summary
● A transistor is a three-layer device used to amplify and switch power and voltage.
● A bipolar transistor is also called a junction transistor or simply a transistor.
● Transistors can be configured as NPN or PNP.
● The middle region of the transistor is called the base, and the two outer regions are called the emitter and collector.
● The schematic symbols used for NPN and PNP transistors are
● Transistors are identified with a prefix of 2N followed by up to four digits.
● The transistor package provides protection, a heat sink, and a support for the leads.
● Transistor packages are identified with the letters TO (transistor outline).
● In a properly biased transistor, the emitter-base junction is forward biased and the collector-base junction is reverse biased.
● PNP transistor bias sources are the reverse of NPN bias sources.
● The internal barrier voltage for germanium transistors is 0.3 V and for silicon transistors is 0.7 V.
collector-base junction is higher than the forward-bias voltage applied to the emitter-base junction.
● When a transistor is tested with an ohmmeter, each junction exhibits a low resistance when it is forward biased and a high resistance when it is
● A transistor is classified according to whether it is NPN or PNP, silicon or germanium, high or low power, and switching or high frequency.
reverse biased.
● Transistor testers are available for testing transistors in and out of circuit.