RoadTest: AIM-TTI Bench Power Supply
Author: Gough Lui
Evaluation Type: Power Supplies
Did you receive all parts the manufacturer stated would be included in the package?: True
What other parts do you consider comparable to this product?: A range of high-power single-rail power supplies including B&K 9205, EA PS 3080-20 C, PSI 5080-20 A, PSI 9080-20 DT, GW Instek PLR 60-12, PSB-2800L, PSW 80-27, TDK Lambda Z60-14-U, GENH 80-9.5, XP Power PLS60010010, Ametek DLM 80-7.5, XG 80-10.5, Keithley 2260B-80-4, Keysight N5748A.
What were the biggest problems encountered?: Minor firmware glitches, PowerFlex+ envelope poorly detailed in intermediate points.
by Gough Lui – Aug-Oct 2021
No matter what sort of electronics you might be repairing or testing, you are probably going to need a source of power for that. The humble bench-top DC power supply usually fulfils this critical role, but they do vary widely in terms of their capabilities in terms of voltages, current, metering, remote sensing, protections, ripple/noise and remote-control capabilities. For most users, an ordinary bench power supply may be one that has anywhere from one to three rails, voltage range of something like 0-32V, a current rating of a few amps and probably only a hundred or so watts of power budget. Remote control abilities may be considered a luxury. But what if that’s not enough?
For those who find themselves working on power electronics, for example in power inverters, they will quickly find themselves looking for a bigger power envelope often in excess of 300W. Those testing MOSFETs under high-current conditions will beg for high current capability of >40A, while those testing telecommunications DC-to-DC equipment such as Power-over-Ethernet (PoE) will be asking for higher voltages, close to 60V. For those who run tests regularly, automation is key and a reliable remote-control interface is required. These demands are a bit more niche and the market for such specialised supplies is relatively limited which can result in some eye-watering prices.
You could try and make-do with the right series/parallel arrangement of floating-output power supplies along with the mess of cabling and co-ordinating the orchestra of instruments. This is a compromise. Or you could grab the Aim-TTi QPX750SP Programmable DC Power Supply with its PowerFlex output which can deliver up to 80V or 50A, up to 750W. While the brand is probably not as famous as the “big names”, it’s not an unknown either and it is affordably priced. Is this the power supply for those demanding a little more grunt? Find out in this review!
I must thank Aim-TTi and element14 for the opportunity to test yet another substantial piece of equipment. If you found this review informative, useful, interesting or entertaining, I would appreciate if you could leave a like, rate or bookmark the document or share it with your friends. If you have any questions or ideas, feel free to leave a comment below and I will endeavour to answer them as soon as I can. Also, my apologies for delivering this right up on the deadline – the issues and time-extension given for my last RoadTest made for a slightly tricky scheduling situation.
Aim-TTi are perhaps not a widely known instrument brand, however, they have been in the market of making test equipment since the 1970s as part of Sinclair Radionics. Currently, they are known as Aim-TTi, short for Aim and Thurlby-Tandar Electronics. I suppose this is especially poignant given the recent passing of Sir Clive Sinclair. True to their roots, Aim-TTi continue to design and manufacture their instruments in the UK, headquartered in Huntingdon near Cambridge.
The QPX750SP is the smallest member of the QPX series with a single-rail, 750W output rating, capable of up to 80V or up to 50A limited by the PowerFlex+ power curve which is specified as 80V/9.4A, 60V/12A, 36V/20A, 18V/36A and 12V/50A. It claims a low ripple and noise figure of <3mV with high resolution setting and metering down to 1mV and 10mA. It offers constant voltage (CV), constant current (CC) and constant power (CP) operation modes with over-voltage protection (OVP) and over-current protection (OCP). It can be controlled through a LXI-LAN (SOCKET) and USB (CDC), with GPIB available as an option. Quasi-analog control and logic input/output are also available. The unit sports both front and rear panel terminals with remote-sense capability to compensate for cable voltage drops.
