Switching power supply based on PC power supply. Scheme, description

Free technical library

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

Switching power supply based on PC power supply. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Power Supplies

Comments on the article

The proposed device, in addition to good technical characteristics, is attractive in that it is based on a switching power supply of an outdated IBM-compatible personal computer. This eliminates the need to purchase many specific radio elements, the manufacture of pulse transformers and chokes.

The described unit allows you to power amateur radio designs with a stabilized voltage and charge various batteries with a stable current.

The power supply is equipped with a digital scale for indicating the output voltage and load current, has output voltage regulators for coarse and fine settings, an output current limiting regulator, a maximum current indicator, a fuse to protect the output circuits in case of reverse polarity of the battery being charged.

The schematic diagram of the device is shown in fig. 2.55, where "PSU PC" is a computer switching power supply; "Prefix" - an indication device with a node for stabilizing the load current.

Rice. 2.55 (click to enlarge)

Main technical characteristics.

input voltage, V..... 110-220;
output stabilized voltage, V.....5-15;
ripple voltage at a current of 5 A, mV, not more than ..... 25;
output stabilized current, A ..... 1-10.

Some changes need to be made to the computer's power supply. Its control unit is usually made on a specialized microcircuit (SHI controller) TL494 or its analogues MB3759, KA7500, KR1114EU4.

Pin 1 of this microcircuit receives a feedback signal from the output voltage rectifiers "+5 V" and "+12 V", and pin 2 receives an exemplary voltage from the internal stabilizer from pin 14. Feedback from the voltage source "+5 V" follows turn off by removing the resistor R4 (hereinafter, the numbering of the elements is conditional), and replace R6 and R8 with resistors of the ratings indicated in the diagram.

Together with the variable resistor R1, they form a feedback voltage divider, which makes it possible to adjust the (coarse) output voltage of the unit. Its exact value is set by a variable resistor R2 connected to pin 2 of the SHI controller.

The power supply is equipped with a built-in fan powered by a 12 V voltage source. Since the output voltage will vary over a wide range, the fan must be connected through a quenching resistor R7 to a rectifier that supplies the SHI controller with a constant voltage of about 24 V.

To the "+ 12 V" output, you need to add a resistor R5, which will ensure stable operation of the power supply in the absence of load at low output voltage. It is also advisable to swap the rectifier diodes of the "+ 5 V" and "+ 12 V" sources, because the first of them uses more powerful diodes.

The output current stabilizer is assembled on an operational amplifier DA1. At its non-inverting input, voltage is applied from the resistor R17, which is included in the negative wire of the output circuit of the power supply.

An exemplary voltage is supplied to the inverting input DA1 from a variable resistor R4, which sets the level of current stabilization. Resistor R9 and capacitor C2 in the OOS circuit, covering the OS, ensure the stability of this node. Through the diode VD1, the feedback voltage is supplied to pin 3 of the SHI controller.

LED HL1 - indicator of maximum current, it glows when the load current is close to or equal to the specified value.

The voltage and current meter is made on the ADC DA3, included according to the typical circuit, and digital indicators HG1-HG4. The mode of its operation is selected by the switch SA1. The contact group SA1.1 switches the measured voltage, SA1.2 - commas of the digital scale.

In the "U" switch position, the ADC input receives the output voltage of the power supply through fuse F1 and a resistive divider R11 -R13, so that when the fuse blows, the indicator shows 0 V. In current control mode (switch in position I), the ADC measures the voltage drop across the sensor current - resistor R17.

The supply voltage "+ 5 V" is stabilized by the integral stabilizer DA1, the voltage "-5 V" - by the parametric stabilizer VD3, R8, connected through the VD2 diode to the negative voltage rectifier of the pulse unit.

Device setup

The establishment of the power supply begins with checking the limits of regulation of the output voltage (switch SA1 - in the "U" position) using a standard voltmeter. The current stabilizer is turned off for this time by unsoldering the wire going from pin 3 of the printed circuit board to pin 3 of the SHI controller. If necessary, the limits are adjusted by selecting resistors R4 and R8. Then, a load with a current consumption of 5-10 A is connected to the block, the switch is set to position "1" and the required reading is set using a standard ammeter with a trimming resistor R12. Further, by switching the indicator to voltage measurement, its readings are corrected according to the exemplary voltmeter with a tuned resistor R9.

After that, the feedback circuit of the current stabilizer is restored, the indicator is switched to measure the current and, by changing the load resistance, they are convinced that the stabilizer is working. If necessary, the boundaries of the current regulation interval are set by selecting resistors R1 and R4.

With a current load of 15 A and a voltage of 15 V, the heating of the L2 inductor winding in the switching power supply may increase slightly. This drawback can be eliminated by rewinding its winding with a wire of twice the cross section.

When charging a battery of batteries with a stable current, you must first set the voltage of the end of charging with regulators R1 and R2, and then, by connecting the battery, with a variable resistor R4 - the required current. During charging, the HL1 LED should light up. At the end of it, when the voltage on the battery rises to the set value, the current will decrease, the LED will turn off and the power supply will go into voltage stabilization mode, in which it can be for a long time. Thus, there is no need to control the charging process and the moment of its completion, it is not necessary to disconnect the battery after charging is completed.

Details

Details of the display device with a load current stabilization unit, together with variable resistors R1, R2, R4 and sockets X1 and X2, are mounted on a printed circuit board (Fig. 1.1), fixed with threaded racks and screws on the front wall of the unit. On it (behind the printed circuit board) an integral voltage regulator DA1 is installed without an insulating gasket.

The power supply used fixed resistors MLT, variable SPZ-9a, tuned SPZ-38.

Resistor R3 is made of three pieces of constantan wire with a diameter of 1 and a length of approximately 50 mm, bent in the form of U-shaped brackets and soldered to the corresponding printed circuit conductors of the board. The deviation of the resistance of this resistor from the value indicated on the diagram (0,01 Ohm) should not exceed ± 20%.

Capacitors C1 ... C3 - K50-35, C9 + C11 - K73-17, the rest - KM.

Diode VD1 - any germanium.

Operational amplifier DA2 - KR140UD608 with any letter index, KR140UD708.

Digital indicators HG1 - HG4 - ALS324B, ALS3ZZB, ALS321B.

Switch S A1 - small-sized push-button for printed wiring B170G or similar.

Fuse F1 - flat car for a current of 10 A.

Author: Shelestov I.P.

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

Useful products for smokers 17.03.2017

Swiss scientists conducted a study in which they identified foods that smokers should consume to reduce the risk of fatal diseases. So, among the most effective products are vegetables and fruits. In particular, apples, peppers and leafy vegetables. But berries, onions and potatoes will not affect the positive process in the body.

According to experts, in the next century the number of victims of smoking will be more than a billion people. Meanwhile, the death rate from these diseases will increase 10 times.

Previously, scientists conducted a study and concluded that smoking during pregnancy can lead to serious hearing problems in a child.

Other interesting news:

▪ 27-inch ASUS VA278Q monitor with a resolution of 2560x1440 pixels

▪ Rotating neutron stars to test and calibrate atomic clocks

▪ New material for nuclear waste disposal

▪ Miniature Reflective Optical Sensor TCND3000

▪ Most durable alloy

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the Electrician website. Article selection

▪ article Moderation and accuracy. Popular expression

▪ article Which kingdom is part of the European Union with only two percent of its territory? Detailed answer

▪ Serengeti article. Nature miracle

▪ article Sulphurous dyeing of fabric and yarn. Simple recipes and tips

▪ article USB charger for LiIon batteries. 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