How do I test a SCR for Gate Trigger Voltage on my curve tracer?
Gate Trigger Voltage - VGT
What It Is:
Gate trigger voltage is the gate voltage 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 voltage 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 VG 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 Voltage
J: Step Generator polarity to +
K: Step/Offset Amplitude to approx 50% of the specified VGT
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 VG until the device switches to the unblocked (On) state - note the value on the Offset readout
4. Compare to data sheet specifications:
Check that VG is less than or equal to the specified maximum
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