Is it possible to vary voltage without much power loss

hi,

is it possible to vary the voltage from a supply, without using a transformer, or variac?

as i have a flyback transformer & driver, and it uses 7A at 40v.

it would be handy if i could vary the mains voltage, from e.g. 10v - 100v, or 0-240 or whatever so i dont have to use a massive transformer, or a set voltage smps.

please tell me if im talking crap :)

thx. Alf.

Transformers do use energy - probably about 75% efficient
You could use a potential divider or variable resistor. These will get warm and so lose energy but probably a similar amount to a transformer or variac. Some voltage droppers use an intermittent current breaker to supply the current for a fraction of the time as in an ac light dimmer.

No I don't think it works like that. You would need a variable transformer to change the amperage and voltage I think.