Light Source Current Replica Circuit for Overcurrent Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for monitoring currents in light emitting elements, such as laser diodes, suffer from inaccuracies due to resistance variance in chip resistors and the potential for undetected current defects, which can lead to unexpected light emission or element failure.
Innovation Solution
A light source device with a first resistor and a second resistor connected in series, along with a first current source, measures voltages at specific connection points to accurately detect overcurrents using a comparator, ensuring precise detection regardless of resistor variations and power supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a detection resistor is inserted into the current path to monitor current, then current monitoring capability is achieved, but measurement precision deteriorates due to resistance variance in chip resistors
Solution Approach 1:
The patent creates a replica current path that copies the essential characteristics of the light emitting element circuit without containing the element itself. This replica path includes a replica resistor that mirrors the detection resistor, allowing current monitoring through voltage measurement on the copy rather than directly on the original current path, thereby avoiding the precision issues of chip resistors while maintaining monitoring capability
Solution Approach 2:
The patent introduces an intermediary measurement approach by measuring voltage across a replica resistor in a separate current path rather than directly measuring current or voltage in the original light emitting element path. This intermediary measurement point provides accurate overcurrent detection without the precision limitations of direct measurement using chip resistors
2Device complexity
If a replica current path is used to monitor current, then device complexity is reduced, but measurement precision deteriorates due to undetected current defects
Solution Approach 1:
The patent applies local quality by making the replica current path have specific characteristics that differ from the original path in controlled ways. The replica path includes a replica resistor with known, stable resistance characteristics, while the original path contains the light emitting element with its unique electrical characteristics. This localized differentiation allows the replica to serve as an accurate reference for detecting deviations in the original path
3Measurement precision
If a detection resistor with stable resistance is used, then measurement precision is improved, but device complexity increases due to additional components
Solution Approach 1:
The patent uses a replica resistor in a separate current path that copies the measurement function without requiring the detection resistor to be placed in the original high-current path. This allows the use of a stable, precision resistor in the replica path where it can operate at lower power levels, achieving high measurement precision without adding complex current-sensing circuitry to the main light emitting element path
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
Accurate detection of overcurrents prevents excessive light emission and potential element breakdown, enhancing safety and reliability in applications like ranging devices.
Implementation Method 1
a first resistor R1 that is connected to a given potential; a light emitting element 12 that is connected in series to the first resistor R1 and that is configured to be supplied with a given current IL and thus emit a given amount of light; a second resistor R2 that is connected to the given potential
Data Source
AI summary
Provided is a light source device that includes a first resistor connected to a given potential, a light emitting element connected in series to the first resistor and that is supplied with a given current and thus emit a given amount of light, and a second resistor connected to the given potential, The light source device further includes a first current source connected in series to the second resistor and that is supplied with a current, and a first voltage at a first connection part where the first resistor and the light emitting element are connected to each other and a second voltage at a second connection part where the second resistor and the first current source are connected to each other are taken out.