What is Power Electronics?
Comprehensive introduction to power electronics fundamentals and applications.
- Basic principles and concepts
- Applications in modern technology
- Key components and systems
Fundamentals
Electrical quantities, circuit basics, AC/DC, waveforms and signals.
T01
Electrical Quantities
9
What is Voltage?
Understanding voltage, its measurement, and role in electrical circuits.
- Definition and units
- Measurement techniques
- AC vs DC voltage
What is Current?
Explore electric current, its types, and measurement in electrical systems.
- Current flow principles
- Types of current
- Current measurement
What is Electric Charge?
Understand electric charge, Coulomb's law, and how charge underpins voltage and current.
- Charge and the coulomb
- Coulomb's law
- Charge in circuits
What is Electric Power?
Explore electric power, watts, the P = VI relationship, AC/DC power and power factor.
- Power and the watt
- P = VI relationship
- AC/DC power & power factor
What is Electrical Energy?
Learn electrical energy, the joule and kilowatt-hour, and how E = P × t drives your electricity bill.
- Energy, the joule & kWh
- E = P × t relationship
- Energy cost & billing
What is Resistance?
Understand electrical resistance, the ohm, and what controls how strongly a material opposes current.
- Resistance & the ohm
- Factors affecting resistance
- Series & parallel resistance
What is Conductance?
Explore conductance (G = 1/R), the siemens, and how easily a material allows current to flow.
- Conductance & the siemens
- G = 1/R relationship
- Use in parallel circuits
What is Frequency?
Understand frequency, the hertz, period (T = 1/f), and its role in AC systems and signals.
- Frequency & the hertz
- Period, T = 1/f
- AC mains & signal frequency
T02
Circuit Basics
9
Series Circuits
Components on one single path — the same current flows through every part, the supply voltage divides across them (V = V1+V2+V3), and resistances add up. Covers KVL, Ohm's law, the voltage divider & series vs parallel.
- Same current: I = I1 = I2 = I3
- V = V1 + V2 + V3 (KVL)
- Rtotal = R1 + R2 + R3
Parallel Circuits
Components on separate branches across the same two nodes — the same voltage across each (V = V1 = V2), the current divides (I = I1+I2+I3), and total resistance is less than the smallest. Covers KCL, the current divider & why homes are wired this way.
- Same voltage: V = V1 = V2
- I = I1 + I2 + I3 (KCL)
- 1/Rtotal = 1/R1 + 1/R2
Series-Parallel Circuits
Combined networks that mix series and parallel connections. Learn to spot the groups and solve them by step-by-step reduction (combine parallel first, then series), with worked examples, ladder networks and the loaded voltage divider.
- Reduce: parallel first, then series
- Equivalent resistance & back-solve
- Ladder networks & loaded dividers
Open & Short Circuits
The two opposite circuit faults — an open circuit is a break (infinite R, no current), a short circuit is a zero-Ω bypass (huge current). Difference, causes, dangers & protection.
- Open = break, ∞ R, I = 0
- Short = 0Ω path, I very large
- Causes, fuses/MCBs & testing
Electric Field
The invisible region of force around every charge. Learn the definition E = F/q, field lines and direction, the dipole, point-charge strength E = kQ/r² and the uniform field between capacitor plates E = V/d.
- E = F/q · unit N/C = V/m
- Field lines: + out, − in; the dipole
- E = kQ/r² & uniform field E = V/d
Magnetic Field
The region around a magnet or current where a magnetic force acts — field lines, the right-hand rule, flux density B = Φ/A, force F = BIL and the B–H curve.
- Field lines & right-hand rule
- Flux density B = Φ/A (tesla)
- Force F = BIL; solenoids & B–H
Electromotive Force (EMF)
The driving energy a source gives per unit charge — EMF ε = W/Q, why it isn't really a force, EMF vs terminal voltage with internal resistance (V = ε − Ir), sources of EMF and cells in series & parallel.
- EMF ε = W/Q, unit volt
- Terminal voltage V = ε − Ir & internal resistance
- Sources of EMF & cell combinations
Potential Difference
The difference in electric potential between two points — the energy per charge (V = W/Q) that drives current. Covers the volt, electric potential & reference, PD vs EMF and terminal voltage (V = ε − Ir), and measuring PD with a voltmeter.
