During turn-on and on-state conditions, the average junction temperature and second breakdown limit the power handling capability of a transistor. The manufacturer usually provides the FBSOA curves under specified test conditions. FBSOA indicates the limits of the transistor and for reliable operation the transistor must not be subjected Ic to greater power dissipation than that shown by the FBSOA curve. The dc FBSOA is shown as shaded area and the expansion of the area for pulsed operation of the BJT with shorter switching times which leads to larger FBSOA. The second break down boundary represents the maximum permissible combinations of voltage and current without getting into the region of plane where second breakdown may occur. ic The final portion of the boundary of the FBSOA is breakdown voltage limit . BVCEO Reverse Biased Safe Operating Area RBSOA During turn-off, a high current and high voltage must be sustained by the transistor, in most cases with the base-emitter junction reverse biased. The collector emitter voltage must be held to a safe level at or below a specified value of collector current. The manufacturer provide limits during reverse-biased turn off as reverse biased safe area (RBSOA). Ic Fig.2.8: RBSOA of a Power BJT The area encompassed by the RBSOA is somewhat larger than FBSOA because of the extension of the area of higher voltages than upto at low collector currents. BVCEO BVCBO This operation of the transistor upto higher voltage is possible because the combination of low collector current and reverse base current has made the beta so small that break down voltage rises towards . BVCBO Power Derating The thermal equivalent is shown. If the total average power loss is , PT The case temperature is . Tc PTT jc The sink temperature is Ts The ambient temperature is and TA Tj P RT jc : Thermal resistance from junction to case Rjc : Thermal resistance from case to sink RCS . 0C : Thermal resistance from sink to ambient RSA
During turn-on and on-state conditions, the average junction temperature and second breakdown limit the power handling capability of a transistor. The manufacturer usually provides the FBSOA curves under specified test conditions. FBSOA indicates the Ic limits of the transistor and for reliable operation the transistor must not be subjected to greater power dissipation than that shown by the FBSOA curve. The dc FBSOA is shown as shaded area and the expansion of the area for pulsed operation of the BJT with shorter switching times which leads to larger FBSOA. The second break down boundary represents the maximum permissible combinations of voltage and current without getting into the region of ic plane where second breakdown may occur. The final portion of the boundary of the FBSOA is breakdown voltage limit BVCEO . Reverse Biased Safe Operating Area RBSOA During turn-off, a high current and high voltage must be sustained by the transistor, in most cases with the base-emitter junction reverse biased. The collector emitter voltage must be held to a safe level at or below a specified value of collector current. The manufacturer provide Ic limits during reverse-biased turn off as reverse biased safe area (RBSOA). Fig.2.8: RBSOA of a Power BJT The area encompassed by the RBSOA is somewhat larger than FBSOA because of the extension of the area of higher voltages than BVCEO upto BVCBO at low collector currents. This operation of the transistor upto higher voltage is possible because the combination of low collector current and reverse base current has made the beta so small that break down voltage rises towards BVCBO . Power Derating The thermal equivalent is shown. If the total average power loss is PT , The case temperature is Tc PTT jc . The sink temperature is Ts The ambient temperature is TA and Tj P RT jc Rjc : Thermal resistance from junction to case RCS : Thermal resistance from case to sink 0C . RSA : Thermal resistance from sink to ambient
U2_L9-Switching-Characteristics.docx