1. Current Capability and Saturation Voltage: The rated collector current of the 2SC5994 (2A) is higher than that of the 2SCR513PT (1A). Additionally, its saturation voltage (Vce(sat)) under a 1A test condition is lower (300mV vs. 350mV, with the latter specified at 500mA). At the same current level, the 2SCR513PT may exhibit higher on-state losses and greater junction temperature rise. If the original design operates close to 2A, substitution could lead to performance degradation or overheating. 2. Power Rating and Package Thermal Resistance: The 2SCR513PT has a higher nominal maximum power dissipation rating (2W). Although both devices share the same physical outline (TO-243AA) with different package designations (MPT3 vs. PCP for the 2SC5994), their actual thermal performance may differ. The power rating alone is not directly comparable; the critical factor is the package thermal resistance (RθJA) under specific mounting conditions. The 2W rating of the 2SCR513PT is meaningful only if its thermal resistance is lower; otherwise, no practical advantage may be realized. 3. Frequency Characteristics: The transition frequency (fT) of the 2SC5994 (420MHz) is higher than that of the 2SCR513PT (360MHz). This suggests that in high-frequency switching or amplification applications, the former may offer better response speed and lower switching losses. Substitution could therefore affect circuit performance at high frequencies. 4. DC Gain (hFE) Test Conditions: The minimum hFE values of both devices are similar, but they are specified at different test currents (100mA vs. 50mA). This indicates potential differences in gain characteristics across operating regions, particularly in the medium-current range (e.g., 500mA–1A). The actual gain curve may impact circuit linearity or drive requirements.