Ian White, G3SEK wrote:

Tim Wescott wrote:

Alan Horowitz wrote:

John Popelish wrote

Microwave oven transformers operate with parts of the core very nearly
saturated during parts of the cycle [...]

why are they designed that way?


Probably to save money on the core -- the oven will cost a few cents
less to make, a few dollars less to buy, then you pay that all back to
the power company as your kitchen gets hot. It would also add a
modicum of voltage regulation to the thing, but I doubt that's the
reason.

It is mostly done for current limiting, which a magnetron needs because
(in DC terms) it looks like a diode connected across the power supply.
Saving size, cost and weight is also important, so the transformers are
pared right down to the bone.


I know they purposely add leakage inductance by putting in a "shorting
bar" between the primary and secondary sides of the coil -- I don't
think allowing the core to saturate would give you any significant
current limiting on the secondary side unless you were willing to put up
with runaway current input on the primary side as your excitation
inductance went away.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com