Page 1
TL/H/7340
LM79XX Series 3-Terminal Negative Regulators
November 1994
LM79XX Series 3-Terminal Negative Regulators
General Description
The LM79XX series of 3-terminal regulators is available with
fixed output voltages of
b
5V,b8V,b12V, andb15V.
These devices need only one external componentÐa compensation capacitor 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 virtually 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 data
sheet.
Features
Y
Thermal, short circuit and safe area protection
Y
High ripple rejection
Y
1.5A output current
Y
4% tolerance on preset output voltage
Connection Diagrams
TO-220 Package
TL/H/7340– 14
Front View
Order Number LM7905CT, LM7912CT or LM7915CT
See NS Package Number TO3B
Typical Applications
Fixed Regulator
TL/H/7340– 3
*Required if regulator is separated from filter capacitor by
more than 3
×
. For value given, capacitor must be solid
tantalum. 25 mF aluminum electrolytic may be substituted.
²
Required for stability. For value given, capacitor must be
solid tantalum. 25 mF aluminum electrolytic may be substituted. Values given may be increased without limit.
For output capacitance in excess of 100 mF, a high current
diode from input to output (1N4001, etc.) will protect the
regulator from momentary input shorts.
C
1995 National Semiconductor Corporation RRD-B30M115/Printed in U. S. A.
Page 2
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
eb
5V)
b
25V
(V
o
eb
12V andb15V)
b
35V
Input-Output Differential
(V
o
eb
5V) 25V
(V
o
eb
12V andb15V) 30V
Power Dissipation (Note 2) Internally Limited
Operating Junction Temperature Range 0§Ctoa125§C
Storage Temperature Range
b
65§Ctoa150§C
Lead Temperature (Soldering, 10 sec.) 230§C
Electrical Characteristics Conditions unless otherwise noted: I
OUT
e
500 mA, C
IN
e
2.2 m F, C
OUT
e
1 m F,
0
§
CsT
J
s
a
125§C, Power Dissipations1.5W.
Part Number LM7905C
Units
Output Voltage
b
5V
Input Voltage (unless otherwise specified)
b
10V
Symbol Parameter Conditions Min Typ Max
V
O
Output Voltage T
J
e
25§C
b
4.8
b
5.0
b
5.2 V
5mA
s
I
OUT
s
1A,
b
4.75
b
5.25 V
Ps15W (b20sV
IN
s
b
7) V
DV
O
Line Regulation T
J
e
25§C, (Note 3) 8 50 mV
(
b
25sV
IN
s
b
7) V
215mV
(
b
12sV
IN
s
b
8) V
DV
O
Load Regulation T
J
e
25§C, (Note 3)
5mA
s
I
OUT
s
1.5A 15 100 mV
250 mAsI
OUT
s
750 mA 5 50 mV
I
Q
Quiescent Current T
J
e
25§C12mA
DI
Q
Quiescent Current With Line 0.5 mA
Change (b25sV
IN
s
b
7) V
With Load, 5 mA
s
I
OUT
s
1A 0.5 mA
V
n
Output Noise Voltage T
A
e
25§C, 10 Hzsfs100 Hz 125 mV
Ripple Rejection fe120 Hz 54 66 dB
(
b
18sV
IN
s
b
8) V
Dropout Voltage T
J
e
25§C, I
OUT
e
1A 1.1 V
I
OMAX
Peak Output Current T
J
e
25§C 2.2 A
Average Temperature I
OUT
e
5 mA, 0.4 mV/§C
Coefficient of 0 C
s
T
J
s
100§C
Output Voltage
Typical Applications (Continued)
Variable Output
TL/H/7340– 2
*Improves transient response and ripple rejection. Do not increase beyond 50 mF.
V
OUT
e
V
SET
#
R1aR2
R2
J
Select R2 as follows:
LM7905CT 300X
LM7912CT 750X
LM7915CT 1k
2
Page 3
Electrical Characteristics (Continued) Conditions unless otherwise noted: I
OUT
e
500 mA, C
IN
e
2.2 m F,
C
OUT
e
1 mF, 0§CsT
J
s
a
125§C, Power Dissipatione1.5W.
