Single Event Latch-Up Protection Circuit for LCD Load Current Monitoring
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Solution Overview
Problem
Existing fault protection solutions fail to detect and protect load devices from single event latch-up (SEL) faults that occur within the normal operating current range, rendering devices like liquid crystal displays (LCDs) unusable due to fault currents that are not sufficiently detected.
Innovation Solution
A single event latch-up detection circuit that includes a first circuitry block to sense instantaneous load current, a second circuitry block to generate a latch-up trigger by comparing instantaneous and average load currents, and a supervisor module to generate an off command after a pre-programmed delay, ensuring power is removed from the load device to prevent damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current limiting solution is designed to trip at some amount of current margin over a maximum load current, then generalized fault protection is provided, but SEL faults with current within the normal operating range are not detected
Solution Approach 1:
The patent changes the detection parameter from absolute current threshold to current derivative (rate of change). By monitoring di/dt rather than absolute current value, the system can detect SEL faults even when the fault current remains within the normal operating range, thus resolving the contradiction between providing generalized fault protection and detecting SEL faults accurately.
Solution Approach 2:
The patent replaces the mechanical current threshold tripping mechanism with an electronic derivative detection system. Instead of using a fixed current margin trigger, the system uses electronic circuitry to calculate and compare current derivatives, enabling precise detection of SEL faults without sacrificing generalized fault protection capability.
2Object-affected harmful factors
If the current limiter trips at maximum load current, then protection from overcurrent is provided, but SEL faults occurring below maximum current are missed
Solution Approach 1:
The patent implements preliminary detection by monitoring the derivative of current before the actual fault condition develops. By detecting rapid changes in current (high di/dt) that precede or accompany SEL faults, the system can trigger protection actions earlier and more accurately, distinguishing SEL events from normal load variations within the operating current range.
3Device complexity
If a fixed threshold current protection is used, then simple implementation is achieved, but false tripping or missed detection occurs during normal load swings
Solution Approach 1:
The patent introduces dynamic detection by monitoring the rate of change of current (derivative) rather than using a fixed static threshold. This dynamic approach allows the protection circuit to adapt to varying load conditions automatically, distinguishing between normal load swings (low derivative) and actual SEL faults (high derivative), thereby maintaining reliability without significantly increasing circuit complexity.
Data Source
AI summary
Embodiments of a single event latch-up (SEL) protection circuit are provided, including: a first circuitry block coupled to a source of an input voltage a load, and digitally controlling a first switch; the first switch generates a load and senses an instantaneous load current iLoad. A second circuitry block is configured to generate an average iLoad and generate single event latch-up triggers (i.e., SEL fault detection) as a function of at least a comparison of the inst_iLoad and average iLoad; wherein this first circuitry block contains the analog based SET filtering needed to reduce false SEL triggers. A supervisor module generates on/off commands for the first switch, responsive to receiving the SEL detection in excess of a pre-programmed delay to provide the final SET filtering to prevent false SEL triggers. The first circuitry block removes the load voltage at N1 upon receiving an off command from the supervisor module.