Semiconductors: Transistors, Thyristors, and TRIACs 352

AC

Alternating current. Electricity that reverses direction at regularly recurring intervals of time. In the United States, AC cycles 60 times per second, or at 60 Hertz (Hz).

all-electrical

A circuit or device without any moving, mechanical parts. All-electrical devices like semiconductor switches are smaller, faster, and more reliable than electromechanical devices.

alternating current

AC. Electricity that reverses direction at regularly recurring intervals of time. In the United States, alternating current cycles 60 times per second, or at 60 Hertz (Hz).

amplification

The process of increasing the size or strength of a signal without changing its content. Amplification by semiconductors can increase signals tens of thousands of times so that they can be transmitted or used by another device.

amplitude

The maximum strength or height of a waveform. Amplitude can be changed during the signal processing operations of amplification or modulation.

analog circuits

An electrical system that processes signals that are continuous and vary over time, such as temperature, sound, and electromagnetic radiation. Analog circuits often use BJTs.

anode

The positively charged electrode of a thyristor in forward conduction mode. Current enters the thyristor at the anode.

base

B. The central terminal of some transistors, especially BJTs, and thyristors. The base controls current flow between the emitter and collector or between the anode and cathode.

bidirectional

Able to conduct current in both the forward and reverse directions. Bidirectional devices like TRIACs can conduct current throughout all parts of the AC cycle.

binary data

Information represented by two digits, 0 and 1, that are arranged in a series of columns. Binary data allows computers to store and use information using switches that can be turned on or off.

bipolar junction transistors

BJTs. A current-controlled transistor that has a three-layer sandwich and terminals called the emitter (E), base (B), and collector (C). Bipolar junction transistors amplify current and are commonly used in analog signal processing.

body

B. The underlying semiconductor material in some transistors, especially FETs and MOSFETs, that is typically connected to the source and drain. The body, or substrate, affects how current flows between the source and drain but is not usually considered a terminal itself.

cathode

The negatively charged electrode of a thyristor in forward conduction mode. Current leaves the thyristor at the cathode.

channel

The conductive path that current follows through the base in a voltage-controlled transistor like a FET or MOSFET, which allows it to flow from the source to the drain. The channel describes the flow of current through the transistor when there is sufficient gate voltage to turn the device on.

charge carrier

A particle with a positive or negative electric charge. Holes are considered positive charge carriers, while electrons are considered negative charge carriers.

collector

C. The terminal at which current exits some semiconductor devices, especially BJTs. Current flows to the collector from the emitter.

control input

The type of signal, usually voltage or current, that a transistor must receive to pass current. A transistor's control input is determined by its geometry and doping.

current

The flow of electricity. Current strength is called amperage and is measured in amperes (A).

current-controlled transistors

A transistor that uses amperage as a control input, which triggers the device and determines output amperage. Current-controlled transistors include BJTs and UJTs.

Darlington transistors

A specialty transistor that can achieve very high current gain and that has emitter (E), base (B), and collector (C) terminals. Darlington transistors are considered to be current controlled.

DC

DC. Electricity that flows in one continuous direction. DC does not reverse the direction of flow.

demodulation

The process of reversing changes made to the properties of a signal wave. Demodulation is usually required so modulated signals can be interpreted once they have been received.

digital circuits

An electrical system that processes discrete digital signals, typically in binary, to transmit data. Digital circuits are required by virtually all modern electronic devices for processing logic and data.

dimmer circuits

A circuit that adjusts the brightness of light by varying the amount of electrical power delivered to it. Dimmer circuits typically use components like less-sensitive TRIACs to control AC voltage and minimize flickering.

direct current

DC. Electricity that flows in one continuous direction. Direct current does not reverse the direction of flow.

doped

Enriched with trace amounts of a rare-earth element. Doped semiconductor materials have improved thermoelectric, resistive, and conductive properties compared to undoped materials.

drain

D. The terminal at which current exits some semiconductor devices, including FETs and MOSFETs. Current flows to the drain from the source.

electric furnaces

An industrial oven that uses electricity to heat and melt materials like glass or metal. Electric furnaces are high-voltage AC systems.

electrodes

A conductive component on an electrical device to which other components can be attached. Electrodes are thyristor terminals that have a negative or a positive charge.

electrons

A negatively charged particle that is free to move through semiconductor material and form new bonds with other electrons. Electrons are negative charge carriers that play integral roles in conducting current.

emitter

E. The terminal at which current enters some semiconductor devices, especially BJTs. Current flows from the emitter to the collector.

