The convenience of an automatic transmission could be worth a few hundred dollars extra, along with power steering, power brakes, cruise control, and other features that you might have put into the necessity category. And how much is comfort worth? All it takes is money.
DC power supplies and AC sources have something in common with the automobile market. Here too, you can find small, low-cost equipment suitable for many applications. Of the approximately 8,000 DC products on the market today, many provide adjustable voltages at several amperes and are well regulated, yet sell for less than $400.
Why pay more? There are some very good reasons. Many applications require features not found in the little guys. For example, mounting and operating in the VXI form factor may make the supply adaptable to your ATE, but it costs a little more than the basic unit. Possibly you need multiple outputs in a small footprint, saving space and simplifying operation. They are available.
Among the AC power source choices, you can have a basic single-phase source or a three-phase model. The output may be 115 V, several hundred volts, or even as much as 30,000 V. What do you need—a real bargain for the run-of-the-mill application or special performance for the more demanding jobs? You can find either, but remember that all these bells and whistles will cost you more.
DC Power Supplies
One thing is very obvious in shopping for DC power supplies. They are getting smarter every year. You may need the intelligence made possible by the ever-increasing availability of appropriate digital signal processing (DSP) circuits. Also, it is not unusual to find sensing and protection for over-temperature, overvoltage, and over-current/short-circuit conditions.
“In the high-power AC-to-DC supply,” according to Mark Edmunds, vice president of engineering at Xantrex Technology, “the biggest advance in the past few years is high-efficiency power conversion. Zero-voltage or soft switching is the technology we use.
“Several of our XFR Series Supplies have 90% efficiency. The circuitry is more complex than with a conventional supply and requires extra components, but it offers several advantages. Noise is lower, and reliability is higher than with other designs. The corresponding reduction in self-generated heat makes the system engineer happy,” he concluded.
This leads to the obvious question: Are linear power supplies on the way out? Linda Broldo and Jae-Yong Chang, product managers at Agilent Technologies, think so. They believe that as the smaller, lighter, less costly switching-mode power supplies approach the performance of linear units, the linear products will become obsolete.
Several products have remote sensing and constant-voltage or constant-current operation. Some supplies can be connected in series for higher-voltage operation or in parallel to get higher current.
“The need for low-noise DC power supplies,” in the opinion of Don Kieffer, IFR Systems distribution manager for Kikusui Electronics and Hameg products in the United States, “is driven by low semiconductor operating voltages. Another factor is the susceptibility of high-speed digital devices to noise and ripple on the power bus.”
Supplies have become more versatile over the years. If you need to operate on single-phase or three-phase power, you can do either. You also can find an on-board digital voltmeter for monitoring the setup, and some supplies have up to three independent outputs. Are you designing with the latest ICs that use 3 V at a few thousand amps? A supply is available to meet your needs.
Battery emulation is important in many applications. Programmable output resistance simulates internal battery-pack operation and provides accurate regulation at the DUT’s battery contacts. Test time can be improved by as much as 30 times with precise battery emulation. This means matching the various battery types and conditions as well as simulating the battery operation as pulsed power is demanded by the DUT.
System friendliness also is improving. Designers are conscious of electromagnetic interference (EMI) limitations on an operating system, and if there is a problem, the power supply shouldn’t be the culprit. Power-factor correction is another significant requirement, and the suppliers are ready. Versatile computer setup using standard commands for programmable instruments (SCPI) now is commonplace and a virtual necessity in ATE applications.
You can find a supply for benchtop operation or full- or part-width rack mounting. For example, Advanced Power has the VXI600 supplies on C-sized VXI cards, each with an on-board microprocessor. Modular supplies are becoming more popular because they provide redundancy, let you expand a test system easily, and have paralleled operation.
Special applications? The manufacturers are ready. You can get a supply for cell phone test where you need recovery from high-speed switching to approximate that of a battery. Some supplies are optimized for testing automobile equipment operating from 11 to 16 VDC. Tests of Internet equipment with high current from 24 V to 48 V also can be accommodated.
