Myauk said:

According to my knowledge, a practical inductor is composed of an ideal

inductance in serires with the effective resistance of that inductor.

That's a decent 1st order model; there are fancier ones available if you need

the extra accuracy.

Skin effect increases effective resistance with the increase in

operating frequency.

It also increases the effective inductance until you hit self-resonance.

For receiver ckt, the selectivity is calculated by 2*pi*f L/r, which

means the selectivity depends on frequency as well as effective

resistance and inductance.

Yes, although in many cases you try to have the inductor's resistance be small

relative to, e.g., load resistance.

So the design of an inductor depends on the

required selectivity and frequency as well as consideration of

effective resistance.

I suppose you could say that, but keep in mind that how the core behaves

(specifically its loses, which go up superlinearly with frequency, and sizing

it to avoid saturation) plays a large part in the overall inductor design as

well.

For a SMPS inductor design, I learned that the inductance for forward

converter is calculated by (Vin-Vo) Ton max/ I min.

For a "standard" buck converter operating in non-continuous mode, yes.

I need to understand more about this.

Well... first, you might want to mentally separate "RF inductor design" from

"SMPS inductor design." In the former, at least for "signal" levels,

frequency response and self-resonance tend to be the driving factors in making

a design work. In the later, the power you need to deliver and the switching

frequency drive current through the inductor, and this drives the wire size

and the core size (to avoid saturation). Unless you're building switchers

above, say, a MHz, you usually don't have to worry much about self-resonance

and frequency response.

How come the inductance depends on the input and output voltage

difference, the maximum on time and the minimum current drawn.

Umm... err... rather than write half a page here, could you get a copy of,

e.g., Abraham Pressman's "Switching Power Supply Design" or similar? (Check

Amazon to find similar tomes.) It goes through the derivation, which isn't

difficult (just algebra), but it helps to have some pictures to look at.

Someone like Eeyore (if he took his meds today

) can probably quote you

the derivation irectly. If you can't get ahold of a book, look for

application notes on switch-mode power supplies on, e.g., Linear's web site.

Are the equations I know right or wrong?

They're "correct" but I get the impression you're not aware of a lot of the

context that they're to be used within.

Where can I find these practical equations for calculations as well as

descriptions on how they are derived from the fundamental theories of

Electricity and Electronics?

University lectures? Books? Application notes on web pages?

If you tell us what you'd like to design, we can probably point you towards a

reasonably specific resource.

---Joel Kolstad