"220V Cooling Fan" to provide maximum Ta, Tj, P-- early chip Datasheet generally this. Theoretically we only need to ensure that the chip near the ambient temperature does not exceed this target can guarantee the chip can work properly. But this is not true. Ta This parameter is derived in accordance with JEDEC standard test. JEDEC standard is defined as: the "220V Cooling Fan" chip placed in a 4-layer PCB 3X4.5 inch middle, ambient temperature test probe PCB board edge distance piece 12 inches. Our products can be seen almost impossible to meet this test condition. So, here for us, does not make sense. In this case, a conservative approach is: to ensure that "220V Cooling Fan" chip case temperature Tc <Ta-max, general chip is working properly. > br>