Semiconductors 2

This section describes schematic symbols for semiconductors such as transistors, diodes, etc. ICs are not included. CLICK HERE IF YOU CAME FROM A WEB SEARCH

Dual Polarity/Dual Colour Light Emitting Diode (LED): A diode is a component that only allows electricity to flow one way. It can be thought as a sort of one way street for electrons. Because of this characteristic, dioded are used to transform or rectify AC voltage into a DC voltage. Diodes have two connections, an anode and a cathode. The cathode is the end on the schematic with the point of the triangle pointing towards a line. In other words, the triangle points toward that cathode. The anode is, of course, the opposite end. Current flows from the anode to the cathode. Light emitting diodes, or LEDs, differ from regular diodes in that when a voltage is applied, they emit light. A the dual colour or dual polarity LED differs from a regular LED in that it can be connected either way in a circuit. The internal schematic looks like two regular LEDs connected back to back. When you connect a dual colour LED one way, it emmits one colour. When you connect it another way, another colour is emitted. Giving the devince an AC voltage causes a mixture of both colours. Dual polarity LEDs contain two LEDs of the same colour connected back to back. Therefore, no matter how the device is connected in the circuit, light will always be emmitted. Most likely, a dual colour or dual polarity LED will never burn out like a regular lamp will and requires many times less current. Because LEDs act like regular diodes and will form a short if connected between + and -, a current limiting resistor is used to prevent that very thing. Dual colour/dual polarity LEDs may or may not be drawn with the circle surrounding them.
Varactor: A varactor is a voltage variable capacitor. In other words, applying a varying voltage will result in a varying in capacitance. This property is taken advantage of in modern digital tuning radio and TV receivers. A capacitor is a device that stores electrons. The basic capacitor is made up of two conductors seperated by an insulator, or dielectric. Depending on how the capacitor is built, the dielectric can be made of paper, plastic, mica, ceramic, glass, a vacume or any other such non conductive material. Capacitor electron storing ability (it's capacitance) is measured in Farads. One Farad is actually a huge number of electrons (6,280,000,000,000,000,000 electrons to be exact), so we usually rate capacitors in microfarads (uF) and picofarads (pF). One uF is equal to 0.000,001F and one pF is equal to 0.000,000,000,001F.
Darlington Transistor: A darlington transistor is actually a transitor made up of two transistors connected in a specific fashon, as shown on the schematic. The base of one transistor is connected to the emittor of another transistor, thereby creating a super sensitive switch or amplifier. Transistors are basically semiconductor switches or amplifiers. In the case of an NPN darlington transistor, a small current applied to the base allows a much larger current to flow from the collector to the emitter. When the maxiimum amount of base current is applied the transistor is saturated and it functions as a switch. With smaller amounts of current applied to the base, the transistor's output changes with the amount of base current. The three connections are represented in the schematic as follows. The base is the lead connected at a 90 degree angle to the thick line. The collector is the one angled line without the arrow. The emitter is the angled line with the arrow pointing down away from the straight line. Of course, in schematics that arrow can also point up. Transistors may or may not be drawn with the circle surrounding them. Some schematics may also label the base, collector and emitter.
N-Channel Unijunction Transistor (N-UJT): A N-Channel Unijunction Transistor is not really a transistor at all. It is more like a diode with two cathode connections. It will function as a switch, but it will not amplify. UJTs have three connections: an emittor, base 1 and base 2. The emittor is the line on the schematic with the arrow. The base 1 and base 2 are the other left over connections, and will be labeled. Base 2 is generally drawn facing up. When there is no current applies to the emittor, a very small current fows from base 1 to base 2. When the voltage applied to the emittor reaches a certain point (the threshold), a much larger current flows from base 1 to the emittor. In case you don't know, a diode is a component that only allows electricity to flow one way. It can be thought as a sort of one way street for electrons. Because of this characteristic, dioded are used to transform or rectify AC voltage into a DC voltage. Diodes have two connections, an anode and a cathode. Transistors are basically semiconductor switches or amplifiers. A small current applied to the base allows a much larger current to flow from the collector to the emitter.
P-Channel Unijunction Transistor (P-UJT): A P-Channel Unijunction Transistor is not really a transistor at all. It is more like a diode with two cathode connections. It will function as a switch, but it will not amplify. UJTs have three connections: an emittor, base 1 and base 2. The emittor is the line on the schematic with the arrow. The base 1 and base 2 are the other left over connections, and will be labeled. Base 2 is generally drawn facing up. When there is no current applies to the emittor, a very small current fows from base 2 to base 1. When the voltage applied to the emittor reaches a certain point (the threshold), a much larger current flows from the emittor to base 1. In case you don't know, a diode is a component that only allows electricity to flow one way. It can be thought as a sort of one way street for electrons. Because of this characteristic, dioded are used to transform or rectify AC voltage into a DC voltage. Diodes have two connections, an anode and a cathode. Transistors are basically semiconductor switches or amplifiers. A small current applied to the base allows a much larger current to flow from the collector to the emitter.
Temperature Sensing Diode: A Temperature Sensing Diode is a diode in which the current flowing from anode to cathode varies depending on the temperature of the device. A diode is a component that only allows electricity to flow one way. It can be thought as a sort of one way street for electrons. Because of this characteristic, dioded are used to transform or rectify AC voltage into a DC voltage. Diodes have two connections, an anode and a cathode. Current flows from anode to cathode.

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