- V = W/Q (1 V = 1 J/C)
- PD vs EMF: V = ε − Ir
- Voltmeter measures across (parallel)
Grounding & Earthing
The safety connection to earth that prevents electric shock — grounding vs earthing, the earth-fault loop, types of earthing (plate/pipe/rod), TN/TT/IT systems, earth resistance & the earth pit.
- Fault current → earth, not through you
- Plate, pipe & rod earthing; TN/TT/IT
- Earth resistance ≤ 1–5 Ω
T03
AC vs DC
8
Direct Current (DC)
One-directional current explained — DC vs AC, sources, rectification, pure vs pulsating DC, formulas and uses.
- DC vs AC & sources
- AC-to-DC rectification
- Formulas & applications
Alternating Current (AC)
The sine-wave current that reverses direction — AC vs DC, generation, peak & RMS, frequency, phases and uses.
- Sine wave & RMS value
- How AC is generated
- Single & three phase
RMS Value
Root mean square — the effective value of AC. Why Vrms = 0.707 × peak, the square–mean–root process, and other waveforms.
- Effective value & heating
- Vrms = Vm/√2
- Form & crest factor
Peak & Peak-to-Peak
The peak value (amplitude, Vm) and peak-to-peak (Vpp = 2Vm) — how they relate to RMS, waveform values and ratings.
- Peak Vm & Vpp = 2Vm
- Peak vs RMS vs average
- Conversions & ratings
Average Value
The mean of a waveform — why the full cycle is zero, the half-cycle average Vavg = 0.637 Vm, and average vs RMS.
- Full-cycle average = 0
- Vavg = 0.637 Vm
- Average vs RMS & form factor
Form & Crest Factor
The two shape ratios of a waveform — form factor (RMS/avg = 1.11) and crest factor (peak/RMS = 1.414), with waveform values and uses.
- Form factor = 1.11 (sine)
- Crest factor = 1.414 (sine)
- Meter calibration & stress
Phase & Phase Difference
The phase angle φ and the offset between two waves — in-phase, quadrature, anti-phase, leading vs lagging and phase in R, L, C.
- Phase angle & difference
- Leading vs lagging (ELI/ICE)
- Phasors & power factor
Period & Frequency
The period T (time for one cycle) and frequency f (cycles per second), the reciprocal T = 1/f, units and mains examples.
- T = 1/f reciprocal
- Units (s, ms, µs, ns)
- 50 Hz → 20 ms & ω = 2π/T
T04
AC Circuit Analysis
9
Impedance
Total AC opposition — Z = R + jX, the impedance triangle, R/L/C impedance, frequency response and Ohm's law for AC.
- Z = R + jX & the triangle
- Impedance of R, L, C
- V = I × Z (AC Ohm’s law)
Reactance (XL & XC)
The AC opposition of inductors & capacitors — XL = 2πfL rises with frequency, XC = 1/2πfC falls, plus phase and resonance.
- XL = 2πfL, XC = 1/2πfC
- Net reactance & resonance
- 90° phase (ELI the ICE man)
Admittance
The ease of AC flow — Y = 1/Z, Y = G + jB, conductance & susceptance, and why admittances add in parallel circuits.
- Y = 1/Z & Y = G + jB
- Conductance & susceptance
- Admittances add in parallel
Phasors & Complex Numbers
The rotating-vector tool that makes AC analysis easy — the j operator, rectangular a + jb & polar r∠θ forms, phasor arithmetic and circuit diagrams.
- Phasor = magnitude & phase (A∠φ)
- a + jb ↔ r∠θ & the j operator
- Add rect, multiply polar; Z = R + jX
Power Factor
How much supplied power does useful work — PF = cosφ = P/S, the power triangle, leading vs lagging PF, and correction with capacitors.
- PF = cosφ = P / S (0–1)
- Real, reactive & apparent power
- Leading vs lagging & PF correction
Real, Reactive & Apparent Power
The three kinds of AC power and how they fit together — real power P = VI cosφ (W), reactive power Q = VI sinφ (VAR) and apparent power S = VI (VA), plus the power triangle and power factor.
- P = VI cosφ, Q = VI sinφ, S = VI
- Power triangle S² = P² + Q²
- Power factor cosφ = P/S & the beer analogy
Resonance (Series & Parallel)
When XL = XC and reactances cancel — f0 = 1/2π√(LC), series (Z min) vs parallel tank (Z max), plus Q factor and bandwidth.
