Power Supply Test Keeps Pace With Technology

Power supply manufacturers contend with the same shrinking production schedules and cost-reduction measures as other electronics manufacturers. Sometimes, though, they hit a snag, especially with the testing of new products.

EE asked power-supply test manufacturers how they helped customers improve throughput or reduce costs, or provide a technical solution to a difficult problem. From their responses, we selected three applications that best typify the type of support manufacturers are providing their customers. The applications presented in this article are from Hewlett-Packard, NH Research and Schaffner EMC. The applications include a redesign of test procedures to keep the production lines running; improvement of test times, even for sophisticated power supplies with features such as N+1 redundancy and communications; and improvements in test times for high-volume production.

Power Supply Testers Measure Up to Changing Needs

Make the product the way the customers want it and when they want it, the philosophy of many fast-food chains, also is the business belief of a Hewlett-Packard customer that makes power supplies. To offer this service, the power supply company needed the test capability for a changing line of products and multiple testers who could keep up with wide-ranging demands.

Most of the company’s designs required the test system to measure noise from 20 Hz to 20 MHz. Occasionally, they needed the capability to make noise measurements in excess of 100 MHz.

The results of a financial analysis convinced the company it had to replace existing testers with a new breed that supported its line of products. The new testers had to provide the flexibility to test all the power supplies, offer a test execution speed that would not cause a bottleneck in the production process, and be able to make critical measurements on many new models.

The manufacturer was also looking for an engineering service to develop test programs. This was especially important because the business plan required 40 designs to be in production within 12 months.

The search for the right tester/service package came to an end with Hewlett-Packard. The HP E3650B Power Test System provided the capability to test both the company’s present and future power supplies and has the test execution speed to keep up with demand. HP also offered the support to help manage test program development, software revisions, test programs and data collection. Hewlett-Packard Co., (800) 452-4844.

Simultaneous Test Saves Time and Money

Power supplies continue to become more intelligent, with more features—such as N+1 redundancy, ranging and communications—added with each upgrade. These improvements, however, have inflated test times to unacceptable levels. Such was the case for a customer of NH Research involved in testing power supplies for the telecommunications industry.

The customer needed to double throughput on the ATE line that tested three power-supply configurations. The current test time was 12 min, including handling. The newer, more complicated supplies had a projected test time of more than 16 min, which was unacceptable. And the existing test systems could not provide growth capability for future power supply complexity.

NH Research’s solution was a system that tested the different power supplies in parallel: the VXI-based POWERTEST 8100i with the Parallel Measurement Module (PMM). The PMM offered four independent, multifunction measurement channels. Similar to an oscilloscope, it engaged four channels simultaneously but isolated each channel and provided better accuracy and resolution than the oscilloscope.

The module contained the measurement circuitry necessary to replace the four standard power supply test instruments: a DMM, an oscilloscope, a counter/timer and a multiplexer. Having these instruments together eliminated the time-consuming process of setting up and serially sequencing through the separate measurement instruments for each power-supply output.

For example, traditional measurement techniques on a four-output supply required 16 instrument setup calls, including multiplexer/scanner communications. The PMM needed only one.

The system also had to be reconfigurable to accommodate a variety of power supplies. NH Research met this need with a power subsystem that controlled dynamic loads and DC sources from the same chassis.

The constant power profile of the input DC sources and the ranging capability of the loads allowed a smaller number of modules to be configured into the test stand. Setting up a sequence of events within the controller allowed the trigger and timing capabilities to be routed from Slot 0 of the VXI chassis to the control chassis. This eliminated repetitive engagements of each module.

The Windows™-based system software provided a comprehensive set of test routines and control dialog boxes that helped reduce the need for writing custom programs. The power supplies, however, had proprietary communications that required custom hardware and software. A prototyping VXIbus card helped implement the circuitry needed to provide the communications.

The completed system tested four power supplies simultaneously in a total of 150 s. Twelve supplies were loaded and tested four at a time. In the time it was projected to test one power supply in the previous test system, they now could test 24 units. The good news was a projected cost savings of more than $1 million in the first year. NH Research, Inc., (714) 474-3900.

The Four Ingredients of Fast Throughput

A high-volume manufacturer of DC-DC converters needed to improve test times as well as reduce the overall cost of the test system. Schaffner EMC had investigated just such a scenario and discovered test throughput was affected by the interaction of hardware, firmware, software and settling delays. To get a significant reduction in test times, it was important to reduce all four components simultaneously, not separately.

Schaffner recommended the Intepro 3000 Test System with POWERSTAR control software. The solution also included customer-selected OEM measurement hardware.

A post-processor was provided as part of the solution because it helped optimize software control of the hardware. It also eliminated redundant bus transmissions.

Schaffner’s investigations determined that 37% of the total test time was attributed to software functions and only 29% to hardware. Decreasing the time taken by the software to resolve variables, building test strings and transmitting the commands to the system hardware had a greater effect on throughput than simply improving the speed of the hardware. The POWERSTAR system helped the customer improve test times by nearly 40% and meet the goal of increasing throughput. Schaffner EMC, Inc., (201) 379-7778.

