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LM117, LM317-N Wide Temperature Three-Pin Adjustable Regulator
1 Features 3 Description
The LM117 and LM317-N series of adjustable 3-pin
1• Typ. 0.1% Load Regulation positive voltage regulators are capable of supplying in
• Typ. 0.01%/V Line Regulation excess of 1.5 A over a 1.25-V to 37-V output range
• 1.5-A Output Current and a wide temperature range. They are
exceptionally easy to use and require only two
• Adjustable Output Down to 1.25 V external resistors to set the output voltage. Further,
• Current Limit Constant With Temperature both line and load regulation are better than standard
• 80-dB Ripple Rejection fixed regulators.
• Short-Circuit Protected Output The LM117 and LM317-N offer full overload
•−55°C to 150°C Operating Temperature Range protection such as current limit, thermal overload
(LM117) protection and safe area protection. All overload
protection circuitry remains fully functional even if the
adjustment terminal is disconnected.
2 Applications
• Automotive LED Lighting Typically, no capacitors are needed unless the device
is situated more than 6 inches from the input filter
• Battery Chargers capacitors, in which case an input bypass is needed.
• Post Regulation for Switching Supplies An optional output capacitor can be added to improve
• Constant Current Regulators transient response. The adjustment terminal can be
bypassed to achieve very high ripple rejection ratios
• Microprocessor Supplies that are difficult to achieve with standard 3-terminal
regulators.
Typical Application Because the regulator is floating and detects only the
input-to-output differential voltage, supplies of several
hundred volts can be regulated as long as the
maximum input-to-output differential is not exceeded.
That is, avoid short-circuiting the output.
By connecting a fixed resistor between the
adjustment pin and output, the LM117 and LM317-N
can be also used as a precision current regulator.
Supplies with electronic shutdown can be achieved
by clamping the adjustment terminal to ground, which
programs the output to 1.25 V where most loads draw
little current.
For applications requiring greater output current, see
data sheets for LM150 series (3 A), SNVS772, and
LM138 series (5 A), SNVS771. For the negative
complement, see LM137 (SNVS778) series data
*Needed if device is more than 6 inches from filter sheet.
capacitors.
†Optional—improves transient response Device Information(1)
PART NUMBER PACKAGE BODY SIZE (NOM)
TO-3 (2) 38.94 mm x 25.40 mm
†† LM117 TO (3) 8.255 mm × 8.255 mm
TO-3 (2) 38.94 mm x 25.40 mm
TO-220 (3) 14.986 mm × 10.16 mm
TO-263 (3) 10.18 mm × 8.41 mm
LM317-N SOT-223 (4) 6.50 mm × 3.50 mm
TO (3) 8.255 mm × 8.255 mm
TO-252 (3) 6.58 mm × 6.10 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
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Table of Contents
8.3 Feature Description................................................. 13
1 Features.................................................................. 18.4 Device Functional Modes........................................ 13
2 Applications ........................................................... 19 Application and Implementation ........................ 15
3 Description............................................................. 19.1 Application Information............................................ 15
4 Revision History..................................................... 29.2 Typical Applications ................................................ 15
5 Device Comparison Table..................................... 310 Power Supply Recommendations ..................... 27
6 Pin Configuration and Functions......................... 311 Layout................................................................... 27
7 Specifications......................................................... 511.1 Layout Guidelines ................................................. 27
7.1 Absolute Maximum Ratings ...................................... 511.2 Layout Example .................................................... 27
7.2 ESD Ratings.............................................................. 511.3 Thermal Considerations........................................ 28
7.3 Recommended Operating Conditions....................... 512 Device and Documentation Support ................. 35
7.4 Thermal Information, LM117..................................... 512.1 Documentation Support ........................................ 35
7.5 Thermal Information, LM317-N................................. 612.2 Related Links ........................................................ 35
7.6 LM117 Electrical Characteristics............................... 612.3 Community Resources.......................................... 35
7.7 LM317-N Electrical Characteristics........................... 712.4 Trademarks........................................................... 35
