Transformerless stabilized power supply on an integrated stabilizer, 220/12 volts 150 milliamps. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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When a constant stabilized voltage source is needed for electronic devices with a low current consumption (up to 150 mA), it is reasonable to use inexpensive (at the cost of discrete elements) transformerless power supplies. Such power supplies find practical application in small-sized household lighting switches based on motion sensors, burglar alarm sensors, and other industrial structures. The literature has repeatedly described the pros and cons of such sources, however, in my opinion, they are certainly suitable for certain tasks of a radio amateur.
In the proposed source, the KR142EN8 microcircuit is used as a stabilizer. The electrical circuit of the device is shown in fig. 1.2.
Rice. 1.2. Electrical diagram of a transformerless power supply
The maximum voltage that this stabilized source produces at the output in this version is 12 V.
With a load current of up to 150 mA, the DA1 chip provides a small voltage drop. The difference between the output and input voltage (provided that pin 2 is connected to the negative wire) will be only 0,4 ... 0,6 V.
This is important, for example, when a step-down transformer with a rectifier produces a constant voltage of 12,5 V at the output, and 12 V is required - in this case, such a stabilizer is practically indispensable.
If it is necessary to adjust the output voltage, then pin 2 of the DA1 microcircuit is connected to a common wire through a potentiometer (a variable resistor, for example, of the SPO-1 type with a linear resistance change characteristic). Then the output voltage can vary in the range of 12...22 V.
Alternatively, any other integrated stabilizer with similar electrical characteristics can be used as the D1 chip, for example, KR1212EN5, KP1157EHSA, KR501OEN5, KR1162EN5, KR1183EN5, etc.
Establishment
The device does not need adjustment.
About details
Fixed resistors R1, R2 - type MLT-0,25. Oxide capacitor C2 acts as a power filter - it smooths out voltage ripples. Capacitor C1 must be required for an operating voltage of at least 300 V, brand K76-3 or similar, non-polar and high-voltage. Capacitor C3 reduces high frequency noise.
Diodes VD1-VD4 can be replaced by KD105B-KD105G, KD103A, KD103B, KD202E.
The VD5 zener diode with a stabilization voltage of 22-27 V protects the microcircuit from voltage surges at the time of supply and disconnection of the transformerless source from the 220 V network.
Attention! When operating the device, you must not touch the non-insulated parts and elements of not only the transformerless source, but also the device connected to it.
Author: Kashkarov A.P.
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