The role and principle of capacitors in circuits are crucial. Below is a detailed explanation of the function and working principle of capacitors in circuits:

The role of a capacitor

1.  Filtering: Capacitors can filter out noise from AC signals, ensuring stable output of DC signals. In power supply circuits, a filter capacitor is connected between the positive and negative terminals of the DC power supply to eliminate unwanted AC components, thus smoothing the DC level. Additionally, small capacitance capacitors can be connected in parallel in the circuit to filter out high-frequency AC signals.

2. Decoupling: Capacitors are used to remove interference between different components in the circuit, stabilize the operating voltage, and ensure pure signals. In amplifier circuits, a decoupling capacitor is connected between the positive and negative terminals of the power supply to prevent parasitic oscillations caused by positive feedback from the internal resistance of the power supply.

3. Coupling: In AC signal processing circuits, capacitors serve as connections between two circuits, allowing AC signals to pass through and be transmitted to the next stage while blocking DC signals. This helps ensure that the DC operating points of the preceding and following stages do not interfere with each other, making circuit debugging easier and performance more stable.

4. Energy Storage: Capacitors can store energy temporarily in a circuit and release it when needed, maintaining the normal operation of the circuit. For example, capacitors play an energy storage role in applications like camera flashes and heating devices.

5. DC Blocking: Capacitors have the ability to block DC while allowing AC signals to pass through. This characteristic makes capacitors crucial in circuits where both DC and AC signals are mixed.

6. Tuning: In resonant circuits, capacitors are connected with oscillating coils to select the oscillation frequency. This is vital for frequency-related circuits such as those in mobile phones, radios, and televisions.

In addition, capacitors also serve functions such as bypass, temperature compensation, timing, and rectification, which may be reflected in specific circuit designs.

           (UV germicidal lamp bulb and matching capacitor)

The working principle of a capacitor

The working principle of a capacitor is based on the electric field effect. A capacitor consists of two conductors (plates) that are electrically insulated from each other, with a dielectric material between them. When a voltage is applied across the capacitor, charges move to the plates under the influence of the electric field, and accumulate on the plates due to the barrier effect of the dielectric, forming a charge storage. When the circuit requires electrical energy, the capacitor can release the stored charge, thereby stabilizing the voltage or current.

The energy storage capacity of a capacitor is determined by its capacitance value (C), measured in farads (F). The formula to calculate the capacitance is: Q = C × V, where Q is the charge amount, C is the capacitance, and V is the voltage.

In summary, capacitors play multiple important roles in circuits, with their working principle based on the effect of electric fields and the storage and release of charges. Understanding the function and principles of capacitors is crucial for circuit design and the maintenance of electronic devices.

（The connection method of UV germicidal lamp bulbs with capacitors or inverters）