Power supply 220/3 volts 0,5 amps with a quenching capacitor. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Power supply 220/3 volts 0,5 amps with a quenching capacitor. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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The use of capacitors to step down the voltage supplied to the load from the lighting network has a long history. In the 50s, radio amateurs widely used capacitors in transformerless power supplies for radio receivers, which were connected in series to the filament circuit of radio tubes. This made it possible to eliminate the quenching resistor, which is a source of heat and heating of the entire structure. Recently, there has been a return of interest in power supplies with a quenching capacitor. The disadvantage inherent in all such devices without exception - increased danger due to the galvanic connection of the output with the electrical network - is clearly recognized, but allowed based on the literacy and accuracy of the user. However, these deterrents are not sufficient to keep out of trouble, which is why transformerless devices can have only very limited use.

Power supply 220/3 volts 0,5 amps with a quenching capacitor

Here it can represent a compromise source that ensures electrical safety, with a quenching capacitor and a simple transformer accessible to a beginner radio amateur. Such a transformer will turn out if the voltage on its primary winding is limited to a value of about 30 V. For this, 600 ... 650 turns of a relatively thick wire, convenient for winding, are enough; for the sake of simplicity, you can use the same wire for both windings. The excess voltage here will be taken over by a capacitor connected in series with the primary winding (the capacitor must be designed for a rated voltage of at least 400 V). According to this principle, it is possible to organize the power supply of low-voltage loads with a current in the primary circuit (taking into account a small transformation ratio) up to 0,5 A.

The figure shows a diagram of such a device, suitable for working with a LED garland of a desktop mini Christmas tree or for an audio player.

Power supply 220/3 volts 0,5 amps with a quenching capacitor

The inclusion of LEDs (8 ... 10 pieces) is carried out in parallel; this eliminates the usual confusion of wires, it is easier to make them invisible in the "needles" of the trunk and twigs. The transformer can be assembled on the magnetic circuit Ш12х16. For winding suitable wire PEV-1 d = 0,16 mm; the number of turns of the primary and secondary windings is 600 and 120 ... 140, respectively. It is not difficult to make such a transformer.

An electrical strength of at least 2 kV will be provided by an insulating gasket between the windings made of 0,1 mm thick lavsan film or capacitor paper. In order for the device not to fail when the load is disconnected, a Zener diode D1G should be connected to the output of the bridge VD4 - VD815. In normal mode, it does not work, because it has a minimum stabilization voltage higher than the operating one at the output of the bridge. Fuse FU1 protects the transformer and stabilizer in the event of a breakdown of capacitor C1. To limit the current when connecting the power supply to the network in series with C1, it is necessary to turn on a resistor with a resistance of several hundred ohms, and to discharge the capacitor after disconnection, a resistor of several hundred kOhms should be connected in parallel with it. In a circuit of series-connected capacitive (capacitor C1) and inductive resistances (transformer T1), voltage resonance may occur. This should be kept in mind when designing such power supplies.

Publication: cxem.net

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