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Capacitor buck circuit principle and what are the considerations
Release date: 2017-09-15 14:56:50 Visits: 1956
The reason why the capacitor buck circuit in some cheap electrical appliances to see, because this circuit relative to the transformer buck and switching power supply cost is much cheaper. It can be said that the low cost is the only advantage of this step-down power supply; its many shortcomings, such as the output current is small, the voltage fluctuations with the load fluctuations, due to direct electricity with the city, very insecure, so this step-down application Limited range, can only be used in the output current is very small, and people are not easy to touch the occasion.
The principle of capacitor step-down is to limit the maximum operating current by using capacitive reactance at a certain AC signal frequency, that is, by limiting the terminal load by limiting the output voltage. The capacitor actually acts as a limiting current and a dynamic distribution capacitor and the voltage across the load. For example, China''s electricity is 220V / 50Hz, a 1μF capacitor capacitance is about Xc = (2mfC) = 1 / (2 × 3.14 × 501 × 10-6) = 3180Ω. The 220V AC voltage is applied to both ends of the capacitor, the maximum current flowing through the capacitor is about IC = U ÷ Xc = 220 ÷ 3180 = 70mA. Know this calculation method, you can use the electrical current to select the capacitor value.
The use of capacitor buck should pay attention to:
(1) buck capacitor must use non-polar capacitor, absolutely can not use electrolytic capacitors. and the capacitance of the pressure 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, it is best to take a suitable regulator.
(4) because the 220V and electricity is not isolated, pay attention to safety, to prevent electric shock!
The principle of capacitor step-down is to limit the maximum operating current by using capacitive reactance at a certain AC signal frequency, that is, by limiting the terminal load by limiting the output voltage. The capacitor actually acts as a limiting current and a dynamic distribution capacitor and the voltage across the load. For example, China''s electricity is 220V / 50Hz, a 1μF capacitor capacitance is about Xc = (2mfC) = 1 / (2 × 3.14 × 501 × 10-6) = 3180Ω. The 220V AC voltage is applied to both ends of the capacitor, the maximum current flowing through the capacitor is about IC = U ÷ Xc = 220 ÷ 3180 = 70mA. Know this calculation method, you can use the electrical current to select the capacitor value.
The use of capacitor buck should pay attention to:
(1) buck capacitor must use non-polar capacitor, absolutely can not use electrolytic capacitors. and the capacitance of the pressure 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, it is best to take a suitable regulator.
(4) because the 220V and electricity is not isolated, pay attention to safety, to prevent electric shock!
(5) maintenance capacitor step-down electrical appliances can not arbitrarily change the capacitance value.
