Inverter PCB Layout With Nested Bootstrap Capacitor Isolation

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Solution Overview

Problem

The challenge of achieving high density integration of components in an inverter device is hindered by the need for a predetermined insulation distance between the bootstrap capacitor and the intelligent power module, which can cause switching noise and malfunction.

Innovation Solution

The bootstrap capacitor is placed between the printed wiring board and the intelligent power module, allowing them to be positioned in the same region while maintaining the required insulation distance, and is located below the lower heat generation region to reduce thermal influence.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the bootstrap capacitor is placed close to the intelligent power module to achieve high density integration, then component integration density is improved, but insulation distance requirement is violated and switching noise may cause malfunction

Engineering Contradiction:

Improvecomponent integration densityVSAvoidinsulation distance

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent transitions from planar arrangement to three-dimensional arrangement by placing the bootstrap capacitor on the back surface of the printed circuit board, utilizing the Z-dimension to achieve both high integration density and required insulation distance simultaneously

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The bootstrap capacitor is nested within the mounting region of the intelligent power module by positioning it on the back surface directly below the module, effectively utilizing the vertical space and achieving compact integration while maintaining electrical insulation

Inventive Principle:

Principle #7Nested doll (Nesting)

2Reliability

If the insulation distance between bootstrap capacitor and intelligent power module terminal is increased to prevent noise interference, then reliability is improved, but component integration density deteriorates

Engineering Contradiction:

Improvenoise immunityVSAvoidcomponent integration density

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

By moving the bootstrap capacitor to the back surface of the PCB, the patent creates sufficient physical separation and insulation distance in the vertical dimension while maintaining compact planar footprint, thus achieving both noise immunity and high integration density

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Ease of manufacture

If the bootstrap capacitor is placed in the high heat generation region near the inverter circuit, then ease of layout is improved, but thermal susceptibility of the capacitor increases

Engineering Contradiction:

Improvelayout convenienceVSAvoidthermal susceptibility

Core Design Contradiction:

Ease of manufactureVSTemperature

Solution Approach 1:

The patent applies local quality by selectively positioning the bootstrap capacitor in a low heat generation zone (back surface below control circuit) rather than uniformly distributing components, thereby protecting the temperature-sensitive capacitor from thermal damage while maintaining overall layout efficiency

Inventive Principle:

Principle #3Local quality

Data Source

PatentEP4175153B1Inverter device

Publication Date: 2025.09.03 DAIKIN INDUSTRIES LTD

Figure 1
Figure 2
Figure 3~4

AI summary

To achieve high density integration of components while securing an insulation distance between a bootstrap capacitor and an intelligent power module. In a printed wiring board (40), a region (R1 to R3) where a capacitor (45) is mounted is located in a region (R4) where an intelligent power module (43) is mounted. Therefore, the capacitor (45) mounted on the printed wiring board (40) is placed between the printed wiring board (40) and the intelligent power module (43).