Primary-side regulation of LED driver output current
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Solution Overview
Problem
Line-powered LED drivers with secondary-side current feedback schemes require additional components, increasing cost and reducing efficiency, while also compromising reliability due to the need for isolated feedback devices like optoisolators or transformers.
Innovation Solution
Implementing primary-side regulation of output current by using a controller and feedback network on the primary side of a transformer to adjust input current and maintain constant input power, eliminating the need for secondary-side components and improving efficiency and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If secondary-side current feedback scheme is used, then output current regulation is achieved, but component count and cost increase
Solution Approach 1:
The patent extracts the current regulation function from the secondary side and relocates it to the primary side. By measuring input voltage and current on the primary side and using these measurements to control the switching duty cycle, the design eliminates the need for secondary-side feedback components such as optoisolators or feedback transformers, thereby reducing component count while maintaining regulation capability
Solution Approach 2:
The patent introduces an intermediary control mechanism where the measured input voltage and current serve as intermediate signals. These intermediaries are processed through scaling and summation to generate a control signal that indirectly regulates output current without requiring direct secondary-side feedback, thus simplifying the overall feedback path
2Measurement precision
If isolated feedback devices are added, then current feedback accuracy is improved, but power consumption increases and efficiency decreases
Solution Approach 1:
The system uses the existing input voltage and current measurements already available on the primary side for its own control purposes. By deriving the control signal from these self-measured quantities rather than requiring additional isolated feedback devices, the design eliminates the extra power consumption that would be required by optoisolators or feedback transformers while maintaining adequate control accuracy
3Reliability
If secondary-side feedback components are used, then output current control is achieved, but circuit efficiency is reduced
Solution Approach 1:
The patent extracts the feedback function from the secondary side and implements it on the primary side using available measurements. This elimination of isolated feedback components removes their associated power losses, thereby improving overall circuit efficiency while maintaining output current control through primary-side measurement and control of the switching duty cycle
Solution Approach 2:
The patent changes the feedback parameter from secondary-side voltage/current measurements to primary-side input voltage and current measurements. By scaling and summing these primary-side parameters, the system achieves equivalent control effect without the power losses associated with isolated feedback devices, thus improving circuit efficiency
Data Source
AI summary
A line-powered LED driver is operable to provide primary-side regulation of output current supplied to LED circuitry. The circuit includes a feedback loop coupled to a power converter, wherein the feedback loop adds scaled input current to scaled input voltage to produce a control signal. The power converter is responsive to the control signal to adjust input current drawn by the power converter in response to changes in line voltage to provide constant input power. The power converter produces output power for supplying constant output current at the LEDs. The feedback loop may use a reference voltage derived from the LED circuitry so that the output power may be regulated to provide constant LED current for varying LED voltages. When compared to secondary-side current feedback schemes, the LED driver provides increased efficiency and reliability at a reduced cost by implementing primary-side regulation of the output current.