Laser Diode Lighting Circuit With Startup Shunt Voltage Control
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Solution Overview
Problem
Semiconductor laser diodes in lighting applications are prone to catastrophic optical damage (COD) due to overheating and surge damage, and current control methods for bundled laser diode packs are inadequate in managing voltage division and protecting individual diodes from overvoltage and thermal issues.
Innovation Solution
A lighting circuit with a current driver circuit, series connection of laser diodes, and a current shunt circuit in parallel with each diode, controlled to manage the rate of change of voltage during startup and reduce the risk of COD, using either local or centralized control to synchronize lasing and balance voltage division.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple laser diodes are bundled in series connection to achieve high light flux, then the overall light output is improved, but the voltage division between individual diodes becomes uncontrollable and susceptible to surges
Solution Approach 1:
The patent divides the single current driver into multiple independent current drivers, each controlling a subset of laser diodes. This segmentation allows individual control of voltage and current to each diode or diode group, preventing uncontrolled voltage division and surge propagation throughout the entire string while maintaining high light flux output from all diodes operating in series.
2Use of energy by moving object
If laser diodes are operated near nominal power to maximize efficiency, then energy efficiency is improved, but the headroom for overheating effects is reduced and susceptibility to COD increases
Solution Approach 1:
The patent implements protection circuits including current limiting mechanisms and thermal monitoring that activate before catastrophic optical damage can occur. These protective measures create a safety buffer or 'cushion' that prevents the laser diodes from entering the dangerous overheating regime even when operated near nominal power, allowing efficient operation while mitigating COD risk through preemptive protection.
3Device complexity
If a single shared driver is used to power the laser diode bank to simplify the circuit, then device complexity is reduced, but individual diode protection and control capability is lost
Solution Approach 1:
The patent segments the single shared driver into multiple independent current drivers, with each driver controlling a specific subset of laser diodes. This segmentation enables individual diode protection and control while keeping each driver module relatively simple in design, balancing the trade-off between circuit complexity and reliability through modular architecture.
4Speed
If high switching speeds are used to improve response time, then speed is improved, but stray inductances and capacitances severely influence voltage division and can cause ringing
Solution Approach 1:
The patent incorporates damping elements and carefully designed PCB trace geometries that preemptively compensate for the effects of stray inductance and capacitance before they can cause harmful ringing or voltage division instability. The circuit layout and component placement are optimized in advance to minimize parasitic effects, allowing high switching speeds to be achieved while maintaining voltage division stability.
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
The solution effectively reduces the risk of COD by controlling current transients and voltage changes, allowing for synchronized lasing and efficient power management, eliminating the need for current binning and enabling lower-cost, high-efficiency laser lighting circuits.
Implementation Method 1
A lighting circuit with a current driver circuit, series connection of laser diodes, and a current shunt circuit in parallel with each diode, controlled to manage the rate of change of voltage during startup
Implementation Method 2
Semiconductor laser diodes in lighting applications
Implementation Method 3
They typically employ a blue laser diode combined with a phosphor converter adding yellow components to the blue laser light resulting in a white light
Implementation Method 4
when lasing increases, the increase in photons leads to heating of the crystal in the area of the mirroring facet. This increases the local temperature, which itself results in an increase in lasing. This positive feedback loop very quickly results in local overheating, causing cracks in the crystal
Data Source
Figure 1
Figure 2~3
AI summary
A lighting circuit comprises a current driver circuit and a series connection of at least two laser diodes, supplied with current from the current driver circuit. A current shunt circuit is in parallel with each laser diode for diverting a shunt current away from the respective laser diode. The level of the shunt currents is controlled during a start-up period of time of the current driver circuit in order to control the rate of change of voltage across selected laser diodes during said start-up period of time.