Semiconductors 1

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

Diode: 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. There are three types of diodes (not counting photonic diode types): silicon, germanium and zener. Silicon diodes are the most common type. They are made of a small chip of silicon and are mostly used as rectifiers in power supplys, absorb voltage spikes, perform logic, etc. Germanium diodes are made of a small chip of germanium, usually in a glass case. These handle much less power than silicon diodes and are usually used to demoduate radio signals, for temperature compensation in a circuit or to perform simple logic. The symbols for these types of diodes are exactly the same on the schematic, execpt that germanium diodes will have a little "Ge" next to the symbol (Ge is the elemental symbol for germanium). 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. Diodes are rated according to the voltage and current they can handle. Diodes may or may not be drawn with the circle surrounding them.
Zener Diode: 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. Zener diodes have a slightly different characteristic however. Zener diodes have a specific reverse breakdown voltage. In other words, one the reverse voltage on the diode reaches a point the diode will start to conduct. This allows the diode to function as a voltage sensitive switch. Because of this, zener diodes are usually used in voltage regulators, voltage references, etc. 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. Zener diodes may or may not be drawn with the circle surrounding them.
Silicon Controlled Rectifier (SCR): A silicon controlled rectifier, or SCR, is like a switchable diode. 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. A SCR adds one more connection: the gate. The SCR does not conduct until a small current is applied to the gate. This is why it is called a switchable diode. Putting a small current on the gate allows a much larger current to flow from anode to cathode. Note that when switching a DC voltage the SCR stays on even when current is removed from the gate, and continues to flow until current is removed from the anode. This is not so with AC applications. SCRs may or may not be drawn with the circle surrounding them.
TRIAC: A TRIAC is like two SCRs connected back to back. Applying a small current to it's gate connection allows a much larger current to flow between it's two main terminals. These terminals are just referred to as main terminals because they are exactly the same. It makes no difference which way the main connections go on a TRIAC. For a little background info, a silicon controlled rectifier, or SCR, is like a switchable diode. 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. A SCR adds one more connection: the gate. The SCR does not conduct until a small current is applied to the gate. This is why it is called a switchable diode. Putting a small current on the gate allows a much larger current to flow from anode to cathode. Note that when switching a DC voltage the SCR stays on even when current is removed from the gate, and continues to flow until current is removed from the anode. This is not so with AC applications. TRIACs may or may not be drawn with the circle surrounding them.
Trigger Diode: 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. A trigger diode is simply a device that allows an AC or DC voltage to flow when the voltage between it's two connections exceeds a certain amount. Note that there are no real anode and cathode connections on this device, as both connections are exactly the same.
Bridge Rectifier: A bridge rectifier is a small circuit made up of four diodes. They are connected in such a way that they take an incoming AC voltage and rectify the whole wave into a DC voltage. This is called a full wave rectifier. 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. Bridge rectifiers are used in power supplies to convert an incoming AC votage into a DC voltage. You may also see a bridge rectifier drawn with the actual four diodes shown.
NPN Transistor: Transistors are basically semiconductor switches or amplifiers. In the case of a NPN 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.
PNP Transistor: Transistors are basically semiconductor switches or amplifiers. In the case of a PNP transistor, a small current applied to the base allows a much larger current to flow from the emitter to the collector. 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 towards the straight line. Of course, in schematics the transistor may be drawn upside down. Transistors may or may not be drawn with the circle surrounding them. Some schematics may also label the base, collector and emitter.
N Channel Junction Field Effect Transistor (N-JFET): A N Channel Junction Field Effect Transistor (or N-JFET) is just like a regular transistor execpt that it has two base layers on the chip. This allows a large reisistance on the base, or gate. The N-JFET doesn't have a emitter, collector and base. Instead, it has a gate, drain and source. The current flows from the source to the drain. In the schematic, the gate is the line with the arrow on it. The source is usually the bottom lead and the drain is usually the top. Note that on some schematics this may be different. If that is the case, it is usually labeled. For a little background, transistors are basically semiconductor switches or amplifiers. Of course, in schematics the N-JFET may be drawn upside down. N-JFETs may or may not be drawn with the circle surrounding them.
P Channel Junction Field Effect Transistor (P-JFET): A P Channel Junction Field Effect Transistor (or P-JFET) is just like a regular transistor execpt that it has two base layers on the chip. This allows a large reisistance on the base, or gate. The P-JFET doesn't have a emitter, collector and base. Instead, it has a gate, drain and source. The current flows from the drain to the source. In the schematic, the gate is the line with the arrow on it. The source is usually the bottom lead and the drain is usually the top. Note that on some schematics this may be different. If that is the case, it is usually labeled. For a little background, transistors are basically semiconductor switches or amplifiers. Of course, in schematics the P-JFET may be drawn upside down. P-JFETs may or may not be drawn with the circle surrounding them.
