Introduction
Capacitor Element is a circuitry in the circuit model in the circuit model in the circuit model except for the resistance element R and the inductor element L. In the linear circuit, the capacitive element is represented by capacitance C. The "Voltiencies" of the component is the necessary constraints other than the laws of Kilkhm analysis in linear circuit analysis. The voltammetry of the capacitive element is I = C (DV / DT), that is, the current in the capacitive element except for the capacitance C, which is different from the resistance element R, which does not depend on the voltage V itself, but depends on The rate of change in the voltage (DV / DT). The faster voltage changes, the current in the capacitor is bigger, and the smaller is. According to this, in the "steady state" case, when the voltage is DC, the current is zero; when the voltage is sine wave, the current in the capacitor is also a sine wave, but the advance voltage (π / 2) is maintained in the phase; When the voltage is a periodic equal waist triangular wave, the current is a rectangular wave, and so, the like. In general, the current waveform in the capacitor is faster than the voltage, containing more high frequency components.
Set of the total parameter circuit is concentrated in the capacitive element in the capacitive element in the total parameter circuit, and the capacitive element is an ideal circuit component necessary to constitute a circuit model of various capacitors.
Capacitor element is an ideal element that characterizes circuit components stored charge characteristics, its original model being a flat plate capacitor spaced from the intermediate insulating medium in two metal plates. When the voltage is added to the differ sheet, the equal amount of positive and negative charge is accumulated, and an electric field is generated between the two poles. The more charge of accumulating, the stronger the electric field formed, and the electric field stored in the capacitive element can be more harder.
The characteristic curve is called linear capacitor element , nonlinear capacitive element nonlinear capacitive element < / b>.
The symbol and characteristic curve of the constant capacitive element when linearly indicated by Figures 1 (c) and (d), and its characteristic curve is a straight line that does not change over time by the origin, its mathematical expression is Q = Cu. c in the
is constant, the slope of the straight line is proportional, referred to as a capacitor, and the unit is a method [pull], which is expressed.
Basic nature
Capacitor element has two basic properties:
(1) memory of capacitor voltage
Paste visible , Any time T Capacitor voltage u c ( T ), to be from -∞ to time t All current current i c ( t ) is determined. That is, any current flowing over the capacitance at this time has a certain contribution of the voltage of the time t . This is completely different from the voltage or current of the resistor element depending on the current or voltage at this time, and we say that the capacitor is a memory component.(2) Continuity of the capacitor voltage
The calculation results of Example 7-2 can be seen that the waveform of the capacitor current is a discontinuous rectangular wave, and the waveform of the capacitor voltage It is continuous. From this smooth capacitive voltage waveform, it can be seen that the capacitor voltage is a continuous general property. That is, the capacitor current is bound in closed interval [ t 1, t 2], the capacitor voltage is in the opening section ( T 1, T 2) is continuous. This can be proved from the integral relationship between the capacitor voltage and current.