capacitors are almost indispensable energy storage components in electronic circuits. they have the characteristics of isolating dc, connecting ac and preventing low frequency. it is widely used in coupling, isolation, bypass, filtering, tuning, energy conversion and automatic control circuits.
1. filter capacitor: connected between the positive and negative pole of dc power supply to filter out unnecessary ac components in dc power supply and make dc current smooth. generally, large capacity electrolytic capacitors or tantalum capacitors are used, and other types of small capacity capacitors can also be connected in the circuit to filter out high-frequency alternating current.
2. bypass capacitance: connected in the circuit of ac and dc signals, connect the capacitors at both ends of the resistance or connect the capacitance to the common potential at a certain point of the circuit, so as to set a path for ac signal or pulse signal, so as to avoid voltage drop attenuation of ac signal components due to resistance.
3. decoupling capacitor: connected between the positive and negative sides of the power supply of the amplifier circuit to prevent the parasitic vibration caused by the positive feedback formed by the internal resistance of the power supply.
4. coupling capacitance: connected in the ac signal processing circuit, it is used to connect the signal source and the signal processing circuit, or as the stage connection between the two amplifiers, so as to cut off the direct current, let the ac signal or pulse signal pass through, so that the dc working points of the front and rear stage amplifier circuits do not affect each other.
5. pad capacitor and resonant capacitor: auxiliary capacitor in series with the main capacitor. adjusting it can reduce the frequency range of oscillation signal and significantly increase the oscillation frequency at the low frequency end.
6. tuning capacitor: connected at both ends of the oscillation coil of the resonant circuit, which plays the role of selecting the oscillation frequency.