Low-Side Laser Diode Drive Circuit with Short Protection
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Solution Overview
Problem
High-side laser diode driver systems are complex and costly, and when a ground short occurs, they continue to pump current, potentially damaging the diode array and increasing power dissipation, while low-side drivers lack protection against shorts.
Innovation Solution
A multi-stage laser drive circuit using low-side linear current sinks with a trickle current circuit and digital controller to monitor voltage and prevent current flow in case of shorts, and adaptive low drop-out regulation to maintain efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-side linear constant current sources are used to protect laser diode arrays from ground shorts, then laser diode protection is improved, but device complexity and cost increase significantly
Solution Approach 1:
The patent inverts the traditional high-side current source approach by using a low-side current sink configuration. Instead of placing the protection mechanism at the high potential side, the invention positions the constant current sink at the low potential side (ground reference), simplifying the overall circuit architecture while maintaining protection capabilities through voltage monitoring at the high-side terminal.
Solution Approach 2:
The patent introduces a voltage monitoring circuit as an intermediary mechanism. Rather than directly implementing complex protection logic in the current source, the invention uses a simple voltage sensor to detect ground shorts and triggers a protection response, decoupling the monitoring function from the current driving function and reducing overall system complexity.
2Reliability
If high-side current sources are used, then laser diode protection is improved, but power dissipation increases when ground short occurs near the top of the diode string
Solution Approach 1:
By inverting the protection architecture from high-side to low-side configuration, the patent ensures that the constant current sink remains referenced to ground potential. This inversion prevents the protection circuit itself from becoming a source of excessive power dissipation, as the low-side sink does not accumulate voltage stress even when shorts occur near the top of the diode string.
Solution Approach 2:
The patent extracts the voltage stress from the protection mechanism by separating the current monitoring function (performed at low potential by the current sink) from the voltage bearing function. This extraction allows the protection circuit to operate without承受ing the full voltage stress that would otherwise be imposed on a high-side current source during ground short conditions.
3Reliability
If high-side current sources are used, then laser diode protection is improved, but the system fails to detect ground shorts immediately continuing to pump current
Solution Approach 1:
The patent implements a feedback mechanism where the voltage monitoring circuit continuously senses the state of the laser diode array and provides real-time information to the control logic. When a ground short is detected through voltage level changes, the feedback signal immediately triggers a protection response, eliminating the detection delay inherent in high-side current source systems that lack direct failure sensing capabilities.
Data Source
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AI summary
A multi-stage laser drive circuit includes a variable common potential source (102), a PA light-emitting array (104) between a storage capacitor (CI) and a current node, first and second low-side linear current sinks (100A, 100B) in electrical communication with the current node, and a second master oscillator (MO) light-emitting array (112) in electrical communication between the current node and the first low side linear current sink. A trickle current circuit (120) drives a low-value trickle current through the arrays, and a sense circuit senses the trickle current. Also, the headroom voltage across a pass element in the first low-side linear constant current sink is monitored and adjusted for maximum efficiency.