[Amps] Peter Dahl transformers

[Manfred Mornhinweg]

Adrian,

> You may like RF Splatter from switching power supplies but I sure do not!

No, my taste isn't that crazy. I also prefer as low a noise level as I 
can get. That's largely why I moved away from the city, to the middle of 
the woods, were there are no bad quality switching supplies or other 
noise sources around. But that does not prevent me from using GOOD 
switching supplies with great results!

> I would much rather see a nice solid hunk of transformer in anything to 
> do with electronics than to see
> * Shock hazard, RF noisy switching power supply of any type. *

You are of course fully entitled to your taste, preferences, opinions, 
and style, but it's just not correct that switching supplies necessarily 
generate RF noise, let alone shock hazards! Sure, they CAN generate an 
awful lot of noise, if badly designed. But a well designed switching 
supply that generates no objectionable RFI is still much lighter, 
smaller, and less expensive than a conventional transformer supply, and 
of course it's regulated and essentially ripple-free.

16 years ago I made a 13.8V, 40A switching power supply, based on the 
very common industry-standard half-bridge design with bipolar 
transistors and pulse width modulation, of which there is one in 
essentially every desktop PC. But I applied some basic techniques to 
avoid RFI: Reasonably slow switching speed, Schottky diodes, generous 
snubbering, ferrite absorbers, an extra stage of RF filtering both at 
the input and the output, and keeping noise currents off the shields. 
This was enough to make this power supply essentially free from RFI. I'm 
using it 24/7 since then, powering my transceivers and accessories, in 
this particularly RF-quiet environment where I live now, and have never 
detected any RF noise above 100kHz. Below that frequency, I can detect 
some noise when I wrap an antenna wire around the power supply, but not 
when using the antenna in my yard.

This power supply was published in QST and in the ARRL Handbook. Later I 
published it on my website too. Many people have built it, and are 
successfully using it.

This power supply is certainly more complex than a conventional linear 
one, but it's also much less expensive to build, smaller, far lighter, 
much more efficient, and much more tolerant of line voltage fluctuations.

It's also short circuit proof. And if you are concerned about safety, 
you should know that it follows international safety recommendations 
regarding insulation, creepage distances, and grounding.

This is only one of many switching power supplies I have made, so I know 
reasonably well what I'm talking about.

With a switching power supply for a linear amplifier, there is an 
additional benefit simplifying things: There is no need whatsoever to 
keep the power supply running during RX! Unless you want to use the amp 
in a multi/multi contest station, you could get away with a very noisy 
power supply, and simply stop it during RX! Given the low capacitance 
needed in the output filters, it's even possible to run full QSK and 
still stop the power supply for RX. Not that I would recommend making a 
dirty switching supply and relying on this technique to be able to use 
it, but someone too cheap to include RFI filters _could_ do it this way! 
That would be intelligent design too. Any way to obtain ones's goals in 
a cheaper/better/faster/safer/more reliable/more efficient way can be 
intelligent design. Instead just copying the ways how things have been 
done for many decades, without improving on them, in my opininion can be 
considered intelligent only if there is a good reason for it, such as a 
big junkbox full of antique components, including transformers.

> OK, back in my rabbit hole.

And I into mine! ;-)

Manfred, XQ6FOD

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