LM317SSLASHNOPB datasheet(25/51 Pages) TI

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LM317-N

LM117, LM317-N

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SNVS774Q – MAY 2004 – REVISED JUNE 2020

Product Folder Links: LM117 LM317-N

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Typical Applications (continued)

9.2.13 AC Voltage Regulator

In Figure 31, the top regulator is +6 V above the bottom regulator. It is clear that when the input rises above +6 V

plus the dropout voltage, only the top LM317-N regulates +6 V at the output. When the input falls below –6 V

minus the dropout voltage, only the bottom LM317-N regulates –6 V at the output. For regions where the output

is not clipped, there is no regulation taking place, so the output follows the input.

Figure 31. AC Voltage Regulator

9.2.14 12-V Battery Charger

The LM317-N can be used in a battery charger application shown in Figure 32, where the device maintains either

constant voltage or constant current mode depending on the current charge of the battery. To do this, the part

senses the voltage drop across the battery and delivers the maximum charging current necessary to charge the

battery. When the battery charge is low, there exists a voltage drop across the sense resistor RS, providing

constant current to the battery at that instant. As the battery approaches full charge, the potential drop across RS

approaches zero, reducing the current and maintaining the fixed voltage of the battery.

Use of RS allows low charging rates with fully charged battery.

Figure 32. 12-V Battery Charger

LM317S/NOPB Datasheet(PDF) 25 Page - Texas Instruments