Special features include the 4.3” 480x272 pixel 16-colour resistive touch screen user interface, bringing a modern touch. The supply is capable of displaying computed power and resistance on the display as well. Metering accuracy seems above-average at 0.1%+2/4mV (depending on range) and 0.3%+20mA. Specially-designed shrouded screwless safety terminals allow for use of standard and shrouded 4mm banana plugs up to 30A and the use of either 6mm plugs, 8mm spades or bare 6mm wire for the full 50A. It is backed by a three-year warranty which is registered through their website.
Compared to its peers, while the QPX750SP may be neck-and-neck with others on many of the key specifications, it is definitely heads-and-shoulders above the rest when it comes to current capability at low-voltages, its colour resistive-touch LCD screen and price. It fares well with regards to ripple and noise, and voltage programming resolution. I think this is a good example of Aim-TTi being true to their motto – “measurably better value”. If I were to buy a supply in this power and voltage range, I think it would be pretty much a no-brainer to choose the QPX750SP.
Such specifications make it ideal for a variety of applications where more voltage, power or current is necessary while maintaining good resolution/accuracy, safety and automation capability. This includes inverters, DC-to-DC converters, brushless motor drivers for electric bikes/scooters, telecommunications equipment, high-current MOSFETs or even some automotive applications.
For more details, see Aim-TTi QPX750SP In-Depth – Ch1: Market Survey and Feature Introduction
The power supply arrived safely, enduring its long round-the-world journey in a relatively plain-looking brown cardboard box. The supply was suspended in the box with foam end-pieces, although documentation and the extra US mains lead were left to float around in the box without any additional protection for the surface finish of the power supply which could have led to a cosmetic blemish I observed in the paintwork. The included mains leads in my package covered UK, Europe and US as the unit was shipped from the US, so I rewired one of the leads to an Australian plug.
The unit has a beige-coloured front-panel with a very straightforward design incorporating the colour resistive-touch LCD interface with a more traditional numerical keypad and rotary encoder inputs which should satisfy all types of users. The design of the unit has clever shrouded terminals to ensure safety but also accommodate a variety of connections including ordinary 4mm shrouded banana plugs up to 30A and 6mm/8mm insulated spade terminals or bare wire up to 50A. The rear panel of the instrument is well labelled, with an output for system-applications and all remote-control interfaces available. The GPIB option was not fitted to this unit but is available for purchase. The unit has a universal voltage input which is quite convenient. Airflow is also very clearly designed for a front-to-back arrangement which uses an 80mm brushless DC fan as the exhaust, although the square intake holes are rather large at 5.7mm which could lead to inadvertent intrusion of items or vermin. The unit rests on rubber feet with props which allow for the unit to be angled at a fixed angle upward for more comfortable use.
For more details, see Aim-TTi QPX750SP In-Depth – Ch2: Unboxing
The Aim-TTi QPX750SP is a little bigger than the average bench power supply, following the same footprint as a half-rack-unit-width device but being three rack units tall. The unit is designed with both bench-top and systems applications in mind with both front and rear terminal connections. The LCD screen is bright, sharp and has a great viewing angle. The user interface accommodates users which prefer touch, rotary knob or button inputs through the front keypad. Feedback is provided with some buttons being backlit by LEDs in addition to the information on the LCD. It is very configurable, offering options including changing the colour theme of the interface, buzzer tones for many different categories of alerts and power-on behaviour to name a few. It also allows for save and recall of settings.
When in use, I found the ten-second boot-up time to be decidedly swift compared to other graphical instruments and the design of the main terminals to be quite flexible in allowing for use of both shrouded and unshrouded 4mm banana plugs for up to 32A and bare wire or spade terminals for the full 50A current. Unfortunately, the sense terminals were not as forgiving in terms of the wires they would hold onto, and I was not convinced of their longevity under frequent connection or disconnection. It is my opinion that ordinary shrouded 4mm banana sockets be preferable despite eliminating the possibility of bare-wire connections.