- f0 = 1/2π√(LC), XL = XC
- Series Z min / parallel Z max
- Q factor, bandwidth & selectivity
Q Factor & Bandwidth
The sharpness of resonance — quality factor Q, bandwidth between the half-power (−3 dB) points, and the link Q = f₀/BW, with RLC formulas and the energy definition.
- Q = f₀/BW & BW = f₂ − f₁
- Half-power (−3 dB) points
- Q = (1/R)√(L/C) & energy ratio
Three-Phase Systems
Three AC voltages 120° apart that power the grid — star vs delta, line vs phase (√3), three-phase power P = √3 VLILcosφ and why it beats single-phase.
- Three phases 120° apart (R, Y, B)
- Star & delta; VL = √3 Vph
- P = √3 VLILcosφ; 400/230 V
T05
Waveforms & Signals
8
Sine Wave
The pure, fundamental AC waveform — v(t) = Vm sin(2πft + φ), with amplitude, period, frequency, phase and peak / RMS / average values.
- v(t) = Vm sin(2πft + φ)
- Amplitude, period T, f = 1/T, phase φ
- Vrms = 0.707Vm, Vavg = 0.637Vm
Square Wave
The two-level ON/OFF waveform of digital & switching circuits — duty cycle D = ton/T, odd-harmonic Fourier series, spectrum, RMS values and PWM.
- Duty cycle D = ton/T (PWM)
- Odd harmonics: f, 3f, 5f… (1/n)
- Vrms = Vm; square vs sine
Triangular & Sawtooth
Ramp-based waveforms used in PWM generation, timing and signal processing.
- Linear rise & fall
- Sawtooth flyback ramp
- Harmonic content & uses
Pulse & PWM Signals
The on/off waveform that controls motors, LEDs & power supplies — pulse anatomy, duty cycle D = ton/T, average voltage Vavg = D×Vin and SPWM generation.
- Duty cycle D = ton/T (0–100%)
- Vavg = D × Vin
- SPWM & motor / LED control
Harmonics & THD
The extra frequencies that distort AC and how we measure them — harmonic order, odd/even/triplen harmonics, the THD formula, the spectrum, nonlinear-load sources, effects and mitigation.
- Harmonic n at n× the fundamental
- THD = √(V₂²+V₃²+…)/V₁
- Triplen harmonics & the neutral
Fourier Series Basics
How any periodic waveform is a sum of sine waves — the Fourier series formula f(t) = a₀/2 + ∑(aₙcos nωt + bₙsin nωt), fundamental & harmonics, building a square wave, symmetry, the spectrum & the Gibbs phenomenon.
- f(t) = a₀/2 + ∑(aₙcos nωt + bₙsin nωt)
- Square wave = odd harmonics (1/n)
- Line spectrum & Gibbs overshoot
Duty Cycle
The fraction of each cycle a signal is ON — duty cycle D = ton/T (0–100%), how it sets the average voltage Vavg = D×V, complementary duty & dead-time, and PWM control of motors, LEDs & power supplies.
- D = ton/T (0–100%)
- Vavg = D × Vsupply
- Complementary duty & dead-time
Ripple & Ripple Factor
How much AC is left on a rectifier’s DC output, and the ripple factor that measures it.
- Ripple factor γ = Vr(rms)/Vdc
- Half-wave 1.21 vs full-wave 0.48
- Capacitor smoothing & reduction
Laws & Analysis
Fundamental laws, network theorems and circuit-analysis methods.
T06
Fundamental Laws
9
Ohm's Law
Fundamental relationship between voltage, current, and resistance.
- V = I × R relationship
- Practical applications
- Problem solving techniques
Kirchhoff's Voltage Law (KVL)
Current and voltage laws for analyzing electrical circuits.
- Kirchhoff's Current Law (KCL)
- Kirchhoff's Voltage Law (KVL)
- Circuit analysis applications
Kirchhoff's Current Law (KCL)
Current and voltage laws for analyzing electrical circuits.
- Kirchhoff's Current Law (KCL)
- Kirchhoff's Voltage Law (KVL)
- Circuit analysis applications
Watt's Law (Power Law)
Power = voltage × current, its three forms, and the 12-formula power wheel.
- P = V·I = I²R = V²/R
- Power triangle & power wheel
- Why 2× current = 4× power
Joule's Law of Heating
The heating effect of current: how much heat a resistance produces, H = I²Rt.
