Amplifier with low dynamic distortion and high thermal stability. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers

 Comments on the article

The decrease in dynamic distortions in the amplifier was achieved by expanding the bandwidth of the original (without common OOS) amplifier, using linearizing local OOS and appropriately choosing the cutoff frequencies of the amplitude-frequency characteristics of the cascades. High thermal stability is ensured by local environmental protection, the use of transistors in the pre-terminal stage, the cases of which have the same thermal resistance, and a relatively large (about 250 mA) quiescent current of the transistors of the final stage.

The main parameters:

• Rated frequency range, Hz.......20...20 000
• Rated output power (in the rated frequency range), W at a load with a resistance of 8 ohms at a harmonic coefficient of 0,5%......20
• on a load with a resistance of 4 ohms with a harmonic coefficient of 0,8%.......25
• Rated input voltage at a load with a resistance of 8 ohms (at an output power of 20 W) ....... 1
• Cutoff frequency without OOS (at output power 1 W), kHz.......30
• OOS depth, dB.......20
• Relative level of noise and background, dB.......-70

The amplifier is three-stage. The first stage is differential on transistors V1, V2, selected according to the static current transfer coefficient h21e and the emitter-base voltage. To obtain a sufficiently high input resistance, low noise level and prevent self-heating of transitions, the collector current of these transistors is chosen to be 250 μA. The total emitter current of the transistors is stabilized by the zener diode V13. Local OOS in the first stage is created by including resistors R2, R2 in the emitter circuits of transistors VI, V3.

The second stage is assembled on a composite transistor V4V5. Local OOS is carried out here through the resistor R10, which connects the collector of the transistor V5 to the emitter of the transistor V4. The load of the cascade is the current generator on transistors V6, V8, the resistor R16 and the input resistance of the cascade on transistors V9, V10. The composite transistor, current generator and resistor R16 form an equivalent signal voltage source for the output stage. The resulting 100% voltage feedback eliminates the non-linearity of the current transfer coefficient and increases the cutoff frequency of the cascade.

The output stage is made on transistors V9-V12. To ensure high thermal stability, P701A and P303A transistors were used in the pre-terminal stage, the cases of which have the same thermal resistance. The high quiescent current of transistors V11 and V12 reduces step-type distortion and eliminates the transient process in the main OOS loop (R15, R14, R4, C6) due to thermal shock during a sharp drop in the output signal level. Thermal stabilization of the quiescent current is carried out by the transistor V7. Diodes V15, V16 of its bias circuit are placed on the heat sink of one of the transistors of the final stage. The frequency response of the amplifier is corrected by capacitors C2 and C8 *.

From a short circuit in the load and current overload, the amplifier is protected by fuses F1 - F3, transistor V3 and diode V14. Transistor V3 limits the current of the composite transistor to 9 ... 55 mA when any of the fuses blows, diode V60 limits the negative voltage at the base of transistor V14 to 2 V when fuse F0,7 blows.

Transistors V5, V8 are mounted on U-shaped heat sinks bent from copper sheet 1 mm thick. Dimensions of the base of each of the heat sinks - 23 x 23 mm, shelves - 10 x 23 mm. The thermal resistance of such a heat sink is approximately 35 °C/W. The heat sinks of transistors V11, V12 are bent from copper sheet 2 mm thick.

Each of them consists of two U-shaped parts, riveted at the corners of the bases with copper rivets. Base dimensions - 80 X 80 mm, shelves - 25 x 80 mm. Thermal resistance - 3,6 ° C / W. Diodes V15, V16 are glued into the holes in the heat sink of the transistor V11.

Coil L1 is wound with wire PEV-2 - 0,5 turn to turn until the housing of the resistor R25 (MLT-2) is filled. The deviation of resistance from the values ​​​​of all resistors indicated on the diagram, except for R24 ​​and R25, should not exceed ± 5%.

First, the part of the amplifier powered by a voltage source of ± 30 V is adjusted. To do this, remove the fuses F1 - F3, break the connection of the emitter of the transistor V5 with the base of the transistor V9, as well as the collector of the transistor V8 with the base of the transistor V10. The emitter of transistor V5 is temporarily connected to the collector of transistor V8, and the connection point of resistors R14 and R15 is connected to a common wire. By selecting the resistor R7 * (in the direction of decreasing, starting from 100 ohms), zero voltage is achieved at the collector of the transistor V8. This voltage should not go beyond ±1 V both immediately after power-up and after a ten-minute warm-up of the transistors.

