Achieving an ‘astonishing’ flat high efficiency profile across the full load range
01 December 2022
Figure 1. Typical 12V/10A LLC PSU showing tail off in efficiency at low loads
In September 2022, a new company, Pulsiv – a spin out from Plymouth University – launched a new approach for achieving ultra-high efficiency power supplies. Now, the technology has been adopted by an early user – a global PSU (power supply unit) manufacturer that provides power solutions to many leading consumer brand names...
This article was originally featured in the December 2022 issue of EPDT magazine [read the digital issue]. And sign up to receive your own copy each month.
Pulsiv technology is also being widely evaluated by industries as diverse as appliances, blade servers for data centres and smart device chargers. Here, Darrel Kingham, CEO at power electronics start-up, Pulsiv takes the lid off the technology and explains the benefits offered…
Before we launch into the technical details, let’s just consider the scale of the problem. After all, new, high efficiency chips are regularly trumpeted – and it is true that great strides have been made. The problem is not simply high efficiency, per se, it is high efficiency across the full load and input voltage range – including at low power, where quite often a supply may be required to function, when trickle-charging a laptop, smartphone or portable device, for example.
Figure 2. Pulsiv’s method of converting AC to DC using an intelligent controller & patented switching techniques
Figure 1 shows the efficiency characteristic for a low-line, wide-input LLC resonant converter for a 12V@10A consumer electronics application from a leading vendor. From above 20W – certainly 40W – the performance looks very solid – in the high 80%, even 90% efficiency range. But crucially, below 20W, performance tails off dramatically – such that when drawing under 10W, the efficiency of the power supply falls to around 50%. In many common use-cases, that means wasting half the energy consumed for most of the time. This unimpressive efficiency profile is typical of consumer products using an LLC solution, without adding significant cost and complexity.
The new method of efficient AC/DC conversion developed by the team at Pulsiv resulted initially from their work in the solar industry. A team at Plymouth University was investigating how to increase the power output from solar panels by modifying the electronics, focusing on minimising losses in the electronics control circuitry. In order to run the algorithms they wanted, the team couldn’t use existing DC to DC or DC to AC converters – so they went back to basics and designed new power circuits from scratch. The resulting work has applications not just in DC to AC conversion, but also in the reverse direction, from AC back to DC – and it is this technology that Pulsiv launched via its OSMIUM microcontroller in summer 2022.
Pulsiv has developed a unique way of converting AC to DC, using an intelligent controller and patented switching techniques. Power Factor Correction (PFC) is achieved without a switched inductor, and requires only a small storage capacitor to be charged/discharged with switches S¹ and S². (see Figure 2).
Figure 3. Basic schematic & operation
The improvements delivered by this new architecture derive from the fact that it uses capacitors as the switching element, rather than inductors, which are much more lossy.
Therefore, instead of having a boost PFC, which is typically what is done, with an inductor in series, Pulsiv uses a capacitor in parallel. The charging path is regulated and has a separate discharge path from the capacitor. Algorithms that run on the OSMIUM microcontroller (MCU) maximise the power factor by regulating the current that is used to charge the capacitor; and the discharge side is controlled effectively by the follow-on DC to DC converter. The energy stored on the capacitor is basically the energy that you need to ride through when the grid is weak. In this way, by bringing intelligence into the charging path, we can achieve very high power factors, as well as meet any line current regulations that are required.
The basic operating principle is shown in Figure 3. Path 1 shows the charging of the storage capacitor. The maximum capacitor voltage is regulated (set by pin 4: 150V or 180V). The grid sense on pins 5 and 6 determines the grid voltage and frequency. Crucially, in many applications, the regulated charging path to Cch means that there is no inrush current. The removal of the requirement for any kind of inrush filtering is another huge advantage of the technology, especially in applications such as LED lighting in smart buildings.
Figure 4. Pulsiv’s front-end performance curves versus EnergyStar
Path 2 follows the discharging of the storage capacitor. Cch is discharged via Dd; the discharge current will depend on the follow-on DC/DC converter.
The efficacy of this approach is demonstrated in Figure 4. The plots for voltage inputs, 90V (purple), 115V (green) and 230V (blue), use the OSMIUM MCU with active bridge and flyback topology. They show that even down to around 2W load, performance remains at between 80% and 90% depending on input voltage. From around 5W until maximum loading, efficiency is in the mid-90% range. For comparison, various EnergyStar standards are also plotted: the OSMIUM solution easily meets the most stringent Energy Star VI requirements.
As well as setting a high bar for efficiency across the full load range and at different input voltages, Pulsiv’s approach also offers other benefits:
Figure 5. Thermal plot of the PSV-AD-250-DS development system operating at 113W from a 230V supply
• Elimination of inrush current. Simply, the Pulsiv technology means that there is no measurable inrush current. That has huge implications for system designers, who now no longer have to employ inrush filters, resulting in significant financial and space savings.
• Do you really need a complex LLC design? Picking up from earlier, Pulsiv OSMIUM front-end microcontrollers and supporting components can be combined with commodity flyback DC-DC converters to displace higher-cost LLC solutions. A 240W interleaved flyback is currently being developed and work is underway to showcase reference designs with even higher power capability.
• Low cost BOM (Bill of Materials). The efficiency of the Pulsiv technology means that it is no longers required to employ costly components such as synchronous rectification, or move to GaN, for example, in order to achieve high-90s% efficiency performance. Of course, for the absolute highest performance power supply, OSMIUM together with GaN, SR and an LLC topology will deliver even more.
• Scalability. By changing just three key components, Pulsiv technology can encompass designs from 1W to 10kW and above.
• Inherent reliability. Thermal plots (see Figure 5) show that there are no damaging hot spots.
Figure 6. Salom’s new 150 flyback platform using the OSMIUM MCU achieves an ‘astonishing flat efficiency profile with no inrush current at both hi & low-line input voltage’
Front end solution
The Pulsiv OSMIUM microcontroller is a front end solution. It can be employed, as previously stated, with other components, and optimised for performance, size or cost. So, when looking at the impressive efficiency performance numbers of the OSMIUM solution, one must also accept that there will be losses in other parts of the circuit. The proof of the pudding, of course, is always in the eating: in this case, what overall numbers can we expect from a Pulsiv implementation?
Leading consumer electronics PSU maker, Salom is already using OSMIUM MCUs in its new 150W PSU flyback platform. Figure 6 shows the overall performance of the new PSU (green), running at 91.5% from 10% load to 100%. The orange line shows the results of other flyback designs employed by Salom, hitting a still impressive mid-80s percentage, but tailing off at below 30% loading. The more complex and expensive LLC PSU is shown in yellow, again tailing off from 40% load, around the point that it exceeds the OSMIUM solution.
Salom’s Andy Richardson CEng MIET, Vice President, Business Development comments: the Pulsiv technology “delivers an astonishing flat efficiency profile with no inrush current at both high- and low-line input voltage. A single PSU can now be used to support multiple applications – previously an optimised PSU was required for each.”
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