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.
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.
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.
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.
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.
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.
It is connected at both ends of the oscillating coil of the resonant circuit to select the oscillating frequency.
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.
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.
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.
Frequency stabilizing capacitor
In the oscillation circuit, it plays a role in stabilizing the oscillation frequency.
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.
It is connected to the feedback circuit of the oscillator to accelerate the positive feedback process and improve the amplitude of the oscillation signal.
In a UHF tuner circuit, a capacitor connected in series to shorten the length of the oscillating inductor.
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.
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.
Amplitude stabilizing capacitance
In the frequency discriminator, it is used to stabilize the amplitude of the output signal.
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.
De weighting capacitor
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.
The capacitance used to change the phase of an AC signal.
The capacitance that spans between the input and output terminals of the amplifier, so that the output signal is returned to the input terminal.
Step down current limiting capacitor
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.
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.
S correction capacitance
It is connected in series in the deflection coil circuit to correct the extended linear distortion of the picture tube edge.
Bootstrap boost capacitor
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.
Anti bright point capacitor
The capacitor is arranged in the video amplifier circuit to eliminate the residual bright spots on the picture tube when it is turned off.
Soft start capacitor
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.
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.
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.
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.