Digital Transistor is a transistor with resistance. Some of them only connect a resistor in series at the base, which is generally called R1, while others connect a resistor R2 in parallel between the base and the emitter. Resistor R1 has many kinds of resistors, which are similar to the standard resistor series, and resistor R2 is similar to R1. Resistor R1 and resistor R2 can be matched in many ways, so there are many kinds of digital transistors.