The unit, when propped up on its feet, stands a little taller than I would expect. On the whole, the user interface is intuitive and easy to use, save for exiting dialogue boxes which requires the push of the cancel button as tapping outside the window does not dismiss it. This has caught me out a few times, but I’m sure I will adapt. I feel that full advantage of the colour LCD may not have been taken, as other supplies I have used will colour-code the digits to indicate operational mode which can be perceived at-a-glance compared to the smaller indicators on this model. Similarly, other supplies have also back-lit their output buttons to indicate operational mode as well, while this unit uses the LED to indicate channel state only. This can be confusing when digital logic input is used, as the channel state may appear on but is disabled by the digital logic input.
Functionally, while uncommon amongst supplies in this power envelope, the omission of the USB Host port is unfortunate, as it means this supply is unable to export its settings or record data, take screen-shots or load sequencing data from an external USB memory device. As this unit lacks these features on-board, it relies on a host (either running bespoke software or using Test Bridge) to command it via the remote-control interface to achieve some of these functions. Some more sophisticated power supplies also take advantage of the LCD to produce graphical trend plots of values over time. However, given that a colour LCD is relatively uncommon amongst supplies of this power class and the likelihood that many units are going to be used in systems applications where the user interface is relatively unimportant, this omission is perhaps not a major issue especially considering the price.
Perhaps the biggest annoyance for bench-top use is the acoustics of the unit. The thermostatically controlled fan runs at a low but definitely audible resonant blowing noise even when the unit is unloaded. Under heavy load, the fan speed does increase and the noise is even more pronounced with a whiny character. The thermostatic control results in a seemingly random “hee-haw” oscillation of fan speed that can be quite distracting. Similar to other switching power supplies, the QPX750SP also has some minor acoustic noise related to the load including a soft “chirp” on start-up, noticeable “ticking” on step load changes and a soft “hissing” under light loads. This is not unusual for switching power supplies.
Documentation available from their website was quite brief but sufficient for most purposes with a focus on practical aspects and screenshot illustrations throughout. An issue was identified with the help functionality which was reported to the manufacturer for rectification in the next firmware release. Similarly updates to the user manuals will more clearly specify the recommended terminals and ferrules to be used with the terminals on the supply for safety and compatibility.
For more details, see Aim-TTi QPX750SP In-Depth – Ch3: Benchtop User Experience & Documentation
The Aim-TTi QPX750SP comes with USB and Ethernet (LAN-LXI) connectivity by default, with GPIB available as an option. Unlike other members of the QPX family, RS-232 Serial is not available. The USB connection is enumerated as a CDC virtual serial port, requiring no drivers on modern operating systems. This is not the customary USB-TMC that may be expected from test instruments, but the choice of CDC does lead to wider compatibility and ease of use in non-VISA environments. The downside of not being able to emulate GPIB asynchronous lines is perhaps not a big issue for an instrument like a general-purpose power supply. The LAN interface is seemingly similar, supporting only SOCKET connectivity rather than VXI-11 with similar drawbacks and advantages. The web interface is also relatively spartan, offering remote command and settings change functionality only.
Tests involving the SCPI remote control proved to be reliable over long test sequences, although the single-socket implementation can leave the instrument in an un-connectable state with a hung open TCP socket connection in case a program is improperly terminated. This has been reported to Aim-TTi who are investigating a revision to improve this through implementing multiple sockets. Response times on SCPI remote control were generally very fast, with simple queries clocking in at 3-4ms, measurements around 6ms and commands involving changes reaching 17-22ms. The reset operation took quite a bit longer at about 360-380ms.
Quasi-analog control and monitoring is offered and tests of the accuracy using the Keithley 2450 SourceMeter as input showed that the unit was accurately digitising the input with a deviations much smaller than implied by manual specifications. At a 50V range, maximum programming error was about 40mV; at 80V range, maximum programming error was about 60mV; and at 50A range, maximum programming error reached 50mA. In all cases, the offsets were dominated by gain-error. Unfortunately, the quasi-analog sampled nature of the input appears to operate at about 4Hz and results in some lag with the monitoring output reflecting changes with a delay around 400ms. Because of this, use of the quasi-analog control to generate waveforms with rapid changes will result in a stair-step output rather than a smooth change.
