Automotive Lighting: Elevating Vehicle Efficiency With Good-Ark

Automotive lighting parts are qualified, not just specified. What AEC-Q101 evidence to request, and how a lamp module's heat budget decides the device.

Request a Quote

Automotive Lighting: Elevating Vehicle Efficiency With Good-Ark

A lamp module that passes on the bench and fails after a year in service almost never failed because of the wrong diode symbol on the schematic. It failed because a part that was specified at 25 °C was never qualified for the temperature, the transients and the vibration the vehicle actually applies — which is why automotive lighting selection starts with the evidence pack, not the part number.

Last updated: October 11, 2026

Key Takeaways

Automotive lighting electronics have to do three jobs at once: switch current efficiently, control dimming, and survive transients on a bus that is never exactly 12 V.
Qualification follows the device family: AEC-Q101 covers discrete semiconductors such as rectifiers, Schottky diodes and TVS devices, while AEC-Q100 covers integrated circuits.
A lamp housing is thermally hostile. A diode that runs at 70 °C on a bench can sit at its junction limit in a sealed module at 105 °C ambient.
The protection plan comes before the part number: load dump, reverse battery, ESD and switching noise each want a different device.
What to request in writing: the qualification report for the exact part, the datasheet with derating curves, package and outline drawings, PPAP if you are in the automotive supply chain, and lot traceability.

What Automotive Lighting Demands From a Discrete Device

A discrete device in a lighting circuit is chosen by what it must survive, not by what it must do on a normal day. The electrical function — rectification, freewheeling, reverse blocking, clamping — is the easy half; the environment is what decides whether the part is acceptable.

The environment is a set of stresses applied over years rather than seconds. Temperature cycling as the lamp heats and cools; continuous vibration from the road; humidity and contamination; and a supply rail whose nominal value is only the middle of its range. A part that meets its datasheet limits on a bench at room temperature has proved very little about year five.

That is why the automotive world separates specification from qualification. A specification is a claim about behaviour under stated conditions. Qualification is evidence that a specific part, built on a specific process, still meets its specification after a defined stress programme. For discrete semiconductors that programme is AEC-Q101; the equivalent for integrated circuits is AEC-Q100, and for optoelectronic devices such as LEDs it is AEC-Q102. A supplier who can hand over the qualification report for the exact part number is answering the question. A supplier who can only say “automotive grade” is not.

Which Evidence Applies to Which Part

Match the requirement to the device family first, then ask for the matching document. The table below reflects the way component makers document this themselves — for example, the Diodes Incorporated datasheet for the 1N4001–1N4007 rectifier family states directly that automotive applications requiring specific change control need parts qualified to AEC-Q100/101/104/200, PPAP capable and manufactured in IATF 16949 certified facilities.

Requirement	Applies to	What it gives the buyer
AEC-Q101	Discrete semiconductors: rectifiers, Schottky diodes, TVS devices, MOSFETs	Stress qualification for the exact device family in a lighting circuit
AEC-Q100	Integrated circuits: driver ICs, controllers, sensor front ends	The IC-level equivalent of the same stress programme
AEC-Q102	Optoelectronic devices: LEDs and optical components	Qualification where the light source itself is a semiconductor
PPAP	Production parts in the automotive supply chain	The production-part approval package: design records, process flow, control plan, dimensional and material results
IATF 16949	The manufacturing site	Evidence that the process producing the part is itself controlled, not just the sample

The distinction matters commercially as much as technically. Two parts with identical datasheet numbers can differ in whether the qualification was run on the part you are buying, on the same die with a different package, or on nothing at all. The document set is what makes that difference visible before purchase instead of after a field return.

The Current Path: A Worked Thermal Example

Thermal margin, not current rating, is what eliminates a candidate part in a lighting module. The calculation below uses published datasheet maximums for a small dual Schottky device and a stated ambient, so the assumptions are visible and can be replaced with your own.

Assume a protection or steering diode in the control section of a lamp module carries 100 mA average, that the part sits in SOT-23 with the recommended pad layout, and that the module interior reaches 105 °C. Take the maximum forward drop for the family at that current, 900 mV, and the junction-to-ambient thermal resistance specified for SOT-23, 500 °C/W.

Conduction loss: P = 0.900 V × 0.100 A = 90 mW.
Junction rise: ΔT = 0.090 W × 500 °C/W = 45 °C.
Junction temperature at 105 °C ambient: approximately 150 °C — exactly the family’s maximum.

