Block Diagram:
Here, it is a
diagram of an active loudspeaker. The LF353 of, National
Semiconductor, is going to split audio signal into three bands.
SANYO'S LA47536 is going to amplify these signals. In stereo
mode, we shall have the action of eight high speakers who are
going to create a very important sound pressure.
Three Band Active Tone
Control:
Description :
LF353 Wide
Bandwidth Dual JFET Input Operational Amplifier.
General Description
These devices
are low cost, high speed, dual JFET input operational amplifiers
with an internally trimmed input offset voltage (BI-FET II
technology). They require low supply current yet maintain a large
gain band width product and fast slew rate.
In addition,
well matched high voltage JFET input devices provide very low
input bias and offset currents.
The LF353 is pin
compatible with the standard LM1558 allowing designers to
immediately upgrade e the overall performance of existing LM1558
and LM358 designs.
These amplifiers
may be used in applications such as high speed integrators, fast
D/A converters, sample and hold circuits and many other circuits
requiring low input offset voltage, low input bias current, high
input impedance, high slew rate and wide bandwidth.
The devices also
exhibit low noise and offset voltage drift. (National
Semiconductor)
Features :
Internally
trimmed offset voltage: 10 mV
Low input bias
current: 50pA
Low input noise
voltage: 25 nV
Low input noise
current: 0.01 pA
Wide gain
bandwidth: 4 MHz
High slew rate:
13 V/us
Low supply
current: 3.6 m
High input
impedance: 1012.
Low total
harmonic distortion : < 0.02%
Low 1/f noise
corner: 50 Hz
Fast settling
time to 0.01%: 2 us
Power Amplifier :
When the
amplifier is installed behind in the suitcase, we shall need a
switch works stop.
The LA47536
possesses a function stand by in it pin4.
This pine
require a small tension superior to 2V in start up the
amplifier.
Transistor Q1
and Q2 makes the function of walking stop for distance.
When the driver
activates the left indicator, either light the back fires or
press on the brake , lamps rear ignite driving Q2 who he even
made to drive Q1 who applies a tension > 2V on it pin4.
LA47536 Four-Channel 45 W BTL Car Audio Power
Amplifier
The LA47536 is a
4-channel BTL power amplifier IC developed for use in car audio
systems. The output stage features.
- A pure
complimentary structure that uses V-PNP transistors on the high
side and NPN transistors on the low side to provide high power
and superb audio quality.
- The LA47536
includes almost all the functions required for car audio use,
including a standby switch, a muting function, and each
protection circuit. It also provides a self-diagnosis function
(output offset detection). (Sanyo)
Functional Description
1. Standby
Switch Function (pin 4)
The pin 4
threshold voltage is set to be 2 VBE. When Vst is 2.0V or higher,
the amplifier will be on, and when Vst, is 0.7V or lower, the
amplifier will be off. Note that pin 4 requires an operating
current of at least 40uA.
2. Muting
Function
The IC is set to
the muted state by setting pin 22 to the ground potential. In
this state, the audio output is muted. The time constant with
which the muting function operates is set by an external RC
circuit, and this time constant influences the pop noise that
occurs when the amplifier is turned on or off.
The muting on
and off times due to the recommended external component values
(R=10k, C=3.3uF) are as follows.
Muting on time:
50ms
Muting off time:
20ms
3.
Self-Diagnosis Function (Speaker burnout prevention)
During steady
state operation, the LA47536 detects, internally, whether or not
an abnormal amplifier output offset has occurred, and outputs
this signal from pin 25. Applications can prevent speaker burnout
and other problems by having the system microcontroller detect
this pin 25 output signal and control either the standby state or
the power supply. (An abnormal output offset may be caused by,
for example, input capacitor leakage current.) The pin 25 signal
is turned off by setting pin 1 to the ground potential.
4. Oscillator
Stability
In some cases,
parasitic oscillations may be induced by the PCB layout. This
oscillation can be eliminated by adding the components listed
below. Note that the optimal capacitor value must be verified by
testing in the actual mounted state in the end product. Connect a
capacitor and resistor (0.1uF and 2.2) in series between each
output pin and ground.
5. Audio Quality
(Low band)
The frequency
characteristics in the low frequencies can be improved by making
the capacitance of the input capacitors variable. The recommended
capacitance is 2.2uF and smaller.
6. Protection
Circuits
Do not ground
the outputs with the STBY voltage at around 1.4V. Also, do not
turn the IC off in the grounded state with a time constant
provided for the STBY voltage.
7. Pop
Noise
Although the
LA47536 includes an pop noise prevention circuit, pop noise can
be reduced even further by using the muting function as well.
Activate the muting function at the same time as power is
applied. Then, after the output DC potential has stabilized, turn
off the muting function. When turning the amplifier off, first
turn on the muting function and then turn off the power supply.
These two methods are effective at minimizing pop noise.
PCB Layout :
