Capacitor Typical Application Circuit Principles (III)

Typical capacitor filter circuit:

There are various types of capacitor filter circuits, such as power circuits with low-frequency filter capacitors, and high-frequency filter circuits with high-frequency filter capacitors.

Circuit analysis

The power supply filter circuit mainly uses a large-capacity capacitor. C1 is a filter capacitor connected between the output terminal of the rectifier circuit and the ground. The unidirectional ripple DC voltage output from the rectifier circuit is applied to C1, and R1 is the load resistance of the rectifier filter circuit.

1) Waveform equivalent analysis

Among the voltages outputted by the rectifier diode VD1, there is a pure DC voltage and a pure AC voltage. According to the waveform analysis principle, this voltage can be decomposed into a DC voltage and a set of AC voltages with different frequencies.

2) DC current

The filter capacitor C1 is open to DC, so DC can only form a loop through the load resistor R1, so that DC power is applied to both ends of the load.

3) AC current

Because of the large capacity of C1, the AC capacitor output to VD1 is less resistant. In this way, the AC power can not flow through R1 through C1 to the ground, thereby achieving the purpose of filtering out the AC component.

4) Filter capacitor

The filter capacitor should have a large capacity and be a polar electrolytic capacitor. The larger the C1 is, the smaller the capacitive reactance to the AC component is, and the smaller the AC component on R1 is, the better the filtering effect is.

2. Fault detection

The simplest method for detecting C1 is to measure the DC output voltage at both ends of C1. After the circuit is energized, it is measured with a multimeter DC voltage file.

1) When the circuit is energized, if the DC voltage across C1 is 0, it indicates that C1 is likely to break down or open.

2) After the circuit is powered off, use the pointer multimeter ohm file to measure C1. If the resistance is 0, it means C1 breakdown. If there is no breakdown, the possibility of open circuit is large. Use the same capacity capacitor to connect to C1, and work normally after power-on. C1 is open.

3) If no problem is found in the above detection, C1 has no fault and detects other components of the circuit.