2N2905A general-purpose PNP bipolar junction transistor (BJT). (NOS)

The 2N2905A is a a popular general-purpose PNP bipolar junction transistor (BJT). It is a silicon planar epitaxial transistor known for high-speed switching and small-signal amplification applications. It is often used in military and high-reliability circuits due to its robust design and hermetically sealed TO-39 metal case, which provides good heat dissipation.

Key Specifications and Characteristics

 * Polarity: PNP

 * Collector-Emitter Voltage (V_{CEO}): -60 V

 * Collector Current (I_C): -600 mA (continuous)

 * Power Dissipation (P_D): 800 mW (at $T_A=25^{\circ}$C) to 3 W (at $T_C=25^{\circ}$C)

 * DC Current Gain (h_{FE}): Typically 100 to 300

 * Transition Frequency (f_T): 200 MHz

 * Package: TO-39 (through-hole metal can)

Pinout and Symbol

The pinout for the TO-39 package is typically as follows when looking at the bottom of the transistor with the tab facing up:

 * Pin 1: Emitter (E)

 * Pin 2: Base (B)

 * Pin 3: Collector (C)

The symbol for a PNP BJT is a circle with a horizontal line representing the base, a vertical line for the collector and emitter, and an arrow on the emitter pointing towards the base. This arrow indicates the direction of conventional current flow.

Common Applications

The 2N2905A's characteristics make it suitable for a variety of circuits, including:

 * High-speed switching circuits: Its fast switching times (e.g., rise time, fall time) are ideal for applications requiring quick on/off transitions.

 * General-purpose amplifiers: It can be used to amplify small signals in audio or other low-power applications.

 * Power control circuits: Capable of handling moderate currents and voltages, it can be used for controlling power to a load.