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Looking for 100 KHz - 10 MHz, 10W

That is a noble effort.

The single OA version is not being discussed here.

Yes. So it is a reasonable starting point for the OP's request. He did not ask for a complete design.

Your LTspice model shows the output -3dB down

3dB down is the usual way to describe bandwidth.

In the OP's original post, he specifies sine wave.

That's okay, it's not your job.

You are getting into more detail than required. If an assumption is incorrect at the start, it makes the rest of your analysis useless.

My simulation uses 33uH per winding. Did you notice? Two of those (coupled) in series is 4x33 or about 132uH for the primary. Also, if you actually read the paper you referenced, you will gain some insight into their thinking about all this.

Your math is usually as good as the rest of us. We all make mistakes. However, I seriously doubt LT made as big a mistake as we ourselves make here.

Enough inductance, according to you, is at least 100uH. So, above, I provided some indication that it is over your requirement.

I did not "find" it. I adjusted the coefficient of coupling and the inductance to match the response curve supplied by LT. I had no other way to deduce those without the data on the transformer that they used. It was an interesting and educational exercise for me.

Good! We should all cherish learning.

Reply to
John S
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em.

Certainly *not* competitors. If we'd had any competition, we'd have thrown in the towel, or not picked up the towel in the first place. Or just purc hased your towel. :^)

OK with the opamp->transistor configuration I haven't look too hard at dist ortion (inter mod or otherwise.) At low frequencies the negative feedback seems to cure a lot of the problems..(and you can run pretty close to the r ails.).. of course once the frequency gets higher and the opamp looses gain it gets worse.

Well we use the term 'physics package' to mean all sorts of different stuff . I guess it's kinda code for the part of the apparatus that can't be purc hased from didgikey nor McMaster-C and thus costs a lot of money. (Big grin :^)

George H.

Reply to
George Herold

I tried VPH5-0155-R as an impedance matching transformer for an RF amp with a 50R output into a 300R load at 16MHz. It didn't work. I suspect this transformer is not much use above 1MHz (as specified in the data sheet). Is there a defect in the model or am I doing something wrong? I'm an experienced engineer but a novice at RF.

Regards Tim.

Reply to
timtanner

That transformer is made for a switching power supply, not a broadband transformer. The data sheet on the VPH5-0155-R shows that it's only good up to about 500KHz. See graphs on Pg 8. The description also includes: "Frequency range to over 1 MHz"

100khz to 10Mhz is about 6.5 octaves of frequency range. Getting that kind of bandwidth is not easy, especially if you're doing high RF power, low losses, and a flat frequency response. This might help:

"Designing Wideband RF Impedance Transformers"

or Google for "wideband RF transfomer design".

Good luck.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

I wind transmission-line transformers with a 1000:1 frequency range. It's really not difficult.

Sevick's book is OK up to 16 MHz. I don't trust his high frequency measurements.

At a fixed frequency, it's easier to use a conventional LC tuned matching network.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics
Reply to
John Larkin

Many thanks for the advice John. I'll have a stab at winding my own transformer on a T200-2 core. I'll try 5 turns with the input across turns 2-4 to give a 2:5 turns ratio. Is this likely to work? The RF amp I'm using goes from 5-30MHz so not a huge range to match across. I'm guessing I don't need to use transmission line winding techniques to cover this small frequency range?

Kind regards, Tim Tanner.

Reply to
timtanner

Doesn't sound like a very good combination. What's the A_L on that core? How much magnetizing inductance will 5 turns yield? How much inductance can you tolerate?

Ferrite is fantastic for transformers.

Note the semantic distinction between transformers (converts voltage/current by ratio with a minimum added current draw) and inductors (stores energy as magnetizing current, may have multiple windings).

You want powdered iron, and gapped ferrite, for inductors, and ungapped ferrite for transformers.

If you need matching reactance as well as transformation, powder cores are good. But then, you'll only be getting a match over a relatively narrow frequency range, if that's the case.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: https://www.seventransistorlabs.com/
Reply to
Tim Williams

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