Why is there a capacitor in the circuit? Let's start from the role of capacitors in the circuit: capacitors are electronic components that hold and release electric charges. The basic working principle of capacitor is charging and discharging, as well as rectification, oscillation and other functions. In addition, the structure of capacitor is very simple, which is mainly composed of two positive and negative electrodes and insulating medium sandwiched in the middle. Therefore, the type of capacitor is mainly determined by the electrode and insulating medium.

　　虽然电容的体积很小，但并不影响其在电路中的重要作用。接下来，就让我们一起来盘点一下电容在电路中的27种作用。

　　Although the volume of capacitance is very small, it does not affect its important role in the circuit. Next, let's check the 27 functions of capacitors in the circuit.

　　1、滤波电容

　　Filter capacitor

　　滤波电容接在直流电压的正负极之间，以滤除直流电源中不需要的交流成分，使直流电平滑，通常采用大容量的电解电容，也可以在电路中同时并接其它类型的小容量电容以滤除高频交流电。

　　The filter capacitor is connected between the positive and negative poles of the DC voltage to filter out the unwanted AC components in the DC power supply and make the DC level slip. Usually, large capacity electrolytic capacitors are used, or other types of small capacity capacitors can be connected in parallel in the circuit to filter out high-frequency AC current.

　　2、退耦电容

　　Decoupling capacitor

　　退耦电容并接于放大电路的电源正负极之间，防止由电源内阻形成的正反馈而引起的寄生振荡。

　　The decoupling capacitor is connected in parallel between the positive and negative poles of the power supply of the amplifier circuit to prevent parasitic oscillation caused by the positive feedback formed by the internal resistance of the power supply.

　　3、旁路电容

　　Bypass capacitance

　　在交直流信号的电路中，将电容并接在电阻两端或由电路的某点跨接到公共电位上，为交流信号或脉冲信号设置一条通路，避免交流信号成分因通过电阻产生压降衰减。

　　In the circuit of AC and DC signals, the capacitance is connected to both ends of the resistance in parallel or connected to the common potential from a point of the circuit, and a path is set for the AC signal or pulse signal to avoid the voltage drop attenuation of the AC signal components due to resistance.

　　4、耦合电容

　　Coupling capacitance

　　在交流信号处理电路中，用于连接信号源和信号处理电路或者作为两放大器的级间连接,用于隔断直流，让交流信号或脉冲信号通过，使前后级放大电路的直流工作点互不影响。

　　In the AC signal processing circuit, it is used to connect the signal source and the signal processing circuit or as the interstage connection of two amplifiers, to isolate the DC, let the AC signal or pulse signal pass through, so that the DC working points of the front and rear amplifier circuits do not affect each other.

　　5、调谐电容

　　Tuning capacitor

　　连接在谐振电路的振荡线圈两端，起到选择振荡频率的作用。

　　It is connected at both ends of the oscillating coil of the resonant circuit to select the oscillating frequency.

　　6、衬垫电容

　　Pad capacitance

　　它与谐振电路主电容串联的辅助性电容，调整它可使振荡信号频率范围变小，并能显著地提高低频端的振荡频率。

　　It is an auxiliary capacitor connected in series with the main capacitor of the resonant circuit. By adjusting it, the frequency range of the oscillating signal can be reduced, and the oscillating frequency at the low frequency end can be significantly increased.

　　7、补偿电容

　　Compensation capacitance

　　补偿电容与谐振电路主电容并联的辅助性电容，调整该电容能使振荡信号频率范围扩大。

　　The compensation capacitor is an auxiliary capacitor in parallel with the main capacitor of the resonant circuit. Adjusting the capacitor can expand the frequency range of the oscillating signal.

　　8、中和电容

　　Neutralizing capacitance

　　并接在三极管放大器的基极与发射极之间，构成负反馈网络，以抑制三极管极间电容造成的自激振荡。

　　It is connected in parallel between the base and emitter of the triode amplifier to form a negative feedback network to suppress the self-excited oscillation caused by the interelectrode capacitance of the triode amplifier.

　　9、稳频电容

　　Frequency stabilizing capacitor

　　在振荡电路中，起稳定振荡频率的作用。

　　In the oscillation circuit, it plays a role in stabilizing the oscillation frequency.

　　10、定时电容

　　Timing capacitor

　　在RC时间常数电路中与电阻R串联，共同决定充放电时间长短的电容。

　　The capacitance that is connected in series with the resistor R in the RC time constant circuit to jointly determine the charging and discharging time.

　　11、加速电容

　　Accelerating capacitor

　　接在振荡器反馈电路中，使正反馈过程加速，提高振荡信号的幅度。

　　It is connected to the feedback circuit of the oscillator to accelerate the positive feedback process and improve the amplitude of the oscillation signal.

　　12、缩短电容

　　Shorten capacitance

　　在UHF高频头电路中，为了缩短振荡电感器长度而串联的电容。

　　In a UHF tuner circuit, a capacitor connected in series to shorten the length of the oscillating inductor.

