Hobbies And Interests
PN Junction Semiconductors
Most semiconductors are formed from PN junctions. These are P-type and N-type semiconductors that are joined together. P-types are positive because they have a surplus of positive charges called holes. N-types are negative, because they have a surplus of free electrons. Diodes and transistors are examples of devices that have PN junctions. Diodes allow current to flow in one direction, while transistors are mainly used to amplify or switch electrical signals.
PN junction devices react to sunlight. This light sensitivity can usually be tested with a multimeter. For example, to test a diode, place a multimeter turned on the ohmmeter setting, which is used to measure resistance. Put the diode in a semi-darkened area. Put one multimeter probe on each of the two leads, and measure the resistance value. Move the diode so that it is exposed to direct sunlight, and measure the resistance again. The value will change. The measurement may be done with different types of diodes, including an LED. LEDs are light-emitting diodes designed to emit light. They are also able to detect light, however.
Photodiodes and Solar Cells
Photodiodes are diodes that are especially designed to detect light. They have many different shapes and sizes. Their casings may be of glass or plastic, and may include lenses and filters. Smaller photodiodes have faster response times than larger ones.
Solar cells are photodiodes, but they have larger surface areas. They are especially constructed to operate in sunlight. The average cell only produces 0.5 volts, regardless of size, and so they are connected in a series in order to generate more voltage. To produce more current, they are connected in parallel, or are made larger. Solar cells are used to power homes, vehicles, and recharge batteries.
Phototransistors
Phototransistors are transistors that are created to detect light. They are sensitive enough to detect light fluctuations. They may have two or three leads, and have a base section that produces a current when it is contacted by light. They are typically used as optical switches. Some of their uses are in encoders and security systems. They are also used as receivers in remote-control systems.
Photothyristors
Thyristors are switches that are electrically controlled. They are similar to transistors, but operate more efficiently. This is because they do not have any in-between states, but are either on or off. Photothyristors are thyristors that are activated with light. They are used in medium and high-voltage systems, where they often function as triggers. For example, they are found in logical, safety, and signaling systems. The two most common types are LASCRS, also known as light-activated silicon controlled rectifiers, and light-activated triacs.
Photocells
Photocells have a resistance that changes when they are exposed to light. Their resistance can change from mega ohms to a few hundred ohms. Unlike the others, they do not have a PN junction. They are normally covered with a glass or plastic casing. The ones made from cadmium sulfide can detect visible light, while ones made from lead sulfide can detect infrared. They are used as detectors in clocks, alarm systems, and street lights.