Re: Twin T circuit wanted

Oh, dumb mistake--if it's spectral purity you want, it'll be better tapped off the tank circuit. Should've thought of that, but was too busy goofing around...

If stability w.r.t. to load is more important, I think it's better as- drawn. YMMV.

-- Cheers, James Arthur

a e

back

een

Yeah yeah, we all get that. The circuits speak for themselves. No need to poke a stick at Jim--he's a good 'ol grizzly bar, just grouchy. The whole country's grouchy, the people ill-at ease. Such are the times.

[snip]

Of course not. He's a physicist. The really good ones don't bathe, either.

-- Best regards, James

Not me.

I recently read two articles about getting older:

1. Unless you have dementia, brainpower tends to increase with age. Exercizing your brain, like designing electronics, keeps it healthy.

1. Personal happiness increases up to age 18, declines until about 50, then increases pretty much for the rest of life after that.

John

I'm not grouchy... just a perfectionist. And I've been a happy camper all my life ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
      The only thing bipartisan in this country is hypocrisy

Thanks Win, I'm not much of a magnetic materials guy. I like magnetic fields best when they are in free space. Helmholtz coils and such.

I've read about gaps in magnetic materials and transformers, but never quite 'gotten' the importance. (I never had to make one.)

I was picturing coils wound in series on a rod... a nice big air gap.

Would coils wound on a torroid give a different response?

George H.

Well default, Though 'default' is not much of a name, I tend to agree with you. I only learn by making mistakes, and if you've stopped making mistakes.... well then you've stopped learning. (Good thing for me, as I can make mistakes faster than....)

George H. =A0

rote:

l c

eak

d e e

tude

es

ings

sor

ght

Thanks James, I use a 70MHz ~1 watt oscillator to run the Rb discharge lamp for an optical pumping apparatus. I'd like to have some 'back-up' ideas if the npn-RF transistor ever disappears.

George H.

This might be of some help?

What gap does is increase the path length, reducing inductivity proportionally (the average permeability of the path gets closer to 1), while flux remains constant. Since L = Phi/I, L drops. Since mu_eff drops, the amps required for a given flux goes up, so you get proportionally more current at saturation, and since energy goes as I^2, you get more energy storage too. The core looks like pole pieces, concentrating magnetization into the airgaps, where the energy is stored.

If the toroid (not "rr") has high permeability, it will saturate pretty quickly and that's that. If it's powdered iron (low permeability), you can drive lots of amp-turns into it (though the stuff tends to be lossy).

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

c

lec_Magnetics.html

ff drops,

e

ion

Thanks Tim, I've been through the math. The air gap helps to smooth out the terrible non-linearity of the magnetic material. I've just never done it in practice. (Which for me, makes all the difference.)

can

Sorry I'm a terrible speller. (If it's a long post I'll run it through a spell checker.)

But I see the problem. Even with iron the non-linearity means that the inductance changes with the current, so the resonance frequency changes as the supply voltage decreases.

George H.

--
About typical for a banty rooster who thinks that his crowing is what
makes the sun rise.

--
Strange, but I thought that two (or more) magnetically coupled
inductors comprised a transformer...

Depends on your definition of "transformer" :-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
      The only thing bipartisan in this country is hypocrisy

On Tue, 08 Jun 2010 15:09:51 -0700, John Larkin wrote:

--- You're being absurd, as usual, but it seems you lucked out this time and your oscillator works in LTspice.

