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Maxim > Design Support > Technical Documents > Application Notes > Interface Circuits > APP 1923
Maxim > Design Support > Technical Documents > Application Notes > Power-Supply Circuits > APP 1923
Maxim > Design Support > Technical Documents > Application Notes > Protection and Isolation > APP 1923
Keywords: Draw 150mW of Isolated Power from Off-Hook Phone Line
APPLICATION NOTE 1923
Draw 150mW of Isolated Power from Off-Hook
Phone Line
Jul 09, 1998
The power supply of Figure 1 is useful in portable systems that connect to subscriber (household) telephone
lines, such as modems and telephone test sets. For systems that require 150mW or less, this circuit
eliminates the need for batteries and ac adapters by drawing power from ordinary phone jacks without
interrupting the voice signal. Built into peripheral equipment such as PCMCIA modem cards, it can spare the
battery in a host computer.
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