The conclusion is not that the part is bad; it is that this duty and this environment consume all of its margin at 100 mA. In the same module at 25 °C the junction would sit near 70 °C and the design would look comfortable. Two honest responses follow: move the current-carrying duty to a device with a better thermal path, or reduce the average current the diode sees. Note that this is a model built from datasheet maximums, not a measurement — the thermal resistance assumes the recommended copper area, and less copper runs hotter.

What the Vehicle Bus Does to the Entry Stage

Each disturbance on the supply has a different energy and duration, which is why one protection device rarely covers them all. Treat this as a checklist, and let the standards your programme follows set the severity levels.

Load dump. A long, high-energy overvoltage event. Handled by energy-absorbing devices — typically a TVS diode sized for the pulse, not by the rectifier in the power path.
Reverse battery. A DC condition rather than a pulse, and the reason a series blocking device or a polarity-protection arrangement appears at the entry stage.
ESD. Fast and low-energy; wants a fast clamp close to the connector or the sensitive pin.
Switching noise and conducted emissions. Not a fault at all, but the reason the freewheel path and the layout of the current loop matter for the module passing EMC rather than merely functioning.

The order of work matters here: define the threats the programme actually requires, then choose devices that answer them. A single TVS part number rarely satisfies load dump, ESD and reverse battery at once, and trying to make it do so is how modules acquire unexpected current paths.

The Documents to Request Before Approval

Convert “our quality is high” into a list of specific documents that can be asked for by name. For a discrete device in a lighting circuit, that list is short and concrete:

The AEC-Q101 qualification report for the exact part number, including the package variant.
The datasheet with its derating curves, not just the headline ratings, so thermal limits can be modelled for the lamp housing.
Package and outline drawings, to confirm footprint, height and clearance in a sealed module.
PPAP documentation and the site’s IATF 16949 certificate if the part is going into a production vehicle programme.
Lot traceability and a material declaration, so a change of source is visible rather than discovered.

Where a supplier cannot provide a document for the exact part, the honest answer is “available on request” or “not applicable to this family”. What should never happen is a certificate number or test result appearing in an article or a quotation without the underlying report existing.

FAQ

Which AEC-Q standard applies to a rectifier or TVS diode?

AEC-Q101, which covers discrete semiconductors. AEC-Q100 covers integrated circuits and AEC-Q102 covers optoelectronic devices such as LEDs, so a lighting module typically mixes at least two of the three families.

Is “automotive grade” the same as AEC-Q101 qualified?

No. “Automotive grade” is marketing language; AEC-Q101 qualification is a defined stress programme whose results are documented for a specific part. Ask for the report rather than the phrase.

Why does a diode pass bench testing and fail in the field?

Because bench testing is usually done at room temperature and in still air. A sealed lamp module at high ambient removes the air path that carried heat away, so the same conduction loss produces a much larger junction rise.

Can one protection device handle load dump, reverse battery and ESD?

Rarely, because the three events differ in energy and duration. Load dump is long and high-energy, reverse battery is a DC condition, and ESD is fast and low-energy; each is normally answered by a different device.

What should be in the approval package before design-in?

The qualification report for the exact part, derating curves, package and outline drawings, PPAP documentation and the manufacturing site’s quality certification, plus lot traceability and a material declaration.

Official Resources

References

Diodes Incorporated, 1N4001–1N4007 1.0 A Rectifier, DS28002 Rev 11–3 — source of the automotive qualification statement (AEC-Q100/101/104/200, PPAP capable, IATF 16949 certified facilities). diodes.com/assets/Datasheets/ds28002.pdf
STMicroelectronics, BAT54 — Small signal Schottky diodes, DocID5505 Rev 12 — source of the forward voltage, thermal resistance and current figures used in the worked example. st.com/resource/en/datasheet/bat54.pdf
AEC-Q101 — stress test qualification for discrete semiconductors, and AEC-Q100 / AEC-Q102 for integrated circuits and optoelectronics (standard designations; documents are distributed by the Automotive Electronics Council).
Nexperia, Automotive — product-family overview used to confirm which device classes are offered against automotive programmes. nexperia.com/applications/automotive

Continue through this engineering topic

For the complete selection, design, verification, and troubleshooting path, explore the Automotive Power Electronics Hub.