Bridged audio power amplifier. TDA7294: amplifier circuit. Bridge amplifier circuit on TDA7294 Bridge low-frequency amplifier

Bridged connection - connection of an amplifier to loudspeakers, in which the channels of a stereo amplifier operate in the mode of monoblock power amplifiers. They amplify the same signal, but in antiphase. In this case, the loudspeaker is switched between the two outputs of the amplification channels.

Bridge connection allows you to significantly increase the power of the amplifier.

The output voltage across the load turns out to be twice as high, therefore, at the same supply voltage and load, the output power of an amplifier using a bridge circuit is theoretically 1.5 - 4 times greater than that of a separate amplifier. Power amplifiers of modern head units are made according to this design. The possibility of bridge connection is provided in almost all models of additional amplifiers.

One way to increase the output power of an amplifier when the supply voltage is low is to turn it on bridge circuit. Two identical stages or amplifiers are switched in antiphase and operate on a common load. The loudspeaker is connected directly to the bridge circuit without the use of coupling capacitors. The output voltage across the load turns out to be twice as high, therefore, at the same supply voltage and load, the output power of the amplifier using a bridge circuit is theoretically 4 times greater than that of a separate amplifier. Power amplifiers of modern head units are made according to this design. The possibility of bridge connection is provided in almost all models of additional amplifiers.

Along with the advantage of greater output power, bridge amplifiers also have disadvantages. First of all, the harmonic coefficient is increased by approximately 1.2-1.7 times compared to the original amplifiers and the damping coefficient is twice as bad (with a constant load resistance). Theoretically, the harmonic distortion should not change, but in practice the increase occurs due to differences in the characteristics of real (even identical) amplifiers. The deterioration of damping is also understandable - the output impedances of the amplifiers have accumulated.
The outputs of the built-in amplifiers of the head units have a potential Upit/2 relative to ground. Therefore, an accidental short circuit of the load to ground leads to failure of the amplifier if it does not have protection systems. However, this has very little to do with sound; this must be remembered during installation. However, this property can be used. Thus, the high-level inputs of additional amplifiers are often equipped with a voltage sensor, and the constant voltage at the output of the head unit is used as a signal to turn on the additional amplifier.

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 an acoustic system for a home computer, TV, or cinema. Its advantage is that it does not require fine adjustment 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.

No high voltage is required to power the anode circuits. Of course, there is heating, as in lamp designs. Therefore, if you plan to use the amplifier for a long time, it is best to install, in addition to an aluminum radiator, at least a small fan for forced airflow. Without it, the amplifier circuit on the TDA7294 microassembly will work, but there is a high probability of it going into temperature protection.

Why TDA7294?

This chip has been very popular for more than 20 years. It has won the trust of radio amateurs, since it has very high characteristics, the amplifiers based on it are simple, and anyone, even a novice radio amateur, can repeat the design. The amplifier on the TDA7294 chip (the circuit is shown in the article) can be either monophonic or stereophonic. The internal structure of the microcircuit consists of: An audio amplifier built on this microcircuit belongs to class AB.

Advantages of the microcircuit

Advantages of using a microcircuit for:

1. Very high power output. About 70 W if the load has a resistance of 4 ohms. In this case, the usual circuit for connecting the microcircuit is used.

2. About 120 W at 8 ohms (bridged).

3. Very low level of extraneous noise, distortion is insignificant, reproduced frequencies lie in the range that is completely perceivable 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 small drawback - it is necessary to 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 surprising how it allows you to get such high-quality sound.

Purpose of the microcircuit pins

And now in more detail about what conclusions the TDA7294 has. The first leg is the “signal ground”, connected to the common wire of the entire structure. Pins “2” and “3” are inverting and non-inverting inputs, respectively. The "4" pin is also the "signal ground" connected to the common wire. The fifth leg is not used in audio amplifiers. “6” leg is a volt add-on; an electrolytic capacitor is connected to it. “7” and “8” pins are plus and minus power supply for the input stages, respectively. Leg “9” – standby mode, used in the control unit.

Similarly: “10” leg - muting mode, also used when designing an amplifier. “11” and “12” pins are not used in the design of audio amplifiers. The output signal is taken from the “14” pin and supplied to the speaker system. “13” and “15” pins of the microcircuit are “+” and “-” for connecting the power to the output stage. On the TDA7294 chip, the circuit is no different from those proposed in the article, it is supplemented only by the circuit that is connected to the input.

