Among the many decisions the ATE integrator must make during the design phase of a new automatic test system is the selection of the best power supplies for the application. In older-generation rack-and-stack test systems, the choices were simpler—they also were much more limited since there were so few. With the advent of embedded VXIbus power supplies and IEEE 488-controlled power subsystems, many more excellent choices are available today.
With these choices come a more complex set of options and many important trade-offs. Understanding these trade-offs is the key to making an informed decision on which power supply approach is best for your application.
Figure 1 shows the three most common power supply approaches used in modern ATE systems. Each of these choices has advantages that can help you meet your design objectives. The right choice can mean a successful, reliable and profitable ATE development project. The wrong choice can be disastrous.
Embedded VXIbus Programmable Power Supplies
Embedded VXIbus power supplies are available in single-, double- and triple-output configurations to a maximum of 600 W, 400 VDC and 60 A, depending on the configuration selected. These supplies are packaged in dual-slot C-size VXIbus format and usually are message-based devices.
Embedded VXIbus power supplies are well suited for ATE applications where small, lightweight units with fast communication speeds are required. These supplies can be the simplest to use and to integrate since they are packaged and communicate just like any other message-based VXIbus instrument.
Embedded VXIbus power supplies reduce ATE size and weight and increase ATE throughputs since they communicate directly over the VXIbus backplane at high data transfer rates. On the downside, embedded VXIbus power supplies require space within the VXIbus card cage. For example, a triple-output supply requires two VXIbus slots, six outputs require four slots.
IEEE 488 Programmable Power Supplies
By far the most common are IEEE 488 supplies controlled directly from the host computer or from any auxiliary GPIB port off the Slot-0 controller. This choice generally provides flexibility since you usually can find supplies to meet almost any power or voltage level from a wide array of vendors.
In this category, two types of supplies are available. The classical one-box-one supply is still very common and a good choice in applications where large power levels are required (>400 W per output).
The second type is newer to the marketplace. This is a modular subsystem approach where a single IEEE 488-controlled chassis can be configured from a variety of power modules. For many applications, these subsystems provide the best of both worlds—modularity for ease of maintenance and repair, and higher power levels.
VXIbus Controller Cards
VXIbus cards that control external power supplies are really a hybrid of the other two choices. This approach uses a VXIbus commander card (single C-size) which receives commands from the Slot-0 card and retransmits them to external voltage programmable or IEEE 488 supplies.
With this approach, you are not limited in the number or the power level of supplies you can use. If voltage-programmable supplies are used (rather than IEEE 488- controlled), theoretically there should be a sizable cost saving since the controller card replaces the distributed control cards that would be required in GPIB one-box-one-supply configurations.
The system architecture is a main disadvantage of VXIbus-controlled supplies. Generally, the architecture is more complex and usually does not accommodate high test speeds since the controller card represents a second layer of communication not required in the other two choices. Also, some vendors use external IEEE 488 supplies in combination with VXIbus controller cards, adding cost since IEEE 488 controller cards are still needed in each supply used.
Summary
Figure 2 summarizes the three power supply choices on the market today. Each of the choices has advantages and disadvantages depending on the specific application and the objectives for the ATE.
For example, if a new VXIbus test system is intended for a high-volume production environment, the best choice would be embedded VXIbus power supplies since they communicate directly over the VXIbus backplane at high data rates. If the ATE is intended for life testing of larger UUTs, IEEE 488 or a VXIbus controller card would probably be more economical depending on the number of channels required and the power levels needed.
In practice, today’s ATE is usually not intended for a single application but most often for many diverse applications. Ultimately, the best power supply approach combines two or three of the choices. For example, a combination of embedded VXIbus supplies for lower-power/high-volume UUTs used with higher-power GPIB supplies for end-item or larger UUTs usually provide optimum cost/performance benefits.
In the end, use sound judgment and be as knowledgeable as possible about the UUTs to be tested. Invest time to study the power supply choices available on the market. With this data in hand, you will be in the best position to make an informed decision on which power supply approach is best for your objectives.
About the Author
Brian J. Doherty is president and CEO of Advanced Power Designs. Previously, he was manager of field and applications support at NH Research for seven years and regional engineering manager for Nixdorf Computer in South Africa for another seven years. Doherty is a graduate of Witwatersrand College, Johannesburg, South Africa, with a degree in electrical engineering. Advanced Power Designs, 17752 Skypark Circle, Suite 240, Irvine, CA 92714, (714) 263-8605.
Figure 2.
Power Supply Type
Pros
Cons
Best Applications
Embedded VXIbus Power Supplies
Simple
Small/lightweight
Fast communication
Requires two VXIbus card slots for triple output
Low-power UUTs (<1,200 W).
Portable, lightweight ATE
High throughput requirements
IEEE 488 Power Supplies
Wide range of models from many vendors
Ideal for high-power applications
Requires additional rack space and weight
Slow due to IEEE 488 protocol
ATE requiring large power programmable supplies (5 kW to 10 kW)
VXIbus Controller Card With External Power Supplies
Allows analog control supplies to be programmed like a VXIbus instrument
No limit to the number or size of supplies
Can be expensive if IEEE 488 supplies are used
ATE requiring analog programmable supplies
ATE requiring large numbers of programmable supplies (>6 or 9 channels)
Copyright 1996 Nelson Publishing Inc.
November 1996