Re: Flyback transformer design confusion!!


Tony wrote:
seegoon99@xxxxxxxxx wrote:
Hi to all.
I am looking to design a flyback transformer , for a small supply. I
have a couple design examples from ON-Semi that I'm looking at , and am
a little confused. Depending on what app note I use ,
I get wildly different results for the same design inputs. For example:
12V out 7W.
One app note shows a primary inductance of 3.3mH and the other app note
works
out at 1.8mH. I seem to come across this problem a lot. All the
different design procedures
seem to come out with totally different values for the same problem.
How do I know
which is the correct solution?

Not enough information is provided. The inductance required will
depend not only upon the supply voltage and current (at maximum load)
but also the design operating frequency.

Those inductances seem very high. The 1.8mH would be about right at
1,150hz, and the 3.3mH would be work at around 627Hz. Usually flyback
supplies are designed to operate above 20Khz to eliminate any
unpleasant noise.

The 3.2mH comes directly out of the data*** design. It runs at 67KHz.
Vmax is 350
Vdc and Vmin is 140Vdc. Vout 12v Iout 560mA.
If I take these Values and apply them to another design note equasions
I come out at 1.8mH.
Same input parameters , different outputs , depending on design
methodology!!

.

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