7.8 Typical Characteristics.............................................. 812.5 Electrostatic Discharge Caution............................ 35
8 Detailed Description............................................ 11 12.6 Glossary................................................................ 35
8.1 Overview................................................................. 11 13 Mechanical, Packaging, and Orderable
8.2 Functional Block Diagram....................................... 12 Information ........................................................... 35
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision O (January 2014) to Revision P Page
• Added, updated, or renamed the following sections: Description;Pin Configuration and Functions;Specifications;
ESD Ratings table; Application and Implementation;Power Supply Recommendations;Layout;Mechanical,
Packaging, and Ordering Information .................................................................................................................................... 1
• Removed information regarding LM317A, formerly part of this data sheet. LM317A can now be found in the TI
catalog under literature number SNVSAC2 ........................................................................................................................... 1
Changes from Revision N (August 2013) to Revision O Page
• Deleted MDT Package (over Full Operating Temperature Range) ....................................................................................... 7
• Changed Current Limit MIN from 0.112 to 0.15 and TYP from 0.3 to 0.4 for (VIN – VOUT) = 40 V in the LM317A
and LM317-N Electrical Characteristics Section .................................................................................................................... 7
• Deleted MDT Package ........................................................................................................................................................... 7
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5 Device Comparison Table
Table 1. LM317 Family Options
PART NUMBER TEMPERATURE DESCRIPTION PRODUCT FOLDER
LM317-N 0°C to 125°C 40-V, 1.5-A Catalog device Click here
LM317A −40°C to 125°C 40-V, 1.5-A Industrial device Click here
LM317HV 0°C to 125°C 60-V, 1.5-A Catalog device Click here
LM317L-N −40°C to 125°C 40-V, 0.1-A, Industrial device Click here
LM117 −55°C to 150°C 40-V, 1.5-A Extended-temperature device Click here
LM117HV −55°C to 150°C 60-V, 1.5-A Extended-temperature device Click here
LM117HVQML −55°C to 125°C 60-V, 1.5-A Military-grade device per spec MIL-PRF-38535 Click here
LM117HVQML-SP −55°C to 125°C 60-V, 1.5-A Space-grade device Click here
LM117JAN −55°C to 125°C 40-V, 1.5-A Military-grade device per spec MIL-PRF-38510 Click here
LM117QML −55°C to 125°C 40-V, 1.5-A Military-grade device per spec MIL-PRF-38535 Click here
LM117QML-SP −55°C to 125°C 40-V, 1.5-A Space-grade device Click here
6 Pin Configuration and Functions
NDS Metal Can Package NDT Metal Can Package
2-Pin TO-3 3-Pin TO
Bottom View Bottom View
Case is Output
Case is Output
Pin Functions, Metal Can Packages
PIN I/O DESCRIPTION
NAME TO-3 TO
ADJ 1 2 — Adjust pin
VOUT CASE 3, CASE O Output voltage pin for the regulator
VIN 2 1 I Input voltage pin for the regulator
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KTT Surface-Mount Package DCY Surface-Mount Package
3-Pin DDPAK/TO-263 4-Pin SOT-223
Top View Top View
NDP Surface-Mount Package
NDE Plastic Package 3-Pin TO-252
3-Pin TO-220 Front View
Front View
Pin Functions
PIN I/O DESCRIPTION
NAME TO-263 TO-220 SOT-223 TO-252
ADJ 1 1 1 1 — Adjust pin
VOUT 2, TAB 2, TAB 2, 4 2, TAB O Output voltage pin for the regulator
VIN 3 3 3 3 I Input voltage pin for the regulator
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7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)(1)(2)
MIN MAX UNIT
Power dissipation Internally Limited
Input-output voltage differential −0.3 40 V
Metal package (soldering, 10 seconds) 300 °C
Lead temperature Plastic package (soldering, 4 seconds) 260 °C
Storage temperature, Tstg −65 150 °C
(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
7.2 ESD Ratings VALUE UNIT
Electrostatic
V(ESD) Human-body model (HBM)(1) ±3000 V
discharge
(1) Manufacturing with less than 500-V HBM is possible with the necessary precautions. Pins listed as ±3000 V may actually have higher
performance.
7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted) MIN MAX UNIT
Operating temperature (LM117) −55 150 °C
Operating temperature (LM317-N) 0 125 °C
7.4 Thermal Information, LM117 LM117
NDS NDT
THERMAL METRIC(1) UNIT
(TO-3) (TO)
2 PINS 3 PINS
RθJA Junction-to-ambient thermal resistance(2) 39 186 °C/W
RθJC(top) Junction-to-case (top) thermal resistance 2 21 °C/W
(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
(2) No heatsink.
