> From:         Peter Mcalpine[SMTP:petemca1@BIGPOND.NET.AU]
> Sent:         Sunday, February 15, 2004 10:29 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [EE]: Boost & Buck regulator in one?

> Hi All,
> Might be stumbling down the wrong track, but worth investigating
> anyway...

> Can anyone recommend a switch mode regulator that will do boost
> and buck regulation?

> Basic usage is for a system that runs in a car, but requires
> backup battery. It also requires good 3.6V regulation.
> Current consumption at 3.6V is around 200ma max. backup battery
> is presently 3xAAA NiMh 650mA

> My idea is the battery can also be feed into the input of
> the switch mode so to maintain good regulation..

> Any help much appreciated as always :)

> Regards,
> Peter Mcalpine
> Sydney, Australia

A circuit that will do exactly what you want was published in the
October 2003 issue of "Nuts & Volts" magazine on page 33. It
uses a novel circuit topology called SEPIC (Single Ended Primary
Inductance Converter). To quote from the article: "The SEPIC
regulator permits both higher and lower voltages than Vin through
a unique arrangement of two coupled inductors." The last phrase
means "transformer".
A sample circuit is given. It is based on an LT1370 chip, and is
designed to convert the output of two Li-ion cells to 5 volts.
The one drawback is the transformer. The circuit calls for a
"BH Electronics 501-0725" but no further information is given.
If you are in a position to wind your own switching transformer,
this would be an interesting circuit to experiment with.

John Power

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