Trailing Edge Dimming LED Light Source Circuit
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing LED light sources dimmed using trailing edge phase cut dimmers experience discontinuity and non-linearity in the relation between adjusted phase angle and light output, due to the impedance mismatch between the snubber capacitor and the LED load, leading to inefficient dimming curves.
Innovation Solution
A dimmable LED light source design that includes a rectifier, a converter circuit, and a dim circuit with specific capacitive and switching components to generate a dim signal that maintains continuity and linearity between the phase angle and light output, using a small capacitive means to ensure steep voltage drops and a bleeder to manage power supply and timing circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a trailing edge phase cut dimmer is used with an LED light source, then power consumption is reduced and dimming capability is achieved, but discontinuity and non-linearity occur in the relation between adjusted phase angle and light output
Solution Approach 1:
A bleeder circuit is introduced as an intermediary component between the rectifier and the LED driver. This bleeder actively discharges the hold-up capacitor at controlled timing, creating a steep voltage drop that serves as a reliable trigger for the dimming cycle. This intermediary mechanism ensures consistent dimming behavior regardless of the impedance mismatch between the snubber capacitor and LED load, thereby achieving linear and continuous dimming control while maintaining energy efficiency.
2Loss of energy
If the impedance of the LED load is much higher than the snubber capacitor, then LED efficiency is improved, but the dimming curve becomes discontinuous and non-linear
Solution Approach 1:
The bleeder circuit performs a preliminary action by actively discharging the hold-up capacitor at a predetermined timing point. This preliminary discharge creates a controlled steep voltage drop before the LED driver begins its switching operation. By preparing this voltage condition in advance, the system ensures that the dimming cycle starts reliably and continuously, overcoming the discontinuity caused by the high impedance mismatch between the LED load and snubber capacitor.
3Reliability
If a bleeder is added to charge the power supply and reset timing circuitry, then dimming reliability is improved, but device complexity increases
Solution Approach 1:
The bleeder circuit is designed to perform multiple functions simultaneously: it discharges the hold-up capacitor to create the steep voltage drop for dimming trigger, charges the power supply for the next cycle, and resets the timing circuitry. By consolidating these three functions into a single circuit block with shared components, the design achieves high dimming reliability without proportionally increasing device complexity. The bleeder shares the rectifier output connection and works cooperatively with existing dimmer components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a dimmable LED light source with continuous and linear control over light output in response to phase angle adjustments, avoiding discontinuities and non-linearities, ensuring efficient dimming performance.
Implementation Method 1
the phase cut sinusoidal supply voltage is rectified by means of a rectifier
Implementation Method 2
a series arrangement comprising a first unidirectional element and first capacitive means connecting the first and second output terminals of the rectifier
Implementation Method 3
a converter circuit, having input terminals coupled to respective sides of the first capacitive means and output terminals coupled to a LED load LED, for generating a current through the LED load LED, in dependence on a dim signal, out of a voltage present across the capacitive means
Implementation Method 4
a LED load LED
Implementation Method 5
generating a current through the LED load LED
Data Source
AI summary
Dimmable LED light source comprising: —a rectifier having rectifier input terminals for connection to respective output terminals of a phase cut dimmer of the trailing edge type, input terminals of the phase cut dimmer being connected to the mains supply, and having a first rectifier output terminal and a second rectifier output terminal, —a bleeder circuit connecting the rectifier output terminals, —a series arrangement comprising a first unidirectional element and first capacitive means connecting the rectifier output terminals, —a converter circuit, having input terminals coupled to respective sides of the first capacitive means and output terminals coupled to a LED load, for generating a current through the LED load, in dependence on a dim signal, out of a voltage present across the capacitive means, —a dim circuit for generating a dim signal as a function of the adjusted phase angle of the phase cut dimmer and for supplying the dim signal to a dim input of the converter circuit, —a series arrangement comprising a switching element and second capacitive means coupled between a terminal between the first unidirectional element and the second output terminal of the rectifier, —a control circuit for controlling the switching element in the conductive state when the voltage between the first and second output terminals of the rectifier drops below a first predetermined reference and for controlling the switching element in the non-conductive state when the voltage across the second capacitive means has reached a second predetermined reference, wherein the first capacitive means is dimensioned so that the voltage between the first and the second output terminal of the rectifier equals the sum of the voltage across the first capacitive means and the voltage across the first unidirectional means if the switching element is non-conductive.