- H = I²Rt formula & derivation
- Heaters, bulbs & the fuse
- Joules, calories & I²R losses
Faraday's Law
Electromagnetic induction — a changing magnetic flux induces a voltage: EMF = −N dΦ/dt. Covers magnetic flux (Φ = BA cosθ), Lenz's law & the minus sign, the three ways to induce an EMF, and the AC generator behind the grid.
- EMF = −N dΦ/dt
- Magnetic flux Φ = BA cosθ
- Lenz's law & the AC generator
Lenz's Law
The direction rule of induction — the induced current always opposes the change in flux that creates it. The minus sign in EMF = −N dΦ/dt, finding the direction, the copper-tube demo, eddy currents & energy conservation.
- Induced current opposes the change
- The − sign in EMF = −N dΦ/dt
- Eddy currents & braking
Coulomb's Law
The electrostatic force between two charges: F = k q1q2/r2. Covers the Coulomb constant (8.99×109), why like charges repel & unlike attract, the inverse-square law, superposition, and the link to the electric field.
- F = k q1q2 / r2
- Like repel, unlike attract
- Inverse-square & superposition
Ampère's Law
The magnetic effect of current: the field around a loop, ∮B·dl = µ₀I.
- Circuital law & right-hand rule
- Wire, solenoid & toroid fields
- Ampère–Maxwell displacement current
T07
Network Theorems
9
Thevenin's Theorem
Reduce any linear network to a single voltage source in series with a resistance.
- Vth open-circuit voltage
- Rth equivalent resistance
- Simplifies load analysis
Norton's Theorem
Replace any linear two-terminal network with a current source IN in parallel with a resistance RN — find IN & RN, source transformation with Thévenin, and load current.
- Norton equivalent: IN ∥ RN
- IN = short-circuit current; RN = RTh
- Norton ↔ Thévenin transformation
Superposition Theorem
One source at a time: in a linear circuit the total current or voltage equals the sum of the effects of each independent source acting alone — turn voltage sources into shorts, current sources into opens, solve, then add.
- V source → short; I source → open
- I = I′ + I″ (algebraic sum)
- Linear circuits only; not for power
Maximum Power Transfer
Maximum power reaches a load when RL = RS — the power curve, Pmax = VTH²/4RS, derivation, the 50% efficiency result and AC conjugate matching.
- Condition RL = RS
- Pmax = VTH²/4RS
- Efficiency = 50% & conjugate match
Millman's Theorem
The fastest way to solve parallel source branches: the common terminal voltage is V = ΣVG / ΣG, where G = 1/R. Reduce many parallel batteries or supplies to one equivalent source (Veq, Req).
- V = ΣVG / ΣG (G = 1/R)
- Single-node method from KCL
- Parallel voltage & current sources
Reciprocity Theorem
A symmetry of linear circuits: in a linear, bilateral, single-source network, swap the source and the meter and the current is unchanged. The transfer resistance V/I is the same both ways — the basis of antenna reciprocity.
- Swap source ↔ meter → same I
- Linear, bilateral, single source
- Transfer resistance V/I invariant
Substitution Theorem
Replace any branch by anything with the same terminal voltage and current — a source or a resistor — and the rest of the circuit is unchanged. Statement, conditions, proof and worked examples.
- Keep the same V & I
- V source / I source / R = V/I
- Underpins Thévenin & Norton
Compensation Theorem
A branch impedance change ΔZ acts like a compensating source Vc = −I·ΔZ with all other sources off — find the effect without re-solving the circuit. Statement, formula, derivation and worked example.
- Vc = −I·ΔZ
- ΔI = Vc/(Zth + ΔZ)
- Sensitivity & bridge analysis
Tellegen's Theorem
The most general power result in circuit theory: for any lumped network obeying KCL and KVL, the branch powers always sum to zero — Σ vk ik = 0. No linearity needed; it depends only on the wiring.
- Σ vk ik = 0 (all branches)
- Follows from KCL + KVL only
- Holds for any network (even non-linear)
T08
Circuit Analysis Methods
8
Nodal Analysis
Solve circuits using node voltages and Kirchhoff's current law.
- Node-voltage method
- KCL at each node
- Matrix / admittance form
Mesh Analysis
Solve circuits using loop currents and Kirchhoff's voltage law.
