12.12 : JFET の特性

The output characteristics of a JFET describe the relationship between the drain current and the drain-source voltage at various levels of gate-source voltage.

At zero drain voltage and gate voltage, there is no net current flow.

At zero gate voltage, the current in the channel initially increases linearly with a varying source-drain voltage but then slows down. This is because the depletion layer of the reverse-biased gate-drain pn-diode expands.

This region is the Ohmic or linear region, where the JFET functions as a voltage-controlled resistor and can serve as an electronic switch.

As the drain-source voltage increases, the upper and lower depletion regions meet, and the JFET enters the saturation or pinch-off region. At this point, the current reaches saturation.

Beyond this point, the drain current remains nearly constant even with increased drain-source voltage. This is the region where JFETs are typically used as amplifiers.

If the drain-source voltage exceeds a certain limit, the JFET enters the breakdown region. In this region, the drain current increases rapidly, potentially damaging the device.