Selecting and applying programmable power supplies

A system-level view of testing is helpful when specifying power requirements.

Jeff Brakley • Ametek Programmable Power Inc.
There are numerous options available for programmable dc power supplies. Users can select from a wide range of voltage, current, and power ratings. Other specifications include input voltage, output voltage regulation, output ripple and noise, and transient response time to a step input. Additionally considerations include digital communications options, software compatibility, and whether there’s a need for manual front-panel controls.

When evaluating applications for programmable power supplies, it is helpful to look at the system as a whole – not just the power supply. A system-level approach helps optimize designs.

Most operations and systems that require power can be divided into three main types: emulation, stimulus, and process applications. Power emulation applications involve simulating a power source or load to test a product. Here, power supplies or electronic loads might mimic, say, a solar panel or a battery in a testing environment. This procedure lets engineers validate their product and system given the properties of these emulated sources.

One aspect of programmable supplies is an autoranging output which produces V-I curves as shown. This example is from the Asterion dc ASA Series. Maximum output voltage varies inversely with maximum output current to maintain a constant output power. The autoranging feature can be particularly helpful in ATE where the required maximum voltage and current ratings may change with successive types of DUTs. Click image to enlarge.

One example of a device used in emulation is a solar array simulator (SAS). SASs are power supplies that simulate the power obtained from solar arrays. SASs allow for efficient and economical lab testing of solar-powered equipment such as spacecraft. Spacecraft solar arrays in particular face large solar irradiance and temperature excursions as the amount of sunlight hitting the array changes. They as well experience mechanical changes that accompany aging.

A good SAS can reproduce all possible solar array outputs based on the different input conditions that include orbital rotation, spin, axis alignment and eclipse events, as well as beginning-of-life or end-of-life operations. Accurate simulation under various space conditions lets system developers comprehensively verify design margins and quickly test spacecraft power systems and any associated electronics. Key qualities to consider for power simulation systems include peak power tracking accuracy, peak power tracking speed, PV array modeling, and automated test support.

Another example of a power supply used in emulation is the battery string simulator (BSS). These power supplies safely and reliably emulate battery power for spacecraft testing and other demanding applications. BSSs typically operate in either static or dynamic modes. In the static mode, the BSS can instantly produce the terminal voltage corresponding to a particular state-of-charge. When in the dynamic mode, the BSS can charge and discharge energies impressed on the supply, modifying the terminal voltage accordingly. With these two modes, the BSS can easily vary voltage to simulate a battery experiencing charge or discharge, eliminating hours of testing.

Engineers and developers simulating batteries and other types of energy storage will primarily be concerned with constant voltage, power, current and resistance modes; ultra-low voltage operations; sequence simulation; continuous, pulsed and toggled transient simulation; and programmable slew-rate simulation.

Basically, a stimulus application involves stimulating a load to do something in response to the input from a power supply. This typically takes place in testing environments. Stimulus applications deal with a wide range of precision ac and dc power sources and eLoads. Every new vehicle has undergone countless product tests during the manufacturing process. Tier One automotive suppliers in particular require fast production without compromising on quality. Automotive research and development labs use power supplies for electronic integration and margin testing.

programmable supply front and back — Top, the front panel of a modern programmable power supply. This example is that of an ASA series supply. A point to note is that the display is a touchscreen. the encoder is a selector which, together with the touch screen, allows for control of output parameters, measurements, configurations, and system settings. Below, the rear panel of an ASA series illustrates the analog and digital interfaces available on modern programmable supplies.

Researchers require power supplies with a high degree of precision, flexibility and programmability. Commercial and industrial R&D labs utilize power supplies for margin and integration testing of materials, electronics and electrical devices during the development cycle.

Power supplies are the go-to choice for simulating the unique conditions found in space. Power systems and components must perform flawlessly, even when exposed to electromagnetic fields. Similarly, electrical testing is crucial to military environments. Power supplies are part of the automatic test equipment that is used for electronics repair in military depots.

