Tamil Nadu HSE First Year Basic Electronics Engineering cheat sheet

Ohm's law: V = IR; power P = VI = I²R = V²/R. Current in amperes, voltage in volts, resistance in ohms.

Series circuit: same current through all elements; R_total = R1 + R2 + …; voltage divides in proportion to resistance.

Parallel circuit: same voltage across all branches; 1/R_total = 1/R1 + 1/R2 + …; current divides inversely with resistance.

Kirchhoff's current law (KCL): algebraic sum of currents at a node is zero; current in equals current out.

Kirchhoff's voltage law (KVL): algebraic sum of voltage drops around any closed loop is zero.

Conductor resistance R = ρL/A: doubles when length doubles, halves when cross-sectional area doubles; ρ depends on material and temperature.

Metals have a positive temperature coefficient (resistance rises with heat); carbon and semiconductors have a negative coefficient.

Energy consumed W = Pt; one unit of electricity = 1 kWh = 3.6 × 10⁶ joules.

Resistor colour code: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9; gold = ±5%, silver = ±10%.

Capacitor stores charge Q = CV; energy stored E = ½CV²; capacitive reactance X_C = 1/(2πfC) falls as frequency rises.

Capacitors in parallel add (C = C1 + C2); in series they combine like parallel resistors: 1/C = 1/C1 + 1/C2.

Inductor opposes change of current; inductive reactance X_L = 2πfL rises with frequency; energy stored E = ½LI².

Air-core and ferrite-core inductors are common in tuned circuits; laminated iron cores reduce eddy-current loss in transformers.

Electrolytic capacitors are polarised: the marked negative lead must go to the lower potential, and reversing polarity can rupture the can.

Potentiometer as a voltage divider gives V_out = V_in × R2/(R1 + R2); a rheostat is a variable series resistance.

LDR resistance falls with increasing light; thermistor resistance changes with temperature (NTC falls on heating).

Silicon diode knee (cut-in) voltage ≈ 0.7 V; germanium ≈ 0.3 V; forward current rises steeply beyond the knee.

Reverse bias gives only microampere leakage until breakdown; a normal rectifier diode must not be operated in reverse breakdown.

Half-wave rectifier: one diode, output ripple frequency = supply frequency, low efficiency; V_dc ≈ V_m/π.

Full-wave centre-tap rectifier: two diodes, ripple frequency = 2f; bridge rectifier: four diodes, ripple frequency = 2f, no centre tap needed.

Full-wave average output V_dc ≈ 2V_m/π ≈ 0.637V_m; ripple factor of full-wave ≈ 0.48 versus 1.21 for half-wave.

Peak inverse voltage: half-wave and full-wave centre-tap ≈ 2V_m; bridge ≈ V_m.

A capacitor-input filter smooths output; larger C or lighter load gives smaller ripple; ripple factor ≈ 1/(4√3 f C R_L) for full-wave.

Zener diode works in reverse breakdown as a voltage regulator; a series resistor drops the excess voltage.

LED forward drop ≈ 1.8–3.3 V depending on colour; series resistor R = (V_supply − V_LED)/I_LED.

NPN and PNP have two junctions: emitter-base (forward biased for active mode) and collector-base (reverse biased).

Terminal currents: I_E = I_B + I_C; current gain α = I_C/I_E (≈0.95–0.99) and β = I_C/I_B; β = α/(1 − α).

Active region gives amplifier action; saturation (both junctions forward) and cut-off (both reverse) are the switch states.

Common-emitter amplifier: high voltage gain, moderate current gain, 180° phase inversion between input and output.

Common-base: voltage gain high, current gain < 1, no phase inversion; common-collector (emitter follower): voltage gain ≈ 1, used as buffer.

DC load line joins V_CE = V_CC (cut-off) and I_C = V_CC/R_C (saturation); the Q point sets the quiescent operating condition.

Voltage-divider bias is the most stable against β variation; emitter resistor provides negative feedback for bias stability.

Class A conducts 360°, Class B 180°, Class AB between 180° and 360°, Class C less than 180°; Class B needs two devices in push-pull.

Gain in decibels: voltage gain dB = 20 log₁₀(V_out/V_in); power gain dB = 10 log₁₀(P_out/P_in).

JFET is a voltage-controlled device: gate-source voltage controls drain current; the gate draws almost no current (very high input impedance).

JFET transfer characteristic: I_D = I_DSS(1 − V_GS/V_P)², where V_P is pinch-off voltage and I_DSS is the saturation drain current.

Depletion MOSFET conducts with V_GS = 0 and is turned off by gate voltage; enhancement MOSFET needs V_GS above threshold to conduct.

MOSFET gate is insulated by a thin oxide layer, giving extremely high input resistance but easy damage by static; handle with grounding.

SCR (thyristor) is a four-layer PNPN device: it latches on when anode is positive and a gate pulse is applied, and stays on until anode current falls below holding current.

TRIAC is a bidirectional thyristor for AC control; phase-angle firing with a DIAC trigger gives lamp dimming and fan speed control.

UJT relaxation oscillator produces the sawtooth trigger pulses used for SCR phase control.

