Power supply Step, 220 / 5,9,12 volts. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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With the advent of inexpensive and reliable three-output integrated voltage stabilizers on sale, you can assemble a simple power supply for a number of the most commonly used voltages (Fig. 2.26).
The power supply unit consists of a step-down transformer 220 V / 30 V, a bridge rectifier based on the KTS405A module and three stabilizers of the 78xx series (K142EN) for 5 V, 9 V and 12 V. The SA2 switch and the display unit on seven-segment indicators are placed on the front panel. The 78xx series of integrated regulators provides output load current up to 1 A, is equipped with internal protection in case of overheating or excessive load current by reducing the output current. The 79xx series of integral stabilizers is designed for negative voltages. The stabilization voltage is indicated in the last two digits of the chip designation.
Compliance of stabilizers of series 78xx and 79xx with domestic series KR142 and KR1162 is shown in Table. 2.1.
Table 2.1
A few notes on application. The input voltage should not exceed 30 ... 35 V. The voltage difference when connecting the stabilizers with a step should be at least 2 V. To smooth out the ripple, an electrolytic capacitor with a capacity of at least 4700 μF should be used at the input, and a high-frequency ceramic capacitor with a capacity of at least 0,47 .XNUMX uF.
If you need to get a bipolar voltage, you can combine the stabilizers of the 78xx and 79xx series (Fig. 2.27).
Diodes connected at the output protect the unit from incorrect switching on.
Author: Semyan A.P.
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