Transistors BC 547, BC 546, BC 548 are all small signal general purpose transistors used widely in electronic circuits. These devices are very versatile and small in size. Almost all types of small circuits can be designed using these transistors. They have basically three pin outs designated as the base which is at the center, the collector at the left and the emitter at the right hand side. The identification is done by keeping their printed surface toward us.
Refer the complete article.
All the above transistors are NPN types, means they must be operated with reference to the ground
The precise parameters may be understood from the following datasheet.
Maximum Tolerable Collector to Emitter Voltage = V C E O = 65 V DC for BC546, 45 V DC for BC 547 and 30 V DC for BC 548
Maximum Tolerable Collector to Base Voltage = V C B O = 80 V DC for BC546, 50 V DC for BC 547 and 30 V DC for BC 548
Maximum Tolerable Emitter to Base Voltage = VEBO = 6 V DC for all the above transistors.
Total Dissipation for the above transistors at 25 degrees Celsius = Pd = 625 mW, which derates by 5 mW per degree Celsius after 25 degree Celsius
Safe area temperature for operating and storing = Tj = minus 55 to 130 degree Celsius.