OLED Driver Dimming Control Using Ramped Pulsed Modulation
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Solution Overview
Problem
Large area solid-state lighting devices, such as OLEDs, face challenges with premature degradation and color shift due to high rates of current change during dimming, which affect their service lifetime and commercial viability.
Innovation Solution
A driver apparatus with a switch mode DC current source and a controller providing ramped pulse modulation control inputs to limit the rate of current change, ensuring controlled transitions between drive current levels, thereby mitigating premature lumen degradation and color shift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional dimming control is used with fast transitions between current levels, then dimming response time is improved, but lumen degradation and color shift occur due to high di/dt rates
Solution Approach 1:
The patent applies pulsed modulation with periodic on/off cycles to control OLED current levels. By using periodic action with controlled pulse widths and frequencies, the system achieves dimming functionality while allowing the OLED to fully turn off during off-cycles, preventing continuous stress and degradation that would occur with conventional linear dimming methods.
Solution Approach 2:
The patent changes the temporal parameters of current delivery by introducing controlled rise times (100 μs to 2 ms) and fall times (100 μs to 2 ms) for current transitions. This parameter modification limits di/dt rates during switching events, preventing the high rate current changes that cause lumen degradation and color shift while still enabling responsive dimming control.
2Manufacturing precision
If fast current transitions are used during dimming, then dimming control precision is improved, but flicker and premature degradation occur
Solution Approach 1:
The patent uses periodic pulsed modulation where the OLED is switched on and off in controlled cycles. This periodic action enables precise dimming control through pulse width modulation while ensuring complete current cessation during off-periods, preventing continuous low-level stress and eliminating the harmful effects of incomplete turn-off that cause flicker and degradation.
Solution Approach 2:
The patent modifies transition parameters by enforcing minimum rise times (100 μs to 2 ms) and fall times (100 μs to 2 ms) on current transitions. This parameter control limits the rate of current change (di/dt) during switching events, preventing the high rate transitions that cause flicker, lumen degradation, and color shift while maintaining precise dimming control through adjusted pulse widths.
3Stability of the object's composition
If continuous current is maintained during dimming, then color uniformity is preserved, but energy consumption increases and service life decreases
Solution Approach 1:
The patent implements periodic pulsed modulation where current is delivered in discrete on/off cycles rather than continuously. During off-cycles, the OLED receives zero current, allowing complete relaxation and preventing continuous electrochemical stress that degrades organic materials. This periodic operation reduces average power consumption while maintaining color uniformity through controlled pulse parameters that prevent degradation during on-cycles.
Solution Approach 2:
The patent changes the temporal delivery pattern of current from continuous to pulsed with controlled duty cycles. By adjusting pulse width, frequency, and transition times, the system optimizes the balance between maintaining sufficient current levels for color uniformity during on-periods and allowing complete current cessation during off-periods to reduce energy consumption and prevent degradation accumulation.
Data Source
AI summary
An electronic driver apparatus and methods are disclosed for driving power an organic LED or other large area solid state light source, in which a switch mode DC current source provides DC current to drive the light source according to a control input and a controller provides a ramped pulse modulated control input to the current source for at least some values of a dimming setpoint signal or value to mitigate damaging current spikes by controlling di/dt of the drive current.