inductance multiplier

[millwood]

capacitance multipliers are pretty common. How about inductance multiplier, either in a ps or as a load (more difficult)?

any thoughts?

[jackinnj]

you mean a gyrator?

[Charles Hansen]

Hello -

I think what he means is some type of circuit that could "multiply" the value of a given inductor. This would be especially useful when trying to build an inductor-input power supply filter. Normally the required inductor is so large and heavy that it roughly doubles the overall cost of the power supply. If there were a clever way to use a "small" inductor and "multiply" its action, then you could make an inexpensive amplifier that had inductor-input power supply filtering.

Unfortunately, this is just a wild goose chase.

A "capacitance multiplier" only mimics one aspect of a capacitor -- it's tendency to oppose a change in voltage. However, a "capacitance multiplier" does *not* multiply the energy stored in a capacitor. (If it did, then we could get rid of all the big capacitor banks typically found in high-quality amplifiers.)

So the analog to a "capacitance multiplier" would be a circuit that tends to oppose changes in current -- i.e., a constant-current source. However, this circuit doesn't increase the energy storage. You would still need a big inductor that would store enough energy to supply a constant charging current to the filter caps.

I think the confusion begins with the misleading term "capacitance multiplier".

Hope this helps,
Charles Hansen

[millwood]

this is what I had in my mind, conceptually.

you can certainly work out the math to see how this whole thing looks like from V1's point of view and compare that to an inductor.

[Charles Hansen]

Hello -

You can ignore my previous post. It looks like jackinnj was right and that millwood wanted a gyrator. Here's one link:

http://www.epanorama.net/documents/telecom/gyrator.html

Best regards,
Charles Hansen

[millwood]

Originally posted by Charles Hansen
Hello -

You can ignore my previous post. It looks like jackinnj was right and that millwood wanted a gyrator. Here's one link:

http://www.epanorama.net/documents/telecom/gyrator.html

Best regards,
Charles Hansen

that's the same set-up as the one using op-amp. Has anyone actually used such a circuitry?

[JensRasmussen]

Hi,

I use the gyrator for making EQ's in my active x over.

Documentation will be ready soon.

\Jens

[JensRasmussen]

The schmatics and math

The circuit forms an RCL circuit

C is C1

[jackinnj]

Originally posted by JensRasmussen
Hi,

I use the gyrator for making EQ's in my active x over.

a gyrator is used to make the RCL transform from active xo to passive

[JensRasmussen]

Hi,

passive to active or active to passive does it really make much difference. The circuit I posted acts like an RCL series connection, with the component sizes as noted.

Well I use it in a voltage devider and in the feedback of opamps as a frequency dependent resistor, This creates an EQ..... works great too

\Jens