Power devices are rated for V_DS/V_CEO, I_D/I_C, and power dissipation; a heat sink is required to keep junction temperature within limits.

Logic levels: binary 1 = HIGH, 0 = LOW; positive logic assigns HIGH to 1.

AND: output 1 only when all inputs are 1 (Y = A·B). OR: output 1 when any input is 1 (Y = A + B). NOT inverts.

NAND and NOR are universal gates: any logic function can be built from either alone.

XOR gives 1 when inputs differ (Y = A⊕B); XNOR gives 1 when inputs are equal; XOR is the basis of half-adder sum.

De Morgan's theorems: (A·B)′ = A′ + B′ and (A + B)′ = A′·B′.

Half adder: Sum = A⊕B, Carry = A·B. Full adder adds three bits and needs two half adders plus an OR gate.

Boolean identity: A + A′ = 1 and A·A′ = 0; absorption law A + AB = A.

Flip-flop holds one bit; SR, JK, D and T types; JK with J = K = 1 toggles, which SR cannot do.

Number systems: binary 1011₂ = 11₁₀; hexadecimal uses 0–9 and A–F, each hex digit equals four binary bits.

IC scale: SSI (<12 gates), MSI (12–99), LSI (100–9999), VLSI (10 000 and above).

Monolithic ICs are fabricated on one silicon chip; hybrid ICs combine separate components on a substrate.

Op-amp ideal properties: infinite open-loop gain, infinite input impedance, zero output impedance, infinite bandwidth, zero offset.

Inverting amplifier: gain = −R_f/R_in; the inverting input is a virtual ground.

Non-inverting amplifier: gain = 1 + R_f/R_in; input and output are in phase.

Voltage follower (unity-gain buffer) has gain 1 and very high input impedance; used for impedance matching.

Op-amp as comparator: output saturates near +V_sat or −V_sat depending on which input is at higher potential.

741 op-amp pinout: pins 2 and 3 are inverting and non-inverting inputs, pin 6 output, pin 4 −V_EE, pin 7 +V_CC.

Slew rate is the maximum rate of output change in V/µs; it limits high-frequency large-signal performance.

Moving-coil (PMMC) meter works on the D'Arsonval principle, measures average DC, and needs a rectifier for AC.

Ammeter is connected in series and must have very low resistance; voltmeter is in parallel and must have very high resistance.

Shunt resistance extends ammeter range: R_sh = R_m/(m − 1), where m is the multiplying factor.

Series multiplier extends voltmeter range: R_s = R_m(m − 1).

CRO: electron gun, deflection plates, fluorescent screen; time base gives horizontal sweep, vertical amplifier drives the Y plates.

CRO measurements: voltage = peak-to-peak divisions × volts/division; period = horizontal divisions × time/division; f = 1/T.

Lissajous figures give frequency ratio from the number of horizontal and vertical tangencies.

Digital multimeter measures V, I, R and often continuity/diode check; select the correct function and range before connecting.

Analogue meter accuracy is specified as a percentage of full-scale deflection; read the scale at eye level to avoid parallax error.

Block chain of communication: source → modulator → transmitter → channel → receiver → demodulator → destination.

Modulation superimposes information on a carrier; needed because antennas for audio frequencies would be impractically long.

AM: carrier amplitude varies; bandwidth ≈ 2f_m; sidebands at f_c ± f_m. FM: carrier frequency varies; wider bandwidth but better noise immunity.

Modulation index for AM: m = V_m/V_c; overmodulation (m > 1) causes distortion and splatter.

Superheterodyne receiver: RF amplifier → mixer with local oscillator → fixed intermediate frequency (455 kHz for AM) → detector → AF amplifier.

Antenna length for a half-wave dipole ≈ 143/f (MHz) metres; quarter-wave monopole ≈ 71.5/f metres.

Consumer devices: microphone converts sound to electrical signal; loudspeaker uses a voice coil in a magnetic field; TV remote uses infrared pulses.

Public address system: microphone → preamplifier → power amplifier → loudspeaker; impedance matching avoids power loss.

Solder alloy for electronics: 60/40 tin-lead (melts ≈183–190 °C) or lead-free SAC alloys (higher melting point, ≈217 °C).

Rosin flux removes oxide and helps wetting; never use acid flux on electronic joints because it corrodes copper.

A good solder joint is shiny, smooth, cone-shaped and wets both pad and lead; a dull rounded blob is a cold joint.

Soldering iron bit should be tinned before use and cleaned on a damp sponge; typical iron power 25–40 W.

PCB: copper tracks connect pads; the solder side has tracks and the component side carries bodies; silkscreen shows component outlines.

Etching removes unwanted copper; a photoresist or resist ink protects the required track pattern.

Component testing: a multimeter diode test shows 0.5–0.7 V forward across a good silicon diode and open circuit in reverse.

Safety: switch off and discharge filter capacitors before touching a board; never solder a live circuit; use pliers as a heat sink on delicate leads.

Desoldering uses a solder sucker or desoldering braid; excessive heat lifts copper pads from the board.