Field-effect transistors

FETs. A voltage-controlled transistor that typically has one main region of semiconductor material called the body; terminals called the source (S), gate (G), and drain (D); and a channel that regulates current between the source and drain. Field-effect transistors are primarily used in digital circuits because of their rapid switching speed and low power use.

filtering

The process of removing unwanted noise, or interference, from a signal wave. Filtering is especially common for improving telecommunication signals.

forward blocking

The thyristor operating mode during which the anode is positive and the cathode is negative, but no current flows. Forward blocking does not pass any current through the thyristor because the gate has not been triggered.

forward conduction

The thyristor operating mode during which the anode is positive, the cathode is negative, and current flows between them. Forward conduction occurs when the device has been triggered by both a positive gate current and a positive voltage at the anode.

forward-bias

A condition in which current flows from the anode to the cathode of a device. Forward-bias thyristors have a positive anode and a negative cathode.

frequency

The number of complete cycles a waveform completes per second, measured in hertz (Hz). Frequency can be changed during modulation.

gain

The ratio of an input signal to the output signal. Gain indicates how much a device has amplified the input.

gate

G. The central terminal of some semiconductor devices, including FETs, MOSFETs, and thyristors. The gate controls current flow between the emitter and collector or between the source and drain.

gate current

The amperage applied to the gate terminal of a device like a thyristor that determines whether or not the device triggers. For a device to turn on, the gate current must be strong enough and applied in the correct direction.

gate voltage

The voltage applied to the gate terminal of a device like a FET or MOSFET that determines whether or not the device triggers. For a device to turn on, the gate voltage must be strong enough and applied in the correct direction.

geometry

The physical dimensions and structure of a semiconductor device, especially the arrangement and thickness of doped layers. A transistor's geometry affects its performance, determines its control input, and alters how current flows through the device.

half-cycle

The positive or the negative portion of the AC waveform. In AC circuits, thyristors reverse polarity every half-cycle.

heterojunction bipolar transistors

HBTs. A specialty voltage-controlled transistor with terminals called the collector (C), base (B), and emitter (E) and that uses different semiconductor materials for the emitter and base to improve speed and efficiency. Heterojunction bipolar transistors are often used in high-frequency and microwave circuits.

high-speed thyristors

A specialty thyristor that is designed for rapid switching applications. High-speed thyristors are used for applications that require pulsed power or high frequency.

high-temperature TRIACs

A specialty TRIAC designed to operate at high temperatures. High-temperature TRIACs can withstand temperatures up to 392°F (200°C), while standard TRIACs typically fail around 257°F (125°C).

holes

An extra opening in a semiconductor material that free electrons can move into and form new bonds. Holes are positive charge carriers that play an integral role in conducting current.

input

Energy received by a device. Input signals can include electricity, heat, light, sound, pressure, and many other signals.

insulated-gate bipolar transistors

IGBTs. A specialty voltage-controlled transistor with terminals called the collector (C), base (B), and emitter (E) and that combines the high input impedance of MOSFETs with a BJT's ability to handle high currents. Insulated-gate bipolar transistors are used in power electronics, especially motor drives.

insulates

Protects from unwanted current flow. In MOSFETs, metal oxide insulates the channel.

junction FETs

JFETs. A specialty FET that has a P-N junction for its gate and is usually reverse-biased. Junction FETs are used for high-impedance applications.

junction potential

The minimum amount of voltage that is required to pass electrons through the depletion region of a semiconductor device and turn it on. Junction potential varies based on the amount of energy required to excite the electrons from the valence state to the conductive state.

latch

To remain on until current or voltage is reversed or removed. Thyristors latch when triggered, which helps maintain stable operation during switching.

light-activated SCRs

LASCRs. A specialty thyristor that is triggered by light rather than a gate current. LASCRs are used in high-voltage or optical switching applications.

logic gates

A digital circuit that performs a logical operation, such as AND, OR, NOT, and NAND, on binary inputs to produce a single binary output. Logic gates use transistors to control rapid decision-making circuits in computers and other digital electronics.

Main Terminal 1

MT1. The terminal through which current enters a TRIAC when the third or fourth quadrant is triggered. Current flows from Main Terminal 1 to Main Terminal 2 when TRIACs are triggered in their third or fourth quadrant.

Main Terminal 2

MT2. The terminal through which current enters a TRIAC when the first or second quadrant is triggered. Current flows from Main Terminal 2 to Main Terminal 1 when TRIACs are triggered in their first or second quadrant.

metal oxide

A compound that forms when oxygen bonds with metal, such as titanium, tantalum, or tungsten. A layer of metal oxide insulates the gate in MOSFETs to improve switching and current control.

metal-oxide-semiconductor FETs

MOSFETs. An FET with a gate that is insulated from the semiconductor body by a layer of metal oxide. Metal-oxide-semiconductor FETs have superior switching capabilities and are the most commonly used FETs.

microprocessors

A small, programmable computer contained on one or more integrated circuits (ICs). Microprocessors use billions of transistors to process signals.

modulation

The process of changing the properties of a signal wave so that it can carry data more effectively. Modulation operations include amplitude, frequency, and phase modulation.

motor controls

A system or device used to start, stop, or change the speed or direction of a motor. Motor controls use thyristors to regulate high-voltage power.

