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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 switching losses continues to be a major challenge for power device engineers.

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 to configure and set up the test.

But now, the Tektronix 4, 5 and 6 Series MSOs offer automated double-pulse testing measurements and the AFG31000 arbitrary function generator has a built-in software application that enables easy double pulse signal generation. This combination dramatically simplifies double pulse testing.

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 generate gate drive signals for a double pulse test

A function generator may be used to generate the gate drive signal to perform a double pulse test. The Tektronix AFG31000 has a built-in double pulse application to create the pulses with varying pulse widths.

Double pulse test circuit

Equipment set up for conducting a double pulse test

Double pulse test circuit

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

Download the free Double Pulse App for the AFG31000

Watch this video on double pulse testing with the AFG31000

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

Double pulse test waveforms on oscilloscope

Double pulse test waveforms shown on the oscilloscope

Typical double pulse test waveforms are captured and measured using an oscilloscope. 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. Care must be taken in setting the gating regions, since any inconsistency will impact repeatability. Even with care, consistent results can be elusive due to ringing caused by parasitics.

The Wide Bandgap Double Pulse Test application (Opt. WBG-DPT) on the 4/5/6 Series B MSO offers precise double-pulse measurements that make testing easier. The application offers automated switching, timing, and diode reverse recovery measurements per JEDEC and IEC standards. Detailed configuration options enable analyzing real world waveforms and testing beyond standards specification. For more information, refer to the short video in the link below.

Watch this demonstration of automated DPT measurements

Learn more about the DPT application in the datasheet

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