Portable electronic devices with low-voltage power supply often calculated on batteries and accumulators.
Among such devices are the most popular Electromechanical and digital clock, radios, flashlights I. wireless calls, working on the radio the frequency of 303 MHz (there are options on the frequency 933,25 MHz). The same devices are digital cameras with connector for external power supply, 3.3 V (for example, Olimpus C-765), portable CD players (players, recorders, cars for cutting hair and even mobile phones.
All of these devices (the list is not limited to the ones listed in the previous the proposal, it is much wider) have in common is that they are designed for power cells (batteries and accumulators, external power supplies) nominal voltage of 3 V ±10%. How to provide them with food when "regular" adapter is lost, defective?
If the current consumption is less than 0.3 And, the easiest way to supply power to low-voltage the device 220 V power source, having the function of "continuity" and provide power in the absence of voltage. In Fig. 1.1 offer readers schematic electrical diagram of the device.
The voltage taken from the divider C1, C2, rectified by diodes VD1, VD2 and smoothed oxide capacitor C3. No load voltage on the capacitor C3 does not exceed 14 V. the Transistor VT3 is connected to the circuit with a common base, and the transition collector-emitter fully open (the voltage drop does not exceed 0.5 V) is the voltage at load (on the lining oxide capacitor C4) is 3.3 V. When the absence of the mains voltage the current through the circuit (when the load is connected) flows through the emitter-base VT1 (the total voltage drop across VD3 not exceed 0.3 In).
And it could be further reduced, if we exclude from the scheme diode VD3, protecting the transistor at the input of the device to the mains voltage. Thus, in offline power to the load is given not less than 2.7 V. This voltage it is already possible to supply power to an Electromechanical alarm clock or wall clock.
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 disabled load amperage could not commit at all.
All diodes VD1, VD2 can be replaced by CDW-CDG, CD, with any D226 alphabetic index. Diode VD3 is desirable to use a series of D, D, D. Oxide capacitors type K50-29 or similar. The capacitor C1 is better apply from unnecessary ballast, Converter for fluorescent (energy saving) bulbs - these capacitors are designed for large reactive power and emit virtually no heat when turned on.
Circuit elements are mounted on a circuit Board the size of the battery compartment.
The phrasing of connection is not critical. When assembling and connecting device be careful, because its elements are energized lighting 220 V
Author: A. P. Kashkarov