No matter the industry or specific operation, system developers looking for ac/dc power simulation in stimulus and measurement applications are typically concerned with brown-outs and black-outs, transients, phase loss, frequency variations, and regenerative sink capabilities. On the electronic load side of stimulus power and testing, system developers often must consider non-linear loads, short circuits, high crest and variable power factor simulation, high peak current and low power factor simulation, ultra-low voltage operations, constant voltage, power, current and resistance modes, sequence simulation, continuous, pulsed and toggled transient simulation , and programmable slew rate simulation.

Process applications use power to transform a product. These applications require precise control of the power system. Rather than simulating a device, power supplies in process applications typically serve as loads and stress the system to eliminate infant mortality or early electronic failure.

The nature of process power applications also forces system developers to more heavily consider external simulation. Semiconductor manufacturing and process monitoring is a major process power application. Semiconductor processes such as ion implantation must be tightly controlled to consistently produce reliable and high-quality devices/circuits. Process monitoring allows system developers to detect problems early. Power solutions that enable this process monitoring must be extremely accurate and precise. Similar process power applications include precision reactor heating , oil exploration/recovery, accelerator magnets, and power safety systems.

An example of programmable supplies designed to handle multiple applications the AMETEK Programmable Power’s multiple output dc programmable power supplies. They include the Sorensen Asterion DC ASA Series and Sorensen Asterion DC ASM Series, which fit in a 1U-high chassis and provide as many as three independent isolated outputs.

The 1U form factor saves space in ATE applications, while the multiple voltages support applications such as functional PCBA test as well as burn-in and environmental test. The Asterion DC ASA Series features autoranging outputs in which maximum output voltage varies inversely with maximum output current to maintain a constant-power characteristic. The autoranging feature provides flexibility for ATE systems, in which required maximum voltage and current ratings may change with successive types of DUTs. The five available output channels in the ASA Series follow a 600-W I-V curve, with maximum ratings per channel of 60 V at 42 A, 80 V at 22 A, 200 V at 17 A, 400 V at 6 A, or 600 V at 2.8 A, with the three-output supply offering 1,800 W total output power.

In contrast, the Asterion DC ASM Series features three independent, isolated rectangular output channels. However, the ASM Series does offer higher power ratings at 1,700W per channel for a total output of 5,100 W for a three-channel supply in a 1U chassis. The ASM Series has nine channel configurations offering fixed voltage and current ratings ranging from 40 V at 42 A to 600 V at 2.8 A.

Specific applications

Specific examples of how the new supplies are used include a prime contractor awarded an Air Force engineering and manufacturing development contract for a new long-range missile system. Over the course of the multi-year, billion-dollar-plus contract, the application will require a variety of ac and dc Asterion programmable power supplies. Here the ability to combine two ASA units to provide six isolated supplies in a 2U rack height provides considerable space savings.

programmable waveforms — Top, an example of a power output profile that can be set up via commands received over the programmable supply’s remote digital interface. ASA and ASM series supplies can store 50 sequences of up to 20 commands each. Sequences can be comprised of step and ramp functions as well as looping and go-to commands. Below, specific sequences can be called as subroutines by other sequences. Here, the sequence producing the top trace was called by another sequence for use in defining another sequence. The use of subroutine sequences can effectively enable longer sequences.

Another firm in the aerospace industry will use the multi-channel supplies in new automated test systems. Important here was the space savings of three independent, isolated outputs in a 1U rack height, and the long-term reliability and support from AMETEK Programmable Power.

Many features of the ASA and ASM Series help optimize applications for either local or remote control. For local operation, a front-panel touchscreen and an encoder selector button allow users to control output parameters, measurements, configurations, and system settings. From the home screen, users can navigate to several top-level menus. Dashboard, for example, allows you to change output parameters and view output measurements for each channel .

Programmable functions for the ASA and ASM Series include on/off delays, voltage and current ramps, and sequencing. On/off delays are useful for devices under test such as PCBAs that require multiple voltage sources that turn on and off at different times. ASA and ASM models support delays from 0.1 sec to 100 sec, which are programmable via the Configure Delay top-level menu or by remote control.

The Virtual Panels graphical user interface provides access to sequencing, which is not supported from the front panel. The ASA and ASM Series can store 50 sequences of up to 20 commands each. Sequences can be made up of an extensive list of step and ramp functions as well as looping and go-to commands. One sequence may call another as a subroutine.