What is Best for LED Dimming:
Constant Voltage or Constant Current?

CV, CL, CC Methods of LED Dimming

ATX LED introduces: CL dimming

Background:
CV (Constant Voltage) uses resistors for dimming but wastes energy (about 20% at 24V) and causes brightness inconsistency due to voltage drop.

CC (Constant Current) is ideal for bare LEDs, ensuring consistent brightness and no energy loss.

CL (Constant Load) delivers stable current and high efficiency but may have inconsistent dimming performance below 10% brightness due to wire length.

CLS is a variant of CL for fixtures over 10W, providing reliable dimming with high efficiency.

DC/DC (The worst): DC/DC fixtures (e.g., Amazon 24V bulbs) require high startup current, waste energy, and are often undimmable.

MEPT

MPPT in solar optimizes power vs load; ATX LED applies a similar concept with MEPT for LED fixtures to maximize efficiency.

MEPT enables CL fixtures to achieve CC and CLS efficiency at up to 100W while tolerating voltage drop, allowing more fixtures to share fewer power supplies efficiently.

Topics:

  • PWM vs CCR (Lutron Application Note #250)
  • Bare LEDs with resistors
  • LEDs with DC/DC drivers are non-dimmable
  • 12V/24V constant voltage LED strips are inefficient
  • MEPT optimizes efficiency and safety
  • Surge current at power ON
  • Turn on delay

Lutron Report: Dimming LEDs via PWM and CCR

Reference: Lutron Application Note #250 (November 2014)

Overview

PWM rapidly switches LEDs on/off to simulate dimming, while CCR adjusts the current directly. CCR reduces flicker and is ideal for longer runs, while PWM is suitable for precise color control.

Definitions

  • PWM (Pulse Width Modulation): Switches LEDs rapidly for dimming.
  • CCR (Constant Current Reduction): Adjusts current to dim LEDs without switching.
ATX Comment: CCR minimizes EMI and simplifies installations.

Why use CCR?

CCR reduces visible flicker and EMI, making it ideal for most ATX LED applications and long wiring runs.

Applications Suitable for PWM

  • Color mixing and tunable white LEDs
  • Precise dimming curves
  • Applications without EMI constraints

Applications Suitable for CCR

  • High-efficiency, low EMI applications
  • Long wiring distances
  • Installations requiring low inrush current

Safety

CCR at LED voltage improves safety by limiting voltage and current, aligning with Class 2 standards.

Efficiency

CCR and flicker-free dimming allow lights to run efficiently at lower dimming levels, reducing energy use and allowing thinner wiring to save copper.

LED with Built-in Resistors

To be added, with photo.

Turn On Delay

To be added.

Surge Current

Un-dimmable LED