N-channel versus P-channel

Chapter N-channel versus P-channel

Teach Yourself Electricity and Electronics Third Edition Book
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Teach Yourself Electricity and Electronics Third Edition Book

  • N-channel versus P-channelA simplified drawing of an N-channel JFET, and its schematic symbol, are shown inFig. 23-1. The N-type material forms the channel, or the path for charge carriers. In theN-channel device, the majority carriers are electrons. The source is at one end of thechannel, and the drain is at the other. You can think of electrons as being “injected” intothe source and “collected” from the drain as they pass through the channel. The drainis positive with respect to the source.N-channel versus P-channel41723-1Simplified cross-sectional drawing of an N-channel JFET (at A) and itsschematic symbol (at B).In an N-channel device, the gate consists of P-type material. Another, larger sectionP-type material, called the substrate, forms a boundary on the side of the channel op-posite the gate. The JFET is formed in the substrate during manufacture by a processknown as diffusion.The voltage on the gate produces an electric field that interferes with the flow ofcharge carriers through the channel. The more negative EG becomes, the more theelectric field chokes off the current though the channel, and the smaller ID becomes.A P-channel JFET (Fig. 23-2) has a channel of P-type semiconductor. The major-ity charge carriers are holes. The drain is negative with respect to the source. In a sense,holes are “injected” into the source and are “collected” from the drain. The gate and thesubstrate are of N-type material.In the P-channel JFET, the more positive EG gets, the more the electric field chokesoff the current through the channel, and the smaller ID becomes.You can recognize the N-channel device by the arrow pointing inward at the gate,and the P-channel JFET by the arrow pointing outward. Also, you can tell which iswhich (sometimes arrows are not included in schematic diagrams) by the power-supplypolarity. A positive drain indicates an N-channel JFET, and a negative drain indicates aP-channel type.