> Bruno L. Albrecht wrote:

> =A0http://focus.ti.com/docs/prod/folders/print/tl497a.html

Looks good.
A number of IC's will implement negative going boost converters in this man=
ner.
MC34063 is another time honoured and cheap one which will implement
the same circuit. Functionality is very similar.

Lowest parts count (but not by much is to drive a high side
'jellybean' bipolar or a P channel FET in the same way as the output
transistor in fig3, using the PIC to drive it .By the time you've
added voltage feedback and possibly a driver the stand alone IC
solution looks attractive.

Do you really need as much as -5V? Supply does not have to be balanced
for the opamps. Only need -5V if output excursion requires it.
Larger caps will give a stiffer supply IF the driver is able to handle
them. You could use a tripler but diminishing returns set in.


       Russell

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