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September 2014 DocID026782 Rev 1 1/18
18
AN4564
Application note
Is a positive power supply mandatory for my application,
or could a negative output work also?
By Laurent Gonthier and Jan Dreser
Introduction
In this application note we explain the reasons why some appliance designers might choose
a positive power supply. This selection is based mainly on the choice of switched mode
power supply (SMPS). Some specific applications cases, which are detailed in Section 3,
may also lead to the choice of a positive power supply.
Using a power supply with a positive output is not convenient for all applications. For
example, as explained in Section 1.2, a negative supply is preferred to drive AC switches.
We provide here an alternative solution which allows a negative output to be implemented
whenever possible. Further, many solutions allow both a negative and a positive output (for
the microcontroller) to be implemented, as shown in Section 2.
www.st.com
