How do I test a bipolar transistor for Collector-Base Breakdown Voltage on my curve tracer?
Collector-Base Breakdown Voltage - V(br)CBO
What It Is:
Collector-base breakdown voltage is the VCB at which a specified ICB flows, with the emitter terminal open. Since it's the reverse current across a junction, the ICB exhibits a knee shaped rise, increasing rapidly once breakdown occurs.
On the curve tracer, reverse bias is applied to the collector-base junction with the Collector Supply. The emitter is held open, and ICB is sensed at the collector terminal.
What The Display Shows:
The display shows VCB on the horizontal axis, and the resulting ICB on the vertical axis. The specification is met when at the specified VCB, ICB 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 VCB
B: Max Peak Power Watts to the lowest setting that satisfies (ICB x VCB)
C: Horizontal Volts/Div to display VCB between the 5th and 10th horizontal divisions
D: Vertical Current/Div to display the ICB between the 5th and 10th vertical divisions
E: Collector Supply Polarity to (+DC) for NPN or (-DC) for PNP
F: Configuration to (Base/Common, Emitter/Open)
G: Variable Collector Supply to minimum % (full ccw)
H: DotCursor ON
2. Apply power to the transistor:
A: Position the Left/Right switch as appropriate
B: Slowly increase the Variable Collector Supply % until either the specified ICB or the specified VCB is attained - whichever comes first
Note - the actual breakdown voltage may be much higher than the specified minimum. If so, use higher Max Peak Volts and Horiz Volts/Div settings
3. Compare to data sheet specifications:
Check that at the specified VCB, ICB is less than or equal to the specified maximum
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