N Channel Metal Oxide Semiconductor Field Effect Transistor (N-MOSFET): A N Channel Metal Oxide Semiconductor Field Effect Transistor (N-MOSFET) is a field effect transistor (transistors are basically semiconductor switches or amplifiers) in which the gate has no electrical contact with the drain and the source. They are seperated by a layer of silicon dioxide which functions as an insulator. This allows extremely high gate resistances. In fact, the input resistance of a MOSFET is the highest of any transistor. In the case of a N-MOSFET, a very small amount of current is applied to the gate causes current to flow from the source to the drain. In the schematic, the gate is the line that looks like a slightly rotated "L". The source is the lead attached to the arrow that points towards the gate. The drain is the lead left over. Of course, in schematics the N-MOSFET may be drawn upside down. N-MOSFETs may or may not be drawn with the circle surrounding them.
P Channel Metal Oxide Semiconductor Field Effect Transistor (N-MOSFET): A P Channel Metal Oxide Semiconductor Field Effect Transistor (N-MOSFET) is a field effect transistor (transistors are basically semiconductor switches or amplifiers) in which the gate has no electrical contact with the drain and the source. They are seperated by a layer of silicon dioxide which functions as an insulator. This allows extremely high gate resistances. In fact, the input resistance of a MOSFET is the highest of any transistor. In the case of a P-MOSFET, a very small amount of current is applied to the gate causes current to flow from the drain to the source. In the schematic, the gate is the line that looks like a slightly rotated "L". The source is the lead attached to the arrow that points away from the gate. The drain is the lead left over. Of course, in schematics the P-MOSFET may be drawn upside down. P-MOSFETs may or may not be drawn with the circle surrounding them.
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. This light can be red (most common), green, yellow, orange, blue (not very common), or infa red. LEDs are used as indicators, transmitters, etc. Most likely, a 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. LEDs may or may not be drawn with the circle surrounding them.
NPN Phototransistor With Base Connection: Transistors are basically semiconductor switches or amplifiers. In the case of a NPN 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. Phototransistors are different in the fact that the base is eithe replaced or replicated by a large exposed base area on the actual chip. Then this area is exposed to light, the transistor will switch or amplify, depending on how much light is present. Note that in this case there is also a electrical base connection. This acts like any other base and will also effect the current flow through the transistor. Phototransistors are most sensitive to IR light, but will also respond to regular light as well. They are used in IR receivers, light sensors, etc. 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. The light sensitivity of the device is represented by the arrows pointing down at it. Phototransistors may or may not be drawn with the circle surrounding them. Some schematics may also label the base, collector and emitter.
NPN Phototransistor Without Base Connection: Transistors are basically semiconductor switches or amplifiers. In the case of a NPN 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. Phototransistors are different in the fact that the base is eithe replaced or replicated by a large exposed base area on the actual chip. Then this area is exposed to light, the transistor will switch or amplify, depending on how much light is present. In this case, there is no electrical base connection. Phototransistors are most sensitive to IR light, but will also respond to regular light as well. They are used in IR receivers, light sensors, etc. The three connections are represented in the schematic as follows. 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. The light sensitivity of the device is represented by the arrows pointing down at it. Phototransistors may or may not be drawn with the circle surrounding them. Some schematics may also label the collector and emitter.
Solar Cell: A Solar Cell is a PN junction photodiode with a large light sensitive area. Light striking the cell causes electrons to flow. Several solar cells may be connected in series or parallel to form a solar panel. The arrows pointing at the cell on teh schematic represend light. Photodiodes are diodes that generate electricity when illuminated. 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.
Light Activated Silicon Controlled Rectifier (LASCR): A silicon controlled rectifier, or SCR, is like a switchable diode. 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. A SCR adds one more connection: the gate. The SCR does not conduct until a small current is applied to the gate. This is why it is called a switchable diode. Putting a small current on the gate allows a much larger current to flow from anode to cathode. The LASCR differs slightly in that it has a large light senitive area. The LASCR can eithe be switched on by using the gate, or by illuminating the device. Note that when switching a DC voltage the LASCR stays on even when current is removed from the gate, and continues to flow until current is removed from the anode. This is not so with AC applications. LASCRs may or may not be drawn with the circle surrounding them. The arrows pointing at the LASCR represent light.
Photoresistor: Resistors are one of the most common electronic componens. A resistor is a device that limits, or resists current. The current limiting ability, or resistance is measured in ohms, represented by the Greek symbol Omega (W [if you see a "W" here instead of the Omega, then you don't have the necessary fonts installed]). You will often see the resistance of resistors written with K (kilohms) after the number value. This means that there are that many thousands of ohms. For example, 1K is 1000 ohm, 2K is 2000 ohm, 3.3K is 3300 ohm, etc. You may also see the suffix M (megohms). This simply means million. Photoresistors do not have a specific fixed resistance. Their resistance is based on the amount of light that falls on them. Photoresistors are basically a chunk of silicon crystal with a lead on each end that is exposed to the light. When there is no light, the resistance is very high (often in the megaohms). When the resistor is illuminated, the resistance falls dramatically, often to several hundered ohms. Photoresistors may also be called CDS cells.
Photodiode: Photodiodes are PN junction diodes that generate electricity when illuminated. A diode is a component that only allows electricity to flow one way. Photodiodes 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 when the device is illuminated. Photodiodes may or may not be drawn with a circle surrounding them.

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