Pulse stabilized voltage converter, 3,5 watts. Scheme, description

Free technical library

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

Pulse stabilized voltage converter, 3,5 watts. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters

Comments on the article

When developing the device described below, the task was to create a small-sized mains power supply with high efficiency, capable of delivering power of 1 ... 3,5 W to a load that is not galvanically connected to the network. These requirements are fully met by a single-cycle pulse stabilized voltage converter, which transfers energy to the secondary circuit in the pauses between current pulses in the primary winding of an isolation transformer.

The main technical characteristics of the stabilizer:

Output voltage, V ....... 12; 16; twenty
Total output power, W ....... 3,5
Conversion frequency, kHz.......20
Limits of mains voltage change, at which the output voltage changes by no more than 1%, V.......160...250
Ripple voltage, V, frequency, Hz: 20.......000
50......0,2

(click to enlarge)

Schematic diagram of the proposed pulse voltage converter is shown in Fig.1. The device includes a mains voltage rectifier (VD1) with a smoothing filter (R4C3C4), a master oscillator (DD1.1-DD1.3) with a start circuit (R17C7), a rectangular pulse shaper (DD1.4-DD1.6, VT2, VT4 ), an electronic key (VT3), a pulse transformer (T1), an adjustable current source (VT5), a protection device against short circuits in the load (R10, VT1), three rectifiers (VD2-VD4) and the same number of filter capacitors (C9-C11) . Capacitors C1, C2 prevent interference with the conversion frequency from penetrating into the network.

With the inclusion of the device in the network, capacitors C3, C4 and C7 begin to charge. After the voltage on the last of them reaches approximately 3 V, the master oscillator (DD1.1-DD1.3) is self-excited. The repetition rate of its pulses (depends on the time constant of the R7C5 circuit) is about 20 kHz, the shape resembles a sawtooth. The shaper (DD1.4-DD1.6, VT2, VT4) converts them into square waves. Since the pulse sequences at the bases of transistors VT2 and VT4 are out of phase, they open in turn, which ensures the minimum opening and closing time of the transistor VT3.

a0deeacda98c645edcc15c90ca1020a5.gif

When this transistor is open, a linearly increasing current flows through the I winding and the transformer T1 accumulates energy, and when it is closed (there is no current through the primary winding), the energy accumulated by the transformer is converted into the current of the secondary windings III-V. After several cycles of operation of the generator, a voltage of 7 ... 8 V is established on the capacitor C10.

The output voltage of the converter is stabilized by an adjustable current source made on transistors of the VT5 assembly (VT5.2 is used as a zener diode). When the voltage fluctuates in the network or at the load, the voltage on the winding II changes and the adjustable current source, acting on the shaper (changing the input current of the DD1.4 inverter), changes the duty cycle of the rectangular pulses based on the transistor VT3.

When the pulse current through the resistor R10 increases above a certain threshold value, the transistor VT1 opens and discharges the capacitor C6 (which serves to prevent false operation of the protective device from short current surges that occur when the converter is turned on, as well as during switching of the transistor VT3). As a result, the pulses of the master oscillator stop coming to the base of the transistor VT3 and the converter stops working. When the overload is eliminated, the device starts again in 0,8 ... 2 s after the capacitors C6 and C7 are charged.

The windings of the T1 pulse transformer are wound on a polystyrene frame with PEV-2 0,12 wire and placed in a B30 armored magnetic circuit made of 2000NM ferrite. Windings I.1 and I.2 contain 220 turns each, windings II, III, IV and V - respectively 19, 18, 9 and 33 turns. Winding I.2 is wound first, then windings II, IV, III, V, and finally winding I.1. Between the windings II and IV, V and I.1, electrostatic screens are placed in the form of a single layer (approximately 65 turns) of PEV-2 0,12 wire. When assembling the transformer between the ends of the central part of the ferrite cups, a gasket made of varnished fabric 0,1 mm thick is inserted.

The transformer can also be made on the basis of a ferrite (of the same brand) B22 armored magnetic circuit. In this case, a PEV-2 wire of 0,09 is used, and the number of turns of the windings I.1 and I.2 is increased to 230. The KT859A transistor can be replaced with KT826A, KT838A, KT846A.

