Principle and Precautions of Capacitor Buck Circuit
Source：http://www.kehong88.comRelease time：2017-01-23 09:02:20Views：
Capacitor buck circuit in some cheap appliances to see, because this circuit relative to the transformer step-down and switching power supply mode cost is much lower. It can be said that low-cost power supply is the only advantage of this step-down; it has many shortcomings, such as the output current is small, the voltage fluctuates with the load changes, due to electricity through, very unsafe, so this step-down The range is limited, can only be used in the output current is very small, and people are not easy to touch the occasion.
Capacitance buck principle is the use of capacitance in a certain frequency of AC signal frequency to limit the maximum operating current, that is, by limiting the load after the terminal pulled down the output voltage, the capacitor actually acts as a limiting current and dynamic distribution capacitors And the role of the voltage across the load. For example, China's mains is 220V / 50Hz, a 1μF capacitor capacitance is about Xc = (2mfC) = 1 / (2 × 3.14 × 501 × 10-6) = 3180Ω. 220V AC voltage is applied to the two ends of the capacitor, the maximum current flowing through the capacitor is about IC = U ÷ Xc = 220 ÷ 3180 = 70mA. Know the calculation method, you can use the operating current to select the capacitor value.
The use of capacitor buck should pay attention to:
(1) step-down capacitor must be non-polar capacitor, must not use electrolytic capacitors. And the capacitor voltage to be more than 400V.
(2) capacitor buck is not suitable for dynamic load, not suitable for capacitive and inductive load.
(3) when the need for DC work, try to use half-wave rectifier, the best access to a suitable regulator.
(4) because it is not and 220V mains isolation, pay attention to safety, prevent electric shock!
(5) maintenance of the capacitor buck capacitor can not be arbitrarily changed.
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