300 V NPN in a SOT-23 — what the ratings mean
The Infineon MMBTA42LT1HTSA1 is a high-voltage NPN bipolar transistor in a SOT-23-3 surface-mount package. The 500 mA maximum collector current (Ic) and 360 mW power dissipation define the safe operating area in that small package; at 300 V you're not pulling 500 mA continuously, but the current rating gives headroom for transient loads like relay coil kickback or flyback snubber circuits.
Switching performance and drive requirements
Transition frequency is 70 MHz, adequate for switching applications up to a few megahertz — think 100 kHz flyback converters, display bias supplies, or solenoid drivers where the 300 V rating is the constraint, not the speed. The 500 mV Vce saturation at 20 mA collector current (with 2 mA base drive) is moderate; the hFE minimum of 40 at 30 mA, 10 V means you need a base current around 2.5% of the collector load to guarantee saturation. The 100 nA collector cutoff current (ICBO) at 25 °C is clean for a high-voltage device, but expect it to double roughly every 10 °C rise — factor that into high-temperature leakage budgets.
Last Buy — what it means for procurement
That means the manufacturer has announced end-of-life and the final ordering window is open. For a BOM line using the MMBTA42LT1HTSA1, the decision is time-sensitive: either place a last-time buy for estimated lifetime demand, or qualify a replacement. The base product number is MMBTA42, so other suffix variants (different hFE grade or packaging) may still be active — check each suffix individually. No lead-time number can be stated here because the Last Buy window is finite and stock is drawn down by the day.