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Advancements in Rapid-Charging Technology: Meeting the Demands of a Fast-Paced World

Article Source：power electronics news | Author：Maurizio Di Paolo Emilio | Issuing Time：2024.01.31
In the present era characterized by high speed and constant activity, the demand for expeditious charging solutions has become vital. Power Integrations (PI) released its InnoSwitch5-Pro line of programmable flyback switcher ICs.

Power Integrations (PI) released its InnoSwitch5-Pro line of programmable flyback switcher ICs. In the present era characterized by high speed and constant activity, the demand for expeditious charging solutions has become vital. With the increasing dependence on electronic devices, ranging from smartphones to laptops to home appliances, there has been a significant surge in the need for rapid and effective charging solutions. The increased demand has triggered a wave of innovation in power supply design, resulting in the creation of cutting-edge technologies focused on providing fast charging while ensuring efficiency and dependability.

The InnoSwitch5-Pro ICs are over 95% efficient, thanks to a unique secondary-side control method for zero-voltage switching (ZVS), which gets rid of the need for an extra expensive FET. Featuring a 750-V or 900-V PowiGaN primary switch, primary-side controller, FluxLink isolated feedback and secondary controller with an I2C interface, it streamlines the creation of compact, highly efficient single- or multi-port USB Power Delivery (USB-PD) adapters and is ideal for notebooks, upscale smartphones and portable consumer electronics, including those requiring the latest USB PD Extended Power Range protocol.

The secondary side of InnoSwitch5-Pro flyback switcher ICs has lossless input line voltage sensing for adaptive discontinuous-conduction mode (DCM)/ continuous-conduction mode (CCM) and ZVS control to make the design as efficient as possible across line and load.

Power design

One of the key players in this technological revolution is the evolution of rapid-charging standards, such as USB-PD and Programmable Power Supply (PPS). These standards, initially tailored for cellphone adapters, have evolved to accommodate a diverse range of devices, including notebooks and appliances, by providing adjustable outcomes for voltage and current through USB Type-C connectors. However, with the introduction of new standards like China’s Universal Mobile Charging Solution (UMCS) and proprietary standards from manufacturers like Samsung, the landscape has become increasingly complex, requiring power supply designs to be flexible and adaptable to various protocols.

The Universal Fast Charging Specification (UFCS) seeks to harmonize rapid charging. By unifying regional proprietary fast-charge protocols, UFCS ensures seamless compatibility for electric devices leveraging D+ and D– communication lines, it offers configurable output with continuous adjustment, supporting power levels from 45 to 200 W. It has four programmable voltage options, with minimum steps of 10 mV and 10 mA.

In an interview with Power Electronics News, Andrew Smith, director of training at PI, noted that in response to these challenges, companies are pushing the boundaries of power supply design to meet the evolving needs of the market. “One such innovation is the development of the latest iteration of InnoSwitch technology, InnoSwitch5-Pro,” he said. “This new version integrates cutting-edge features, including higher efficiency through technologies like gallium nitride and zero-voltage switching, which minimizes power loss and maximizes charging speed.”

Furthermore, advancements in communication protocols, such as the integration of primary and secondary controllers into a single IC, enable precise control over voltage and current, ensuring compatibility with a wide range of charging standards. Additionally, the implementation of fault-logging capabilities and telemetry reporting enhances reliability and facilitates troubleshooting during development.


ZVS

InnoSwitch5-Pro stands out with its innovative approach to ZVS without the need for additional components. Traditional power supply designs often grapple with switching losses, primarily attributed to the voltage drop across the power switch as it turns on and the current starts to rise. This phenomenon results in significant power dissipation, particularly in larger power converters.

ZVS presents a solution by ensuring that the voltage across the transistor falls to zero before the current starts to rise during switching events. This eliminates switching losses, leading to enhanced efficiency and reduced power dissipation.

Conventionally, achieving ZVS necessitates the use of additional components, such as resonant half-bridges or active-clamp circuits, adding complexity and cost to the design. However, as mentioned, the InnoSwitch5-Pro pioneers a new approach by integrating ZVS without the need for extra components.


In flyback converters, the transition of the primary switch from off to on is inefficient. (Source: Power Integrations)

The key to this innovation lies in the synchronization of the primary switching transistor and the synchronous rectifier (SR) transistor. By controlling both transistors with a single controller, the InnoSwitch5-Pro optimizes the timing of the SR transistor, ensuring minimal conduction loss in the output.

“The technique we employ is known as non-complimentary SR control, a nuanced approach to managing the switching behavior in power systems,” Smith said. “Unlike conventional methods, where the synchronous rectifier switch operates in tandem with the primary switch, we exercise a higher degree of control over when the SR switch engages. This control isn’t directly tethered to the actions of the primary side, although we ensure that both switches are never active simultaneously. Instead, we meticulously adjust the timing of the SR switch activation.”

