Analysis of the application of filter capacitor in voltage adjusting circuit

In the system of consumer electronic products, the volume is smaller and smaller, and the devices are placed more and more closely. It is difficult to separate the analog and digital parts effectively through the layout. System design engineers often use a lot of capacitors in the power network to attenuate high-frequency digital noise, expecting to "purify" the power supply and reduce the interference to the analog circuit.

In a voltage regulator, there is usually a capacitor at the input and output terminals, which is jumper between the input and output pins and ground (GND). The main function of the input capacitor is to filter out the AC noise and suppress the voltage change of the input terminal. In addition to forming a part of the feedback loop (adding an additional zero point, of course, it is inevitable to bring a pole and improve the phase margin of the loop), the output capacitance can also suppress the output voltage changes caused by the load current or input voltage transients. From a certain point of view, filtering the AC noise and suppressing the voltage mutation are essentially the same thing, that is, removing the AC signal.

Characteristics of capacitance

Different kinds of capacitors have different characteristics. Before describing the characteristics of capacitors, we need to understand the following parameters:

Resistance - symbol R, the ratio of DC voltage to current through a conductor, in ohms.

Reactance - symbol x, the impedance part of an AC circuit caused by inductance and capacitance, including inductive reactance (XL) and capacitive reactance (XC), in ohms.

Impedance symbol Z is a composite parameter, the real part is resistance, the imaginary part is reactance, and the unit is Ohm, so the impedance can also be expressed as: z = R + JX.

Conductance symbol g refers to the ratio of DC current to voltage passing through the conductor and the reciprocal of resistance, in Siemens.

Admittance - symbol B, the imaginary part of admittance, including accommodation (BC) and inductance (BL), in Siemens.

Admittance symbol y is the reciprocal of impedance Z and also a composite parameter. The real part is conductance and the imaginary part is susceptance. The unit is Siemens. It can also be expressed as y = G + JB

Admittance y usually refers to the parallel connection of devices, while impedance Z refers to the series connection of devices. News company news company news company news company news company news company news company news company news company news company