# How do I test a JFET for Gate-Source Breakdown Voltage on my curve tracer?

### 问题：

How do I test a JFET for Gate-Source Breakdown Voltage on my curve tracer?

### 答案：

Gate-Source Breakdown Voltage - V(br)GSS

What It Is:

Gate-source breakdown voltage is the VGS at which a specified IG flows with VDS=0.  Since it's the reverse current across a junction, IG exhibits a knee shaped rise, increasing rapidly once breakdown occurs.

On the curve tracer, the test is performed by grounding the drain and applying reverse bias to the gate with the Collector Supply.  The drain is shorted to the source with an external jumper so that VDS=0.
What The Display Shows:

The display shows VGS on the horizontal axis, and the resulting IG on the vertical axis.  The specification is met when at the specified IG, VGS is greater than or equal to the specified minimum.

How To Do It:

1. Set controls:

A: Max Peak Volts to the lowest setting above the specified VGS

B: Max Peak Power Watts to the lowest setting that satisfies (specified IG x specified VGS)

C: Horizontal Volts/Div to display VGS between the 5th and 10th horizontal divisions

D: Vertical Current/Div to display IG between the 5th and 10th vertical divisions

E: Collector Supply Polarity to (-DC) for N-channel or (+DC) for P-channel

F: Configuration to (Base/Common, Emitter/Open)

G: Variable Collector Supply to minimum % (full ccw)

H: DotCursor ON

2. Connect jumper:

Using a jumper, short the source and drain holes on the socket adapter

3. Apply power to the JFET:

A: Position the Left/Right switch as appropriate

B: Slowly increase the Variable Collector Supply % until the specified IG is attained

4. Compare to data sheet specifications:

Check that at the specified IG, the VGS is greater than or equal to the specified minimum