Principle of High Power DC Power Supply Filtering Circuit

Rectifier circuit is a kind of circuit that converts alternating current into high-power direct current power supply, but the pulsation component of high-power direct current power supply output is larger, and the pulsation coefficient of high-power direct current power supply required by general electronic equipment is less than 0.01. Therefore, some measures must be taken to rectify the output voltage.

To minimize the fluctuating component of the output voltage, and to preserve the DC component of the output voltage as far as possible, so that the output voltage is close to the ideal high-power DC power supply, such a circuit is the filter circuit in the high-power DC power supply.

Passive filter and active filter are two kinds of commonly used filter circuits. The main forms of passive filtering are capacitive filtering, inductance filtering and complex filtering (including inverted L-type, LC filtering, LC-pi filtering and RC-pi filtering). The main form of active filter is active RC filter, also known as electronic filter.

The magnitude of the pulsation component in high power DC power supply is expressed by the pulsation coefficient. The larger the value, the worse the filtering effect of the filter.

Pulse coefficient (S) = larger fundamental value of AC component of output voltage/DC component of output voltage

The fluctuation coefficient of output voltage of half-wave rectifier is S=1.57, and that of output voltage of full-wave rectifier and bridge rectifier is S_O.67. For full-wave and bridge rectifier circuits, the pulsation coefficient S = 1/4 (RLC/T-1) is obtained by using C-type filter circuit. T is the period of DC pulsating voltage of rectifier output. )

RC-pi filter circuit is essentially composed of capacitive filter and first-order RC filter circuit. In Figure 1, the dotted line frame is the added first-order RC filter circuit. If S is used to represent the fluctuation coefficients of the voltages at both ends of C1, then the fluctuation coefficients at both ends of the output voltage S=(1/_C2R)S.

According to the analysis, the larger R and C2, the smaller the fluctuation coefficient, that is to say, the better the filtering effect, when the value of_is fixed. When the R value increases, the DC voltage drop on the resistance will increase, which will increase the internal loss of the high-power DC power supply. If the capacity of C2 is increased, the volume and weight of the capacitor will be increased, which is unrealistic.

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