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7.5 Thermal Information, LM317-N LM317-N
KTT NDE DCY NDT NDP
THERMAL METRIC(1)(2) UNIT
(TO-263) (TO-220) (SOT-223) (TO) (TO-252)
3 PINS 3 PINS 4 PINS 3 PINS 3 PINS
RθJA Junction-to-ambient thermal resistance 41.0 23.3 59.6 186(3) 54 °C/W
RθJC(top) Junction-to-case (top) thermal resistance 43.6 16.2 39.3 21 51.3 °C/W
RθJB Junction-to-board thermal resistance 23.6 4.9 8.4 — 28.6 °C/W
ψJT Junction-to-top characterization parameter 10.4 2.7 1.8 — 3.9 °C/W
ψJB Junction-to-board characterization parameter 22.6 4.9 8.3 — 28.1 °C/W
RθJC(bot) Junction-to-case (bottom) thermal resistance 0.9 1.1 — — 0.9 °C/W
(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
(2) When surface mount packages are used (SOT-223, TO-252), the junction to ambient thermal resistance can be reduced by increasing
the PCB copper area that is thermally connected to the package. See Heatsink Requirements for heatsink techniques.
(3) No heatsink
7.6 LM117 Electrical Characteristics
Some specifications apply over full Operating Temperature Range as noted. Unless otherwise specified, TJ= 25°C, VIN −
VOUT = 5 V, and IOUT = 10 mA.(1)(2)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
3 V ≤(VIN −VOUT)≤40 V,
Reference voltage 1.2 1.25 1.3 V
10 mA ≤IOUT ≤IMAX(1) (over full operating temperature range)
TJ= 25°C 0.01 0.02
Line regulation 3 V ≤(VIN −VOUT)≤40 V(3) %/V
over full operating 0.02 0.05
temperature range
TJ= 25°C 0.1% 0.3%
Load regulation 10 mA ≤IOUT ≤IMAX(1)(3) over full operating 0.3% 1%
temperature range
Thermal regulation 20-ms pulse 0.03 0.07 %/W
Adjustment pin current over full operating temperature range 50 100 μA
10 mA ≤IOUT ≤IMAX(1)
Adjustment pin current change 0.2 5 μA
3 V ≤(VIN −VOUT)≤40 V (over full operating temperature range)
Temperature stability TMIN ≤TJ≤TMAX (over full operating temperature range) 1%
Minimum load current (VIN −VOUT) = 40 V (over full operating temperature range) 3.5 5 mA
TO-3 Package (over full 1.5 2.2 3.4
operating temperature range)
(VIN −VOUT)≤15 V A
TO-39 Package (over full 0.5 0.8 1.8
Current limit operating temperature range)
TO-3 package 0.3 0.4
(VIN −VOUT) = 40 V A
TO-39 package 0.15 0.2
RMS output noise, % of VOUT 10 Hz ≤f≤10 kHz 0.003%
VOUT = 10 V, f = 120 Hz, CADJ = 0 μF (over full operating 65 dB
temperature range)
Ripple rejection ratio VOUT = 10 V, f = 120 Hz, CADJ = 10 μF (over full operating 66 80 dB
temperature range)
Long-term stability TJ= 125°C, 1000 hrs 0.3% 1%
(1) IMAX = 1.5 A for the NDS (TO-3), NDE (TO-220), and KTT (TO-263) packages. IMAX = 1.0 A for the DCY (SOT-223) package.
IMAX = 0.5 A for the NDT (TO) and NDP (TO-252) packages. Device power dissipation (PD) is limited by ambient temperature (TA),
device maximum junction temperature (TJ), and package thermal resistance (θJA). The maximum allowable power dissipation at any
temperature is : PD(MAX) = ((TJ(MAX) – TA) / θJA). All Min. and Max. limits are ensured to TI's Average Outgoing Quality Level (AOQL).
(2) Specifications and availability for military and space grades of LM117/883 can be found in the LM117QML data sheet (SNVS356).
Specifications and availability for military and space grades of LM117 can be found in the LM117JAN data sheet (SNVS365).
(3) Regulation is measured at a constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to
heating effects are covered under the specifications for thermal regulation.
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7.7 LM317-N Electrical Characteristics(1)
Some specifications apply over full Operating Temperature Range as noted. Unless otherwise specified, TJ= 25°C, VIN −
VOUT = 5 V, and IOUT = 10 mA.
