Laser Diode Drive Circuit with Switched Control Constants
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Solution Overview
Problem
Existing light-emitting element drive circuits experience unstable current control and oscillation when switching between high and low voltage sources, leading to inefficient current rise rates and potential oscillations in light-emitting elements like laser diodes.
Innovation Solution
A light-emitting element drive circuit with first and second DC power supplies, a switch element, a backflow prevention element, and a linear regulator, incorporating a drive unit with multiple control constants and a switch mechanism to stabilize current flow by selecting appropriate control settings based on voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a high-voltage source is used to increase the current rise rate immediately after the light-emitting element is turned on, then the current rise rate is improved, but the control becomes unstable causing oscillation of the current
Solution Approach 1:
The control constant is dynamically changed based on the operating state. Specifically, a first control constant is used during the current rise period to achieve rapid current increase, and a second control constant is used during the constant current period to maintain stable control. This dynamic adaptation of control parameters resolves the contradiction between fast response and stability.
Solution Approach 2:
The invention changes the control parameter (control constant) according to the operating conditions. By switching between different control constants based on whether the light-emitting element is in the current rise phase or constant current phase, the system achieves both rapid current rise and stable control without oscillation.
2Loss of energy
If the voltage of the constant-voltage source is set slightly higher than the forward voltage to reduce losses, then energy efficiency is improved, but the current rise becomes extremely slow due to wiring inductance
Solution Approach 1:
The invention applies a higher voltage than the forward voltage during the initial current rise period to overcome the wiring inductance and achieve rapid current increase. After the current reaches the desired level, the voltage is reduced to maintain stable operation. This preliminary high-voltage action resolves the contradiction between energy efficiency and fast current rise.
Data Source
AI summary
A light-emitting element drive circuit includes a boost voltage source that applies a first voltage to an LD, a main voltage source that applies a second voltage lower than the first voltage to the LD, a MOSFET that switches on and off the application of the first voltage to the LD, and a linear regulator that controls current flowing through the LD. The linear regulator includes a MOSFET through which the current flowing through the LD flows, and a drive unit that drives the MOSFET. The drive unit includes a gate drive circuit that drives the MOSFET, two or more constant circuits having mutually different control constants set, and a switch mechanism that selects one of the two or more constant circuits and connects the selected one to the gate drive circuit, according to whether a voltage applied to the LD is the first voltage or the second voltage.