Tech Tip

Testing Limitations of the Consolidated Electronics PST2000 & PST5000


Some numbers of our customers who have used the Consolidated Electronics, Inc., www.con-elec.com, PST2000 and PST5000 analyzer to test power semiconductors have concluded (based on the PST2000 and PST5000 test results) that certain power semiconductor devices are out of spec and therefore defective. In most cases such conclusions were incorrect, and were caused by limitations or operating principles of the PST2000 and PST5000. These situations have been cause for confusion. This is not to say that there is anything wrong with the PST2000 or PST5000. In all such cases it is just a situation of understanding the instrument's limitations and operating principles. This is important to avoid an erroneous conclusion that the semiconductors are "bad" , based on the characteristics of the PST2000 and PST5000, when, in fact, the devices are good.

The major limitation of the PST2000 and PST5000 is that in the high voltage test mode, the maximum current output is 2.3ma. In this test the voltage and resulting leakage current are used to evaluate device blocking voltage capability. Once this limit of 2.3ma is reached, the tester will no longer increase voltage output. If the 2.3ma limit is reached before the device rated blocking voltage is achieved, most customers conclude the device is below spec on blocking voltage. A high percentage of power semiconductor devices have maximum leakage current ratings well above 2.3ma (ratings up to 100ma or higher may be common). Therefore, in many cases a good device is assumed to be "bad" based on the test results.

Another area of concern is that the tester will continue to increase applied voltage to a device under test as long as the test button is depressed and the 2.3ma limit has not been reached. It is therefore possible to impose a higher voltage on the device than it is rated for, which may damage or destroy the device.

Information deemed reliable but not guaranteed due to constant changes that are occurring in governing codes and regulated official documents. When in doubt, consult with the appropriate governing authority for the latest information.

Information taken from Neil K. LeJeune, BSEE Westcode Semiconductors, Inc. Long Beach, CA. www.westcode.com.

conelectric (rev.#1-3/10/05