TinySwitchIII power supply question

[[email protected]]

Hi to all.
I am looking to desigh a power supply , based largely on the Design
Idea DI-117 from
Power Integrations
Link : http://www.powerint.com/PDFFiles/di117.pdf

The question I have is what is the reason for the big difference in
value of L4 and L5. 1mH and 3.3uH respectively. The 2 inductors are
there as a filter in conjunction with the resivour cap which has been
split into 10u and 22u.
The rest of the circuit is fairly strait forward , but I'm a little
unsure about these inductors.

Cheers
Rob

 

[Paul Mathews]

Hi to all.
I am looking to desigh a power supply , based largely on the Design
Idea DI-117 from
Power Integrations
Link : http://www.powerint.com/PDFFiles/di117.pdf

The question I have is what is the reason for the big difference in
value of L4 and L5. 1mH and 3.3uH respectively. The 2 inductors are
there as a filter in conjunction with the resivour cap which has been
split into 10u and 22u.
The rest of the circuit is fairly strait forward , but I'm a little
unsure about these inductors.

Cheers
Rob

The larger inductor is non-ideal, so its parasitic capacitance will
pass high frequency energy (primarily from rectifier switching).
The smaller inductance should have very low parasitic capacitance and
is intended to filter spikes remaining after earlier filter stage.
Paul Mathews