OhmPedia

电路词林

A reference shelf for electronics fundamentals, ordered by term.

Every entry is a single term: the quantity it names, the unit it is measured in, the relation it obeys, and the mistakes that surround it. Entries are added in a fixed publishing order rather than all at once, so the shelf grows the way a printed reference grows across editions.

B
Bipolar Junction TransistorI_C = β · I_B

A three-terminal current-controlled device in which a small base current regulates a much larger collector current. · Semiconductor Devices
Boolean AlgebraY = A·B + Ā·C

The algebra of two-valued variables that underlies every digital circuit. · Digital Logic
C
CapacitanceC = Q / V

The ability of two insulated conductors to store charge, one coulomb per volt. · Passive Components and Laws
D
DecibeldB = 20 log₁₀(V₂/V₁)

A logarithmic ratio used to express gain, loss or level, so that multiplication becomes addition. · Signal and Measurement
DiodeI = I_S (e^(V/nV_T) − 1)

A two-terminal junction that conducts in one direction once the forward voltage exceeds about 0.6 V. · Semiconductor Devices
E
Electric PowerP = V · I

The rate at which electrical energy is converted, equal to voltage times current. · Power Conversion
I
ImpedanceZ = R + jX

The complex generalisation of resistance that also accounts for energy stored and returned by capacitance and inductance. · Passive Components and Laws
K
Kirchhoff's Circuit LawsΣ I = 0 (node) · Σ V = 0 (loop)

Charge and energy conservation applied to a circuit: currents into a node sum to zero, voltages around a loop sum to zero. · Passive Components and Laws
L
Logic GateY = f(A, B, …)

A circuit that computes one Boolean function of its inputs and restores the result to a valid logic level. · Digital Logic
Low-Pass Filterf_c = 1 / (2πRC)

A network that passes frequencies below a cutoff and attenuates those above it. · Signal and Measurement
M
MOSFETI_D = ½ k (V_GS − V_th)²

A voltage-controlled transistor in which an insulated gate sets how much current flows between drain and source. · Semiconductor Devices
O
Ohm's LawV = I · R

The linear relation between voltage, current and resistance in a resistive element. · Power Conversion
R
ResistanceR = ρ · l / A

The property of a material that converts electrical energy to heat at a rate proportional to the square of the current. · Passive Components and Laws
T
TransformerV₂ / V₁ = N₂ / N₁

Two coupled windings on a shared magnetic core that trade voltage for current. · Power Conversion

Sections

Passive Components and Laws — I · Resistance, capacitance, inductance and the laws that constrain them. Nothing here supplies energy; everything here absorbs, stores or redistributes it.
Semiconductor Devices — II · Junctions, transistors and the small-signal models used to reason about them before a single number is calculated.
Digital Logic — III · Two levels, a set of standard symbols, and the algebra that lets a design be reduced before it is built.
Power Conversion — IV · Getting energy from an outlet to a load: rectification, regulation, and the dissipation each method pays for.
Signal and Measurement — V · Ratios expressed in decibels, bandwidths expressed in time, and the instruments that decide which number is real.