Overcurrent Protection Circuit for Vehicle Laser Diodes
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Solution Overview
Problem
Vehicle lamps with semiconductor light sources, such as laser diodes, face challenges in overcurrent protection due to the inability to withstand excessive current, which can lead to reliability issues and safety concerns, especially when power source voltage fluctuations occur.
Innovation Solution
A lighting circuit with an overcurrent protection (OCP) circuit that includes a transistor, inductor, rectifier, and current sensor, where the transistor is switched ON/OFF based on current detection signals to prevent overcurrent, and a rectifier clamps counter electromotive force, ensuring high-speed protection and low power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of repair
If a connector connection point fluctuates between contact and non-contact states, then the laser diode can be replaced for maintainability, but charge stored in the output capacitor flows into the laser diode causing overcurrent
Solution Approach 1:
The patent introduces an overcurrent protection circuit as an intermediary component between the drive circuit and the laser diode. This OCP circuit includes a current sensor, comparator, and switching element that detects overcurrent conditions and interrupts the current path, thereby protecting the laser diode from damage during connector fluctuations while maintaining replaceability.
Solution Approach 2:
The overcurrent protection circuit performs preliminary detection of current levels before damage occurs. The current sensor continuously monitors the current flowing to the laser diode, and the comparator compares this against a predetermined threshold, enabling the switching element to preemptively interrupt the current path before overcurrent can damage the laser diode.
2Reliability
If the duty ratio is lowered immediately to keep drive current constant during power source voltage increase, then current stability is improved, but feedback loop delay causes switching at large duty ratio resulting in overcurrent
Solution Approach 1:
The overcurrent protection circuit performs preliminary detection of overcurrent conditions independent of the feedback loop. By directly sensing the current and comparing it against thresholds, the system can detect and respond to overcurrent conditions before the delayed feedback loop would otherwise cause damage, effectively compensating for the response delay.
Solution Approach 2:
The patent implements a dual feedback mechanism: the original feedback loop for duty ratio control and an additional fast feedback path through the current sensor and comparator in the OCP circuit. This secondary feedback path provides immediate response to current deviations, enabling faster correction than the primary feedback loop alone.
3Reliability
If a variable resistor transistor is used for overcurrent protection, then overcurrent suppression is achieved, but switching speed is insufficient and power loss increases
Solution Approach 1:
The patent employs a switching element that dynamically transitions between fully ON and fully OFF states based on real-time current detection. This dynamic switching behavior, controlled by the comparator output, enables the circuit to provide maximum protection when needed while minimizing power loss during normal operation, overcoming the limitations of fixed resistance approaches.
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 OCP circuit effectively suppresses overcurrents, ensuring the light source operates within safe current thresholds, even with delays in transistor switching, and prevents continuous overcurrent states, enhancing the reliability and safety of the vehicle lamp.
Implementation Method 1
a current sensor 32 that generates a current detection signal according to the lamp current
Implementation Method 2
an overcurrent protection circuit 30 that includes a transistor M31, an inductor L31, and a rectifier D31, wherein the transistor, the inductor and the rectifier are disposed in a T-shape
Data Source
AI summary
A lighting circuit for a light source includes a drive circuit and an overcurrent protection circuit. The drive circuit supplies power to the light source. The overcurrent protection circuit is inserted between the drive circuit and the light source. The overcurrent protection circuit restricts a lamp current flowing into the light source so that the lamp current does not exceed an overcurrent threshold value. The overcurrent protection circuit includes a transistor, an inductor, a rectifier, a current sensor and an overcurrent protection controller. The current sensor generates a current detection signal according to the lamp current. The overcurrent protection controller controls ON/OFF of the transistor based on the current detection signal and the overcurrent threshold value. The transistor, the inductor and the rectifier are disposed in a T-shape.