LM217L View Datasheet(PDF) - STMicroelectronics

Part Name

Description

MFG CO.

LM217L

Low current 1.2 to 37 V adjustable voltage regulators

STMicroelectronics 

LM217L, LM317L

6

Application information

Application information

The LM317L provides an internal reference voltage of 1.25 V between the output and

adjustments terminals. This is used to set a constant current flow across an external resistor

divider (see Figure 6.), giving an output voltage VO of:

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

The device was designed to minimize the term IADJ (100 µA 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 regulator

as the maximum input-to-output differential is not exceeded. Furthermore, programmable

regulators 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 Figure 6.) 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.

DocID2168 Rev 7

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