LM79XX Series
3-Terminal Negative Regulators
General Description
The LM79XX series of 3-terminal regulators is available with
fixed output voltages of −5V, −12V, and −15V. These devices
need only one external component—a compensation ca-
pacitor at the output. The LM79XX series is packaged in the
TO-220 power package and is capable of supplying 1.5A of
output current.
These regulators employ internal current limiting safe area
protection and thermal shutdown for protection against vir-
tually all overload conditions.
Low ground pin current of the LM79XX series allows output
voltage to be easily boosted above the preset value with a
resistor divider. The low quiescent current drain of these
devices with a specified maximum change with line and load
ensures good regulation in the voltage boosted mode.
For applications requiring other voltages, see LM137
datasheet.
Features
nThermal, short circuit and safe area protection
nHigh ripple rejection
n1.5A output current
n4% tolerance on preset output voltage
Connection Diagrams Typical Applications
*Required if regulator is separated from filter capacitor by
more than 3". For value given, capacitor must be solid
tantalum. 25µF aluminum electrolytic may be substituted.
†Required for stability. For value given, capacitor must be
solid tantalum. 25µF aluminum electrolytic may be substi-
tuted. Values given may be increased without limit.
For output capacitance in excess of 100µF, a high current
diode from input to output (1N4001, etc.) will protect the
regulator from momentary input shorts.
TO-220 Package
DS007340-14
Front View
Order Number LM7905CT, LM7912CT or LM7915CT
See NS Package Number TO3B
Fixed Regulator
DS007340-3
September 2001
LM79XX Series 3-Terminal Negative Regulators
© 2001 National Semiconductor Corporation DS007340 www.national.com
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Voltage
(V
o
= −5V) −25V
(V
o
= −12V and −15V) −35V
Input-Output Differential
(V
o
= −5V) 25V
(V
o
= −12V and −15V) 30V
Power Dissipation (Note 2) Internally Limited
Operating Junction Temperature Range 0˚C to +125˚C
Storage Temperature Range −65˚C to +150˚C
Lead Temperature (Soldering, 10 sec.) 230˚C
Electrical Characteristics
Conditions unless otherwise noted: I
OUT
= 500mA, C
IN
= 2.2µF, C
OUT
= 1µF, 0˚C ≤T
J
≤+125˚C, Power Dissipation ≤1.5W.
Part Number LM7905C Units
Output Voltage −5V
Input Voltage (unless otherwise specified) −10V
Symbol Parameter Conditions Min Typ Max
V
O
Output Voltage T
J
= 25˚C −4.8 −5.0 −5.2 V
5mA ≤I
OUT
≤1A, −4.75 −5.25 V
P≤15W (−20 ≤V
IN
≤−7) V
∆V
O
Line Regulation T
J
= 25˚C, (Note 3) 8 50 mV
(−25 ≤V
IN
≤−7) V
215mV
(−12 ≤V
IN
≤−8) V
∆V
O
Load Regulation T
J
= 25˚C, (Note 3)
5mA ≤I
OUT
≤1.5A 15 100 mV
250mA ≤I
OUT
≤750mA 5 50 mV
I
Q
Quiescent Current T
J
= 25˚C 1 2 mA
∆I
Q
Quiescent Current With Line 0.5 mA
Change (−25 ≤V
IN
≤−7) V
With Load, 5mA ≤I
OUT
≤1A 0.5 mA
V
n
Output Noise Voltage T
A
= 25˚C, 10Hz ≤f≤100Hz 125 µV
Ripple Rejection f = 120Hz 54 66 dB
(−18 ≤V
IN
≤−8) V
Dropout Voltage T
J
= 25˚C, I
OUT
= 1A 1.1 V
I
OMAX
Peak Output Current T
J
= 25˚C 2.2 A
Average Temperature I
OUT
= 5mA, 0.4 mV/˚C
Coefficient of 0 C ≤T
J
≤100˚C
Output Voltage
Electrical Characteristics
Conditions unless otherwise noted: I
OUT
= 500mA, C
IN
= 2.2µF, C
OUT
= 1µF, 0˚C ≤T
J
≤+125˚C, Power Dissipation ≤1.5W.
Part Number LM7912C LM7915C Units
Output Voltage −12V −15V
Input Voltage (unless otherwise specified) −19V −23V
Symbol Parameter Conditions Min Typ Max Min Typ Max
V
O
Output Voltage T
J
= 25˚C −11.5 −12.0 −12.5 −14.4 −15.0 −15.6 V
5mA ≤I
OUT
≤1A, −11.4 −12.6 −14.25 −15.75 V
P≤15W (−27 ≤V
IN
≤−14.5) (−30 ≤V
IN
≤−17.5) V
∆V
O
Line Regulation T
J
= 25˚C, (Note 3) 5 80 5 100 mV
(−30 ≤V
IN
≤−14.5) (−30 ≤V
IN
≤−17.5) V
3 30 3 50 mV
(−22 ≤V
IN
≤−16) (−26 ≤V
IN
≤−20) V
∆V
O
Load Regulation T
J
= 25˚C, (Note 3)
LM79XX Series
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Electrical Characteristics (Continued)
Conditions unless otherwise noted: I
OUT
= 500mA, C
IN
= 2.2µF, C
OUT
= 1µF, 0˚C ≤T
J
≤+125˚C, Power Dissipation ≤1.5W.
