Switching power supply for amplifier tda7294. A powerful amplifier based on tda7294, assembled according to the ITUN circuit. Typical connection diagram

There are quite a few varieties of budget amplifiers and this is one of them. The circuit is very simple and contains only one microcircuit, several resistors and capacitors. The characteristics of the amplifier are quite serious, at such a low cost. The output power reaches 100W at maximum power. Absolutely pure output is 70 W.

Amplifier Specifications

More detailed characteristics amplifier on TDA7294:

The power supply is bipolar with a midpoint of 12 to 40 V.
F out - 20-20000 Hz
R out. Max. (supply +-40V, Rn=8 Ohm) - 100 W.
R out. Max. (supply +-35V, Rn=4 Ohm) - 100 W.
To the harmonics (Pout = 0.7 R max.) - 0.1%.
Uin - 700 mV.

The TDA7294 chip is cheap and costs a penny, I bought it - .

These amplifiers work great in pairs, so make two of these and you'll have a simple stereo amplifier. More detailed characteristics of the amplifier and switching circuits can be found in.
It is advisable to choose a power supply for the amplifier that is one and a half times more powerful, so keep this in mind.

Amplifier PCB

Drawing of the arrangement of elements:

Download to the board in lay format:

(downloads: 1084)

When printing, set the scale to 70%.

Ready amplifier

The microcircuit must be installed on a radiator, preferably with a fan, since it will be smaller in size. Making a printed circuit board is not at all necessary. You can take a breadboard with a large number of holes and assemble the amplifier in 30 minutes.
I advise you to build such a simple amplifier that has proven itself to be excellent.

power unit

The power supply is completed according to the classical scheme with a 150 W transformer. I recommend taking a transformer with a ring core, as it is more powerful, smaller and emits a minimum of network interference and electromagnetic background AC voltage. The filter capacitors of each arm are 10,000 µF.

Collect your amplifier and see you soon!

The TDA7294 microcircuit is an integrated low-frequency amplifier, which is very popular among electronics engineers, both beginners and professionals. The network is full of different reviews about this chip. I decided to build an amplifier on it. I took the diagram from the datasheet.

This “micruha” feeds on a bipolar diet. For beginners, I will explain that it is not enough to have a “plus” and a “minus”.

You need a source with a positive terminal, a negative terminal and a common one. For example, relative to the common wire there should be plus 30 Volts, and in the other arm minus 30 Volts.

The amplifier on the TDA7294 is quite powerful. The maximum rated power is 100 W, but this is with nonlinear distortion of 10% and at maximum voltage (depending on load resistance). You can reliably shoot at 70W. Thus, on my birthday, I listened to two parallel-connected “Radio Engineering S30” speakers on one TDA 7294 channel. The entire evening and half of the night, the speakers sounded, sometimes putting them into overdrive. But the amplifier withstood it calmly, although it sometimes overheated (due to poor cooling).

Main characteristicsTDA7294

Supply voltage +-10V…+-40V

Peak output current up to 10A

Operating temperature of the crystal up to 150 degrees Celsius

Output power at d=0.5%:

At +-35V and R=8Ohm 70W

At +-31V and R=6Ohm 70W

At +-27V and R=4Ohm 70W

With d=10% and increased voltage (see), you can achieve 100W, but it will be a dirty 100W.

Amplifier circuit for TDA7294

The diagram shown is taken from the passport, all denominations are preserved. With proper installation and correctly selected element values, the amplifier starts the first time and does not require any settings.

Amplifier elements

The values of all elements are indicated in the diagram. Resistor power 0.25 W.

The “microphone” itself should be installed on the radiator. If the radiator is in contact with other metal elements of the case, or the case itself is the radiator, then it is necessary to install a dielectric gasket between the radiator and the TDA7294 case.

The gasket can be silicone or mica.

The radiator area should be at least 500 sq.cm, the larger the better.

Initially, I assembled two channels of the amplifier, since the power supply allowed, but I didn’t choose the right housing and both channels simply did not fit into the housing in terms of dimensions. I tried to make the PCB smaller, but it didn't work.