Optoisolated digital logic input and output is also available, with testing showing that a logic input is reflected to the logic output within about 40ms. Channel switch-on seems to require another 40ms, although turning channels off were much more in-sync with everything completed within about 40ms. If this mechanism is used to generate pulse waves, this discrepancy may cause some duty-cycle distortion, but otherwise, it seems relatively quick compared to the analog control.
The Test Bridge software is not yet in its final release state, but as it stands, it offers quite a bit of value for new users who may not want or are not able to program their own software. It offers functionality including remote operation, configuration, sequencing, charting and data logging. It is free-of-charge and goes in some way to ameliorating the fact that the QPX750SP has no onboard logging, sequencing or USB host functionalities. The software is fairly easy to use once the cluttered interface is mastered and is capable of supporting multiple instruments from Aim-TTi as your needs grow. Unfortunately, it seems to only be available for Microsoft Windows operating systems and renders poorly on displays smaller than 1920 x 1080 resolution. While the sequencing function is very enticing, its capabilities are limited by both instrument capabilities and communication overhead.
For more details, see Aim-TTi QPX750SP In-Depth – Ch4: Remote Interfaces & PC Connectivity
High current capability is useful when it comes to characterising MOSFET capability under the expected application loads. Luckily for me, I was interested in the newly released Infineon Source-Down MOSFET series which offers a smaller package size with excellent Rds values and thermals, so I would compare how they fare with the best TO-220 and PowerPAK SO-8 MOSFETs I had on hand. For this test, my previous set-ups were relatively limited, so I had to make a few purchases and design a completely new PCB with 2oz copper to handle the high current.
Through a multi-instrument collaboration involving the Aim-TTi QPX750SP, Rohde & Schwarz HMP4040, Keysight E36103A, Keithley 2450 and Harting MICA Industrial Computer controlling the ensemble through a modified pyvisa script, I was able to automate the test procedure which involved sweeping the gate voltage while a constant current was being passed through the drain-source connection and recording the drain-source voltage at the package. The system automated a cool-down period on each run while also ensuring power dissipation would remain limited to 3W to avoid overheating of the MOSFETs which relied on PCB heatsinking. This allowed me to plot Rds(on) versus gate voltage plots which allowed for comparison of performance.
This process ran smoothly and the capability of the QPX750SP was instrumental in testing all MOSFETs. The tested NXP PSMN1R1-30PL and Vishay SiRA50ADP-T1-RE3 both reached 49A before hitting the power dissipation limit. The Infineon IQE006NE2LM5CGATMA1 proved to be a champion though, requiring a hefty 63A to reach the power dissipation limit. Of all the tested units, it offered the lowest Rds(on) even under load, however, it should be noted that there are better PowerPAK SO-8 MOSFETs so perhaps I should also give the SiR500DP-T1-RE3 a try as it claims an even more impressive 30V/0.39mΩ/350A specification.
Throughout the test regime, the QPX750SP was reliably in-control via LAN and performed flawlessly. While I chose not to use its internal metering in favour of an SMU acting as a DMM to obtain higher accuracy in the computed plots, use of the sense terminals can certainly provide accurate readings down to 1mV resolution if that is sufficient.
For more details, see Aim-TTi QPX750SP In-Depth – Ch5: High Current MOSFET Rds Measurements
The extended voltage range of the QPX750SP can be quite useful for those who need to test telecommunications-based equipment which may be rated at 48V nominal, as they may need to operate close to 60V under extreme conditions.
To demonstrate this and allow the QPX750SP a chance to show its internal metering capability, a creative approach was taken to measure the efficiency of the Microchip PoE-to-USB-C PD Adapter that was recently RoadTested. By modifying the 802.3bt power injector, it was possible to retain the output negotiation logic while feeding your own “48V nominal” supply. Taking baseline readings to compensate for this circuit’s quiescent consumption, it was possible to measure the quiescent consumption of the adapter to be about 0.8-1.5W depending on voltage. Testing the unit under USB-C PD 20V/60W capable load created using a B&K Precision Model 8600 DC Electronic Load and a USB-C PD Decoy Board demonstrated peak efficiency of about 90.8% which is pretty impressive, with 75% efficiency being attained by a load of 8W. This is inclusive of the power loss in 3m of 24AWG Cat5e cable and quiescent loss in the decoy board and USB-C cable losses. The actual efficiency is probably a little higher, but the QPX750SP’s capability to source higher voltages and meter down to 1mA below 1A via SCPI was instrumental to obtaining such good results.
