TRIAC Dimming for LED Drivers: What Must Match?

Identify leading-edge and trailing-edge controls

Phase-cut dimmers reduce the power delivered to a lamp or driver by switching off part of each mains half-cycle. Leading-edge dimmers, usually TRIAC-based, cut the start of each half-cycle; trailing-edge dimmers cut the end. A driver has to be documented for the type of dimmer in use, and many dimmable drivers are not dimmed through the mains at all but through a separate control input.

PCD-60 is the example used here because its PDF documents phase-cut dimming directly: it describes AC phase-cut dimming that works with leading edge and trailing edge TRIAC dimmers, with a constant current design. That statement belongs to PCD-60; it says nothing about other MEAN WELL families.

Check both driver and dimmer documentation

A compatibility check needs two documents. From the driver PDF, take the dimming method, the input voltage and frequency range, the output current and operating voltage range, and any list of tested dimmers. From the dimmer manual, take its edge type, its rated voltage and frequency, its minimum and maximum load and any LED-specific instructions.

PCD-60-1400B is rated at 1400mA and 60.2W with an operating voltage range of 25 ~ 43V, and the series accepts 180~295VAC. Its AC dimming page adds a dimmer compatibility chart that names specific models from LUTRON, JUNG, BERKER and CLIPSAL together with their rated voltages and frequencies, such as 277VAC / 60Hz or 220-240VAC / 50Hz, and gives a conduction angle of 30 degrees minimum and 180 degrees maximum.

• Driver: dimming method named in its PDF, input range, output current and operating voltage range
• Driver: tested-dimmer chart and conduction-angle limits, where listed
• Dimmer: leading or trailing edge, rated voltage and frequency
• Dimmer: minimum and maximum load with LED drivers, and LED-load guidance
• Site: mains voltage and frequency, and the number of drivers per dimmer

Explain why nominal wattage is not enough

A dimmer's load rating refers to what the dimmer sees, and with LEDs that is the driver's input rather than the LED wattage printed on a fixture. At full load, the typical 87% efficiency of PCD-60-1400B implies an input of about 60.2W / 0.87 = 69.2W per driver, and the input falls further as the light is dimmed.

Hypothetically, if a dimmer's manual stated a minimum load of 100W, one driver alone would sit below it even at full output, while two drivers, about 138.4W, would exceed it at full output yet could still fall below it when dimmed. Only the dimmer's own documentation settles its minimum and maximum load with LED drivers.

Current and voltage still have to match the LEDs, as for any constant-current driver. PCD-60 Note 2 suggests connecting the LEDs directly and states that it is not suitable for using additional drivers, and under direct driving its output voltage is clamped by the sum of the LED forward voltages.

Compare analog and phase-cut dimming

Analog dimming, such as 0-10V, PWM or resistance control, uses a separate low-voltage control input on the driver, while phase-cut dimming modulates the mains that feeds it. The two are not interchangeable: a driver documented only for a control input cannot be dimmed by cutting its mains, and PCD-60 shows only mains input leads and LED output leads, with no control terminals.

Phase-cut dimming also moves the driver away from the conditions under which its mains-side figures are stated. PCD-60 specifies THD< 20% when output loading is at least 60% at 230VAC, so deep dimming falls outside that condition. The analog dimming guide covers the control-input methods.

Investigate flicker and limited range

Flicker, a limited dimming range, or drivers that switch off at the bottom of the range have several possible causes. Check each one against both documents rather than treating one symptom as a diagnosis.

Change one thing at a time, keep the mains isolated while working on connections, and leave any rewiring to a qualified electrician.

• Dimmer not in the driver's compatibility chart, or used at a voltage or frequency other than the one listed
• Total driver input below the dimmer's minimum load, especially at low dim levels
• Conduction angle outside the driver's documented range; PCD-60 gives 30 degrees minimum
• LED forward voltage outside the driver's operating voltage range, such as 25 ~ 43V for PCD-60-1400B
• Edge setting of a universal dimmer not matching the configuration being tested
• Ambient temperature above the driver's working range; PCD-60 lists -30 ~ +45℃

Choose only verified configurations

Treat a configuration as verified only when the dimmer model appears in the driver's compatibility chart at the site voltage and frequency, the LED load sits inside the driver's operating voltage range at its rated current, and the dimmer's own minimum and maximum load are met. Anything else is a candidate that needs a test installation.

PCD-60 adds installation conditions of its own. Note 3 states that, to meet the latest ErP regulation for lighting fixtures, it can only be used behind a switch and not permanently connected to the mains, and its 180~295VAC input range does not include a 120VAC supply. Its chart includes dimmers rated for 277VAC / 60Hz and for 220-240VAC / 50Hz, so the site mains must match the listed dimmer rating as well.