LED Driver Open-Loop Current Control for Lower Conduction Loss
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Solution Overview
Problem
Conventional LED driving methods, particularly the linear driving method, face challenges with complex control mechanisms and high conduction losses due to the need for closed-loop feedback control to maintain constant current, which increases circuit complexity and reduces efficiency.
Innovation Solution
An open-loop control method is introduced for the power transistor in the LED driving circuit, where the instantaneous current is controlled based on the difference between the input voltage and the driving voltage, eliminating the need for error calculation and reducing conduction losses by varying the transistor current accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If linear driving method is used to drive LED load, then circuit cost is reduced by eliminating magnetic components, but control complexity increases due to requirement of closed-loop feedback control circuit
Solution Approach 1:
The patent extracts and eliminates the closed-loop feedback control mechanism from the linear driving circuit, replacing it with an open-loop control approach. By removing the feedback path that requires continuous error calculation and adjustment, the circuit maintains cost-effectiveness while reducing control complexity.
Solution Approach 2:
Instead of using the conventional approach of closed-loop feedback control where the system continuously measures output and adjusts input, the patent inverts the control strategy by using open-loop control where the input is predetermined based on input voltage conditions, eliminating the need for continuous feedback processing.
2Stability of the object's composition
If closed-loop feedback control is implemented to maintain constant current, then current stability is improved, but conduction loss increases due to continuous adjustment requirements
Solution Approach 1:
The patent applies preliminary action by pre-determining the drive signal characteristics based on the input voltage level before the control period begins. The control circuit identifies whether the input voltage is high or low at the start of each control period and selects the appropriate drive signal accordingly, eliminating the need for continuous feedback adjustments during conduction and reducing energy loss.
3Stability of the object's composition
If conventional linear driving method with closed-loop control is used, then constant current control is achieved, but control response time increases due to continuous error calculation
Solution Approach 1:
The patent implements periodic action by dividing the control into distinct control periods where the drive signal is updated at specific intervals based on input voltage conditions. Instead of continuous adjustment, the system periodically refreshes the drive signal, which reduces processing time while maintaining adequate current control for the LED load.
Data Source
Figure 1~2A
Figure 2B
Figure 3
AI summary
There are provided a driving method and a driving circuit for driving a light emitting diode (LED) load. In the driving method, an error between a real-time average current and a desired current is not required to be calculated. In a time period in which an input voltage is higher than a driving voltage, a real-time current flowing through a power transistor may have multiple different values depending on a difference between the input voltage and the driving voltage. In this way, the current flowing through the power transistor may be controlled to be small if the difference between the input voltage and the driving voltage is large, and the current flowing through the power transistor may be controlled to be large if the difference between the input voltage and the driving voltage is small, reducing a conduction loss of the power transistor, while causing the average current flowing through the LED load to meet a requirement for driving the LED load to emit a light having a desired brightness.