A spur-of-the-moment experiment had me measuring the trip times for a Weidmuller SU1C10UC C-curve circuit breaker by using the QPX750SP to source a range of currents up to 50A. By measuring times with an oscilloscope, it was possible to confirm the breaker was behaving as specified. I was also able to make use of the voltage and current capabilities to do some magic smoke liberation experiments in the name of science.
For more details, see Aim-TTi QPX750SP In-Depth – Ch6: PoE Converter & Breaker Tests
It would be a shame if this power supply didn’t have a chance to demonstrate what it is capable of in terms of power delivery. To this end, I had planned to test it under full-load using automotive inverters running mains appliances, however, after receiving a faulty inverter and realising this would only result in a “single-point” result, I decided to try something different.
I spent about AU$80 on a TE Connectivity/CGS TE750B1R0J 1Ω 750W-rated chassis-mount wire-wound resistor (Order Code 1760835) from element14 that arrived within a week. Using this, I was expecting that it would be able to dissipate 750W by operating at 27.386V and 27.386A, hooked up with the 6mm2 wire from the previous MOSFET experiments and sat on a terracotta tile for protection against heat.
I discovered that the unit was only capable of putting 707W into the resistor due to a minor technicality regarding the PowerFlex+ curve. Contacting the manufacturer, I was informed that the power output is only guaranteed under the indicated points. The interpolation function between these points is not specified and power output is hence only “up to” 750W. This was a little misleading to me especially when the front page of the brochure says “limited by the power curve” which implied to me that it would be able to deliver 750W as long as maximum voltage and current limits are respected.
Regardless, the unit was capable of delivering 707W into the load and didn’t sound like it was breaking much of a sweat, only being subtly louder than when it was at idle. Efficiency into the load measured 50% by 60W; 60% by 110W; 70% by 205W; 80% for 550W and peaked at 81% for 707W which is not a bad performance. The active power factor correction of this unit also did a good job keeping the power factor above 0.5 almost immediately under any load, and above 0.8 for load above 100W.
It should be noted that these load and efficiency results are only valid for the condition for a 1Ω constant resistance – other loads result in different voltage and current operating points which would have different efficiency levels. This is explored in the later Instrument Performance Tests chapter.
For more details, see Aim-TTi QPX750SP In-Depth – Ch7: Full Power Load Testing
Putting the QPX750SP through a number of tests using a Tektronix PA1000 Power Analyzer, B&K Precision Model 8600 DC Electronic Load, Rohde and Schwarz RTM3004 Oscilloscope and Keithley 2450 SourceMeter proved quite revealing with regards to instrument capabilities and shortcomings.
Programming and readback accuracy for both voltage and current were excellent across the full range, comfortably beating the datasheet specifications. Channel power-up to 40V unloaded was a bit leisurely with a rise tome close to 70ms, while power-down was a little quicker at closer to 67ms. If power was turned off to the instrument via the front-panel power switch or by unexpected power removal, no unregulated “spike” was recorded, indicating the load would be safe but the voltage did not fall as quickly, instead being bled off slowly over around 10s.
Transient performance of the QPX750SP was a bit difficult to judge as the recorded signal showed significant baseline shift under load which could be related to electrical field distribution on the terminals and fast-changing transients not providing enough time for the regulation to “settle”. Regardless, the results demonstrated that fast transients with rise times of 18 and 241µs were able to provoke sharp dips and overshoots in the voltage due to the performance of the regulation loop. Slower rise times in the >5ms range showed more favourable performance, as expected of the 2ms transient response specification, but the deviations were still noticeable reaching 803.6mV peak-to-peak (18%) inclusive of baseline shift. Higher-frequency load pulse trains resulted in behaviour which included collapsing the rail to zero entirely as the load comes on while the supply is recovering from an overshoot. While this did not provoke an instrument error, this behaviour is not ideal and could arise when running hard-switched loads (e.g. PWM).
