Digital Transistor (Digital Transistor), the English name Bias Resistor Transistor, is a transistor with resistance, some only a resistance in series on the base, generally known as R1, and some in parallel between the base and the emitter a resistance R2. Resistor R1 has a variety of resistors, similar to the standard resistor series, and resistor R2 is similar to R1. Resistors R1 and R2 can be matched in many ways, so there are many varieties of digital transistors.
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