How do I test a SCR for Gate Trigger Current on my curve tracer?
Gate Trigger Current - IGT
What It Is:
Gate trigger current is the gate current required to switch the device from the blocked (Off) state to the unblocked (On) state.
On the curve tracer, the anode is driven by the Collector Supply and the gate is driven by the Step Generator. The test is made by applying the specified anode voltage, then slowly increasing gate current until the SCR switches to the unblocked (On) state.
What The Display Shows:
VD is displayed on the horizontal axis, and the resulting ID is displayed on the vertical axis. The specification is met when the IG required to switch the device to the unblocked (On) state 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 VD
B: Max Peak Power Watts to the lowest setting that satisfies (ID x VD)
C: Horizontal Volts/Div to display VD 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
F: Configuration to (Base/Step Gen, Emitter/Common)
G: Variable Collector Supply to minimum % (full ccw)
H: Number of steps to minimum (zero)
I: Step Generator to Current
J: Step Generator polarity to +
K: Step/Offset Amplitude to approx 50% of the specified IGT
L: Variable Collector Supply % to minimum (full ccw)
2. Apply power to the SCR:
A: Position the Left/Right switch as appropriate
B: Slowly increase the Variable Collector Supply % until the specified VD is reached
3: Apply gate current:
A: Press Offset Aid to gradually increase IG until the device switches to the unblocked (On) state - note the IG value on the StepGen Offset readout
4. Compare to data sheet specifications:
Check that IG is less than or equal to the specified maximum
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