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.