　　13、克拉波电容

　　Crabbe capacitance

　　在电容三点式振荡电路中，与电感振荡线圈串联的电容，起到消除晶体管结电容对频率稳定性影响的作用。

　　In the capacitance three-point oscillation circuit, the capacitance in series with the inductance oscillation coil plays a role in eliminating the influence of the transistor junction capacitance on the frequency stability.

　　14、锡拉电容

　　Scylla capacitor

　　在电容三点式振荡电路中，与电感振荡线圈两端并联的电容，起到消除晶体管结电容的影响，使振荡器在高频端容易起振。

　　In the capacitor three-point oscillation circuit, the capacitance in parallel with both ends of the inductance oscillation coil can eliminate the influence of the transistor junction capacitance, making the oscillator easy to start oscillation at the high-frequency end.

　　15、稳幅电容

　　Amplitude stabilizing capacitance

　　在鉴频器中，用于稳定输出信号的幅度。

　　In the frequency discriminator, it is used to stabilize the amplitude of the output signal.

　　16、预加重电容

　　Preemphasis capacitor

　　为了避免音频调制信号在处理过程中造成对分频量衰减和丢失，而设置的RC高频分量提升网络电容。

　　In order to avoid the attenuation and loss of the frequency divider during the processing of the audio modulation signal, the RC high-frequency component is set to enhance the network capacitance.

　　17、去加重电容

　　De weighting capacitor

　　为了恢复原伴音信号，要求对音频信号中经预加重所提升的高频分量和噪声一起衰减掉，设置RC在网络中的电容。

　　In order to recover the original accompanying sound signal, it is required to attenuate the high frequency component and noise in the audio signal that are enhanced by pre emphasis together, and set the RC capacitance in the network.

　　18、移相电容

　　Phase-shifting capacitor

　　移相电容用于改变交流信号相位的电容。

　　The capacitance used to change the phase of an AC signal.

　　19、反馈电容

　　Feedback capacitor

　　跨接于放大器的输入与输出端之间，使输出信号回输到输入端的电容。

　　The capacitance that spans between the input and output terminals of the amplifier, so that the output signal is returned to the input terminal.

　　20、降压限流电容

　　Step down current limiting capacitor

　　串联在交流回路中，利用电容对交流电的容抗特性，对交流电进行限流，从而构成分压电路。

　　It is connected in series in the AC circuit, and uses the capacitive reactance characteristics of capacitors to limit the current of AC, thus forming a voltage divider circuit.

　　21、逆程电容

　　Reverse capacitance

　　用于行扫描输出电路，并接在行输出管的集电极与发射极之间，以产生高压行扫描锯齿波逆程脉冲，其耐压一般在1500伏以上。

　　It is used for line scanning output circuit and connected between collector and emitter of line output tube to generate high-voltage line scanning sawtooth wave reverse pulse. Its withstand voltage is generally above 1500 V.

　　22、S校正电容

　　S correction capacitance

　　串接在偏转线圈回路中，用于校正显像管边缘的延伸线性失真。

　　It is connected in series in the deflection coil circuit to correct the extended linear distortion of the picture tube edge.

　　23、自举升压电容

　　Bootstrap boost capacitor

　　利用电容器的充、放电储能特性提升电路某点的电位,使该点电位达到供电端电压值的2倍。

　　Use the charging and discharging energy storage characteristics of the capacitor to increase the potential of a point in the circuit, so that the potential of the point is twice the voltage value of the power supply terminal.

　　24、消亮点电容

　　Anti bright point capacitor

　　设置在视放电路中，用于关机时消除显像管上残余亮点的电容。

　　The capacitor is arranged in the video amplifier circuit to eliminate the residual bright spots on the picture tube when it is turned off.

　　25、软启动电容

　　Soft start capacitor

　　一般接在开关电源的开关管基极上，防止在开启电源时，过大的浪涌电流或过高的峰值电压加到开关管基极上，导致开关管损坏。

　　It is generally connected to the switch tube base of the switching power supply to prevent the switch tube from being damaged when excessive surge current or excessive peak voltage is applied to the switch tube base when the power supply is turned on.

　　26、启动电容

　　Starting capacitance

　　串接在单相电动机的副绕组上，为电动机提供启动移相交流电压，在电动机正常运转后与副绕组断开。

　　It is connected to the secondary winding of single-phase motor in series to provide the motor with starting phase-shifting AC voltage, and is disconnected from the secondary winding after the motor operates normally.

　　27、运转电容

　　Operating capacitance

　　与单相电动机的副绕组串联，为电动机副绕组提供移相交流电流。在电动机正常运行时，与副绕组保持串接。

　　It is connected in series with the secondary winding of single-phase motor to provide phase-shifting AC current for the secondary winding of motor. When the motor operates normally, it shall be connected in series with the auxiliary winding.

　　综上就是电容器在电路中的作用，虽说小小的电容器看起来很不起眼，但是在电路中却发挥着非常重要的作用，选择适合的电容器发挥其作用才能体现其最优的价值。

　　To sum up, it is the role of capacitors in the circuit. Although small capacitors look inconspicuous, they play a very important role in the circuit. Only by selecting suitable capacitors to play their role can their optimal value be reflected.