Basic Electronics – P-N Junction Diodes, Rectifiers & Regulators

A comprehensive set of vocabulary flashcards covering diode basics, rectifier circuits, filtering, voltage regulation, and special-purpose diodes as outlined in the ECE_1071 lecture notes.

P-N Junction Diode

A two-terminal, two-layer semiconductor device formed by joining p-type and n-type materials; used as switch, rectifier, regulator, etc.

Anode (Diode)

The terminal connected to the p-type side of a diode.

Cathode (Diode)

The terminal connected to the n-type side of a diode.

Acceptor Impurity

Trivalent dopant that creates holes and produces p-type semiconductor material.

Donor Impurity

Pentavalent dopant that donates free electrons and produces n-type semiconductor material.

Depletion Region

Region around the p-n junction devoid of free carriers; acts as a barrier to further diffusion.

Barrier Potential

Built-in potential across a p-n junction created by the space-charge region; typically ≈0.3 V (Ge) or 0.7 V (Si).

Biasing (Diode)

Application of an external voltage across a diode’s terminals.

Forward Bias

Condition where anode is positive relative to cathode, narrowing the depletion region and allowing large current flow.

Reverse Bias

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

Minority Carrier

Charge carrier present in small concentration (holes in n-type, electrons in p-type) that dominates reverse current.

Reverse Saturation Current (Io)

Small current (µA or nA) that flows under reverse bias due to thermally generated minority carriers.

Cut-in (Knee) Voltage

Forward voltage at which diode current begins to rise rapidly (≈0.3 V Ge, 0.7 V Si).

Thermal Voltage (VT)

Voltage proportional to temperature: VT = T/11600 volts; ≈25.9 mV at 300 K.

Ideality Factor (η)

Constant in diode equation; η = 1 for Ge, ≈2 for Si.

Diode Current Equation

ID = Io[exp(VD/ηVT) − 1], relating current to applied voltage.

Static (DC) Resistance (Rd)

Ratio VD/ID at a fixed operating point on a diode’s characteristic.

Dynamic (AC) Resistance (rd)

Small-signal resistance dVD/dID; approximately ηVT/(ID + Io).

Operating (Q) Point

Steady-state point on the I-V curve determined by applied dc voltages.

First-Approximation Diode Model

Replaces diode with ideal switch plus forward resistance RF and threshold Vγ; reverse resistance assumed infinite.

Second-Approximation Model

Assumes RF = 0, includes threshold Vγ, reverse resistance infinite.

Third-Approximation Model

Ideal diode: RF = 0, Vγ = 0, reverse resistance infinite.

Temperature Coefficient of Io

Reverse saturation current approximately doubles for every 10 °C rise in temperature.

Avalanche Breakdown

High-field multiplication process in lightly doped diodes causing sudden large reverse current at high voltage.

Zener Breakdown

Field-ionisation breakdown in heavily doped junctions at relatively low reverse voltages; used for voltage regulation.

Peak Inverse Voltage (PIV)

Maximum reverse voltage a diode must withstand without breakdown.

Half-Wave Rectifier (HWR)

Circuit using one diode to convert only one half-cycle of ac into pulsating dc.

Full-Wave Rectifier (FWR)

Circuit that converts both half-cycles of ac into pulsating dc; implemented using centre-tap or bridge.

Centre-Tapped FWR

Full-wave rectifier that uses a transformer with centre-tapped secondary and two diodes; PIV = 2Vm.

Bridge Rectifier

Full-wave rectifier employing four diodes in bridge; no centre tap needed; PIV = Vm per diode.

Ripple Factor (γ)

Ratio Iac/Idc or Vac/Vdc; lower values indicate smoother dc output (HWR ≈1.21, FWR ≈0.483).

Rectifier Efficiency (η)

Conversion efficiency Pdc/Pac; ≈40.6 % for HWR, ≈81.2 % for FWR.

Capacitor Filter

Filter that connects a capacitor across load to smooth rectifier output by charging to peaks and discharging through RL.

Line Regulation

Ability of regulator to keep Vout constant as input voltage varies, with constant load current.

Load Regulation

Ability of regulator to keep Vout constant as load current varies, with constant input voltage.

Zener Diode

Heavily doped diode designed to operate in reverse breakdown region at a specified voltage VZ.

Zener Voltage (VZ)

Specified breakdown voltage at which Zener diode maintains nearly constant voltage.

IZK (Knee Current)

Minimum current required to keep a Zener diode in breakdown region.

IZM (Maximum Zener Current)

Highest safe current a Zener diode can conduct without exceeding power rating.

PZM (Zener Power Rating)

Maximum power dissipation: PZM = VZ × IZM.

78XX Regulator

Three-terminal positive fixed-voltage IC regulator family (e.g., 7805 outputs +5 V).

79XX Regulator

Three-terminal negative fixed-voltage IC regulator family (e.g., 7905 outputs −5 V).

LM317

Adjustable three-terminal positive regulator; output range 1.2 V–37 V, >1.5 A.

Light-Emitting Diode (LED)

GaAs-based diode that emits light when forward biased due to electron-hole recombination.

Seven-Segment Display

Preset LED array of seven segments used to display decimal digits.

Photodiode

P-N junction diode operated in reverse bias; produces current proportional to incident light intensity.

Average (DC) Value

Mean value of a periodic waveform over one full cycle.

Root-Mean-Square (RMS) Value

Effective value of an ac waveform: Vrms = √(1/T ∫ v² dt).

Rectified Output Frequency (FWR)

For full-wave rectifier, output frequency f0 = 2 × input frequency fi.

Cut-in Voltage vs Temperature

Forward threshold voltage decreases as temperature increases.

Reverse Current Doubling Rule

Reverse saturation current doubles for every 10 °C increase in temperature.

Bridge Rectifier Advantage

Requires no centre-tap transformer and has PIV = Vm per diode.

Bridge Rectifier Disadvantage

Uses four diodes, causing two diode drops in the conduction path.

HWR PIV Requirement

Diode must withstand a reverse voltage greater than Vm.

Centre-Tapped FWR PIV

Each diode must withstand PIV > 2Vm.

Capacitor Filter Ripple (HWR)

Ripple factor ≈ 1/(2√3 f RL C); larger RL C product yields lower ripple.

Capacitor Filter Ripple (FWR)

Ripple factor ≈ 1/(4√3 f RL C); smoother than HWR for same C.

Dynamic Resistance in Reverse

Very high because slope of reverse I-V characteristic is nearly zero.

Minority Carrier Lifetime

Average time a minority carrier exists before recombination; affects reverse current.

Space-Charge Region

Another term for depletion region containing fixed ionised donor and acceptor atoms.

Barrier Potential Symbols

Often denoted Vγ (cut-in voltage) or φB (built-in potential).