The rapid popularity of electric bicycles is closely linked to China's rapid urbanization process. From bicycles replacing walking to e-bikes replacing traditional bicycles, it is an inevitable outcome of the deepening and intensifying urbanization process in China.
Quoting data from the "2017 China Electric Bicycle Industry Development White Paper" released by Zhongguancun Online, China's cumulative production of electric two-wheeled bicycles reached 30.979 million units. By 2022, this number has grown to 52.2623 million units, making China the world's largest producer and consumer of e-bikes.
However, the lack of uniformity in electric bicycle charger standards makes chargers from different brands and models incompatible. In order to create a safer charging environment, the new national standard for electric bicycle chargers has been officially implemented from July 1, 2023.
Figure 1: Mandatory National Standard for the New National Standard Electric Bicycle Charger
The new national standard charger standardizes the charging interface and adds EMI requirements, increasing the design complexity compared to traditional chargers. Based on the relevant standards of the new national standard charger, this article will introduce a charging solution based on a one-stage half PFC flyback AC-DC topology. Independently designed by WAYON, this solution meets the charging requirements of leading domestic vehicle manufacturers.
Figure 2: WAYON New National Standard Charger Prototype (4820)
Solution Features and Advantages
● Overall efficiency ≥ 89.0%
(Including the power consumption of controllable silicon and the fan)
This solution uses valley switching technology for the main controller to reduce main switch losses. The secondary side uses Schottky rectifier diodes and PMOS load switches to achieve fanless passive heat dissipation. Compared to traditional valley fill circuits, the efficiency is improved by 4-5%.
● High EMI Margin
(Conducted and radiated interference margin ≥6 dB)
The primary side adopts a one-stage half PFC and valley switching quasi-resonant topology, significantly improving harmonic and EMI margins.
● Wide Input Voltage Range: 180-240Vac
(Lowest input voltage: 165V/AC, highest input voltage: 264V/AC)
The secondary side uses a one-stage half PFC, valley switching quasi-resonant topology, and a high-power 700V MOSFET. The input voltage supports a range of 165-264VAC, wider than traditional valley fill circuits.
● Output Specifications: 60V/3A
(Lowest output: 30V/3A, highest output: 60V/3A)
Power Factor (PF): 0.75
Design Highlights
1. Primary Design
The primary part of the new national standard charger solution uses WD1082G, which integrates a PWM controller and a 700V/0.9Ω high-power MOSFET internally. It features characteristics such as valley bottom conduction, low power consumption, and high efficiency. When the charger operates under light load or no load, WD1082G enters Burst mode to reduce switch losses, thereby lowering standby power consumption and improving light load efficiency. When operating under normal load, WD1082G is in QR valley bottom conduction mode, improving overall efficiency and reducing EMI noise sources.
WD1082G also includes functions such as over-current protection (OCP), over-load protection (OLP), over-temperature protection (OTP), and output over-voltage protection (OVP).
The primary design for PFC uses the scheme shown in Figure 3, with LB, DBYP, and DB as components for the PFC section. This makes the input current follow the sine wave variation of the input voltage, improving the power factor of the overall system. Ingeniously using one-stage half-seal power MOSFET technology, compared to active APFC circuits, it saves one power MOSFET and PFC circuit control, with the advantages of a simple circuit and low cost. In this solution, the average power factor is 0.75, and the harmonics meet the requirements of the new national standard.
Figure 3: WAYON New National Standard Charger Power Stage Simplified Circuit
2. Secondary Design
To meet the mandatory "communication protocol" charging requirement of the new national standard charger, the secondary controller in this solution uses a highly programmable mixed-signal intelligent charging management chip. Its built-in constant voltage and constant current control module achieves precise control of the three-stage charging for lead-acid batteries, thereby improving the lifespan of lead-acid batteries. The charging voltage is compared with the voltage obtained from the output terminal voltage division network and the built-in 2.5V voltage source as the output voltage control signal and system feedback signal. The charging current is compared with the voltage obtained from the sampling resistor and the 50mV voltage source built into the controller as the output current control signal and system feedback signal.
3. Prototype Test Results of the Solution
Key Waveforms
Figures 4-6 show the key wave forms of the prototype's primary and LN lines.
Figure 4: Primary Main Switch VDS Waveform
(Vin: 230 VAC; Vout: 60V/3A)
Figure 5: Secondary Schottky Waveform and PFC Inductor Current Waveform
(Vin: 230 VAC; Vout: 60V/3A)
Figure 6: LN Line Waveform VBUS, LN, IL-PFC
(Vin: 230 VAC; Vout: 60V/3A)
Figures 4-6 show that the primary power MOSFET and secondary rectifier diode have a large stress margin, and the input inductor current waveform envelope is close to a sine wave.
EMI Testing
The new national standard electric vehicle charger must meet the GB 42296-2022 EMC (Electromagnetic Compatibility) standard. The new national standard charger needs to pass EMI testing, including conducted interference, radiated interference, and harmonics. Figures 7-9 show the EMI test results of the prototype of this solution, where the conducted margin reaches up to 19dB (QP), the harassment margin is greater than 10dB, and the harmonics also have a large margin.
Figure 7: WAYON New National Standard Charger EMI Conducted Test Results
Figure 8: WAYON New National Standard Charger EMI Harassment Power Test Results
Figure 9: WAYON New National Standard Charger EMI Harmonics Results
Summary
The electric vehicle charger designed in this solution supports a maximum power of 180W, with advantages such as high overall efficiency, wide input voltage range, high EMI margin, and low cost. The core key components used, such as WD1082G (AC-DC), MOSFET, are independently developed and mass-produced models by WAYON. The success of this solution design has been demonstrated through practical testing, and it can achieve a power supply design that fully complies with the "new national standard."
Visit the official WAYON website for more information on AC-DC and MOSFET products:
https://www.way-on.cn/Product-Center/293.html
