|
|
PDF LM391 Data sheet ( Hoja de datos )
| Número de pieza | LM391 | |
| Descripción | LM391 Audio Power Driver | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LM391 (archivo pdf) en la parte inferior de esta página. Total 12 Páginas | ||
|
No Preview Available !
December 1994
LM391 Audio Power Driver
General Description
The LM391 audio power driver is designed to drive external
power transistors in 10 to 100 watt power amplifier designs
High power supply voltage operation and true high fidelity
performance distinguish this IC The LM391 is internally pro-
tected for output faults and thermal overloads circuitry pro-
viding output transistor protection is user programmable
Features
Y High Supply Voltage
Y Low Distortion
Y Low Input Noise
Y High Supply Rejection
Y Gain and Bandwidth Selectable
Y Dual Slope SOA Protection
Y Shutdown Pin
Equivalent Schematic and Connection Diagram
g50V max
0 01%
3 mV
90 dB
Dual-In-Line Package
TL H 7146 – 1
Top View
Order Number LM391N-100
See NS Package Number N16A
C1995 National Semiconductor Corporation TL H 7146
TL H 7146 – 2
RRD-B30M115 Printed in U S A
1 page  
Application Hints
GENERALIZED AUDIO POWER AMP DESIGN
Givens Power Output
Load Impedance
Input Sensitivity
Input Impedance
Bandwidth
The power output and load impedance determine the power
supply requirements Output signal swing and current are
found from
VOpeak e 02 RL PO
(1)
0IOpeak e
2 PO
RL
(2)
Add 5 volts to the peak output swing (VOP) for transistor
voltage to get the supplies i e g (VOP a 5V) at a current
of Ipeak The regulation of the supply determines the unload-
ed voltage usually about 15% higher Supply voltage will
also rise 10% during high line conditions
max supplies g(VOpeak a 5) (1 a regulation) (1 1) (3)
The input sensitivity and output power specs determine the
required gain
AV
t
0PO RL
VIN
e
VORMS
VINRMS
(4)
Normally the gain is set between 20 and 200 for a 25 watt
8 ohm amplifier this results in a sensitivity of 710 mV and 71
mV respectively The higher the gain the higher the THD
as can be seen from the characteristics curves Higher gain
also results in more hum and noise at the output
The desired input impedance is set by RIN Very high values
can cause board layout problems and DC offsets at the out-
put The bandwidth requirements determine the size of Cf
and CC as indicated in the external component listing
The output transistors and drivers must have a breakdown
voltage greater than the voltage determined by equation (3)
The current gain of the drive and output device must be high
enough to supply IOpeak with 5 mA of drive from the LM391
The power transistors must be able to dissipate approxi-
mately 40% of the maximum output power the drivers must
dissipate this amount divided by the current gain of the out-
puts See the output transistor selection guide Table A
To prevent thermal runaway of the AB bias current the fol-
lowing equation must be valid
where
iJA
s
RE (bMIN a 1)
VCEQMAX (K)
(5)
iJA is the thermal resistance of the driver transistor junc-
tion to ambient in C W
RE is the emitter degeneration resistance in ohms
bmin is that of the output transistor
VCEQMAX is the highest possible value of one supply from
equation (3)
K is the temperature coefficient of the driver base-emitter
voltage typically 2 mV C
Often the value of RE is to be determined and equation (5)
is rearranged to be
RE
t
iJA (VCEQMAX)
bMIN a 1
K
(6)
The maximum average power dissipation in each output
transistor is
PDMAX e 0 4 POMAX
The power dissipation in the driver transistor is
(7)
PDRIVER(MAX)
e
PDMAX
bMIN
(8)
Heat sink requirements are found using the following formu-
las
where
iJA
s
TJMAX
b TAMAX
PD
iSA s iJA b iJC b iCS
(9)
(10)
TjMAX is the maximum transistor junction temperature
TAMAX is the maximum ambient temperature
iJA is thermal resistance junction to ambient
iSA is thermal resistance sink to ambient
iJC is thermal resistance junction to case
iCS is thermal resistance case to sink typically 1 C W for
most mountings
5
5 Page 
Application Hints (Continued)
The formulas for RE R1 and R2 do not change
0 65
RE e 3A e 0 22X
R2 e 1k
80 b 0 65
R1 e 1k 0 65 e 120k
The formula for R3 now gives RTH when the Va in the for-
mula becomes VB
(RTH e R2
VB b 1
IL RE b w
(47
e 1k
b 1 e 25 55k
11 (0 22) b 0 65
VTH is the additional voltage added to the supply voltage to
get VB
VTH e b(VB b Va) e b(47 b 30) e b17V
Now we must find RA3 and RB3 using the Thevenin formulas
Putting VTH Vb and RTH into the appropriate formulas re-
duces to
llRB3 e 0 76 RA3
and
25 55k e RA3
R
B
3
The easiest way to solve these equations is to iterate with
standard values
If
we
guess
R
A
3
e
62k
then RB3 e 47 12k
use 47k The Thevenin impedance comes out 26 7k which
is close enough to 25 55k
Now we will use equation (5) to determine the heat sinking
requirements of the drivers to insure thermal stability
0 22 (20 a 1)
iJA s 40 (0 002)
57 C W
(5)
This value is lower than we got with equation (9) so we will
use it in equation (10)
iSA s 57 b 6 b 1 e 50 C W
(10)
This is the required heat sink for each driver For low TIM
we add the 1 MX resistor from pin 3 to the output and a
910k resistor from pin 4 to ground The complete schematic
is shown below
If the output is shorted the transistor voltage is about 28V
and the current is 5A Therefore the average power is
short PD e (28) 5 e 70W
This is much larger than the power used to calculate the
heat sinks and the output transistors will overheat if the out-
put is shorted too long
Typical Applications (Continued)
40W-8X 60W-4X Amplifier
High Frequency Ground
Input Ground
Speaker Ground
Note All Grounds Should be Tied Together
Only at Power Supply Ground
Additional protection for LM391N Schottky diodes and R j 100X
11
TL H 7146 – 13
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LM391.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LM390 | LM390 1W Battery Operated Audio Power Amplifier | National Semiconductor |
| LM390 | LM390 1W Battery Operated Audio Power Amplifier (Rev. A) |  Texas Instruments |
| LM3900 | LM2900/LM3900/LM3301 Quad Amplifiers | Texas Instruments |
| LM3900 | (LM3900 / LM3901 / LM3401) Quad Amplifiers | National Semiconductor |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |