Overcurrent Detection Circuit Using Clock Timing for Capacitive Loads
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Solution Overview
Problem
Existing overcurrent detection circuits for capacitance loads in liquid crystal display panels struggle to accurately detect overcurrent due to variations in the time constant of RC filters, leading to inconsistent detection of abnormalities.
Innovation Solution
An overcurrent detection circuit that includes a clock signal generation unit, a comparator, and a determination unit, which compares the drain-source voltage of MOS transistors with a reference voltage at specific timing points, using a clock signal to count cycles during charging and discharging periods, allowing for more accurate determination of overcurrent based on threshold values or ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an RC filter is used to discriminate between charge/discharge current and overcurrent, then the detection circuit can identify abnormality, but the detection accuracy deteriorates due to time constant variations
Solution Approach 1:
The patent changes the detection parameter from voltage-based (comparing VDS with VREF at a fixed time point determined by RC time constant) to frequency-based (counting clock cycles during the mask period). This parameter change eliminates sensitivity to RC time constant variations, as the clock frequency is stable and the mask period is determined by fixed-frequency clock cycles rather than RC charging/discharging time constants.
Solution Approach 2:
The patent replaces the passive RC filter-based time delay mechanism with an active clock signal-based timing mechanism. Instead of relying on the RC circuit's natural charging/discharging time constant to define the mask period, the invention uses a clock signal with fixed frequency to generate precise timing intervals, substituting the mechanical/electrical RC timing system with a more stable frequency-based timing system.
2Reliability
If the mask period is determined by RC filter time constant, then the circuit can filter out charging current, but detection consistency deteriorates due to capacitance value changes
Solution Approach 1:
The patent changes the timing reference from RC time constant (which varies with capacitance) to fixed-frequency clock cycles. The mask period is now defined by a predetermined number of clock cycles rather than by the RC charging time, making the detection consistent regardless of capacitance value changes in the load.
Solution Approach 2:
The patent segments the detection period into discrete clock cycles, counting the number of clock periods within the mask period. This segmentation into fixed-time intervals based on clock cycles allows for precise and consistent timing measurement that is independent of RC circuit variations.
Data Source
AI summary
An overcurrent detection circuit, which detects overcurrent of a load driving device arranged to drive a capacitance load by switching a voltage applied to the capacitance load between high level and low level, includes a clock signal generation unit arranged to generate a clock signal, a comparing unit arranged to compare a physical quantity corresponding to current supplied from the load driving device to the capacitance load with a predetermined value, and a determination unit arranged to determine whether or not the load driving device is in an overcurrent state based on the clock signal and a result of the comparison by the comparing unit, during a period in which the load driving device applies a high level voltage to the capacitance load.