Semiconductor Relay Unit for Inrush Current and Noise Reduction

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Solution Overview

Problem

Existing relay units in motor-driven vehicles, such as hybrid or electric cars, are large, heavy, and unreliable due to mechanical contact type relays, which produce noise and have limited lifespan due to welded contacts and electric arcs, and require current limiting resistors that consume power and increase size.

Innovation Solution

Replace mechanical contact type relays with insulated gate bipolar transistors (IGBTs) and reverse blocking IGBTs to function as main and pre-charging relays, eliminating the need for current limiting resistors and mechanical relays, thereby reducing size, weight, and noise while maintaining reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If mechanical contact type relays are used for main relay and pre-charging relay, then the relay unit can control current flow, but the relay unit becomes large and heavy

Engineering Contradiction:

Improvecurrent control reliabilityVSAvoidrelay unit weight

Core Design Contradiction:

ReliabilityVSWeight of stationary object

Solution Approach 1:

The patent replaces mechanical contact type relays with semiconductor devices (IGBTs and diodes) to eliminate moving parts and mechanical wear. The semiconductor-based main relay circuit and pre-charging relay circuit perform the same current control function without mechanical contacts, thereby reducing relay unit weight while maintaining reliability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent extracts and eliminates unnecessary components from the relay unit, specifically removing the current limiting resistor that was required in mechanical relay systems. The semiconductor-based architecture inherently limits inrush current through the diode's reverse blocking capability, allowing the system to function without the additional weight of separate current limiting components.

Inventive Principle:

Principle #2Taking out (Extraction)

2Ease of operation

If mechanical contact type relays are used, then the relay unit can be implemented, but noise is produced when opening and closing

Engineering Contradiction:

Improverelay operation capabilityVSAvoidnoise production

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The patent substitutes mechanical switching operations with semiconductor switching. The IGBTs and diodes switch currents electronically without mechanical contact opening and closing, which eliminates the arcing and contact bounce that generate noise in mechanical relay systems while maintaining full operational capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If current limiting resistor is used to limit inrush current, then the inrush current is limited, but the resistor consumes power and increases size

Engineering Contradiction:

Improveinrush current limitationVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent replaces the passive current limiting resistor with an active semiconductor-based pre-charging relay circuit. The circuit uses an IGBT and diode to control current flow dynamically, limiting inrush current only when necessary during pre-charging, while allowing full current flow during normal operation, thereby eliminating continuous power consumption.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The pre-charging relay circuit operates periodically or conditionally rather than continuously. The IGBT is switched on only during the pre-charging phase to limit inrush current, then switched off during normal operation, allowing the system to achieve inrush current limitation without continuous power loss.

Inventive Principle:

Principle #19Periodic action

4Reliability

If mechanical contact type main relay is used, then the relay can block current, but the contact welds and fails to block current under high-voltage high-current

Engineering Contradiction:

Improvecurrent blocking capabilityVSAvoidrelay lifespan

Core Design Contradiction:

ReliabilityVSDuration of action of moving object

Solution Approach 1:

The patent replaces mechanical contact switching with semiconductor switching devices (IGBTs). The IGBTs control current flow through field-effect transistors without physical contact, eliminating the welding and erosion problems that limit mechanical relay lifespan under high-voltage high-current conditions while maintaining reliable current blocking capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS20250343545A1Semiconductor device, semiconductor module, relay unit, battery unit, and vehicle

Publication Date: 2025.11.06 ROHM CO LTD

AI summary

A semiconductor device includes a first terminal for a battery, a second terminal for an inverter circuit, and a transistor. The semiconductor device is configured to control a voltage applied to a control terminal of the transistor to allow supply of a current from the first terminal to the second terminal and allow supply of a current from the second terminal to the first terminal. A withstand voltage between the first terminal and the second terminal is greater than or equal to a voltage between the battery and the inverter circuit.