MT1

Main Terminal 1. The terminal through which current enters a TRIAC when the third or fourth quadrant is triggered. Current flows from MT1 to MT2 when TRIACs are triggered in their third or fourth quadrant.

MT2

Main Terminal 2. The terminal through which current enters a TRIAC when the first or second quadrant is triggered. Current flows from MT2 to MT1 when TRIACs are triggered in their first or second quadrant.

N-channel FETs

An FET with an N-type channel that carries electrons from the source to the drain. N-channel FETs typically perform better than P-channel FETs.

noise

Unwanted interference. Noise is removed from a signal wave during filtering.

NPN

A semiconductor device that consists of a layer of P-type material sandwiched between two layers of N-type material. NPN transistors require a positive input voltage to turn on and pass electrons.

N-type

A semiconductor material that causes current to flow by creating free electrons that are easily excited into movement. N-type semiconductors are considered electron donors and are commonly doped with arsenic, bismuth, phosphorus, and antimony.

operating modes

One of three states a thyristor can be in, depending on the voltage and current applied to the device. Operating modes for standard SCR thyristors include forward blocking, forward conduction, and reverse blocking.

output

Energy released by a device. Output energy is often electrical signals.

P-channel FETs

An FET with a P-type channel that carries holes from the source to the drain. P-channel FETs typically conduct negative gate voltage.

phase

The relative position of a point in one waveform compared to another. Phase can be changed during modulation.

phase-control thyristors

A specialty thyristor that modulates an AC waveform to control power output. Phase-control thyristors are often used in dimmers, heating systems, and motor controls.

P-N junction diode

An electrical device that combines a P-type semiconductor and an N-type semiconductor to control the direction of current flow. The P-N junction diode only allows electricity to flow from the N-type semiconductor to the P-type semiconductor.

PNP

A semiconductor device that consists of a layer of N-type material sandwiched between two layers of P-type material. PNP transistors require a negative input voltage to turn on and pass holes.

PNPN

A semiconductor device that consists of four alternating layers of P- and N-type material. PNPN sandwiches are usually found in standard thyristors.

polarity

The difference in charge between the anode and cathode of the thyristor. In forward polarity, the anode is positive relative to the cathode.

power

The rate at which a device converts electrical energy into another form, such as heat or light. Power is the product of amperage and voltage and is measured in watts.

power regulation

The process of controlling and stabilizing electrical power to ensure consistent voltage and current levels for devices or systems. Power regulation often uses transistors, thyristors, or TRIACs to protect components, improve efficiency, and maintain reliable operation under varying loads.

P-type

A semiconductor material that causes current to flow by creating holes that enable the movement of valence electrons. P-type semiconductors are considered electron acceptors and are commonly doped with gallium, boron, and indium.

pulse

A brief burst of current. A pulse of positive current at the gate is required to trigger a thyristor.

Quadrant 1

Q1. The region in which a TRIAC triggers when the gate current and the voltage at MT2 are both positive. Triggering in Quadrant 1 occurs during the first half of the positive AC wave half-cycle and allows current to flow from MT2 to MT1.

Quadrant 2

Q2. The region in which a TRIAC triggers when the gate current is positive and the voltage at MT2 is negative. Triggering in Quadrant 2 occurs during the second half of the positive AC wave half-cycle and allows current to flow from MT2 to MT1.

Quadrant 3

Q3. The region in which a TRIAC triggers when the gate current and the voltage at MT2 are both negative. Triggering in Quadrant 3 occurs during the first half of the negative AC wave half-cycle and allows current to flow from MT1 to MT2.

Quadrant 4

Q4. The region in which a TRIAC triggers when the gate current is negative and the voltage at MT2 is positive. Triggering in Quadrant 3 occurs during the second half of the negative AC wave half-cycle and allows current to flow from MT1 to MT2.

quadrants

One of four possible regions that determine how or if a device will trigger. Having quadrants allows TRIACs to trigger during all parts of the AC wave cycle.

ratio

A comparison showing how two values relate to one another. A ratio is often expressed as a fraction, as a decimal, or with a colon.

