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# How do I test a diode for Forward Voltage on my curve tracer?

### Question :

How do I test a diode for Forward Voltage on my curve tracer?

Forward Voltage - VF

What It Is:

Forward voltage is the anode voltage when the diode is conducting a specified forward current.

On the curve tracer, the anode is driven by the Collector Supply.

When testing VF on the 370(A), forward current is limited to 10A maximum since pulsed mode only applies to the base generator.  If the 371(A) is used, forward current can be as high as 400A.  This is achieved by operating the 371(A) in it’s High Current mode, in which the collector supply is pulsed with 250uS pulses @ twice the AC line frequency.

What The Display Shows:

The display shows forward anode voltage on the horizontal axis and forward anode current on the vertical axis.  The specification is met when at the specified IF, VF 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 VF

B: Max Peak Power Watts to the lowest setting that satisfies (IF x VF)

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

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

E: Collector Supply Polarity to +DC

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

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

L: Dot Cursor (On)
2. Apply power to the diode:

A: Position the Left/Right switch as appropriate

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

3. Compare to data sheet specifications:

A: Check that at the specified IF, VF is less than or equal to the specified

maximum

This FAQ Applies to:

No product series

Product:

FAQ ID 52641

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