By Jim Pennington
Autotest Company, San Antonio, TX

Test Engineers may be finding it more and more difficult to keep up with the growing and changing demands created by the never ending craze for "High(er) Tech" power supplies.  I suspect that to the volume manufacturers of power supplies, the battle seems unending.  There is, of course, the always-present demand for greater IC integration, involving higher component and power density.  

Notwithstanding these expected and ongoing developments with product design and performance requirements, there's a fairly new "trick" available for helping engineers to better accomplish these goals.  The "trick" is to make power supplies that "talk" as well as "listen".  Communication "enhancements" enable the power supply to assume more responsibility for monitoring and governing its own "health".

As Applications Engineering Manager for Autotest Company, I see a lot of new stuff - and over the years have witnessed the migration of many new technologies into the world of power supplies.  Our Functional ATE systems have always required specialized Unit Under Test (UUT) communications. These needs have been addressed with a variety of solutions involving protocols, busses, and advanced levels of component integration and complexity.  For some high tech Department of Defense (DOD) products, we employed what have become now proven and accepted solutions such as RS232, RS 485, IEEE 802.3 Ethernet, IEEE 488, MIL 1553, I²C, and many others.  These technologies can simply read a serial number from a register or actually direct the Power Supply through a complete routine of calibration and internal verification.  In such cases, the ATE's hardware or equipment responsibilities may be simple, but the communication process, coordination and test sequencing can be quite complex.  

Along with the continuing trend for making the power supplies more technologically capable, powerful, versatile and complex there's a rapidly expanding area of expansion in the field of self-diagnostics and maintenance.   We are also seeing more and more the use of processors in power supplies ... to make them more versatile and flexible for diverse applications.  A typical application is with power supplies that are employed as sub-systems of a more complex DOD product.  These power supplies are often asked to provide much more than just delivering system power.  They are often integrated and designed to monitor, react and respond to variable and changing requirements of a much more complex system.

At Autotest, we first addressed these more complex phenomena with the introduction of our UPS ATE.  The Uninterruptible Power Supply (UPS), by design, has a responsibility to communicate with the computer to which it is delivering backup power.  UPS manufacturers, taking advantage of the need for UPSs to have communication and processing ability decided to let the processor do other things as well, like calibrate output parameters and provide functional controls for supporting them.   Built In Test (BIT) functionality is becoming more common with power supplies, making them capable of being programmed to sequence through an internally controlled test process and to report the results.  With the integration of a processor and a bi-directional, software-controlled communication bus to manage this process, significant additional diagnostics and information can be provided.

The latest communication trend in communications for commercial power supplies is in the application of the IIC Bus (Inter-Integrated Circuit), or I²C as it has come to be called.  The I²C Bus is an essentially a two-wire, low to medium speed, communication bus developed by Philips Semiconductors in the early 1980s.  It was created to provide a low-cost chip-to-chip communication links for such things as volume and contrast controls in radios and televisions. Over the past two decades, the I²C has expanded its communications role to include power supplies.

So how do Power Supply ATE manufacturers, such as Autotest, address the changing needs of the Test Engineer? Communication has always been an integral part of Autotest's ATEs.  We use IEEE 488 extensively to control instrumentation, making communication integral with all our systems.  Our open-ended software and language simplifies development of Windows supported communication as an inherent function of test programs for the UUT.  Perhaps our greatest challenge has been in developing the language library to simplify the process of building flexible and comprehensive routines into tests.  The I²C posed a challenge in that regard.  A commercially available PC bus controller, however, provided a simple solution for adapting the I²C to developing hardware and software integration for controlling communication as a part of testing the power supply.  Our APG for Windows^TM software, implementing and integrating new protocols and busses, has provided test engineers with an automated test programming and system control environment tailored to the needs of most any Power Supply.  It allows a Test Engineer to design simple solutions for complex routines for engaging a power supply to whatever type of interaction may be required.

In essence, the marriage between power supplies and functional testing is a longstanding and always developing relationship.  To coin a proven metaphor, "the key to any good marriage is communication."