Tech Tip

SENCORE LC102 and SCR250 (Auto-Z)

There are testing limitations of the Sencore, LC102 and the SCR test accessory the SCR250 (Auto-Z) with regard to power semiconductor testing. These limitations need to be understood in order to avoid an erroneous conclusion that certain power semiconductors are "bad", based on the characteristics of the LC102/SCR250, when, in fact, the devices are good. In the Sencore Tech Tips publication number 140, it states that during a leakage test that a thyristor is defective if the leakage is over 10 microamps (0.000,01 amps). A high percentage of power semiconductor devices have maximum leakage current ratings well above 10 microamps (ratings up to 100ma or higher may be common), 10,000 times over what the Sencore Auto-Z's documentation states to be acceptable. This may mislead one to unknowingly discard a perfectly good device.

Another limitation of the Auto-Z is that it has a maximum test voltage of 1,000V. Maximum Vdrm on power semiconductors exceeding 1,000 volts are not uncommon. The Auto-Z is not capable of testing leakage at the rated Vdrm on these devices. It is possible that you may falsely determine that a device is good because you have less than 10 microamps of leakage at 1,000 volts, when in fact, the device may exceed the rated leakage at rated Vdrm and be defective. This may mislead one to unknowingly conclude that a bad device is good.

This test is only acceptable for devices with a maximum Vdrm of 1,000 volts and a maximum Idrm @ Vdrm of 10?A specification.  Tests on devices with higher ratings should be considered invalid.

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.

sencore (rev.#1-3/10/05)