【Simulation Model】02-Capacitor

1. Capacitor basics

        A capacitor is a common electronic component composed of two parallel metal conductive plates separated by an insulating material filled with a dielectric in between. The capacitor can store electric charges, thus generating an electric field. Due to the existence of the electric field, energy storage is achieved. Therefore, a capacitor is an energy storage device, and a capacitor can also be referred to as a capacitor.

        There are many types of capacitors. Common ones include chip capacitors (MLCC), aluminum electrolytic capacitors, ceramic capacitors, tantalum capacitors, safety capacitors and variable capacitors. During the circuit design process, the characteristics of different capacitors should be considered to achieve the desired effect.

        Capacitors are widely used and can often be seen in filter circuits. They remove excess signals from the total signal and play a filtering role. In addition, capacitors are also widely used in decoupling, resonance, timing, differential and integral circuits.

        During Lichuang EDA simulation, the capacitor can be selected from non-polar capacitors or polarized capacitor styles. There are American standards, European standards and 3D picture models to choose from. The capacitance value parameters can be modified arbitrarily by placing the device on the canvas.

2. Capacitor charging and discharging simulation

        Connect the capacitor to the circuit, close the S1 switch, and when the DC power supply V3 is connected to the capacitor, the capacitor begins to charge. After the switch is turned off, the charge in the capacitor will be retained for a long time. If both ends of the capacitor are short-circuited and the S2 switch is closed, the excess charge will move through the circuit due to the voltage difference across the capacitor, and the capacitor will continue to discharge until the energy is exhausted.

        The relationship between voltage and time in the capacitor charging and discharging process is nonlinear. The charging curve grows exponentially, while the discharging curve decays exponentially. Here we often use the time constant τ to express (τ=R*C). When the capacitor charging time reaches 5 times the time constant, the capacitor is fully charged. Let’s do a simulation experiment to verify:

        Open EasyEDA and switch to simulation mode. Call resistors, capacitors and a pulse source in a voltage source from the simulation base library, and draw the circuit as follows:

        Draw two circuits separately to facilitate understanding of the difference between different parameters on charging time. Set the R1 resistor to 100K, the R2 resistor to 50K, and the capacitor to 1U. Add ic=5 after the C2 capacitor, which means the initial capacitor voltage is 5V. Simulate charging from 5V to 10V. The voltage pulse source configuration is as follows:

        The pulse value is set to 10V, the delay is 0, the pulse rise time and fall time are set to 1ns, the pulse width is 500ms, and the period is set to 1000m.

        The circuit time constant on the left is τ1=100K*1u=0.1s, and the time constant on the right is τ2=50K*1u=0.05s. Click simulation (shortcut key F8) to view the simulation phenomenon in the waveform diagram:

        It can be seen from the image that the purple V (out1) represents the pulse source input, and the blue line is the capacitor charge and discharge waveform in the circuit diagram on the left. Since the time constant of 5 times is equal to 0.1*5=0.5s, the pulse duty cycle is 50%, the high level time is exactly 0.5s. At this time, the capacitor charging is approximately equal to the power supply voltage value; and the time required for the yellow line to be fully charged is 0.05*5=0.25s. Since the initial setting capacitor voltage is 5V, the time required to fully charge it is Shorter, larger slope, normal after the second charging cycle.

        The knowledge of capacitors is not limited to this. In the subsequent simulation demonstrations, we will show you more characteristics and applications of capacitors. Welcome everyone to continue to pay attention to Lichuang EDA simulation teaching class.

Click to view the video explanation: https://www.bilibili.com/video/BV1wq4y1R7Sn