After fully assembling the amplifier, I realized that the case was not enough to cool one channel of the amplifier. My case was a radiator. In short, I rolled out the lip into two channels.

When listening to my device at full volume, the crystal began to overheat, but I lowered the volume level and continued testing. As a result, I listened to music at a moderate volume until midnight, periodically causing the amplifier to overheat. The TDA7294 amplifier turned out to be very reliable.

ModeSTAND- BY TDA7294

If 3.5V or more is applied to the 9th leg, the microcircuit exits sleep mode; if less than 1.5V is applied, it will enter sleep mode.

In order to wake the device from sleep mode, you need to connect the 9th leg through a 22 kOhm resistor to the positive terminal (bipolar power source).

And if the 9th leg is connected through the same resistor to the GND terminal (bipolar power source), then the device will enter sleep mode.

The printed circuit board located under the article is routed so that leg 9 is connected via a 22 kOhm resistor to the positive terminal of the power supply. Consequently, when the power source is turned on, the amplifier immediately begins to operate in sleep mode.

ModeMUTE TDA7294

If 3.5V or more is applied to the 10th leg of the TDA7294, the device will exit the muting mode. If you apply less than 1.5V, the device will enter muting mode.

In practice, this is done like this: through a 10 kOhm resistor, connect the 10 leg of the microcircuit to the plus of a bipolar power source. The amplifier will “sing”, that is, it will not be muted. On the printed circuit board attached to the article, this is done using a track. When power is applied to the amplifier, it immediately begins to sing, without any jumpers or toggle switches.

If we connect the TDA7294 leg through a 10 kOhm resistor 10 to the GND pin of the power supply, then our “amplifier” will enter mute mode.

Power supply.

The voltage source for the device was an assembled one, which showed itself very well. When listening to one channel, the keys are warm. Schottky diodes are also warm, although there are no radiators installed on them. IIP without protection and soft start.

The circuit of this SMPS is criticized by many, but it is very easy to assemble. It works reliably without soft start. This circuit is very suitable for novice electronics engineers because of its prostate.

Frame.

The case was purchased.

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.

Not required high voltage for powering 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, which 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 in this case The usual circuit for connecting the microcircuit is used.

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

3. Very low level extraneous noise, insignificant distortion, reproduced frequencies lie in the range 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 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 removed from the “14” pin and supplied to sound 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 also has overload protection 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.

Updated: 04/27/2016

An excellent amplifier for home can be assembled using the TDA7294 chip. If you are not strong in electronics, then such an amplifier is an ideal option; it does not require fine tuning and debugging like a transistor amplifier and is easy to build, unlike a tube amplifier.

The TDA7294 microcircuit has been in production for 20 years and has still not lost its relevance and is still in demand among radio amateurs. For a novice radio amateur, this article will be a good help in getting to know integrated audio amplifiers.

In this article I will try to describe in detail the design of the amplifier on the TDA7294. I will focus on a stereo amplifier assembled according to the usual circuit (1 microcircuit per channel) and will briefly talk about the bridge circuit (2 microcircuits per channel).

TDA7294 chip and its features

TDA7294 is the brainchild of SGS-THOMSON Microelectronics, this chip is an AB class low-frequency amplifier, and is built on field-effect transistors.

The advantages of the TDA7294 include the following:

output power, with distortion 0.3–0.8%:
- 70 W for 4 ohm load, conventional circuit;
- 120 W for 8 ohm load, bridge circuit;
Mute function and Stand-By function;
low noise level, low distortion, frequency range 20–20000 Hz, wide operating voltage range - ±10–40 V.

