Thermally stable power amplifier. Scheme, description

Free technical library

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

Thermally stable power amplifier. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers

Comments on the article

A distinctive feature of the device is its extreme simplicity and high temperature stability, which makes it possible to operate the output stage transistors at junction temperatures close to the limit.

Thermally stable power amplifier

The main parameters:

Rated output power, W, at a load with a resistance of 4 Ohm.......25
Rated input voltage, V ....... 1
Harmonic coefficient, %, no more, at frequency, Hz 1.......000
5 000......0,14
10 000......0,2
20 000......0,35
Intermodulation distortion coefficient (when applying signals with a frequency of 160 Hz and 1,4 kHz and an amplitude ratio of 4: 1),%, no more ....... 0,3
Power band, Hz.......20...150 000
Maximum output voltage slew rate, V/µs.......8
Input impedance, kOhm.......150

The amplifier is two-stage. The first stage is made on the op-amp A1, the second - on transistors V3, V5-V7. To obtain the maximum possible range of the amplified signal, the so-called "floating" power supply of the op-amp was used (by supplying a part of the output signal through the resistor R6 to the power circuit). The output stage is based on the circuit of the so-called "parallel" amplifier, which has found application in low-power (up to 1 W) power amplifiers.

To improve the amplitude characteristics between the bases of transistors V6, V7, a diode V4 is included. In the absence of a signal and until it reaches a certain level, this diode is closed and does not affect the operation of the cascade. At the moment of limiting the signal growing in the positive direction, when the currents through the resistor R7 and the base of the transistor V6 become equal, and the transistor V5 closes, the reverse bias voltage on the diode V4 begins to decrease, since the transistor V3 is open, and the signal on its emitter continues to increase. Finally, there comes a moment when the diode opens, and instead of the amplification channel V5-V6, the channel V3-V4-V6 is formed. When amplifying a signal that grows in the negative direction, the V5-V4-V7 channel is similarly formed. Resistor R8, shunting diode V4, eliminates sharp breaks in the output signal at the moments of closing transistors V3, V5 and opening diode V4.

The high thermal stability of the amplifier is achieved by using good thermal coupling between transistors V3, V6 and V5, V7.

The presence of two inputs simplifies the use of the amplifier in multiband systems with crossover filters at the input. So, in a two-way system, it is enough to install only one high-pass filter between the inputs of one of the amplifiers (the low-frequency signal is formed as a result of subtracting the signals from the input and output of the filter). When using inverting input 2, remember that the resistance of the signal source is included in the negative feedback circuit ^ covering op-amp A1, so it should not exceed 15 kOhm. The unused input must in any case be connected to a common wire. To increase the stability of the amplifier against self-excitation at the input, it is necessary to turn on a low-pass filter with a cutoff frequency of 20 kHz.

The indicated parameters were obtained when the amplifier was powered from a stabilized source. If the source is not stabilized, the supply voltage must be reduced by 20%.

Transistors V3, V6 and V5, V7 are mounted in pairs on plate heat sinks 80 X 70 mm in size, made of 2 mm thick aluminum alloy sheet, anodized black. Before installation, the cooling surfaces of the transistors must be lubricated with TsIATIM-201 grease. Transistors are installed on both sides of the heat sink and secured with one screw and nut. To ensure reliable thermal contact during the entire period of operation, split lock washers must be placed under the nuts. The amplifier with the specified heat sinks is operational at ambient temperatures up to 35 CC. The quiescent current (at normal temperature - about 50 mA) increases during heating by no more than 15%.

Instead of the OU K140UD8A in the amplifier, you can use the OU K140UD8B, K140UD6, K140UD10, K140UD11, K544UD1, K574UD1. Coil L1 can be wound on a frame with a diameter of 7 and a length of 25 mm. In this case, it should contain 30 turns of wire PEV-2 - 1,0, wound in two layers.

A properly assembled amplifier does not require adjustment.

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

DC/DC Converters L598x 29.10.2010

The L598x is STMicroelectronics' new family of switching buck converters that is small in size and low in price. Converters are widely used in industrial, consumer segments, personal computers and data transmission. With an output current of up to 2A, a lower output voltage limit of 0,6V, and a wide input voltage range of 2,9V to 18V, this family offers great flexibility and versatility.

The built-in p-channel MOSFET (150 mΩ) with low drain-to-source resistance allows the converter to control the duty cycle up to 100%. The switching frequency can be configured from 250 kHz to 1 MHz using an external resistor. The family has additional monitoring and protection functions: overcurrent control, supply voltage control (UVLO), overtemperature control and built-in digital soft start mode.

Combined in the heat-resistant DFN3x3-8L package, these features allow you to implement reliable and compact applications with a minimum number of external components. The L598x family can be externally synchronized to each other in a master/slave configuration with a phase shift of 180°C and can be used with multilayer ceramic capacitors (MLCCs) as an output filter.

The L598x family consists of four microcircuits: L5980, L5981, L5983 and L5985, which differ in output current parameters.

Other interesting news:

▪ Movie Chest

▪ Rapid seawater desalination method

▪ Walruses do not have enough space in the sea

▪ New form of magnetism discovered

▪ diamond diode

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Instructions for use. Article selection

▪ article tit for tat. Popular expression

▪ article Which planets rotate in the opposite direction? Detailed answer

▪ article Determination of distances by visible details of objects. Travel Tips

▪ article Protection of high-power LEDs from excessive current. Encyclopedia of radio electronics and electrical engineering

▪ article Safety device, 12 volts 1 amp. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages of this page

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