Revolutionizing e-Bike Charger Efficiency

Author:
Aleksey Pantsirev, Application Marketing Manager, Battery Chargers, Infineon Technologies

Date
08/29/2023

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How Infineon exploits new topologies and wide bandgap technology for cool, compact, and efficient e-bike chargers

Click image to enlarge

Figure 1. PFC-flyback currents with regard to the input voltage

­E-bike chargers play a pivotal role in addressing common pain points riders face, such as the fear of running out of power and the burden of carrying or storing portable chargers. As e-bikes continue to gain traction as a sustainable and economical mode of transportation, it becomes imperative to emphasize the significance of efficiency in e-bike charger design.

An efficient charger translates into enhanced charging speed. By maximizing the conversion of electrical energy into stored battery power, a highly efficient charger significantly reduces the time required to replenish the battery. This allows riders to spend less time waiting for their e-bikes to charge and more time actively using them.

In addition, optimizing the e-bike user experience is paramount in charger design. Efficient chargers provide consistent and reliable charging performance, ensuring a seamless charging process. Moreover, they generate minimal heat during operation, mitigating the risk of overheating and alleviating the need for extensive cooling measures. As a result, the weight and size of the charger can be reduced, enhancing the overall portability and convenience for riders.

At the same time, efficiency is vital in minimizing the environmental impact of e-bike charging. By minimizing energy losses during the charging process, efficient chargers contribute to conserving valuable resources and promoting sustainable transportation solutions.

Infineon’s offering for efficient e-bike charging

Recognizing the importance of these key factors for efficient e-bike charging is crucial for the seamless integration of e-bikes into our daily lives. To address the design challenges, Infineon offers a comprehensive portfolio of semiconductor products tailored for all essential components of e-bike battery chargers.

The range of dedicated battery management systems (BMS), controller ICs, and switches, like CoolGaN™ and CoolMOS™, caters to both cost-effective and ultra-high efficiency battery charging designs, showcasing Infineon’s expertise in providing solutions addressing a wide spectrum of charging requirements prevalent in the e-bike industry.

In addition to the comprehensive semiconductor offerings, Infineon goes above and beyond by providing complete reference designs tailored explicitly for e-bike chargers. These reference designs closely resemble real-world systems, enabling customers to streamline their development process effectively. By leveraging these reference designs, customers can significantly reduce development time, enhance system integration, and achieve optimized performance. Ultimately, this translates to a simplified design process and accelerated time-to-market for their e-bike charger solutions.

PFC flyback solution – Achieving excellent efficiency at an affordable cost

Charger designers face the challenge of balancing technical parameters, such as efficiency and universal input, while simultaneously considering cost constraints to develop optimal solutions.

Infineon utilized the PFC-flyback converter topology commonly used in LED lighting applications to design an economical yet efficient charger solution with a 116 W power output. The basic idea behind the PFC flyback is to control it using a boundary conduction mode (BCM) [1]. A controller like ICL8810 forces the peak drain current to follow the shape of the input voltage, similar to a PFC pre-regulator in boost topology but with some differences in operation. As a result, the bulk capacitor after the rectifier can be replaced by a small capacitance film capacitor, thus minimizing the system bill of materials (BOM).

Consequently, the flyback converter is not supplied by a DC voltage but by half-waves with double the line frequency. As seen in Figure 1, the switching period is continuously adjusted by keeping the ton constant and changing the toff depending on the input voltage half-wave. As a result, a good power factor and low THD are achieved with only one AC-DC stage.

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Figure 2.  Design image of the 116 W reference design with PFC-flyback topology

 

The reference design (Figure 2), which will be available in Q3 2023, covers the full AC input voltage range and achieves more than 90 percent power conversion efficiency at 230 VAC, RMS input. With the supported output voltage range between 30 to 58 V, this solution is particularly suitable for e-bike chargers for 48 V battery packs that are common in China and other countries in Asia.

Hybrid flyback for efficient and fast chargers

Fast e-bike chargers typically feature 4 A or 5 A charging current, allowing riders to get back on the road swiftly. When the output power of chargers increases, several challenges arise, particularly related to losses. Among these, switching- and conduction losses in semiconductor switches, as well as magnetics losses, such as core- and winding losses in transformers and inductors, require careful design considerations.

The main limitations of conventional topologies like active clamp flyback (ACF) are their inability to recycle energy from the parasitic components and the large transformer size. Infineon has introduced several charger solutions based on a hybrid flyback converter, also known as an asymmetrical half-bridge flyback converter. This resonant topology uses the magnetization current to achieve ZVS on the primary-side half-bridge and ZCS operation on the synchronous rectification switch [2].

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Figure 3.  Hybrid flyback significantly reduces transformer size compared to ACF by sharing stored energy.

 

Figure 3 shows an example of energy sharing in a hybrid flyback converter compared to ACF. In the case of hybrid flyback, a proportion of the energy stored in the transformer and capacitor depends on the load condition.

Infineon’s REF_XDPS2201_170W_BPA 170 W AC-DC reference design for an e-bike battery charger (Figure 4) demonstrates that hybrid flyback can operate directly from rectified mains with no PFC input stage. It outputs a wide DC voltage from 18 V to 42 V and up to 4 A current. The peak efficiency reaches 95 percent at full load with no heat sinks or fans attached. The reference design can be parameterized using the novel digital controller XDP™ XDPS2201 with multimode operation for optimized efficiency.

