If the secondary of a push-pull ferrite transformer requires significant HV clearance from the ferrite core will there still be enough coupling for it to operate efficiently assuming the primary is wrapped right onto the core? Also is it possible to use a simple ferrite rod as a transformer at least somewhat efficiently? For making a secondary with high clearance a ferrite rod is a lot easier than using a toroid or core. I was thinking of a 1" diameter, 6" long ferrite rod, with a single layer secondary 3" diameter and 6" long.
You aren't saying how much voltage is "high", or how much coupling your anticipated circuit needs for "efficiency", or what your threshold is between "efficient" and "not efficient", etc., etc.
So here are a whole bunch of guesses with no absolutes, because you're not giving anyone enough information to go on.
To some extent that depends on your circuit. If you're using an E-core or a bobbin you're not going to lose a whole lot of coupling. You may need more snubbing than you would with a more tightly coupled transformer, though.
Your coupling would go way down, so I assume that your efficiency would suffer considerably, too.
It sounds like you're winding your own -- use an E-core of the appropriate size, and a bobbin. Winding will be easy, the bobbin will help keep the spacing right for isolation, and an E-core should keep the leakage down even with well separated windings.
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Also is it possible to use a simple ferrite rod as a
There will be a lot of pri-sec leakage inductance, so the secondary, as a voltage source, will be soft, relatively high impedance. If you only need a small output current, it might work. You could resonate one or both windings just for fun.
How much output voltage and current do you need? AC or DC load?
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John Larkin Highland Technology, Inc
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Ferrite, or ferroxcube, or some company, published a single page of EXACTLY what you're asking. The chart shows EFFECTIVE permeability of a rod versus length/diameter ratios [plus rod's permeability, which once more than a certain amount has little impact]
For example a rod of infinite permeability still looks like around 100 if it's 1 inch long and 1/8 inch diameter [made that up, but you get the idea]
Plus, with a rod, you have to battle having all your field out in space being picked up by other electronics.
EXACTLY what you're asking. The chart shows EFFECTIVE permeability of a rod versus length/diameter ratios [plus rod's permeability, which once more than a certain amount has little impact]
Not exactly; OP is talking about a transformer. Rods make poor transformers due to the low inductivity and k. If you put another rod on the other side, and some flat pieces to bridge across them and make a connected magnetic path, you'll do alright. Such construction looks very much like the average flyback transformer core.
The page you're thinking of may very well be,
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I snipped it from a book online by Pressman, Billings and Morey; evidently they got it from Micrometals, but I don't recall finding it on their website (it's probably buried in their literature somewhere).
Note also that the inductivity (uH/t^2) varies with position, so that turns towards the center have the highest, and turns at the exact end have about half the inductivity. These figures are the average over a winding covering the entire core. The turns on the end contribute little, so they are often omitted (which likewise raises the apparent average), as can be seen in most commercial parts. Those turns probably have higher eddy current losses, too, further lowering the Q.
Tim
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Has reasonable efficiency if you're doing a resonant converter. You may even need to add leakage inductance (assuming you start with a closed loop core, like a flyback transformer core). Tricky part is calculating how much.
An open rod makes a terrible transformer, but it can still be usable. Before deflection was integrated, the oldest prototype TV sets used a (air cored) Tesla coil, or rod-cored construction, to generate HV from an oscillator. Later on, the whole deal (HV, focus, deflection, isolated filament voltages, auxiliary power and sync signals) was integrated, and the flyback transformer we know today has changed little since.
Tim
-- Deep Friar: a very philosophical monk. Website:
Even older TVs, including ones sold to the public, had 60 Hz HV transformers.
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
I built one like that in 1948 using surplus radar parts. It's a wonder I didn't kill myself! The P7 phosphor on the CRT made for some interesting pictures. :-)
I have a 4FP7 on the bookshelf right above me. It glows nicely when I turn the light off.
It was an aircraft radar display CRT, a 4" square electrostatic-deflection PDA tube. I used to buy these from Fair Radio Sales when I was a kid. Just for fun, I emailed them recently just to see if they had any left. Yes, $25 each, so I got two.
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John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
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For a custom ferrite core prototype, how well would packed ferrite powder work compared to a solid ferrite core? I guess the inductance would be lower due to the larger distributed air gap. I was thinking of making a wood or plastic form to hold the ferrite powder and also act as the primary to secondary insulation.
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