Re: Inductors
- From: "Myauk" <aungkokothet@xxxxxxxxx>
- Date: 24 Oct 2006 22:02:20 -0700
I would like to work on the flyback and resonant power supplies.
Joel Kolstad wrote:
"Myauk" <aungkokothet@xxxxxxxxx> wrote in message
news:1161737314.083528.185740@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
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
.
- Follow-Ups:
- Re: Inductors
- From: Joerg
- Re: Inductors
- References:
- Inductors
- From: Myauk
- Re: Inductors
- From: Joel Kolstad
- Inductors
- Prev by Date: Re: Inductors
- Next by Date: Re: Design a VGA control board for an LCD.
- Previous by thread: Re: Inductors
- Next by thread: Re: Inductors
- Index(es):
Relevant Pages
|
