LED Driver Circuit Stabilizing Luminance During PWM Soft-Start
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Solution Overview
Problem
In light emitting element driving systems, the combination of PWM and Soft-Start operations often results in unstable LED lighting due to a short time period for maintaining the second current value during the ON-period, especially when the duty cycle is set to a relatively short time, leading to fluctuations in current supply and reduced luminance stability.
Innovation Solution
A light emitting element driving apparatus that includes parameter adjusting means to set the second constant current value higher than the minimum stable range and duty cycle adjusting means to extend the ON-period, ensuring the second current value is maintained for a longer duration than the transition period, thereby stabilizing the light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If PWM driving technique is used with a short duty cycle to achieve fast response and energy efficiency, then productivity and energy efficiency are improved, but the time period for maintaining the second current value becomes extremely short causing lighting instability
Solution Approach 1:
The patent applies preliminary action by extending the ON-period duration before the current reaches the second value, and by maintaining the second current value for a sufficient period. This ensures that the LED receives adequate current exposure time even during short duty cycles, preventing lighting instability while maintaining fast response capabilities.
2Reliability
If Soft-Start driving operation is implemented to prevent inrush current and protect the circuit, then reliability is improved, but the transition period reduces the time available for stable light emission
Solution Approach 1:
The patent applies dynamics by making the ON-period adjustable and extendable beyond the fixed transition period. The control circuit dynamically extends the ON-period duration to compensate for the transition period consumed by Soft-Start, ensuring that the remaining time for stable light emission is sufficient even when circuit protection measures are in place.
3Use of energy by moving object
If the second current value is set to the minimum stable range to reduce power consumption, then energy efficiency is improved, but current fluctuations increase due to environmental temperature changes
Solution Approach 1:
The patent applies preliminary action by extending the ON-period duration to compensate for the increased sensitivity of low current values to temperature fluctuations. This extended duration allows the LED to accumulate sufficient light output despite the instability, while the parameter adjusting means optimizes the balance between power consumption and current stability.
Data Source
AI summary
A light emitting element driving apparatus for driving a light emitting element, includes driving means for a executing PWM driving operation to drive the light emitting element at a predetermined duty cycle and for executing a soft-start driving operation during each ON-period in the PWM driving operation. During the soft-start driving operation, a current value of current supplied to the light emitting element is increased from a first constant current value up to a second constant current value. The driving apparatus includes parameter adjusting means for controlling the driving means such that the second constant current value is supplied to the light emitting element for a period that is longer than a period from a beginning of the ON-period to a time at which the current value of the current supplied to the light emitting element reaches the second constant current value.