2026-09-09

What Is an LED Driver? How It Works and How to Choose One

Q: What happens if the driver is under-powered?

With constant current drivers, an undersized part cannot reach the required string voltage and will shut down, cycle, or run hot at its limit. Size for the actual forward voltage at operating temperature, not the room-temperature datasheet figure.

LED DriversFundamentalsGuide

An LED driver is the power supply that turns mains electricity into the form an LED can actually use, and then holds it there. It is the single component that decides how long a luminaire lasts, how steadily it dims, and whether it flickers on camera. This guide explains what drivers do, the specifications that actually matter, and how to pick one.

Why an LED cannot run on mains power

An LED is a current-driven device. Its forward voltage (V_f) is a property of the semiconductor die, and it moves with temperature, with manufacturing bin and from unit to unit. Apply a fixed voltage and the current is set by whatever the die happens to do at that moment — and because LED forward voltage falls as the junction heats, current rises, which heats the junction further. Left unchecked that loop is thermal runaway.

Mains is also the wrong shape entirely: 120/230 V AC, whereas a single LED die wants roughly 2.8–3.6 V DC. Something has to convert one to the other and then regulate it. That something is the driver.

What the driver actually does

Beyond conversion and regulation, a modern LED driver is the protection layer of the luminaire:

Conversion — rectify and switch the mains down to a low DC voltage, with power-factor correction so the fixture does not distort the building's supply.
Regulation — hold output current (or voltage) constant as mains, temperature and LED characteristics move.
Protection — over-voltage, over-current, short-circuit and over-temperature shutdown, plus surge absorption on the mains side.
Control interface — accepting a dimming signal: 0–10 V, 1–10 V, PWM, resistance, DALI, or a wireless node.

Constant current or constant voltage

Drivers regulate either current or voltage, and the choice follows the LED assembly. Luminaires built from LED boards or COBs with no onboard current limiting need a constant current driver. Products with built-in resistors or a driver-on-board — strips, modules, signage — need a constant voltage driver, usually 12 V, 24 V or 48 V. See our dedicated comparison: Constant Current vs Constant Voltage LED Drivers.

The specifications that decide the outcome

Output current and voltage window — for constant current drivers, the current (350 mA, 700 mA, 1050 mA…) plus the voltage range it can reach. The LED string's total V_f must sit inside that window.
Wattage and headroom — loading a driver at 100% of nameplate shortens its life. Sizing at 80–90% is standard practice.
Efficiency — every point lost is heat inside the housing, and heat is what kills electrolytic capacitors.
Power factor and THD — PF > 0.9 and low total harmonic distortion are usually a compliance requirement, not a nice-to-have.
Dimming range and flicker — a driver that dims to 1% but flickers at 10% is useless in a camera-facing or office application. Ask for percent-flicker data across the range.
IP rating — IP20 for indoor enclosed fixtures; IP65–IP67 where water, dust or wash-down is in play. Read the rating properly: Choosing an IP67 LED Driver.
t_c point and lifetime — the declared case temperature at which the rated hours apply. A 50,000-hour driver rated at t_c 75 ℃ will not deliver 50,000 hours at t_c 90 ℃.
Surge protection — for outdoor and industrial sites, check the differential and common-mode ratings and add an SPD where the risk justifies it.

How to choose one: a five-step check

Establish the LED load: number of LEDs, their V_f at operating temperature, and drive current.
Decide constant current or constant voltage from the LED assembly, not from habit.
Sum the string voltage, add 10–20% headroom, and pick the current that matches the design flux.
Confirm the dimming protocol the project uses — and the range, not just the interface.
Check the environment: ambient temperature, IP rating, surge exposure, and the t_c the housing can actually hold.

Frequently Asked Questions

Is an LED driver the same as a power supply?

It is a power supply, but a regulated one built for LED loads. A general-purpose switching supply holds a fixed voltage; an LED driver holds current constant (or a voltage designed for LED modules) and adds LED-specific protection, dimming control and thermal behaviour.

Can I use a higher-current driver than the LED needs?

No, unless it is an adjustable driver set to the correct current. A 1050 mA driver feeding a 700 mA LED board will overdrive it. Adjustable drivers with NFC or DIP-switch current selection exist precisely to avoid stocking one part number per current.

What happens if the driver is under-powered?

With constant current drivers, an undersized part simply cannot reach the required string voltage and will either shut down, cycle, or run hot at its limit. Size for the actual V_f at operating temperature, not the room-temperature datasheet figure.

Why do identical-looking drivers differ so much in price?

Mostly capacitor grade, thermal design and claimed lifetime. A driver rated 50,000 hours at t_c 90 ℃ with genuine long-life electrolytics costs more than one rated 25,000 hours at t_c 70 ℃ — and the difference shows up after year three, not on day one.