What do the letters that come after the names of the transistors mean? What is the difference between a TIP31A and a TIP31B?
Manufacturers of transistors can not do them all with the same gain and with the same voltage characteristics. Thus, in the same batch we can have different transistors. To make it easier to use and even separate for sale, manufacturers use suffixes that can indicate both the gain and the voltage. Thus, for the TIP series, the letters indicate the gains. The TIP31A supports 60 V while the TIP31B supports 80 V of maximum voltage between the collector and emitter. The suffix TIP31 has a maximum collector-emitter voltage of 40 V. For other types, the suffix may indicate the gain. For example, the 2SC3066F has a gain between 160 and 320 while the 2SC3966C has a gain between 280 and 560. See that this information is important at the time of replacement. We can use a TIP31B instead of a TIP31A, but the reverse can give problems depending on the voltage in the circuit