Power supplies and sources have become progressively more sophisticated in response to the needs of today’s ultrasensitive electronic products. Changing voltage requirements of a product call for a supply that is easily programmed.
Whether linear or switched-mode technology, most power supplies offer programming capabilities. They may be programmed with a keypad or potentiometer or remotely with analog or digital interfaces. The analog programming method includes the application of external voltage, current, or variable resistance. Analog interfaces often are sufficient for simple applications such as programming the output voltage of a power supply. For example, a production test of consumer appliances may need to vary the voltage between the upper and lower limits that the appliance normally encounters.
Digital control usually is accomplished via an IEEE 488 or RS-232 interface, with the program residing in an external controller or PC. Generally, digital control is required for extended test sequences. Applications are high- and low-voltage margin tests and power interruption for transients tests.1
New uses for AC sources include specialized power needs for the lighting industry, telecommunications AC/DC adapters and chargers, and telephone ringer simulation, said Dan Jaeger, sales development engineer at Hewlett-Packard. The lighting product manufacturers, for example, need AC sources to test electronic ballasts at different voltages and frequencies.
The telecommunications AC/DC adapters and chargers also are tested with AC power sources, said Mr. Jaeger. Millions of these products are made every year, and they need high-quality and reliable AC power sources for design verification and stress testing.
Regulatory testing is another use for AC power sources. The harmonic-current emissions limits imposed by the European Union require AC power sources with low distortion and impedance to perform the necessary compliance tests, said Herman van Eijkelenburg, product manager at California Instruments. Manufacturers in the United States also need 50-Hz frequency capability for products bound for Europe.
In addition to current-harmonic emissions, AC disturbance susceptibility must be tested, including dropouts and power interruptions on AC-powered equipment. Many of the susceptibility tests require AC transient programming capability with precise angle control, said Mr. van Eijkelenburg.
Programmable power supplies are now used to test portable, wireless devices such as cellular phones and mobile radios, said Robert Green, product marketing manager at Keithley Instruments. Testing a cellular phone requires a power supply with a fast recovery to load changes so it can provide a stable output. This is especially important when the cellular phone transitions from a low-current standby mode to a full-power transmit mode. During these transitions, it is not uncommon for the load on the battery to change from tens of milliamps to several amps in just 20 to 50 m s.
For Time Division Multiple Access cellular phones that transmit data in pulses shorter than 1 ms, the transmission can be over before the power supply has recovered, said Mr. Green. A slow recovery power supply would not supply sufficient power during the pulse transition and could compromise phone performance. Testing is difficult because problems with the power supply would have to be compensated for in the fixturing, test-time, and test-procedure modifications.
Power supplies also must provide 48 VDC for telecommunications manufacturers and supply an 80-V to 90-V signal for checking ring circuits, added HP’s Mr. Jaeger. A flexible power supply allows you to stress test your designs by applying higher voltages than the product rating.
The global growth in the use of RF and wireless technology has increased the use of power supplies in satellite power-system testing and array simulation, said Ron Nauman, an applications engineer at Sorensen. These applications require that the power supplies, batteries, and telemetry equipment be simulated before the final module is mounted in the launch vehicle. The power supply must precisely control voltage and current and read back the test module conditions in real time.
Today’s automobiles also have incorporated many electronic packages into their final product that need power supplies for testing. The automotive modules control heating, air conditioning, front-panel dashboard controls, headlight dimming, and even global positioning systems. All of these subsystems require DC testing and evaluation, said Mr. Nauman.
The supply must simulate an automotive DC bus ranging from 11 to 16 V. It lets you test the system precisely and analyze data in real time using remote read-back of voltage and current from the power supply.
Manufacturers testing battery-life specifications require power supplies with built-in measurement capabilities that test current consumption, said Mr. Green of Keithley. You can do this with power supplies that measure DC standby currents with 0.1-m A sensitivity and full-load pulse currents as short as 60 ns.
Another factor to consider is the output noise generated by the supply. Batteries used in portable devices provide inherently low noise power.
To test a battery-operated device with a power supply, make certain the noise generated by the supply will not affect testing or operation of the device. Power-supply noise usually consists of some voltage ripple and also could contain some higher- frequency ringing and spikes.
Generally, linear supplies generate less noise than switching power supplies. However, some linear supplies can be noisy if their internal power-conversion circuitry creates noise. While switching supplies are inherently noisy because of high-frequency switching, they can be made less noisy through careful design, good layout, and use of appropriate output filters.