In synchronous rectification, the SR switch is typically activated when energy is being supplied to the output, a logical configuration that remains unchanged. However, in discontinuous mode, where the current through the switch drops to zero, PI introduces a novel strategy using the InnoSwitch5-Pro.

“Just prior to initiating the primary switch, we briefly activate the secondary switch,” Smith said. “This momentary activation induces a current in the magnetizing inductance of the transformer. Although we subsequently deactivate the secondary switch, the inherent nature of an inductor causes the current to persist.”

In transformers, there are two types of inductance: magnetizing inductance and leakage inductance. Magnetizing inductance stores energy in the transformer and controls the rate of current rise through the primary switch, facilitating power transfer from the primary side to the secondary side. It is coupled between the primary and secondary windings. On the other hand, leakage inductance is not coupled to the secondary side and is more like parasitic inductance, a consequence of transformer construction.

The transfer mechanism primarily relies on the magnetizing inductance of the transformer, which effectively couples the primary and secondary windings. In contrast, leakage inductance, by definition, does not facilitate coupling between the primary and secondary sides of the transformer. To minimize leakage inductance in a design, several strategies can be employed. First, reducing the number of turns in the winding can effectively decrease the amount of magnetic flux that escapes the core, thereby reducing leakage inductance. Similarly, reducing the number of layers in the winding arrangement can also mitigate this issue by minimizing the distance between adjacent turns.

By carefully manipulating the timing and duration of the secondary switch activation, the system effectively depletes the charge across the primary transistor. This depletion causes the voltage across the transistor to plummet. As a result, when the primary switch is eventually turned on, it operates with minimal voltage across it, a phenomenon known as ZVS.

“This innovative approach achieves ZVS without the need for additional components,” Smith said. “Instead, we harness the inherent properties of the transformer and employ the control capabilities of the InnoSwitch5-Pro to orchestrate current flows with precision.”

Basically, this method allows ZVS by discharging the capacitance in the primary switch using current instigated by a transformer current induced by the SR circuit. It’s an esoteric but component-efficient way to improve the performance of a power system.

This groundbreaking technique not only improves efficiency but also simplifies the design process, making ZVS accessible without the usual complexity associated with additional components.

With its microcontroller-controlled functionality, the power supply can adapt to various output voltage and current requirements, catering to different standards and customer preferences. Moreover, the device incorporates robust protection features and telemetry reporting, ensuring reliable operation and providing valuable insights for system diagnosis and development.

Efficiency

Additionally, quasi-resonant (QR) switching is commonly employed in power-conversion circuits to reduce energy loss. QR reduces the voltage across the transistor during switching, thereby minimizing bulk losses and improving efficiency. Comparing QR with ZVS, ZVS achieves nearly 96% efficiency, a 0.6% improvement over QR at high load. This seemingly small increase translates to a significant reduction in heat generation, approximately 12%, which is crucial for high-power chargers and compact designs.

QR switching, a technique harnessed in systems like InnoSwitch3, optimizes power efficiency by leveraging the voltage relaxation ring across the primary MOSFET in DCM. This phenomenon, occurring post-switching MOSFET turn-off, utilizes valleys formed by primary magnetizing inductance and drain-node parasitic capacitance. Switching during these valleys drastically reduces MOSFET turn-on losses, crucial for minimizing switching losses proportional to the MOSFET voltage squared. QR switching is exclusive to DCM, ensuring peak efficiency. However, in CCM, valley switching is not possible (there is no relaxation ring). Overall, QR switching stands as a cornerstone in modern power electronics, enhancing energy efficiency with each cycle.

As market demands for higher efficiency and smaller form factors increase, advancements like ZVS are essential to meet these needs.

Applications

In the quest for energy efficiency and sustainability, the design and construction of power supplies play a crucial role. According to Smith, one innovative approach involves rethinking the traditional low- to mid-power (140 W) power supply, aiming to reduce unnecessary components and materials.

The idea is simple yet impactful: By reducing part count in the power supply and eliminating excess heatsink components, manufacturers can significantly cut down on the use of metal heatsinks and spreaders. This not only leads to cost savings but also aligns with the growing emphasis on eco-friendly practices.

“A demonstration has showcased USB-PD adapters with an impressive power output of 140 W at 28 V, all packaged within a compact 4.2 cubic inches and utilizing only 106 components,” Smith said. “This achievement was made possible through the utilization of InnoSwitch5-Pro ICs employing a flyback topology. Notably, this topology offers ease of implementation compared with AHB [asymmetric half-bridge] and can function efficiently from universal mains, with or without a PFC stage.”

As Smith noted, one strategy is the minimization of heat spreaders, particularly those that wrap around the power supply. While these components, often made of highly flexible steel, are effective in heat dissipation, they come at a higher cost. Engineers are exploring alternatives and seeking ways to achieve optimal thermal management without relying on expensive materials.
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