SMD capacitor knowledge summary, what a pity if you don't share it! !

Capacitor are the most commonly used in circuit design, and they often play a key role in high-speed circuits.

Next, talk about the role and use of capacitor:

1 DC blocking means to let AC pass and block DC to pass.

2 Bypass Provides a low-impedance path for some components connected in parallel in the AC circuit.

Bypass capacitor, also known as decoupling capacitor, are devices that provide energy storage for the device. The frequency characteristics of an ideal capacitor will increase with the frequency, while the impedance will decrease, so that the output voltage will be uniform and the load voltage fluctuation will be reduced.

The bypass capacitor should be as close as possible to the load device (power supply pin and ground pin). It should also be noted that only when it is close to a certain component, can the noise caused by excessive voltage or other output signals be suppressed.

Decoupling capacitor: The decoupling capacitor takes the interference of the output signal as the filtering object. The decoupling capacitor is equivalent to the battery and uses its charge and discharge so that the amplified signal will not be interfered by the sudden change of the current. Its capacity is based on.

Depending on the frequency of the signal and the degree of ripple suppression, the decoupling capacitor acts as a "battery" to meet the current changes in the drive circuit and avoid mutual coupling interference.

The difference between bypass capacitor and decoupling capacitor:

Bypass is to take the interference in the input signal as the filtering object, and decoupling is to take the interference of the output signal as the filtering object. The capacitor is used as a coupling element to pass the signal from the previous stage to the next stage, and to block the front First level.

The influence of DC on the latter stage makes circuit debugging simple and stable performance.

Temperature compensation: In view of the impact of other components' insufficient adaptability to temperature, compensation is made to improve the stability of the circuit.

Analysis: Since the capacity of the timing capacitor determines the oscillation frequency of the line oscillator, the capacity of the timing capacitor is required to be very stable and does not change with changes in environmental humidity. The capacitor with positive and negative 

temperature coefficients are used to release the connection.

Complementary temperature. In this way, the oscillation frequency of the line oscillator can be stabilized. When the working temperature rises, the capacity of Cl is increasing, while the capacity of C2 is decreasing. The total capacity of the two capacitor in parallel is the sum of the capacity of the two capacitor.

Filtering: The capacitor behind the CPU basically has this function and plays a key role. The larger the frequency f, the smaller the impedance Z of the capacitor. At low frequencies, capacitor C can pass useful signals smoothly due to its relatively large impedance Z; at 

high frequencies, electrical. Capacitance C is already very small due to impedance Z, which is equivalent to shorting high-frequency noise to GND.

Filtering function: Electrolytic capacitor are generally more than 1uF, but the impedance will be larger when the frequency is high. The higher the frequency of the capacitor, the greater the attenuation, which means that when the voltage fluctuation is not very large, the voltage can buffer the large capacitor and pass the low frequency.

Only when the capacitor passes high frequency can the high and low frequency be fully filtered.

Energy storage: store electrical energy and release it when necessary.

Energy storage function: The mechanism of capacitor energy storage is electric double layer capacitor and Faraday capacitor. Its main form is super capacitor energy storage. Under the action of the electric field generated by the charge on the two electrode plates of the super capacitor, it is between the electrolyte and the electrode.

Opposite charges are formed on the interface to balance the internal electric field of the electrolyte. The positive and negative charges are arranged in opposite positions on the contact surface between the two different phases with a very short gap between the positive and 

negative charges. This charge.

The distribution layer is called an electric double layer, so the capacitance is very large. Among them, the supercapacitor is a capacitor using the principle of electric double layer. When an external voltage is applied to the two plates of the supercapacitor, it is the same as an ordinary capacitor.

The positive electrode stores positive charges, the negative plate stores negative charges.When the temperature decreases, the capacity of one capacitor is decreasing and the other is increasing, which stabilizes the oscillation frequency and realizes the purpose of temperature 

compensation.