Xiaofan Chen wrote:
> Lower the output voltage to say 3V and you will know the effect of
> low duty ratio. Or increase the input voltage to say 100V.

I can't.  This particular supply was designed to work with 20-60V input.
You can't expect it to work outside of its design range.

The point is that efficiency does not inherently need to suffer as input
voltages go up.  Note I'm talking about "reasonable" input voltages where
suitable transistors are available for the switch.  Things get different
above a few 100 volts because available switches become less and less ideal
and driving them becomes tricky too.


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