Transcript Capacitors
Capacitors The capacitor is an element that continuously stores charge (energy), for later use over a period of time! In its simplest form, a capacitor consists of two conducting plates separated by an insulating material called the dielectric. The dielectric The dielectric can be air, paper, plastic or anything else that does not conduct electricity and keeps the plates from touching each other. The larger the plate area and the smaller the area between the plates, the larger the capacitance. Which also depends on the type of insulating material between the plates which is the smallest with air. The dielectric constant Capacitance is directly proportional to the surface areas of the plates, and is inversely proportional to the plates' separation. Capacitance depends on the dielectric constant of the dielectric material separating the plates. When you connect a capacitor to a battery The plate on the capacitor that attaches to the negative terminal of the battery accepts electrons that the battery is producing. The plate on the capacitor that attaches to the positive terminal of the battery loses electrons to the battery. Once it's charged, the capacitor has the same voltage as the battery (1.5 volts on the battery means 1.5 volts on the capacitor). see what happens Units of Capacitance The amount of stored electricity on the plates is the ‘charge’, or actually the electric field between theses plates, and is proportional to the applied voltage and capacitor's 'capacitance'. The Formula to calculate the amount of capacitance is Q = C * V where: Q = Charge in Coulombs [A coulomb is 6.25e18 (or 6.25 billion billion) electrons.] C = Capacitance in Farads V = Voltage in Volts The standard units of Capacitance, – farad: F, microfarad: µF (1 µF = 10-6 F), – nanofarad: nF (1 nF = 10-9 F) , – picofarad: pF (1 pF = 10-12 F) Capacitor Codes If a capacitor is marked like this 105, it just means 10+5zeros = 10 + 00000 = 1.000.000pF = 1000 nF = 1 µF. The letters added to the value is the tolerance and in some cases a second letter is the temperature coefficient mostly only used in military applications 474J printed on it it means: 47+4zeros = 470000 = 470.000pF, J=5% tolerance. (470.000pF = 470nF = 0.47µF) Capacitor Type Examples Electrolytic - Made of electrolyte, basically conductive salt in solvent. Most common type of polarized capacitor. Cheap, readily available, good for storage of charge (energy). Not very accurate, marginal electrical properties, leakage etc. They WILL explode if the rated working voltage is exceeded or polarity is reversed, so be careful! The rule-of-thumb for this type of capacitor is to choose one which is twice the supply voltage. e.g. if your supply power is 12 volt you would choose a 24volt (25V) type. Capacitor Type Examples Ceramic - Internally these capacitors are not constructed as a coil, so they are well suited for use in high frequency applications. They are not polar so there is no positive or negative side. They are shaped like a disk, available in very small capacitance values and very small sizes. Together with the electrolytics the most widely available and used capacitor around. Comes in very small size and value, very cheap, reliable. Capacitors in Parallel Capacitance added together opposite the resistors Increases the total storage capacity of an electric charge Voltage is same for each capacitor in parallel Be careful not to exceed the specified voltage on the capacitors when combining them all with different voltage ratings, or they may explode. Rule-of-thumb, always choose a capacitor which is twice the supplied input voltage. Ctotal = C1 + C2 + C3 Capacitors in Series Again,opposite of calculating resistors. In series the total capacitance is lower than the lowest single value capacitor in that circuit. 1= 1+1+…+1 Ct C1 C2 Cn Applications The difference between a capacitor and a battery is that a capacitor can dump its entire charge in a tiny fraction of a second, where a battery would take minutes to completely discharge itself. That's why the electronic flash on a camera uses a capacitor -- the battery charges up the flash's capacitor over several seconds, and then the capacitor dumps the full charge into the flash tube almost instantly. Lightening example Credits http://micro.magnet.fsu.edu/electromag/java/index.html http://electronics.howstuffworks.com/capacitor3.htm http://www.uoguelph.ca/~antoon/gadgets/caps/caps.html http://en.wikipedia.org/ http://www.iguanalabs.com/Compnets.htm http://www.electronics-tutorials.com