Do you know how RC step-down works?

“With the diversified development of the world, our lives are constantly changing, including the various Electronic products we come into contact with. Then you must not know some of the components of these products, such as resistance-capacitance step-down.

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With the diversified development of the world, our lives are constantly changing, including the various electronic products we come into contact with. Then you must not know some of the components of these products, such as resistance-capacitance step-down.

The resistance-capacitance step-down is to use the capacitive reactance generated by the capacitor at a certain AC signal frequency to limit the maximum operating current.

For example, under 50Hz power frequency conditions, the capacitive reactance generated by a 1uF capacitor is about 3180 ohms. When 220V AC voltage is applied to both ends of the capacitor, the maximum current flowing through the capacitor is about 70mA. Although the current flowing through the capacitor is 70mA, there is no power consumption in the capacitor, because if the capacitor is an ideal capacitor, the current flowing through the capacitor is the imaginary current, and the work it does is reactive power. According to this feature, if we connect a resistive element in series with a 1uF capacitor, the voltage obtained at both ends of the resistive element and the power consumption it generates completely depend on the characteristics of the resistive element. For example, we connect a 110V/8W light bulb with a 1uF capacitor in series, and when it is connected to an AC voltage of 220V/50Hz, the light bulb is lit and emits normal brightness without being burnt.

Resistance-capacitance step-down is a circuit that uses the capacitive reactance generated by a capacitor under an AC signal of a certain frequency to limit the maximum operating current.

Because the current required by the 110V/8W bulb is 8W/110V=72mA, it is consistent with the current-limiting characteristics produced by the 1uF capacitor. In the same way, we can also connect a 5W/65V bulb with a 1uF capacitor in series to a 220V/50Hz AC, and the bulb will also be lit instead of being burned. Because the working current of a 5W/65V bulb is about 70mA. Therefore, the capacitor step-down is actually the use of capacitive reactance to limit current. The capacitor actually plays a role in limiting the current and dynamically distributing the voltage across the capacitor and the load.

The resistance-capacitance step-down voltage is composed of a step-down module, a rectifier module, a voltage regulator module and a filter module.

Pay attention to the following points when using capacitors to step down:

Choose the appropriate capacitance according to the current size of the load and the working frequency of the alternating current, rather than the voltage and power of the load. Current-limiting capacitors must be non-polar capacitors, and electrolytic capacitors must not be used. And the withstand voltage of the capacitor must be above 400V. The most ideal capacitor is the iron case oil immersed capacitor.

When designing the circuit, the maximum operating current of the load should be determined first, and the capacitance value of the capacitor should be calculated by this current value, so as to select an appropriate capacitor.

Capacitor step-down cannot be used for high-power loads because it is not safe. Capacitor step-down is not suitable for dynamic loads. Similarly, capacitor step-down is not suitable for capacitive and inductive loads. When DC work is required, half-wave rectification should be used as much as possible. Bridge rectification is not recommended, because full-wave rectification generates a floating ground and generates high voltage between the neutral wire and the live wire, which may cause electric shock to the human body. And to meet the condition of constant load.

In the process of research and design, there must be problems of this kind or that kind, which requires our scientific research workers to constantly sum up experience in the design process, so as to promote the continuous innovation of products.