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An example of linear regulator with 5V input is:
5.3.1.2 + 12V input Source Power Supply Design
Guidelines
The desired output for the power supply is 3.8V, hence due to the big difference between the
input source and the desired output, a linear regulator is not suited and shall not be used. A
switching power supply will be preferable because of its better efficiency especially with the
2A peak current load represented by the UE910.
When using a switching regulator, a 500kHz or more switching frequency regulator is
preferable because of its smaller inductor size and its faster transient response. This allows
the regulator to respond quickly to the current peaks absorption.
In any case the frequency and Switching design selection is related to the application to be
developed due to the fact the switching frequency could also generate EMC interferences.
For car PB battery the input voltage can rise up to 15,8V and this should be kept in mind
when choosing components: all components in the power supply must withstand this
voltage.
A Bypass low ESR capacitor of adequate capacity must be provided in order to cut the
current absorption peaks, a 100μF tantalum capacitor is usually suited.
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