How to Code LED Arduino PWM Circuits for High-Power Mains Drivers

When you transition from blinking 5mm indicator LEDs to controlling high-power architectural lighting, writing analogWrite() is no longer enough. To successfully code LED Arduino projects for mains-voltage fixtures, you must bridge the gap between microcontroller logic and the electrical realities of capacitive LED drivers. This means matching PWM frequencies to avoid camera flicker, calculating inrush currents so you do not trip your panel breakers, and respecting the minimum load requirements of trailing-edge dimmers.

The direct answer for high-power control: use an Arduino to generate a 20kHz PWM signal (or a 0-10V analog signal via a DAC) to drive the dimming input of a constant-current LED driver like the Mean Well HLG series, rather than switching the AC mains directly with a relay or TRIAC.

Sizing the Driver and Calculating Circuit Impact

Before writing a single line of code, you must size your LED driver and calculate the circuit impact. High-power LEDs are rated in watts, but your electrical panel cares about Volt-Amps (VA) and inrush current. LED drivers contain large input capacitors. When you energize them, they draw a massive spike of current for a few milliseconds. If you put too many drivers on a single breaker, the cumulative inrush will trip a standard magnetic breaker instantly, even if the steady-state load is well under the limit.

The Math: A 200W LED array at a modern efficacy of 140 lumens per watt yields 28,000 lumens. However, the driver is not 100% efficient, and the Power Factor (PF) is typically 0.9 at full load. The apparent power drawn from the wall is 200W / 0.9 = 222 VA. According to the Mean Well HLG-240H datasheet, a 240W driver can pull up to 40A of inrush current at 230VAC on a cold start. A standard 16A Type B breaker will trip magnetically at 3x to 5x its rating (48A-80A). Therefore, you must use a Type C or Type D breaker, which has a higher magnetic trip threshold to tolerate capacitive inrush.

Dimmer Compatibility and PWM Coding Strategies

How you dim the fixture depends entirely on the driver interface and the number of fixtures on the circuit. Here is the decision framework for selecting the right dimming topology:

• 1 to 4 Fixtures (Mains Dimming): Use a trailing-edge (ELV) smart dimmer controlled by an Arduino via a smart switch API. Constraint: Trailing-edge dimmers require a minimum load to keep their internal MOSFETs biased. The Lutron LED Dimming Guide specifies a minimum of 10W for most ELV dimmers. If your Arduino switches a single 5W bulb, the dimmer will strobe. Fix: add a 10W bypass resistor in parallel.
• 5+ Fixtures or High-Power COBs (0-10V / PWM): Use a dedicated constant-current driver with a low-voltage dimming input. This bypasses mains-dimming min-load issues entirely and provides flicker-free control down to 1%.

Why Flicker Happens and the Code Fix

If you use the standard Arduino analogWrite() function on pins 3, 5, 6, 9, 10, or 11, the default PWM frequency is approximately 490Hz. While the human eye integrates this into a steady glow, digital camera shutters and peripheral vision will detect a severe strobe effect. This happens because the 490Hz refresh rate creates a beat frequency with the camera's rolling shutter.

The Fix: You must push the PWM frequency above 20kHz (ultrasonic) or drop it below 100Hz (where persistence of vision blends it, though this is bad for drivers). The 20kHz+ route is the industry standard for architectural lighting. On an Arduino Uno/Nano (ATmega328P), you can use the TimerOne library to reconfigure Timer1 (pins 9 and 10) to 20kHz.

#include <TimerOne.h>

const int pwmPin = 9; // Must be pin 9 or 10 for Timer1

void setup() {
  // Initialize Timer1 with a 50 microsecond period (20,000 Hz)
  Timer1.initialize(50); 
  
  // Set initial brightness to 50% (512 out of 1023)
  Timer1.pwm(pwmPin, 512); 
}

void loop() {
  // Smoothly fade the high-power LED driver
  for (int i = 0; i < 1024; i++) {
    Timer1.pwm(pwmPin, i);
    delay(5);
  }
}

If you are using an ESP32 instead of a classic AVR Arduino, the hardware is vastly superior for this task. The ESP32's LED Control (LEDC) peripheral natively supports high-frequency PWM without hogging CPU interrupts. You simply call ledcSetup(0, 20000, 8) to set channel 0 to 20kHz at 8-bit resolution.

Heat, Enclosures, and Hardware Interfacing

Code is only half the battle; the physical interface between your microcontroller and the high-voltage environment dictates long-term reliability.

Isolation and Signal Integrity

Never wire an Arduino GPIO pin directly to a 0-10V dimming input if the driver's ground is not perfectly isolated from the AC mains. A ground loop or a failed isolation barrier inside the driver will send 120V/230V straight into your microcontroller, instantly bricking it and creating a shock hazard. Use an optocoupler (like the PC817) for PWM signals, or an isolated DAC module (like the Adafruit MCP4725 with an I2C isolator) for 0-10V analog signals. Always tie the Arduino ground to the driver's DIM- terminal, but keep the AC Earth Ground strictly separate until the main panel.

Thermal Derating and Enclosure Constraints

High-power LEDs and their drivers generate significant heat. A 200W LED array at 30% efficiency still dumps 60W of heat into the heatsink. If you mount the LED driver inside a sealed IP65 wooden or plastic enclosure for a DIY smart light, the ambient temperature inside the box will quickly exceed the driver's 60°C rating.

When selecting an enclosure, prioritize aluminum extrusions with thermal pads for the LED COB (Chip-on-Board) arrays. For the driver, use an IP67-rated potted driver (like the Mean Well HLG series) mounted outside the sealed optical chamber, or ensure the enclosure has passive convection vents positioned at the bottom and top to create a chimney effect. Never bury a non-potted (IP20) driver like the LRS series in a location where condensation or humidity can bridge the high-voltage terminals to the low-voltage Arduino wiring.