the BC108. This group of NPN transistors share many specifications and characteristic curves, but differ in voltage ratings - the BC546 and BC547 are essentially the same as the BC548 but selected with higher breakdown voltages, while the BC549 is a low noise version, and the BC550 is both high-voltage and low-noise. The BC556 to BC560 are the PNP counterparts of the BC546 to BC550, respectively. See the BC108 family for a table of these differences, and comparisons with predecessor types. Some manufacturers specify their parts with higher ratings, for example the Fairchild 1997 datasheet (547ABC, Rev B) for the BC547, sourced from Process 10 gave 500mA as the maximum collector current, while their datasheets dated 2002 have dropped the current rating to the standard 100mA. The power rating (in free air at 25 °C) is also subject to variation, from 500 mW to 625 mW; the latter now being the most common. There is lot of variation in the ft-transition maximum frequency from manufacturer to manufacturer. Gain groups The type number of any of the devices in this "family" may be followed by a letter, "A" to "C", indicating devices that have been selected that fall within a narrow range of gain (hFE). The same letters are used for this purpose in several other European transistors, and is similar in principle to the "Yellow", "Blue" (and so on) gain groupings in Japanese transistors, but should not be confused with the "A" suffix used with some American (JEDEC) devices, such as the 2N2222A, to indicate a variety of differences or enhancements over the base type. The BC548 is available in three different gain groups:. "A" indicates low gain (110 to 220, typically 180) at 2 mA collector current, "B" indicates medium gain (200 to 450) "C" indicates high gain (420 to 800) So a BC548 might have a current gain anywhere between 110 and 800, but the gain of a BC548A would be within the range of 110 to 220. Notes: Some manufacturers place slightly different limits on the gain groups, for example the "B" group has been quoted as 220-475 in a Philips 1997 datasheet. The BC547 variant rarely is available in the "C" gain group, and the BC549 rarely in the "A" gain group. Complementary pairs The PNP counterparts of the BC546 to BC550 are the BC556 to BC560 respectively, i.e. the type numbers are higher by ten.