Testing for overshoot similarly showed the QPX750SP could make some improvements, as the supply often did have significant levels of overshoot in spite of the setting of the current limiter due to the regulation loop speed. This can result in 1-2ms of significant overshoot, reaching 30A (load maximum) when a setting of 1A was engaged. Using the most sensitive test, I tried to run a 5mm LED directly from the outputs, set to 4.5V/20mA and it was able to destroy the LED every time. Choosing a more conservative 10mA setting allowed one LED to survive, but perhaps that was due to its hardiness as it reached 4.5V (constant voltage) for about 175ms before regulating into constant current. I would not recommend relying on the current limiter on the QPX750SP to provide protection for sensitive semiconductors where overshoot could compromise device reliability or cause immediate destruction. However, as a general-purpose power supply, this level of performance may be sufficient and without having any point-of-reference for a power supply in this power class, I cannot be sure how its performance compares to its peers.
Overvoltage protection operated quickly, although the actual time to trigger was obscured by the output capacitor discharge time. Overcurrent protection was a bit slower, however, in my test case requiring about 204ms to trip.
A single ripple and noise measurement at 4.5V/30A was made, resulting in 42.6mV peak-to-peak and 4.6mV RMS measured. This is more than the datasheet specification of 20mV peak-to-peak and 3mV RMS, however, is close enough to be plausible as my testing may have other sources of noise inducted into the measurement or from the load.
Standby power consumption of the unit in the off state was relatively high at 4.145W and with the unit powered on and the channel switched off, this reached 20.772W. This is definitely an area which could be improved and may explain why the cooling fan runs audibly even when the unit is not under any load. Constant-voltage tests of efficiency under loads up to 150W saw a peak efficiency of about 70%, likely in part to the high quiescent consumption, although better efficiency is expected as load increases.
For more details, see Aim-TTi QPX750SP In-Depth – Ch8: Instrument Performance Tests
I couldn’t resist the opportunity to round-off this review by taking a peek under the covers. What I saw was quite impressive – internals that occupied most of the space available inside by having PCBs span across the bottom, sides and even sticking out like a mezzanine. The components were practically all from reputable manufacturers, some a bit old-fashioned, with appropriately high-precision parts where needed. Electrolytic capacitors were well-chosen with practically all units from reputable Japanese brands. Magnetics appear to have come from a local supplier (to them), F.I. Technology. Construction quality is excellent, although the system does have a buried 40mm Sunon fan inside that is secured by only one screw to a heatsink.
The other questionable aspects were the placement of the mains fuse in the bottom corner of the PFC board where it cannot be easily accessed. While a fuse blow would be very unexpected given its large 15A time-delay rating, replacement is complicated by the limited clearance due to neighbouring components.
Another questionable aspect, from my view, was the use of a consumer-grade Transcend 300S 8GB microSDHC card using TLC Flash to hold critical system information that is required for the operation of the supply. Conventionally, perhaps an SPI/QSPI NOR Flash component would be used to store the data, but their choice of microSDHC could also have been satisfied with industrial-grade MLC cards which may have longer lifetime. That being said, with such a small amount of data and a read-mostly operation, provided the controller does a good job of managing read-disturb and slow charge-leakage, the set-up should still work just fine assuming the card stays in place. That being said, I felt more comfortable backing up the card’s data, just in case, even though this is not a manufacturer authorised procedure. That also gave me the opportunity to modify some of the data (at my own risk) and have some fun with it.
For more details, see Aim-TTi QPX750SP In-Depth – Ch9: Teardown
Aim-TTi’s QPX750SP programmable DC power supply is a compelling product that definitely fits their motto of “measurably better value.” The unit is amongst the cheapest in the market survey round-up on power supplies while delivering innovation when it comes to current capability at low-voltages, a resistive-touch colour LCD touch screen interface while remaining competitive throughout the other specifications. It offers an 80V/50A/750W PowerFlex+ envelope within a half-rack-width and three rack-unit-height package. There are many things to like about the unit, although this is tempered by a few minor drawbacks.
