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Selection of capacitor in capacitor depressurization power supply
Addtime:2012-08-20 10:46:06

In the common low voltage power supply, the voltage depressurization is small, economical, reliable and efficient compared with the use of the transformer. The disadvantage is that the power supply is not as good as transformer voltage transformer. By introducing a capacitor to the load by a capacitor, there is a 220V voltage on the ground, and the person is easy to touch electricity, but this weakness can be overcome if it is used in a circuit that does not need to be exposed to human contact. For example, refrigerators, electronic thermostat or remote control power supply are made of capacitors.

Compared with the resistance depressurization, for the lower frequency 50Hz alternating current, the heat loss on the capacitor is very small, so the capacitor is better than the resistance depressurization.

By the size of the capacitor current, the capacitor is resistant to Xc=1 / (2π fC), and the unit of the Xc is Ohm; the unit of the AC frequency f is Hertz; the unit of the capacitor C is Fala.

When the capacitor C of different capacity (as shown in Fig. 1) is connected to the AC circuit of AC220V 50Hz, the capacitance of C and the current it can pass are listed in the schedule. This current is the maximum current value provided by capacitor C.

When using capacitors to reduce power supply, we must pay attention to the following points:

(1) after the capacitor is depressurization, a voltage stable power supply must be obtained, as shown in Figure 2, after the rectifier, filter, and voltage stabilized diode is stabilized (Note: the rectifying circuit can also be rectified by half wave).

(2) capacitor withstand voltage is preferably above 630V, and the use of non polarity capacitor, polarity capacitor can not be used.

(3) discharge resistor parallel to 500K-1M at both ends of capacitor.

(4) if a power switch is needed to prevent inrush current from parallel to the load RL, as shown in Figure 3.

(5) in the process of assembly and debugging, 1:1 isolation transformer should be used to connect to AC220V circuit to avoid electric shock.