![]() ![]() And that means if you have mixed sexes, each and every transistor has to have a sex change. Bottom line, most small-signal amplifiers will work equally well if you replace an NPN with a PNP and reverse the power supply polarity. Substituting a PNP in the circuit reverses the current flow through the base-emitter diode and the voltage on the collector. The amount of influence is called the gain of the transistor, or hFE. The current through the collector-emitter path is controlled by the current flowing through the base-emitter junction. The breakover voltage of this diode is the VCE parameter listed on the spec sheet, and varies from one transistor type to another. The collector (C), on the other hand, goes to +V - in effect, reverse biasing that diode. This forward-biases the base-emitter diode, which exhibits the characteristic 0.7 volts voltage drop. The base (B) goes to +V via the Rb resistor. In the NPN configuration, the emitter (the lead that looks like the arrow of a diode, labeled (E) goes to negative (ground). The polarity of the power supply is reversed. Notice that both circuits are identical - except for one thing. On the left is an NPN (negative-positive-negative) transistor and on the right is a PNP (positive-negative-positive) transistor. Let’s take the common-emitter amplifier as shown below, for example. For a transistor to work, one diode is forward biased and the other is reverse biased. NPN and PNP transistors are interchangeable if you remember one simple rule: A bipolar transistor is essentially two back-to-back diodes with the base being the common connection. With TJ Byers Semiconductor Sex Explained Question:Ĭan an NPN transistor be wired as a PNP transistor? Is it a matter of reversing connections?
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