Specifications

Technical characteristics of the TDA7294 chip
Parameter	Conditions	Minimum	Typical	Maximum	Units
Supply voltage		±10		±40	IN
Frequency range	Signal 3 db Output power 1W	20-20000			Hz
Long-term output power (RMS)	harmonic coefficient 0.5%: Up = ±35 V, Rн = 8 Ohm Up = ±31 V, Rн = 6 Ohm Up = ±27 V, Rн = 4 Ohm	60 60 60	70 70 70		W
Peak music output power (RMS), duration 1 sec.	harmonic factor 10%: Up = ±38 V, Rн = 8 Ohm Up = ±33 V, Rн = 6 Ohm Up = ±29 V, Rн = 4 Ohm		100 100 100		W
Total harmonic distortion	Po = 5W; 1kHz Po = 0.1–50W; 20–20000Hz		0,005	0,1	%
Total harmonic distortion	Up = ±27 V, Rн = 4 Ohm: Po = 5W; 1kHz Po = 0.1–50W; 20–20000Hz		0,01	0,1	%
Protection response temperature		145			°C
Quiescent current		20	30	60	mA
Input impedance		100			kOhm
Voltage Gain		24	30	40	dB
Peak output current		10			A
Operating temperature range		0		70	°C
Case thermal resistance				1,5	°C/W

Pin assignment

Pin assignment of the TDA7294 chip
IC output	Designation	Purpose	Connection
1	Stby-GND	"Signal Ground"	"General"
2	In-	Inverting input	Feedback
3	In+	Non-inverting input	Audio input via coupling capacitor
4	In+Mute	"Signal Ground"	"General"
5	N.C.	Not used	–
6	Bootstrap	"Voltage boost"	Capacitor
7	+Vs	Input stage power supply (+)
8	-Vs	Input stage power supply (-)
9	Stby	Standby mode	Control block
10	Mute	Mute mode	Control block
11	N.C.	Not used	–
12	N.C.	Not used	–
13	+PwVs	Output stage power supply (+)	Positive terminal (+) of the power supply
14	Out	Exit	Audio output
15	-PwVs	Output stage power supply (-)	Negative terminal (-) of the power supply

Note. The microcircuit body is connected to the power supply negative (pins 8 and 15). Do not forget about insulating the radiator from the amplifier body or insulating the microcircuit from the radiator by installing it through a thermal pad.

I would also like to note that in my circuit (as well as in the datasheet) there is no separation of input and output lands. Therefore, in the description and in the diagram, the definitions of “general”, “ground”, “housing”, GND should be perceived as concepts of the same sense.

The difference is in the cases

The TDA7294 chip is available in two types - V (vertical) and HS (horizontal). The TDA7294V, having a classic vertical body design, was the first to roll off the production line and is still the most common and affordable.

Complex of protections

The TDA7294 chip has a number of protections:

protection against power surges;
protection of the output stage from short circuit or overload;
thermal protection. When the microcircuit heats up to 145 °C, the mute mode is activated, and at 150 °C the standby mode is activated;
protection of microcircuit pins from electrostatic discharges.

Power amplifier on TDA7294

A minimum of parts in the harness, a simple printed circuit board, patience and known good parts will allow you to easily assemble an inexpensive TDA7294 UMZCH with clear sound and good power for home use.

You can connect this amplifier directly to the line output of your computer sound card, because The nominal input voltage of the amplifier is 700 mV. And the nominal voltage level of the linear output of the sound card is regulated within 0.7–2 V.

Amplifier block diagram

The diagram shows a version of a stereo amplifier. The structure of the amplifier using a bridge circuit is similar - there are also two boards with TDA7294.

A0. power unit
A1. Control unit for Mute and Stand-By modes
A2. UMZCH (left channel)
A3. UMZCH (right channel)

Pay attention to the connection of the blocks. Improper wiring inside the amplifier may cause additional interference. To minimize noise as much as possible, follow several rules:

Power must be supplied to each amplifier board using a separate harness.
The power wires must be twisted into a braid (harness). This will compensate for the magnetic fields created by the current flowing through the conductors. We take three wires (“+”, “-”, “Common”) and weave them into a pigtail with a slight tension.
Avoid ground loops. This is a situation where a common conductor, connecting blocks, forms a closed circuit (loop). The connection of the common wire must go in series from the input connectors to the volume control, from it to the UMZCH board and then to the output connectors. It is advisable to use connectors isolated from the housing. And for input circuits there are also shielded and insulated wires.

