The working principle of capacitive voltage reduction is not complicated. Its principle is to use the reactance generated by a capacitor at a certain AC signal frequency to limit the maximum operating current. For example, under a 50Hz mains frequency, a 1μF capacitor generates a reactance of about 3180 ohms. When a 220V AC voltage is applied across the capacitor, the maximum current through the capacitor is about 70mA. Although the current through the capacitor is 70mA, no power is consumed in the capacitor because if the capacitor is ideal, the current through it is reactive current, and the work it performs is reactive power. Based on this characteristic, if we connect a resistive element in series with a 1μF capacitor, the voltage across the resistive element and the power it consumes entirely depend on the characteristics of the resistive element. For instance, if we connect a 110V/8W light bulb in series with a 1μF capacitor and apply a 220V/50Hz AC voltage, the light bulb will light up at normal brightness without being damaged. This is because the current required for a 110V/8W light bulb is 8W/110V = 72mA, which matches the current-limiting property of the 1μF capacitor. Similarly, a 5W/65V light bulb can also be connected in series with a 1μF capacitor to a 220V/50Hz AC supply, and it will light up without being damaged since its operating current is also around 70mA. Therefore, capacitive voltage reduction actually uses capacitive reactance for current limitation. In practice, the capacitor serves to limit the current and dynamically distribute the voltage between the capacitor and the load.
When using capacitive voltage reduction, the following points should be noted:
1. Select a suitable capacitor according to the load current and AC operating frequency, not according to load voltage and power.
2. The current-limiting capacitor must be a non-polarized capacitor; electrolytic capacitors must not be used. The capacitor voltage rating must be above 400V. The ideal capacitor is an iron-cased oil-immersed capacitor.
3. Capacitive voltage reduction should not be used under high power conditions due to safety concerns.
4. Capacitive voltage reduction is not suitable for dynamic load conditions.
5. Likewise, capacitive voltage reduction is not suitable for capacitive or inductive loads.
6. When DC operation is required, half-wave rectification is recommended. Bridge rectification is not advised, and the condition of a constant load must be met.
Simple introduction to the principles of safety-standard capacitive voltage reduction.