The ideal power supply for a cellular phone test system should respond like a voltage-programmable battery. Unfortunately, the typical power supply has less than ideal load-transient recovery response.
The voltage will droop and the supply will require some period of time to recover. This slow response makes it difficult to test the UUT’s pulse operating conditions at the low end of the specified battery voltage. In some types of equipment, an insufficient level of voltage trips the under-voltage detect circuit, shutting down the device.2
The ability of the power supply to respond to load transients is directly related to its open-loop response characteristics. The open-loop response of a power supply is a way to measure its stability and transient response. The response is affected by the type of load applied.
The power-supply designer uses the open-loop response characteristics to optimize the transient response of the power supply while ensuring its stability under all possible loads. It usually requires a trade-off between transient performance and stability.
Two important parameters of a system’s open-loop response are the bandwidth and gain. The greater the bandwidth, the better the capability of the power supply to respond to rapid load changes. The higher the gain, the less the supply will droop in response to the pulse load. The magnitude of both variables, however, is limited by the supply’s stability requirements.
The challenge is to select a power supply that will be stable with the device’s load characteristics, while having enough gain and bandwidth to respond to the device pulse requirements.
Software Capability
Customers are requesting software that allows them to ramp up the power supply, said Sorensen’s Mr. Nauman. They want to start at a preset voltage or current and ramp up to a predetermined set point at a preselected time increment.
In the past, this was accomplished by writing loops in the program which resulted in quasistep waveforms, added Mr. Nauman. If you were lucky, you might get only a 10% voltage overshoot.
Newer power supplies that offer programming support provide ramp up of the power supply with a single standard command for programmable instruments (SCPI) instruction. This sequence means loop commands no longer have to be written.
The growing demand for programmable power supplies requires the use of standardized programming mnemonics such as SCPI and makes it necessary for units to be compatible with graphical user interface (GUI) programs such as LabVIEW® and LabWindows®, said Vince Mutascio at Power Ten. The SCPI command set lets you interface directly with other equipment on the bus without writing new software to handle the power supply.
A power supply with a GUI program also permits you to perform power-supply data acquisition and analysis and present it on a PC screen. It simplifies the process of monitoring and controlling the power supply directly from your computer.
Power supplies and sources continue to add new capabilities to help you perform your testing quickly and easily. They are available to support your power needs for a myriad of applications from production line testing to research and development.
References
1. Jacob, G., “Examining Power Supply Architectures and Capabilities,” EE-Evaluation Engineering, September 1996, pp. 79-89.
NOTE: This article can be accessed on EE’s Test Site at www.nelsonpub.com/ee/. Select EE Archives and use the key word search.
2. Cawley, K., Power Supply Transient Response Considerations When Testing Portable Wireless Devices, Keithley Instruments, October, 1996.
Power Supplies/Sources
Supply Offers 5-V to 250-V
And 20-W to 600-W Models
The PowerDigm Series of programmable DC power supplies is offered in 5-V to 250-V, 20-W to 600-W models. The user-configurable modules are available in 1/4-, 1/2-, and 3/4-rack-width sizes. A single command can provide access to eight output channels. Test interfaces include GPIB, VXI, and RS-232. Closed-case calibration is provided, and a master unit controls up to eight auxiliary supplies. Starting at $795. American Reliance, (818) 303-6688.
Low-Height AC Source Delivers
Up to 270 Vrms
The 1251RP is a low-cabinet-height, 1,250-VA AC power source that delivers a sinusoidal output voltage to 270 Vrms at frequencies from 16 Hz to 500 Hz. Voltage, frequency, and current can be adjusted from the front panel. A universal power-factor corrected input accepts 85 VAC to 265 VAC from 47 Hz to 63 Hz. Applications include testing per the requirements of IEC 555-2, IEC 1000-3-2, and EN 61000-3-2 harmonics standards. RS-232 and IEEE 488 interfaces are provided for remote control of the source. $3,950. California Instruments, (800) 422-7693.
Programmable Power Supply
Has Four Output Channels
The PC-462 Programmable Power Supply Board has four output channels individually selected by software for ranges to ±6.1425 V at 1 A and to ±20.475 V at 250 mA. Each channel includes output current limiting for protection from overload and short-circuit conditions. Remote sensing helps regulate voltage with respect to load. Four analog input channels and four digital I/O lines can be used to monitor and control external devices. Two MOSFET digital output lines switch loads up to 300 V at 100 mA. $1,495. Datel, (508) 339-3000.
