# How do I test a JFET for Reverse Gate Leakage on my curve tracer?

### 問題：

How do I test a JFET for Reverse Gate Leakage on my curve tracer?

### 答案：

Reverse Gate Leakage - IGSS

What It Is:

Reverse gate leakage is the IG that flows at a specified VGS and 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 VGS, IG is less than or equal to the specified maximum.

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: Configuration to (Base/Common, Emitter/Open

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

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 VGS is reached

4. Compare to data sheet specifications:

Check that at the specified VGS, IG is less than or equal to the specified maximum

Note 1: The gate current may be so low that it becomes necessary to use Mag mode to obtain a meaningful reading.  Press the Mag X 10 button and use the Display Position buttons to center the display.

Note 2: If noise becomes a problem, select Avg as the Acquisition mode.  Avg  averages 16 samples to reduce noise.