[JonDoeEngineer]

I recall once seeing a fully solid state circuit that uses capacitors,
resistors and a transistor to "mimic" the effects of an inductor. I
can't seem to find it now. Can anyone point me in the right direction?

 

[Kryten]

I recall once seeing a fully solid state circuit that uses capacitors,
resistors and a transistor to "mimic" the effects of an inductor. I
can't seem to find it now. Can anyone point me in the right direction?

Google for "gyrator"

 

[John Popelish]

I recall once seeing a fully solid state circuit that uses capacitors,
resistors and a transistor to "mimic" the effects of an inductor. I
can't seem to find it now. Can anyone point me in the right direction?

Simulated inductance that is grounded on one end is easiest, I think.

http://www.maxim-ic.com/appnotes.cfm/appnote_number/98
http://www.maxim-ic.com/appnotes.cfm/appnote_number/138
http://www.s2.chalmers.se/graduate/courses/analogVLSI/doc/lecture6.pdf
http://www.kemt.fei.tuke.sk/predmety/KEMT350_EP/_materialy/ch029.pdf

 

[Jim Thompson]

I recall once seeing a fully solid state circuit that uses capacitors,
resistors and a transistor to "mimic" the effects of an inductor. I
can't seem to find it now. Can anyone point me in the right direction?

See the various Gyrator-based filters on the S.E.D/Schematics page of
my website.

...Jim Thompson

 

[Paul Burridge]

Simulated inductance that is grounded on one end is easiest, I think.

Why would anyone bother? Is there some obscure advantage with it over
conventional coils?

 

[Reg Edwards]

Why would anyone bother? Is there some obscure advantage with it over

conventional coils?
--

===============================

A conventional hundred henry coil weighs several pounds, is bigger than the
printed circuit board, and has a terrible Q.

 

[John Woodgate]

I read in sci.electronics.design that Reg Edwards

===============================

A conventional hundred henry coil weighs several pounds, is bigger than the
printed circuit board, and has a terrible Q.

Get some decent Mumetal cores. 10kH in about a 2 inch cube, with a
laminated core. More with a toroid. Q indeed was not promising at 1 kHz,
but this operated at 10 to 20 kHz.

 

[john jardine]

+9V
o----------o
| |
.-.220k |
| |R3 |
| | |
'-' |
| |
C1 | |
100u 1uF | Jelly Bean NPN
- + | |
|| || | |/
A o---||-----o----||-----o--------| (BC546)
|| | || | |>
CC | | |
| ___ | |
'--|___|--- | ---------o
100 | |
R1 | |
B o .-.220k .-.1k
| | |R4 | |
| | | | |
| '-' '-'
| | |
=o= =o= =o=
GND GND GND

Capacitor CC is just for decoupling.
Inductance appears across points A and B
Henries approx' (R3 in parr' with R4) x C1 x R1
This example gives L = 10H
R1 controls the 'Q' value

As you can see the circuit is very similar to a simple emitter follower but
adding just R1 makes a vast difference electrically .
It's more usual to use a opamp follower in place of the transistor as it can
give better performance. There was last Feb', a long thread here from Terry
Pinnell, ("Coupling capacitor voltage rating") demonstrating that this kind
of gyrated inductance can inadvertantly appear without even being asked for.

(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)

 

[Pat Ford]

isn't copper solid state? Everytime I see this tread that pops into my
mind.
Pat

 

[Ben Bradley]

Why would anyone bother? Is there some obscure advantage with it over
conventional coils?

It's much more immune to external signals induced by external
varying magnetic fields. Traditional coils may require mu-metal
shielding to get near as much immunity, which usually costs a lot of
money, and there's nothing obscure about money.
There are probably a few more obscure things such as hysteresis,
core saturation and inducing signals into nearby coils that an
"electronic inductor" doesn't do. OTOH, real inductors don't need a
separate DC power supply to have inductance.
Like most anything in engineering, there are many trade-offs, and
which one is best depends on the application. There are still plenty
of applications where a "real" inductor is the best or only solution.

 

[Ben Bradley]

isn't copper solid state? Everytime I see this tread that pops into my
mind.

To understand the concept you have to go back to the '60's where
every new product that used transistors instead of tubes had the words
"Solid State" proudly displayed, often in a fancy cursive italic font,
on the front panel. Just using copper wasn't enough.

OTOH, you can make a gyrator with a vacuum tube as the active
element...

 

[Roger Hamlett]

One reason is size...
You can build a massive inductor with a gyrator, in a volume that is tiny
compared to the equivalent real inductor.
Some years ago, I designed the first modem, to use this design to handle
the internal inductor needed. The key was in this case, that the inductor
at that time could not be fitted into the low profile wanted, without
taking an inordinate amount of board space.
At the time the people handling the approval testing were amazed at how
well it performed, and just how small the line interface could be made.
Most modern modems now do this.

Best Wishes

 

[Joseph Goldburg]

The name of the circuit to make an equ inductances is called a "Gyrator".

A study was done by Roger Rerden (spelling) on Gyrators.


One advantange is to replace inductors in LC filter designs.


A tranistor common emitter circuit with the capacitor across the base
emitter will simulate an inductor at the tied collector end.

As freq goes up the cap starves the base current turning the transistor more
off.

This is obvious as the common emitter inverts signals (180deg) phase shift.

JG

 

[Pat Ford]

To understand the concept you have to go back to the '60's where
every new product that used transistors instead of tubes had the words
"Solid State" proudly displayed, often in a fancy cursive italic font,
on the front panel. Just using copper wasn't enough.

OTOH, you can make a gyrator with a vacuum tube as the active
element...

Damn I forgot the smiley!
Pat