Light Emission Control Circuit Synchronizes Switching Elements
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Solution Overview
Problem
In light source apparatuses using both analog and digital light control, there is a power loss due to energy discharge from an inductor when switching elements operate independently, and insufficient current flow to light-emitting elements can result in reduced brightness, especially in projection-type video display devices.
Innovation Solution
A light emission control circuit that synchronizes the operation of switching elements to prevent energy discharge from the inductor and maintain adequate current flow by adjusting control signals based on the on-duty ratio of the digital light control signal, ensuring the second switching element is in an off-state during the first switching element's off-state and maintaining it in an on-state during necessary periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If both analog light control and digital light control are performed with independent switching elements, then light control flexibility is improved, but power loss increases due to energy discharge from inductor
Solution Approach 1:
The patent combines the control of two switching elements (first switching element for digital light control and second switching element for analog light control) into a unified control structure. The control circuit synchronizes both switching elements to operate together, merging their functions rather than operating independently. This integration ensures that when the first switching element is off, the second switching element is also prevented from discharging energy from the inductor, thereby reducing power loss while maintaining both digital and analog light control capabilities.
2Loss of energy
If the second switching element is maintained in off-state during the first switching element's off-state, then power loss is reduced, but current flow to light-emitting element may become insufficient
Solution Approach 1:
The patent implements dynamic control of the second switching element based on the operational state of the first switching element. The control circuit continuously adjusts the second switching element's state: keeping it off during the first switching element's off-state to prevent energy discharge and reduce power loss, while allowing it to operate normally during the first switching element's on-state to ensure adequate current flow to the light-emitting element. This dynamic adaptation resolves the contradiction between reducing power loss and maintaining current flow adequacy.
3Measurement precision
If the on-period of the first switching element is shorter than the essential on-period of the second switching element, then digital light control resolution is improved, but inductor energy accumulation becomes insufficient
Solution Approach 1:
The patent ensures continuous energy accumulation in the inductor by coordinating the operation of both switching elements. Even when the first switching element has a short on-period for high digital light control resolution, the control circuit ensures that the inductor receives continuous energy input through the second switching element's operation during the first switching element's off-state. This continuous action maintains sufficient energy accumulation in the inductor while preserving the high resolution of digital light control.
Data Source
AI summary
This light emission control circuit controls a first switching element for controlling a current that flows to a light-emitting element connected between a first node and one end of an inductor, and a second switching element for controlling a current that flows from the other end of the inductor to a second node. The light emission control circuit has a driving circuit that generates a first control signal for controlling the first switching element, and a switching control circuit that generate a second control signal for controlling the second switching element, and deactivates the second control signal in order to bring the second switching element into an off-state, during a period during which the first switching element is in an off-state.