On the TDA7294 chip, the amplifier circuit is quite simple, even a person who is not very strong in electrical engineering can repeat it. The ULF on this chip will be ideal for use as part of the speaker system for a home computer, TV, movie theater. Its advantage is that it does not require fine-tuning and tuning, as is the case with transistor amplifiers. And what can we say about the difference from lamp designs - the dimensions are much smaller.
High voltage is not required to power the anode circuits. Of course, there is heating, as in lamp designs. Therefore, in the event that it is planned to use the amplifier for a long time, it is best to install, in addition to the aluminum radiator, at least a small fan for performing forced blowing. Without it, the amplifier circuit will work on the TDA7294 microassembly, but there is a high probability of a transition to temperature protection.
Why TDA7294?
This chip is very popular for over 20 years. She won the trust of radio amateurs, since she has very high characteristics, the amplifiers based on it are simple, anyone, even a novice ham radio, can repeat the design. The amplifier on the TDA7294 chip (the circuit is shown in the article) can be either monaural or stereo. The internal device of the microcircuit consists of field-effect transistors. The audio frequency amplifier built on this chip belongs to class AB.
Advantages of the chip
Advantages of using a chip for audio amplifiers :
1. Very large output power. About 70 watts if the load has a resistance of 4 ohms. In this case, the usual circuit for switching on the chip is used.
2. About 120 watts at a load of 8 ohms (in the bridge circuit).
3. A very low level of extraneous noise, distortions are insignificant, reproducible frequencies lie in the range completely perceived by the human ear - from 20 Hz to 20 kHz.
4. The microcircuit can be powered from a DC voltage source of 10-40 V. But there is a slight drawback - you must use a bipolar power source.
It is worth paying attention to one feature - the distortion coefficient does not exceed 1%. On the TDA7294 microassembly, the power amplifier circuit is so simple that it’s even amazing how it allows you to get such high-quality sound.
IC pin assignment
And now in more detail about what conclusions are available in TDA7294. The first leg is the “signal ground”, connected to the common wire of the entire structure. Conclusions "2" and "3" - inverting and non-inverting inputs, respectively. The “4” terminal is also a “signal ground” connected to a common wire. The fifth leg is not used in audio amplifiers. The “6” leg is a volt-supplement, an electrolytic capacitor is connected to it. "7" and "8" conclusions - plus and minus the power of the input stages, respectively. Leg "9" - standby mode, used in the control unit.
Similarly: “10” leg - muting mode, also used in the design of the amplifier control unit. "11" and "12" conclusions are not used in the design of sound frequency amplifiers. The output signal is taken from the “14” output and fed to the speaker system. “13” and “15” microcircuit pins are “+” and “-” for connecting the output stage power. On the TDA7294 chip, the amplifier circuit for the subwoofer is no different from the ones proposed in the article, it is supplemented only by a low-pass filter that connects to the input.
Micro assembly features
When designing an audio frequency amplifier, you need to pay attention to one feature - minus the power, and these are the legs "15" and "8", are electrically connected to the housing of the chip. Therefore, it is necessary to isolate it from the radiator, which in any case will be used in the amplifier. For this purpose, it is necessary to use a special thermal pad. If you are using an amplifier bridge on the TDA7294, pay attention to the housing option. It can be vertical or horizontal type. The most common is the embodiment designated as TDA7294V.
Protective Functions of TDA7294 Chip
The chip provides several types of protection, in particular, against a voltage drop. If the supply voltage suddenly changes, the microcircuit will go into protection mode, therefore, there will be no electrical damage. The output stage also has overload and short circuit protection. If the case of the device heats up to a temperature of 145 degrees, the sound is muted. When it reaches 150 degrees, it goes into standby mode. All pins of the TDA7294 chip are protected against electrostatics.
Amplifier
Simple, affordable for everyone, and most importantly - cheap. In just a few hours, you can assemble a very good sound frequency amplifier. And you will spend most of the time to etch the board. The structure of the entire amplifier consists of power supplies and control, as well as 2 channels of ULF. Try to use as few wires as possible in the design of the amplifier. Follow simple guidelines:
1. A prerequisite is the connection of the power source with wires to each UZCh board.
2. Tie the power wires into the harness. With this, it will be possible to slightly compensate for the magnetic field that is created by the electric current. To do this, you need to take all three supply wires - “common”, “minus” and “plus”, with a slight tension, weave them into one pigtail.
3. In no case do not use the so-called “earthen loops” in the construction. This is the case when the common wire connecting all the blocks of the structure is closed in a loop. The mass wire must be connected sequentially, starting from the input volume controls, then to the UHF board, and should end on the output connectors. It is imperative to connect the input circuits with shielded wires in isolation.
Standby and Mute Control Unit
This chip has a standby and muting mode . It is necessary to carry out control of functions by means of conclusions "9" and "10". The mode is activated if there is no voltage on these legs of the microcircuit, or if it is less than one and a half volts. To enable the mode, it is necessary to apply voltage to the legs of the microcircuit, the value of which exceeds 3.5 V. To control the amplifier boards at the same time, which is important for circuits constructed by the type of bridge, one control unit is assembled for all stages.
When the amplifier turns on, all capacitors are charged in the power supply. In the control unit also one capacitor accumulates a charge. When accumulating the maximum possible charge, the standby mode is turned off. The second capacitor used in the control unit is responsible for the operation of the muting mode. It charges a little later, so the mute mode is turned off second.