Stabilized power supply for six output voltages, 220 / 3,4,5,6,7.5,9,12 volts 0,25 amperes. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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This power supply has a fairly wide range and stability of the output voltage.
Main technical characteristics:
- Rated output voltage with a tolerance of ±5%, V.....3; 4; 5; 6; 7,5; 9; 12;
- Maximum load current, A ..... 0,25;
- Pulsation amplitude, mV.....10;
- External dimensions, mm.....77x57x50;
The power supply circuit is shown in fig. 1.7. The alternating voltage from the sectioned winding of the network transformer T1 through the contacts of the switch SA1.1 (depending on the selected limit) is supplied to the diode bridge VD1 ... VD4 and rectified by it. The voltage rectified and smoothed by capacitor C2 is then fed to input 2 of the DA1 microcircuit, which is an integrated stabilizer with an adjustable beneficial voltage. From its output 8, a stabilized voltage is supplied to the output connector X2, Resistors R1 ... R7 form a voltage divider. Resistors R2...R7 are switched by the SA1.2 switch simultaneously with the taps of the winding sections II of the mains transformer. Capacitor C3 is necessary to reduce the noise level and increase the ripple smoothing factor.
(click to enlarge)
C1 acts as a line filter, capacitor C4 - the output filter of the power supply. The printed circuit board of the power supply is shown in fig. 1.8. Resistors R2...R7 and switch SA1 are mounted on the bottom side of the printed circuit board, the rest of the parts are on the top. Transformer T1 is installed on the board with the winding leads down and glued to the board with BF-4 glue. The outputs of the primary winding of the transformer are soldered directly to the pins of the mains plug (XI). Capacitor C1 is also soldered to them.
The magnetic circuit of the transformer is assembled from plates Ш10х20. The primary winding (I) of the transformer contains 3600 turns of PEV-2-0,1 wire, and the secondary (II) - 368 turns of PEV-2-0,35 with taps from 166, 200, 234, 268, 302 turns. All resistors used in the power supply are MLT-0,125. Capacitor C1 - K73-17 for a rated voltage of 630 V, C2 and C3 - oxide K50-35, C4 - KM-5. Switch SA1 - sliding type PD-41.
Installing it on the board from the power plug side eliminates accidental switching of the output voltage when the unit is running with a connected load.
Chip KR142EN12A can be replaced by KR142EN12B. The heat sink, on which it is fixed with a screw and nut, is made of 2,5 mm thick aluminum sheet.
Establishing a power supply consists in careful selection of resistors R2 ... R7 of the output voltage divider. This work is very painstaking and, of course, requires special attention and perseverance. The more carefully each of the divider resistors is selected, the more accurate the voltage corresponding to it at the output of the power supply will be.
In the absence of an integrated stabilizer, a similar power supply can be assembled according to the diagram shown in Fig. 1.9. Here, a KT829 transistor is used as a regulatory element, and there is no need to switch the transformer windings.
Author: O.Sidorovich
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