- Loop-current method
- KVL around each mesh
- Independent loop equations
Loop / Branch Analysis
Solve any circuit with Kirchhoff's laws: the branch-current & loop-current methods.
- Branch, node, loop & mesh
- Independent loops L = b − n + 1
- Worked two-loop example
Source Transformation
Swap a voltage source (series R) for a current source (parallel R): I = V/R, V = I×R.
- Voltage ⇄ current source
- Rules, conditions & example
- Thévenin ⇄ Norton bridge
Delta-Wye (Star-Delta)
Swap a triangle (Δ) of resistors for an equivalent star (Y) — and back. The Δ→Y and Y→Δ formulas, the balanced case RΔ = 3RY, worked examples and cracking bridge circuits.
- Δ ↔ Y (π ↔ T) networks
- Adjacent-product ÷ sum; P ÷ opposite arm
- Solves unbalanced bridge circuits
Voltage Divider Rule
Two series resistors split a voltage: Vout = Vin·R2/(R1+R2). Covers the derivation, resistor ratios, multi-resistor taps, the loading effect, and the potentiometer as an adjustable divider.
- Vout = Vin·R2/(R1+R2)
- Equal resistors → half the input
- Loading effect & potentiometer
Current Divider Rule
How current splits between parallel branches — the opposite-resistor formula and conductance form.
- I₁ = IT·R₂/(R₁+R₂)
- Opposite resistor on top
- Smaller R carries more current
Two-Port Networks
Model any circuit as a black box with an input & output port — four variables V1, I1, V2, I2. The Z, Y, h & ABCD parameters, their open/short-circuit tests, the transistor h-model & the cascade rule.
- 4 variables, 2 equations
- Z, Y, h & ABCD parameter sets
- Cascade → multiply ABCD matrices
Passive & Magnetics
Resistors, capacitors, inductors, magnetics, transformers and EMI parts.
T09
Resistive Components
1
What are Resistors?
Basic passive components that oppose current flow and control voltage levels.
- Resistance and Ohm's law
- Types and color coding
- Power ratings
T10
Capacitors
1
What is Capacitor?
Energy storage device that stores electrical charge and opposes voltage changes.
- Charge storage mechanism
- Types and applications
- Charging and discharging
T11
Inductors
1
What is Inductor?
Passive component that stores energy in magnetic field and opposes current changes.
- Magnetic energy storage
- Inductance and reactance
- AC and DC behavior
T12
Magnetic Fundamentals
9
Magnetic Flux
The total magnetic field through an area — Φ = B·A·cosθ, the weber, flux density and Faraday's law.
- Φ = B·A·cosθ · unit weber (Wb)
- Flux density B = Φ/A & flux linkage NΦ
- Faraday's law & the magnetic circuit
Flux Density (B)
The magnetic field per unit area — B = Φ/A in tesla, permeability, the force F = BIL and typical values.
- B = Φ/A · unit tesla (Wb/m²)
- B = μ₀μᵣH & the force F = BIL
- Earth 50µT to MRI & lab magnets
Magnetomotive Force (MMF)
The magnetic “pressure” that drives flux around a circuit — MMF = N·I in ampere-turns. The EMF analogy (Φ = MMF/reluctance), field strength H = NI/l, and electromagnets.
- MMF = N·I (ampere-turns)
- Φ = MMF / reluctance (magnetic Ohm’s law)
- H = N·I / l; electromagnets & relays
Reluctance & Permeance
A magnetic circuit's resistance to flux: reluctance ℛ = ℓ/(μA), and its inverse, permeance. Covers the magnetic Ohm's law MMF = Φ×ℛ (Hopkinson), series & parallel reluctance, the air gap, and permeability.
- ℛ = ℓ/(μA) · P = 1/ℛ
- MMF = Φ × ℛ (magnetic Ohm's law)
- Air gap & permeability
Permeability
How easily a material carries magnetic flux: B = μH, μ = μ₀μr.
- μ₀ & relative permeability μr
- Dia / para / ferromagnetic
- B–H curve & saturation
B-H Curve & Hysteresis
How magnetic materials magnetize: the B-H curve and hysteresis loop, saturation, retentivity (Br) & coercivity (Hc), permeability μ = B/H, hysteresis & core loss, and soft vs hard magnetic materials.
