New Webtools Speed IGBT Selection and Design

Feb 1, 2011 12:00 PM
Steve Clemente, Senior Technologist, International Rectifier Corp. STEVE WIDMAR, Manager, Product Ev

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Introduced in the late eighties, The IGBT quickly displaced high-voltage power Darlingtons in motor drive modules and gradually worked its way down into all kinds of off-line motor drives in consumer products, particularly air conditioners and washers. From there it migrated into a diverse range of applications, from plasma displays to welders, from induction cookers to piezoelectric ignition and hybrid powertrains.

IGBTs have a number of advantages, stemming from its high power output per dollar (see sidebar: The Success of IGBTs). IGBTs rated up to 3kV have been commercially available for a number of years and they are widely used in traction applications. At these voltages, the IGBT does not have credible contenders, even though carrier recombination limits its frequency of operation to a few kHz. The only competing technology is silicon carbide. Transistors implemented on silicon carbide structures are majority carrier devices and can operate at very high frequency. They will become a very serious threat once a cost-effective manufacturing process comes online.

But choosing the right IGBT for the application is no simple task. The equipment designer's foremost concern is to find which device is the most cost-effective in his application. He cannot deal with technology curves; he has to deal with part numbers from several suppliers.

For a given voltage, package and short-circuit capability, there will be many possible candidates. Some will be more efficient than others and, possibly, more expensive. In those applications where power density is important, a smaller heat sink is a desirable feature that may justify the extra cost of a more efficient IGBT.

Years ago, International Rectifier pioneered the Current vs. Frequency curve to help designers compare different IGBTs in an application-related environment (Fig. 1). It provided valuable information at a time when the equipment designer had a limited number of choices and available IGBTs shared similar technologies. Today, the choices are many, characteristics are different, BOM (bill of materials) cost has become critical, and time-to-market has shortened.

This boils down to a massive headache for the designer who has to pick up the right device for the application through a laborious iterative process. This process cannot be short-circuited but can be streamlined and rationalized with some helpful tools. International Rectifier has just introduced one such tool: The IGBT Selector tool.

The purpose of the tool is to trim the list of candidates to a handful, sorted out by price or power dissipation. Some key data need to be entered, like voltage, current and frequency, as well as package type and short circuit rating, as shown in Fig. 2. The tool uses this data to calculate power losses in the specified application conditions and only those devices that would operate at a junction temperature at least 25°C below maximum rating are returned as potential candidates. Enough heat sinking is assumed to keep case temperature at 100°C.

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