LED Power Driver

An LED Driver is an electronic device that regulates the power supplied to an LED module or array. Unlike traditional lamps that operate directly from the AC mains or a constant current source (like a CCR), LEDs require a precisely controlled current or voltage to operate efficiently and reliably. The LED driver converts the input power (which may be AC or DC, and may vary in voltage) into a stable, regulated output that matches the LED's requirements.

Key functions of an LED driver include:

• Current Regulation: Providing a constant current (e.g., 350 mA, 700 mA, 1 A) to the LED module, regardless of input voltage fluctuations or temperature changes.
• Voltage Regulation: Providing a constant voltage (e.g., 24 V, 48 V) when driving multiple LEDs in parallel.
• Protection: Incorporating over‑current, over‑voltage, short‑circuit, and thermal protection to prevent damage to the LEDs and the driver itself.
• Dimming Control: Supporting PWM (Pulse Width Modulation) or analogue dimming to adjust the brightness of the LED, often used in conjunction with the CCR's intensity steps.
• Power Factor Correction (PFC): Ensuring that the driver draws power efficiently from the mains, minimising harmonic distortion.

In AGL applications, LED drivers are typically potted or encapsulated to withstand moisture, vibration, and temperature extremes, and they are designed to meet the stringent reliability requirements of airfield lighting.

The LED driver's purpose is to bridge the gap between whatever power is actually available — mains AC, a CCR's stepped current, a DC supply — and the precisely regulated current an LED module needs to produce stable, compliant light output, a translation that has no equivalent requirement for a simple incandescent or halogen lamp. Because an unregulated or fluctuating current would cause an LED's brightness and colour to drift and could shorten its life dramatically, the driver's current-regulation feedback loop is what allows LED fixtures to actually achieve their advertised advantages of long life, colour stability, and low maintenance. Its protection circuitry serves the same purpose from a different angle, shielding the comparatively delicate LED module from the overvoltage and short-circuit events that a hardier halogen lamp would simply tolerate.

LED drivers are used in virtually all LED‑based AGL fixtures, including:

• Runway Edge Lights: Driving the LED arrays in elevated and inset runway edge lights.
• Runway Centreline Lights: Supplying power to the multi‑LED modules in centreline fixtures.
• Taxiway Edge and Centreline Lights: Providing regulated current to LED‑based taxiway guidance lights.
• Approach Lighting: Driving the high‑intensity LED arrays in approach light fixtures.
• Obstruction Lights: Powering the LEDs in obstruction warning beacons.
• Apron Floodlights: Supplying the high‑power LED modules used in apron lighting.
• PAPI and VASI Units: Driving the LED elements in visual approach slope indicators.

LED drivers are also used in:

• Retrofit Projects: When upgrading existing halogen or incandescent AGL fixtures to LED, the driver is an essential component of the conversion.
• New LED Fixtures: Integrated into the fixture housing or provided as a separate module.
• Maintenance and Repair: Replacing faulty drivers in the field to restore fixture operation.

The driver board mounts inside the fixture's base or lamp housing, positioned close to the LED PCB it feeds so the low-voltage DC leads stay short, with its own compartment or potting sealed against the same moisture and vibration environment as the rest of the fixture. Where the fixture is powered from a CCR series circuit, the driver's AC/series input terminates on the fixture's isolating transformer secondary rather than being wired directly to the field cable; where used in a mains-fed apron or building-mounted fixture, the driver's input wiring is kept on its own terminal block separate from the LED output leads. No separate field installation is required beyond what the host fixture's own housing and cabling already provide.

An LED driver typically operates through several stages:

• Input Stage: The driver accepts an input voltage, which may be from the AC mains (e.g., 230 V AC), from the AC output of a constant current regulator via the fixture's isolating transformer, or from a genuine DC source (e.g., a battery or DC bus in some retrofit designs). For AGL applications, drivers often accept a wide input range (e.g., 100–277 V AC) to accommodate varying supply conditions.
• Power Conversion (AC‑DC): If the input is AC, the driver rectifies it to DC and uses a switching converter (e.g., flyback, buck, boost) to produce a stable, isolated DC output. This stage also includes power factor correction to improve efficiency and reduce harmonic currents.
• Current/Voltage Regulation: The driver uses a feedback loop to maintain a constant output current (for series LED strings) or constant voltage (for parallel arrays). This is achieved using a controller IC that monitors the output and adjusts the switching duty cycle.
• Protection Circuits: The driver includes over‑voltage protection (OVP), over‑current protection (OCP), short‑circuit protection (SCP), and overtemperature protection (OTP). These safeguards shut down or limit the output to prevent damage.
• Dimming Interface: Many LED drivers support dimming via PWM (Pulse Width Modulation) or 0–10 V analogue signals. In AGL systems, dimming is often controlled by the CCR's current steps, which adjust the input voltage or current to the driver, or by a separate dimming bus.
• Output Connection: The driver's output is connected to the LED module(s) via wires or connectors. The output voltage and current are matched to the LED specifications.

In AGL fixtures, the driver is typically potted (encapsulated in resin) to provide environmental protection and thermal management. The driver may be integrated into the fixture's base or housed in a separate compartment.

The LED driver sits between the airfield's loop-level control decision and the physical LED module, converting a system-level command it doesn't originate into a locally-regulated output. In a conventional series-circuit fixture, the driver's input is the loop current the CCR is already regulating, set by the ALCMS's chosen step; in a mains- or DC-bus-fed installation, the driver's dimming interface receives that same step translated into a PWM or 0–10 V signal instead. Either way, the driver has no independent authority over brightness — it only ever converts and regulates toward whatever intensity the upstream control layer has already decided on, using its own fast internal feedback loop (constant current or constant voltage regulation via the controller IC) to hold that output steady regardless of variation in its input supply. Its protection circuits (OVP, OCP, SCP, OTP) operate autonomously at this local level: a fault trips the driver's own shutdown or current-limit response immediately, without waiting for or reporting through the ALCMS, which is why a fixture's failure is generally first visible to the wider control system only indirectly, as a loop voltage anomaly at the CCR rather than as a driver-level fault message. This layered structure — system-level step command, driver-level conversion and fast local regulation, module-level output — is what lets the same ALCMS command scale correctly across many different driver designs and LED module ratings across the airfield.

The driver is a compact power-conversion PCB — rectifier, PFC stage, switching regulator, and output filter built around a transformer or inductor core — typically 50–150mm long and 30–60mm wide, sized to fit inside the fixture housing alongside the LED array it feeds. For field fixtures the finished board is fully potted in epoxy resin inside its own small enclosure to reach an IP67/IP68 submersible rating and to isolate the primary and secondary sides to a 3kV standard, since a driver failure that bridges isolation is a safety fault, not just a lighting one. The potting also anchors the board against vibration from aircraft and vehicle traffic and conducts heat from the switching components out to the case, which is what the case-temperature-rated -40°C to +70°C operating range actually describes.