I have been working with a semiconductor test and measurement company who are long time friends to develop a SOA [Safe Operating Area] testing system for discrete semiconductor devices. The company isand I worked for them designing test and measurement hardware for their products for over 5 years before I went solo.
More info on what SOA is and how and why its tested can be found
The Safe Operating Area test system will apply a specified voltage and current to a MOSFET or BJT transistor for a specified time period ranging from 10uS to 10 seconds. This will place the device under test into its linear region, forcing it to dissipate a high amount of power. The test ensures that the DUT (Device Under Test) can sustain the applied power for the required time without failure. The test system will be able to supply up to 200 amps of current and 600 volts – though not at the same time. Higher currents are available only at lower voltages, and higher voltages come with lower current delivery. Even the SOA tester has an SOA rating. Ha.
Designing a system that can deliver a tightly regulated 200 amps of current for 10 seconds is no easy task! The Focused Test SOA Tester will utilize a switched mode current source for high current long duration SOA tests, as well as a high speed linear regulated source for the shorter duration tests that require a faster rise time than the switched mode source can deliver.
My role in this project is PCB layout and design consultation.
Here is what is going on in the lab at Focused Test :
To the right is a prototype of the linear current source interfaced to the FTI1000 test system for control.
A close up of the linear current regulator. The output stage devices can be seen along the bottom on small heat sinks with a To220 current sharing resistor. The breadboard contains gate driver circuity, and the main control / error amplifier. This circuit takes an input from a DAC, and converts it to a corresponding output current.