UMZCH switching network power supply, 200-240 / 10,20,25 volts 3 amperes. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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The main technical characteristics of the power supply are as follows: supply voltage - 200 ... 240 V, output voltages - ± 25 V, 20 V and 10 V at load currents of 3 A, 1 A and 3 A, respectively; Efficiency - 0,75.
The schematic diagram of the device is shown in fig. one.
(click to enlarge)
The functions of the network filter are performed by elements C2, T1, C3. The rectifier of the voltage converter is a full-wave bridge on diodes VD1 ... VD4, the transistor filter is formed by elements R3, C5, R4, VT1, C7. It reduces the ripple of the rectified voltage with a frequency of 100 Hz, which is necessary to prevent them from modulating the square-wave voltage of the high-frequency converter. The latter is made on transistors VT5, VT6. Through a step-down transformer T3, its output voltage is fed to full-wave rectifiers VD13, VD16; VD17, VD20. The rectified voltage ripples are smoothed out by capacitors C14, C18.
The master oscillator is assembled on the elements of the microcircuit DD1. Trimmer resistor R1 frequency of its pulses can be changed in the range from 100 to 200 kHz. Trigger DD2.1 generates from them pulses with steeper fronts and half the repetition rate. The generator is connected to the voltage converter through a complementary emitter follower on transistors VT3, VT4 and transformer T2. Power is supplied to the master generator through a rectifier (VD5 ... VD8) and a voltage regulator (VT2, R5, VD9, VD10). Excess mains voltage extinguishes the capacitor C4.
In the power supply, any resistors and capacitors that are suitable in size and parameters can be used. Instead of KT812A transistors, you can use KT809A or KT704B. The static current transfer coefficients of transistors VT5, VT6 should be approximately the same. It is not recommended to replace the K511 series microcircuits with any others, since they are the least susceptible to high-frequency interference and allow you to get a fairly large (about 13 V) pulse range at the trigger output.
In extreme cases, you can use the K155 series microcircuits, however, this will require additional amplification of the pulses supplied to the bases of transistors VT3, VT4. Diodes KD213G and KD212A should not be replaced either, since they have a rather high cutoff frequency (about 100 kHz), which allows you to select the same conversion frequency and, as a result, reduce the size of the output transformer. T3 and increase the efficiency of the power supply.
The mains filter transformer T1 is made on an annular magnetic circuit of the size K20x10x5 made of ferrite. M2000NMZ, both of its windings contain 17 turns of wire each. MGTF-0,5. The magnetic circuit of the converter transformer T2 - K16x8x6 from ferrite. M2000NN-1, all its windings are wound in three wires (PELSHO 0,12) and contain 90 turns each. In the output transformer T3, a K38x24x7 magnetic core made of the same material is used. Its windings 1-2, 3-4-5 and 9-10 contain, respectively, 30+5+5; 5 + 5 and 2 turns of wire PEV-2-1,0; winding 6-7-8 contains 4 + 4 turns of wire PEV-1-0,6. All windings are evenly distributed over the ring and carefully fixed, and to prevent interwinding short circuits, they are separated from one another with a fluoroplastic film. Powerful transistors VT2, VT5, VT6 are placed on three heat sinks with a cooling surface area of 65 cm2 each.
Author: Semyan A.P.
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