RCTs

Reverse-conducting thyristors. A specialty thyristor that includes an integrated diode so that it can conduct in both the forward and reverse directions. RCTs are used in some AC applications that require both switching and rectification.

rectification

The process of converting alternating current to direct current for use in an electrical circuit. Rectification is often necessary to convert electricity supplied by the utility into power that devices can use.

resistance

A material's tendency to oppose the flow of current. The resistance of many semiconductor devices decreases as their temperature increases.

reverse bias

A condition in which current flows from the cathode to the anode of a device. Reverse bias is uncommon in thyristors.

reverse blocking

The thyristor operating mode during which the anode is negative, the cathode is positive, and no current flows. Reverse blocking prevents the flow of current from cathode to anode in forward-biased devices.

reverse-conducting thyristors

RCTs. A specialty thyristor that includes an integrated diode so that it can conduct in both the forward and reverse directions. Reverse-conducting thyristors are used in some AC applications that require both switching and rectification.

sandwich

The layered structure of a semiconductor device formed by stacking semiconductor materials with alternating charges. A semiconductor sandwich alternates between P- and N-type layers.

SCR

SCR. The most common type of thyristor that is composed of a PNPN sandwich; has terminals called the anode, cathode, and gate; and is used in both AC and DC applications. Silicon-controlled rectifiers conduct in the forward direction.

semiconductor switch

An all-electrical control device that can make or break a circuit and is composed of semiconductor materials. Semiconductor switches include diodes, thyristors, transistors, and TRIACs.

semiconductors

An all-electrical component made from semiconductor materials. Semiconductor devices such as diodes, transistors, thyristors, and TRIACs are small, fast, reliable components.

sensitive gate TRIACs

A specialty TRIAC that is designed to trigger at very low gate currents. Sensitive gate TRIACs are best for low-power control systems.

signal processing

The analysis, synthesis, or altering of signals, such as sound waves and electrical current. Signal processing operations include amplification, rectification, modulation, and filtering.

signals

Energy that varies over time and is used to carry information. Signals include changes in electrical energy, heat, light, sound, pressure, magnetic fields, and other stimuli.

silicon-controlled rectifier

SCR. The most common type of thyristor that is composed of a PNPN sandwich; has terminals called the anode, cathode, and gate; and is used in both AC and DC applications. Silicon-controlled rectifiers conduct in the forward direction.

snubberless TRIACs

A specialty TRIAC that does not require an external snubber circuit to operate. Snubberless TRIACs are best for applications that experience large spikes in voltage.

source

S. The terminal at which current enters some semiconductor devices, including FETs and MOSFETs. Current flows from the source to the drain.

switching

Turning the flow of electricity in a circuit on and off. Switching multiple connected circuits on and off can be accomplished with an optocoupler.

terminals

A conductive component on an electrical device to which other components can be attached. Terminals generally have a negative or a positive charge.

thyristors

A complex semiconductor switch that has a four-layer sandwich and four terminals called the gate, base, anode, and cathode. Thyristors are primarily used for high-power and high-voltage applications and work with both AC and DC.

timing circuits

An electrical system that controls time-dependent functions like delays or pulse generation in devices like oscillators or clocks. Timing circuits often use UJTs.

transistors

A complex semiconductor switch that has three terminals that are called the emitter (E), base (B), and collector (C) or the source (S), gate (G), and drain (D) depending on its control input. Transistors are best for lower-power and lower-voltage applications, such as computing.

TRIACs

Triodes for Alternating Current. A complex semiconductor switch that has a four- or five-layer sandwich and three terminals called the gate, Main Terminal 1 (MT1), and Main Terminal 2 (MT2). TRIACs are designed specifically for AC and are primarily used for high-power and high-voltage applications.

trigger

Cause to turn on. Semiconductor switches trigger in response to current and/or voltage that meets the conditions to overcome their junction potential.

Triodes for Alternating Current

TRIACs. A complex semiconductor switch that has a four- or five-layer sandwich and three terminals called the gate, Main Terminal 1 (MT1), and Main Terminal 2 (MT2). Triodes for Alternating Current are designed specifically for AC and are primarily used for high-power and high-voltage applications.

tunnel transistors

A specialty voltage-controlled transistor with terminals called the source (S), gate (G), and drain (D) and that uses quantum tunnelling to control current between the source and drain. Tunnel transistors allow extremely low-power operations.

unidirectional

Able to conduct current in only one direction, usually the forward direction. Unidirectional devices like thyristors are best for DC applications.

unijunction transistors

UJTs. A specialty current-controlled transistor that has only one P-N junction and has three terminals called the emitter (E), Base 1 (B1), and Base 2 (B2). Unijunction transistors are primarily used for timing applications.

voltage

A measure of the electrical pressure or potential that causes current to flow in a circuit. Voltage is measured in volts (V).

voltage-controlled transistors

A transistor that uses voltage as a control input, which triggers the device and determines output current. Voltage-controlled transistors include FETs and MOSFETs.

wave

A repeating variation, disturbance, or vibration that varies over time and transfers energy over space. A wave, or waveform, is often described by properties like its amplitude, frequency, and phase.

wear

Any damage caused by friction or use. Wear is not a concern for all-electrical semiconductor devices.