Datasheet
LM217L/LM317L Application information
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6 Application information
The LM317L provides an internal reference voltage of 1.25V between the output and
adjustments terminals. This is used to set a constant current flow across an external resistor
divider (see Figure 4.), giving an output voltage V
O
of:
V
O
= V
REF
(1 + R
2
/R
1
) + I
ADJ
R
2
The device was designed to minimize the term I
ADJ
(100µA max) and to maintain it very
constant with line and load changes. Usually, the error term I
ADJ
× R
2
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 is 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 R
1
(see Figure 4.) should be tied as close as possible to
the regulator, while the ground terminal of R
2
should be near the ground of the load to
provide remote ground sensing.