LM317L 查看數據表（PDF） - ON Semiconductor
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LM317L Datasheet PDF : 12 Pages
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LM317L, NCV317LB
1.5
1.0
CL = 1.0 mF;
0.5
CAdj = 10 mF
0
-0.5
-1.0
Vout = 10 V
IL = 50 mA
-1.5
TJ = 25°C
1.0
0.5
CL = 0;
Without CAdj
Vin
0
0
10
20
30
40
t, TIME (ms)
Figure 16. Line Transient Response
0.3
0.2 CL = 1 mF; CAdj = 10 mF
0.1
0
-0.1
-0.2
CL = 0.3 mF; CAdj = 10 mF
-0.3
Vin = 15 V
Vout = 10 V
INL = 50 mA
TJ = 25°C
100
50
IL
0
0
10
20
30
40
t, TIME (ms)
Figure 17. Load Transient Response
APPLICATIONS INFORMATION
Basic Circuit Operation
The LM317L is a 3-terminal floating regulator. In
operation, the LM317L develops and maintains a nominal
1.25 V reference (Vref) between its output and adjustment
terminals. This reference voltage is converted to a
programming current (IPROG) by R1 (see Figure 13), and this
constant current flows through R2 to ground. The regulated
output voltage is given by:
Vout = Vref (1 +
R2
R1
) + IAdj R2
Since the current from the adjustment terminal (IAdj)
represents an error term in the equation, the LM317L was
designed to control IAdj to less than 100 mA and keep it
constant. To do this, all quiescent operating current is
returned to the output terminal. This imposes the
requirement for a minimum load current. If the load current
is less than this minimum, the output voltage will rise.
Since the LM317L is a floating regulator, it is only the
voltage differential across the circuit which is important to
performance, and operation at high voltages with respect to
ground is possible.
Vin
LM317L
Adjust
Vout
Vref
+
R1
IPROG
Vout
IAdj
R2
Vref = 1.25 V Typical
Load Regulation
The LM317L 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 as close to
the regulator as possible to minimize line drops which
effectively appear in series with the reference, thereby
degrading regulation. The ground end of R2 can be returned
near the load ground to provide remote ground sensing and
improve load regulation.
External Capacitors
A 0.1 mF disc or 1.0 mF 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 10ĂmF capacitor should improve ripple
rejection about 15 dB at 120 Hz in a 10 V application.
Although the LM317L is stable with no output
capacitance, like any feedback circuit, certain values of
external capacitance can cause excessive ringing. An output
capacitance (CO) in the form of a 1.0 mF tantalum or 25 mF
aluminum electrolytic capacitor on the output swamps this
effect and insures stability.
Figure 18. Basic Circuit Configuration
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