Part Number LM7912C LM7915C Units
Output Voltage −12V −15V
Input Voltage (unless otherwise specified) −19V −23V
Symbol Parameter Conditions Min Typ Max Min Typ Max
5mA ≤I
OUT
≤1.5A 15 200 15 200 mV
250mA ≤I
OUT
≤750mA 5 75 5 75 mV
I
Q
Quiescent Current T
J
= 25˚C 1.5 3 1.5 3 mA
∆I
Q
Quiescent Current With Line 0.5 0.5 mA
Change (−30 ≤V
IN
≤−14.5) (−30 ≤V
IN
≤−17.5) V
With Load, 5mA ≤I
OUT
≤1A 0.5 0.5 mA
V
n
Output Noise Voltage T
A
= 25˚C, 10Hz ≤f≤100Hz 300 375 µV
Ripple Rejection f = 120 Hz 54 70 54 70 dB
(−25 ≤V
IN
≤−15) (−30 ≤V
IN
≤−17.5) V
Dropout Voltage T
J
= 25˚C, I
OUT
= 1A 1.1 1.1 V
I
OMAX
Peak Output Current T
J
= 25˚C 2.2 2.2 A
Average Temperature I
OUT
= 5mA, −0.8 −1.0 mV/˚C
Coefficient of 0 C ≤T
J
≤100˚C
Output Voltage
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but do not guarantee Specific Performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: Refer to Typical Performance Characteristics and Design Considerations for details.
Note 3: Regulation is measured at a constant junction temperature by pulse testing with a low duty cycle. Changes in output voltage due to heating effects must
be taken into account.
Design Considerations
The LM79XX fixed voltage regulator series has thermal
overload protection from excessive power dissipation, inter-
nal short circuit protection which limits the circuit’s maximum
current, and output transistor safe-area compensation for
reducing the output current as the voltage across the pass
transistor is increased.
Although the internal power dissipation is limited, the junc-
tion temperature must be kept below the maximum specified
temperature (125˚C) in order to meet data sheet specifica-
tions. To calculate the maximum junction temperature or
heat sink required, the following thermal resistance values
should be used:
Typ Max Typ Max
Package θ
JC
θ
JC
θ
JA
θ
JA
˚C/W ˚C/W ˚C/W ˚C/W
TO-220 3.0 5.0 60 40
Solving for T
J
:
T
J
=T
A
+P
D
(θ
JC
+θ
CA
)or
=T
A
+P
D
θ
JA
(without heat sink)
Where:
T
J
= Junction Temperature
T
A
= Ambient Temperature
P
D
= Power Dissipation
θ
JA
= Junction-to-Ambient Thermal Resistance
θ
JC
= Junction-to-Case Thermal Resistance
θ
CA
= Case-to-Ambient Thermal Resistance
θ
CS
= Case-to-Heat Sink Thermal Resistance
θ
SA
= Heat Sink-to-Ambient Thermal Resistance
LM79XX Series
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Typical Applications
Bypass capacitors are necessary for stable operation of the
LM79XX series of regulators over the input voltage and
output current ranges. Output bypass capacitors will improve
the transient response by the regulator.
The bypass capacitors, (2.2µF on the input, 1.0µF on the
output) should be ceramic or solid tantalum which have good
high frequency characteristics. If aluminum electrolytics are
used, their values should be 10µF or larger. The bypass
capacitors should be mounted with the shortest leads, and if
possible, directly across the regulator terminals.
High Stability 1 Amp Regulator
DS007340-5
Load and line regulation <0.01% temperature stability ≤0.2%
†Determine Zener current
††Solid tantalum
*Select resistors to set output voltage. 2 ppm/˚C tracking suggested
Current Source
DS007340-7
LM79XX Series
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Typical Applications (Continued)
Light Controller Using Silicon Photo Cell
DS007340-8
*Lamp brightness increase until iI=i
Q(≈1 mA) + 5V/R1.
†Necessary only if raw supply filter capacitor is more that 2" from LM7905CT
High-Sensitivity Light Controller
DS007340-9
*Lamp brightness increases until ii= 5V/R1 (Iican be set as low as 1 µA)
†Necessary only if raw supply filter capacitor is more that 2" from LM7905
Variable Output
DS007340-2
*Improves transient response and ripple rejection. Do not increase beyond 50 µF.
Select R2 as follows:
LM7905CT 300Ω
LM7912CT 750Ω
LM7915CT 1k
LM79XX Series
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Typical Applications (Continued)
±15V, 1 Amp Tracking Regulators
DS007340-1
(-15) (+15)
Load Regulation at ∆I
L
= 1A 40mV 2mV
Output Ripple, C
IN
= 3000µF, I
L
= 1A 100 µVms 100 µVms
Temperature Stability 50mV 50mV
Output Noise 10Hz ≤f≤10kHz 150 µVms 150 µVms
*Resistor tolerance of R4 and R5 determine matching of (+) and (−) outputs.
**Necessary only if raw supply filter capacitors are more than 3" from regulators.
Dual Trimmed Supply
DS007340-4
LM79XX Series
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Schematic Diagrams
−5V
DS007340-12
LM79XX Series
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Schematic Diagrams (Continued)
−12V and −15V
DS007340-13
LM79XX Series
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Physical Dimensions inches (millimeters) unless otherwise noted
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DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
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www.national.com
TO-220 Outline Package (T)
Order Number LM7905CT, LM7912CT or LM7915CT
NS Package Number T03B
LM79XX Series 3-Terminal Negative Regulators
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
