Light Source Device Overcurrent Detection via Replica Circuit
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Solution Overview
Problem
Existing methods for monitoring currents in light emitting elements, such as laser diodes, face accuracy issues due to variable resistor values in chip-based detection systems and the possibility of undetecting defects in the current flowing into these elements.
Innovation Solution
A light source device with a first resistor connected to a given potential, a light emitting element in series with the first resistor, a second resistor connected to the same potential, and a first current source in series with the second resistor, allowing for the measurement of voltages at specific connection points to accurately determine if an overcurrent is supplied to the light emitting element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a detection resistor is inserted into a current path to monitor current, then current monitoring capability is improved, but measurement precision deteriorates because the resistance of chip-based resistors varies widely
Solution Approach 1:
The patent creates a replica circuit that copies the essential characteristics of the main current path without using a detection resistor. The replica current source (205) generates a copy current (Ic) that flows through a replica path with identical resistance characteristics to the main path, allowing voltage measurement to reflect the actual current without introducing resistance variation errors
Solution Approach 2:
The patent introduces a replica path as an intermediary system that indirectly measures the main current characteristics. Instead of directly measuring voltage across a resistor in the main path (which introduces errors), the measurement is performed on a separate replica path that mirrors the electrical characteristics, serving as an intermediary measurement system
2Ease of operation
If a replica current is monitored to infer the current flowing into a light emitting element, then monitoring is simplified, but reliability deteriorates because defects in the current flowing into the light emitting element cannot be detected
Solution Approach 1:
The patent segments the monitoring function into two independent parts: the main current path that supplies current to the light emitting element, and a separate replica path that mirrors the electrical characteristics. This segmentation allows the replica path to be monitored for defects while the main path continues to operate, enabling defect detection without interfering with the primary function
Solution Approach 2:
The patent implements feedback by comparing the voltage measured in the replica path against expected values to detect defects. The control unit continuously monitors the replica voltage and can identify abnormalities in the current supply path, providing feedback about the health of the current delivery system to the light emitting element
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 enables more accurate detection of overcurrents in light emitting elements, preventing damage and ensuring reliable operation in applications like ranging devices and vehicle control systems.
Implementation Method 1
a first voltage is taken out from a first connection part where the first resistor and the light emitting element are connected to each other and a second voltage is taken out from a second connection part where the second resistor and the first current source are connected to each other
Data Source
AI summary
A light source device that includes a first resistor that is connected to a given potential, a light emitting element that is connected in series to the first resistor, a second resistor that is connected to the given potential, and a first current source that is connected in series to the second resistor and that is configured to supply a freely-selected current within a given range are included. A first voltage is taken out from a first connection part where the first resistor and the light emitting element are connected to each other and a second voltage is taken out from a second connection part where the second resistor and the first current source are connected to each other.