Short-Circuit Protection Circuit Using Rectifier Capacitance Timing
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Solution Overview
Problem
Existing short-circuit protection circuits for semiconductor devices, such as those using DESAT type protection, fail to protect semiconductor switch elements from large short-circuit currents at appropriate timings due to changes in DESAT voltage, leading to increased current flow duration and requiring additional semiconductor elements, which increases cost and reduces output density.
Innovation Solution
A short-circuit protection circuit incorporating a voltage dividing circuit, a semiconductor rectifying element, and an RC parallel circuit, where the rectifying element's stray capacitance ensures a voltage differential that triggers the drive unit to turn off the semiconductor switch element at the right time, without increasing the number of elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a detection resistor is used to detect overcurrent in a power semiconductor, then overcurrent protection is achieved, but the detection resistor cannot withstand large short-circuit current values
Solution Approach 1:
The patent introduces a current transformer as an intermediary device between the power semiconductor and the detection circuit. The current transformer couples the primary winding (through which the semiconductor current flows) to the secondary winding (connected to the detection resistor), allowing the detection resistor to sense the current without directly withstanding the full short-circuit current stress. This mediator approach resolves the contradiction by protecting the weak detection resistor from the harsh high-current environment.
2Strength
If a DESAT type protection circuit is used to handle large short-circuit currents, then the detection resistor can withstand the current, but the circuit cannot protect at appropriate timings due to voltage changes
Solution Approach 1:
The patent replaces the voltage-based DESAT detection mechanism with a current-based detection mechanism using a current transformer. Instead of monitoring voltage drops across the semiconductor (which are affected by parasitic inductance and timing delays), the system directly transforms and detects the actual current flowing through the semiconductor. This substitution of the detection principle eliminates the timing delays inherent in voltage-based methods while maintaining the ability to handle large currents.
3Reliability
If additional semiconductor elements are added to improve protection timing, then protection accuracy is improved, but output density decreases and cost increases
Solution Approach 1:
The current transformer serves as an external intermediary device that provides accurate current detection without requiring additional semiconductor elements within the power module. By moving the detection function to an external magnetic coupling device, the patent achieves precise protection timing while maintaining high output density, as no extra semiconductor chips or complex internal detection circuits are needed.
Solution Approach 2:
The patent moves the current detection function from the electrical domain (voltage sensing within the semiconductor circuit) to the magnetic domain (current transformation through magnetic coupling). This dimensional shift allows accurate current measurement and protection timing to be achieved externally, avoiding the need for additional semiconductor elements that would reduce output density.
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
The solution effectively protects semiconductor switch elements from short-circuit currents at appropriate timings, preventing voltage drops and reducing the duration of current flow, thus maintaining output density and avoiding the need for additional elements.
Implementation Method 1
a semiconductor rectifying element 14, one end of which is connected between resistance elements 21 and 22 of the voltage dividing circuit 12 and the other end of which is connected onto a path of a conductive wire 61 connected to a current-inflow-side terminal of the semiconductor switch element 11 to be protected, the connection being made such that a direction from the one end to the other end becomes a rectifying direction
Implementation Method 2
a stray capacitance of the semiconductor rectifying element 14 is a stray capacitance that satisfies a condition that a voltage at one end of the capacitor element 31 of the RC parallel circuit 15, which is connected to the voltage dividing circuit 12, is higher than a voltage at the other end of the capacitor element 31
Data Source
AI summary
Disclosed is a short-circuit protection circuit including: a voltage dividing circuit that divides a power supply voltage supplied from a power supply connected to one end thereof; a semiconductor rectifying element, one end of which is connected between resistance elements of the voltage dividing circuit and the other end of which is connected onto a path of a conductive wire connected to a current-inflow-side terminal of a semiconductor switch element to be protected, the connection being made such that a direction from the one end to the other end becomes a rectifying direction; an RC parallel circuit connected to the other end of the voltage dividing circuit; and a drive unit that turns off the semiconductor switch element when it is detected that a short-circuit current flows through the conductive wire, on the basis of a voltage of a capacitor element of the RC parallel circuit, in a case in which the semiconductor switch element is turned on, wherein a stray capacitance of the semiconductor rectifying element is a stray capacitance that satisfies a condition that a voltage at one end of the capacitor element of the RC parallel circuit, which is connected to the voltage dividing circuit, is higher than a voltage at the other end of the capacitor element, when the short-circuit current flows through the conductive wire.