The touch-screen interface was intuitive and easy to use, while the option of a rotary knob and keypad ensures all users are catered for. The LCD is sharp, bright and has an excellent viewing angle. The unit’s output terminals have been cleverly designed to ensure safety and flexibility, while remote control interfaces and rear terminals ensures the unit is suited for both bench-top and systems applications. The main drawbacks appear to be the sense terminals and their pickiness with regards to wires, the acoustic noise of the fan which can be loud and whiny enough to be distracting and the lack of a USB Host port which could have enabled additional onboard functionality.
Remote control operation of the unit was reliable and straightforward through the USB-CDC and LAN SOCKET interfaces. Response times for commands ranged from 3-4ms for simple queries, 17-22ms for those that involved some action and 360-380ms for resets. Quasi-analog control operated at a rate of around 4Hz with output seemingly smoothed and delayed by about 400ms. Digital logic control was effective with a delay of about 40ms.
The Test Bridge software, while still in a beta/release-candidate state at the point of review, adds value to the package, allowing users to have remote panel, configuration, logging, charting and sequencing capabilities without needing to code anything of their own. The software is available free and can support multiple Aim-TTi instruments across multiple series, allowing for expansion in the future. While the software is functional, the interface renders poorly on smaller screens and can feel quite cluttered at first.
The power supply proved to be quite capable in enabling testing of MOSFETs and circuit breakers at high currents, a PoE converter with its extended voltage envelope and in the torture of components as part of a bonus exercise. Tested at full power using a wire-wound resistor as a load, it was determined that the PowerFlex+ curve is not “purely” based on the power and some additional limitations can occur in-between the guaranteed points on the curve. Thus, testing only reached 707W of the rated 750W with a 1Ω load despite the manual claiming 720W in their example. Better specifying the interpolation function between points of the curve will allow users to avoid disappointment if they are very close to the power envelope.
Testing of instrument performance overall showed that accuracy of voltage and current programming and readback were far better than implied by the datasheet. Similarly, the accuracy of quasi-analog programming of voltage and current were also far better than implied by the datasheet. Overvoltage protection was effective and rapid, while overcurrent protection took a little longer, closer to 200ms to activate. Ripple and noise figures in the datasheet appeared plausible despite measurements differing slightly. Channel power-off behaviour under unexpected conditions revealed no unregulated condition, thus ensuring the safety of the load.
Testing of transient response revealed that the power supply appears to handle rapid transitions poorly and, in some cases, collapse of the voltage rail or significant overshoot can be observed despite not operating at full load. This may be down to the test scenario which simulated a 0-30A repetitive 50% duty-cycle load step with rise times as short as 18µs. Slower load steps were better handled, however, there was still a baseline shift observed which could not be eliminated and may be due to electric field distribution on the terminals or measurement issue. Constant current regulation performance was also somewhat lacking, with overshoot on channel start-up and transition into CC mode allowing for significant overshoot which could destroy sensitive semiconductors. As I haven’t any experience with any other power supply in this power envelope, perhaps this is not unusual for such power supplies to have these difficulties.
Another downside of the unit was a relatively high standby power consumption of 4.145W which increased to 20.772W when powered up with the channel deactivated. This is also reflected in the tested efficiency figures which only reached 70% at a constant voltage operation up to 150W load (as that was the limit of my equipment) or about 81% at 707W under a 1Ω constant resistance load.
Thanks again to Aim-TTi and element14 for this valuable opportunity. My sincere gratitude to Aim-TTi especially for their prompt responses to support requests and commitment to product improvement. I look forward to seeing the promised firmware update being released on their website to resolve minor issues identified in this review.
Great questions colporteur! I won't blame you for some confusion regarding USB, but what this unit lacks is a USB Host Port. Consider this a USB-A type receptacle in which you plug a device into (e.g. a port that accepts a USB flash drive). Having this port, with firmware support of course, would allow for things like recording screenshots, internal data logging, loading of arbitrary waveform data, exporting settings, uploading new firmware, all without the need for an attached host (computer) controlling the device.
