Is it correct to consider Pulsed DC as AC?

Hello folks!
I have read about some conflicting contentions on the web.

Is it correct to consider Pulsed DC as AC?

ac to dc then dc to ac definitions

AC current is a specific type of electric current in which the direction of the current's flow is reversed, or alternated, on a regular basis. Direct current is no different electrically from alternating current except for the fact that it flows in the same direction at all times.

Regards,
IanP

when ac is apprioprate against dc current

Thank yopu ianp.
Would it be appropriate to call Ac as AC with a dc shift applied to it?
As i have understood over the years, AC is alternating CURRENT, and as you have pointed out, the current 'alternates' in opposite directions periodically.
If this is true, isn't it wrong to say pulsed Dc is nothing but AC with a DC shift?
I would like a clarification as some teachers are explaining it this way.

blocking ac in a single direction

docel said:

Thank yopu ianp.
Would it be appropriate to call Ac as AC with a dc shift applied to it?
As i have understood over the years, AC is alternating CURRENT, and as you have pointed out, the current 'alternates' in opposite directions periodically.
If this is true, isn't it wrong to say pulsed Dc is nothing but AC with a DC shift?
I would like a clarification as some teachers are explaining it this way.

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any voltage (or current) waveform have 2 components,
AC component and DC component.
as you said DC component is the same as voltage shift.
any of these 2 component can be zero.
if AC component is zero we have, just , DC value , for example battery.
if DC component is zero we have, just , AC value, for example mains voltage.
if we have 2 component in the same time (like your example) we can not say it is AC or DC voltage.

Regards,
Davood.

charge cap ac vs dc

I can only repeat what I have already said before, that the difference between AC and DC has to do with the direction in which the electrons flow ..
In DC, the electrons flow steadily in a single direction, or "forward."
In AC, electrons keep switching directions, sometimes going "forwards" and then going "backwards." ..

Your teachers may have their own point(s) of view, not necessarily correct, but they are your techers and sometimes it doesn't pay off to argue with them ..

Personally I wouldn't call "Pulsed DC" AC, however, according to the "definition" given above if these pulses "change" direction of electrons .. and so on ..

Regards,
IanP

ac capacitor dc component

In AC, electrons keep switching directions, sometimes going "forwards" and then going "backwards." ..

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if a voltage signal changes positive and negative continuously (switching electron direction), but has non
zero DC average value, is that signal still can be considered AC? if yes, what happen if I apply
DC blocking capacitor to that signal? is the average value of that signal will be zero?

Re: AC and DC

if a voltage signal changes positive and negative continuously (switching electron direction), but has non
zero DC average value, is that signal still can be considered AC?

Click to expand...

Its not right to call it AC or DC (IMHO), because it is AC plus DC.

if yes, what happen if I apply
DC blocking capacitor to that signal?

Click to expand...

Many different things may hapen, depending on the signal and capacitor combination

is the average value of that signal will be zero?

Click to expand...

No, only the low frequency DC bias will be zero

Re: AC and DC

thank for your reply, t_maggot.
It makes certain things clear to me.

but, I still bit confused about blocking capacitor operation.
if, for ex, on the first place the signal is a positive sinusoidal (positive value on both peaks),
like one produced by microphone powered by positive supply, and I place capacitor
(assumed the capacitor pass only audio frequency) after that signal, what happen to that signal?
will the voltage level be the same?

Re: AC and DC

@lanovan:
Through the capacitor terminals, flows current only in the phase of charge or discharge. So with a capacitor in series this means that only in this phases voltage will appear on th load side. More voltage appears on the load side while in this phases, and capacitor has less voltage across its terminals (Ohms law). The circuit behavior depends on the combination of source, load and capacitor characteristics. The capacitor charges/discharges through the load. In general with more load impendance, capacitor will dis/charge slower (and more voltage appears on the load side). Also a bigger capacitor takes more charge to reach Vinput. So, in a periodic dis/charge** input, if the capacitor in each cycle will not reach full charge (Vinput), the voltage on the load side will appear more or less the same with the input. But if the capacitor charges then current drops and so the voltage on the load.

Think the simplest situation as a single dc pulse that goes at time t from 0 to x Voltage and stayes there. As the capacitor charges, current flows through the load. When the capacitor is charged (reaches inputs x Volt) the current stops and voltage on the load side drops to zero (the input is still x Volt). So in a dc 0 to x Volt change, only a limited duration pulse will appear on the load side with a capacitor in series connected. (assuming the capacitor is discharged before this)

Many pc sound cards have a series input capacitor in their input to block dc, so if you want to experiment, apply (small) test voltages/waveforms on the input and look what hapens in low frequencies (0<f<20Hz) whith a recording sofware. (better not route this things to speakers )

** The input must be able to also "give" and "draw" current in/from the circuit ( i am not talking about changing polarity ) whitch is not the case e.g. after diode rectifiers, because when they output less-than-circuit voltage, they cannot "draw" current from the circuit and so a series capacitor never will be discharged.

Re: AC and DC

I got your point, t_maggot.
it's all about 'Kirchoff's voltage law' and 'time constant RC'
Thank you for your explanation.

Re: AC and DC

Hello!
In my opinion “DC” is a misleading term.
If you have “direct current” you should have also “indirect current” which seems to me a bit strange.
It is better to remove the term “direct current” and to replace it with more appropriate term according to the case, e.g.:
“very low frequency signal”
“constant signal”,
“constant voltage signal”
“constant current signal” ,
“ vertical displacement “
etc.
Every term should be clear and easy to decode and use.
This is not the case with “direct current”
BR
Petre Petrov

Re: AC and DC

If you have
DC = B = constant voltage
and
AC = sinusoidal signal = Am*sin(wt+phi)+0

and if you make an addition

DC + AC

you will have as a result the simplest band limited signal (SBLS) with two lines into its spectrum or

SBLS = Am*sin(wt+phi)+ B

In my opinion in mots of the cases it is better to specify the type of the signal and not to use DC and or AC.

Re: AC and DC

@Petre Petrov

well in my view the term Direct in DC is for the direction . i mean it is a current or voltage which has got a direction and it does not change its direction with time unlike alternating

so i think its still obvious terminology

regards

Re: AC and DC

Hello shahid78 and the others!

Thank you for your attention and for your replay.

I know your argument but I think that it is not good enough for a basic rem in EE, etc.

Unfortunately at the moment I am busy with some urgent and unexpected long term issues.

If you are interested in my opinion in DC/AC, sine/cosine waves, etc, could you please visit

**broken link removed**

A note about the definitions of "sine/cosine wave", "sinusoidal/co-sinusoidal signal” and the "simplest band limited signals".

May be you will understand better my position

Of course the paper is not perfect, but I think the position is clear and the arguments are good enough to be accepted ( may be after some modifications?)

BR