Dynamic Parameters Measurement for Fast Switching Devices


Dr. Christian Rod and Mr. Pierre Goumaz at LEMSYS SA

Continued improvements in the performance of power semiconductors drives demand for corresponding improvements in testing technology. LEMSYS, as a leading supplier with more than 1300 delivered test systems since 1972, has developed a solution specifically dedicated to fast medium power semiconductor devices.

With the LEMSYS PRO-AC test equipment, both manufacturers and users now have access to a performant and economical solution for dynamic parameters measurement.

 

The Motivation Behind PRO-AC Test Equipment

In a world where energy becomes more and more valuable, efficient power electronics devices are bound to increase their market share. The necessary increase in the production capability implies a specific and adapted solution for testing these new and efficient devices, characterized by fast commutations and a high sensitivity to parasitic elements, such as inductance. In order to provide the market with such an adapted solution, LEMSYS has designed the PRO-AC test equipment, which is presented in this article.

 

The LEMSYS PRO-AC 

The test equipment is presented in Figure 1. Restrained in a single compact cabinet. The PRO-AC will fit as easily inside a fully automatic production line as in a qualification laboratory. In the later situation especially, the dedicated electrical output will allow you to change the adaptor in no more than a few minutes, allowing you to easily use the same test equipment with a multitude of different devices and packages. 

 

Lemsys New Pro-AC Test Equipment

Figure 1: Lemsys New Pro-AC Test Equipment

 

The mechanical adaptor is included in a specifically designed test frame that comprises a heating system for tests at devices rated temperature. This test frame can be used in a semi-automatic way (the user start the test sequence through the graphical user interface) or in a full-automatic way (the test sequence is started by the closure of the device-under-test drawer). Depending on the application, the choice between these two modes can be done easily through a dedicated user interface directly on the test frame.  


Regarding the inner conception, it follows the goal of maximum simplicity. The repetitive and modular design leads to maintenance down-times as low as possible, increasing as much the production capability and decreasing the need for spare parts stock.


The graphical user interface of the in-house developed control software (Figure 2) has been conceived to limit to its minimum the time required by the addition of a test sequence. Moreover, this control software includes a lot of useful functionalities such as the possibility to run a test equipment auto-diagnostic, the possibility  to save both plot images and measurement points in case of a failed test for analysis and reporting purposes and the real-time statistics (Figure 3) allowing the user to easily keep an eye on the production quality.  

 

Main control software GUI for test addition

Figure 2: Main Control Software GUI for test edition

 

Display of Real-Time Statistics in the Main Control Software

Figure 3: Display of Real-Time Statistics in the Main Control Software

 

PRO-AC Key Features

Fast switching devices require a test equipment with dynamic parasitic values (inductance and capacitance) as low as possible. The new LEMSYS PRO-AC has been designed with the primary goal to provide the lowest parasitic inductance on the market. LEMSYS is proud to announce that this goal has been successfully reached. Indeed, the measurements taken directly on the device under test (and therefore including both the test equipment and the adaptor) show a value as low as 37.12 nH, as can be observed in Figure 4. 


Such a low parasitic inductance value enables the PRO-AC to perform tests on very sensitive devices, such as the GaN transistor GS66508P, in conditions that create damaging oscillations if performed on other testers available on the market. 

 

Effect of the parasitic inductance on the DC-link voltage during a turn-off

Figure 4: Effect of the parasitic inductance on the DC-link voltage during a turn-off

 

The key dynamic features of the LEMSYS PRO-AC

Table 1: The Key Dynamic Features of the LEMSYS PRO-AC

 

All common switching values, such as turn-on delay, rise-time or switching losses can be measured through different tests using standard single and double-pulse waveforms. Figure 5 illustrates a turn-on test at the LEMSYS PRO-AC rated voltage and current, respectively 1500V and 600A.

 

1500V-600A Double Pulse Waveform on an FZ1200R33KF2 IGBT module

Figure 5: 1500V-600A Double Pulse Waveform on an FZ1200R33KF2 IGBT module

 

Figure 6 illustrates the turn-on behavior of a C3M0065090D SiC device measured on the new LEMSYS PRO-AC.  It can be seen the fast switching capability of the test equipment since the measured rise-time corresponds to the typical value indicated by the manufacturer datasheet, confirming the adequacy of the LEMSYS PRO-AC with the test of wide-bandgap devices.

 

Turn-on behavior of a SiC device (C3M0065090D)

Figure 6: Turn-on behavior of a SiC device (C3M0065090D)

 

Integration of Static Tests

The last key advantage of the new LEMSYS PRO-AC is its ability to be easily upgraded to a full AC and DC test system. Including all the standard static tests, such as leakage current and breakdown voltage up to 3kV, RDSon and/or forward voltage drop up to 2000A and gate leakage current measurements down to only a few nA, this test equipment will be the perfect solution for both production and qualification tests. Moreover, such an upgrade can be done without the need to upgrade the adaptor since they are already fully compatible with LEMSYS full range of tests.

 

Integrating PRO AC-DC into Qualification Laboratories

With the release of the new PRO AC-DC product family, LEMSYS confirms its status of a key player in the power semiconductor test equipment market. With this new product range which addresses both high-performance aspects requested by engineers and economical imperatives imposed by the market and technical issues faced by test engineers. Developed with the goal to gather both high technical performances and the simplest possible use, the PRO AC-DC product family will integrate a production line as easily as a qualification laboratory. Indeed, according to the previously presented results, users can expect:

  1. The lowest stray inductance on the market.
  2. A solution specifically designed for the devices generation.
  3. A use as simple as possible, regarding both the graphical user interface and the change of mechanical adaptor, that allows quick test sequences design and reduced idle time.
  4. The possibility to add an option including all the standard static tests.  

 

More information: LEMSYS    Source: Bodo's Power Systems, March 2016