LM7912C National Semiconductor, LM7912C Datasheet - Page 4

• Manufacturer Part Number: LM7912C
• Description: LM79XX Series 3-Terminal Negative Regulators
• Manufacturer: National Semiconductor

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 maxi-
mum 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 speci-
fied temperature (125 C) in order to meet data sheet specifi-
cations To calculate the maximum junction temperature or
heat sink required the following thermal resistance values
should be used
Solving for T
Load and line regulation
Determine Zener current
Solid tantalum
Select resistors to set output voltage 2 ppm C tracking suggested
P
T
Package
TO-220
D MAX
CA
J
e
e
e
T
T
A
A
e
CS
a
a
J
T
P
P
a
J Max
JC
D
D JA
(
a
Typ
C W
SA
3 0
JC
JC
b
(without heat sink)
(without heat sink)
k
CA
a
T
0 01% temperature stability
A
or
CA
T
) or
Max
C W
5 0
J Max
JC
JA
T
A
Typ
C W
60
JA
s
High Stability 1 Amp Regulator
0 2%
Max
C W
40
JA
4
Where
Typical Applications
Bypass capacitors are necessary for stable operation of the
LM79XX series of regulators over the input voltage and out-
put current ranges Output bypass capacitors will improve
the transient response by the regulator
The bypass capacitors (2 2 F on the input 1 0 F on the
output) should be ceramic or solid tantalum which have
good high frequency characteristics If aluminum electrolyt-
ics are used their values should be 10
bypass capacitors should be mounted with the shortest
leads and if possible directly across the regulator termi-
nals
T
T
P
JA
JC
CA
CS
SA
J
A
D
e
e
e
e
e
e
e
e
Junction Temperature
Ambient Temperature
Power Dissipation
Junction-to-Ambient Thermal Resistance
Junction-to-Case Thermal Resistance
Case-to-Ambient Thermal Resistance
Case-to-Heat Sink Thermal Resistance
Heat Sink-to-Ambient Thermal Resistance
(Continued)
F or larger The
TL H 7340 – 5