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
TJ= 25°C 1.25 V
3 V ≤(VIN −VOUT)≤40 V,
Reference voltage 10 mA ≤IOUT ≤IMAX(1) (over Full Operating Temperature 1.2 1.25 1.3 V
Range) TJ= 25°C 0.01 0.04
Line regulation 3V ≤(VIN −VOUT)≤40 V(2) %/V
(over full operating 0.02 0.07
temperature range)
TJ= 25°C 0.1% 0.5%
Load regulation 10 mA ≤IOUT ≤IMAX(1)(2) (over full operating 0.3% 1.5%
temperature range)
Thermal regulation 20-ms pulse 0.04 0.07 %/W
Adjustment pin current (over full operating temperature range) 50 100 μA
10 mA ≤IOUT ≤IMAX(1) (over full operating
Adjustment pin current change 0.2 5 μA
3V ≤(VIN −VOUT)≤40V temperature range)
(over full operating
Temperature stability TMIN ≤TJ≤TMAX 1%
temperature range)
(over full operating
Minimum load current (VIN −VOUT) = 40 V 3.5 10 mA
temperature range)
TO-3, TO-263 Packages
(over full operating 1.5 2.2 3.4
temperature range)
SOT-223, TO-220
Packages (over full
(VIN −VOUT)≤15 V 1.5 2.2 3.4 A
operating temperature
range)
Current limit TO, TO-252 Package (over
full operating temperature 0.5 0.8 1.8
range)
TO-3, TO-263 packages 0.15 0.4
(VIN −VOUT) = 40 V SOT-223, TO-220 packages 0.15 0.4 A
TO, TO-252 package 0.075 0.2
RMS output noise, % of VOUT 10 Hz ≤f≤10 kHz 0.003%
VOUT = 10 V, f = 120 Hz, CADJ = 0 μF (over full operating 65 dB
temperature range)
Ripple rejection ratio VOUT = 10V, f = 120 Hz, CADJ = 10 μF (over full operating 66 80 dB
temperature range)
Long-term stability TJ= 125°C, 1000 hrs 0.3% 1%
(1) IMAX = 1.5 A for the NDS (TO-3), NDE (TO-220), and KTT (TO-263) packages. IMAX = 1.0 A for the DCY (SOT-223) package.
IMAX = 0.5 A for the NDT (TO) and NDP (TO-252) packages. Device power dissipation (PD) is limited by ambient temperature (TA),
device maximum junction temperature (TJ), and package thermal resistance (θJA). The maximum allowable power dissipation at any
temperature is : PD(MAX) = ((TJ(MAX) – TA) / θJA). All Min. and Max. limits are ensured to TI's Average Outgoing Quality Level (AOQL).
(2) Regulation is measured at a constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to
heating effects are covered under the specifications for thermal regulation.
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7.8 Typical Characteristics
Output Capacitor = 0 μF, unless otherwise noted.
Figure 1. Load Regulation Figure 2. Current Limit
Figure 4. Dropout Voltage
Figure 3. Adjustment Current
Figure 5. VOUT vs VIN, VOUT = VREF Figure 6. VOUT vs VIN, VOUT = 5 V
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Typical Characteristics (continued)
Output Capacitor = 0 μF, unless otherwise noted.
Figure 7. Temperature Stability Figure 8. Minimum Operating Current
Figure 9. Ripple Rejection Figure 10. Ripple Rejection
Figure 12. Output Impedance
Figure 11. Ripple Rejection
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Typical Characteristics (continued)
Output Capacitor = 0 μF, unless otherwise noted.
Figure 13. Line Transient Response Figure 14. Load Transient Response
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8 Detailed Description
8.1 Overview
In operation, the LM317-N develops a nominal 1.25-V reference voltage, VREF, between the output and
adjustment terminal. The reference voltage is impressed across program resistor R1 and, because the voltage is
constant, a constant current I1then flows through the output set resistor R2, giving an output voltage calculated
by Equation 1:
(1)
Figure 15. Setting the VOUT Voltage
Because the 100-μA current from the adjustment terminal represents an error term, the LM317-N 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 requirement. If there is insufficient load on the
output, the output will rise.
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8.3 Feature Description
8.3.1 Load Regulation
The LM317-N is capable of providing extremely good load regulation but a few precautions are needed to obtain
maximum performance. The current set resistor, R1, must be connected near the output terminal of the regulator
rather than near the load. If R1 is placed too far from the output terminal, then the increased trace resistance, RS,
will cause an error voltage drop in the adjustment loop and degrade load regulation performance. Therefore, R1
must be placed as close as possible to the output terminal to minimize RSand maximize load regulation
performance.
