Final Term Exam Review: Logic Circuits & Switching Theory (ECE 014)

Vocabulary flashcards covering key components and terms from the notes on SCR, Triac, DIAC, UJT, and PUT, including operating principles and terminal configurations.

DIAC

Bidirectional trigger diode that conducts in either direction once its breakover voltage is reached; used to trigger Triacs and SCRs.

Trigger voltage

Voltage required to turn on a thyristor (gate threshold); initiates conduction in devices like SCR.

Four-layer diode

Another name for the DIAC; a PNPN device that triggers in both directions.

PUT (Programmable Unijunction Transistor)

PNPN device similar to a UJT with a gate that sets the peak point; used to trigger thyristors.

UJT (Unijunction Transistor)

Transistor with a single emitter and two bases that generates a sharp triggering pulse with a negative resistance region.

SCR (Silicon Controlled Rectifier)

Unidirectional three-terminal thyristor that latches on when its gate is triggered and remains conducting until current falls below holding current.

Firing delay angle

The portion of the AC cycle after zero crossing during which an SCR remains OFF before triggering.

Holding current

Minimum current required to keep an SCR conducting after it has been triggered.

Triac

Bidirectional thyristor (three-terminal) that conducts in both directions when triggered.

Breakover voltage

Voltage at which a DIAC (or similar device) undergoes breakdown and begins conducting; typical value for a DIAC is around 32 V.

Peak point voltage (VP) of PUT

The anode voltage at which a PUT switches from off to on; determined by gate bias and supply network.

Anode

Positive terminal of a diode or thyristor through which conventional current flows into the device.

Cathode

Negative terminal of a diode or thyristor through which conventional current exits the device.

Emitter

Triggering terminal of a UJT from which charge carriers are emitted; connected to Base 1 and Base 2 in operation.

Base 1

One of the two bases of a UJT, forming the other side of the device’s triggering region.

Base 2

The second base of a UJT, completing the emitter-base structure used for triggering.