BC547A

The BC547A is a small‑signal NPN bipolar junction transistor commonly used in low‑power linear and switching applications. It is part of the 2N390x series family and is marketed by several manufacturers, including ON Semiconductor, Fairchild, and Vishay. The “A” suffix denotes a variant with a higher maximum collector current and a higher DC current gain (hFE) than the base BC547. Typical electrical characteristics for a BC547A include a maximum collector current of 100 mA, a maximum collector‑emitter voltage of 45 V, and a typical DC current gain ranging from 110 to 800 depending on the test conditions. Its maximum power dissipation is 625 mW. The transistor is packaged in a TO‑92 case and features standard lead spacing of 2.54 mm.

In practical circuits, the BC547A is employed in signal amplification, oscillator components, and as a driver for LEDs, relays, or other moderate‑power loads. Its low parasitic capacitance and relatively high gain make it suitable for audio and radio frequency (RF) applications that require fine signal control. Because of its low noise figure and good linearity, it is also frequently found in low‑noise amplifier designs. When selecting a BC547A for a project, designers should compare the transistor’s temperature coefficient and maximum operating temperature (usually 150 °C) against the system requirements to ensure reliable performance over the intended range.