How can I test a MOSFET for Gate Threshold Voltage on my curve tracer?
Gate Threshold Voltage - VGS(th)
What It Is:
Gate threshold voltage is the lowest VGS at which a specified small amount of ID flows. The test is run with VGS = VDS.
On the curve tracer, the Collector Supply provides VDS. Patch cords are used to short the gate to the drain so that VGS=VDS.
What The Display Shows:
VGS is displayed on the horizontal axis, and the resulting ID is displayed on the vertical axis. The specification is met when, at the specified ID, VGS is within the min/max limits.
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 (ID x VDS)
C: Horizontal Volts/Div to display VGS between the 5th and 10th horizontal divisions
D: Vertical Current/Div to display the specified ID 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/Open, Emitter/Common)
G: Variable Collector Supply to minimum % (full ccw)
H: DotCursor ON
2: Attach patch cords:
A: Connect a patch cord between the base and collector terminals on the unused side of the interface area
B: Connect a second patch cord between the base sense and collector sense terminals on the unused side of the fixture area
3. Apply power to the MOSFET:
A: Position the Left/Right switch to Both
B: Slowly increase the Variable Collector Supply % until either the specified ID or the maximum threshold voltage is attained – whichever comes first
4. Compare to data sheet specifications:
Check that the gate threshold voltage is within the specified min/max limits
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