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Double pulse testing on the AFG31000 arbitrary function generator

Double pulse testing

Create waveforms and automate
testing of power devices

Faster time to market for your power conversion designs

Semiconductor materials used in power electronics are transitioning from silicon to wide bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) due to their superior performance in automotive and industrial applications. However, minimizing switch losses continues to be a major challenge for power device engineers. These designs must be rigorously measured to ensure compliance.

Double Pulse Testing is the standard method for measuring the switching parameters of MOSFETs or IGBT power devices. Historically this has been a time-consuming process to set up the double pulse test since function generators do not have a built-in way configure and set up the test.

But now, the Tektronix AFG31000 arbitrary function generator has a built-in software application that enables double pulse testing right from the touchscreen interface of the instrument dramatically simplifying the process for engineers.

Download the Double Pulse Test Software

How Double Pulse Test Works

The double pulse test is done with an inductive load and a power supply. The inductor is used to replicate circuit conditions in a converter design. The power supply is used to provide voltage to the inductor. An arbitrary function generator is used to output pulses that triggers the gate of the MOSFET and thus turns it on to start conduction of current.

Double pulse test circuit

Double pulse test circuit

Double pulse test circuit

Current flow with MOSFETs as DUTs

How to set up and perform a double pulse test

In order to conduct a double pulse test, you will need the following instruments:

  • Arbitrary function generator – The Tektronix AFG31000 has a built-in double pulse application to create the pulses with varying pulse widths
  • Oscilloscope to measure Vds, Vgs and Id.
  • IsoVu Probe - A high-common mode rejection probe to measure Vgs
  • DC power supply or source measure unit (SMU)
Double pulse test circuit

Equipment set up for conducting a double pulse test

Once your equipment is set up, you can create pulses with varying pulses widths right on the AFG31000 from the touchscreen display.

Double pulse test circuit

Double Pulse Test set up screen on the AFG31000 arbitrary function generator

Now you are ready to conduct the test and review the results on the oscilloscope.

How to measure turn-on and turn-off timing and energy losses

Double pulse test circuit

Double pulse test waveforms shown on the oscilloscope

Typical double pulse test waveforms are captured on the oscilloscope and shown below.In order to calculate the turn-on and the turn-off parameters, we look at the falling edge of the first pulse and the rising edge of the second pulse. The industry standard to measure the turn-on and turn-off parameters is shown in the image. The screen captures below show the waveforms captured on the scope and the measurements for turn-on parameters. Using the cursors, the timing parameters can be retrieved. Using the Math function, the turn-on loss during that transition can be calculated.

Measure reverse recovery

Reverse recovery current occurs during the turn-on of the second pulse. As shown in Figure 20, the diode is conducting in a forward condition during phase 2. As the low side MOSFET turns on again, the diode should immediately switch to a reverse blocking condition; however, the diode will conduct in a reverse condition for a short period of time, which is known as the reverse recovery current. This reverse recovery current is translated into energy losses, which directly impact the efficiency of the power converter. The measurements are now done on the high side MOSFET. Id is measured through the high side MOSFET and Vsd across the diode.

Double pulse test circuit

Diode reverse recovery