UMZCH based on the operational amplifier KR544UD2. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers

 Comments on the article

The proposed UMZCH (Fig. 1) is built on the basis of the KR544UD2 operational amplifier.

UMZCH parameters

Operating frequency range, Hz, not less than 15...30000
Nonlinearity of the amplitude-frequency characteristic, dB, no more than 2
Rated power at load:
- 4 Ohm, W 40
- 8 Ohm, W 20
Harmonic coefficient, at Рnom, % no more than 0,01
Rated input voltage, V 0,7
Input resistance, kOhm, not less than 47
Output resistance, Ohm, no more than 0,03
Relative level of noise and background, dB, no more than -86
Rated supply voltages, V ±30

Operational amplifier DA1 is powered through transistors VT1 and VT2, which reduce the supply voltage to the values ​​set by the dividers R3, R4 and R5, R6. The bias voltages of transistors VT3, VT4 are determined by the voltage drop across resistors R8, R9. If necessary, DA1 can be balanced using the divider R14, R15.

(click to enlarge)

The quiescent current of the terminal transistors VT3, VT4 determines the bias voltage across the resistors R11, R12 (0,35 ... 0,4 V), which, at low signal levels, keeps the transistors VT5, VT6 in the closed state even when the supply voltage is increased by 10 .. .15% or overheating by 60...80°. Resistors R11, R12 simultaneously stabilize the operation mode of the pre-terminal cascade VT3, VT4, creating local negative current feedback (OOS). The total OOS for voltage is formed by the divider R7, R10.

Low-pass filters R2, C2 and R13, C7 with cutoff frequencies in the region of 60 kHz prevent self-excitation of the amplifier at high frequencies. Capacitors C5, C6 correct the phase-frequency characteristic of the pre-terminal and final stages. Coil L1 increases the stability of the amplifier when operating on a load with increased reactivity.

Assembly and installation. When assembling the structure, it is necessary to use a soldering iron with good insulation and a power of not more than 40 watts. A drawing of the UMZCH printed circuit board is shown in fig. 2, and the assembly drawing - in fig. 3.

The assembly order is as follows: jumper S1, resistors, capacitors, coil L1, operational amplifier (DA1), transistors VT1 ... VT4, after preliminary adjustment - transistors VT5, VT6. Frameless coil L1 contains 10 turns of any copper winding wire with a diameter of 1 ... 2 mm. It is wound on a temporary mandrel with a diameter of 4 ... 6 mm, for example, on a thin ballpoint pen or pencil.

In order to minimize non-linear distortion, transistors VT3 ... VT6 must be connected to the printed circuit board with conductors no longer than 50 mm.

The optimal design of the UMZCH is shown in Fig. 3. With the help of two corners, the board is screwed to the heat sink, and the transistors are soldered directly into the board. It is most convenient to do this in the following sequence:

- mark the heat sink, drill the necessary holes and cut the MOH thread into them. The design of the heat sink can be arbitrary, however, its surface area for a maximum output power of 60 W must be at least 500 cm2;

- screw the board to the heat sink;

- install transistors VT3, VT4 in the corresponding holes of the board, then screw them to the heat sink, and then solder them;

- after preliminary adjustment, similarly mount transistors VT5, VT6;

- after that, solder wires for connecting power and load with a cross section of at least 0,5 mm2.

Adjustment

To set up the amplifier, you need an oscilloscope, a low-frequency generator, a tester, a load dummy and a bipolar power supply with an output voltage of ±30 V at a load current of at least 4 A.

The high stability of the UMZCH allows it to be powered from a simple unstabilized power source. During its adjustment and operation, power is supplied to the amplifier through 5 A fuses. The adjustment is started with the transistors VT5, VT6 turned off and the input shorted (points 1 and 2 are connected).

