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What is a safe operating area?

The safe operating area (SOA) is defined as the current and voltage conditions over which an IGBT can be expected to operate without self-damage or degradation. In practice, it is necessary not only to use an IGBT within the safe operating area but also to derate its area for temperature. There are forward-bias and reverse-bias safe operating areas (FBSOA and RBSOA). The forward-bias safe operating area defines the usable current and voltage conditions for the period of time while the IGBT is on. The reverse-bias safe operating area defines the usable current and voltage conditions during the turn-off period of the IGBT.

Figure (a) shows an example of a forward-bias safe operating area, which consists of four regions: (1) a region limited by the maximum collector current rating, (2) a region limited by collector power dissipation (thermal breakdown), (3) a region limited by secondary breakdown, and (4) a region limited by the maximum collector-emitter voltage rating. Care should be exercised as to the region limited by secondary breakdown because it differs, depending on the device design.

Figure (b) shows an example of a reverse-bias safe operating area, which consists of three regions: (1) a region limited by the maximum collector current rating (ICP), (2) a region limited by the inherent characteristics of a device, and (3) a region limited by the maximum collector-emitter voltage rating (VCES). In the second region, the maximum current is in inverse proportion to VCE. Hard-switching applications, in particular, should be designed so as to satisfy the limit of this SOA region.

(a) Forward-bias SOA

(a) Forward-bias SOA

(b) Reverse-bias SOA

(b) Reverse-bias SOA

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·Before creating and producing designs and using, customers must also refer to and comply with the latest versions of all relevant TOSHIBA information and the instructions for the application that Product will be used with or for.