Tektronix Encore




Advances in DC Power Supplies



September 08, 2020

Power is essential to any test setup and the DC power supply at one time might have been among the most overlooked instruments in a test system. Modern DC power supplies are no longer simply sources of current and voltage in a test system; they are being designed with versatile functionality and intelligent protection for extended operating lifetimes. They provide details at a glance using LCD screens and touchscreen displays. Even as power supplies increase in capabilities, they become easier to use by means of programmability and computer control. Of course, sorting through a wide selection of advanced DC power supplies for a benchtop or system application can be challenging, but the choice can be made a little easier by understanding about the different types of DC power supplies and how they fit with different applications.

Selection of an adjustable power supply for test purposes has evolved beyond finding an instrument with suitable voltage and current ranges along with maximum voltage and current that exceed the maximum expectations of a measurement application, such as providing bias to an amplifier. Some DC supplies may also be rated for a short-duration, maximum current level.

In general, test-instrument power supplies are available with low-voltage/low-current, high-voltage/low-current, and high-voltage/high-current capabilities. Sometimes the choice of a power supply for an automatic-test-equipment (ATE) system is a matter of finding an instrument with high-enough power density to fit within the available space of the system while still providing the required ranges of currents and voltages along with the features that can support and assist a measurement agenda.

Instrumentation power supplies are available in different formats, such as benchtop and laboratory grade, and with numerous operating modes, such as regulated, tracking, and parallel modes. Many offer constant-current (CC) and constant-voltage (CV) testing modes. Benchtop units are usually designed into compact enclosures that can be left next to other test equipment in a workplace. They may provide one, two, three, or more DC outputs, assuming test setups that may contain multiple active components, such as testing a pair of amplifiers side by side. Laboratory-grade power supplies are typically designed into a 19-inch-wide rack-mount enclosure for use in an ATE system. Rather than the multiple outputs, they typically provide a single dedicated DC output port.

Although power supplies may be taken for granted in many test setups, measurements on active components and devices will not start without them. The information they provide to an operator should be clear and easy to understand and access. Whether it is via connection to an external computer and the Internet and aided by software or by using the instrument’s displays and controls, communication with a power supply should be straightforward. Power supplies can be evaluated quite simply, by the range of power in terms of current and voltage that they control, or more elaborately, by the complexity of their functions and the levels of programmability that they provide. For example, how much supervision from an operator do they require? Can they perform a series of complex functions according to their own firmware or do they require an external control computer and additional software? Depending upon the test application, the number of automated functions required of a power supply can vary widely, and the number of functions for which it can be programmed will determine the amount of supervision required of an operator or ATE manager.

Many newer power supplies incorporate several types of protection, such as current-limiting and voltage-overload protection, to guard the instrument against unsound operating conditions. Additional forms of power supply protection are thermal protection and short-circuit protection. Something as seemingly routine as short-circuit protection can guard a DC power supply against a simple poorly placed voltage probe. Newer DC power supplies may integrate what was once commonly a separate instrument, an electronic load, in the same enclosure to save space in a test setup and simplify bidirectional testing with fewer instruments. Newer power supply designs offer extensive features and functions that will not be reviewed here but are covered at least in part in an earlier blog post, “Perusing Specs for Power Supplies and Electronic Loads,” gives cover to both AC and DC power supplies.

 

Exploring Examples

In addition to ever-evolving electronic measurement requirements, such as for rapidly expanding Fifth Generation (5G) wireless systems and even installation of solar-power sites, demand for programmable DC power supplies with source and load functionality and bidirectional capability is growing. For example, test applications are quickly emerging for growing numbers of electric vehicles (EVs), hybrid electric vehicles (HEVs), and the batteries within those vehicles. Electric power is being used in regulated and unregulated forms and it must be measured and controlled for an increasing number of applications. DC power supplies with suitable voltage, current, and power ranges as well as adequate functionality and accuracy are part of the measurement solution.

As an example, the 62000D Series of programmable DC power supplies from Chroma are bidirectional, with electronic source and load capabilities to allow feedback of power from a device under test (DUT) even as it is being fed with supply power. The 62000D Series instruments are designed to operate as a DC power supply and a regenerative DC electronic load in one enclosure. They can operate in CV, CC, and constant-power regenerative-load modes to accommodate many electronic test requirements. The instruments can channel positive current and positive voltage as well as negative current and positive voltage. They are efficient, returning energy absorbed during testing back to the power grid with as much as 93% conversion efficiency.

The Chroma 62000D Series includes eight models with high power density, with maximum power of 18 kW from a 3U-high 19-in.-wide rack-mount enclosure. Models in the series have DC voltage ranges of 0 to 100 V, 0 to 600 V, 0 to 1200 V, and 0 to 1800 V, with maximum power of 6, 12, and 18 kW and available source-to-sink current ranges of ±40, ±80, ±120, ±180, ±360, and ±540 A. The Chroma 62000D Series power supplies feature a CV dynamic response slope as fast as 180 V/ms, helping the power supplies meet LV123 electrical test standard guidelines for testing high-voltage components and LV148 automotive electrical standard guidelines for testing 48-V vehicular electrical systems.

A specific unit, Chroma’s 62180D-100, provides source-to-sink voltage range of 0 to 100 V with source-to-sink current range of ±540 A resulting in a source-to-sink power range of ±18 kW. For power-intensive applications, as many as 10 Chroma 62000D DC power supplies can be connected in parallel in a smart master/slave configuration to supply as much as 180 kW output power.

The power supplies are equipped with 100 programmable settings and they provide the control flexibility of many different interfaces, including USB, LAN (LXI), CAN, and GPIB connections. The instruments are locally simple to operate using a touch screen with icons. They are well suited for testing power conversion systems (PCS), as battery simulators, and for testing charging/discharging components. A higher-voltage model, the Chroma 62180D-600, is well suited for testing power components in EVs. With its 0 to 600 V, ±120 A, and ±18 kW ranges, it is a possible test source for such EV components as bidirectional on-board chargers (BOBCs), bidirectional DC converters, and DC-to-AC motor drivers.

Model PSB10060-1000 from Elektro-Automatik is a bidirectional DC power supply in a 4U-high rack-mount instrument enclosure that delivers as much as 30 kW power. As with the Chroma units, it combines an automated power supply with an electronic load for energy recovery. It includes an autoranging bidirectional power stage for automatic adjustments of voltage and current outputs, limited by the 30-kW maximum output power rating of the instrument. In his way, users can set up dynamically changing output power to evaluate a DUT under dynamic power conditions.

With its onboard DC load, the Elektro-Automatik PSB10060-1000 can return recovered energy to the power grid. It uses the AC input as the access point to the power grid for returned energy, reaching conversion efficiency as high as 95.5% for returned energy. The power supply works with function-generation software to create a wide range of functions that can be applied to the output voltage or current, enabling dynamic changes in the output power according to the slew-rate limits of the instrument.

These are a few examples of some of the newer features appearing in the latest DC power supplies, in efforts by these manufacturers to serve a wide range of measurement needs while also providing efficient, cost-effective operation by recovering unused energy.

Details and data sheets for many more programmable DC power supplies can always be found on the Axiom Test Equipment website at axiomtest.com/Power-Supplies/ by contacting Axiom Test Equipment’s sales department at sales@axiomtest.com, or 760-806-6600.



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