LM391 National Semiconductor Corporation, LM391 Datasheet - Page 9

• Manufacturer Part Number: LM391
• Description: Audio Power Driver (discontinued)
• Manufacturer: National Semiconductor Corporation

Application Hints
Since the free air thermal resistance of the MJE711
MJE721 is 100 C W no heat sink is required Using this
information and equation (6) we can find the minimum value
of R
We must now use the SOA data on the TIP42 TIP41 tran-
sistors to set up the protection circuit Below is the SOA
curve with the 4
desired protection lines Note the value of V
supply voltage so we use the formulas in the table
Typical Applications
E
required to prevent thermal runaway
R
D C SOA of TIP42 TIP41
Transistors
E t
and 8
100 (30) (0 002)
30
a
load lines Also shown are the
(Continued)
1
20W-8
(Continued)
e
Additional protection for LM391N Schottky diodes and R j 100
0 19
30W-4
B
is equal to the
TL H 7146 – 8
Amplifier with 1 Second Turn-ON Delay
(6)
9
The data points from the curve are
Using the dual slope protection formulas
Note that an R
schematic of this amplifier is below If the output is shorted
the current will be 1 8A and V
AC the average power is
This power is greater than was used in the heat sink calcula-
tions so the transistors will overheat for long-duration
shorts unless a larger heat sink is used
V
R
M
3
e
e
short P
R
60V V
E
1k
1
of 0 22
e
R
1k
7(0 22)
D
E
B
e
e
e
R
60
0 65
2
23
23V I
3
satisfies equation (6) The final
(1 8) (23)
0 65
b
e
b
CE
e
0 65
0 65
1k
L
0 22
is 23V Since the input is
e
b
3A I
1
21W
91k
L
e
24k
7A
TL H 7146– 9