45 V NPN in a PG-SOT23 — the general-purpose switch
The Infineon BC817K40E6433HTMA1 is a 45 V, 500 mA NPN epitaxial silicon transistor in a PG-SOT23 surface-mount package. It is designed for general-purpose switching and amplification where the collector current stays under half an amp and the rail voltage does not exceed 45 V. The 170 MHz transition frequency keeps it useful for low-to-mid frequency switching up into the tens of megahertz.
The 250 minimum hFE at 100 mA — where the gain lands
The DC current gain is specified at 250 minimum when the collector sits at 100 mA and Vce is 1 V. That is the gain the designer budgets for base drive calculations — below this the transistor may not saturate properly. The 700 mV Vce(sat) maximum at 50 mA base / 500 mA collector gives the on-state voltage drop; at 500 mA load the transistor drops nearly three-quarters of a volt, so the power dissipation at full load runs about 350 mW, inside the 500 mW package limit.
Last Buy — the sourcing window is closing
Infineon has placed the BC817K40E6433HTMA1 in Last Buy status. That means the manufacturer is no longer accepting new orders for this specific ordering code after the final order date. If you have an active BOM line using this exact suffix, the window to secure lifetime-buy quantities is open now. Once the last-buy period closes, the only channel will be independent distribution for new-old-stock or surplus reels.