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Figure 4.  Design image of the 170 W reference design with hybrid flyback topology

 

Hybrid flyback with GaN solution for the highest efficiency and power density

Infineon has been exploring the numerous benefits that Gallium Nitride (GaN) technology brings to e-bike chargers, including increased power density, higher switching frequencies, improved thermal management, and enhanced overall efficiency.

Compared to their silicon counterparts, GaN transistors demonstrate the ability to achieve reduced total gate charge and parasitic capacitances while exhibiting a zero reverse-recovery charge for a given breakdown voltage and RDS(on) characteristics. This translates to ZVS with a lower magnetization current, reduced conduction losses in the switches, and a more compact transformer size. These characteristics of GaN transistors lead to enhanced efficiency and improved switching performance, enabling higher switching frequencies. This, in turn, allows for the utilization of smaller passive components, increasing power density.

Infineon’s CoolGaN™ GaN transistor technology enhances the performance of power conversion for e-bike chargers. Products in the portfolio include the CoolGaN™ IGLD60R190D1 and IGLD60R070D1 – industrial-qualified 600 V normally-off power transistors in a PG-HSOF-8-3 surface-mount package. They have current ratings of 15 A and 10 A with a typical RDS(ON) of 190 mΩ and 70 mΩ at 25°C, respectively. A separate Kelvin-source connection eliminates the common source inductance and allows optimized gate driving.

XDP™ XDPS2221 controller from Infineon is a highly integrated device combining both a multimode PFC controller and a multimode DC-DC hybrid-flyback controller, offering harmonized operation of the two power stages. The further integration of all gate drivers and a 600 V high-voltage start-up cell for the initial IC voltage supply enables a low external component count.

The ZVS operation of the hybrid flyback topology and the advantages of CoolGaN™ technology can be combined to design a high-efficient and compact e-bike charger (Figure 5).

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Figure 5.  Simplified power architecture of a high power density charger using XDP™ XDPS2221 combo IC and CoolGaN™ transistors

 

Charging an e-bike over USB-C

An emerging trend in the realm of e-bikes is the adoption of USB-C ports for sourcing or sinking power. E-bikes equipped with USB type C PD technology can be powered efficiently and safely from a high-voltage USB- PD port using a conventional smartphone adapter.

Infineon’s EZ-PD™ PMG1 (Power Delivery (PD) microcontroller gen-1) is a family of high voltage microcontrollers (MCUs) with USB-PD with integrated ARM® Cortex® M0/M0+ CPUs with up to 256 KB flash memory, up to 32 KB RAM, a USB full-speed device and programmable analog and digital peripherals. The portfolio covers the specific requirements of e-bike charging, ensuring optimal power management and compatibility with USB-PD charging infrastructure (Figure 6).

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Figure 6.  EZ-PD™ PMG1 family is a high-voltage microcontroller USB-C PD solution that targets systems powered by a high-voltage USB-C port

 

The EZ-PD™ PMG1-S3 high-voltage MCU is the industry’s leading MCU series that supports USB-PD 3.1 EPR (extended power range), which can replenish e-bikes’ batteries with up to 28 V at 5 A (140 W). It can communicate to the system buck-boost controller through I2C or GPIO to provide the negotiated USB-C PD power. The MCU series is available in two packages – the QFN-48 package supports one USB-C port, while the 97-BGA package supports dual USB-C ports.

Another highly integrated USB-PD solution from Infineon’s portfolio is the EZ-PD™ PMG1-B1 MCU which features an integrated buck-boost controller with a wide input voltage range (5.5 V to 24 V with 40 V tolerance) and 3.3 V to 21.5 V output voltage range. It enables a robust and easy-to-use solution while reducing BOM costs through integration. All EZ-PD™ PMG1 MCUs are field programmable to allow signed firmware updates for improved efficiency.

Summary

The article discussed the importance of efficient e-bike charger design and how Infineon is revolutionizing charging for e-bikes and light electric vehicles. Efficient chargers not only reduce charging time but also enhance the user experience, minimize environmental impact, and promote sustainable transportation solutions.

Infineon offers a comprehensive portfolio of semiconductor products, including battery management systems, controller ICs, and switches, tailored for e-bike battery chargers. They also provide complete reference designs that enable customers to streamline their development process, reduce time-to-market, and optimize performance.

We highlighted several key solutions from Infineon: a PFC flyback solution for economical and efficient charging, a hybrid flyback converter for fast chargers with high efficiency, and a hybrid flyback in conjunction with CoolGaN™ technology for even higher efficiency and power density. The article also mentioned that e-bikes could benefit from charging through USB-C PD connectors by highlighting Infineon’s EZ-PD™ PMG1 family of high-voltage microcontrollers. These solutions provide optimal power management and compatibility with USB-PD charging infrastructure.

Click here to learn more about how Infineon’s innovative solutions and comprehensive semiconductor offerings aim to improve charging efficiency, user experience, and sustainability in the e-bike industry.

 

References

[1]   Michael Weirich, “A dimmable, high efficiency, high power factor, primary side regulated flyback for LED Lighting applications,” eeNews Europe, September 7, 2011 [Available online]

[2]   Tim Hu, Gautam Chinagundi, Rashed Ahmed, “Infineon’s recommendations and solutions for USB-C PD chargers,” Whitepaper, April 2021, [Available online]

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