Overcurrent Protection Circuit with Dual Threshold Timer
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Solution Overview
Problem
Conventional overcurrent protection circuits fail to immediately shut down devices when excessive current flows, potentially causing damage due to reliance on a predetermined time threshold for noise masking, and require additional components like CPUs and memories, increasing device size and cost.
Innovation Solution
An overcurrent protection circuit with a sense resistor, multiple comparators, and a timer circuit that generates a protection signal based on detection voltage thresholds, allowing immediate shutdown and automatic restart without the need for CPUs and memories.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a predetermined time threshold is used for noise masking in overcurrent protection, then instantaneous noise is filtered out, but excessive current may continue to flow and damage the object to be protected
Solution Approach 1:
The protection response is segmented into two distinct threshold levels: a first threshold voltage (VrefL) for normal overcurrent protection with time delay, and a second threshold voltage (VrefH) for severe overcurrent protection with immediate response. This segmentation allows the system to differentiate between transient noise and dangerous overcurrent conditions, providing appropriate protection levels for each scenario.
Solution Approach 2:
The system changes the reference parameter (threshold voltage) based on the severity of the detected overcurrent condition. When the detection voltage exceeds the first threshold, the system uses a time delay for protection. When it exceeds the higher second threshold, the system immediately responds without time delay, effectively changing the protection parameter based on the situation.
2Reliability
If additional components like CPU and memory are added for improved overcurrent protection, then protection accuracy is enhanced, but device size and cost increase
Solution Approach 1:
The overcurrent protection circuit is self-service in that it automatically detects overcurrent conditions, compares them against predefined thresholds, and triggers appropriate protection responses without requiring external CPU intervention or memory storage. The circuit uses dedicated hardware components (comparators, voltage references, and timing circuits) that autonomously perform the protection function.
Solution Approach 2:
The invention extracts the essential overcurrent protection function from complex CPU-based systems and implements it using dedicated, simplified hardware components. By taking out only the necessary comparison and timing functions and implementing them with specialized circuits, the system achieves accurate protection without the overhead of general-purpose processors and memory.
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
Provides timely protection against excessive currents, reduces device size and cost, and enables automatic restart after the cause of overcurrent is addressed.
Implementation Method 1
a sense resistor that generates a detection voltage corresponding to a current flowing through an object to be protected
Implementation Method 2
a first comparator that compares the detection voltage with a first threshold voltage
Implementation Method 3
a second comparator that compares the detection voltage with a second threshold voltage that is higher than the first threshold voltage
Data Source
AI summary
In an overcurrent protection circuit 23 according to the present invention, a timer circuit TMR that generates an overcurrent protection signal EN according to the results of comparison between a detection voltage Va (Vb) and VrefL and VrefH is configured as follows. When Va (Vb) has reached VrefL, the timer circuit TMR starts to count T1. When T1 has elapsed with Va (Vb) kept above VrefL, the timer circuit TMR changes EN to a disabled state and starts to count T2. When T2 has elapsed, the timer circuit TMR returns EN to an enabled state. On the other hand, after Va (Vb) has reached VrefL and T1 starts to be counted, when Va (Vb) has reached VrefH, the timer circuit TMR forcibly stops the counting of T1 without waiting for T1 to elapse, changes EN to a disabled state, and starts to count T2. With this configuration, it is possible to offer necessary and sufficient protection for an object to be protected (for example, a load or an element provided inside a device).