|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Two-stroke voltage converters 12/220 volts. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters In push-pull converters, the magnetic core of the pulse transformer is used more efficiently. In such circuits, it is not necessary to deal with the magnetization of the core, which makes it possible to reduce its dimensions. The output voltage is symmetrical. In addition, the converter transistors operate in a lighter mode. Sometimes, for low power (up to 15 W), the simplest converter is used, made according to the oscillator circuit (Fig. 4.16, a). This circuit is not critical to the parts used, but selecting the operating point of the transistor operation mode using resistor R2 can improve the performance of the device (sometimes a capacitor is installed in parallel with R2). The divider of resistors R1-R2 provides the necessary initial current to start the oscillator.
The universal 2N3055 transistors used are replaced by similar domestic KT818GM, KT8150A, and if you change the polarity of the supplied power, you can also use pn-p transistors. The supply voltage of the circuit can be from 12 to 24 V. For long-term operation of the device, transistors must be installed on radiators. The transformer can be made on a ferrite M2000NM1 ring magnetic conductor, its working section depends. from the power in the load. For a simplified choice, you can use the recommendations, see table. 4.5. Table 4.5. Permissible maximum power for ring ferrite magnetic circuits of the M2000NM1 brand
In the manufacture of transformer T1, windings 1 and 2 are wound at the same time, but the phasing of their connection must correspond to that shown in the diagram. For the section of the annular magnetic circuit of size K32x20x6, windings 1 and 2 each contain 8 turns (PEL wire with a diameter of 1,2 ... 0,81 mm); 3 and 4, 2 turns each (0,23 mm); 5 - the number of turns of the secondary winding depends on the required voltage (0,1 ... 0,23 mm). Using this circuit, you can get voltages up to 30 kV if you use a magnetic circuit from transformers used in modern TVs. A similar oscillator circuit, made on field-effect transistors, is shown in fig. 4.16b. It allows the use of a simpler transformer that does not require feedback windings. Zener diodes VD1, VD2 prevent dangerous voltages from appearing on the gates of transistors. The operating frequency of such circuits is set by the parameters of the transformer magnetic circuit and the inductance of the windings, since the delay of the feedback signal depends on this (it is better if the frequency is in the range of 20 ... 50 kHz). As a disadvantage of these circuits, one can note a low efficiency, which makes it difficult to use them at high power, as well as an unstabilized output voltage, which can vary greatly depending on the change in the supply voltage. A more successful push-pull converter circuit, made using a specialized microcircuit (Fig. 4.17), is highly efficient and can maintain a stable voltage at the load.
The converter is made on the widely used T114EU4 PWM controller chip (a complete imported analogue of TL494), which makes the circuit quite simple. In the normal state (at zero gate voltage), transistors VT1, VT2 are closed and open with pulses from the corresponding outputs of the microcircuit. Resistors R7-R9 and R8-R10 limit the output current of the microcircuit, as well as the voltage at the gate of the keys. A chain of elements C1-R2 provides a smooth exit to the operating mode when the power is turned on (a gradual increase in the width of the pulses at the outputs of the microcircuit). Diode VD1 prevents damage to circuit elements when the power polarity is connected by mistake. Voltage diagrams explaining the operation are shown in fig. 4.18. As can be seen in figure (a), the trailing edge of the pulse has a longer duration than the leading one. This is due to the presence of the gate capacitance of the field-effect transistor, the charge of which is absorbed through the resistor R9 (R10) at the time when the output transistor of the microcircuit is closed. This increases the closing time of the key. Since in the open state the voltage drops on the field-effect transistor is not more than 0,1 V, power losses in the form of a slight heating of VT1 and VT2 occur mainly due to the slow closing of the transistors (this is what limits the maximum allowable load power).
The parameters of this circuit when working on a lamp with a power of 100 W are given in Table. 4.6. At idle, the current consumption is 0,11 A (9 V) and 0,07 A (15 V). The operating frequency of the converter is about 20 kHz. Table 4.6. Main parameters of the scheme
The T1 transformer is made on two ring cores folded together made of M2000NM1 ferrite grade K32x20x6. The winding parameters are indicated in Table. 4.7. Table 4.7. Parameters of the windings of the transformer T1
Before winding, the sharp edges of the core must be rounded off with a file or coarse sandpaper. In the manufacture of a transformer, the secondary winding is first wound. Winding is performed turn to turn, in one layer, followed by insulation with varnished cloth or fluoroplastic tape. Primary windings 1 and 2 are wound with two wires at the same time, as shown in fig. 4.19 (evenly distributing the turns on the magnetic circuit). Such winding makes it possible to significantly reduce voltage surges at the fronts when closing the field keys. Transistors are installed on a heat sink, which is used as a duralumin profile (Fig. 4.20).
Radiators are fixed on the edges of the printed circuit board. A single-sided printed circuit board made of fiberglass with a thickness of 1,5 ... 2 mm has dimensions of 110x90 mm (see Fig. 4.21 and 4.22).
This scheme can be used to power a load that constantly consumes power up to 100 watts. For more power, it is necessary to reduce the switching time of the field switches. This can be done by specially designed microcircuits that have a complementary output stage designed to control powerful field-effect transistors, for example, K1156EU2, UC3825. As power switches for power up to 60 W in the above circuit, you can also use N-type transistors with static induction KP958A (BCIT- Bipolar Static Induction Transistor). They are designed specifically for operation in high-frequency power supplies. The physics of operation of such a transistor is close to that of a conventional bipolar one, but due to its design features, it has a number of advantages: 1) low voltage drop source-drain in the open state;
In this case, it is better to select transistors with the same parameters, and reduce the resistors R9 and R10 to 100 ... 150 Ohms. Author: Shelestov I.P.
Machine for thinning flowers in gardens
02.05.2024 Advanced Infrared Microscope
02.05.2024 Air trap for insects
01.05.2024
▪ LM5115 high-frequency regulator-controller microcircuit ▪ Atomic clocks will make space exploration easier ▪ A luminous bandage will warn about the inflammation of the burn
▪ section of the site Big encyclopedia for children and adults. Selection of articles ▪ article Waste-free production. Basics of safe life ▪ article How were fire cutlets invented? Detailed answer ▪ article Capturing knot. Tourist tips ▪ article Apertures for the skin. Simple recipes and tips ▪ article Dragonfly on the tip of a pencil. Focus Secret
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page