What is a double pulse test?

A double pulse test is a way of checking the time domain behavior of a half bridge power module (transistors and associated circuitry).

In this test the transistor is loaded with current for a very short period. This allows losses, energy and other parameters to be measured without building heat. The temperature can be considered as a control variable.

If desired, heat can be added with a hot plate or climate/environmental chamber to simulate different operating conditions.

Standard “Low Side” Double Pulse Test

Step 1: The low side transistor is turned on, this allows zero current parameters such as stored energy to be measured. The transistor is used to charge a large inductor with current. The inductor is usually air-cored to avoid saturation.

Step 2: The transistor is turned off this allows Turn-off parameters such as Eoff to be measured; the current circulates in the inductor.

Step 3: The transistor is turned on again. This allows turn on parameters such as Eon to be measured. The inductor acts like a current source (similar to many real loads).

Steps 2 and 3 can be repeated to measure different currents (Multiple pulses). Be careful as heat may start to build. Typically, <5 pulses are used.

Step 4: The transistor is turned off to complete the test and stop the current from rising. The current in the inductor will slowly decay due to resistive and body diode losses. Again, Turn-Off parameters such as Eoff can be measured.

Real Waveform: Below is a real waveform from a “Triple Pulse Test” of GaN. Measured On an IWATSU DS-8000 Series Oscilloscope with PMK Probes.

Required Equipment

Half bridge to be tested Load inductor (Should not saturate at maximum test current). Power supply for DC-Link voltage. Power supply for half bridge gate drive and auxiliary circuits.

High voltage oscilloscope probes for VDS (selection)

Low voltage oscilloscope probes for VGS (selection)

HighBandwidth current measurement probes (selection)