The growth of optical technology has led to the introduction of laser diode modules to replace electro-optic regenerators. This created all-optical networks and led Keithley Instruments to develop a precise thermoelectric cooler (TEC) source meter for these new modules, enabling them to maintain wavelength stability.
“The Model 2510’s 50-W source is among the highest available in this type instrument and reflects the industry’s demand for higher-power instruments,” according to Linda Rae, business manager of the component test group. “Another trend is higher channel count in a dense wavelength division multiplex (DWDM) network, which increases the demand for laser modules for optical transmission. Wavelength precision becomes a necessity, and all this requires a new generation of power sources and measurement equipment.”
An out-of-this-world application shows some of the versatility of power supply designs. “If you happen to visit the earth-orbiting international space station next year,” Mr. Edmunds of Xantrex Technology said, “look for the two 1,000-W supplies Xantrex built to operate on the DC power bus of the station. The supplies have a wide range of outputs to aid in troubleshooting the electronic systems up there.”
AC Power Sources
You can find a wide array of features in AC power sources, too. Some supplies offer up to 300 VAC at frequencies from 16 to 500 Hz for commercial or avionics applications. The California Instruments’ 2003RP generates up to 5,000 Hz. For extremely high power outputs, the Ling Electronics’ STARsine® family has a modular 120-kVA source, and Pacific Power Source offers a 625-kVA supply.
There is another factor to be considered, however. “Solid value in test equipment does not necessarily mean more features, but rather the right set of features for their application-specific products,” pointed out Herman van Eijkelenburg, product manager at California Instruments. “Our 2001RP and 2003RP AC Power Sources provide as many volt-amperes as possible without sacrificing performance features such as low noise, low distortion, and good regulation. Discretionary features such as displays, remote control, and transient capability can be added in the applications where they are needed.”
The two most common applications of the Ling Electronics’ AC sources are production test of commercial products at 50 Hz for the export market and test of avionics equipment at 400 Hz, according to Mitchel Orr, the power products sales manager. “About 80% of the AC power market needs simple, high-quality frequency conversion,” he said.
For users who want higher performance, several sources offer a complete set of features such as arbitrary waveform generation, programmable output impedance, harmonic and waveform analysis, single- and three-phase modes, and AC, DC, or AC+DC operation for applications like compliance testing.
Want to simulate disturbances on the line? No problem. You can generate power with dropouts, voltage or phase transients, brownouts, surges, sags, spikes, distortion, noise, and overvoltage or undervoltage excursions. Several models generate arbitrary waveforms, even storing them so you can call them in different sequences.
Power sources can be system friendly, too. Some of them display frequency, voltage, current, power, and power factor. You can take system friendliness a step further with a three-output AC/DC source. You can configure it as a single-output high-current AC or DC source with frequencies up to 1,000 Hz and voltages up to 280 VAC or 400 VDC. Or, you can combine the AC outputs to get a three-phase source or operate as three independent AC or DC sources.
“In measurement and analysis,” Mr. van Eijkelenburg of California Instruments said, “DSPs enable us to offload some complex tasks from the ATE controller to the AC power source. Floating-point DSPs are used in our iX Series controllers for both control and data processing. This technique will migrate down to our lower-cost products as the price of DSPs continues to decrease.”
These versatile power supplies can help you determine what your commercial or avionics product will do if its power source becomes unfriendly. They are ideal for checking product compliance to EU standards for harmonics and emissions. Other applications include phone-ringer simulation, telecom adapter and charger tests, and lighting ballast checks.
“Our most recent AC source designs cover the high currents needed to test big-screen TVs and the high frequencies used in avionics,” Frank Menichello, National sales manager at Global Specialties, noted. “When we see a special requirement, we supply the equipment and start looking for other people who may have the same needs. That’s the best way to expand a product line.”
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September 2000