Diodes - Diodes Diodes Semiconductors Semiconductors Can...

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Unformatted text preview: Diodes Diodes Semiconductors Semiconductors Can act like a conductor or an insulator Most semiconductor chips and transistors are created with silicon. Silicon Silicon Silicon is a very common element Example: it is the main element in sand and quartz. Carbon, silicon and germanium have a unique property in their electron structure ­­ each has four electrons in its outer orbital. Forms nice crystals. The four electrons form perfect covalent bonds with four neighboring atoms, creating a lattice. In silicon, the crystalline form is a silvery, metallic­looking substance. In a silicon lattice, all silicon atoms bond perfectly to four neighbors, leaving no free electrons to conduct electric current. This makes a silicon crystal an insulator rather than a conductor. Doping Doping You can change the behavior of silicon and turn it into a conductor by doping it. In doping, you mix a small amount of an impurity into the silicon crystal. There are two types of impurities: N­type P­type N­type Doping N­type Doping Phosphorous is added to the silicon in small quantities. It has five outer electrons, so it’s out of place when it gets into the silicon lattice. Fifth electron has nothing to bond to, so it's free to move around. N­type Doping N­type Doping Takes only a very small quantity of the impurity to create enough free electrons to allow an electric current to flow through the silicon. N­type silicon is a good conductor. Electrons have a negative charge, hence the name N­type. P­type Doping P­type Doping Boron is the dopant. It has only three outer electrons. When mixed into the silicon lattice, it form "holes" in the lattice where a silicon electron has nothing to bond to. The absence of an electron creates the effect of a positive charge, hence the name P­type. P­type Doping P­type Doping Holes can conduct current. A hole accepts an electron from a neighbor, moving the hole over a space. P­type silicon is a good conductor. What is a diode What is a diode A diode is the simplest possible semiconductor device A diode allows current to flow in one direction but not the other. Used for illumination These are diodes. These are diodes. Reverse Bias When you put N­type and P­type silicon together as shown in this diagram, you get a very interesting phenomenon that gives a diode its unique properties. •Combination shown in the diagram does not conduct any electricity. Forward Bias If you flip the battery around, the diode conducts electricity. The free electrons in the N­type silicon are repelled by the negative terminal of the battery. At the junction between the N­type and P­ type silicon, holes and free electrons meet. Electrons fill the holes. Current flow takes place. Diode Uses Diode Uses A device that uses batteries often contains a diode that protects the device if you insert the batteries backward. The diode simply blocks any current from leaving the battery if it is reversed ­­ this protects the sensitive electronics in the device. Anode and Cathode Anode and Cathode FANCY words for + side and – side Anode = positive Cathode = negative Identification Identification Cathode Cathode Anode Anode Diodes in a circuit Diodes in a circuit Cathode Cathode Anode Anode Wiring up a diode Wiring up a diode + ...
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This note was uploaded on 10/23/2011 for the course DESHIGN AN 1910265 taught by Professor Lewis during the Spring '11 term at Thomas Jefferson School of Law.

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