Conex Club Magazine - no.12 - 2005

Conex Club Magazine - no.12 - 2005 - TDA7384 - 4x25W quad audio amplifier

Reading time: 5 minute

The main topics presented

1. TDA7384 - Quad audio amplifier, 4 x 25W

Amateur manufacturers can equip their car with a high-performance audio system made on the skeleton of the integrated power amplifier TDA7384, designed by SGS-Thomson Microelectronics (ST) to generate maximum audio power at low supply voltage, respectively 14.4V, as much as it can offer maximum, in normal conditions a car battery.

Are available four output channels that can each deliver a maximum of 35W on 4 Ohm loads.

Made in a new technology at the time (1997), in the AB operating class and packaged in a 25-pin Flexiwatt capsule, the TDA7384 is a four-channel audio power amplifier that does not require a bootstrap capacitor, and which can charge a considerable power (maximum 4 x 35W / 4 Ohms, according to EIAJ standards), powered at low voltages, from sources that have a very high current capacity (such as accumulator batteries).

The manufacturer recommended it especially for use in high-performance audio equipment that equips cars.

Among the TDA7384's performance are:

  • output power: 4x25W / 4 Ohms measured at 14.4V supply voltage, frequency 1kHz and distortion, THD, 10% or 4x21W / 4 Ohms measured at 13.2V supply voltage, frequency 1 kHz and THD maximum 10%.
  • low distortion, low output noise;
  • stand-by and muting functions;
  • auto-muting when the supply voltage drops below a certain threshold;
  • fixed gain of 26dB;
  • without external components for compensation or bootstrap.

2. MC34064 - Undervoltage sensing circuit (supply voltage monitor)

The series started in the last issue continues with the presentation of circuits for monitoring the supply voltage of some systems, with a specialized circuit, produced by ON Semiconductor, MC34064.

It is specially designed for generating the reset signal to a microcontroller, but direct applications can be multiple, as will be presented.

MC34064 is a circuit for detecting low supply voltage, for systems powered by + 5V. Below 4.6V, it generates an error signal (Reset) on one of its 3 pins ("output" pin, 1).

Requires a minimum of external components. The current controlled by the transistor with the collector empty at the output (pin 1) is a maximum of 10mA, and the circuit operates up to 1V supply voltage.

It has an internal reference of 1.2V thermocompensated. The internal comparator, in positive logic, offers its own hysteresis of 0.02V, for safe operation. It is possible to schedule an extreme hysteresis. The threshold voltage limit is: 4.5… 4.7V.

At 25 ° C the threshold value is guaranteed at 4.6V. In standby the consumed current is of the order of uA. An internal diode provides protection when discharging capacitive loads on the output pin.

3. Audio frequency amplifiers with TDA2822M

There is a frequency audio amplifier, in two variants, stereo or mono, which uses the TDA2822M integrated circuit. This amplifier is supplied with "very low" voltage, starting from 1.8V.

Depending on the size of the supply voltage, different impedance speakers are used, in order not to exceed the maximum dissipated power allowed by the integrated circuit, according to the data in table 1 (from the article).

Considering the low consumption of electricity, at rest (without input signal) of about 6mA, this amplifier is very useful in portable equipment.

This amplifier, regardless of the variant - stereo or mono - has a high voltage amplification of 40dB. In both versions presented in the article, the bandwidth is 50Hz… 22kHz, with a deviation of +/- 1dB.

The stereo amplifier can also be used with dual (stereo) headphones with impedance 16 plus 16 Ohms (total 32 Ohms).

The great advantage of these amplifiers is that they can be supplied with a low voltage, for example from two R6 batteries. If they are discharged, reaching a voltage-sum of 1.8V, the amplifier will still work properly, without distortion.

4. Universal siren module with back-up source

Most commercial sirens designed for burglary warning systems have complex functions that make them impossible to sabotage by criminals by non-destructive methods!

The activation functions (trigger) on a certain level of the control signal, the tamper inputs of the siren box or the service ones necessary for the intervention of the authorized installer in the system, as well as the self-supply are mentioned here.

The idea of ​​this assembly was to ensure a higher safety of the system, encompassing in a single module (as is the case of some commercial equipment) both the control module of the piezoelectric siren or hoop (activated with relay, because it is safer in operation than transistors!), as well as the back-up power supply of the entire system.

Thus, in the way it is designed, the interruption of the "communication" (translated by the cutting of the connection wires by a possible offender) between the alarm control panel and the siren module in question, determines the actuation of the relay.

The intervention in the system is accessible only to the installer, using the Service input to which the correct potential is applied.

5. Dynamic lights and signaling arrow

using the "duo" LM555 and CD4017, various applications can be made, from entertainment to uses in the field of street signs or in shops or in the field of "security".

Introduces himself two basic applications, which covers the areas mentioned above, and will return in future issues with other equally interesting applications.

In both schemes (figures 1 and 3 of the article), circuit 555 is configured as low frequency stable. The frequency is adjustable between certain limits (from a few Hz to tens of Hz) in the semi-adjustable R13 (respectively, R3).

6. 4-channel digital thermometer

Mounting, by the possibility to measure the temperature in several areas (on 4 channels), can be used as a temperature monitoring unit in a system, or as an indoor / outdoor thermometer.

The applications that can be imagined can be numerous. The temperature sensor used is LM35, a temperature / voltage converter.

Four such sensors are switched automatically or manually at the input of the voltmeter made with ICL7107 for measuring the voltage provided by the sensors, and a 3-digit display displays the measured temperature (to one decimal place).

An LED attached to the display system also indicates the sign of the displayed value. In order not to be "noisy", the sensors are switched by means of Reed relays.

7. Flash signal light (beacons)

Beacons (lights) are warning elements with applications in various places and purposes (directing traffic, signaling damage, entertainment, etc.).

Depending on the application, the light intensity and the color with which the beacons signal differ, in order to make the desired event observable from a distance.

Two electronic light signaling assemblies, powered by low voltages, can be used as "mini" beacons. One of the mounts is powered by a 12V source and uses a halogen bulb as the light source, and the other mount is powered by 9V and has as light source two series LEDs, high efficiency (brightness), preferably color white or blue.

In figure 1 (from the article) the version with halogen lamp (12V) is presented. 20… 60W bright "spots" can be used. The maximum consumption will be 1.8A, and the "flashing" frequency (oscillation) is adjustable between 0.4 and 2.5Hz.

This frequency is controlled by the circuit consisting of R2, R3 and C1. This adjustment is made with the help of the 2 KOhm trimmer potentiometer R47.

The multivibrator type tactile generator is made with an integrated circuit CMOS4093 followed by a MOSFET type power transistor IRFZ44. The halogen lamp connects in series with the drain of this transistor.

8. Maintaining between two limits the water level in a tank

With a simple electronic circuit (figure 1 in the article) you can get an application that allows automation of an installation with water served from a pool supplied by an electric pump.

At the base of the application is a voltage comparator LM311. Three sensors, A (for the upper level), B (intermediate or minimum level) and C (minimum level, reference) must be mounted in the water basin.

The thyristor can be of any type, preferably for general use of low power (BT169, P0102DA, C106, TIC106, etc.). There are no special indications regarding the choice of the relay, but it must have a normally closed contact, NC.


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