Figure 16 shows the effect of the trace resistance, RS, when R1 is placed far from the output terminal of the
regulator. It is clear that RSwill cause an error voltage drop especially during higher current loads, so it is
important to minimize the RStrace resistance by keeping R1 close to the regulator output terminal.
Figure 16. Regulator With Line Resistance in Output Lead
With the TO-3 package, it is easy to minimize the resistance from the case to the set resistor, by using two
separate leads to the case. However, with the TO package, care must be taken to minimize the wire length of the
output lead. The ground of R2 can be returned near the ground of the load to provide remote ground sensing
and improve load regulation.
8.4 Device Functional Modes
8.4.1 External Capacitors
An input bypass capacitor is recommended. A 0.1-μF disc or 1-μF solid tantalum on the input is suitable input
bypassing for almost all applications. The device is more sensitive to the absence of input bypassing when
adjustment or output capacitors are used, but the above values will eliminate the possibility of problems.
The adjustment terminal can be bypassed to ground on the LM317-N to improve ripple rejection. This bypass
capacitor prevents ripple from being amplified as the output voltage is increased. With a 10-μF bypass capacitor,
80-dB ripple rejection is obtainable at any output level. Increases over 10 μF do not appreciably improve the
ripple rejection at frequencies above 120 Hz. If the bypass capacitor is used, it is sometimes necessary to
include protection diodes to prevent the capacitor from discharging through internal low current paths and
damaging the device.
In general, the best type of capacitors to use is solid tantalum. Solid tantalum capacitors have low impedance
even at high frequencies. Depending upon capacitor construction, it takes about 25 μF in aluminum electrolytic to
equal 1-μF solid tantalum at high frequencies. Ceramic capacitors are also good at high frequencies. However,
some types have a large decrease in capacitance at frequencies around 0.5 MHz. For this reason, 0.01-μF disc
may seem to work better than a 0.1-μF disc as a bypass.
Although the LM317-N is stable with no output capacitors, like any feedback circuit, certain values of external
capacitance can cause excessive ringing. This occurs with values between 500 pF and 5000 pF. A 1-μF solid
tantalum (or 25-μF aluminum electrolytic) on the output swamps this effect and insures stability. Any increase of
the load capacitance larger than 10 μF will merely improve the loop stability and output impedance.
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Device Functional Modes (continued)
8.4.2 Protection Diodes
When external capacitors are used with any IC regulator, it is sometimes necessary to add protection diodes to
prevent the capacitors from discharging through low current points into the regulator. Most 10-μF capacitors have
low enough internal series resistance to deliver 20-A spikes when shorted. Although the surge is short, there is
enough energy to damage parts of the IC.
When an output capacitor is connected to a regulator and the input is shorted, the output capacitor will discharge
into the output of the regulator. The discharge current depends on the value of the capacitor, the output voltage
of the regulator, and the rate of decrease of VIN. In the LM317-N, this discharge path is through a large junction
that is able to sustain 15-A surge with no problem. This is not true of other types of positive regulators. For
output capacitors of 25 μF or less, there is no need to use diodes.
The bypass capacitor on the adjustment terminal can discharge through a low current junction. Discharge occurs
when either the input, or the output, is shorted. Internal to the LM317-N is a 50-Ωresistor which limits the peak
discharge current. No protection is needed for output voltages of 25 V or less and 10-μF capacitance. Figure 17
shows an LM317-N with protection diodes included for use with outputs greater than 25 V and high values of
output capacitance.
D1 protects against C1
D2 protects against C2
Figure 17. Regulator With Protection Diodes
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9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers must
validate and test their design implementation to confirm system functionality.
9.1 Application Information
The LM117 and LM317-N are versatile, high performance, linear regulators with high accuracy and a wide
temperature range. An output capacitor can be added to further improve transient response, and the ADJ pin can
be bypassed to achieve very high ripple-rejection ratios. Its functionality can be utilized in many different
applications that require high performance regulation, such as battery chargers, constant current regulators, and
microprocessor supplies.
9.2 Typical Applications
9.2.1 1.25-V to 25-V Adjustable Regulator
The LM117 can be used as a simple, low-dropout regulator to enable a variety of output voltages needed for
demanding applications. By using an adjustable R2 resistor, a variety of output voltages can be made possible
as shown in Figure 18.
NOTE: Full output current not available at high input-output voltages
*Needed if device is more than 6 inches from filter capacitors.
†Optional—improves transient response. Output capacitors in the range of 1 μF to 1000 μF of aluminum or tantalum
electrolytic are commonly used to provide improved output impedance and rejection of transients.
