Re: flybacks & transformer leakage
- From: analog <analog@xxxxxxxx>
- Date: Tue, 17 May 2005 08:56:02 -0700
cbarn24050@xxxxxxx wrote:
> Hi Adam, leakage is relatively high in flybacks because the windings
> conduct at different periods, this means that the fields of the 2
> windings cannot cancel each other therefore split sandwiching doesn't
> help very much unlike in a forward transformer.
The leakage inductance of a flyback transformer is typically about
the same as that of any other topology's similarly sized transformer.
It is its own deliberately lowered magnetizing inductance (to which
its leakage inductance is proportionally larger) that makes leakage
inductance seem greater than it really is.
A flyback transformer is best thought of as an ideal inductor in
parallel with an ideal transformer (winding resistances and leakage
inductances are added outside this ideal core). The ideal transformer
part behaves like any ideal transformer, where (for two windings) the
windings only conduct simultaneous currents of equal and opposite-
ampere turns.
The ideal inductor part may conduct some ac current, or, if large,
may only conduct substantial dc. As a thought experiment, imagine
an ideal flyback transformer consisting of infinite inductor
(initialized to one amp) in parallel with an ideal 1:1 transformer,
all driven at 50 percent duty cycle. The inductor can pass no ac
and the transformer can pass no net dc. Think about it.
Regards -- analog
.
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