Capacitors Capacitance is the ability of a component to store energy in the form of an electrostatic charge. A Capacitor is a component designed to provide a specific measure of capacitance. EGR 101

Capacitor Construction Parallel plates separated by a dielectric layer EGR 101

Fixed Value Capacitors Polarized Electrolytic Capacitors Most electrolytic capacitors are polarized EGR 101

Interleaved-Plate Capacitors Variable Capacitors Interleaved-Plate Capacitors EGR 101

Charging a Capacitor Electrostatic Charge Develops on the Plates Electrostatic Field Stores energy EGR 101

Discharging a Capacitor Apply a discharging component (here a short circuit) across the capacitor. (Safer to use a resistor!) EGR 101

Capacity (Capacitance) of a Device Capacity is the amount of charge that a capacitor can store per unit volt applied. Capacity is directly proportional to charge and inversely proportional to voltage EGR 101

Q = the total charge stored by the component where C = the capacity (or capacitance) of the component, in coulombs per volt, or Farads Q = the total charge stored by the component V= the voltage across the capacitor EGR 101

Example EGR 101

Capacitor Ratings Most capacitors rated in the picofarad (pF) to microfarad (F) range Capacitors in the millifarad range are commonly rated in thousands of microfarads: 68 mF = 68,000 F Capacitors in the nanofarad range are also commonly rated in microfarads: 68 nF = 0.068 F EGR 101

Variable capacitors used where exact values required Capacitors in the nanofarad range are also commonly rated in microfarads: 68 nF = 0.068 F Tolerance Usually fairly poor Variable capacitors used where exact values required EGR 101

Capacitor Value Codes Physically large capacitors usually have their values printed directly on the case Smaller capacitors are generally labeled using a code: 2-digit code: the number represents the value of the component in pF Example: 15 = 15 pF 3-digit code: the code is interpreted like the first three digits of a resistor code Example: 473 = 47 x 103 pF = 47 nF The numbers 6 and 7 are not used as multiplier values The numbers 8 and 9 are decoded as follows: 8 = 0.01 and 9 = 0.1 Example: 158 = 0.15 pF

Capacitance of a Parallel Plate Capacitor EGR 101

C = the capacity of the component, in farads (8.85 X 10-12)= the permittivity of a vacuum, in farads per meter (F/m) r = the relative permittivity of the dielectric A= the area of either plate, in square meters (m2) d = the distance between the plates, in meters (m) EGR 101

Plate Area: capacitance is directly proportional to plate area Dielectric Thickness: capacitance is inversely proportional to dielectric thickness Dielectric Permittivity: the ease with which lines of electrical force are established in the dielectric material Relative Permittivity: the ratio of a material’s permittivity to that of a vacuum EGR 101

Capacitors in Series CT = the total series capacitance Cn = the highest-numbered capacitor in the circuit EGR 101

Capacitors in Parallel Cn = the highest-numbered capacitor in the parallel circuit EGR 101