LED Driver Circuit Dimming Control via Current Sensing
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Solution Overview
Problem
Existing LED lighting systems using AC/DC constant voltage converters struggle to implement dimming effectively, as they maintain constant DC output voltage during dimming, leading to increased current draw and potential damage to dimming controllers.
Innovation Solution
A method and system that provide a dimming control signal directly to the downstream DC/DC converter, bypassing the AC/DC constant voltage converter, allowing for precise control of the DC output current and limiting current draw during dimming, using a dimming detection circuit to track variations from the dimming controller and adjust the dimming control signal accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an AC/DC constant voltage converter is used to drive LED arrays, then the converter topology is familiar and well-understood with accommodating design and lower cost, but the converter cannot readily provide dimming and will try to maintain constant DC output voltage during dimming, causing increased current draw that may exceed the dimming controller current rating and potentially damage the controller
Solution Approach 1:
The patent introduces a current sensing resistor as an intermediary element between the AC/DC constant voltage converter and the LED arrays. This resistor senses the current flowing to the LED arrays and generates a voltage signal proportional to the current. This intermediary sensing mechanism allows the system to monitor and control current without requiring the AC/DC converter itself to have current regulation capability, thus maintaining the familiar constant voltage topology while enabling safe dimming operation.
Solution Approach 2:
The patent implements a feedback control mechanism where the voltage signal from the current sensing resistor is fed back to the dimming controller. The dimming controller uses this feedback signal to adjust the dimming output accordingly, preventing excessive current draw during dimming operations. This feedback loop enables the system to maintain current within safe limits while preserving the benefits of using a familiar AC/DC constant voltage converter topology.
2Device complexity
If an AC/DC constant voltage converter is used, then the design is simpler and more cost-effective, but the converter will draw more current from the dimming controller during dimming to offset the decrease in AC output, potentially exceeding current ratings
Solution Approach 1:
The current sensing resistor serves as an intermediary that enables precise measurement of actual current consumption. By monitoring the voltage across this resistor, the system can detect when current draw approaches dangerous levels and adjust dimming output accordingly, preventing the AC/DC converter from drawing excessive current during dimming operations.
Solution Approach 2:
The feedback mechanism using the current sensing resistor voltage signal allows the dimming controller to dynamically adjust its output to prevent excessive current draw. When the sensed current approaches the maximum rating, the feedback signal triggers the dimming controller to reduce its output, thereby limiting current consumption and preventing damage while maintaining design simplicity.
3Stability of the object's composition
If the AC/DC constant voltage converter maintains constant DC output voltage during dimming, then the voltage regulation is stable, but the LED arrays do not dim and the converter draws more current to compensate for decreased AC output
Solution Approach 1:
The patent employs feedback control where the voltage signal from the current sensing resistor is used to modulate the dimming controller output. When current approaches maximum levels, the feedback signal automatically reduces the dimming controller's AC output, which in turn allows the DC output voltage to decrease proportionally. This enables the LED arrays to dim effectively while preventing excessive current draw, resolving the contradiction between voltage stability and dimming effectiveness.
Solution Approach 2:
The system transitions from a static constant voltage regulation mode to a dynamic control mode during dimming operations. The feedback mechanism enables the DC output voltage to dynamically adjust based on actual current consumption, allowing the system to maintain voltage stability under normal operation while enabling effective dimming when required, thus adapting to different operational requirements.
Data Source
AI summary
An LED driver circuit provides dimming control in LED lighting applications that can accommodate an AC/DC constant voltage converter. The driver circuit provides a dimming control signal that is used to directly control the DC output current of a downstream DC/DC converter driving an LED array. The dimming control signal tracks the AC or DC output from a dimming controller such that variations in the AC or DC voltage are reflected in the dimming control signal. This dimming control signal is then provided to the downstream DC/DC converter, bypassing the AC/DC constant voltage converter to directly control dimming of the LED array. Such an arrangement lets lighting design engineers deploy the familiar and well-understood constant voltage converter topology in LED lighting applications while retaining the ability to control dimming in the LED lighting applications.