Power supply for car amplifier, 12/±20 volts 70 watts. Scheme, description

Free technical library

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

Power supply for car amplifier, 12/±20 volts 70 watts. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Power Supplies

Comments on the article

The supply voltage of the on-board network of a passenger car is 12 V. If we set the acoustic system impedance to 4 ohms, then the maximum power that can be obtained with this supply voltage will be 36 watts. This is the most theoretical maximum, assuming the bridged connection of the amplifier and zero resistance of the transistors of the output stage in the open state, that is, practically for a digital switching amplifier.

For an analog amplifier, the maximum power will be no more than 20 watts per channel when bridged.

To obtain more power, it is necessary either to use a pulsed output stage that generates an audio signal using the pulse-width modulation method, or it is necessary to lower the impedance of the speaker system. In the first case, the ultrasonic component from PWM will be present in the sound, as well. more complex measures to combat signal distortion will be needed.

In the second case, the resistance of the voice coil will already be comparable to the resistance of the wires going to it, which, in general, can nullify such measures. There is another way - the organization of a volt-addition of power in the output stage due to the rectification of the output signal and a large storage capacity. But this is also not very good, since it is difficult to obtain a sufficiently linear frequency response, and there may be an uneven dependence of the power transfer coefficient on the input signal.

Of course, all the measures listed above to increase the output power of an amplifier powered by a low-voltage source have the right to exist, and with careful and competent execution they give good results. But, there is a more traditional way to increase the power of the ULF - simply by increasing its supply voltage using a voltage converter, and even organizing bipolar power with its help.

This method allows you to use in a car not a compromise automotive version of ULF, but almost any ULF circuit used in stationary equipment that can provide significantly better sound quality than ingenious powerful auto-ULF circuits, with voltage boosts on capacitors and low-impedance acoustic systems, because as they say any Hl-end lover - the best sound is given by a simple single-tube cascade without feedback circuits and with a high-impedance output. But this is of course the other extreme.

Whatever the scheme of the "ordinary" ULF that you plan to use in a car, you need a power supply voltage converter for it. This converter must produce an increased bipolar voltage, in this case ± 20 V at an output current of up to 4 A. Such a power supply can supply ULF with an output power of up to 60-70 W, made according to the traditional scheme.

The schematic diagram of the converter is shown in the figure. The scheme is largely typical. The master oscillator with a PWM output voltage stabilization circuit is made on the A1 chip. The nominal generation frequency is about 50 kHz (adjustable by resistor R3). The exemplary voltage from the output is fed to the input of the comparator (pin 1) and, depending on the voltage at pin 1, the comparator changes the width of the pulses generated by the microcircuit so as to maintain the output voltage stable. The value of the output voltage is precisely set by the tuning resistor R8, which will form this measuring voltage.

(click to enlarge)

The VD1-C3-R4-R5 circuit forms a soft start circuit.

Output antiphase pulses are taken from pins 8 and 11 of A1 to be fed to the output stages, but here they first go to the output transistor driver on the A2 chip. The task of this microcircuit is to amplify the power of these pulses, since powerful field-effect transistors with a low open channel resistance are used here. Such transistors have a significant gate capacitance. To ensure sufficient speed of opening transistors, it is necessary to ensure the fastest possible charging and discharging of the capacitances of their gates, and this is what the driver on A2 serves for.

Large capacitors C6 and C7 are installed along the power circuit, they must be soldered with a thick wire directly at the tap point of the primary winding of the transformer.

For the option that gives a bipolar supply voltage (as in the diagram), the secondary winding has a tap from the middle. This tap through the inductance L2 is connected to a common wire. A rectifier is made on diodes VD2-VD5 (Schottky diodes), giving positive and negative voltages. In a unipolar supply circuit, the secondary winding does not have a tap, and the negative terminal of the rectifier bridge must be connected to a common minus. In this case, if a voltage of 40V is required, the resistance of the resistor R9 must be doubled compared to that indicated in the diagram.

As a basis for the transformer, a neatly disassembled and unwound transformer from the power source of an old color TV of the 3-USCT line models is used. It should be noted that the core of the transformer is glued quite firmly there and not every attempt to separate its halves ends in success. In this sense, in my opinion, it is better to have two such transformers (fortunately, there are plenty of unnecessary power supplies MP-1, MP-3, etc. now). At one transformer, cut the frame along with the winding and remove it. The core remains, which, without a frame and winding, is much easier and more effective to divide. At the second transformer, carefully break and break the core so as not to damage the frame. As a result of this "barbarity" you get one good core and one good carcass.

Now about winding. The winding must hold a large current, so a thick wire is needed for it. For winding the primary winding, a triple folded PEV 0,61 wire is used. For the secondary, the same wire, but folded in half. Primary winding - 5 + 5 turns, secondary - 10 + 10 turns.

Coil L1 is not a coil, but a ferrite tube worn on a wire. L2 - 5 turns of a PEV 0,61 folded three times on a ferrite ring with a diameter of 28 mm.

Rare FDB045AN transistors can be replaced by others, and the choice is quite large, since a maximum drain-source voltage of at least 50 V is required, a drain current of at least 70 A and an open resistance of channel 8 of no more than 0,01 Ohm. According to these parameters, you can select a lot of replacement candidates, that is, almost any FET transistor for automotive ignition switches and other things.

Capacitors C11 and C12 for a voltage of at least 25 V, the remaining capacitors for a voltage of at least 16 V.

Author: Gorchuk N.V.

See other articles Section Power Supplies.

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

LG Pocket Photo 2 27.12.2013

LG introduced the second model of miniature Pocket Photo printer. The device as a whole has become somewhat smaller: 120 x 76 x 20 mm versus 121 x 72 x 24 mm for the first model. The built-in battery is enough to print 30 photos, and the internal tray is designed for the same number of sheets.

As before, the baby can receive printable files via Bluetooth or NFC. Android, iOS and Windows 8 operating systems are supported. The resolution of the final photo is 600 x 313 pixels.

The novelty, like the first model, uses ZINK Imaging technology, requiring no ink or toner for printing. Instead, ZINK technology is used: a special paper is used with four-color dye crystals embedded in the structure. The crystals are activated by a thermal point effect, which is exerted on them by a special heating element. Thus, a full-color image is obtained on paper.

The mini printer is equipped with a Bluetooth adapter and an NFC microchip for wireless connection to a cell phone or computer. The companion app lets you edit images, apply effects and frames, add a QR code, and prepare pictures for ID printing.

LG Pocket Photo 2 will be available in January 2014 in white, pink and yellow.

Other interesting news:

▪ Smartphone ZTE Star 1

▪ Smartphone with infinite memory

▪ Acoustics Microlab H30BT with NFC support

▪ Black caviar from Switzerland

▪ MOSFET driver type MAX5078

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site The most important scientific discoveries. Article selection

▪ article Nervous diseases. Lecture notes

▪ article Where and when were two brothers hit on the same moped by the same taxi driver with an interval of a year? Detailed answer

▪ article fitter. Standard instruction on labor protection