Electronic loads may be somewhat mysterious to some engineers, but they can be invaluable test instruments in the development of power circuitry. Electronic loads provide the means to generate precisely controlled electrical power for simulation and test, with control of key parameters, such as current, voltage, and load impedance/resistance, to aid in development of new products and in the maintenance of existing products. Electronic loads come in various forms, including AC electronic loads, DC electronic loads, and even combination AC / DC electronic loads. Learning more about electronic loads and how they work can encourage electronic designers to achieve optimum performance levels from the power circuitry, power supplies, batteries, and fuel cells in their designs.
Both AC and DC electronic loads provide the capabilities to measure voltage, current, resistance, and power, whether for AC or DC powered circuits and systems. Both types of electronic loads provide several operating modes, maintaining one electrical power parameter constant to study the effects of a unit under test (UUT) on other electrical parameters, such as constant current, constant voltage, constant resistance, and constant power. As with other electrical test instruments, different AC and DC electronic loads cover different operating ranges for their electrical parameters, and the voltage, current, and power ranges of commercial AC and DC electronic loads can serve as useful starting points in the search for an electronic load for an application. In terms of power ratings, most electronic loads convert electrical power into heat, which must be dissipated, although regenerative electronic loads are also available in which the electronic load efficiently converts load power into reusable electric power rather than heat.
Development of power-supply circuitry, or power supplies, or even batteries can help set the requirements for an AC or DC electronic load, such as whether it will be used for manual or automatic measurements, for testing only one circuit or unit under test (UUT) at a time or multiple UUTs at one time, and whether an AC or DC electronic load provides fixed functionality, flexible manual control, or local or remote programmability to adjust settings quickly for performing different measurements on different UUTs during one work period. For applications requiring both AC and DC power measurements, it is also possible to specify combination AC/DC electronic loads that can support measurements on both AC and DC UUTs.
Looking for Loads
Reliable, high-performance DC and AC electronic loads are available from numerous suppliers, typically categorized as low-, medium-, and high-power loads, including manual and programmable units from Chroma Systems Solutions, BK Precision, Kikusui, and NH Research. For example, Chroma’s model 63600-5 programmable DC electronic-load mainframe represents a flexible solution for testing power components and systems since it offers slots for as many as five load modules for as many as 10 electronic-load channels per mainframe. It can generate as much as 400 W power per module and as much as 2000 W when interconnecting five power modules. The mainframe has standard USB interfaces, with options for Ethernet and GPIB interconnections. Load modules for the mainframe include the Chroma 63640-150-60 module, the 63630-600-15 module, and the 63610-80-20 module.
The ease of interchanging load modules allows a user to almost instantly modify the capabilities of the Chroma 63600-5 DC electronic load mainframe to fit a wide range of applications within its total power limits. The Chroma 63640-150-60 module provides as much as 400 W power, with voltage range of 0 to 150 V and current range of 0 to 60 A. The 63630-600-15 Chroma module is capable of as much as 300 W power, with voltage range of 0 to 600 V and current range of 0 to 15 A. The Chroma 63610-80-20 module produces as much as 400 W power, with voltage range of o to 80 V and current range of 0 to 20 A.
Chroma also offers combination DC and AC electronic loads, such as the the 63800 series of programmable electronic loads which can operate as AC and DC electronic loads with maximum current ratings of 18, 36, and 45 A RMS and voltage ranges of 50 to 350 V RMS and models capable of power levels as high as 1800, 3600, and 4500 W. All models provide adjustable frequency ranges of 45 to 440 Hz.
Pursuing More Power
For what might be considered medium-power test requirements, the NH Research 4760 LXI Series electronic loads offer highly integrated and reliable, air-cooled DC load functionality covering a voltage range of 7 to 600 V for all units. Individual models are available for maximum power ratings of 1, 2, 3, 6, 12, 18, 24, and 36 kW and corresponding maximum current ratings of 50, 100, 150, 300, 600, 900, 1200, and 1800 A. An easy-to-use front touch panel is included for manual control, while automatic computer control is possible by means of several software tools, including LabVIEW software. These electronic loads keep delays to a minimum with microsecond 10%-to-90% slew rates and they all incorporate a special Auto Mode that provides automatic switching between constant-resistance, constant-current, constant-voltage, and constant-power limits for extensive automated testing.
The AMREL eLoad PLA series of programmable DC electronic loads cover a wide range of maximum power limits. With models available for voltages from 10 to 1200 V, current from 10 to 1500 A, and power levels from 800 W to 7.5 kW, these rack-mount instruments contain multiple loads, allowing a user to set multiple ranges for voltage, current, resistance, and power. One such model in the series is the Amrel PLA800-120-120 electronic DC load, which features 120V, 120A, and 800W.
The DC electronic loads can operate stably with very low voltages, approaching 0.1 V. They are available with multiple control interfaces (USB, GPIB, Ethernet, and RS-232) and provide reliable operation by means of a “closed-case” calibration routine that can be performed from the front panel to avoid the delays of shipping the instrument back and forth to the manufacturer.
Chroma’s 63224A-600-1680 is an example of a high-power DC electronic load, with maximum power ratings of 2, 3, 4, 5, 6, 8, 10, 12, 15, 18, 20, and 24 kW for use in constant constant-current, constant-voltage, constant-resistance, and constant-power operating modes. Units are available with maximum voltages of 150, 600, and 1200 V and maximum current of 2000 A for all models. As many as 10 units can be combined in master-slave parallel control configurations to achieve higher power levels as needed. These DC electronic loads also feature a unique dynamic frequency sweep with variable frequencies up to 50 kHz. In addition, they provide short-circuit simulation to support automated testing that studies the effects of short-circuit conditions on a UUT.
A regenerative DC electronic load saves energy by converting load power into reusable electric power, rather than converting it into heat which must be dissipated and/or managed. The Kikusui PLZ6000R regenerative electronic load, for example, is a DC electronic load that regenerates load power for use on an AC power line. It is rated for maximum DC voltage of 60 V and maximum current of 200 A at 60 V and 400 A at 30 V, with a maximum power rating of 6 kW. It achieves as much as 90% power regeneration efficiency in converting load power to reusable AC power. This regenerative DC load provides the four standard operating modes with built-in protection against overvoltage, overcurrent, overpower, overheating, and reverse-connection conditions.
Applying AC Loads
When in need of both AC and DC loads, Chroma’s 63804 serves as both an AC and DC electronic load. It uses digital-signal-processing (DSP) technology to simulate nonlinear rectified loads. By detecting the impedance of a UUT and dynamically adjusting the control bandwidth of the load, it can maintain high stability. The 63804 offers several operating modes, including a constant load mode and rectified AC load mode to support a wide range of testing applications. The Chroma 63804 is rated for maximum power of 4.5 kW, with adjustable voltage range of 50 to 350 V, 0 to 45 A, and DC frequencies of 45 to 440 Hz. In addition, it can perform short-circuit simulations.
The NH Research 4600 Series of programmable AC electronic loads are supplied with six different power levels from 3 to 36 kW and units can be field-upgraded in 3-kW increments for higher-power applications. All the models have voltage ranges of 50 to 350 V with maximum current ratings of 30 to 360 A. As an example, the NH Research 4600-6 AC load is rated for maximum power of 6 kW with maximum current of 60 A for the 50-to-350-V voltage range. These compact AC electronic loads are controlled by a Windows-based PC soft panel interface.
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