Flexible and Uncorrupted Power
by Tom Lecklider, Senior Technical Editor
DC power supplies and AC sources have very long service lives, which generally is a good thing. On the other hand, if you haven’t recently bought one, you may not be aware of the latest features and benefits they offer.
Increased flexibility is a major theme that has influenced today’s supplies and sources in many ways. Power-rated supplies are a good example. Instead of buying a high-voltage, low-current supply as well as a high-current, low-voltage one, a single supply can be used over a wide range of current and voltage combinations within its maximum power rating.
Power source emulation is another kind of flexibility that allows a standard power supply to replace a solar panel or battery. If the application calls for control system testing, it is advantageous to replace the actual power source with one that is fully programmable. In other cases, emulation can provide a more practical test environment or simply stand in for the real power source that may not be available.
Test system simplification is a benefit supported by a supply’s pulse and measurement capabilities. Rather than needing a separate DMM, pulse generator, and amplifier, you can get the same functionality from a modern power supply.
A demand for higher power also is evident. Several new high-power supplies have been introduced, some as source measure units (SMUs) with two- or four-quadrant operation. When you are dealing with tens of kilowatts, the cost of power becomes important. Operating as electronic loads, several of these SMUs return a large portion of the current back to the AC line. And, whether single- or multiquadrant, many supplies support parallel or serial connections to further increase output I or V.
Of course, all these features and benefits must be delivered within constraints. For example, a fast pulse mode of operation isn’t too useful unless you can accurately measure the pulse shape. High-speed digitizers are needed to measure transients but may not be compatible with the more common requirement for high accuracy at DC.
Similarly, programmability is important, but so too is ease of programming. The PMBus™ protocol is used specifically in power applications although you also will find USB, RS-485, GPIB, and LXI.
Throughput
A large number of interrelated features are being emphasized by DC power supply and AC source manufacturers with the mix depending on the intended use. ATE includes many power supplies, and some of the newer features help to improve test throughput.
PMBus
TDK-Lambda Americas’ David Norton, vice president of marketing, discussed the importance of the PMBus protocol in this application. “With our HFE Series, the power supplies can be adjusted via PMBus to optimize the output voltage of the product to obtain the lowest power draw or even to disable one or more units during periods of reduced demand, aka load shedding. I2C also is being used to interrogate power supplies remotely to better schedule service calls and reduce equipment downtime,” he explained.
Rather than being just another protocol, PMBus specifically addresses power applications. It requires all slave devices to power-up in their default condition without any bus communications. This ensures that power-up is rapid because the bus master does not take part in initialization. The system host can be an FPGA, a laptop PC, or ATE because all communication is based on the bus and no proprietary silicon is involved.
The commands fall into eight groups: on, off, and margin testing; output voltage-related; addressing, memory, communications, and capability; fault management; sequencing; status; telemetry; and other.
One way that the PMBus protocol improves flexibility is in DC-DC converter voltage margining. Simple VOUT_MARGIN_HIGH and VOUT_MARGIN_LOW commands preset the required voltages. The OPERATION command causes the converter to change its output voltage from the nominal to the high margin and then to the low margin, during which time the driven system’s performance is monitored. Before point-of-load converters adopted the PMBus protocol, margining involved physically changing the value of programming resistors.1
Operating at Full Power
AMETEK Programmable Power offers the product breadth and expertise test engineers rely upon for precision power supplies and electronic loads. Deep application expertise and the best selection of AC and DC programmable power supplies and loads from the most reliable and trusted power brands: California Instruments, Elgar and Sorensen.