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For power semiconductor devices (such as BJT, MOSFET, thyristor or IGBT), the safe operating area (SOA) is defined as the voltage and current conditions over which the device can be expected to operate without self-damage.〔Tim Williams ,''The circuit designer's companion 2nd ed.'',Butterworth-Heinemann, 2004 ISBN 0-7506-6370-7, pp.129-130〕 SOA is usually presented in transistor datasheets as a graph with VCE (collector-emitter voltage) on the abscissa and ICE (collector-emitter current) on the ordinate; the safe 'area' referring to the area under the curve. The SOA specification combines the various limitations of the device — maximum voltage, current, power, junction temperature, secondary breakdown — into one curve, allowing simplified design of protection circuitry. Often, in addition to the continuous rating, separate SOA curves are plotted for short duration pulse conditions (1 ms pulse, 10 ms pulse, etc.). The safe operating area curve is a graphical representation of the power handling capability of the device under various conditions. The SOA curve takes into account the wire bond current carrying capability, transistor junction temperature, internal power dissipation and secondary breakdown limitations. ==Limits of the safe operating area== Where both current and voltage are plotted on logarithmic scales, the borders of the SOA are straight lines: # IC = ICmax — current limit # VCE = VCEmax — voltage limit # IC VCE = Pmax — dissipation limit, thermal breakdown # IC VCEα = const — this is the limit given by the secondary breakdown (bipolar junction transistors only) SOA specifications are useful to the design engineer working on power circuits such as amplifiers and power supplies as they allow quick assessment of the limits of device performance, the design of appropriate protection circuitry, or selection of a more capable device. SOA curves are also important in the design of foldback circuits. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Safe operating area」の詳細全文を読む スポンサード リンク
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