Reducing the heating of transformers of low-power power supplies. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

 Comments on the article

When making low-power mains-powered electronic devices on their own, radio amateurs often encounter a situation where the mains transformer turns out to be the only noticeably heating element of the device, dissipating power in the form of heat, sometimes several times higher than the useful one. The thing is that industrially manufactured transformers, having suitable dimensions and voltage, are sometimes made so "economically" that even the no-load current causes them to heat up.

Especially often transformers manufactured in Southeast Asia have this drawback [1]. They are more suitable for countries where the mains voltage is 220 V with a frequency of 60 Hz, but for normal operation in a network with a frequency of 50 Hz, the number of turns of the mains winding is insufficient.

On fig. 1 shows the dependence of the no-load current on the mains voltage of some transformers. Curve 1 corresponds to transformers from universal adapters "SANWALL" and "BELLSONIC" with a power of 5 W, with a maximum load current of 300 mA, an output voltage of 3 ... 12 V, having magnetic circuits with a cross section of 1,4 cm2. For comparison, curves 2 and 3 are transformers of domestic production TP - 133 and TP - 321, in which the cross-sectional area of ​​the magnetic conductors is 2 and 1,6 cm2, respectively.

Given that the mains voltage, especially in cities, can exceed 235 V for a long time, and an increase in voltage above the nominal causes a disproportionately large increase in no-load current, the use of such transformers, especially in devices designed for long-term operation without supervision (timers, thermostats, antenna amplifiers, etc.) should be approached with great care.

There is a way out in this situation. It is necessary to include an active or reactive ballast resistance in the primary winding circuit of the mains transformer to reduce the voltage on it by 20 ... 30 V. The no-load current and heating of the transformer will noticeably decrease. Of course, this reduces the secondary voltage and power of the transformer. However, if the power consumed by the device is much less than the overall power of the transformer, then this is quite acceptable.

Usually resistors or capacitors are used for such purposes [2]. The main disadvantage of a resistive ballast is its heating, which limits the scope of this method. Moreover, the voltages on the primary winding of a lightly loaded transformer and on the resistor have different phases (the phase shift can reach up to 70 ... 80 degrees), so the voltage across the resistor is usually higher than expected. For example, with a mains voltage of 220 V and on the primary winding of an unloaded transformer of 195 V, the voltage across the resistor can reach up to 45 V. When the load of the transformer increases to values ​​close to the nominal value, the phase shift decreases almost to zero.

Capacitive ballast practically does not generate heat, but as practice shows, it is most advisable to use capacitors when the voltage on the transformer windings needs to be reduced by more than 25 ... 30%. In any case, if capacitors are used, it is necessary to make sure that when the load and supply voltage change in the primary circuit, there are no resonant phenomena when the voltage across the transformer can increase sharply [3].

In the case of using an inductive ballast, such phenomena do not occur, since the voltage phases are almost the same, heat is released only on the active resistance of the ballast winding, which is several times less than that of an equivalent ballast resistor.

It is convenient to use DC electromagnetic relays for an operating voltage of more than 20 V as inductive ballasts, for example, PCM, RES6, RES9, RES22, etc. To reduce their dimensions, the relay can be disassembled and only a coil with a magnetic circuit can be used. To eliminate chatter, the relay armature should be fixed in the attracted state by bending or using a pointed match and glue. When choosing a relay, it is necessary to take into account the maximum current in the primary circuit of the transformer, which must not exceed the rated operating current of the relay.

Curve 4 in Fig. 1 shows the change in the no-load current of the transformer (dependence 1 in Fig. 1) with an inductive ballast (relay PCM-2 for a voltage of 24 V with a winding resistance of 750 Ohm, a rated operating current of 35 mA). On fig. 2 shows the load characteristics of the same transformer (voltage at the output of the rectifier with a filter): curve 1 - without ballast; 2 - with inductive ballast (relay PCM-2); 3 - with an equivalent (for a load current of 20 mA) resistive ballast - a resistor with a resistance of 3 kOhm and a power of 4 W.

The large load capacity of a transformer with an inductive ballast compared to an equivalent resistive ballast is apparently due to a decrease in the ballast inductance due to saturation of the magnetic circuit with an increase in the flowing current. This is noticeable by the characteristic change in the curvature of dependence 2 in relation to graphs 1 and 3 at a load current of 150...200 mA.

Literature

1. Biryukov S. Network adapters. - Radio, 1998, No. 6, p. 66, 67.
2. Biryukov S. Connecting small-sized remote 120-volt power supplies to a 220 V network. - Radio, 1998, No. 7, p. 49, 54.
3. Sadovskov B. Transformer blocks with a ballast capacitor. - Radio, 2000, No. 1, p. 40, 41.

Author: V. Andreev, Tolyatti, Samara region.

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 When we sleep we remember 20.10.2012 For the first time, Los Angeles researchers have measured the activity of an area of ​​the brain involved in learning, memory, and Alzheimer's disease during sleep. They found that even in sleep and under anesthesia, this part of the brain is active and behaves as if trying to remember something. This discovery not only supports the theory of the importance of sleep in ordering and consolidating memories, but also provides important information about the correct daily routine. The research team simultaneously measured the activity of individual neurons from different parts of the brain involved in memory formation. The scientists were able to determine which areas of the mice's brains were activated by others, and how that activation spread. Early research has already indicated that the cerebral cortex and the hippocampus "talk" to each other during sleep - this "talk" is believed to play an important role in memory creation or memory consolidation. People spend a third of their lives sleeping, and lack of sleep leads to health problems, including memory problems. Professor Mayank Mehta and his team observed three connected brain regions in mice: the neocortex, the hippocampus, and the entorhinal region (the intermediate region that connects the previous two). Although it was already known from previous research that the dialogue between the old and new brains during sleep is important for memory formation, the contribution of the entorial cortex to this "talk" has not been previously considered. And this contribution, according to Professor Meta, turned out to be key. The entorial cortex, which is active in real life when we try to remember something, behaved in the same way in a dream. "The big surprise is that this kind of sustained activity happens almost all the time during sleep," says Meta. Enthorial neurons in mice showed constant activity. Even when she was anesthetized and therefore unable to hear or smell anything, she acted as if she remembered something. It is noteworthy that sometimes this lasted more than a minute - a huge time for brain activity, usually measured in thousandths of a second. Scientists believe that the active activity of the brain during sleep is associated with attempts to "unload" memory and remove information that was processed during the day, but is not of great importance. As a result, important memories become more accessible and easily retrieved from memory. In practice, this means that chronic lack of sleep can cause much more serious problems than fatigue and inattention.

Other interesting news:

▪ The new filter will separate the oil from the water

▪ Flowers and the vision of bees

▪ RF Integrated Circuits ADL537x

▪ Optical gyroscope using rotating light

▪ LDC0851 High Accuracy Inductance Comparator

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Amateur radio calculations. Article selection

▪ article by Eugene Ionesco. Famous aphorisms

▪ article Which feline can be trained to hunt with a man and ride a horse? Detailed answer

▪ article Worker cutting bread. Standard instruction on labor protection

▪ article How to search for native gold. Encyclopedia of radio electronics and electrical engineering

▪ article Overhead power lines with voltage above 1 kV. Passage of overhead lines on bridges. 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