LM317L Ver la hoja de datos (PDF) - Tiger Electronic
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LM317L Datasheet PDF : 14 Pages
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LM317
APPLICATION INFORMATION
1. Basic circuit operation
In operation, the LM317 develops a nominal 1.25V reference voltage, Vref, between
the output and adjustment terminal. The reference voltage is impressed across program
resistor R1 and, since the voltage is constant, a constant current I1 then flows through
the output set resistor R2, giving an output voltage of
Vout=Vref(1+R2/R1)+Iadj* (R2)
Since the 100µA current from the adjustment
terminal represents an error term, the LM317
was designed to minimize Iadj and make it very
constant with line and load changes. To do this,
all quiescent operating current is returned to the
output establishing a minimum load current
LLW 3 1 7 L
VIN
VOU
ADJ
I1
VRE
I AD
R2
J
R1
VOU
requirement. If there is insufficient load on the
output, the output will rise.
Figure: Basic circuit configuration
2. Load Regulation
The LM317 is capable of providing extremely good load regulation, but a few
precautions are needed to obtain maximum
performance. For best performance, the
programming resistor (R1) should be connected
VIN
LMW31371 L7 L
VIN
VOUT
ADJ
as close to the regulator as possible to
minimize line drops which effectively appear in
Rs
VOUT
R1
240
series with the reference, thereby degrading
regulation. The ground end of R2 can be
R2
returned near the load ground to provide remote
ground sensing and improve load regulation
Regulator with line resistance
in output lead
3.External capacitors
A 0.1µF disc or 1.0µF tantalum input bypass capacitor (Cin) is recommended to
reduce the sensitivity to input line impedance.
The adjustment terminal may be bypassed to ground to improve ripple rejection.
This capacitor (Cadj) prevents ripple from being amplified as the output voltage is
increased. A 10µF capacitor should improve ripple rejection about 15dB at 120Hz in a
4/14
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