A fully automatic critical slew rate tester for thyristors

The author describes a critical slew rate (dv/dt) test method for thyristors (p-n-p-n switches). A voltage-controlled ramp function generator has been developed with an adjustable slew rate. The maximum voltage is 400 V and the maximum slew rate is 3000 V/μs. For high-speed measurements, a novel method, denoted as the after-firing method, is developed which reduces the measurement time down to between 1/100 and 1/1000 of the conventional method time. Critical slew rates over the range of 1-3000 V/μs can be measured using this method in about 100 ms.