What it does have is a USB-CDC support which is a USB-B type receptacle which acts like a device. In this case, CDC is Communications Device Class, meaning that the unit is designed to plug into a computer or other host, and will act like a USB-to-Serial adapter, coming up as a virtual COM port. This allows us to command the instrument over this virtual COM port. This is distinct to the USB-TMC version where TMC stands for Test and Measurement Class, which is more common amongst test equipment that is intended to connect with a VISA layer and IVI drivers. Some devices are "switchable" and support both CDC and TMC options for maximum flexibility, as TMC devices can implement a USB-488 protocol that supports emulation of GPIB asynchronous handshaking lines for more accurate triggering and faster status reporting.
In regards to personal funding that went into this RoadTest, the total would be around AU$250 in this instance. I did itemise the spends on the MOSFET testing in the detailed blog. It's not insignificant, not everyone can just "do this" and I didn't propose this originally in my application. As often is the case during a review, I decide that something is warranted and go ahead and do it. I don't mind spending some money especially as sometimes parts will be required that can help demonstrate the full ability of the product and for more sophisticated products, I feel that spending the money may be warranted for my own educational benefit as well and I'm just thankful that my local element14 was able to deliver in time to make it happen!
I feel that RoadTests generally will include some specific supporting components for the review to help the reviewer, they never will be able to include "everything" one needs to perform their intended review or fulfill their own inquisitive desires. That's why the application asks whether you are equipped to perform the review - I've always answered that I am, and thus I feel there is a responsibility on my part to contribute something to a good result. In my previous RoadTest, I look at it from the perspective of getting the "expensive part" covered, so I'll cover the accessories. This fact might not exclude anyone directly from participation, as this was a decision made after the unit arrived in the interest of offering a more complete review.
Conversely, might I offer the counterpoint - had I not gone a bit further and spent the extra money, would the review been as useful or comprehensive? Would it still have met your expectations?
I am, and have always been, grateful to the RoadTest program for many years of accumulated wins and the learning that comes along with it. Indeed, I acknowledge that the suite of equipment is not something most will have access to, and having them is creating a "snowball effect" where having more gear can allow you greater latitude in the testing you perform in order to build a more comprehensive review. I feel it is a duty as someone who has been a beneficiary of the program to use the equipment to further explore and contribute back to the community and this is one way in which I am doing it. In doing so, I'm sure I am fulfilling the desire for some of these equipment vendors to see their gear being used in applications, years down the track. I would consider this the "all-win" scenario.
Thanks for the comment kmikemoo. Indeed, at face-value, I would have expected it to hit 750W based on "limited by the power curve", but the example given in the manual does mention a 1-ohm load:
In this instance, it does imply 720W would be available in CP mode, but instead I saw 707W in reality, so there is definitely a discrepancy. I did request that Aim-TTi clarify the interpolation function used between the "guaranteed" points on the PowerFlex+ curve to avoid disappointment where user's needs may be very close to the maximum, or at least indicate the maximum discrepancy between the ideal power curve and their implementation.
A gold standard review that I come to expect from a GL RoadTest.
You indicate there is no USB and then further on you speak to USB-CDC. I'm a bit confused and its purely because I lack knowledge. I didn't see a USB connector only the push pin block at the back. Is that the USB-CDC output?
I'm curious about how much personal funding went into the review? You mention the cost of the resistor but I suspect there are others (i.e. printed circuit board design) that you are out of pocket for. Care to share your total?
The reason I ask is to explore the commitment that is invested for a top shelf RoadTest like this. It is assumed the RoadTest will provide everything an individual needs to do complete the review. I have participated in RoadTests that required additional components like wall warts, memory cards and power supplies (i.e. PoE) in order to use the product. Having to purchase components to conduct the RoadTest can eliminate some individual from participating. The understanding that participation is free may be misleading.
Your extensive knowledge and access to test equipment provides you an advantage in quality and quantity in a RoadTest. I look forward to reading them and am just a little bit green with envy. Great job.