- Hysteresis loop: saturation, retentivity, coercivity
- Permeability μ = B/H & hysteresis (core) loss
- Soft vs hard magnetic materials & domains
Eddy Currents
Circulating currents a changing magnetic flux induces in a conductor — Lenz's law, I²R heating & core losses, laminations, plus uses in induction heating, brakes & NDT.
- Induced loops (Faraday & Lenz)
- Core loss ∝ B²f²t²; laminations cut it
- Induction heating, braking, NDT
Core Losses
The heat wasted in a magnetic core under AC — hysteresis loss (B–H loop area) + eddy-current loss, the Steinmetz formula, lamination, and iron vs copper loss.
- Pc = Ph + Pe (iron loss)
- Hysteresis & eddy-current loss
- Lamination, Steinmetz, efficiency
Magnetic Saturation
The flux ceiling of every magnetic core. Learn the B-H curve and knee, saturation flux density B(sat), magnetic domains, hysteresis, permeability collapse, and how core saturation causes inrush current and inductance drop.
- B-H curve, knee & B(sat)
- Domains, hysteresis & μ collapse
- Inrush current & inductance drop
T13
Transformers
1
What is Transformer?
Device that transfers electrical energy between circuits through electromagnetic induction.
- Voltage transformation
- Step-up and step-down
- Isolation and efficiency
T14
EMI & Power-Quality Components
8
Ferrite Bead
The passive EMI/RFI component that passes DC & signals but turns high-frequency noise into heat. Covers impedance vs frequency (rated at 100 MHz), the equivalent R-L-C circuit, types, how to choose one, the bead + capacitor LC filter, and ferrite bead vs inductor vs choke.
- Suppresses high-frequency EMI/RFI
- Rated by impedance @ 100 MHz
- Bead + capacitor = LC filter
Common-Mode Choke
The two-winding EMI-suppression inductor that blocks common-mode noise but passes the signal — common-mode vs differential-mode, dot convention, impedance vs frequency, the X/Y-capacitor EMI filter, and how to choose one.
- CM noise blocked (high Z), signal passes (low Z)
- Core of every EMI / EMC input filter
- SMPS, USB, Ethernet, motor drives & EVs
EMI / Line Filter
Mains low-pass filter that blocks conducted EMI with X/Y caps & a common-mode choke.
- X-cap & Y-cap, CM choke
- Common vs differential noise
- Insertion loss & EMC standards
Line / Load Reactor
Series inductors that smooth drive current and suppress harmonics.
- Current smoothing
- Harmonic reduction
- Drive protection
Capacitor Bank (PFC)
The bank of power capacitors that supplies leading reactive power (kVAR) to raise power factor — how it works, kVAR sizing, fixed vs automatic (APFC) vs detuned banks, and star vs delta connection.
- Supplies leading kVAR, cancels lagging load
- kVAR sizing Q=P(tanφ₁−tanφ₂) & APFC steps
- Lower bills, released capacity, better voltage
Snubber Network
The small R–C (or R–C–D) circuit across a power switch that clamps the turn-off voltage spike and damps ringing — RC vs RCD snubbers, the flyback leakage clamp, design formulas for the resistor and capacitor, the SOA, and applications.
- Clamps dV/dt spike, damps switching ringing
- Rs=√(L/C), PR=C·V²·f design formulas
- SMPS, flyback, inverters, IGBT/thyristor, relays
Crystal & Resonator
The quartz crystal and ceramic resonator that vibrate at one precise frequency to clock every device — the piezoelectric effect, the equivalent circuit, series vs parallel resonance, the Pierce oscillator, load capacitance and ppm accuracy.
- Piezoelectric quartz, extremely high Q
- Pierce oscillator: amp + Rf + 2 load caps
- 32.768 kHz RTC, MCU, USB & radio clocks
Gas Discharge Tube (GDT)
The gas-filled spark-gap surge arrester that stays open until a spike hits, then ionises and crowbars the surge to earth — sparkover, glow & arc, the V–I curve, 2 vs 3 electrode, GDT vs MOV vs TVS, and hybrid SPDs.
- Crowbars high-energy surges to ground
- Very low capacitance (<1 pF), high surge kA
- Telecom, data, coax, antenna & AC mains SPDs
Semiconductors
Device physics, diodes, transistors, thyristors and integrated circuits.
T15
Semiconductor Physics
8
Semiconductor Basics
The material between a conductor and an insulator that powers all electronics — the silicon crystal & covalent bonds, energy bands and the band gap, electrons & holes, doping into N-type & P-type, and the P–N junction.