Version 4 SHEET 1 880 680 WIRE -384 48 -592 48 WIRE -320 48 -384 48 WIRE -128 48 -224 48 WIRE 16 48 -128 48 WIRE 144 48 16 48 WIRE 240 48 144 48 WIRE 144 64 144 48 WIRE 240 64 240 48 WIRE -384 96 -384 48 WIRE 16 96 16 48 WIRE -448 144 -496 144 WIRE 144 160 144 128 WIRE 240 160 240 144 WIRE 240 160 144 160 WIRE -496 176 -496 144 WIRE -592 192 -592 48 WIRE -272 192 -272 112 WIRE -272 192 -384 192 WIRE 144 192 144 160 WIRE -128 208 -128 48 WIRE 16 240 16 176 WIRE 80 240 16 240 WIRE -384 272 -384 192 WIRE -272 272 -272 192 WIRE -496 288 -496 256 WIRE 16 304 16 240 WIRE 144 320 144 288 WIRE 240 320 144 320 WIRE 144 336 144 320 WIRE 240 336 240 320 WIRE -592 432 -592 272 WIRE -496 432 -496 368 WIRE -496 432 -592 432 WIRE -384 432 -384 352 WIRE -384 432 -496 432 WIRE -272 432 -272 336 WIRE -272 432 -384 432 WIRE -128 432 -128 272 WIRE -128 432 -272 432 WIRE 16 432 16 368 WIRE 16 432 -128 432 WIRE 144 432 144 416 WIRE 144 432 16 432 WIRE 240 432 240 416 WIRE 240 432 144 432 WIRE -592 496 -592 432 FLAG -592 496 0 SYMBOL ind2 224 48 R0 SYMATTR InstName L1 SYMATTR Value 10e-3 SYMATTR Type ind SYMBOL ind2 224 432 M180 WINDOW 0 36 80 Left 0 WINDOW 3 36 40 Left 0 SYMATTR InstName L2 SYMATTR Value 250e-6 SYMATTR Type ind SYMATTR SpiceLine Rser=.01 SYMBOL npn 80 192 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL res 0 80 R0 SYMATTR InstName R1 SYMATTR Value 100k SYMBOL cap 128 64 R0 SYMATTR InstName C1 SYMATTR Value 1e-6 SYMBOL voltage -592 176 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 3 24 104 Invisible 0 SYMATTR Value 5 SYMATTR InstName V2 SYMBOL pnp -448 192 M180 SYMATTR InstName Q3 SYMATTR Value 2N4403 SYMBOL voltage -496 272 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 3 24 104 Invisible 0 SYMATTR Value PULSE(5 0 0 1e-6 1e-6 .01) SYMATTR InstName V1 SYMBOL npn -320 112 R270 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL cap -288 272 R0 SYMATTR InstName C4 SYMATTR Value 1e-6 SYMBOL res -400 256 R0 SYMATTR InstName R2 SYMATTR Value 1000 SYMBOL res -512 160 R0 SYMATTR InstName R3 SYMATTR Value 1000 SYMBOL cap 0 304 R0 SYMATTR InstName C2 SYMATTR Value 1e-8 SYMBOL res 128 320 R0 SYMATTR InstName R4 SYMATTR Value 1000 SYMBOL cap -144 208 R0 SYMATTR InstName C3 SYMATTR Value .1e-6 TEXT 160 184 Left 0 !K1 L1 L2 1 TEXT -576 464 Left 0 !.tran .5

Since we manufactured and sold lots of them before Spice was available, and they worked just fine, the luck is on Spice's part. Or yours.

This will shock the kiddies, but it *is* possible to design circuits without using Spice. Usually it's faster and better.

John

That's what I tell them. Archimedes, Newton and Einstein perfectly managed without Matlabs, Simulinks and Spices.

VLV

This is partly true, but flux is still flux, so for example, saturation occurs at the exact same time if you're applying the same square wave, regardless of gap (in practice, fringing flux spreads it out slightly). If you're testing an inductor by applying a squarewave and measuring current, and you see the current jump up when it saturates, the time that occurs does not change as you move the core in and out.

Powdered iron inductors are kind of peculiar. They store lots of energy at high magnetization, and they saturate gradually (even a widely gapped ferrite saturates fairly suddenly, though you may not notice the difference because the gap is so wide to begin with). A 10uH inductor might drop to

3uH at peak current handling.

It's just like using a Z5U ceramic to bypass a power line, but its capacitance drops 70% because you're using it at rated voltage..

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

John Fields a écrit :

It's more related to how the xfrmer/inductor is used. An xfrmer is used to directly transfer energy from its primary to its secondary. An inductor is used to store it then release it.

In an xfrmer the magnetizing inductance does not matter much provided it's high enough and it can often be non linear without any worries.

Here it'll have to have a well defined value and be linear.

--
Thanks,
Fred.

--
You're preaching to the choir, bucko.

In your world, maybe, but when you're talking circuits with hundreds
of thousands or millions of transistors, it's not possible.  

This may come as a surprise to you, but many (if not most) of the
circuits which you buy and incorporate into your products were
designed using SPICE, so the fact that you assemble them into working
product that you don't simulate doesn't mean it's free of SPICE.

I believe Win is saying that the core in a transformer can be designed without necessarily caring so much for (or wanting) a known A_L and/or energy storage in interstitial vacuum. While an inductor usually has the L as a design parameter and in that case using _some_ transformer cores (iron) where the A_L isn't a goal in their design can mean that the L is not nearly as 'designable' with those materials.

Energy is stored in vacuum, not atoms (most of it, anyway, though there is, I believe, a _miniscule_ storage of energy used in aligning.) Including an air gap (in iron) completely dominates by providing a huge, known gap for energy storage and what tiny bit of vacuum remains in the iron path is nearly completely swamped out by it. So that makes the A_L designable in that case.

Another way of saying all the above is that in transformers the flux through the core links the windings together and energy storage is actually parasitic, not desired. The A_L is basically "not wanted" and therefore minimized, but not designed to some specific value. Inductors are designed for specific values and therefore the A_L needs to be known, not merely minimized, and otherwise the core is actually supposed to provide flux linkage to the known effective gap, not two windings. The 'flyback transformer' is kind of a misnomer to me, since in reality it is really an inductor that uses a known A_L or gap to store energy and also is designed to link the flux to the gap, except that it _also_ needs to provide subsequent linkage from the gap to a secondary winding, as well.

Or, at least, that's how it seems to me.

Jon