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Thermal Management Designs for Natural Convection Cooled Low Profile Adaptor

IP.com Disclosure Number: IPCOM000012543D
Publication Date: 2003-May-14
Document File: 14 page(s) / 3M

Publishing Venue

The IP.com Prior Art Database

Abstract

Abstract: This paper describes the experience gained from the mechanical and thermal management design of a slim (12mm thickness) AC/DC adaptor used in notebook computer or portable devices. In general, the mechanical and thermal design of adapter products is extremely challenging due to increased power density requirements. The following describes the key thermal management challenges, introduces a novel method of partitioning the housing structure, and shares innovative construction concepts. The method of partitioning provides a cooler housing enclosure that can extend the lifetime of electronic components, in particular, electrolytic capacitors.

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Thermal Management Designs for

Natural Convection Cooled Low Profile Adaptor


 

Abstract: This paper describes the experience gained from the mechanical and thermal management design of a slim (12mm thickness) AC/DC adaptor used in notebook computer or portable devices. In general, the mechanical and thermal design of adapter products is extremely challenging due to increased power density requirements. The following describes the key thermal management challenges, introduces a novel method of partitioning the housing structure, and shares innovative construction concepts. The method of partitioning provides a cooler housing enclosure that can extend the lifetime of electronic components, in particular, electrolytic capacitors.

 

Background

A typical laptop adapter has a height or thickness of between 30-40mm depending on the output power requirement. This is a report about the experience gained from the thermal management design of a slim (12mm thickness), 50W output power, AC/DC adaptor used in notebook computer or portable devices. It is well known that the heat dissipation capacity of an object is governed by its surface area. Package manufacturers (e.g. Hoffman Specifier’s guide 1995~1996 P 594) provide specified chart curve for selected materials as shown below ; by plotting the temperature rise against the power dissipation per unit area.

This provides an idea about the average temperature rise of a certain shape. However, it does not show temperature distribution inside the shape and, therefore, cannot be used as a tool for identifying possible reliability issues. The graphical method also does not work very well for geometries with extreme aspect ratio.

 


A general description of the requirements

In this design, the enclosure is a box measures 50x80x12mm. The box is moulded from plastic material to comply with consumer safety requirements. Copper plates are located at the inner surface of the box that "spreads" the heat generated internally and equalize the temperature gradient along the inner surface of the box. The metal plates also double as electrical shield for minimizing electromagnetic radiation.

The laptop ACDC adapter is a switched mode power supply design. Electronic components are mounted on a 1mm FR-4 glass epoxy double sided printed circuit board. The heat generating components are summarized as follows:

- Input EMI filter.                                                         - Input rectifier.

- Main primary power switch.                               - Primary snubber.

- Primary control circuits.                                      - Power transformer.

- Secondary Rectifier.                                                   - Secondary snubber.

- Secondary control circuit.                                   - Output capacitors.

The simulation model

Thermal simulation is used to investigate the air flow pattern when the enclosure is sitting in a horizontal orientation. Fig.1 and 2 are the two dimensional cr...