LED Dimming Circuit with Triac Simulation Load
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Solution Overview
Problem
Conventional AC dimmers are not suitable for LEDs due to issues like flicker, power factor reduction, voltage instability, and limited dimming range, as they are designed for AC-operated lamps and lack efficient control over LED intensity.
Innovation Solution
A method and circuit using a controllable DC voltage source independent of the AC dimmer output, powered by a separate source, and a controller responsive to the dimmer's firing angle to vary the DC voltage, ensuring continuous and flicker-free intensity control of LEDs over a full dimmer range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional AC dimmers are used with LEDs, then LED intensity control is achieved, but flicker occurs due to insufficient load on the triac
Solution Approach 1:
A triac simulation load circuit is introduced as an intermediary component that mimics the electrical characteristics of a conventional incandescent lamp. This load circuit is connected in parallel with the LED driver and actively draws current from the AC dimmer output, ensuring the triac always operates with sufficient load. The load circuit includes a rectifier bridge, filter capacitor, and controlled current draw mechanism that replicates resistive loading behavior, thereby preventing flicker while allowing genuine LED intensity control through PWM or other dimming methods.
2Ease of operation
If conventional AC dimmers are used with LEDs, then dimming function is achieved, but power factor falls to as low as 0.3
Solution Approach 1:
The triac simulation load circuit serves as a power factor correction intermediary by drawing current in a manner that improves the overall power factor of the system. The load circuit includes a rectifier and filter that create a more sinusoidal current draw pattern, reducing harmonic distortion and improving the displacement power factor. This allows the LED driver to operate with improved power factor while still responding to dimmer control signals for intensity adjustment.
Solution Approach 2:
The invention changes the electrical parameters of the system by introducing a load circuit that operates at different power consumption levels depending on the dimming state. When the dimmer is at full brightness, the load circuit draws minimal current; when dimming is applied, the load circuit increases its current draw to compensate for the reduced LED power consumption. This dynamic parameter adjustment maintains stable power factor across the entire dimming range.
3Ease of operation
If conventional AC dimmers are used with LEDs, then intensity adjustment is achieved, but voltage fluctuations from mains affect LED output stability
Solution Approach 1:
The triac simulation load circuit acts as a voltage stabilization intermediary by drawing current that compensates for mains voltage fluctuations. The load circuit includes a rectifier and filter capacitor that smooth out voltage variations, and its controlled current draw creates a stabilizing effect on the AC bus voltage. This intermediary circuit isolates the LED driver from direct exposure to mains voltage variations, allowing the LED output to remain stable despite input voltage fluctuations.
4Ease of operation
If conventional AC dimmers are used with LEDs, then dimming control is achieved, but high frequency harmonics from converter output are undesirable
Solution Approach 1:
The triac simulation load circuit serves as a harmonic filtering intermediary by providing a low-impedance path for high-frequency harmonics generated by the LED driver's switching converter. The load circuit includes a rectifier bridge and filter capacitor that effectively shunt switching frequency harmonics to ground, preventing them from propagating back through the AC dimmer and mains supply. This intermediary filtering action reduces electromagnetic interference and harmonic distortion while preserving the dimming control function.
Data Source
AI summary
A flicker-free method and a control circuit is used in conjunction with a conventional AC dimmer coupled to a main-AC supply to continuously control an intensity of a Light Emitting Diode (LED) over substantially a full range of the dimmer. The control circuit has a controllable source of DC voltage that is configured for coupling to at least one LED and that is powered independently of an output of the AC dimmer thereby isolating the LED voltage from the output of the AC dimmer; and a controller coupled to the source of DC voltage. The controller is powered independently of the output of the AC dimmer and is responsive to a firing angle of the AC dimmer for varying a level of the DC voltage as a function of said firing angle.