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• A diode colour code is a legacy marking scheme—mainly for small axial “1N-series” diodes—where 3 … 5 coloured bands replace the printed part number.
• Each colour corresponds to a digit 0-9 (identical to the resistor code).
• Read the bands from the anode towards the cathode (the cathode is already marked by a wider silver/black ring).
• Assume the implicit prefix “1N”; the bands give the remaining digits, e.g. yellow-brown-yellow-grey → 4148 ⇒ 1N4148.
• A fifth (suffix) band, if present, may denote a variant letter (A, B, …) or manufacturer option.
• Modern diodes are almost never colour-coded; they use laser-etched or printed alphanumerics or tiny SMD codes.
Historical background
• In the 1960-80 s glass-encapsulated diodes were too small for legible printing; JEDEC therefore allowed colour bands similar to resistor codes.
• Most devices involved were low-power signal diodes (1N4148/1N914), low-current rectifiers, or 400 mW Zeners (1N47xx).
Colour-to-digit table
| Colour | Digit | Mnemonic |
|---|---|---|
| Black | 0 | “0 ohm” |
| Brown | 1 | “1 st” |
| Red | 2 | “R = 2” |
| Orange | 3 | “O = 3” |
| Yellow | 4 | “Y = 4” |
| Green | 5 | “5 greens” |
| Blue | 6 | |
| Violet | 7 | |
| Grey | 8 | |
| White | 9 |
Reading rules
a) Identify the cathode ring first (silver, black or band farthest from the cluster of colour bands).
b) Turn the diode so the colour cluster is at the anode end and read towards the cathode.
c) Translate colours to digits; prepend “1N”; append a suffix if a 5ᵗʰ band exists.
d) Typical band counts:
– 3 bands: last three digits of a three-digit JEDEC code (rare).
– 4 bands: common; e.g. 1 N 4 1 4 8.
– 5 bands: four digits + suffix; e.g. 1N4733A (yellow-violet-orange-orange-brown).
Worked examples
• Brown-white-yellow → 914 → 1N914.
• Yellow-brown-yellow-grey → 4148 → 1N4148.
• Yellow-violet-orange-orange-brown → 4733 + A → 1N4733A (5.1 V Zener).
Special/partial markings
– Some vendors used a single coloured ring (besides the cathode stripe) to indicate diode type family only (green = Schottky, blue = Zener, etc.). Without documentation this is ambiguous.
– Power diodes and anything younger than roughly year 2000 normally carry laser-etched IDs, so colour bands seen today are largely on surplus or vintage parts.
Verification & risk reduction
• Because paint can fade and manufacturers were not 100 % consistent, always cross-check with:
– Multimeter diode test (forward drop clue: ≈0.25 V Schottky, ≈0.6 V Si, ≈0.3 V Ge).
– Curve tracer or inexpensive component tester (identifies Zener voltage, leakage, etc.).
– Circuit context: location and service manual.
• For SMD parts use an SMD code database instead—colour codes do not apply.
• Industry has moved to laser or ink-jet marking, even on 0402/SOD-923 packages, enabled by UV-laser micro-printing.
• Large-scale production uses 2-D datamatrix or QR codes on tape, not on the device.
• Counterfeit mitigation drives unique ID & traceability, rendering colour codes obsolete.
• Automated optical inspection (AOI) cameras read alphanumeric or machine-readable marks, not colours.
• Why not code electrical parameters? Because diodes vary widely (IF, VRRM, VF) and part numbers already encapsulate all specs; colour-coding the part number avoids an ever-growing table of parameter codes.
• Analogy: think of the “1N” as the family surname printed elsewhere; the colours give the “house number”.
• Misidentification in safety-critical designs (e.g. medical, avionics) can lead to catastrophic failure—do not rely solely on a paint band of uncertain age.
• RoHS / REACH: some legacy glass diodes may contain lead-bearing solder internally; refurbishing such boards may invoke compliance issues.
• Counterfeits often use incorrect colour banding; verification procedures above mitigate this risk.
• No single official international standard document exists; the practice emerged informally under JEDEC.
• Some manufacturers reused colours to denote house-coded parts unrelated to JEDEC numbers—documentation triumphs eye-balling in those cases.
• Colours fade under heat and UV; 50-year-old parts can be unreadable.
• Collect manufacturer application notes from the 1970-80 s (Motorola, Philips, Siemens) on diode identification.
• Study automated machine-vision recognition for vintage colour-banded components.
• Investigate whether AI-based spectral imaging could recover faded band colours for conservation of historic electronics.
Diode colour codes map standard resistor colours to the numeric portion of a JEDEC “1Nxxxx” part number, read from anode to cathode. Four bands are most common (e.g. 4148 → 1N4148). Because banding is manufacturer-specific, prone to fading and now largely obsolete, always confirm identification with a datasheet and electrical measurement.