Figure 18. 1.25-V to 25-V Adjustable Regulator
9.2.1.1 Design Requirements
The device component count is very minimal, employing two resistors as part of a voltage divider circuit and an
output capacitor for load regulation. An input capacitor is needed if the device is more than 6 inches from filter
capacitors. An optional bypass capacitor across R2 can also be used to improve PSRR.
9.2.1.2 Detailed Design Procedure
The output voltage is set based on the selection of the two resistors, R1 and R2, as shown in Figure 18. For
details on capacitor selection, refer to External Capacitors.
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Typical Applications (continued)
9.2.1.3 Application Curve
As shown in Figure 19, VOUT will rise with VIN minus some dropout voltage. This dropout voltage during startup
will vary with ROUT.
Figure 19. VOUT vs VIN, VOUT = 5V
9.2.2 5-V Logic Regulator With Electronic Shutdown
Figure 20 shows a variation of the 5-V output regulator application uses the L117 along with an NPN transistor to
provide shutdown control. The NPN will either block or sink the current from the ADJ pin by responding to the
TTL pin logic. When TTL is pulled high, the NPN is on and pulls the ADJ pin to GND, and the LM117 outputs
about
1.25 V. When TTL is pulled low, the NPN is off and the regulator outputs according to the programmed
adjustable voltage.
NOTE: Min. output ≊1.2 V
Figure 20. 5-V Logic Regulator With Electronic Shutdown
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Typical Applications (continued)
9.2.3 Slow Turnon 15-V Regulator
An application of LM117 includes a PNP transistor with a capacitor to implement slow turnon functionality (see
Figure 21). As VIN rises, the PNP sinks current from the ADJ rail. The output voltage at start up is the addition of
the 1.25-V reference plus the drop across the base to emitter. While this is happening, the capacitor begins to
charge and eventually opens the PNP. At this point, the device functions normally, regulating the output at 15 V.
A diode is placed between C1 and VOUT to provide a path for the capacitor to discharge. Such controlled turnon
is useful for limiting the in-rush current.
Figure 21. Slow Turnon 15-V Regulator
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R3
267
1%
R2
1.5 k
1%
R1
2 k
5%
C1
0.1 µF
LM329
VIN
15 V VOUT
10 V
VIN VOUT
LM117
ADJ
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LM117
,
LM317-N
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Typical Applications (continued)
9.2.4 Adjustable Regulator With Improved Ripple Rejection
To improve ripple rejection, a capacitor is used to bypass the ADJ pin to GND (see Figure 22). This is used to
smooth output ripple by cleaning the feedback path and stopping unnecessary noise from being fed back into the
device, propagating the noise.
NOTE: †Solid tantalum
*Discharges C1 if output is shorted to ground
Figure 22. Adjustable Regulator With Improved Ripple Rejection
9.2.5 High Stability 10-V Regulator
Using a high stability shunt voltage reference in the feedback path, such as the LM329, provides damping
necessary for a stable, low noise output (see Figure 23).
Figure 23. High Stability 10-V Regulator
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three LM195 devices in parallel
LM117
LM117
,
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Typical Applications (continued)
9.2.6 High-Current Adjustable Regulator
Using the LM195 power transistor in parallel with the LM117 can increase the maximum possible output load
current (see Figure 24). Sense resistor R1 provides the 0.6 V across base to emitter to turn on the PNP. This on
switch allows current to flow, and the voltage drop across R3 drives three LM195 power transistors designed to
carry an excess of 1 A each.
NOTE
The selection of R1 determines a minimum load current for the PNP to turn on. The higher
the resistor value, the lower the load current must be before the transistors turn on.
NOTE: ‡Optional—improves ripple rejection
†Solid tantalum
*Minimum load current = 30 mA
Figure 24. High-Current Adjustable Regulator
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Typical Applications (continued)
9.2.7 Emitter-Follower Current Amplifier
The LM117 is used as a constant current source in the emitter follower circuit (see Figure 25). The LM195 power
transistor is being used as a current gain amplifier, boosting the INPUT current. The LM117 provides a stable
current bias than just using a resistor.
Figure 25. Emitter-Follower Current Amplifier
9.2.8 1-A Current Regulator
A simple, fixed current regulator can be made by placing a resistor between the VOUT and ADJ pins of the LM117
(see Figure 26). By regulating a constant 1.25 V between these two terminals, a constant current is delivered to
the load.
Figure 26. 1-A Current Regulator
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