Diodes & Thyristors – Core Vocabulary

75 vocabulary flashcards summarizing essential terms, devices, parameters, and circuit functions related to diodes, rectifiers, filters, wave-shaping networks, and thyristor family devices as covered in the lecture notes.

Doping

Process of intentionally adding impurities to an intrinsic semiconductor to increase its conductivity.

Intrinsic Semiconductor

Pure semiconductor material with very few charge carriers before doping.

Pentavalent Impurity

Donor atom with five valence electrons that supplies extra electrons (e.g., P, As, Sb) to create N-type material.

Trivalent Impurity

Acceptor atom with three valence electrons that creates holes (e.g., B, In, Ga) to form P-type material.

N-Type Semiconductor

Doped material whose majority charge carriers are free electrons.

P-Type Semiconductor

Doped material whose majority charge carriers are holes.

PN Junction

Boundary where P- and N-type materials meet, forming the basic diode structure.

Depletion Layer

Region around a PN junction depleted of mobile carriers, containing fixed charges.

Barrier Potential

Built-in voltage across the depletion region that opposes further carrier diffusion (≈0.7 V Si, 0.3 V Ge).

Anode (Diode)

P-type terminal of a diode; conventional current enters here in forward bias.

Cathode (Diode)

N-type terminal of a diode; conventional current exits here in forward bias.

Forward Bias

Condition where anode is positive relative to cathode, reducing depletion width and allowing current flow.

Reverse Bias

Condition where cathode is positive relative to anode, widening depletion region and blocking current.

Reverse Leakage Current

Tiny current that flows under reverse bias due to minority carriers; higher in germanium than silicon.

Forward Voltage (VF)

Voltage required to forward-bias a diode into conduction (≈0.7 V Si, ≈1.2–3.2 V LED).

Maximum Repetitive Reverse Voltage (VRRM)

Highest reverse voltage a diode can withstand repeatedly without breakdown.

Avalanche Breakdown

Sudden increase in reverse current when VR exceeds VRRM, risking diode damage.

Temperature Effect on Diodes

Higher temperature lowers VF, raises IF and IR, and reduces breakdown voltage.

Junction Capacitance

Small capacitance (pF range) formed by the depletion region acting as a dielectric between anode and cathode.

Reverse Recovery Time (trr)

Time a diode needs to cease conduction when switching from forward to reverse bias.

Rectifier Diode

Power diode used to convert AC to DC; optimized for low forward drop and high current.

Light Emitting Diode (LED)

Diode that emits light when forward-biased; color depends on semiconductor’s bandgap.

Zener Diode

Diode designed to operate in reverse breakdown region to provide a constant voltage (VZ).

Zener Voltage (VZ)

Stable reverse voltage maintained across a Zener diode during regulation.

Zener Knee Current (IZK)

Minimum reverse current required for a Zener diode to reach its breakdown region.

Maximum Zener Current (IZM)

Highest safe reverse current in the Zener breakdown region.

Steering Diode

Diode used to route current automatically between alternate sources.

Freewheeling Diode

Diode connected across an inductive load to shunt back-EMF when the driving switch opens.

Half-Wave Rectifier

Rectifier using one diode to pass only one half-cycle of AC input.

Center-Tapped Full-Wave Rectifier

Rectifier employing two diodes and a center-tapped transformer to produce full-wave DC.

Bridge Rectifier

Four-diode configuration that provides full-wave rectification without a center-tap.

Ripple

Residual AC variation superimposed on rectified DC output.

Capacitor Filter

Filter that smooths rectifier output by charging and discharging a parallel capacitor.

RC Filter

Ripple-reduction network using a series resistor and shunt capacitor; wastes DC power across the resistor.

LC Filter

Filter combining an inductor and capacitor for low ripple with minimal DC loss but larger size/cost.

Voltage Regulator

Circuit that maintains a constant output voltage despite load or supply changes.

Clipper

Diode network that removes portions of an input waveform exceeding a reference voltage.