Features of microassembly

When designing an audio amplifier, you need to pay attention to one feature - the minus power supply, and these are the legs “15” and “8”, electrically connected to the microcircuit body. Therefore, it is necessary to isolate it from the radiator, which will be used in the amplifier in any case. For this purpose it is necessary to use a special thermal pad. If you are using a bridge amplifier circuit on the TDA7294, pay attention to the housing design. It can be vertical or horizontal type. The most common version is designated TDA7294V.

Protective functions of the TDA7294 chip

The microcircuit provides several types of protection, in particular, against supply 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 is also protected against overload and short circuit. If the device body heats up to a temperature of 145 degrees, the sound turns off. When 150 degrees is reached, it switches to standby mode. All pins of the TDA7294 chip are protected from electrostatics.

Amplifier

Simple, accessible to everyone, and most importantly - cheap. In just a few hours you can assemble a very good audio amplifier. Moreover, you will spend most of the time etching the board. The structure of the entire amplifier consists of power and control units, as well as 2 ULF channels. Try to use as few wires as possible in the amplifier design. Follow simple recommendations:

1. A prerequisite is to connect the power source with wires to each ultrasonic circuit board.

2. Tie the power wires into a bundle. With this, you can slightly compensate for the magnetic field created by electric current. To do this, you need to take all three power wires - “common”, “minus” and “plus”, and with a little tension weave them into one braid.

3. Under no circumstances use so-called “earth loops” in the design. This is the case when the common wire connecting all the blocks of the structure is closed into a loop. The ground wire must be connected sequentially, starting from the input terminals further to the ultrasonic circuit board, and ending at the output connectors. It is extremely important to connect the input circuits using shielded and insulated wires.

Control unit for standby and muting modes

This chip also has muting. Functions must be controlled using pins “9” and “10”. The mode is turned on if there is no voltage on these legs of the microcircuit, or it is less than one and a half volts. To enable the mode, it is necessary to apply a voltage to the legs of the microcircuit, the value of which exceeds 3.5 V. In order for the amplifier boards to be controlled simultaneously, which is important for bridge-type circuits, one control unit is assembled for all stages.

When the amplifier is turned on, all the capacitors in the power supply are charged. There is also one capacitor in the control unit that stores charge. When the maximum possible charge is accumulated, 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 turns off second.

Assembling a car subwoofer with your own hands is quite an honorable task, but there are often difficulties with assembling the power amplifier that should power the subwoofer head. For fairly powerful heads, the standard 12 Volt network is not enough, and you need to increase the voltage with a voltage converter.

It’s not possible to achieve high power without using a converter, but what to do if you don’t have the proper experience in building a converter, but you really want to build an amplifier for a subwoofer?

According to the laws of physics, it is impossible to obtain more than 18 watts of power from a 12 Volt network into a 4 Ohm load - we are talking about pure, sinusoidal output power, but as always there are exceptions. There is a variety of amplifiers operating in class H, which allow you to get an output power of 50-70 watts from a 12 Volt network, but such microcircuit amplifiers (for example, TDA1562) are very expensive, therefore, you need to look for another solution.

Today we will consider one of the cheapest options for UMZCH for a subwoofer. The well-known TDA2003 microcircuit is at least the cheapest UMZCH microcircuit. It is powered by 12 Volts and can provide a maximum power of up to 10-12 watts into a 2 ohm load.

The main advantage of the microcircuit itself is that it can work with low-impedance dynamic heads with coil resistance up to 2 ohms. The microcircuit is monophonic in nature (single-channel), therefore there must be a bridge circuit that will increase the output power of the amplifier.

The bridge version works great with standard 4 Ohm heads for a long time, the output power is around 20 Watts, peak surges during deep low frequencies are up to 30 Watts, but of course this is not pure power. But it is quite possible to power a medium-power subwoofer using this option.

The second feature of this option is that the microcircuit costs a penny (half a dollar apiece), the element base contains only a few components, with a total cost of no more than a dollar, but if you have old boards, you can unsolder all the necessary components from them.

The microcircuit operates in class AB, therefore it is impossible to avoid overheating, so the microcircuits must be installed on a common heat sink, and there is no need to use additional insulating gaskets, since the mass of the microcircuits is the same.

Well, yes - we don’t have the part number and number of channels right now - what can you do about it?
Now we will talk about 4 channel amplifiers. For the most part, they are used for automotive use, but, in principle, nothing prevents them from being used at home - their characteristics are quite decent, especially the latest generation.
Let's start with TDA7560, production SGS-Thomson. As usual, this is a class AB bridge amplifier with all kinds of protections and functions Mute And StanBy, and just as you will see in the diagram - the almost complete absence of hanging elements.
Well, this microcircuit also works great at a load of 2 Ohms.

