On Wed, Nov 26, 2008 at 1:28 PM, apptech <apptech@paradise.net.nz> wrote:
> The LED current path path when Sw is not grounded is:
>
> 100 mohm resistor
> P Channel external LED (TURNED ON BY IC)
> LEDs
> Inductor
> Schottky diode
> Back via wire to 100 m.ohm resistor.
>
> The inductor is the energy source.
>
> For practical put\rposes the P FET here could be a piece of wire.
>
> Without wading through their explanations I'd go so far as to say that the P
> FET is not required for basic buck operation.

You are of course right. But the OP is asking for explanations
for the page 15 Buck-Boost operation. You are explaining the
operation of the page 1 Buck mode operation.

> The "key" in the original circuit is deciding that the PFET
> must be on at all times during LED conduction.

Xiaofan
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