2SK170 Transfer Curve Sweep

Application

This circuit shows the 2SK170 as a depletion-mode N-channel JFET under DC transfer-characteristic test conditions. It is useful when choosing a gate-bias range for low-noise input stages, current sources, and small-signal analog front ends.

Design Context

VDD holds the drain load at 5 V through RD while the source is tied to the common return. VGS drives the gate from -2 V to 0 V in a DC sweep, so the chart plots drain current as the gate becomes less reverse-biased. The current probe in the drain branch reports Id.

Expected Behavior

At the most negative VGS values, the channel should be nearly pinched off and Id should be small. As VGS approaches 0 V, the depletion-mode channel opens and drain current rises toward the zero-bias operating point. The curve should make the pinch-off region and useful bias range easy to compare.

Key Values

• VDD: 5 V fixed drain supply.
• RD: 1 kOhm drain load.
• VGS sweep: -2 V to 0 V in 20 mV steps.
• Id: drain current measured in the upper drain branch.

Suggested Experiments

• Narrow the sweep around the knee to inspect the pinch-off transition more closely.
• Increase RD to see how load resistance limits the upper drain-current range.
• Compare the transfer curve with a P-channel JFET by reversing the bias polarity.

Featured Component

The 2SK170 N-channel JFET is the device under test. Its gate voltage controls the drain-source channel current, so this transfer sweep highlights the relationship between gate-source bias and drain current.