Connection diagram:

That is, in fact, you take a microcircuit, attach inputs and outputs to it, and everything works. Fairy tale.
This creation is produced in a case Flexiwatt25- again with half holes on the sides.

Our next patient is a microcircuit TDA8571J from Philips Semiconductors. With this amplifier, the comrades decided to show off and made it a bridge amplifier, like everyone else, but at the same time - class B. And for the rest, as usual - a full set of output protection and temperature protection. Moreover, like the previous one being prepared, practically no attachments are required.

The main characteristics are as follows:

Connection diagram:

And the amp is bare.
Well, if you just go to the entrance Mute hang. All this is happily in the building SOT411-1, again with half holes on the sides.

That's all - the last one is enough.
This time the last one will be the amplifier TDA8591 all the same Philips Semiconductors. In terms of its characteristics, it is similar to the previous speaker, however, it can work with a 2-ohm load and is somewhat more powerful. Plus, it has a pretty clever DC output voltage detection circuit.

The main characteristics are as follows:

Connection diagram:

Well, in general, nothing particularly terrible, you just need to take into account that for the amplifier to work, the button S1 needs to be closed. Otherwise, he will remain partisan silent.
As for the DC output voltage detection circuit, if you don’t need it, you can throw out almost half of the passive components from the circuit. Let's list these heroes by name: R1-R6, C14. And we connect pin 26 of the microcircuit to the common wire.

Well, that's all for now. Of course, we don’t end the Bridjump theme here - in fact, we’ve only just begun.

State Committee of the Russian Federation for Higher Education

Ural State Technical University - UPI

Department of REIS

DIPLOMA THESIS ON THE TOPIC:

BRIDGED AUDITION POWER AMPLIFIER

Ekaterinburg 2006

Introduction

1. Purpose of the work

2. Terms of reference

3. Operating principle of the bridge UMZCH circuit

4. Preparing the boot file

4.1 Drawing up a description of the circuit model

4.2 Selecting design analysis procedures

4.2.1 Options map.

4.2.2 Print bus installation map.

4.2.3 Temperature setting map.

4.2.4 DC sensitivity calculation map.

4.2.5 Calculation of transmission coefficient in small signal mode.

4.2.6 Calculation of the spectral density of internal noise.

4.2.7 Transition analysis.

4.2.8 Fourier harmonic analysis.

4.2.9 Analysis on alternating current.

4.2.10 Printing results.

4.2.11 Monte Carlo method.

4.2.12 Data preparation map for PROBE.

4.3 Compiling a boot file

5. Debugging the circuit model

6. Analysis of the results of machine calculations

6.1 The influence of temperature on the operation of the circuit

6.2 Spectral density of internal noise

6.3 Amplifier transient response

6.4 Fourier harmonic analysis

6.5 Frequency response

6.6 Monte Carlo analysis

6.7 Determining circuit sensitivity

Conclusion

Bibliography

Annex 1

Appendix 2

Introduction

An audio frequency power amplifier (AMP) is designed to transmit a signal from an excitation source to a load while simultaneously amplifying the signal in terms of power. UMZCH can also be considered as a generator in which the energy of the power source is converted into the energy of an alternating signal under the influence of an input voltage of a certain amplitude. Therefore, UMZCHs are also called generators with external excitation.

UMZCH are generally characterized by the following parameters:

Pout – output power;

K – gain;

Efficiency – efficiency factor;

DF – operating frequency range;

AFC – amplitude-frequency response;

N – level of nonlinear distortion;

Ш – intrinsic noise level.

This work examines the UMZCH bridge, the characteristic features of which are:

maximum use of power supply voltage;

high output power compared to other simple UMZCH;

high circuit stability;

wide range of reproducible frequencies in rated power mode;

comparatively low harmonic distortion.

1. Purpose of the work

Coursework provides the student with the following main opportunities:

learn to analyze the technical specifications (TOR) for the design of radio-electronic circuits (RES);

gain the skills to search for scientific and technical literature and work with it, correctly compile and execute technical documentation;

understand the basic concepts and terms related to computer-aided design of electronic distribution systems;

get acquainted with the basic design procedures for analyzing the circuit design stage of electronic equipment;

get acquainted with the modern package of Pspice application programs for circuit design;

learn to set and perform circuit design tasks;

consolidate and deepen knowledge of methods for calculating RES and the elemental base of REA.

