Pre-biased NPN in a tiny SOT-323 — what it does
The Infineon BCR 148W H6433 is an NPN pre-biased digital transistor in a PG-SOT323 package (SC-70 equivalent). It integrates two 47 kOhm resistors — one in series with the base, one between base and emitter — so the transistor switches on with a logic-level drive and no external bias network. The collector is rated for 100 mA continuous and the Vce breakdown sits at 50 V, covering 5 V and 12 V logic-level loads, relay coils, and small-signal switching in industrial and consumer boards. Transition frequency is 100 MHz, fast enough for low-speed PWM and serial data gating up to a few megahertz.
Obsolete — sourcing reality
Infineon lists the BCR 148W H6433 as obsolete. If the design can tolerate a different base-resistor ratio, the broader BCR 148 family (base product number BCR 148) includes active variants worth evaluating for new builds.
Built-in resistors shrink the BOM
With R1 and R2 both at 47 kOhms, the BCR 148W H6433 saturates at 300 mV typical with 500 µA base drive and 10 mA collector load. The minimum DC current gain is 70 at 5 mA, 5 V. The 100 nA collector cutoff keeps off-state leakage negligible. The pre-biased construction saves two resistors per transistor and shrinks the placement footprint — useful in dense mixed-signal boards where every 0402 slot matters.