Two transformerless power supplies, 220/1,4 volts 1 milliamp. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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Despite the fact that theoretically capacitors in an AC circuit do not consume power, in reality, some heat can be generated in them due to the presence of losses.
You can check in advance the suitability of the capacitor for use in the source by simply connecting it to the mains and estimating the case temperature after half an hour. If the capacitor has time to noticeably warm up, it should be considered unsuitable for use in the source.
Special capacitors for industrial electrical installations practically do not heat up - they are designed for high reactive power. Such capacitors are used in fluorescent lamps, in ballasts of asynchronous electric motors, etc.
Below are two practical power supply circuits with a capacitor divider: a five-volt general purpose one for a load current of up to 0,3 A (Fig. 6.3) and an uninterruptible power supply for quartz electronic-mechanical watches (Fig. 6.4).
The voltage divider of a five-volt source consists of a paper capacitor C1 and two oxide capacitors C2 and C3, forming a non-polar shoulder with a capacity of 100 microfarads. The polarizing diodes for the oxide pair are left bridge diodes according to the scheme.
With the ratings of the elements indicated in the diagram, the short-circuit current at the output of the power supply is 600 mA, the voltage across capacitor C4 in the absence of load is 27 V.
Widespread Chinese-made electronic-mechanical alarm clocks are usually powered by a single 1,5 V galvanic cell.
The proposed source generates a voltage of 1,4 V at an average load current of 1 mA. The voltage removed from the divider C1, C2 rectifies the node on the elements VD1, VD2, C3. Without load, the voltage across capacitor C3 does not exceed 12 V.
Author: Semyan A.P.
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