When necessary, the DC stabilized voltage for electronic devices with low current consumption 150 mA), reasonably to apply inexpensive (at cost discrete elements) transformerless power sources. Such power supplies are of practical use in small household light switches for the on the basis of the motion sensors, the intrusion sensors and other industrial structures. In the literature repeatedly described the pros and cons of such sources, however, in my opinion, under certain tasks ham they definitely fit.
In the proposed source as the stabilizer applied chip KREN. Electric diagram of the device represented in Fig. 1.2.
Fig. 1.2. Electrical diagram of a transformerless power supply
The maximum voltage that produces the stable source for the output, in this version, is 12 V.
At load currents up to 150 mA DA1 chip provides low dropout voltage. The difference between output and input voltage (assuming connect pin 2 to the negative wire) amount to only 0.4...0.6 V.
This is important, for example when a step-down transformer with a rectifier issue the output DC voltage of 12.5 V, and requires 12 In - in this case, such the stabilizer is almost indispensable.
If necessary adjust the output voltage, the output DA1 2 chips connect to GND via a potentiometer (variable resistor, for example, type SPO-1 with a linear characteristic resistance). Then the output voltage can be changed in the range 12...22 V.
Alternatively, as a chip D1 can be applied to any other integral stabilizer with similar electrical characteristics, for example, KREN, KP1157EHSA, CRON, CRON, CRON, etc.
Establishing
The device in adjustment not needed.
Details
Fixed resistors R1, R2 - type MLT-0,25. The oxide capacitor C2 performs the role of filter on the power - smoothing the ripple voltage. Capacitor C1 should always be on the operating voltage of not lower than 300 V, the brand K-3 or a similar, non-polar and high voltage. Capacitor C3 reduces noise by a high frequency.
Diodes VD1-VD4 can be replaced KD105B-CDG, CDA, CDB, CDE.
The Zener diode VD5 with voltage stabilization 22-27 In protects the chip from surge voltage at the time of filing and off transformerless source from 220 V.
Attention! In operation of the device do not touch uninsulated parts and the elements not only bestransportnogo source, and connected to the device.
Author: A. P. Kashkarov