LED Controllers – AC Phase-Cut / TRIAC Dimming

AC Phase-Cut / TRIAC System Architecture for LED Control

Standard

AC Phase-Cut / TRIAC LED controllers use phase-cut dimming to regulate the brightness of loads powered by 110–220 VAC. Originally developed for halogen and incandescent lamps, this principle is now widely applied to dimmable LED drivers and lamps thanks to circuits specifically designed for phase-control compatibility.

AC dimming works by “cutting” portions of the AC waveform to reduce the average power supplied to the load. Two main techniques are used:

  • Leading-edge (TRIAC): the dimmer blocks current at the beginning of each half-cycle; the most traditional method, common in residential applications.
  • Trailing-edge (electronic): current starts at the zero-crossing and is cut off before the end of the half-cycle; better suited for LED drivers, offering lower interference and higher efficiency.

System Architecture

  • AC Phase-Cut Dimmer / Controller: installed in series with the AC line, it regulates the conduction angle of the waveform.
  • AC Dimmable LED Driver: converts the modulated voltage into a regulated current to power LED modules or luminaires.
  • Dimmable LED Loads: strips, downlights, or lamps marked “AC dimmable” or “phase-cut compatible.”
  • Control Inputs: wall potentiometers, push-buttons, remotes, or smart interfaces such as DALI, RF, ZigBee, Z-Wave, Bluetooth, DMX, etc., or multi-protocol gateways.
  • Wiring: only line and neutral, with attention to EMI filtering and EMC compliance to prevent interference.

Advanced Features

  • Compatibility with existing installations: allows reuse of legacy dimmers with compatible LED drivers, without major rewiring.
  • Low infrastructure cost: requires no communication bus or additional control wiring.
  • Dimming range >5%: typical range 5–100%, depending on driver and connected load type.
  • Minimum load requirement: some dimmers require a minimum current to maintain stable operation.
  • EMI management: phase-cut modulation may cause interference; use filtered, EMC-certified drivers.
  • Dimming curve alignment: linear or logarithmic dimming perception depends on synchronization between dimmer and driver.
  • Push-input function: many models support push-button input for direct ON/OFF and brightness control.
  • Technical note: for multi-channel systems (CCT, RGB, RGBW, RGBWA), PWM dimming technology is recommended for higher precision and stability at low brightness levels.

Typical Applications

  • Residential and small offices: dimmable lighting control using TRIAC or electronic dimmers.
  • Retrofit installations: replacement of halogen lamps with LED while keeping existing AC dimmers.
  • Commercial and hospitality spaces: dimmable lighting for hotels, restaurants, shops, and shared areas.
  • Architectural lighting: ideal for simple setups compatible with standard dimmers.

Available Types

  • Single-channel (Dimmer 1 CH): for white or fixed-color LEDs (red, green, blue, amber, UV, etc.).
  • CCT (2 CH): dynamic warm/cool white adjustment with compatible drivers.
  • RGB / RGBW (3–4 CH): multi-channel configurations available in dedicated AC-dimmable versions.