzzz

i think i mentioned that this was from a book. so i guess its not crap. when i first read this i was also skeptic about this but this is true.

the only thing that limits DC from being passed through a transformer is the fact that the core saturates and the flux stops to change. but we can change that as i mentioned. now its up to you to call it anything u want !!!!