Semiconductor Overcurrent Protection Circuit with Dynamic Threshold
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing semiconductor devices with overcurrent protection circuits experience erroneous operations and delays in detection during the mirror period after switching element turn-on, leading to potential damage due to increased sense current and voltage, especially with free wheel diodes connected.
Innovation Solution
A semiconductor device design that includes a switching element, a passive sense resistor, and an overcurrent protection circuit with a low-pass filter and a delay circuit to adjust the sense voltage threshold during the mirror period, preventing erroneous operations and maintaining timely detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sense current division ratio is increased during the mirror period to improve detection sensitivity, then the sense voltage exceeds the threshold causing erroneous overcurrent detection, but if the division ratio is kept constant, the detection accuracy during steady state is compromised
Solution Approach 1:
The patent applies dynamics by making the current division ratio variable rather than constant. The ratio changes based on the operational state of the switching element: during the mirror period when turning on, the ratio is increased to prevent erroneous detection, while during steady state operation, the ratio returns to normal for accurate overcurrent detection. This dynamic adjustment resolves the contradiction between detection sensitivity and erroneous operation prevention.
Solution Approach 2:
The patent changes the electrical parameter (current division ratio) based on operational conditions. By adjusting the division ratio parameter dynamically - increasing it during the mirror period and maintaining normal values during steady state - the system achieves both erroneous operation prevention and accurate overcurrent detection without compromise.
2Reliability
If a low-pass filter with a time constant corresponding to the mirror period length is used to prevent erroneous detection, then the filter masks the sense voltage during the mirror period, but this causes delays in overcurrent detection and protection operation
Solution Approach 1:
The patent uses dynamics by dynamically adjusting the current division ratio in response to operational state changes. During the mirror period, the ratio is increased to prevent erroneous detection without requiring a low-pass filter that would mask the sense voltage. During steady state, normal detection operates without delay. This dynamic approach eliminates the time loss associated with filter masking while maintaining reliable erroneous detection prevention.
Solution Approach 2:
The patent applies preliminary action by proactively adjusting the current division ratio before erroneous detection can occur. The control circuit detects the mirror period condition and increases the division ratio in advance, preventing the sense voltage from erroneously exceeding the threshold. This preliminary adjustment eliminates the need for post-processing filters that would cause detection delays.
3Reliability
If the sense voltage is masked during the mirror period to prevent erroneous operation, then the overcurrent protection circuit does not operate or experiences delay, but this fails to protect the switching element during actual short circuit conditions immediately after turn-on
Solution Approach 1:
The patent applies dynamics by making the current division ratio variable based on operational state. During the mirror period, the ratio is increased to prevent erroneous detection while still allowing actual overcurrent protection. During steady state, normal detection operates. This dynamic adjustment prevents masking of genuine overcurrent conditions while blocking erroneous detections, thereby protecting the switching element without false negatives.
Solution Approach 2:
The patent applies local quality by applying different detection characteristics to different operational periods. During the mirror period, the system uses a higher current division ratio that is locally optimized to prevent erroneous detection while maintaining protection capability. During steady state, normal detection characteristics apply. This localized quality adjustment ensures protection against actual faults while preventing erroneous operations.
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
Prevents erroneous overcurrent detection and reduces detection delays, ensuring proper protection of the switching element even during abnormal conditions like short circuits, by maintaining a stable sense voltage threshold during the mirror period.
Implementation Method 1
a passive element that generates a sense voltage obtained by converting to a voltage a sense current divided from a main current flowing through the switching element
Data Source
AI summary
A semiconductor device includes a sense resistor that converts a sense current flowing through a sense terminal of a switching element to a voltage (sense voltage), and an overcurrent protection circuit that performs a protection operation for the switching element when the sense voltage exceeds a threshold. The overcurrent protection circuit can switch the threshold to a first reference voltage, or to a second reference voltage which is lower than the first reference voltage. The overcurrent protection circuit sets the threshold to the second reference voltage at the time of the switching element being in a steady state, and sets the threshold to the first reference voltage during a mirror period immediately after turning-on of the switching element.