markp@CANNONTECH.COM wrote:
> I am beginning the design of a switching power supply.  The input must
> accept 120VAC or 125VDC and the output needs to be 24VDC at 3A.

[snip]

> I'm thinking about having the front end bridge followed by a non-regulated
> switcher and transformer and some filtering circuitry.  This will provide
> the isolation I need with an off the shelf transformer.  I'll then take
> this isolated DC and apply it to a classic buck converter that utilizes an
> off the shelf inductor.  It seems strange to chop the DC up twice but this
> appears like a simple way to get the required isolation while using off the
> shelf parts.

At this power level, you're going to want to consider having PFC (power
factor correction) on the input side, especially if you want to sell
internationally. PFC can also provide the isolation you need while
delivering a relatively loosely-regulated DC bus for driving your final
buck regulator. This arrangement is actually quite common.

-- Dave Tweed

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