Capacitive power supply

It is a relatively inexpensive method compared to typical solutions using a transformer, however, a relatively large mains-voltage capacitor is required and its capacitance must increase with the output current, which leads to a higher-cost and bulky capacitor.

For safety reasons, this type of power supply and every circuit connected to it must be double insulated in all places where a person could come into electrical contact with it.

[3] In addition, failure of a single component can result in unacceptably high voltages at the output.

A capacitive power supply usually has a rectifier and filter to generate a direct current from the reduced alternating voltage.

Such a supply comprises a capacitor, C1 whose reactance limits the current flowing through the rectifier bridge D1.

A resistor, R1, connected in series with it protects against voltage spikes during switching operations.

An electrolytic capacitor, C2, is used to smooth the DC voltage and the peak current (in the range of amps) in switching operations.

Analyzing the circuit of the lamp shown in the image, at 50 Hz, the 1.2 μF capacitor has a reactance of 2.653 kΩ.

By Ohm's law, the current is limited to 240 V/2653 Ω ≈ 90 mA, assuming that voltage and frequency remain constant.

The LEDs are connected in parallel with the 10 μF electrolytic filter capacitor.