1. Power and Current Ratings: The FCX619TA's rated power (2W) is four times that of the 2SC4672T100Q (0.5W), and its maximum collector current (3A) is 1.5 times higher. The FCX619TA can handle substantially higher power dissipation and current, leading to more relaxed thermal design and higher reliability in switching, linear regulation, or load-driving applications. Direct replacement risks premature failure of the 2SC4672T100Q due to overheating. 2. Saturation Voltage (Vce(sat)): The FCX619TA's Vce(sat) specification (320mV @ 2.75A) is superior to that of the 2SC4672T100Q (350mV @ 1A) under more demanding conditions. At comparable operating currents (especially above 1A), the FCX619TA exhibits lower conduction loss, resulting in higher efficiency and reduced heat generation. Substitution may degrade system efficiency and increase thermal rise. 3. DC Current Gain (hFE) Test Conditions: The FCX619TA's minimum hFE (100) is specified at 2A, whereas the 2SC4672T100Q's (120) is tested at 0.5A. The FCX619TA's gain characteristics are guaranteed for a higher current operating region, providing more stable and reliable drive capability under high current. Substitution may alter the actual drive requirements of the circuit under high-current conditions, necessitating a re-evaluation of the base drive current.