One of the most demanding challenges of power electronics concerns efficiency, which must be maximized both to meet the requirements imposed by international standards and to reduce power waste, creating more sustainable products.
Power supplies are required for any AC-powered application, from the simplest mobile phone chargers to the most complex and powerful SMPS for industrial applications. In an ideal power supply, all the power drawn from the AC mains is available to the load. In reality, this is possible only if the current is in phase with the voltage. If current and voltage are out of phase with each other, part of the energy absorbed by the grid is lost. The power-factor correction (PFC) stage of a power supply performs precisely this task, trying to get as close as possible to the ideal case corresponding to a unity power factor.
With the release of its power electronics technology, Cambridge-based startup Pulsiv came out of stealth mode today. With no need for a PFC inductor, Pulsiv OSMIUM converts AC to DC via a proprietary process that includes charging and discharging a tiny storage capacitor. High power factor, continuously high efficiency, and ultra-compact system architecture are all features of this solution. Utilizing Pulsiv OSMIUM technology may minimize costs, increase system efficiency overall, and help cut down on global energy usage.
Pulsiv’s intelligent control
Pulsiv, a company established in 2013 as a spinout from Plymouth University, was formed by a small team of leading professionals in sales, product development, and finance. While studying technologies for solar micro inverters, engineers at Pulsiv discovered a new way of extracting more energy from a solar panel. They also found out that, by applying similar principles in the reverse direction, the technology is applicable to LED lighting, battery charging, and AC/DC conversion. Even though solar technology is still a business unit of Pulsiv, the company has recently diversified to deliver power supply solutions.
“Our product basically consists of a major U.S. Tier 1 semiconductor device, to which we add our proprietary IP,” said Darrel Kingham, CEO at Pulsiv. “The result is the Pulsiv OSMIUM microcontroller [MCU], the basis for creating power electronics front ends that cover a wide power range.”
All of the valuable technology is inside the Pulsiv OSMIUM MCU, in which the main task is to produce a high power factor while maintaining high efficiency across the full load range. In a basic PFC controller, a switched current passes through a series inductor, and by measuring the phase shift in voltage and current, the power factor can be corrected.
“Our solution is based on an alternative approach, where we control the charge and discharge of a storage capacitor,” said Kingham. “This is the basis of our patent and provides us with a lot of additional benefits, not just the power-factor correction.”
As shown in Figure 1, PFC can be achieved without any inductor and requires only a small storage X-capacitor to be charged and discharged through a suitable circuit design (symbolized by switches S1 and S2). The MCU controls the charging of the capacitor up to a certain maximum voltage in synchronization with the grid, thus maximizing the power factor in any condition. Moreover, because the current path is under full MCU control, when the circuit is initially powered up, there is no inrush current. Pulsiv’s solution eliminates inrush currents from the front end of the power supply because it regulates the current going into the bulk capacitor; the only inrush is the transient of the X-capacitor. The discharge from the storage capacitor, which is not regulated, is done through a simple diode with a current that depends on the DC/DC converter following the front-end stage.
Because the controller does not allow the voltage to go too high, a standard 160-V capacitor can be used in place of normally used 450-V capacitors, reducing costs. Additionally, because only the needed energy is effectively stored when the grid voltage goes down to zero, you don’t need to store a lot of energy. That allows you to use smaller capacitors with a lower voltage rating.
“When you use an inductor in series, all the energy has to go through the inductor all the time, but when you use a capacitor in parallel, you only need to store a small amount of energy for the time when you need it,” said Kingham.
Another benefit of Pulsiv’s solution is the efficiency profile. Unlike boost converters, in which the efficiency starts dropping off quite rapidly, this converter can maintain a very high efficiency at very low power. That’s because in the low-power region, where most boost PFCs start collapsing, with this converter, the capacitor will be charged only by the amount of energy that is needed. Pulsiv OSMIUM technology supports Active Bridge Control, Configurable Hold-Up, X-Cap Discharge, HVDC Output Selection, a Power Consumption Indicator and Grid Failure Detection. These optional features can be selected as required to meet the needs of different end applications.
As shown in Figures 3 and 4, Pulsiv’s technology not only achieves high efficiency but enables it to remain high and stable across the full power range, including low power. Up to 99% efficiency can be achieved with consistent performance and meeting Energy Star VI requirements. A relevant aspect of this solution is that it achieves efficiency by using 95% commodity components, meaning that we get a very low-cost bill of materials (BOM) ($6 to $15) and, obviously, it makes the procurement of such components much simpler.
Scalability is another key factor of Pulsiv’s technology. Because the MCU does not determine the output power, by changing just three key components (one inductor, one MOSFET, and one capacitor), the required output power, scalable from 1 W up to 10 kW+, can be supported by the same circuit (all other components remain unchanged).
“By comparing our complete flyback 150-W design against what other semiconductor companies are doing with their reference designs, it turns out that we require one-third to half fewer components in the BOM, and our design is very simple,” said Kingham.
Two Pulsiv OSMIUM controllers will soon be released (PSV-AD-150 and PSV-AD-250 sampling now) to support applications requiring up to 250 W in power. Complete circuit configurations for the Pulsiv AC/DC front end will be made available to simplify the design process. These include a full schematic, BOM, Altium file, and component calculator. A 75-W 48-V flyback reference design and a 120-W 48-V flyback reference design are being launched at the same time, which include an optimized DC/DC stage. These will be followed by a full 150-W 20-V interleave PSU reference design and a full 150-W USB-C reference design. By the end of this year, a full 500-W current-source PSU reference design will complete the portfolio. A 240W interleaved flyback is currently being developed and work is underway to showcase reference designs with even higher power capability.
“We want to put on the market something that is more efficient, that meets Energy Star standards, that is fairly economical to build, and that anybody can adopt,” said Kingham.
The three main application areas for which Pulsiv technology is suited include:
- Integrated power electronics, which are usually high-volume applications in which customers are not buying commercial off-the-shelf power supplies because they’re too big or too expensive
- Switch-mode power supply manufacturers, who can use Pulsiv technology for increased power, density, and performance
- Finished solutions, mostly surrounding USB applications, and compelling power banks
The PSV-AD-250-DS development system can be used by engineers to evaluate Pulsiv OSMIUM technology, and connecting a suitable DC-DC converter will produce a complete power supply prototype. Full reference designs are being made freely available via the company’s website, to showcase what’s possible when Pulsiv OSMIUM is combined with a carefully selected DC-DC converter.