- Silicon, band gap ~1.1 eV, holes & electrons
- Doping → N-type (donor) & P-type (acceptor)
- P–N junction: the seed of every chip
Intrinsic & Extrinsic
Pure vs doped semiconductors — covalent bonds & electron-hole pairs, the energy band gap & Fermi level, n-type (donor) vs p-type (acceptor), majority/minority carriers and the mass-action law n·p = ni2.
- Intrinsic: pure Si/Ge, n = p = ni
- N-type (pentavalent) vs P-type (trivalent)
- Foundation of the diode & transistor
P-Type & N-Type Doping
How a trace of impurity turns pure silicon into engineered material — n-type donors vs p-type acceptors, donor/acceptor ionization, dopant elements, doping methods (diffusion, ion implantation, epitaxy) and doping levels.
- N-type = donor (n≈ND); P-type = acceptor (p≈NA)
- Diffusion, ion implantation & epitaxy methods
- Doping level sets resistivity (N− to degenerate)
PN Junction
Where P-type meets N-type to form the basic diode — the depletion region & barrier potential (0.7 V), forward vs reverse bias, the V-I curve and breakdown.
- Depletion region & barrier potential
- Forward bias ON, reverse bias OFF
- V-I characteristics & breakdown
Depletion Region
The carrier-free space-charge zone at a PN junction — formation, barrier potential (0.7 V Si), forward/reverse bias, depletion width & junction capacitance.
- Space-charge region & fixed ions
- Barrier Vbi; forward narrows / reverse widens
- Width W & Cj = εA/W (varactor)
Forward & Reverse Bias
How a diode conducts or blocks — forward bias (ON, above 0.7 V), reverse bias (OFF, tiny leakage), the I-V characteristic, knee voltage & breakdown.
- Forward = ON, reverse = OFF
- Knee 0.7 V (Si), 0.3 V (Ge)
- Diode I-V characteristic curve
Energy Bands & Band Gap
Why materials conduct or not — the valence & conduction bands, the forbidden band gap (Eg), conductor vs semiconductor vs insulator, the Fermi level and doping.
- Valence & conduction bands, Eg
- Conductor / semiconductor / insulator
- Fermi level, holes & doping
Charge Carriers
The mobile charges that carry current — free electrons & holes in semiconductors, electrons in metals, ions in electrolytes. How holes move, majority/minority carriers, drift & diffusion.
- Electrons (−) & holes (+)
- Majority / minority; n·p = ni²
- Drift, diffusion, generation
T16
Diodes
1
What is Diode?
Fundamental semiconductor device allowing current flow in one direction.
- PN junction structure
- Forward and reverse bias
- Rectification applications
T17
Transistors
3
What is BJT Transistor?
Bipolar Junction Transistor for amplification and switching applications.
- NPN and PNP types
- Current amplification
- Switching characteristics
What is MOSFET Transistor?
Metal-Oxide-Semiconductor Field-Effect Transistor for efficient switching.
- Voltage-controlled device
- High switching speeds
- Low power consumption
What is IGBT Transistor?
Insulated Gate Bipolar Transistor combining MOSFET and BJT advantages.
- High voltage capability
- Fast switching
- Power electronics applications
T18
Thyristors & Power Switches
1
What is SCR?
Silicon Controlled Rectifier - a powerful semiconductor switching device.
- Three-terminal device
- Gate triggering mechanism
- Power control applications
T21
Integrated Circuits
5
Voltage Regulator IC (78xx/LDO)
The chip that makes a fixed power rail: a 7805 gives a steady +5 V from messy DC, and an LDO does it with tiny dropout. Pinout, the basic circuit, dropout & heat, 78xx vs LDO — plus three buildable projects.
- 7805/78xx fixed & LDO regulators
- Pinout: IN · GND · OUT
- 3 projects (5V, 3.3V, LM317)
Operational Amplifier (Op-Amp)
The core analog building block: a high-gain differential amplifier. With two resistors it becomes an amplifier, buffer, adder, subtractor or comparator. Symbol, 741 pinout, the golden rules and every core circuit with gain formulas.
- Inverting & non-inverting gain
- Golden rules & virtual short
- Buffer, summing, difference, comparator
555 Timer IC
The most popular timer chip: with a few resistors and a capacitor it becomes an oscillator, one-shot timer or flip-flop. Pinout, internals, the astable/monostable/bistable modes with formulas, waveforms and an LED-blinker project.
