# Filter Inductor The Main Form

Filter Inductor The main form

Rectifier circuit output voltage is not pure DC, from the oscilloscope to observe the output of the rectifier circuit, and DC difference is large, the waveform contains a large pulsation component, called ripple. In order to obtain an ideal DC voltage, it is necessary to filter the pulsating component in the output voltage of the rectifier circuit by using a filter circuit composed of a capacitive element (such as a capacitor and an inductance) having an energy storage effect to obtain a DC voltage. Commonly used filter circuit passive filter and active filter two categories. The main forms of passive filtering are capacitive filtering, inductive filtering and complex filtering (including inverted L-type, LC filter, LCπ filter and RCπ filter, etc.). The main form of active filtering is active RC filtering, also known as the electronic filter. The magnitude of the pulsating component in the direct current is expressed by the ripple factor. The larger the value is, the worse the filter is. Pulsation coefficient (S) = output voltage AC component of the fundamental maximum / output voltage of the DC component. The pulsating coefficient of the half-wave rectified output voltage is S = 1.57, and the ripple coefficient S ≈ O of the full-wave rectified and bridge rectified output voltage. 67. For the full-wave and bridge rectifier circuit using C-type filter circuit, the pulse coefficient S = 1 / (4 (RLC / T-1). (T for the rectified output DC pulse voltage cycle.) First, the resistance filter circuit : RC-π filter circuit, in essence, is based on the capacitor filter plus a RC filter circuit. Figure 1 (B) RC filter circuit. If S said C1 voltage ripple at both ends of the voltage, then The ripple coefficient S = (1 / ωC2R) S at both ends of the output voltage. It can be seen from the analysis that the function of the resistor R is to drop the residual ripple voltage at both ends of the resistor and finally bypass it by C2. , The greater the R, the larger the C2, the smaller the ripple factor, that is, the better the filtering effect, and the R value increases, the DC voltage drop across the resistor increases, thus increasing the internal Loss; if the increase in C2 capacitance, will increase the size and weight of the capacitor, to achieve it is not realistic. This circuit is generally used for relatively small load current occasions.

Inductive filter circuit: According to the reactive components of the AC and DC impedance of the different, by the capacitance C and inductance L composed of the basic form of the filter circuit shown in Figure 1. Since the capacitor C is open to DC and has a small AC impedance, C is connected in parallel at both ends of the load. The inductor L has a small DC impedance and is large for the AC impedance, so L should be connected in series with the load. The parallel capacitor C, when the input voltage rises, charges the capacitor and stores part of the energy in the capacitor. And when the input voltage decreases, the capacitor voltage across the exponential discharge, you can put the stored energy released. After the filter circuit to the load discharge, the load on the output voltage is relatively smooth, played a role in the smooth wave. If the inductance filter is used, the current in the inductor L connected in series with the load increases when the input voltage increases, so the inductance L will store the partial magnetic field energy, and when the current decreases, the energy is released and the load current becomes smooth. , Inductance L also has a smooth wave effect. The use of energy storage components inductor L can not change the characteristics of the current, in the rectifier circuit load loop in series with an inductor, the output current waveform is more smooth. Because the inductance of the DC impedance is small, the impedance of the exchange is large, so can get a better filtering effect and DC loss is small. Inductance filter shortcomings are bulky, high cost.

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