To measure the reverse breakdown voltage of a diode being tested, the PXIe-4133 outputs a negative current to reverse bias the diode under test, and returns a measurement of the breakdown voltage across the diode. The bias current is programmable up to 10 µA. The PXIe-4133 can measure voltages up to 100 V. You can set a programmable voltage limit that clamps the maximum voltage allowed by the PXIe-4133. Use this feature to limit voltage in the event of an open circuit, a faulty DUT, or a faulty connection failing to provide a path for the flow of bias current.

Refer to the examples included with the NI-4133 Driver software for an example of this operating mode.

Noise Rejection

A common source of unwanted noise for sensitive current measurements is current induced into wiring or test fixtures by external circuits, often at harmonics of the local power line frequency. You can reject noise at these frequencies by averaging samples over an integer number of power line cycles.

In Single Point Per Pulse mode, set the measurement time to a multiple of 20 ms (with 50 Hz power frequency) or 16.666 ms (with 60 Hz power frequency). In Waveform mode, take an average of samples over equivalent periods.

Voltage Clamp Behavior

The reverse output bias current maintains accuracy for load voltages within the specified output clamp voltage. At load voltages beyond (more negative than) the specified clamp voltage, the output current bias current is reduced. The output bias current shuts off and reaches zero current typically between 0.5 V and 2.5 V beyond the programmed clamp voltage. The following figure depicts an example of varying output load voltage with the clamp voltage set to -50 V, for three different output bias current settings.

Figure 17. Output Current Behavior for an Output Voltage Limit of -50 V