Open Loop LED Driver with Primary-Side Control
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Solution Overview
Problem
Existing LED drivers often rely on closed loop, constant current modes with isolated power converter topologies, which can be complex and inefficient, particularly in achieving active power factor correction and stable output current at varying input voltages.
Innovation Solution
An LED driver operating in an open loop mode with a power converter that maintains a substantially fixed frequency, using a controller to adjust the on-time of a switch based on current through an inductive element and rectified AC voltage, providing active power factor correction and stable output current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If closed loop constant current mode with isolated power converter topology is used, then stable output current is achieved, but device complexity and inefficiency increase
Solution Approach 1:
The patent removes the secondary-side current sensing and optocoupler feedback mechanisms from the traditional isolated power converter topology. By extracting these components, the system achieves simplified open-loop operation while maintaining stable output current through primary-side control methods, directly resolving the contradiction between stability and complexity
Solution Approach 2:
The controller on the primary side autonomously adjusts the switch on-time based on input voltage and inductor current to maintain stable output current without requiring feedback from the secondary side. This self-service control mechanism eliminates the need for complex closed-loop isolation circuits while ensuring reliable operation
2Reliability
If closed loop constant current mode is used, then stable output current is achieved, but active power factor correction efficiency decreases
Solution Approach 1:
The patent implements dynamic adjustment of the switch on-time based on real-time detection of input voltage and inductor current. This dynamic control allows the system to optimize power factor correction at each operating point, achieving high efficiency while maintaining stable output current through adaptive rather than static operation
Solution Approach 2:
The controller modifies the switch on-time parameter as a function of input voltage and inductor current to achieve both stable output current and high power factor correction efficiency. By changing the control parameter dynamically based on operating conditions, the system resolves the contradiction between stability and efficiency
3Reliability
If optocoupler-based feedback is used, then isolated power conversion is achieved, but device complexity and cost increase
Solution Approach 1:
The patent extracts and removes the optocoupler component from the power conversion system. By eliminating this isolated feedback component, the design achieves simpler architecture and lower cost while maintaining isolated power conversion through alternative primary-side control methods that do not require secondary-side sensing
Solution Approach 2:
The patent uses the inductor current as an intermediary parameter to indirectly control the output. Instead of directly sensing output current through optocouplers, the system uses inductor current information combined with input voltage to calculate and adjust the switch on-time, achieving control without the need for complex isolated feedback circuits
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
This approach allows for high power factor correction and stable output current across varying input voltages without the need for optocouplers, enhancing efficiency and simplifying the driver design.
Implementation Method 1
a power converter coupled between an input to receive a rectified AC voltage and an output for providing the output current to the LED
Implementation Method 2
The power converter includes a switch and an inductive element. The switch is coupled to the inductive element. The controller is configured to control an on time of the switch as a function of a current through the inductive element and the rectified AC voltage.
Data Source
AI summary
A method of operating an LED driver including a power converter to generate an output current for powering an LED and to provide active power factor correction is disclosed. The power converter is coupled between an input to receive a rectified AC voltage and an output for providing the output current to the LED. The method includes operating the power converter at a substantially fixed frequency in an open loop mode based on a current through the inductive element and the rectified AC voltage. LED drivers operable in accordance with the disclosed method are disclosed.