Programmable Modules
Supply 400-W Load Capacity
The EL Series of analog-programmable electronic load modules consists of three models rated from 50 V to 500 V with load currents from 0.1 A to 25 A. Up to 400 W can be dissipated with external heat sinking. The modules combine with the company’s EL-465 Load Controller Board and EL-467 Power Supply Measurement Board for power supply testing applications. Additional applications include battery, current source, and capacitor discharge testing as well as power-resistor substitution, real-time load simulation, and dynamic power-supply burn-in. $999. Eltest, (508) 339-8210.
DC Power Supply
Has Triple Output
The 1302-B Power Supply is a triple-output DC unit for industrial and laboratory uses. Two outputs are continuously variable from 0 to 32 V and supply up to 2 A each. They operate in the constant-voltage or constant-current mode. A separate 5-V output is provided variable from 4.5 VDC to 5.5 VDC with a maximum current of 5 A. Automatic overload protection is accomplished via fast transitions from the CV to the CC mode and can be set at any point in the current or voltage range. $595. Global Specialties, (800) 572-1028.
Supply Used as Sink/Load
And Power Amplifier
The Programmable HM8142 Power Supply offers a regulated triple output and can be used as an electronic sink/load, a power amplifier, and an arbitrary waveform generator. The linear supply has two variable and electrically isolated outputs with a maximum voltage to 30 V and 1 A. Both outputs can be combined in series or parallel. The third output provides 5 V at a maximum of 2 A. The sense operation compensates for voltage drops between the supply and connected load. The arbitrary waveform function generates a time-varying waveform from a table of 512 pairs of voltage and time-duration parameters. $1,188. Hameg, (760) 630-4080.
DC Power Supply Has
0.01% Load/Line Regulation
The HP E3632A DC Power Supply is a dual-range, programmable unit with 0.01% load and line regulation. Output voltages are 0 to 15 V @ 7 A and 0 to 30 V @ 4 A. The linear supply offers normal-mode voltage noise of <350 µVrms/2 m Vpp noise and common- mode current noise of <1.5 µA rms. It provides IEEE 488 and RS-232 interfaces. Programming is performed using SCPI instructions. $995. Hewlett-Packard, (800) 452-4844.
Source Delivers
375 VA AC Power
The HP 6811A AC Power Source/Analyzer supplies 375 VA AC power. The unit offers a built-in power analyzer, a programmable line-impedance network, an arbitrary waveform generator, and a power amplifier. It sources peak currents up to 40 A, which is 12× its maximum rms current rating. Additional capabilities include rms-, peak-, and inrush-current measurements as well as generation of dropout and arbitrary waveforms. $3,850. Hewlett-Packard, (800) 452-4844.
Precision Voltage/Current
Source Is Programmable
The VI-700 is a precision manually controlled or remotely programmable voltage and current source. Three ranges provide up to 20-V full scale and better than 100-m V resolution or 20-mA full scale with 0.1-m A resolution. Both voltage and current outputs are available simultaneously. The unit features 5 mW output impedance, and noise and ripple is 50 uV rms. VI-700: $495; remote programming option: $195. IET Labs, (516) 334-5959.
Triple Output Supply
Provides ±32 V, ±3 A
The Model PPE-1323 Power Supply provides programmable voltage from 0 to 32 V and current from 0 to 3 A. It has over-voltage protection from 0 to 33 V. The voltage-load effect is £ 6 mV and the current load effect is £ 3 mA. The unit stores and recalls 100 points and includes an RS-232 interface. $745. Instek, (818) 336-6537.
Power Source Developed
For Automated Testing
The 2304 Power Supply provides power control, load sinking, and current monitoring for IEEE 488-based test systems. With a capacity of 100 W, it delivers 5 A at 20 V. The source can also be used as an electronic load and sink current up to 3 A. The 2304 measures peak current on pulses as narrow as 500 m s. $2,495. Keithley Instruments, (800) 552-1115.
Upgraded Series Has
Three Output Ranges
The BHK-MG Series of power supplies has three output ranges from 0 to 500 V @ 400 mA, from 0 to 1,000 V @ 200 mA, and from 0 to 2,000 V @ 100 mA. The linear design uses a high-voltage FET stage for a fast-responding output. Control is via a front- panel keypad with 12-bit resolution or remotely via a built-in GPIB interface. Accuracy is <0.025% with stabilization better than 0.005% for a full load change. $2,595. Kepco, (718) 461-7000.