Part Number LM7912C LM7915C
Units
Output Voltage
b
12V
b
15V
Input Voltage (unless otherwise specified)
b
19V
b
23V
Symbol Parameter Conditions Min Typ Max Min Typ Max
V
O
Output Voltage T
J
e
25§C
b
11.5b12.0b12.5b14.4b15.0b15.6 V
5mA
s
I
OUT
s
1A,
b
11.4
b
12.6b14.25
b
15.75 V
Ps15W (b27sV
IN
s
b
14.5) (b30sV
IN
s
b
17.5) V
DV
O
Line Regulation T
J
e
25§C, (Note 3) 5 80 5 100 mV
(
b
30sV
IN
s
b
14.5) (b30sV
IN
s
b
17.5) V
3 30 3 50 mV
(b22sV
IN
s
b
16) (b26sV
IN
s
b
20) V
DV
O
Load Regulation T
J
e
25§C, (Note 3)
5mA
s
I
OUT
s
1.5A 15 200 15 200 mV
250 mAsI
OUT
s
750 mA 5 75 5 75 mV
I
Q
Quiescent Current T
J
e
25§C 1.5 3 1.5 3 mA
DI
Q
Quiescent Current With Line 0.5 0.5 mA
Change (b30sV
IN
s
b
14.5) (b30sV
IN
s
b
17.5) V
With Load, 5 mA
s
I
OUT
s
1A 0.5 0.5 mA
V
n
Output Noise Voltage T
A
e
25§C, 10 Hzsfs100 Hz 300 375 mV
Ripple Rejection fe120 Hz 54 70 54 70 dB
(
b
25sV
IN
s
b
15) (b30sV
IN
s
b
17.5) V
Dropout Voltage T
J
e
25§C, I
OUT
e
1A 1.1 1.1 V
I
OMAX
Peak Output Current T
J
e
25§C 2.2 2.2 A
Average Temperature I
OUT
e
5 mA,
b
0.8
b
1.0 mV/§C
Coefficient of 0 C
s
T
J
s
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.
Typical Applications (Continued)
Dual Trimmed Supply
TL/H/7340– 4
3
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Design Considerations
The LM79XX fixed voltage regulator series has thermal
overload protection from excessive power dissipation, internal 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 junction temperature must be kept below the maximum specified temperature (125
§
C) in order to meet data sheet specifications. To calculate the maximum junction temperature or
heat sink required, the following thermal resistance values
should be used:
Typ Max Typ Max
Package i
JC
i
JC
i
JA
i
JA
§
C/W§C/W§C/W§C/W
TO-220 3.0 5.0 60 40
P
D MAX
e
T
J Max
b
T
A
i
JC
a
i
CA
or
T
J MaxTA
i
JA
i
CA
e
i
CS
a
iSA(without heat sink)
Solving for T
J
:
T
J
e
T
A
a
PD(i
JC
a
iCA)or
e
T
A
a
PDiJA(without heat sink)
Where:
T
J
e
Junction Temperature
T
A
e
Ambient Temperature
P
D
e
Power Dissipation
i
JA
e
Junction-to-Ambient Thermal Resistance
i
JC
e
Junction-to-Case Thermal Resistance
i
CA
e
Case-to-Ambient Thermal Resistance
i
CS
e
Case-to-Heat Sink Thermal Resistance
i
SA
e
Heat Sink-to-Ambient Thermal Resistance
Typical Applications (Continued)
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, (2.2 mF on the input, 1.0 mFonthe
output) should be ceramic or solid tantalum which have
good high frequency characteristics. If aluminum electrolytics are used, their values should be 10 mF 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
TL/H/7340– 5
Load and line regulationk0.01% temperature stabilitys0.2%
²
Determine Zener current
²²
Solid tantalum
*Select resistors to set output voltage. 2 ppm/
§
C tracking suggested
4
Page 5
Typical Applications (Continued)
Current Source
*I
OUT
e
1mA
a
5V
R1
TL/H/7340– 7
Light Controller Using Silicon Photo Cell
TL/H/7340– 8
*Lamp brightness increase until i
I
e
iQ(&1 mA)a5V/R1.
²
Necessary only if raw supply filter capacitor is more than 2×from LM7905CT
5
Page 6
Typical Applications (Continued)
High-Sensitivity Light Controller
TL/H/7340– 9
*Lamp brightness increases until i
i
e
5V/R1 (Iican be set as low as 1 m A)
²
Necessary only if raw supply filter capacitor is more than 2×from LM7905
g
15V, 1 Amp Tracking Regulators
TL/H/7340– 1
(b15) (a15)
Load Regulation at DI
L
e
1A 40 mV 2 mV
Output Ripple, C
IN
e
3000 mF, I
L
e
1A 100 mVrms 100 mVrms
Temperature Stability 50 mV 50 mV
Output Noise 10 Hz
sfs
10 kHz 150 mVrms 150 m Vrms
*Resistor tolerance of R4 and R5 determine matching of (
a
) and (b)
outputs.
**Necessary only if raw supply filter capacitors are more than 3
×
from regu-
lators.
6
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Schematic Diagrams
b
5V
TL/H/7340– 12
7
Page 8
Schematic Diagrams (Continued)
b
12V and
b
15V
TL/H/7340– 13
8
Page 9
9
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LM79XX Series 3-Terminal Negative Regulators
Physical Dimensions inches (millimeters)
TO-220 Outline Package (T)
Order Number LM7905CT, LM7912CT or LM7915CT
NS Package Number T03B
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DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL
SEMICONDUCTOR CORPORATION. As used herein:
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systems which, (a) are intended for surgical implant support device or system whose failure to perform can
into the body, or (b) support or sustain life, and whose be reasonably expected to cause the failure of the life
failure to perform, when properly used in accordance support device or system, or to affect its safety or
with instructions for use provided in the labeling, can effectiveness.
be reasonably expected to result in a significant injury
to the user.
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Corporation Europe Hong Kong Ltd. Japan Ltd.
1111 West Bardin Road Fax: (
a
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