This technical column describes the basic facts about capacitors. This lesson describes the voltage characteristics of electrostatic capacitance. The phenomenon where the effective capacitance value of a capacitor changes according to the direct current (DC) or alternating current (AC) voltage is called the voltage characteristics.
Therefore we can state a particularly important characteristic of capacitors: The voltage across a capacitor cannot change instantaneously. (8.2.7) (8.2.7) The voltage across a capacitor cannot change instantaneously. This observation will be key to understanding the operation of capacitors in DC circuits.
The capacitance of a capacitor can change value with the circuit frequency (Hz) y with the ambient temperature. Smaller ceramic capacitors can have a nominal value as low as one pico-Farad, ( 1pF ) while larger electrolytic’s can have a nominal capacitance value of up to one Farad, ( 1F ).
Capacitors are said to have good voltage characteristics when this variance width is small, or poor temperature characteristics when the variance width is large. When using capacitors in electronic equipment used for applications such as ripple rejection in power lines, the design must take into account the operating voltage conditions. 1.
Electrolytic capacitors have high capacitance values. The temperature rise affects the electrolyte’s viscosity and conductivity, affecting the capacitance value and its performance. Also, at extremely cold temperatures, the electrolyte can freeze, affecting its capacitance value. (6). Capacitor Characteristics – Temperature Coefficient:
Given a fixed voltage, the capacitor current is zero and thus the capacitor behaves like an open. If the voltage is changing rapidly, the current will be high and the capacitor behaves more like a short. Expressed as a formula: i = Cdv dt (8.2.5) (8.2.5) i = C d v d t Where i i is the current flowing through the capacitor, C C is the capacitance,