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Maxim > Design Support > Technical Documents > Application Notes > Automotive > APP 1136
Maxim > Design Support > Technical Documents > Application Notes > Microprocessor Supervisor Circuits > APP 1136
Keywords: battery backup, power switching, external power sources, battery switchover, switchover
APPLICATION NOTE 1136
Switching Between Battery and External Power
Sources
Jun 27, 2002
Abstract: The following application note discusses a circuit that switches power sources efficiently without
switching noise using the MAX6326. It discusses the advantages of using this technique over a simple
diode-ord method.
A similar version of this article appeared in the May 13, 2002 issue of Electronic Design magazine.
Portable equipment that can operate from a battery pack or an external power source (such as a wall-
adapter or external supply) needs to be able to smoothly switch between the two power sources. This
application note describes a circuit (Figure 1) that switches power sources with good efficiency and
without switching noise.
Figure 1. This circuit provides battery/wall-source switchover while debouncing the wall-source output.
Power Switching Problems
Two problems are addressed. First, contact bounce effects can occur when the external source is
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