Light Source Drive Circuit With Bias Current Against Undershoot
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Solution Overview
Problem
Undershoot during pulse oscillation of light-emitting elements in drive circuits leads to degradation of the elements and connected protecting elements, which is not effectively addressed in existing technologies.
Innovation Solution
A drive circuit incorporating a switching circuit and a direct current adjustment circuit to manage current levels, switching between emission and non-emission states, and supplying a bias current to mitigate undershoot effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pulse oscillation is applied to the light-emitting element, then productivity is improved through repeated emission and stoppage, but undershoot occurs causing degradation of the light-emitting element and protecting element
Solution Approach 1:
A bias current circuit is introduced to supply a preliminary bias current to the light-emitting element before the main drive current is applied. This preliminary action establishes a baseline current level that prevents the voltage and current from dropping below zero during pulse oscillation, thereby eliminating undershoot while maintaining high-speed switching capability for productive light emission.
2Ease of operation
If switching circuit is used to control pulse oscillation, then light emission control is improved, but voltage and current undershoot occur at falling edges
Solution Approach 1:
The bias current circuit acts as an intermediary between the power supply and the light-emitting element. It provides a continuous baseline current that mediates the transition during switching operations, preventing abrupt voltage and current drops at falling edges while still allowing the switching circuit to effectively control light emission timing and duration.
3Power
If high current is supplied for light emission, then output is improved, but degradation of elements accelerates due to undershoot
Solution Approach 1:
The bias current circuit implements preliminary anti-action by supplying a current in the opposite direction to the harmful undershoot effect. When the main drive current decreases or stops, the bias current prevents the total current from becoming negative, thereby counteracting the degradation mechanism while allowing high current operation for maximum light output during the emission phase.
Data Source
AI summary
A drive circuit that includes a switching circuit switching between a first state and a second state to cause a light-emitting element to perform pulse oscillation, and a direct current adjustment circuit. In the first state, light is emitted from a light-emitting element by supplying the light-emitting element with a current having a magnitude equal to or greater than a threshold current enabling the light-emitting element to emit light having an output equal to or greater than a predetermined output. In the second state, the magnitude of the current supplied to the light-emitting element is less than the threshold current. The direct current adjustment circuit supplies, to the light-emitting element, a bias current within a range less than the threshold current of the light-emitting element in the second state. The bias current has a magnitude corresponding to a magnitude of undershoot occurring at a falling edge of the pulse oscillation.