Inductors, how and why ?

[Saad]

Hi there !
I am posting this message to ask that is there anything else we can
use in place of inductors in a circuit and how do we determine the
value of a capacitor or inductor in a circuit and i can't find
inductors physically....where do i find them ? Please answer my
queries soon.

 

[John Popelish]

Saad wrote:

Hi there !
I am posting this message to ask that is there anything else we can
use in place of inductors in a circuit and how do we determine the
value of a capacitor or inductor in a circuit and i can't find
inductors physically....where do i find them ? Please answer my
queries soon.

Without changing the design of a circuit, there is no equivalent part
for inductors. They have unique properties.

Most capacitors are marked with a code for their value. See:
http://www.twysted-pair.com/capidcds.htm
Lots of good info on capacitors:
http://my.execpc.com/~endlr/index.html

Inductors are often made custom and often have no markings that tell
you their values, though there are some standards for some forms:
http://www.elexp.com/t_induct.htm
http://www.marvac.com/funpages/chokes.htm

The neat thing about inductors is that they are the one component you
may be able to make as good as those you can buy.

I don't know what country you live in, but Digikey now carries quite a
line of inductors available in the U.S. and Canada.

http://www.digikey.com/
Enter inductor in the search box.

--
John Popelish

 

[Michael Black]

Saad (saad_shabbir@hotmail.com) writes:

Hi there !
I am posting this message to ask that is there anything else we can
use in place of inductors in a circuit and how do we determine the
value of a capacitor or inductor in a circuit and i can't find
inductors physically....where do i find them ? Please answer my
queries soon.

Whether one can do without an inductor would depend on what's needed.

Gyrators (using op-amps to synthesize inductors) have seen use at
audio frequencies, where the inductors would be way too bulky for
many applications. But, it's not a perfect replacement, so it can't
be used for every inductor, and it can't be used as a direct replacement.

What you're more likely to see is using circuits that replace the
function of a circuit that requires an inductor, with a circuit that
does the same thing without inductors.

For instance, active filters have become quite popular, again at
audio. They are substituting a complete stage that filters for
some sort of filter that uses an inductor.

One would see a switch from an oscillator that requires an inductor
to an oscillator that uses resistors and capacitors as the frequency
determining element.

A lot of IC designs may use more complicated circuitry because it
does away with inductors, which can't be done in ICs, and might dwarf
the IC when external. One example of this would be the NE567 tone
decoder IC, that is over thirty years old now. It uses a phase locked
loop and some additional circuitry to detect when a given frequency is
present at the input. The IC has multiple stages of multiple active
elements, and would be terribly cumbersome with discrete transistors,
but it all fits into an 8-pin IC. Before that, one would tend to see
bulky inductors and relatively large capacitors to provide a filter
to detect a given frequency, and it wasn't nearly as tuneable.

There was a time when inductors were often used in order to get
needed gain out of a stage, rather than to provide real selectivity.
With ICs, there was so much gain available that one could do away with
such inductors, and broadband to boot.

At radio frequencies, some filters went from inductor based to
ceramic and crystal filters. They come to you as black boxes,
and require no tuning. Before they came along, one would require
multiple inductors to provide the same selectivity.

Michael

 

[Tim Auton]

saad_shabbir@hotmail.com (Saad) wrote:

I am posting this message to ask that is there anything else we can
use in place of inductors in a circuit and how do we determine the
value of a capacitor or inductor in a circuit and i can't find
inductors physically....where do i find them ? Please answer my
queries soon.

I'm not sure what you're trying to do (design a circuit, understand an
existing circuit etc.), but if you're looking at an existing circuit
trying to see where the inductor is then be aware that they aren't all
obvious. For example, in this circuit:

http://www.romanblack.com/a00.htm

the inductor is the green thing in the middle that looks like it could
easily be something else.


Tim
--
Love is a travelator.