1. Typical π RC Filter Circuit
Figure 7-27 shows a typical tunnel RC Filter Circuit. The CL and C2 in the circuit are two filter capacitors, and RL is the filter resistor. cl, RL and C2 constitute a π type RC Filter Circuit. Because the form of this filter circuit is like π and adopts resistance and capacitance, it is called π RC Filter Circuit. From the circuit, we can see that the π RC Filter Circuit is connected to the output end of the rectification circuit.
The filtering principle of this circuit is that the voltage output from the rectification circuit first passes through Cl filtering to filter out most of the AC components, as shown in the figure below.
The voltage filtered by Cl is then added to the filter circuit consisting of RL and 02. capacitor C2 further filters the AC components, and a small amount of AC current reaches the ground through C2, the current shown in the figure.
The filter circuit has two DC voltage output ends, namely u01 and u02. Among them, u01 is filtered only by the capacitor Cl; u02 is filtered by the CL, rl, and C2 circuits, so the filtering effect is better, and the AC composition in the DC output voltage u02 is smaller.
The size of the above two DC output voltages is different. uo1 has the highest voltage. Generally, this voltage is directly added to the power amplifier circuit, or to the circuit that requires the highest DC operating voltage and the highest operating current, this is because the DC output voltage does not pass through the filter resistor, and the maximum DC voltage and DC current can be output; the DC output voltage u02 is slightly lower, because the resistor RL has a voltage drop on the DC voltage, at the same time, due to the existence of the filtering resistor RL, the size of the DC current output by this filter circuit is also limited.
2. Multi-section π RC Filter Circuit
The practical filter circuit is usually composed of several π-type RC Filter Circuits. the π-type RC Filter Circuits can be connected in series or in parallel. The π-type RC filter circuit consists of a filter capacitor and a filter resistor.
Figure 7-29 shows a multi-section π RC Filter Circuit. In the circuit, Cl, C2, and C3 are three filter capacitors. Cl is the filter capacitor in the first section, and C3 is the filter capacitor in the last section. RL and R2 are filter resistors.
The working principle of this filter circuit is basically the same as that of the above π RC Filter Circuit.
3. Multi-section π RC Filter string and parallel circuit
π Filter
