How to design an Interesting inductor

If the "dc control winding has huge inductance", what difference does it make? You will be applying DC.

I want to use the same winding that I'm using for the inductance. This is my starting point, But I only want one winding,

Mikek

If they are wound on the same core, applying a voltage source to the control winding shorts the signal. Applying a current source has its own problems.

There are constructions where the mag fields are orthoginal, so the control current doesn't link to the signal.

Mikek, why do you want a variable inductor?

Why, how fast do you need to control it?

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website:

Given two separate ferrite-core inductors, you could put them in parallel for AC and in series for DC. Then it's easy to inject the DC control current without shorting the AC signal.

But why?

Use sufficient current, say more than 10 A to cause a sufficient magnetic flux. In order to keep the voltage drop and hence power dissipation down, thick wire is needed. This can be a problem especially if Litz wire is used.

However, I do not understand how you are going to connect the DC current into the LC? circuit since the DC power supply would be in parallel with the inductance.

sounds like a magnetic amplifier, Q will probably be so-so.

Slow, in seconds. Mikek

In previous responses I gave the proposed use is for a "Beverage on Ground" antenna. I had a GOG before and used a beds that had a Q of 1 or 2. so if I could get 20 it would be better. Mikek

Some RM cores and pot cores have a central hole through which you could wind your 100uH, and the DC winding goes on the bobbin...

...this is a 5.5uH core so approx 4 turns for 100uH if it were wound on the bobbin, I don't know how many if wound through the hole, but I'd guess it would be similar. I'd try to grind the hole edges to take off the sharp edge if possible.

Cheers

How about a mechanical variometer.

Make a bar that fits into the coil. One end of the bar is made of some ferrite material the other of aluminum. Connect it to a screw and run it with a stepper motor.

See later posts Thanks, Mikek

Sorry, responses have made it clear I didn't ask my question well. I only want one winding of 100uh, that winding will both the ac and the dc.

Thanks, Mikek

OK, so the DC is from a high impedance current source I guess. As an indication, a 100uH inductor on an RM4 3C92 core 722nH/T^2 will be 12 turns and saturate at around 500mA. There's a program, ferroxcube.exe entitled Ferroxcube SFDT 2010 which is handy.

Cheers

as huge

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replace diode with your inductor and adjust values to match your freqency r ange

One could also use PIN diodes, or relays, or latching relays to switch taps on an air-core inductor, in interesting combinations. Q would be high.

What power level? Frequency range?

Tim

One minor tweak to that idea is to run an odd number of half-turns on the bobbin, and use a high-mu pot core with an adjustable centre gap.

The extra half-turn will generate a large field going round the outside of the core (avoiding the post) and so will saturate it fairly readily.

Cheers

Phil Hobbs

A cpnventional current-controlled inductor has two magnetic paths that are configured to carry antiphase windings, with the third 'inductor winding sharing both. The control windings' AC flux, from the third winding, cancels out.

You can do this with an e-core (control windings on outer arms), two toroids (each with control winding - sandwitched to support single 'inductor' winding around both) or solenoids (two solenoid cores support control windings, 'inductor' wound around both.).

RL