Dwayne Reid wrote:

> At 08:54 PM 8/16/2005, Martin Klingensmith wrote:
>
>> Assume there is a transformer with an arbitrary secondary voltage,
>> isolated.
>> Is it inappropriate to run a low-side buck SMPS off of this secondary?
>> It seems to me that it makes no difference because it is already
>> isolated. The fact that the low side is not at the traditional ground
>> level seems irrelevant. The control IC ground potential would be the
>> negative end of the secondary and the positive would be a low power
>> linear housekeeping supply.
>
>
> Your assumptions are spot on.  The transformer provides whatever
> isolation it was rated for, the output of the transformer is rectified
> and filtered, the SMPS buck convertor changes the filtered DC with
> lots of ripple into the desired output voltage.
>
> Make sure that the reservoir cap is large enough to ensure the buck
> convertor does not run out of headroom during the low points of the DC
> ripple.
>
> dwayne
>
Hi Dwayne,
I didn't think of how to sense voltage though. The control IC expects a
2.5v voltage error signal. It is unclear how I would do this with a
low-side buck. Any ideas?

-- 
Martin Klingensmith
http://wwia.org/
http://nnytech.net/

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