- Astable / monostable / bistable
- f = 1.44/((R1+2R2)C); T = 1.1RC
- LED blinker project included
Comparator
The circuit that asks “is this voltage bigger than that one?” It snaps its output HIGH or LOW at a threshold. Symbol, comparator vs op-amp, hysteresis (Schmitt trigger), window & open-collector types, the LM393, plus a light-sensor project.
- Open-loop, digital output
- Hysteresis / Schmitt trigger
- Window & open-collector; LM393
Gate Driver IC
The muscle that switches power MOSFETs & IGBTs: a fast current buffer + level shifter. Why it's needed (gate charge), low-side vs high-side, the bootstrap supply, half-bridge dead-time, the gate resistor, isolated drivers and the IR2110.
- Amps of gate current; I = Qg/t
- Low/high-side, bootstrap, half-bridge
- Dead-time, Rg, isolation; IR2110
Protection & Wiring
Breakers, switchgear, relays, wiring and earthing.
T24
Switchgear & Distribution
1
What is Relay?
Electrically operated switch that uses electromagnetic principles for control.
- Electromagnetic switching
- Contact types and ratings
- Control applications
Microcontrollers
Arduino, ESP32, STM32, 8051, PIC and Raspberry Pi boards.
T37
Arduino (AVR Boards)
5
Arduino Uno (ATmega328P)
The most popular microcontroller board, built on the 8-bit ATmega328P. Full board anatomy, a complete labelled pinout with every pin explained, power & programming, the UART/SPI/I2C buses, plus code examples and beginner mini-projects.
- ATmega328P, 16 MHz, 5 V logic
- 14 digital (6 PWM) + 6 analog pins
- Full pinout, code & mini-projects
Arduino Nano
The breadboard-friendly Arduino: the same 8-bit ATmega328P as the Uno in a tiny board, with two extra analog pins. Full board anatomy, a complete labelled pinout with every pin explained, power & programming, a Nano vs Uno comparison, plus code and mini-projects.
- ATmega328P, 16 MHz, breadboard size
- 14 digital (6 PWM) + 8 analog (A0–A7)
- Full pinout, Nano vs Uno, code & projects
Arduino Mega 2560
The big-board Arduino, built on the ATmega2560. When the Uno runs out of room: 54 digital pins, 16 analog inputs, four serial ports and 256 KB flash. Full board anatomy, a complete labelled pinout with every pin explained, the buses, a Mega vs Uno vs Nano comparison, plus code and mini-projects.
- ATmega2560, 16 MHz, 256 KB flash
- 54 digital (15 PWM) + 16 analog + 4 serial
- Full pinout, Mega vs Uno, code & projects
Arduino Leonardo
The Arduino that can be a USB keyboard or mouse. Built on the ATmega32U4 with native USB, so it needs no separate USB chip. Full board anatomy, a complete labelled pinout with every pin explained, the HID trick, a Leonardo vs Uno comparison, plus code and mini-projects.
- ATmega32U4, native USB, 5 V logic
- 20 digital (7 PWM) + 12 analog inputs
- Keyboard/mouse HID, full pinout, code
Arduino Pro Mini
The smallest, cheapest ATmega328P board — with no USB. You program it with an external FTDI adapter. Full board anatomy, a complete labelled pinout with every pin explained, FTDI programming, the 5V vs 3.3V versions, a Pro Mini vs Uno comparison, plus code and mini-projects.
- ATmega328P, no USB, program via FTDI
- 14 digital (6 PWM) + 8 analog (A0–A7)
- 5V/16MHz & 3.3V/8MHz, code & projects
T38
ESP (Espressif Wi-Fi / BLE)
1
ESP32 (WROOM-32)
The Wi-Fi + Bluetooth microcontroller behind countless IoT projects. Dual-core 240 MHz, 520 KB RAM and a rich set of peripherals. The DevKitC board and WROOM-32 module, a complete 38-pin pinout with every GPIO explained, safe vs strapping pins, ADC/DAC, touch, PWM, deep sleep, plus code and mini-projects.
- Dual-core 240 MHz, Wi-Fi + BLE, 3.3 V
- 38-pin pinout, safe-pin guide, ADC/DAC/touch
- Web server, deep sleep, code & projects