PNP pre-biased transistor in SC-75 — what the built-in resistors mean for the BOM
The Infineon BCR 164T E6327 is a PNP pre-biased transistor in a surface-mount SC-75 (SOT-416) package. The base and base-emitter resistors are integrated on-chip — 4.7 kΩ for R1 and 10 kΩ for R2 — so the design needs no external bias network. That saves two passive components per transistor and shrinks the placement footprint to the 3-pin SC-75 outline. Collector-emitter breakdown is rated at 50 V, continuous collector current at 100 mA, and total power dissipation at 250 mW. The 160 MHz transition frequency means it handles switching well above audio and low-speed logic — think DC-DC converter gate drive, relay coil drivers, or signal-level switching up into the low-MHz range.
Saturation and gain — where the pre-bias helps and where it limits
Vce(sat) is specified at 300 mV maximum with a 500 µA base drive and 10 mA collector current — a typical saturated switch condition. DC current gain minimum is 30 at 5 mA collector current and 5 V Vce. Because the base resistor is fixed at 4.7 kΩ, the available base drive is set by the input voltage and the resistor divider; the designer cannot independently raise base current beyond that divider ratio. For loads near the 100 mA maximum, confirm that the input voltage and the 4.7 kΩ R1 deliver enough base current to keep the transistor in saturation.
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