List of parts for TDA7294 power supply:

When purchasing a transformer, please note that the effective voltage value is written on it - U D, and by measuring it with a voltmeter you will also see the effective value. At the output after the rectifier bridge, the capacitors are charged to the amplitude voltage - U A. The amplitude and effective voltages are related by the following relationship:

U A = 1.41 × U D

According to the characteristics of the TDA7294, for a load with a resistance of 4 Ohms, the optimal supply voltage is ±27 volts (U A). The output power at this voltage will be 70 W. This is the optimal power for the TDA7294 - the distortion level will be 0.3–0.8%. There is no point in increasing the power supply to increase power because... the level of distortion increases like an avalanche (see graph).

We calculate the required voltage of each secondary winding of the transformer:

U D = 27 ÷ 1.41 ≈ 19 V

I have a transformer with two secondary windings, with a voltage of 20 volts on each winding. Therefore, in the diagram I designated the power terminals as ± 28 V.

To obtain 70 W per channel, taking into account the efficiency of the microcircuit of 66%, we calculate the power of the transformer:

P = 70 ÷ 0.66 ≈ 106 VA

Accordingly, for two TDA7294 this is 212 VA. The nearest standard transformer, with a margin, will be 250 VA.

It is appropriate to state here that the power of the transformer is calculated for a pure sinusoidal signal; corrections are possible for a real musical sound. So, Igor Rogov claims that for a 50 W amplifier, a 60 VA transformer will be sufficient.

The high-voltage part of the power supply (before the transformer) is assembled on a 35x20 mm printed circuit board; it can also be mounted:

The low-voltage part (A0 according to the structural diagram) is assembled on a 115x45 mm printed circuit board:

All amplifier boards are available in one.

This power supply for the TDA7294 is designed for two chips. For more chips will have to be replaced diode bridge and increase the capacitor capacity, which will entail a change in the dimensions of the board.

Control unit for Mute and Stand-By modes

The TDA7294 chip has a Stand-By mode and a Mute mode. These functions are controlled through pins 9 and 10, respectively. The modes will be enabled as long as there is no voltage on these pins or it is less than +1.5 V. To “wake up” the microcircuit, it is enough to apply a voltage greater than +3.5 V to pins 9 and 10.

To simultaneously control all UMZCH boards (especially important for bridge circuits) and save radio components, there is a reason to assemble a separate control unit (A1 according to the block diagram):

Parts list for control box:

Diode (VD1). 1N4001 or similar.
Capacitors (C1, C2). Polar electrolytic, domestic K50-35 or imported, 47 uF 25 V.
Resistors (R1–R4). Ordinary low-power ones.

The printed circuit board of the block has dimensions of 35×32 mm:

The control unit's task is to ensure silent switching on and off of the amplifier using the Stand-By and Mute modes.

The operating principle is as follows. When the amplifier is turned on, along with the capacitors of the power supply, capacitor C2 of the control unit is also charged. Once it is charged, Stand-By mode will turn off. It takes a little longer for capacitor C1 to charge, so Mute mode will turn off second.

When the amplifier is disconnected from the network, capacitor C1 discharges first through diode VD1 and turns on the Mute mode. Then capacitor C2 discharges and sets the Stand-By mode. The microcircuit becomes silent when the power supply capacitors have a charge of about 12 volts, so no clicks or other sounds are heard.

Amplifier based on TDA7294 according to the usual circuit

The microcircuit's connection circuit is non-inverting, the concept corresponds to the original one from the datasheet, only the component values have been changed to improve the sound characteristics.

Parts List:

Capacitors:
- C1. Film, 0.33–1 µF.
- C2, C3. Electrolytic, 100-470 µF 50 V.
- C4, C5. Film, 0.68 µF 63 V.
- C6, C7. Electrolytic, 1000 µF 50 V.
Resistors:
- R1. Variable dual with linear characteristic.
- R2–R4. Ordinary low-power ones.

Resistor R1 is double because stereo amplifier. Resistance of no more than 50 kOhm with a linear rather than logarithmic characteristic for smooth volume control.

