The Role Of The Capacitor

In DC circuits, capacitors are equivalent to open circuits. A capacitor is a component capable of storing electrical charge and is one of the most commonly used electronic components.

This has to start with the structure of the capacitor. The simplest capacitor consists of plates at both ends and an insulating dielectric (including air) in the middle. After being energized, the plates are charged and a voltage (potential difference) is formed, but the entire capacitor is not conductive due to the insulating substance in the middle. However, this is the case without exceeding the critical voltage (breakdown voltage) of the capacitor. We know that any substance is relatively insulated, when the voltage at both ends of the substance increases to a certain extent, the substance can conduct electricity, we call this voltage breakdown voltage. Capacitors are no exception, and after the capacitor is broken down, it is not an insulator. However, in middle school, such voltages are not seen in circuits, so they all work below the breakdown voltage and can be regarded as insulators. 

However, in AC circuits, because the direction of the current changes as a function of time. The process of charging and discharging capacitors has time, at this time, a changing electric field is formed between the plates, and this electric field is also a function of time. In fact, an electric current passes between the capacitors in the form of an electric field.

The role of the capacitor:
●Coupling: The capacitor used in the coupling circuit is called coupling capacitor, and this capacitor circuit is widely used in resistive capacitance coupling amplifiers and other capacitive coupling circuits to play the role of DC and AC isolation.
● Filtering: The capacitor used in the filter circuit is called a filter capacitor, which is used in power supply filtering and various filter circuits, and the filter capacitor removes the signal in a certain frequency band from the total signal.
● Decoupling: The capacitor used in the decoupling circuit is called the decoupling capacitor, which is used in the DC voltage supply circuit of the multi-stage amplifier, and the decoupling capacitor eliminates the harmful low-frequency cross-connection between each stage of the amplifier.
● High-frequency vibration damping: The capacitor used in the high-frequency vibration damping circuit is called high-frequency vibration damping capacitor, in the audio negative feedback amplifier, in order to dampen the possible high-frequency self-excitation, this capacitor circuit is used to eliminate the high-frequency howling that may occur in the amplifier.
● Resonance: The capacitor used in the LC resonant circuit is called a resonant capacitor, and this capacitor circuit is required in both LC parallel and series resonant circuits.
● Bypass: The capacitor used in the bypass circuit is called the bypass capacitor, if the circuit needs to remove a certain frequency band signal from the signal, the bypass capacitor circuit can be used, according to the frequency of the removed signal, there are full-frequency domain (all AC signals) bypass capacitor circuit and high-frequency bypass capacitor circuit.
● Neutralization: The capacitor used in the neutralization circuit is called the neutralization capacitor. In radio high-frequency and medium-frequency amplifiers, television high-frequency amplifiers, this neutralizing capacitor circuit is used to eliminate self-excitation.
● Timing: The capacitor used in the timing circuit is called the timing capacitor. A timing capacitor circuit is used in a circuit that requires time control by charging and discharging a capacitor, and the capacitor plays the role of controlling the magnitude of the time constant.
●Integration: The capacitors used in the integration circuit are called integral capacitors. In the synchronous separation circuit of potential field scanning, this integrating capacitor circuit allows the field synchronization signal to be taken from the field composite synchronization signal.
● Differentiation: Capacitors used in differential circuits are called differential capacitors. In order to obtain the spike trigger signal in the trigger circuit, this differential capacitor circuit is used to obtain the spike pulse trigger signal from various (mainly rectangular pulse) signals.
● Compensation: The capacitor used in the compensation circuit is called the compensation capacitor, and in the bass compensation circuit of the deck, this low-frequency compensation capacitor circuit is used to improve the low-frequency signal in the playback signal, in addition, there is a high-frequency compensation capacitor circuit.
● Bootstrapping: The capacitor used in the bootstrap circuit is called bootstrap capacitor, and the commonly used OTL power amplifier output stage circuit uses this bootstrap capacitor circuit to increase the positive half-cycle amplitude of the signal by means of positive feedback.
● Crossover: The capacitor in the crossover circuit is called crossover capacitor, and in the speaker's crossover circuit, the crossover capacitor circuit is used to make the tweeter work in the high frequency band, the mid-frequency speaker works in the middle frequency band, and the low-frequency speaker works in the low frequency band.
● Load capacitance: refers to the effective external capacitance that determines the load resonance frequency together with the quartz crystal resonator. Common standard values for load capacitance are 16pF, 20pF, 30pF, 50pF, and 100pF. The load capacitance can be adjusted appropriately according to the specific situation, and the operating frequency of the resonator can generally be adjusted to the nominal value.