Connect the oscilloscope to the UMZCH output without load in the maximum sensitivity mode and briefly apply power. If there is no AC voltage at the output, i.e. the amplifier is not excited, measure the operating modes VT3, VT4; voltage at pins 7 and 4 DA1. They must be within 13,4 ... 14 V and differ from each other by no more than 0,3 V. The voltage drops across the resistors R11, R12 must be within 0,35 ... 0,4 V. If they differ by more than 10%, it is necessary to select resistors R8, R9. At the same time, their new values ​​should still be approximately equal to each other.

In the case of self-excitation of the amplifier, it is necessary to increase the capacitances of capacitors C5, C6, or by cutting the path connecting pins 1 and 8

DA1 solder a capacitor of the KM-5 type with a capacity of 5 ... 10 pF to them.

Measure the DC output voltage and if it exceeds 30 mV, balance DA1. To do this, solder a variable resistor with a resistance of 100 ... 200 kOhm instead of resistors R14 and R15 (the middle output to the point of their connection with pin 7 of DA1). By rotating the axis of this resistor, achieve the desired output voltage value, measure the obtained resistance values ​​​​and solder the corresponding fixed resistors R14 and R15. It is undesirable to use a trimming resistor as a balancing resistor - due to the aging of this resistor, the amplifier may be unbalanced during its operation.

Install transistors VT5, VT6 on the heat sink and on the board. Briefly applying power, make sure that the UMZCH is not excited.

Connect a resistor with a resistance of 16 ohms with a power of 10 ... 15 W to the output of the UMZCH, and apply a signal from the generator to the input (disconnect points 1 and 2) with a level of 0,05 V with a frequency of 1 kHz.

Check the symmetry of the limitation of both half-waves of the sine wave.

If necessary, by final balancing of DA1, achieve the minimum constant voltage at the UMZCH output.

Connect the nominal load - a resistor with a resistance of 4 ... 8 ohms with a power of at least 50 W (for example, a rheostat) - and once again measure the main characteristics of the UMZCH.

After the final adjustment, connect the music source and the actual speaker system.

To operate the power amplifier from signal sources with a standard 250 mV line output (tape recorder, player, etc.), you should use a preamplifier with the ability to adjust the volume and tone.

If the input signal source is assembled according to a unipolar supply circuit, when the amplifier is turned on, "clicks" in the speakers may be heard. To eliminate this phenomenon, you can assemble a circuit for delaying the connection of the speaker system and protecting the speakers from short circuits, for example, according to the circuits given in [1...3].

Literature

1. Radio, 1990, N8.C.63.
2. Radio, 1991, N1, p.59.
3. Radio, 1992, N4, p.37.

Author: A. Fefelov; Publication: cxem.net

See other articles Section Transistor power amplifiers.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive Explosives will improve the safety of electric cars 01.10.2019 Bosch has developed a new system that is designed to reduce the risk of electric vehicle battery fire and electric shock to people in the event of an accident. Many potential buyers of vehicles with an electric propulsion system have expressed concern that in the event of an accident, metal parts of the car body could be energized. And this can become an obstacle in the way of saving people. In addition, in such a situation, the risk of fire increases. Bosch proposes to solve the problem by using small explosive packs. Such charges in the event of a traffic accident will instantly cut off entire sections of cables going to the battery pack. As a result, the car will be completely de-energized. Explosive packages can be activated by signals from various on-board sensors - for example, from airbag sensors. The CG912 microchip, which was originally designed to control the airbags, will be able to control the operation of the system. Breaking the cables leading to the batteries will eliminate the possibility of electric shock to people and reduce the likelihood of a battery fire.

Other interesting news:

▪ Smartphone hurts work

▪ Israeli Butterfly Drone

▪ Cyborg Olympics planned

▪ Edible packaging for fish

▪ Energy from the air will recharge the smartphone

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the Electrician website. PTE. Article selection

▪ article Lord Tashkenters. Popular expression

▪ article Which Catholic priests made scientific discoveries that contradicted religious dogmas? Detailed answer

▪ Astilba David article. Legends, cultivation, methods of application

▪ article Acoustic telescope. Encyclopedia of radio electronics and electrical engineering

▪ article The principle of operation of AON. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024