Testing Power Supplies for Fighter Aircraft

Requires Unique Solution

To launch Advanced medium-Range Air-to-Air Missiles from jet fighters requires a sophisticated power system in the aircraft. The power supplies, located in the pylons of the fighter, provide the power and control for launching a variety of missiles. These

supplies include high-voltage outputs to ignite the missile’s propellant and to arm the warheads.

Audio signals from the launcher keep the pilot apprised of the status of the missile. A complex arrangement of relays and launch control signals interlocks and releases the missile at the appropriate command. Testing these highly specialized power supplies requires a full featured tester.

Part of the testing requirement was to simulate and verify the launch command sequence. When control signals were sent to the power supply, a series of internal relays and resistors was energized. Precisely timed short pulses had to be measured for use in gain calculations to determine correct power-resistor values within the supply. Because of the fast-measurement requirement, a single-system DMM and switch matrix could not select, trigger, measure and report results in real time. To capture the required readings, it would be necessary to synchronize the DMM trigger, stimulus signals and multiplexed UUT outputs while allowing relay, closure delays and meter settling.

Autotest offered a solution: a dedicated control card embedded in the applications fixture (Figure 1). A single software command triggered the card’s state machine to start the launch-command test sequence.

The state machine consisted of a debounced solid-state switch to start the sequence. A variable clock provided the time base to increment a state counter.

The state counter stepped through consecutive addresses in a PROM. Each address held a 7-bit binary mask. Three bits were used to control an eight-channel multiplexer to route the UUT output signals to the DMM. One bit triggered the DMM through an opto-isolated buffer driver to preserve the digital circuit ground.

Voltage drops set up by the series resistor combinations produced the target voltages used to calculate the precise values of the embedded resistors in the UUT. This test scenario also verified the contact closure and conductivity of the relay.

As each relay and resistor combination was energized, the successive PROM addresses set the multiplexer channel and triggered the system DMM to read and store the appropriate voltage in the next memory location.

Since the system DMM had a built-in memory buffer, individual meter readings were stored and retrieved after processing and evaluating the event. A secondary DC supply in the tester provided the required standby power to activate the relays and power the resistors.

The concept proved to be highly stable, reliable and versatile. To date, there are five separate implementations of this application. Minor PROM variations also made it possible to implement this design in similar applications. This approach provided a cost-effective solution to a difficult testing requirement.

Power Supply Testers

High-Density Module

Provides 500-W Loads

The High Power Load Modules can be configured for load requirements from 500 W to 10,000 W. The modules can perform transient steps from zero to full scale of the configured load current. The plug-in modules mount on the back of the company’s power supply test system. A double control loop improves load performance. Standard voltages range from 3 V to 60 V and 3 V to 120 V. A 1.7-V option also is available. Autotest, (210) 661-8661.

AC Source and Software Added

To Modular Test System

The HP E3650B Power Test System now offers the HP 6800 Series AC source which integrates an AC power amplifier, an arbitrary waveform generator and an AC power analyzer. It provides 16-bit measurement capability and permits testing of products to AC-line regulatory standards, including IEC 555-2. The system software has been updated to include more test procedures and drivers. Subsystems include a general-purpose measurement system to make DC and waveform measurements. Hewlett-Packard Co., (800) 452-4844.

Programmable System Tests

Power Supplies Up to 500 W

The 3600 Series Automatic Power Supply Tester performs AC and DC verification and DC-DC converter testing. The programmable unit includes a 600-VA AC source, four electronic loads, four peak-to-peak detectors, a controller, and built-in Centronics and RS-232 interfaces. The system tests supplies up to 500 W. The 3600 has eight storage locations accessible from front-panel switches and capable of storing 32 test parameters. IMC-PRODIGIT, (800) 798-9615.

VXIbus Module Measures

Four Outputs Simultaneously

The Parallel Measurement Module performs measurements on up to four power-supply outputs simultaneously. The VXIbus module contains essential portions of five single-function measurement instruments. The digital multimeter provides 6 1/2-digit accuracy, the high-frequency peak-noise detector has 12-bit resolution and 1% accuracy, the low-frequency transient detector has a bandwidth ranging from DC to 5 kHz, the threshold detector has a window compare capability and the counter-timer offers seven gating modes. NH Research, Inc., (714) 474-3900.

Modular System Contains

Six Load Modules

The Intepro 3000 is an upgradable power-supply test system with a multifunction module, a high-frequency scanner, a real-time monitor, 15-A power relay, 4-A power relay and a dual-load unit. The AC input is provided by a 2.5-kVA motorized variac and features cycle dropping, phase-angle turn-on control and true power measurement. The system is controlled by POWERSTAR IV, a software package that supplies 120 standard tests. Schaffner EMC, Inc., (201) 379-7778.

Copyright 1995 Nelson Publishing Inc.

June 1995

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