LED Control Circuit Short Detection via PWM Signal Segmentation
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Solution Overview
Problem
Existing LED power control circuits with dimming functions have limited capability to detect short circuit conditions, as they can only accurately determine a short circuit when LEDs are at maximum brightness, leading to misjudgments under various dimming conditions.
Innovation Solution
A light emitting device control circuit and short detection circuit that includes sensing nodes, a signal comparison circuit, and a determining circuit to generate comparison signals and a short detection signal based on predetermined settings, allowing for accurate short circuit detection regardless of dimming conditions by counting the number of voltage signals higher than a reference signal between specific setting values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If PWM dimming function is implemented to adjust LED brightness, then lighting control flexibility is improved, but short circuit detection accuracy deteriorates due to voltage drop changes
Solution Approach 1:
The patent segments the detection process into multiple stages: during PWM high period, it detects voltage drops to identify short circuits; during PWM low period, it maintains detection readiness. This segmentation allows the system to distinguish between normal dimming operation and actual short circuit conditions by analyzing voltage characteristics at different times within the PWM cycle.
Solution Approach 2:
The patent performs preliminary detection actions during the PWM high period when voltage drops are most pronounced. By proactively detecting voltage characteristics during this phase, the system can identify potential short circuits before they cause damage, while the PWM low period allows the system to prepare for the next detection cycle without false positives from dimming operation.
2Reliability
If short circuit detection is performed during PWM low period to avoid false positives, then detection reliability is improved, but detection responsiveness deteriorates
Solution Approach 1:
The patent implements periodic detection during the PWM high period, leveraging the periodic nature of PWM operation. This allows the system to perform reliable detection at regular intervals when voltage characteristics are most indicative of short circuit conditions, while the periodic structure ensures consistent detection opportunities without requiring continuous monitoring that would increase false positives.
Solution Approach 2:
The patent maintains continuous detection capability by ensuring the detection circuit is active and ready during both PWM high and low periods, though actual measurement occurs primarily during the high period. This continuity ensures the system responds immediately to short circuit conditions without detection gaps, while the PWM low period serves as a transition state that maintains system readiness without requiring full measurement operation.
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
Enables reliable short circuit detection across various dimming conditions, preventing misjudgments and ensuring accurate identification of short circuits in LED arrays, even when LEDs are not at maximum brightness.
Implementation Method 1
generating a plurality of comparison signals according to the second terminal signals and at least one reference signal
Data Source
AI summary
A light emitting device control circuit controls a light emitting array which includes a plurality of light emitting device strings. Each light emitting device string includes a first terminal which is connected to a common node, a second terminal, and a plurality of light emitting devices connected in series. The light emitting device control circuit includes: a short detection circuit, coupled to the second terminals to receive second terminal signals from the second terminals, generating comparison signals according to whether the second terminal signals are higher than a reference signal, and generating a short detection signal according to whether a number of the comparison signals is between a first setting value and a second setting value.