Portable electronic devices with low-voltage power supply is typically designed for batteries and accumulators. Among such devices the most popular electro-mechanical and digital clocks, radios, etc.
Last year I purchased and installed in the village house wireless doorbell, working on radio frequency 303 MHz (there are options on the frequency 933,25 MHz) and having a "range" of about 100 m (from zvonkova button until a beep block in the room).
The call used one battery type S a voltage of 3 V. It is enough for about six months work. However, in order to replace it, it is necessary to remove from the holder of the "bell" button, mounted on a concrete fence, re-install the fasteners, in General uncomfortable.
Easiest way to supply power to the transmitter 220 V, however, in the village network "is problems", and "electricity" often disappears. That is such a source is required, which provides power even when the network (220). Low-power local consumers (not related to a ground loop or with other consumers) it can be built according to the transformerless circuit.
The proposed source the power supply provides a voltage of 1.5 to 3.3 V and the load current up to 30 mA.
The voltage taken from the divisor C1-C2, rectified by diodes VD1, VD2 and smoothed oxide capacitor C3.
No load voltage on C3 does not exceed 14 V. the Transistor VT1 is connected the common-base circuit, and its transition collector-emitter fully opened (falling the voltage does not exceed 0.5 In). As a result, the voltage at the load (at plates oxide capacitor C4) is 3.3 V. When no network voltage current (when the load is connected) flows from the battery through the diode VD3 and the emitter-base VT1 (total drop voltage does not exceed 0,3...0,6 In). and it can be even further reduced if exclude diode VD3, protecting the transistor at input the device of the mains voltage.
Thus, in offline power to the load is given not less than 2.5 V, which is quite enough to power button (transmitter unit) wireless radiosonde.
The device doesn't contain a single resistor and practically does not emit heat, even transistor VT1, since the current through its transition is very small. When the load is switched off the current failed to fix at all.
Diodes VD1 and VD2 can to replace, KDV...CDG, CD, D226 with any letter index, preferably VD3 to apply the germanium from the series. D, D, D. Oxide capacitors - type C50-29 or similar.
The capacitor C1 is better to use from unnecessary ballast for fluorescent (energy saving) lamps, such as capacitors designed for large reactive power and emit virtually no heat. When the device is connected be careful, because its elements are energized lighting 220 V
Author: A. Kashkarov