Setting up the device is easy. Having set the engine of the tuning resistor R15 to the upper (according to the scheme) position, turn on the converter to the network and set the required output voltage values with this resistor.

To reduce interference in secondary circuits with a conversion frequency (20 kHz), it is necessary to experimentally select the connection point of the electrostatic screens with one of the wires of the primary circuit, as well as the connection points of the capacitor C8. To do this, it is enough to connect one of the conclusions of any secondary winding through an alternating current milliammeter to the primary circuit and determine the named points according to the minimum readings of the device.

It should be noted that the capacitor C8 reduces the level of interference with the conversion frequency only in circuits powered by winding V. To achieve the same goal in circuits connected to windings III and IV, you can either connect the output "Common." with the negative terminal of the rectifier with an output voltage of 20 V, or (if the first is unacceptable) turn on another capacitor between the output "Common." and the connection point of the lower (according to the diagram) output of the capacitor C8.

The converter, assembled according to the described scheme, was tested to power a load that consumes 10 W of power. In this version, the number of turns of windings I.1 and I.2 was reduced to 120 (with B30 magnetic circuit), capacitors C3, C4 were replaced by one oxide capacitance of 10 μF (nominal voltage 450 V), the resistance of resistor R10 was reduced to 2,7 Ohm, and resistor R18 - up to 330 ohms.

If it is necessary to have output voltages other than those indicated in the technical specifications, the number of turns of the III-V windings should be changed accordingly, filter capacitors with the appropriate rated voltages and rectifier diodes with a permissible pulsed reverse voltage of at least 3,5 times the voltage should be used on load.

See other articles Section Voltage converters, rectifiers, inverters.

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

Renewable energy sources will become more popular than natural gas 08.07.2013

According to the International Energy Agency IEA (IEA), already in 2018 solar and wind energy will account for a quarter of all energy sources used in the world. In 2016, all renewable energy sources combined will overtake natural gas in terms of use, double the use of nuclear energy, and become second only to coal as an energy source. Thus, the arguments about the "frivolity" of alternative energy seem, to put it mildly, thoughtless.

Experts are full of optimism about the use of renewable energy sources, and believe that their widespread use is an important step in reducing environmental pollution. Solar, wind, geothermal, hydropower, bioenergy have shown their competitiveness in comparison with fossil fuels. Therefore, it is not surprising that the frequency of the use of renewable sources is increasing. The pioneers in this area are China, as well as other developing countries and countries with economies in transition.

Leaving aside hydropower, wind and solar energy use alone will rise from 4% in 2011 to 8% in 2018. This is good news for the global economy and the world's energy system, which should become cleaner. The use of current fossil energy sources is detrimental to the environment, and according to a recent report from the International Energy Agency, fossil fuels are a far greater threat to the climate than previously thought. Therefore, experts are calling for urgent action, including reducing the number of coal-fired power plants and phasing out other fossil energy sources.

However, the International Energy Agency warns that the use of alternative energy sources is associated with a number of serious problems. For example, in some countries, government policy does not include investment in renewable energy, and subsidies are reduced due to economic problems. In addition, the development of shale gas deposits - a promising direction in the energy sector - reduces interest in renewable sources.

The report of the Agency says that often the smart use of renewable energy sources can be competitive, such as onshore winds in Brazil or in Australia, where wind energy competes with coal and natural gas. Japan also intends to stimulate the use of solar energy in the country.

But most of the renewable energy is used in China, where this type of fuel will take about 40% of the total capacity in 2012-2018. Already, the Chinese government is investing in hydropower, solar and wind energy. The report also notes that in the near future, coal will still account for 65% of total generating capacity in 2015.

Other interesting news:

▪ The cat's brain shrinks

▪ Math is better studied in the game

▪ Phone with repeat

▪ Created a device to simulate odors in computer games

▪ LED car headlight

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site for the radio amateur-designer. Article selection

▪ article Beluga roar. Popular expression

▪ article Where did the name of the women's bikini swimsuit come from? Detailed answer

▪ article Measurement of insulation resistance of electrical wiring and cables. Standard instruction on labor protection

▪ article Installation of grounding conductors. Encyclopedia of radio electronics and electrical engineering

▪ article Wand-chameleon. Focus Secret

Leave your comment on this article:

All languages of this page

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