This series of transistors low-power NPN, commonly used, is the most currently used in projects of all kinds. The transistors may oscillate at relatively high frequencies and lend themselves to a multitude of applications in audio and DC. The difference of the different types is the gain, the maximum collector voltage and also the noise factor, with the BC549 is the most widely used in applications where this factor is important as audio preamplifiers. The table below shows the pinout and characteristics of the various types of the series.
