Smaller is better

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Boy, that sounds like a no-win claim. :) In the case of a transformer, however, bigger is always better relative to what the designer is trying to accomplish from the viewpoint of power delivery at a certain frequency - at least from a sonic standpoint that's true.

Years ago we pioneered the use of oversize power transformers in audio equipment and to this day, our power transformers are easily 50% bigger than most other company's transformers in source and control equipment. Bigger transformer have lower output impedance because of their heavier gauge wires in the coil and the sonic differences we hear between smaller and larger are significant.

But when we deal with a Switch Mode Power Supply (SMPS) the landscape is very different for a number of good reasons. Here, our traditional thinking about transformers, power supplies and what makes something sound a certain way are all turned upside down and we need to apply a different set of rules.

In yesterday's post we covered the fact that the size of a power transformer is directly related to the frequency it is working at: the lower the frequency of the wall AC the bigger the transformer has to be to deliver power. This also means the opposite is true and this is where it gets interesting for SMPS.

A 1000 watt SMPS can be built in a form factor smaller than a CD case. In fact, advanced version have been built not too much larger than a pack of cigarettes. A linear supply of the same size would be huge - just picture a big power amplifier weighing in at 50 or so pounds - most of that being the power supply.

So what's the difference? Mainly the size of the power transformer. On a SMPS the power transformer has been shrunk to almost nothing, yet it still manages to isolate and deliver huge amounts of power. How does that happen? Higher frequency.

If you'll remember yesterday we saw that a transformer running at 50Hz is approximately 25% larger than one running at 60Hz. Now imagine that same scale in reverse: run you power transformer at 100,000 Hz and the size drops down to almost nothing.

How in the heck do they do that? Sounds like a line out of Modern Marvels, eh?

Tomorrow we shall see.

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Paul McGowan

Founder & CEO

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