Positive Clipper

Circuit that clips the positive peaks of a waveform above Vref.

Negative Clipper

Circuit that clips the negative peaks of a waveform below Vref.

Clamper

Diode-capacitor circuit that shifts an entire waveform to a desired DC level.

Villard Circuit

Simple diode-capacitor clamper used in voltage multiplier stages.

Voltage Multiplier

Network of diodes and capacitors that steps up AC to higher DC voltage with low current capability.

Delon Circuit

Two-capacitor voltage doubler that uses both halves of the AC cycle.

Small Signal Diode

Low-power, high-speed diode (e.g., 1N4148) suited for RF and switching tasks.

Schottky Diode

Metal-to-semiconductor diode with majority-carrier conduction, low VF (≈0.2 V) and very fast switching.

Varactor Diode

Reverse-biased diode whose junction capacitance varies with applied voltage; used for tuning.

Voltage-Controlled Oscillator (VCO)

Oscillator whose frequency varies with a control voltage, often using a varactor in its LC tank.

Photodiode

Light-sensitive diode that conducts proportional reverse current when illuminated.

Opto-coupler

Device combining an LED and photosensor to transfer signals while providing electrical isolation.

Varistor (VDR)

Voltage-dependent resistor that clamps high-voltage transients to protect circuits.

Shockley Diode

Four-layer (PNPN) diode that switches ON sharply at forward break-over voltage and lacks a gate.

Silicon Controlled Rectifier (SCR)

Four-layer, three-terminal thyristor that conducts from anode to cathode when triggered by a gate pulse.

Gate Current (IG)

Control current applied to an SCR or TRIAC gate to initiate conduction.

Forward Break-over Voltage (VBR(F))

Anode-cathode voltage at which a thyristor switches to conduction without gate drive.

Holding Current (IH)

Minimum anode current required to keep a thyristor in the conducting state.

Latching Current (IL)

Minimum anode current that must be reached immediately after turn-on to maintain conduction when gate drive is removed.

Natural Commutation

Turning off a thyristor by the natural zero crossing of an AC source.

Forced Commutation

External circuitry that actively drives a thyristor’s current below IH to turn it off.

DIAC

Bidirectional trigger diode that conducts in either direction once its break-over voltage is reached; lacks a gate.

TRIAC

Bidirectional, three-terminal thyristor that conducts current in both directions and is triggered by gate current.

Delay Angle (Triac)

Portion of each half-cycle before a TRIAC is triggered, determining output power.

Conduction Angle

Duration within each half-cycle that a TRIAC or SCR remains ON.

Reverse Blocking Region

Operating region where a device is reverse-biased and ideally non-conducting.

Forward Blocking Region

Region where a thyristor is forward-biased but not yet triggered into conduction.

Reverse Breakdown Voltage (VBR(R))

Voltage at which a diode or thyristor avalanches under reverse bias.

Reverse Avalanche Region

Post-breakdown region where large reverse current flows; can damage the device if uncontrolled.

Junction Temperature

Internal temperature of a semiconductor device; excessive values degrade performance and reliability.

Minority Carriers

Charge carriers present in smaller concentration in a semiconductor region (holes in N-type, electrons in P-type).

Majority Carriers

Dominant charge carriers in a semiconductor region (electrons in N-type, holes in P-type).

Turn-On Voltage (Schottky)

Low forward voltage (≈0.15–0.45 V) characteristic of Schottky diodes.

Reverse Current (IR)

Current that flows under specified reverse bias; used to characterize leakage.

Peak Inverse Voltage (PIV)

Maximum reverse voltage a rectifier diode must withstand in a rectifier circuit.

Derating

Reducing a device’s rated limits (current, voltage, power) to improve reliability under adverse conditions.

Resonant Frequency (LC)

Frequency at which an LC circuit naturally oscillates, f = 1∕(2π√LC).

Full-Wave Output Frequency

Frequency of pulsations from a full-wave rectifier; twice the AC input frequency.