Electronic Components & Circuits
A broad reference to parts, instruments and circuit functions, explained in everyday language with labeled illustrations, examples and specification checks.
How to use this list
Open an entry to see its illustration, what it does, an example and the specifications that matter. Tap any image to enlarge it. Images are original representative illustrations, not photographs, exact pinouts or guarantees of physical identification. Component families and circuit arrangements are distinct: a capacitor is a part; a filter is a circuit that may use several parts. This reference covers common and important families, rather than every manufacturer part number or specialized circuit ever made.
Examples explain function; they are not universal replacement or wiring instructions. Appearance, package size and a matching nominal value do not establish compatibility. Stored charge, mains, vehicle batteries and high-voltage equipment require appropriate precautions and qualified procedures.
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7 of 160 entries shown. Search matches all entered words across names and explanations.
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FuseProtection Parts
What it does
Interrupts a circuit according to its specified time-current and breaking behavior.
Example
A protected power input.
Important distinction
Never increase its rating to hide recurring failure; current rating is not its only specification.
Specifications to read
Approved function, ratings, fault behavior, breaking/energy capability and required protection coordination.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
Gas discharge tubeProtection Parts
What it does
Uses controlled gas breakdown to divert certain transient events in a designed protection path.
Example
A communication or surge interface.
Important distinction
Its operation differs from a low-voltage diode clamp.
Specifications to read
Approved function, ratings, fault behavior, breaking/energy capability and required protection coordination.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
MOV varistorProtection Parts
What it does
Provides voltage-dependent behavior useful for specified transient suppression.
Example
An approved surge-protection network.
Important distinction
Clamping, energy, aging and protection coordination matter.
Specifications to read
Approved function, ratings, fault behavior, breaking/energy capability and required protection coordination.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
Optocoupler and isolation barrierProtection Parts
What it does
An optocoupler transfers information through light within its specified isolation arrangement. Other technologies also implement isolation barriers.
Example
An isolated feedback or interface path.
Important distinction
Isolation voltage alone is not a complete safety assessment of the installed system.
Specifications to read
Approved function, ratings, fault behavior, breaking/energy capability and required protection coordination.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
Resettable polymer protectorProtection Parts
What it does
A temperature/current-dependent protective device that increases resistance under specified conditions.
Example
A limited-energy protection arrangement.
Important distinction
It has hold/trip and environmental requirements and is not identical to a conventional fuse.
Specifications to read
Approved function, ratings, fault behavior, breaking/energy capability and required protection coordination.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
Reverse-polarity protectionProtection Parts
What it does
A circuit function that limits consequences of an incorrect source orientation using a suitable design.
Example
A protected DC input.
Important distinction
Protection topology, drop, current and failure behavior must be assessed.
Specifications to read
Approved function, ratings, fault behavior, breaking/energy capability and required protection coordination.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
Thermal fuse and thermostatProtection Parts
What it does
A thermal fuse provides a specified non-resetting interruption; a thermostat has a defined temperature-switching behavior.
Example
Overtemperature protection.
Important distinction
Do not bridge either device or substitute one without the design requirements.
Specifications to read
Approved function, ratings, fault behavior, breaking/energy capability and required protection coordination.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
Visual comparison guides
Compare representative physical forms, then read the entries for their different functions. Many parts share package shapes. Appearance alone cannot identify ratings, internal construction or terminal assignments.
Units and worked examples
| Quantity | Unit | Meaning |
|---|---|---|
| Voltage | V, volts | Potential difference between two points. |
| Current | A, amperes | Rate of charge flow. |
| Resistance | Ω, ohms | Resistance to current flow. |
| Power | W, watts | Rate of energy transfer or dissipation. |
| Capacitance | F, farads | Charge change per voltage change. |
| Inductance | H, henries | Relationship between current change and induced voltage. |
| Frequency | Hz, hertz | Cycles per second. |
Prefixes: k = 1,000; M = 1,000,000; m = 0.001; μ = 0.000001; n = 0.000000001; p = 0.000000000001. Case matters: M and m are different.
Resistor example
For an ideal 1 kΩ resistor with 5 V across it: I = V/R = 5/1,000 = 0.005 A = 5 mA. Dissipation is P = V²/R = 25/1,000 = 0.025 W. This arithmetic does not select a real part without its temperature, voltage and application requirements.
Tolerance example
A 1 kΩ resistor with ±5% nominal tolerance spans 950 Ω to 1,050 Ω at the specified conditions. Tolerance is different from drift with temperature or aging.
Capacitance and timing example
10 μF = 10,000 nF. An ideal first-order RC network with R = 1 kΩ and C = 10 μF has τ = RC = 0.01 s = 10 ms. A time constant is not automatically the delay of every timer using those parts.
Stored energy
Ideal capacitor charge is Q = CV; stored energy is E = ½CV². Doubling voltage at the same capacitance quadruples the stored energy. These are learning equations, not a discharge procedure.
Schematic symbols, labels and markings
Reference letters identify components in a drawing; conventions vary by manufacturer and standard. Always read the drawing's legend.
| Common label | Often used for |
|---|---|
| R | Resistor |
| C | Capacitor |
| L | Inductor |
| D | Diode |
| Q | Transistor |
| U / IC | Integrated circuit |
| T | Transformer |
| K / RL | Relay |
| SW / S | Switch |
| J / P / CN | Connector |
| F | Fuse |
| Y / X | Crystal or resonator |
| TP | Test point |
| V / VT | Tube in some historical documentation |
R17 identifies a component location, not a resistance value. A marking such as 4R7 may mean 4.7 Ω in an applicable resistor convention. Three-digit markings such as 104 often represent 100,000 base units: 100 kΩ for a resistor or 100,000 pF = 100 nF for an applicable capacitor code. Confirm the component family and marking system; short codes can be ambiguous.
Common questions
Can I replace a part with any higher-rated one?
No. A higher headline rating does not ensure suitable function, polarity, frequency behavior, package, protective approval or circuit stability.
Does a part that looks normal have to be good?
No. Visual observations can help, but many electrical changes leave no obvious external sign.
Are capacitance, ESR and leakage the same?
No. They describe different properties. A single test cannot establish every capacitor failure mode.
Can I measure every component while it remains connected?
Other paths can affect an in-circuit result. Interpretation depends on the circuit and instrument. Internal work also requires a suitable qualified safety procedure.
Does a matching package establish a transistor or IC replacement?
No. Pinout, function, voltage, drive, timing, heat and application requirements must match.
Is a component the same thing as a circuit?
A component is a building block. A circuit connects building blocks to perform a function. The same component family can serve many circuit roles.
How do I begin learning?
Start with units, schematic labels, resistor/capacitor/inductor functions and signal-versus-power paths. Use disconnected parts or an instructor-approved low-voltage trainer before considering customer equipment.
Is this reference free?
Yes. Every entry, example and reference on this page is public. The separate repair masterclasses have their own free previews and paid lessons.
Manufacturer references
Original plain-language summaries and educational examples. These references support further study; exact product data sheets and equipment manuals remain authoritative for a real application.
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