An npn Transistor Tester

摘要

A frequently-used method of checking that an npn transistor is not faulty involves measuring the resistance of its p-n junctions, ie between the base and emitter and the base and collector. These resistance values should be low when the junction is forward-biased (anode positive, cathode negative), and high when reverse-biased (anode negative, cathode positive). Additionally, the measured resistance between the collector and emitter should always be high since, whatever the polarity of the test voltage, one of the two 'back-to-back' junctions will always be reverse-biased. This means a minimum of five checks must be made with a multimeter, for example, before a transistor can be considered good.