Selection and matters needing attention of Capacitors in Capacitor Step-down Power supply(I)

In common low-voltage power supply, the power supply with capacitor is smaller, economical, reliable and efficient compared with transformer. The disadvantage is that it is not as safe as transformer. If AC is introduced into the load by capacitors, there is 220V voltage on the ground, and people are easily shocked. However, if it is used in the internal circuit power supply without human contact, the weakness can be overcome. Such as the refrigerator electronic thermostat or remote control power supply on and off and so on are all made with capacitors.

Compared with the resistance voltage reduction, for the low frequency 50Hz AC, the thermal energy loss generated on the capacitor is very small, so the capacitor voltage reduction is better than the resistance voltage reduction.

the current through the capacitor, the unit of capacitive impedance of the capacitor Xc=1 ~ 2 π fC ~ + Xc is ohmic; the unit of alternating current frequency f is Hertz; and the unit of capacitor C is Farah.

When the capacitor C of different capacitance (as shown in fig. 1) is connected to the AC circuit of the AC220V 50Hz, the capacitive reactance of its C and the current it can pass through are listed in the schedule. The current is the maximum current that the capacitor C can provide.