AC Source Provides
4.5 kVA to 9 kVA Power
The Starsine® AC Power Source features controlled power from 4.5 kVA to 9 kVA from 47 Hz to 63 Hz. Standard features include direct voltages to 525 VAC, one or three phases, 24 selectable waveforms, and an RS-232 interface for remote programming. A special input circuit ramps the input turn-on; other circuitry removes output load prior to shutting down the input power. Typical efficiency is 90% at full load. $17,450. Ling Electronics, (800) 321-1781.
DC Power System Has Dual
Linear Supply Modules
The 92C163 Linear Power Supply System provides redundant output of 28 VDC at 0 to 10 A. The system has two AC inputs so it can be powered from two separate AC sources. The internal power-supply modules are independent units that use a diode OR method for redundant mode operation. Either power supply can be removed from the assembly without disturbing the unit’s operation. Line regulation is <0.05% and load regulation is <0.05% for a no-load to full-load step. $1,498. Mid-Eastern Industries, (201) 385-0500.
Programmable DC Supply
Provides 20-kW Output
The I66 Series DC Power Supplies provide up to 20 kW in a single rack-mount chassis. The 10½”-high units are designed for ATE, process-control, RF- amplifier, and medical applications. Read-back of voltage and current and 12-bit resolution programming for querying settings, faults, and errors are supported. Sixteen output-voltage and current combinations range from 0 to 80 V @ 250 A to 400 V @ 50 A. Constant current and voltage are user-selectable with auto crossover. Starts at $7,000. Power Ten, (408) 871-1700.
Power Amp Precisely Controls
Output Voltages to 10 kV DC
The Model 10/10A High-Voltage Power Amplifier controls output voltages from 0 to ±10 kV DC or peak AC with an output current range from 0 to ±10 mA DC or peak AC. The noninverting amplifier has a fixed gain of 1,000 V/V. The unit is protected from over-voltage and over-current conditions. A high-voltage on/off feature provides a connection for a remote device to turn on and off the high-voltage output. The 10/10A can be used on a benchtop or in a 19″ rack (optional hardware needed). $7,695. Trek, (800) FOR-TREK.
Autoranging DC Supply
Supports Three Ranges
The AP Series of autoranging DC power supplies are available in 500-W, 1-kW, and 3-kW power envelopes. The supplies use switch-mode topology to provide a range of adjustable voltage and current combinations for benchtop or system use. Additional operating modes include automated parallel, series, and tracking and remote sensing or programming of resistance or voltage. Multiple AP power supplies are configurable in a master-slave operation. From $1,690 to $3,490. Wayne Kerr Electronics, (800) 933-9319.
Rack-Mount DC Supply Available
In 1.2-kW and 2.8-kW Versions
The XFR Series of DC power supplies is available in 1,200-W and 2,800-W versions. Applications include electroplating and process control. Front-panel and remote analog programming are standard features. Optional features include RS-232, GPIB, and fiber-optic single-address, multichannel interfaces. The power supplies use zero-voltage switching for efficiency and low noise. A soft-start feature limits in-rush current. 1.2 kW: $1,350; 2.8 kW: $2,495. Xantrex Technology, (604) 421-3031.
Power Sources Meet AC
Low-Frequency Requirements
The SWA-106 and the SWAE AC Power Sources meet the requirements of low-frequency AC test sources and compliance testing to power-line-related EMC standards. The sources simulate line disturbances including dropouts, spikes, distorted waveforms, noise, sudden phase shift, over- and under-voltages, and frequency changes. Output impedance is selectable for harmonic emissions or flicker testing. The output power ranges from 1,750 VA to 5,250 VA with an accuracy of ±0.1% of range. Call company for price. Elgar, (800) 733-5427.
AC to DC Power Supply Has
Adjustable Main Output
The RP Series of AC to DC power supplies offers adjustable main output and 64 standard combinations of up to five outputs as well as signaling features. The series has power ratings of 500 W, 750 W, and 1,000 W. The main output is adjustable between 3.0 and 5.75 V. Standard auxiliary outputs include -12 V and +12 V. Optional auxiliary selections are 3.3 V and 5.0 V, or additional 12-V, 24-V, and 48-V outputs. The series features power-factor correction, compatibility with inputs from 85 VAC to 265 VAC, remote on and off, remote load sensing, overvoltage and thermal protection, and operational status signals. $600 to $1,000. Lambda Electronics, (516) 694-4200.
Copyright 1997 Nelson Publishing Inc.
September 1997