# Do AC current sources exist and why or why not? For both actual and theoretical

I got confused when I encountered this problem on Chegg.

Question: 5.

a) Find the AC current source, Iin in polar form.

b) Find VT .

c) Choose one:

i) The source current leads the source voltage.

ii) The source current lags the source voltage.

My question isn't about solving the problem. Do AC current sources exist? I've tried searching and they don't pop up except for the Chegg problem I saw. I also recently took a Circuits class and three basic active components discussed to us are the DC voltage source, AC voltage source and DC current source. I don't get if they exist at all, and if so why is information about it not as common?

EDIT: People might answer only about the actual AC current source. I am also talking about theoretical. Like can I do the same thing in Chegg where you put a wave symbol and an arrow and call it a theoretical AC current source? How would you then use it in computations? Do you just attach a phasor to it and use current in the x-axis instead of voltage for vector diagrams?

It's because I'm curious on both. Yes I want to know whether they exist in real life but I also want to know their "existence" on our theoretical computations. Are they there but scarcely used? Or do they not exist at all on common electrical circuit related courses?

• Perfect voltage and current sources DO NOT exist. So, if you are prepared to accept an imperfect source then sure, they can be made and that means they exist. Commented Jan 17, 2021 at 13:40
• Would you consider a current transformer as an AC current source (within certain bounds)? Commented Jan 17, 2021 at 22:07
• For actual, I guess. But for theoretical, I was wondering if there is a certain symbol or concept that is actually made for an AC current source and not "this works like that so it counts" since we are talking about theoretical anyway. Commented Jan 17, 2021 at 23:25

Ideal AC and DC voltage and current sources are useful for analysis (theoretical) purposes.

It could be said that an AC generator that supplies power to a grid operates as an AC current source. There are also AC motor controllers that act as current sources. However it may be more accurate to say that they are DC current sources that control motors through inverters. That is a DC current source drives an inverter that supplies current to a motor. Grid connected solar and wind power inverters are similar.

Re edit:

Like can I do the same thing in Chegg where you put a wave symbol and an arrow and call it a theoretical AC current source? How would you then use it in computations? Do you just attach a phasor to it and use current in the x-axis instead of voltage for vector diagrams?

Yes

Re Comment:

Here is an example from Scott, Linear Circuits, 1960. It clearly shows an AC current source, but the symbol doesn't include as sin wave symbol. I also found textbook problems that simply identified the source i(t). Some of those were sine wave sources and others defined some other periodic waveform.

Also note that a current transformer act as a current source.

• Just want to ask, are you aware of other references that show an AC current symbol that has a wave and arrow? I'm just really curious because why don't they teach something like that commonly when it's a theoretical anyway? Commented Jan 17, 2021 at 23:27