LM217L datasheet(5/13 Pages) STMICROELECTRONICS

5 / 13 page

LM217L/LM317L

5/13

APPLICATION INFORMATION

The LM317L provides an internal reference

voltage

1.25V

between

the

output

and

adjustments terminals. This is used to set a

constant current flow across an external resistor

divider (see fig. 4), giving an output voltage VO of:

VO = VREF (1 + R2/R1) + IADJ R2

The device was designed to minimize the term

IADJ (100µA max) and to maintain it very constant

with line and load changes. Usually, the error term

IADJ × R2 can be neglected. To obtain the previous

requirement, all the regulator quiescent current is

returned to the output terminal, imposing a

minimum load current condition. If the load is

insufficient, the output voltage will rise.

Since the LM317L is a floating regulator and

"sees" only the input-to-output differential voltage,

supplies of very high voltage with respect to

ground can be regulated as long as the maximum

input-to-output

differential

not

exceeded.

Furthermore, programmable regulator are easily

obtainable and, by connecting a fixed resistor

between the adjustment and output, the device

can be used as a precision current regulator. In

order to optimize the load regulation, the current

set resistor R1 (see fig. 4) should be tied as close

as possible to the regulator, while the ground

terminal of R2 should be near the ground of the

load to provide remote ground sensing.

Figure 6: Basic Adjustable Regulator

Figure 7: Voltage Regulator with Protection Diodes

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