NCV317 ON Semiconductor, NCV317 Datasheet - Page 7

• Manufacturer Part Number: NCV317
• Description: Positive Voltage Regulator
• Manufacturer: ON Semiconductor

Basic Circuit Operation
operation, the LM317 develops and maintains a nominal
1.25 V reference (V
terminals. This reference voltage is converted to a
programming current (I
constant current flows through R
represents an error term in the equation, the LM317 was
designed to control I
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.
voltage differential across the circuit which is important to
performance, and operation at high voltages with respect to
ground is possible.
Load Regulation
regulation, but a few precautions are needed to obtain
maximum performance. For best performance, the
programming resistor (R
the regulator as possible to minimize line drops which
effectively appear in series with the reference, thereby
degrading regulation. The ground end of R
near the load ground to provide remote ground sensing and
improve load regulation.
The LM317 is a 3−terminal floating regulator. In
The regulated output voltage is given by:
Since the current from the adjustment terminal (I
Since the LM317 is a floating regulator, it is only the
The LM317 is capable of providing extremely good load
V
Figure 19. Basic Circuit Configuration
in
V
ref
Adjust
= 1.25 V Typical
V out + V
LM317
ref
I
Adj
Adj
) between its output and adjustment
PROG
ref
1
to less than 100 mA and keep it
) should be connected as close to
1 )
V
) by R
V
ref
out
R 2
R 1
2
1
to ground.
+
(see Figure 17), and this
) I
R
R
I
2
1
PROG
Adj
2
R 2
APPLICATIONS INFORMATION
can be returned
V
V
out
out
LM317, NCV317
http://onsemi.com
Adj
)
7
External Capacitors
(C
impedance.
improve ripple rejection. This capacitor (C
ripple from being amplified as the output voltage is
increased. A 10 mF capacitor should improve ripple
rejection about 15 dB at 120 Hz in a 10 V application.
like any feedback circuit, certain values of external
capacitance can cause excessive ringing. An output
capacitance (C
aluminum electrolytic capacitor on the output swamps this
effect and insures stability.
Protection Diodes
it is sometimes necessary to add protection diodes to prevent
the capacitors from discharging through low current points
into the regulator.
protection diodes for output voltages in excess of 25 V or
high capacitance values (C
D
short circuit. Diode D
discharging through the IC during an output short circuit.
The combination of diodes D
discharging through the IC during an input short circuit.
Figure 20. Voltage Regulator with Protection Diodes
1
A 0.1 mF disc or 1.0 mF tantalum input bypass capacitor
The adjustment terminal may be bypassed to ground to
Although the LM317 is stable with no output capacitance,
When external capacitors are used with any IC regulator
Figure 18 shows the LM317 with the recommended
in
prevents C
) is recommended to reduce the sensitivity to input line
V
C
in
in
O
O
from discharging thru the IC during an input
) in the form of a 1.0 mF tantalum or 25 mF
Adjust
1N4002
LM317
D
2
1
R
protects against capacitor C
O
2
> 25 mF, C
1
and D
R
1
V
out
2
Adj
prevents C
C
Adj
D
> 10 mF). Diode
2
1N4002
Adj
+
) prevents
C
Adj
O
from
Adj