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]

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]

Gyrator

Hi,

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

Documentation will be ready soon.

\Jens

 

[JensRasmussen]

Ups I forgot this

The schmatics and math

The circuit forms an RCL circuit

C is C1

 

[jackinnj]

Re: Gyrator

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]

Re: Re: Gyrator

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

 

[jackinnj]

there's an article on FDR's somewhere on Analog's website, i think they give the math.

 

[hacknet]

does the much simpler 1 transistor circuit work? i`ve done a simulation and it doesn`t seem to work...

 

[millwood]

it seems to have worked in my simulation.

the left side is essentially a traditional L/C circuitry and the right side the "inductance multiplier". one big draw back for the inductance multiplier is its heavy internal resistance (thus voltage drop).

 

[hacknet]

oh, thats what i got too, i was looking for something that looked exactly the same... haha! this is a good lesson in inductance multipiers...

 

[Eva]

Just a funny thing...

The op-amp gyrator circuit is actually a butterworth 2nd order low-pass active filter with input and ground connections reversed and output discarded

 

[jewilson]

Millwood,

here a good link to designing gyrator for graphic equalizers.

http://www.rane.com/pdf/constanq.pdf

I use a Gyrato years ago for the filtering the output of a DAC. It just did not sound as good as a simple RC filter which I replaced it with. Also it just used to many parts.