AC & DC current

Plz anyone explain me elaborately on AC current & DC current.And how it can be designed in PCB Design?

Don't really understand the question. AC stands for "Alternating Current" and DC, "Direct Current". DC current flows in one direction only. AC current flows one direction and then back again, over and over (thus the name "alternating"), usually with a sinusoidal rate of change. Because AC alternates, it has a frequency, or rate of alternation. DC can pulse or fluctuate, but unless it changes polarity, it is not considered AC. AC can have a DC component, which is the positive or negative difference between the magnitudes of the two polarities over one cycle of change (i.e. if that difference is 0, then it's pure AC, if that difference is equal to the peak voltage, then it pure DC, otherwise its AC with a DC component. That's all I can think of in terms of AC and DC current.

As for how that relates to PCB design, you got me.

The only thing that comes to mind is what is the frequency of the AC current?? For low frequency there is no difference that I can think of. At high frequency you have the problem of radiation. Then placement of the traces is a big problem as you then need lots of ground plane and have to worry about de-coupling capacitors - etc...

Ohhhhh, that 's right. It didn't even occur to me that you were asking how AC or DC might effect how you design a PCB. Yes, what David said, plus, for high frequencies, also avoid sharp bends, isolate inputs and outputs, make traces as short as possible, and learn about the effects of PCB material, trace thickness, etc, on impedance matching and transmission lines.

Google: "high frequency PCB design considerations" for LOTs more info!