LED Isolating Transformer

The LED Isolating Transformer is a variant of the standard AGL isolating transformer, purpose‑built for the unique electrical demands of LED lighting. While retaining the fundamental function of galvanic isolation and constant‑current transfer from the 6.6A (or 20A) primary series circuit, this transformer is optimised with design features that enhance compatibility with LED drivers, improve system efficiency, and address the specific power quality requirements of solid‑state lighting.

Key differentiators include:

• Optimised Secondary Voltage: Secondary voltages are often standardised to common LED driver input voltages (e.g., 12V, 24V, 48V AC) rather than traditional lamp voltages (6.82V, 9.85V). This reduces the rectification burden on the LED driver and minimises losses.
• Reduced Core Loss: Using high‑grade grain‑oriented steel with lower hysteresis and eddy‑current losses, the transformer exhibits higher efficiency, especially at low dimming currents, which is critical for LED systems that often operate at reduced brightness for extended periods.
• Superior Voltage Regulation: Tighter regulation (±3% vs. ±5%) ensures that the LED driver receives a stable input voltage across the entire current range, preventing flicker and colour shift.
• Lower Leakage Inductance: The winding design is optimised to minimise leakage inductance, reducing voltage spikes and electromagnetic interference (EMI) that can affect sensitive LED driver electronics.
• Thermal Management: With lower losses and improved heat dissipation, these transformers run cooler, contributing to the overall reliability of the LED system.

The transformer is fully encapsulated (IP68) and available in the same power ratings (15W to 100W) and installation types (buried, elevated, plug‑in) as conventional units, providing a seamless drop‑in replacement for legacy halogen systems when upgrading to LED.

The LED isolating transformer exists because pairing an LED driver with a conventional halogen-era transformer creates real compatibility problems: mismatched secondary voltages, looser regulation, and higher leakage inductance can all degrade the driver's performance or shorten its life, showing up as flicker, colour shift, or premature failure in a fixture that should otherwise be highly reliable. By tailoring the transformer's electrical characteristics to what an LED driver actually needs, this variant protects the reliability gains LED fixtures are supposed to deliver.

Because it's built as a drop-in replacement across the same power ratings and installation types as legacy transformers, it also serves a transition purpose — letting an airfield upgrade individual fixtures or whole circuits to LED without redesigning the underlying series-circuit infrastructure, so the safety and fault-tolerance benefits of the existing loop carry over unchanged.

This transformer is the ideal choice for any AGL installation using LED fixtures, including:

• Runway Lighting: LED edge lights, centreline lights, threshold lights, end lights, and touchdown zone lights on precision runways.
• Taxiway Lighting: LED edge lights, centreline lights, stop bars, clearance bars, and guidance signs.
• Approach Lighting Systems: ALSF‑1, ALSF‑2, MALSR, and other approach configurations upgraded to LED.
• Obstruction Lighting: Low‑, medium‑, and high‑intensity LED obstruction lights on structures of all heights.
• Illuminated Airfield Signs: LED‑lit mandatory instruction, information, and direction signs.
• Airport Beacons: LED rotating beacons and heliport beacons.
• Retrofit Projects: Replacing traditional halogen transformers with LED‑optimised units when upgrading legacy systems to LED.

The transformer is compatible with all major LED driver topologies (constant current, constant voltage, dimmable) and is designed to work seamlessly with the CCR dimming steps (2.8A to 6.6A or 6.6A to 20A), ensuring smooth brightness control without flicker or instability.

The LED-optimised transformer is installed in the same handhole, pit, or direct-buried enclosure as its halogen equivalent, adjacent to the fixture it feeds, so it can drop into an existing footprint during a retrofit without new civil works. The primary is spliced into the series loop with a standard L-823 connector, and the secondary is run to the LED fixture's driver input. Because LED drivers are more sensitive to waveform quality than halogen lamps, care is taken during installation to keep secondary cable runs within the manufacturer's specified length and to avoid shared enclosures with sources of electrical noise, ensuring the CCR's dimming steps translate into stable, flicker-free brightness at the fixture.

Like all AGL isolating transformers, the LED variant operates on the principle of electromagnetic induction. The primary winding is connected in series with the constant‑current loop, and the secondary winding delivers power to the LED driver. However, the design is refined to address the specific requirements of LED loads:

• Primary Side: Identical to standard transformers, with L‑823 or compatible connectors, rated for 6.6A (or 20A) primary current and designed to withstand the high transient voltages of the series loop.
• Secondary Side: The secondary winding is configured to provide a higher voltage (e.g., 12V, 24V, 48V) at the rated primary current. This allows the LED driver to operate at a higher input voltage, reducing I²R losses in the secondary cabling and improving overall efficiency.
• Core Design: The core is constructed from high‑permeability, low‑loss steel, often with thinner laminations to reduce eddy current losses at higher frequencies (some LED drivers use higher switching frequencies that may introduce harmonics).
• Winding Technique: Winding geometry is optimised to minimise leakage inductance and inter‑winding capacitance, reducing EMI and voltage ringing that can interfere with driver operation.
• Regulation Performance: The transformer maintains secondary voltage within ±3% of the nominal value across the full current range (2.8A to 6.6A), ensuring that the LED driver receives a stable input regardless of the selected brightness level.

The transformer is compatible with both leading‑edge and trailing‑edge dimming methods, and its low leakage inductance makes it particularly suitable for drivers with active power factor correction (PFC).

The LED-optimised transformer occupies the same position in the control chain as any other isolating transformer: an Airfield Lighting Control and Monitoring System (ALCMS) selects the required brightness step, the CCR regulates the whole loop to the corresponding fixed current, and the transformer has no addressable identity of its own — it converts whatever current the loop is carrying at that moment into the voltage its downstream load needs. The difference is what sits on the other side of that secondary winding: a halogen lamp draws current in rough proportion to voltage regardless of waveform quality, while an LED driver expects a stable, low-ripple supply to translate the CCR's discrete current steps into consistent, flicker-free brightness. This is why waveform quality, not just voltage level, becomes part of the transformer's job here — a unit that would pass a functional test into a resistive halogen load can still produce visible flicker or step-transition instability into an LED driver if its regulation isn't tight enough, which is the reasoning behind the secondary-side design refinements covered next.

Mechanically the LED-optimised transformer is built the same way as any potted AGL transformer — windings around a laminated core, fully encapsulated in epoxy or polyurethane for its IP68 rating — but the core and winding design inside that potting is refined for lower loss and tighter regulation: core loss is held to 0.5W or less at rated current and leakage inductance to within 5% of rated inductance, both tighter tolerances than a standard lamp-rated transformer needs, since they translate directly into the low-ripple secondary an LED driver requires. Insulation is specified to Class F or Class H depending on rating, and completed units weigh 1.5–4.0 kg depending on power option and whether the unit is potted for burial or housed for elevated mounting. Leads terminate in connectors sized for 12V, 24V, or 48V AC secondary outputs matched to common LED driver inputs, rather than the wider voltage range a halogen-compatible unit might offer.