BC257 Bipolar Transistor

• Type: PNP
• Collector-Emitter Voltage, max: -45 V
• Collector-Base Voltage, max: -50 V
• Emitter-Base Voltage, max: -6 V
• Collector Current − Continuous, max: -0.1 A
• Collector Dissipation: 0.3 W
• DC Current Gain (h_fe): 110 to 800
• Transition Frequency, min: 180 MHz
• Noise Figure, max: 2 dB
• Operating and Storage Junction Temperature Range: -55 to +150 °C
• Package: TO-92

The BC257 is manufactured in a plastic TO-92 case. When looking at the flat side with the leads pointed downward, the three leads emerging from the transistor are, from left to right, the emitter, collector, and base leads.
Here is an image showing the pin diagram of this transistor.The BC257 transistor can have a current gain of 110 to 800. The gain of the BC257A will be in the range from 110 to 220, for the BC257B it will be in the range from 200 to 450, for the BC257C it will be in the range from 420 to 800.The complementary NPN transistor to the BC257 is the BC167.The BC857 (SOT-23), BC857W (SOT-323), BC860 (SOT-23) and BC860W (SOT-323) is the SMD version of the BC257 transistor. These transistors are of the same type, have similar parameters and are designed for surface mounting.You can replace the BC257 with the 2SA1522, 2SA1523, 2SA1524, 2SA1525, 2SA1526, 2SA1527, 2SA1528 or 2SA1529.