Summary of Field effect transistors (Fets)

Summary

● A JFET uses a channel instead of junctions (as in transistors) for controlling a signal.

● The three leads of a JFET are attached to the gate, source, and drain.

● The input signal is applied between the gate and the source for controlling a JFET.

● JFETs have extremely high input resistance.

● MOSFETs (insulated gate FETs) isolate the metal gate from the channel with a thin oxide layer.

● Depletion mode MOSFETs are usually N-channel devices and are classified as normally on.

● Enhancement mode MOSFETs are usually P-channel devices and are normally off.

● One difference between JFETs and MOSFETs is that the gate can be made positive or negative on MOSFETs.

● The source and drain leads can be interchanged on most JFETs and MOSFETs because the devices are symmetrical.

● Electrostatic charges from fingers can damage a MOSFET.

● Before using, keep the leads of a MOSFET shorted together.

● Use a grounded soldering iron when soldering MOSFETs into a circuit, and make sure the power to the circuit is off.

MOSFETs must be handled carefully to avoid rupture of the thin oxide layer separating the metal gate from the channel.

● JFETs and MOSFETs can be tested using a commercial transistor tester or an ohmmeter.

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