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
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.
--
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.
I know John won't respond, but could someone, perhaps Win, tell me how the "AGC" works? ...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
I'm not a big SPICE user in general, though I've done more SPICEing in the last year than in the 20 previous.
For some things, such as really weird photodiode preamps where nonlinear capacitances and so on are important, it can help a lot--provided the models are semi-decent. For most other things, I prefer algebra. You learn a lot more about how the circuit works by crunching the math than by poking the simulation until it seems to work.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
Spice is handy for tweaking control loops, especially higher-order loops that matter, or when anything nonlinear is going on. Or when you don't have a hard definition of what "right" is. Simple opamp type things are better to do with guesswork, or a scribbled Bode plot. You lose points if you use a calculator.
Spice is good for filters, too.
I did a constant-voltage/constant-current crossover power supply sort of thing recently, analog ORing two loop error signals, with a wide range of possible customer loads, and it was great for tweaking. The actual implementation will be firmware.
The other good use for Spice is grinding out the numbers on voltage dividers, pure DC analysis, just to save a lot of calculator stuff.
We never simulate whole products, or even whole circuits, just little pieces, or control loop abstractions.
I'm sure he would, but why should I, over the years you've insulted me at least as much as him, and perhaps more aggressively?
Anyway, he did explain it, SFAICT.
Note the BJT is over-biased - plenty of base current, that if left unchecked would charge the base-to-ground capacitor and over-current the transistor. So the oscillator runs and examining cycle-by-cycle, the collector swings higher and higher until it goes negative with respect to the base voltage, close to saturating the transistor, and turning on the base-collector diode a bit, robbing current from the base capacitor. This process servos the BJT current to just the right level to sustain an oscillation collector-voltage level where just the right amount of current is robbed each cycle to control the base voltage. Thereby insuring that the collector goes close to the emitter on each cycle, establishing a tightly-controlled amplitude, which as John pointed out, is temperature independent to first order since Vce(sat) is relatively temperature independent.
John said Vcc peak, but actually it must be closer to Vcc - Vce(sat).
I'll buy that the collector forwards biases, and you enter a limit cycle. Thus I'd call it ALC. I don't see any _gain_ variation that "AGC" would imply. ...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
Hi Jon, so good to see a post from you. Everything OK?
I'm going to have to go an reread Fenyman on this... (I thought I got it the last time, but that's how it is with Feynman.) I think there's a magnetic field everywhere in the magnetic circuit. In an electro- magnet it starts with the current in the coils and is transfered to the gap by the magnetic material...iron. But the field is everywhere in the circuit. It may very well be that the gap determines the field strength. But the magnetic energy is stored over the entire volume of the field.
Picky, picky. To my mind, the base current robbed by the collector starves the base, lowering the CE stage's gain, until the exact equilibrium is achieved. ALC, AGC, pick your name as you like. Either way it gets the job done rather nicely, and is a bit different from what we've seen elsewhere, such as in old radio circuits. I see that it has been analyzed as a possible RF oscillator technique. But it seems to me that, working as we imagine, Vce(sat) and all, this trick would be limited to far far below fT.
Yep, one winding has a well-establish inductance, not at all like a common transformer, but the second winding is well coupled to it, and with low leakage inductance, just like a good transformer.
We really need a new name for these beasts, inductors with transformer windings. BTW, toroid cores need not apply. Very poor AL control.
Nah. Still horribly busy around here -- probably going to be killing myself through the summer... too much to do (or, at least, I hope I can force myself to keep at it without giving up at some point.)
I _imagine_ aligned atoms as 'short circuits' that bridge vacuum. Vacuum is where the energy gets stored. (I think a tiny amount of energy is 'used' to align an iron atom, for example. But it is tiny and doesn't represent recoverable energy... I think it gets converted to heat in the end.) I'm very much open to being wrong, of course.
With all this in mind, it's easy to imagine the concept of permeability arising. For air core, it's vacuum all the way down, so to speak. All of the loop length is, in effect, the magnetic path length where energy gets packed away. But when you insert iron atoms chained end to end they act as short circuits, each of them bridging across a small bit of vacuum to make the effective length of vacuum shorter (when aligned
-- the molecules of O2 and N2 don't align and don't bridge so in effect they simply don't count and don't short the vacuum.) So if you imagine a core material inserted there, what counts is the interstitial vacuum that remains when computing the magnetic path length. But what remains?? Well, that depends. You can take a ruler and measure that core piece, of course. But that ruler won't help you figure out what the effective remaining vacuum length is and that is what you need to know. So in order to come up with a number that represents the percentage of the measurable length, you need a factor of some kind. This is the permeability figure. A permeability of 1000 would mean that if you had a toroid with a mean centerline path length measurable with a ruler of say 100mm, that the actual vacuum path length would be 100 microns and the other 99.9mm would be shorted out by the iron that is present there. A permeability of 100 would mean that
1mm would be vacuum and 99mm would be iron. Since all of us can only use observable measures, we need to have some idea about what it looks like from the magnetic field's point of view, vacuum wise. At least, this is how I like to imagine all of this... energy gets stored in vacuum and the rest is just fudge factors to get around how we practically measure lengths.
The peak detection can put a tiny flat on the negative swing of the sine wave. A small resistor in series with the collector fixes that and doesn't seem to do a lot of harm otherwise.
But he didn't insult your wife, too.
Oh, picky picky. It's actually, probably, a bit more complex, since the emitter is a little negative at the instant of collision, and the transistor is almost saturating, so some of the stolen base current is going into the collector and some is going into the emitter. It would be interesting to simulate, just to see where the currents really go. Adding the collector resistor changes things, too.
But the AGC thing does work, and the TC is close to zero.
Just to clarify, the RF versions I posted are similar to, but not the same as John's. They're standard UHF designs, Class A, without John's precision AGC. I don't think they can use John's AGC method directly-- if saturated, the transistors would be too slow--but maybe a Baker-ish clamp thing would do the job.
Oh, and John's oscillator really swings ~ 2* (Vcc + Vbe), not 2* (Vcc
- Vbe). Reason being, the AGC operates as the average base voltage gets sucked down to near 0v, killing the gain.
The collector has to swing downward from Vcc to ~Vbc _below_ GND to forward bias the b-c junction on the negative peaks, and swings up a symmetrical amount on the positive peaks.
Z5U, and to a lesser extent X5R, are so bad you have to use almost 1uF when you wanted 0.1uF. Since X7Rs are the same size and price (almost), I get X7Rs too. :)
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
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