Light Emission Control Circuit for Projection Displays
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Solution Overview
Problem
In projection type video display apparatuses using light source devices with both analog and digital dimming, there is a power loss due to energy accumulated in the inductor being released without being used for light emission, and insufficient current flow through the light emitting element, leading to inadequate brightness, especially when the ON duty ratio of the digital dimming signal is low.
Innovation Solution
A light emission control circuit that controls switching elements to maintain the second switching element in an ON state during short ON periods of the first switching element, and adjusts the ON duty ratio of the second control signal based on the ON duty ratio of the first control signal, ensuring energy is replenished in the inductor and preventing current flow below the instructed level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If both analog dimming and digital dimming circuits are operated independently, then dimming control flexibility is improved, but power loss increases due to energy release from inductor without light emission
Solution Approach 1:
The patent merges the control of analog and digital dimming circuits by making the second switching element (analog dimming) depend on the state of the first switching element (digital dimming). Specifically, the second switching element is controlled to be turned off when the first switching element is turned off, thereby combining their operations to prevent energy waste while maintaining dimming flexibility.
Solution Approach 2:
The patent applies preliminary action by proactively controlling the second switching element based on the predicted state of the first switching element. The control circuit prepares the second switching element to be turned off in advance when the first switching element is turned off, preventing the harmful energy release from the inductor before it occurs.
2Loss of energy
If the second switching element is kept OFF during the first switching element's OFF period, then power loss is reduced, but current flow through light emitting element becomes insufficient when digital dimming duty ratio is low
Solution Approach 1:
The patent applies local quality by differentiating the control strategy for the second switching element based on the specific operating conditions. When the first switching element's OFF period is short, the second switching element is kept ON to ensure sufficient current flow. When the OFF period is long, the second switching element is turned off to reduce power loss. This localized adaptation resolves the contradiction between energy efficiency and current sufficiency.
3Loss of energy
If the ON period of the second switching element is shortened to match short ON periods of the first switching element, then power efficiency is improved, but energy accumulation in inductor becomes insufficient
Solution Approach 1:
The patent applies dynamics by making the control strategy adaptive to varying operating conditions. The control circuit dynamically adjusts the behavior of the second switching element based on the duration of the first switching element's OFF period and the energy accumulation state of the inductor. This dynamic adjustment allows the system to optimize between power efficiency and energy accumulation in real-time.
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 configuration reduces power loss and ensures sufficient current flow through the light emitting element, maintaining adequate brightness by preventing energy release from the inductor and adjusting the second control signal's duration to match the first control signal's duty ratio.
Implementation Method 1
energy accumulated in the inductor is released without being used for light emission
Data Source
AI summary
A light emission control circuit includes a drive circuit that generates a first control signal in order to control a first switching element, and a switching control circuit that generates a second control signal in order to control a second switching element. The switching control circuit maintains the second control signal in an inactivation state in a period in which the first control signal is inactivated in a case where an ON duty ratio of the first control signal is equal to or more than a predetermined value, and maintains the second control signal in an activation state in a part of the period in which the first control signal is inactivated in a case where the ON duty ratio of the first control signal is less than the predetermined value.