Reference
3-37
370B User Manual
Opposing offset is most useful when generating voltage steps to test field effect
transistors. When current steps are being generated, the maximum opposing
voltage is limited to 15 volts. This voltage limiting protects the base-emitter
junction of a bipolar transistor from reverse breakdown.
The Step Generator POLARITY INVERT button allows the Step Generator
output (both steps and offset) to be inverted. It has no effect when the CON-
FIGURATION setting is BASE COMMON. Use caution to avoid causing
reverse current to flow between the base and emitter terminals. Voltage limiting
occurs when current steps are being generated and the OPPOSE button is
pressed.
When LONG or SHORT is selected by the PULSE switch, steps are generated in
pulses having a duration of either 300 ms or 80 ms. With the aiding offset, the
offset is added to the step signal as a pulse. With the opposing offset, the offset is
added to the step signal as a DC. Pulsed operation is useful when testing a device
at power levels that might damage the device if applied for a sustained length of
time. Pulsed steps of 300 ms duration occur when LONG is selected. When
SHORT is selected, the duration of the pulsed steps is 80 ms. When either LONG
or SHORT is selected, the Collector Supply mode is automatically set to DC.
The step generator has two mode, Pulsed Offset and DC Offset.
When the device under test (DUT) is Normally-On type transistor,
Pulsed Offset will cause additional heat-up for the DUT. For the Normally-On
type transistor, DC Offset mode should be used.
Pulsed Offset. When the measurement mode is set to Single or Sweep, and the
Step Generator Voltage is set, the base line offset is applied only in the internal
measurement operation interval.
When the device under test (DUT) is Normally-Off type transistor, DC
Offset will cause additional heat-up for the DUT. For the Normally-Off type
transistor, Pulsed Offset mode should be used.
DC Offset. Base line offset voltage is always applied to the DUT in spite of Step
Generator mode and the Measurement Mode setting.
The Pulse Offset is the default mode.
Step Generator Offset
Mode
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