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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. You may also see a bridge rectifier drawn with the actual four diodes shown. (See Diode)

Darlington Transistor - A darlington transistor is actually a transistor made up of two transistors connected in a specific fashion, as shown on the schematic. The base of one transistor is connected to the emitter 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 maximum 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.

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, diode 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 supplies, 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 demodulate 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, except 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.

Dual Polarity/Dual Color Light Emitting Diode (LED) - Light emitting diodes, or LEDs, differ from regular diodes in that when a voltage is applied, they emit light. A the dual color 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 color LED one way, it emits one color. When you connect it another way, another color is emitted. Giving the device an AC voltage causes a mixture of both colors. Dual polarity LEDs contain two LEDs of the same color connected back to back. Therefore, no matter how the device is connected in the circuit, light will always be emitted. Most likely, a dual color 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 color/dual polarity LEDs may or may not be drawn with the circle surrounding them.

or 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, diode 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 sensitive 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.

orLight Emitting Diode (LED) - 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 infra 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.

N Channel Junction Field Effect Transistor (N-JFET) - A N Channel Junction Field Effect Transistor (or N-JFET) is just like a regular transistor except that it has two base layers on the chip. This allows a large resistance 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.

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 separated 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.

N-Channel Uni-junction Transistor (N-UJT) - A N-Channel Uni-junction 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 emitter, base 1 and base 2. The emitter 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 emitter, a very small current flows from base 1 to base 2. When the voltage applied to the emitter reaches a certain point (the threshold), a much larger current flows from base 1 to the emitter. 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, diode 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.

NPN Phototransistor With Base Connection - Phototransistors are different than regular transistors in the fact that the base is either 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 - Phototransistors are different than regular transistors in the fact that the base is either 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.

or 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 maximum 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.

P Channel Junction Field Effect Transistor (P-JFET) - A P Channel Junction Field Effect Transistor (or P-JFET) is just like a regular transistor except that it has two base layers on the chip. This allows a large resistance 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.

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 separated 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."

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 emitter, base 1 and base 2. The emitter 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 emitter, a very small current flows from base 2 to base 1. When the voltage applied to the emittrr reaches a certain point (the threshold), a much larger current flows from the emitter 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, diode 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.

or 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.

Photo-resistor - Resistors are one of the most common electronic components. 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. You will often see the resistance of resistors written with K (kilo ohms) 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 (mega ohms). This simply means million. Photo-resistors do not have a specific fixed resistance. Their resistance is based on the amount of light that falls on them. Photo-resistors 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 mega ohms). When the resistor is illuminated, the resistance falls dramatically, often to several hundred ohms. Photo-resistors may also be called CDS cells.

orPNP 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 maximum 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.

orSilicon 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, diode 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.

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 the schematic represent 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.

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, diode 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.

orTRIAC - 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, diode 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 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.

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 separated by an insulator, or dielectric. Depending on how the capacitor is built, the dielectric can be made of paper, plastic, mica, ceramic, glass, a vacuum 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.

Zener Diode - 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.