2. Terms of reference

Design a bridge UMZCH using data from Radio magazine No. 1/1992

Technical requirements for UMZCH:

Nominal input voltage 0.35 V

Rated (maximum) output power at

load resistance 4 Ohm 16 (20) W

Nominal frequency range 40…20000 Hz

Output voltage slew rate 25 V/µs

Harmonic distortion at rated power at

Schematic electrical diagram of a bridge UMZCH

Fig. 1. Schematic diagram of the bridge UMZCH.

3. Operating principle of the bridge UMZCH circuit

UMZCH consists of two amplifiers. Let's consider one of them based on a power amplifier. Transistor VT1 operates in the voltage amplification stage, and the remaining VT2-VT5 (all with low saturation voltages Us) form a composite emitter power amplification follower operating in AB mode (quiescent current 20...30 mA).

Diodes VD1 and VD2 improve the thermal stability of the quiescent current. Transistor VT3 provides the necessary drive for transistor VT5. In order to maximize the use of the power supply voltage, two positive voltage feedback circuits (POF) are introduced into the amplifier. With a positive half-wave of the amplified signal, circuit R5R6C3 operates, and with a negative half-wave, R8R9C4.

A distinctive feature of such feedback is its introduction into the collector circuit of transistors VT2, VT3, which leads to an increase in the amplitude of the signal at the output of the amplifier to the maximum possible.

In order to reduce nonlinear distortions caused by the asymmetry of the arm-end stage and the action of the PIC, the amplifier is covered by a general negative feedback (NFO) voltage through the circuit R1 - R4C1. The parameters of this circuit are selected in such a way as to, on the one hand, ensure the stability of the amplifier operating mode according to direct current (due to the action of galvanic feedback through resistor R4), and on the other hand, to obtain the required gain of the entire amplifier (R1, R4). The feedback depth for alternating voltage is about 28 dB. Capacitors C2 and C4 provide the necessary stability of the entire amplifier.

Since the described base amplifier is inverting, in order to simplify the circuit, the signal to the second amplifier is supplied from the output of the first through a voltage divider R10R11.

4. Preparing the boot file

4.1 Drawing up a description of the circuit model

At this stage, the input language Pspace, commands for executing design procedures, auxiliary and service tools, and built-in models of RES components were studied.

The initial circuit contains nodes that form the basis for the description of the circuit. Circuit elements are described using the nodes to which they are connected and their nominal values. Moreover, resistors and capacitors are described directly, but for diodes and transistors, their models are required, which are located in electronic libraries.

4.2 Selecting design analysis procedures

4.2.1 Options map

OPTIONS ACCT NOECHO NOPAGE RELTOL =0.0001

ACCT- provides in the output file static information about the simulated circuit and information about the computing resources used - processor time for performing various analysis procedures;

NOECHO prohibits printing the input file in the output file;

NOPAGE prohibits page numbering, printing of the title line and heading for each type of analysis in the output file;

RELTOL – Sets the relative error of voltage and current.

4 .2.2 Print bus installation map

WIDTH OUT=80

The number 80 sets the number of columns in the output file.

4.2.3 Temperature setting map

TEMP 27 –60 80

This card is required to ensure that all analyzes are performed at three different temperatures.

4.2.4 Card for calculating DC sensitivity

SENS V(13,18),

Using this map, small-signal sensitivities of output variables to changes in internal parameters at direct current are calculated.

4.2.5 Calculation of gain in small signal mode

TF V (13,18) VIN ,

where VIN is the input signal generator.

Using this directive, the small signal DC gain, input and output impedance of the amplifier are calculated.

4.2.6 Calculation of the spectral density of internal noise

NOISE V(13,18) VIN

Because resistors and volume resistances of transistors are sources of thermal noise. In addition, semiconductor devices have shot noise and flicker noise. Using the .NOISE map, the spectral density of the internal noise voltage is calculated at each frequency analysis frequency, which is recalculated to the input of the circuit and to its output.

4.2.7 Transition analysis

TRAN/OP 1U 3M

This directive is used to calculate the circuit's response to a given input stimulus. The OP key is required to display detailed information about the operating point.

4.2.8 Fourier harmonic analysis

FOUR V (6) V (13,18)

This card performs Fourier spectral analysis.

FOUR V(6) – harmonic distortion at the circuit input;