T&M: Benchtop DC power supplies – now “on steroids”
01 April 2022
Figure 1. Keithley 2231A-30-3 triple channel power supply, a top seller for engineering & science student labs
DC power supplies used to power up any circuit board device under test (DUT) are an essential tool sitting on any design or test engineer's bench – with several brands to pick from, at quite affordable prices. Some applications requirements though are evolving, necessitating specific features for benchtop & power supplies systems – even for users who haven’t needed particular precision & stability from these devices before.
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So as Andrea Vinci, Senior Technical Marketing Manager at test & measurement firm, Tektronix explains here, the most basic instrument on electronics design benches is evolving as applications demand new features and flexibility…
In this article, we will provide a quick overview of what “high precision”, “remote control”, “programmability” and other terms mean today, in relation to this instrument, as well as exploring the types of specialised applications that mostly determine these extra requirements for standard DC (direct current) bench PSUs (power supply units)…
Whether you are working on electric vehicle (EV) power converters designs, power management units for smart IoT devices or portable device battery chargers, the required power level (Watt), voltage and current ranges are only the first of a long list of requirements for selecting your perfect DC PSU.
Outside R&D (research & development), production benches are adding extra needs on top of the above specified ranges, the ability to set master-slave parallel and serial configurations, and the obvious possibility to ‘rack-mount’ units.
Figure 2. Keithley Kickstart software configuring sourcing sequences independently for each power supply input with ease
The first keyword is “programmable”: engineers need to set voltage levels lasting for very specific times, then changing or dwelling to another level setup in a tight controlled way. This is key in simulating specific real behavior the circuit board DUT will experience. Also, semiconductor production testing labs, working specifically on the qualification and reliability testing of devices, may need to program precise sourcing sequences in long and complex tests, and make sure the levels are disconnected when failure conditions occur.
Given these requirements, from a practical usability perspective, front panel edits provide only a partial answer, and potentially may result in a painful and time-consuming experience, prone to errors.
It’s better to look for instruments where a sophisticated and regularly maintained software application can take control of the instrument via standard common I/O (input/output) interfaces, providing the flexibility to proceed with the programming of sequences.
The Keithley Kickstart Power Supply application, for instance, allows users to practically load testing sequences in a simple, quick way for each of the independent outputs of the multi-channel power supplies.
Another key request today is “battery simulation”, as power supplies are requested not only to source the circuit as a battery, but also being able to emulate exactly how the battery itself would perform while discharging over time. This fundamental feature allows a designer to determine how long their product will operate, and how it would cope as the state of battery charge changes – and therefore of the source internal resistance change over time. Needing the power supply unit to be “programmable” in simulating battery state from full charge to completely discharged state is a rapidly rising request.
Figure 3. Keithley 2281S-20-6 is a high precision power supply, as well as a very effective battery simulator
DC power supply vendors must ensure this functionality matches with precision capabilities and the clear graphical interface information display of the unit.
It must offer users the possibility to upload sequences of open circuit voltage to source and relative equivalent series resistance to present to the load, for different levels of State of Charge. Users demand that this be an easy operation to perform, with minimal clicks on the entry panel.
In production, this need may not be as vital as in R&D, but other requests are posed to the DC power supply by automated test equipment designers in order to simulate real world conditions in production, effectively testing multiple units.
The DC power supply units in these cases need to precisely measure load currents for power consumption verification or analysis with very high sensitivity. This adds extra complexity to the previously mentioned features of variable programmable output resistance and fast response to transient load currents. There are multiple suppliers offering remote sense lead detection in their PSUs, but not everyone supports the readback accuracy of a “built-in” digital voltmeter, which is what these applications demand.
With regards to transient load currents, generally the need is for the power supply to be capable of a “fast response”. This is because the power supply must present output characteristics identical to an actual battery, hence keeping a stable voltage output, even when the load circuit makes a rapid state transition (such as from a standby “low current” state to an RF transmission “high current” state).
Figure 4. The rear panel of LAN controllable Keithley dual channel 2306 Battery/Charger Simulator. These units provide stable voltage outputs, but also measure both DC currents & pulse load currents accurately
The Tektronix Keithley 2306-LAN battery-simulator is an example of PSU that allows its output channel to be programmed to simulate the output response of a battery with fast recovery to the effective programmed voltage.
New selection criteria are adding to the usual ones for determining the most suitable DC PSU for engineer’s test benches.
The number of output channels, output voltage, current and power, and the related resolution and accuracy (ripple and noise) are today ever more paired with extra features and advanced programmability requests. Nanoamp current measuring resolution, easy sequencing setup at different independent channels, presence of analogue and digital I/O, and other such requirements drive engineers’ decisions.
But what really matters today is the ability of suppliers to respond to the need to “hack the hardware” with ease, supporting new upcoming test conditions, while at the same time not affecting safety and instrument reliability over time. For this reason, it’s key to choose suppliers offering the possibility to discuss and regularly test and implement extra requirements via value driven control software upgrades, keeping usability and fast test implementation as the main central ability to satisfy.
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