Circuit R2C1 is a high pass filter (HPF) that suppresses frequencies below 7 Hz without passing them to the amplifier input. Resistors R2 and R4 must be equal to ensure stable operation of the amplifier.

Resistors R3 and R4 organize a negative feedback circuit (NFC) and set the gain:

Ku = R4 ÷ R3 = 22 ÷ 0.68 ≈ 32 dB

According to the datasheet, the gain should be in the range of 24–40 dB. If it is less, the microcircuit will self-excite; if it is more, distortion will increase.

Capacitor C2 is involved in the OOS circuit; it is better to take one with a larger capacitance to reduce its influence on low frequencies. Capacitor C3 provides an increase in the supply voltage of the output stages of the microcircuit - “voltage boost”. Capacitors C4, C5 eliminate noise introduced by wires, and C6, C7 complement the power supply filter capacitance. All amplifier capacitors, except C1, must have a voltage reserve, so we take 50 V.

The amplifier's printed circuit board is single-sided, quite compact - 55x70 mm. When developing it, the goal was to separate the “ground” with a star, ensure versatility and at the same time maintain minimal dimensions. I think this is one of the smallest boards for TDA7294. This board is designed for installation of one microcircuit. For the stereo option, accordingly, you will need two boards. They can be installed side by side or one above the other like mine. I’ll tell you more about versatility a little later.

The radiator, as you can see, is indicated on one board, and the second, similar one, is attached to it from above. Photos will be a little further.

Amplifier based on TDA7294 using a bridge circuit

A bridge circuit is a pairing of two conventional amplifiers with some adjustments. This circuit solution is designed for connecting acoustics with a resistance of not 4, but 8 ohms! Acoustics are connected between the amplifier outputs.

There are only two differences from the usual scheme:

the input capacitor C1 of the second amplifier is connected to ground;
added feedback resistor (R5).

The printed circuit board is also a combination of amplifiers according to the usual circuit. Board size – 110×70 mm.

Universal board for TDA7294

As you have already noticed, the above boards are essentially the same. The following version of the printed circuit board fully confirms the versatility. On this board you can assemble a 2x70 W stereo amplifier (regular circuit) or a 1x120 W mono amplifier (bridged). Board size – 110×70 mm.

Note. To use this board in a bridge version, you need to install resistor R5 and install jumper S1 in a horizontal position. In the figure, these elements are shown as dotted lines.

For a conventional circuit, resistor R5 is not needed, and the jumper must be installed in a vertical position.

Assembly and adjustment

Assembling the amplifier will not pose any particular difficulties. The amplifier does not require any adjustment as such and will work immediately, provided that everything is assembled correctly and the microcircuit is not defective.

Before first use:

Make sure the radio components are installed correctly.
Check that the power wires are connected correctly, do not forget that on my amplifier board the ground is not centered between plus and minus, but on the edge.
Make sure that the microcircuits are isolated from the radiator; if not, then check that the radiator is not in contact with ground.
Apply power to each amplifier in turn, so there is a chance you won’t burn out all the TDA7294 at once.

First start:

We do not connect the load (acoustics).
We connect the amplifier inputs to ground (connect X1 to X2 on the amplifier board).
We serve food. If everything is fine with the fuses in the power supply and nothing smokes, then the launch was a success.
Using a multimeter, we check the absence of direct and alternating voltage at the output of the amplifier. Minor is allowed constant pressure, no more than ±0.05 volts.
Turn off the power and check the chip body for heating. Be careful, the capacitors in the power supply take a long time to discharge.
Through a variable resistor (R1 according to the diagram) we supply sound signal. Turn on the amplifier. The sound should appear with a slight delay, and disappear immediately when turned off; this characterizes the operation of the control unit (A1).

Conclusion

I hope this article will help you build a high-quality amplifier using the TDA7294. Finally, I present a few photos of the assembly process, do not pay attention to the quality of the board, the old PCB is unevenly etched. Based on the assembly results, some edits were made, so the boards in the .lay file are slightly different from the boards in the photographs.

The amplifier was made for a good friend, he came up with and implemented such an original housing. Photos of the assembled stereo amplifier on the TDA7294: