In circuit design, we often need to use capacitors. In different circuits, their functions will be different. The following introduces the 9 major functions and 27 applications of capacitors.
What are the functions of capacitors?
1. DC isolation, which means blocking DC from passing and allowing AC to pass.
2. Bypass (decoupling) function, which means providing a low impedance path for certain related components in the AC circuit. Generally, bypass takes the interference in the input signal as the object to be filtered out, while decoupling takes the interference in the output signal as the object to be filtered out to prevent the interference signal from returning to the power supply.
3. Coupling function, as a connection between two circuits, allows AC signals to pass and be transmitted to the next level circuit.
4. Filtering function, this function is very important for the output of AC-DC power supply modules. Generally, the capacitors behind the CPU basically play a filtering role.
5. Temperature compensation function: Compensate for the impact of other components' insufficient adaptability to temperature, which helps improve the stability of the circuit.
6. Timing function: Capacitors and resistors can be used together to determine the time constant of the circuit.
7. Tuning function: System tuning of frequency-related circuits, such as mobile phones, radios, televisions, etc.
8. Rectification function: Open or close semi-closed conductor switching elements at a predetermined time.
9. Energy storage function: Store electrical energy for release when necessary.
Main applications of capacitors:
1. Filtering application: If connected between the positive and negative poles of the DC output of the power module, it can filter out the unnecessary AC components in the DC module and make the DC power smoother.
2. Decoupling application, connected between the positive and negative poles of the power supply of the amplifier circuit, can prevent parasitic oscillation caused by positive feedback formed by the internal resistance of the power supply.
3. Bypass application, in the circuit of AC and DC signals, the capacitor is connected in parallel to the two ends of the resistor or a certain point of the circuit is connected to the common potential, which can set a path for the AC signal or pulse signal to avoid the voltage drop attenuation of the AC signal component due to passing through the resistor.
4. Coupling application, in the AC signal processing circuit, it is used to connect the signal source and the signal processing circuit or as an inter-stage connection between two amplifiers to isolate the DC and allow the AC signal or pulse signal to pass through, so that the DC operating points of the front and rear amplifier circuits do not affect each other.
5. Tuning application, connected at both ends of the oscillation coil of the resonant circuit, plays the role of selecting the oscillation frequency.
6. Pad application, auxiliary capacitor connected in series with the main capacitor of the resonant circuit, adjusting it can reduce the frequency range of the oscillation signal and significantly increase the oscillation frequency at the low frequency end.
7. Compensation application, auxiliary capacitor connected in parallel with the main capacitor of the resonant circuit, adjusting this capacitor can expand the frequency range of the oscillation signal.
8. Neutralization application, connected between the base and emitter of the transistor amplifier to form a negative feedback network to suppress the self-excited oscillation caused by the capacitance between the transistor electrodes.
9. Frequency stabilization application, plays a role in stabilizing the oscillation frequency in the oscillation circuit.
10. Timing application, capacitor connected in series with resistor R in the RC time constant circuit to jointly determine the length of the charge and discharge time.
11. Acceleration application: connected in the oscillator feedback circuit to accelerate the positive feedback process and increase the amplitude of the oscillation signal.
12. Shortening application: a capacitor connected in series in the UHF high-frequency head circuit to shorten the length of the oscillation inductor.
13. Crapo capacitor: a capacitor connected in series with the inductor oscillation coil in the capacitor three-point oscillation circuit to eliminate the effect of the transistor junction capacitance on the frequency stability.
14. Tin pull application: a capacitor connected in parallel with both ends of the inductor oscillation coil in the capacitor three-point oscillation circuit to eliminate the effect of the transistor junction capacitance and make the oscillator easier to oscillate at the high frequency end.
15. Amplitude stabilization application: used to stabilize the amplitude of the output signal in the frequency detector.
16. Pre-emphasis application: in order to avoid the attenuation and loss of the frequency division amount caused by the audio modulation signal during the processing, the RC high-frequency component enhancement network capacitor is set.
17. De-emphasis application: in order to restore the original audio signal, it is required to attenuate the high-frequency components and noise in the audio signal enhanced by pre-emphasis, and set the RC capacitor in the network.
18. Phase shift application: capacitor used to change the phase of the AC signal.
19. Feedback application: capacitor connected between the input and output terminals of the amplifier to feed the output signal back to the input terminal.
20. Buck-current limiting application: connected in series in the AC circuit, using the capacitive reactance characteristics of the capacitor to the AC current to limit the current of the AC current, thereby forming a voltage divider circuit.
21. Reverse application, used in line scan output circuit, and connected between the collector and emitter of the line output tube to generate high voltage line scan sawtooth wave reverse pulse, its withstand voltage is generally above 1500 volts.
22. S correction application, connected in series in the deflection coil loop, used to correct the extended linear distortion of the edge of the picture tube.
23. Bootstrap boost application, using the charge and discharge energy storage characteristics of the capacitor to increase the potential of a certain point in the circuit, so that the potential of the point can reach 2 times the voltage value of the power supply end.
24. Bright spot elimination application, often set in the video and playback circuit, used to eliminate the residual bright spot capacitor on the picture tube when shutting down.
25. Soft start application, often connected to the base of the switch tube of the switching power supply, in order to prevent excessive surge current or excessive peak voltage from being added to the base of the switch tube when the power is turned on, causing damage to the switch tube.
26. Starting application, connected in series to the auxiliary winding of a single-phase motor, providing the motor with a starting phase-shifted AC voltage, and disconnected from the auxiliary winding after the motor is running normally.
27. In operation applications, it is connected in series with the secondary winding of a single-phase motor to provide phase-shifted AC current for the secondary winding of the motor. It is connected in series with the secondary winding when the motor is operating normally.
Three common misunderstandings about capacitors: the larger the capacitance, the better. For capacitors of the same capacity, the more small capacitors are connected in parallel, the lower the ESR, the better the effect. Capacitors have many functions, and in practical applications, they must be selected according to actual conditions.