Switch Circuit Overcurrent Protection Soft Turn-Off

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Solution Overview

Problem

Existing switch circuits for overcurrent protection in power converter apparatuses are complex, costly, and introduce delays due to multiple components and stages, which affects the switching speed and efficiency of high-speed power semiconductor elements like SJMOS, SiC, and GaN.

Innovation Solution

A simplified switch circuit configuration using a first switch element, a driver circuit, a second switch element, an overcurrent detector circuit, and resistors to achieve soft turn-off and fast overcurrent protection, reducing circuit complexity and inductance while maintaining normal operation efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If many components are connected between the signal insulator and the voltage-driven semiconductor element for overcurrent protection, then overcurrent protection function is achieved, but the circuit's scale and cost increase

Engineering Contradiction:

Improveovercurrent protection functionVSAvoidcircuit scale

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent combines the overcurrent protection function with the existing driver circuit by integrating a switch element and control circuit into the driver circuit structure. This merging approach allows overcurrent protection to be achieved without adding separate independent protection circuits, thereby reducing overall circuit scale while maintaining the protection function.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The driver circuit is designed to serve multiple functions: normal gate driving and overcurrent protection. By making the driver circuit universal, the patent eliminates the need for separate dedicated protection circuits, reducing circuit complexity and component count while achieving both driving and protection functions.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

Engineering Contradiction:

Improveovercurrent protection functionVSAvoidinductance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent extracts the essential overcurrent protection function from a complex multi-component circuit configuration and implements it using a simplified structure with minimal components. By taking out only the necessary elements (switch element and control circuit) and removing unnecessary components, the patent reduces circuit inductance while preserving the protection function.

Inventive Principle:

Principle #2Taking out (Extraction)

3Reliability

If semiconductor elements operable complementarily are provided between the switch element for overcurrent protection and the voltage-driven semiconductor element, then overcurrent protection is achieved, but a delay occurs from turning on of the switch element to turning off of the voltage-driven semiconductor element

Engineering Contradiction:

Improveovercurrent protectionVSAvoiddelay time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The control circuit continuously monitors current through the voltage-driven semiconductor element and prepares the switch element for immediate activation. By maintaining readiness conditions in advance (pre-charging gate capacitance of the switch element), the patent minimizes the delay between overcurrent detection and the switching action that protects the voltage-driven element.

Inventive Principle:

Principle #10Preliminary action

4Reliability

If a capacitor is connected between the connection point and the emitter terminal for overcurrent protection, then overcurrent protection is achieved, but the switching speed of the voltage-driven semiconductor element during normal operation is slowed

Engineering Contradiction:

Improveovercurrent protectionVSAvoidswitching speed

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent implements a dynamic configuration where the capacitor is selectively connected only during overcurrent conditions rather than being permanently connected. The control circuit activates the capacitor connection when overcurrent is detected and disconnects it during normal operation, allowing the voltage-driven semiconductor element to operate at full switching speed while still receiving overcurrent protection when needed.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS11496125B2Switch circuit capable of overcurrent protection with small and simple circuit, and with simple operation, without affecting normal operation

Publication Date: 2022.11.08 OMRON CORP

AI summary

A driver circuit controls a first switch element. A first resistor is connected between the driver circuit and the first switch element. A second switch element is connected to the first switch element. An overcurrent detector circuit controls the second switch element based on an overcurrent current flowing through the first switch element. A second resistor is connected between the overcurrent detector circuit and the second switch element. The first and second resistor is set such that a turn-off time of the first switch element when the second switch element is turned on by the overcurrent detector circuit is longer than a turn-off time of the first switch element when the first switch element is turned off by the driver circuit.