The symmetry of the signal limitation is checked using an oscilloscope by applying an alternating sinusoidal voltage of 100 mV to the input of the amplifier. The voltage swing at the collector of the transistor V8 must be at least ± 24 V, and the cutoff frequency must be at least 200 kHz. To check the transient response of the first two stages, the emitter of the transistor V5 is connected to the connection point of the resistors RJ4, R15 and rectangular pulses with an amplitude of 0,5 V and a frequency of 1 kHz are applied to the input. The pulses on the oscilloscope screen should have a steep (no spikes) rise and fall. If necessary, select the capacitor C8 *.

After that, all connections are restored in accordance with the diagram, the fuses Fl-F3 are put in place, the coil L1 is short-circuited, a capacitor with a capacitance of 14 ... power dissipation 15...5 W. Turning on the power, measure the DC voltage at the output of the amplifier (it should not go beyond ± 10 mV), the background level (permissible range of ripples with a frequency of 8 Hz - no more than 25 mV) and the amplitude of the undistorted output signal (at a load with a resistance of 30 ohms - at least 100 V). The quiescent current of transistors V100, V300 (8 mA) is set by selecting the resistor R20 * (in the direction of decreasing, starting from 11 ... 12 kOhm). After that, the capacitor connecting the resistors R250, R18 with a common wire is removed, and the adjustment can be considered complete.

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 B&O BeoVision Avant 4K TV 15.05.2014 Bang & Olufsen has unveiled the premium BeoVision Avant 4K TV, featuring a range of unique features and proprietary technologies. The panel has a diagonal of 55 inches. As the name implies, it corresponds to the 4K (Ultra HD) format: the resolution is 3840x2160 pixels. The manufacturer notes that the TV is able to muffle the distracting glare on the screen by more than 98% thanks to the high-quality anti-reflective coating on the front and rear surfaces of the two-layer reinforced glass. BeoVision Avant's adaptive mode constantly adjusts the picture automatically, but the viewer can choose from special settings to optimize the visual experience of games, movies or multimedia content. The novelty implements adaptive sensitivity technology with two sensors. The main sensor measures the light intensity in front of the panel, while the secondary sensor measures the light and its hue behind the screen. BeoVision Avant continually adjusts the white balance based on the data it receives to ensure optimal picture quality with bright and saturated colors. The high-quality three-channel speaker system deserves special attention. It includes three dedicated tweeters, three midranges and two powerful woofers. Additionally, you can connect two front speakers, a subwoofer and two rear speakers. Or BeoVision Avant can replace the two additional front speakers by reassigning its own speakers to dedicated right, left and center channels. Various types of stands are available for the TV. For example, the motorized floor stand allows the panel to rotate 90 degrees away from the wall for optimal viewing angles. The motorized wall mount allows you to silently rotate your TV up to 60 degrees from its original position. The desktop stand allows the panel to tilt back slightly, which "gives the impression of the screen floating above the table" and hides the stand itself from view. The TV turns on when placed in a vertical position while opening the speakers below the screen. Low frequency optimization technology is also mentioned. The designer says that the distance from the speaker to the nearest wall drastically affects the depth and strength of the bass output. To counteract this effect, when the TV is mounted on a motorized wall bracket, technology is used to continuously adjust the speaker's bass output according to its position relative to the wall. The BeoVision Avant 4K is already on sale and is priced at approximately US$8000.

Other interesting news:

▪ Orbital connection of qubits improves quantum computing

▪ You can go to jail for watching a pirated DVD movie in Germany

▪ New Garmin fenix 5 multisport smart watch series

▪ Renoir 7nm Desktop APUs - Ryzen 4000G, PRO 4000G and Athlon PRO 3000G

▪ Pioneer slim external burner with BDXL support

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Tips for radio amateurs. Selection of articles

▪ article Language is given to a diplomat in order to hide his thoughts. Popular expression

▪ article In what country did one in five people attempt suicide? Detailed answer

▪ article Securinega semi-shrub. Legends, cultivation, methods of application

▪ article Smoking substances. Simple recipes and tips

▪ TV off timer article. 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