Product Overview
The charging system of a new energy vehicle consists of the on-board charger (OBC), DC charging station power modules and the on-board DC-DC converter, typically operating at 3.3 kW to 22 kW with high switching frequencies and steep dv/dt transients — a far more demanding electromagnetic environment than conventional consumer power supplies. The SQ and UC series flat wire common mode chokes from Dongguan Chaorong Electronics Co., Ltd. are core filtering components developed specifically for automotive electronics and EV charging applications. Wound with flat copper wire on high-permeability ferrite cores, they address both conducted and radiated EMI in charging systems and help power electronics pass automotive EMC standards such as CISPR 25 and GB/T 18655.
Core Technical Features
1. High Power Density and Low Loss
Flat copper windings increase the effective conductor cross-section by approximately 25%, reducing DC resistance (DCR) by 30%–50% compared with round-wire designs of the same footprint. Taking the front-end filter of an 11 kW OBC as an example, SQ series chokes achieve rated currents of 15 A–25 A with DCR below 5 mΩ. Combined with a system efficiency target of η≥95%, winding temperature rise can be limited to within 40 K, significantly reducing overall power consumption and thermal management burden.
2. Wide Temperature Range and Automotive-Grade Reliability
Vehicle environments demand stable operation from −40 °C to +125 °C. SQ/UC series chokes use Class H (180 °C) enamel wire and high-temperature core formulations. The full series passes AEC-Q200 automotive qualification, covering high-temperature operating life (HTOL), temperature cycling (−55 °C to +150 °C), mechanical shock and vibration testing — ready for front-loading automotive programs.
3. Reinforced Insulation for High-Voltage Platforms
Charging systems require isolation between the 400 V / 800 V high-voltage bus and low-voltage control circuits. Reinforced-insulation versions of the SQ/UC series achieve 4 kV AC (60 s) winding-to-core withstand voltage, with creepage distance and clearance designed to IEC 62368-1 and IEC 60664, effectively preventing high-voltage crosstalk into signal circuits and safeguarding charging safety.
4. Broadband Common-Mode Attenuation
Charging-system switching noise is concentrated in the 150 kHz–30 MHz band. Through optimized turns ratio and core gap design, SQ/UC series chokes deliver 100 Ω–1000 Ω of common-mode impedance across the target band, with additional suppression of differential-mode noise converted through common-mode paths. Measured conducted-emission margins typically exceed the limit line by more than 6 dB.
Typical Applications
On-Board Chargers (OBC)
The OBC converts grid AC into high-voltage DC for the traction battery. Both the input PFC stage and the downstream LLC resonant stage are strong noise sources. Recommended selection by power class:
- 3.3 kW–6.6 kW OBC: UC series, 2.2 mH–4.7 mH, rated current 10 A–15 A
- 11 kW OBC: SQ series, 1.5 mH–3.3 mH, rated current 15 A–25 A
- 22 kW bidirectional OBC: SQ series, 1.0 mH–2.2 mH, rated current 25 A–40 A
DC Fast-Charging Station Power Modules
In the front-end rectification and output stages of 20 kW–60 kW DC fast-charging modules, SQ series high-current flat wire chokes withstand continuous currents of 30 A–60 A, suppressing circulating currents and common-mode interference between paralleled modules and helping charging stations comply with GB/T 18487 and NB/T 33001.
On-Board DC-DC Converters
When stepping the high-voltage traction battery down to the 12 V / 24 V low-voltage bus, high-frequency switching again generates EMI. The ultra-low-profile horizontal packages of the SQ/UC series (8 mm–12 mm height) mount on compact converter PCBs for low-profile designs.
Selection Guide and Design Recommendations
Defining Key Parameters
- Determine rated operating current: calculate from maximum charging power and bus voltage; continuous operating current should not exceed 70% of the rating.
- Calculate required inductance: based on the target attenuation band, choose a specification delivering ≥300 Ω common-mode impedance across 150 kHz–30 MHz.
- Verify insulation class: for high-voltage platforms, confirm the reinforced-insulation version and creepage/clearance meet the design requirements.
- Validate temperature rise and efficiency: perform full-load temperature-rise and DCR measurements at maximum ambient temperature.
PCB Layout Recommendations
- Route traces before and after the input-side common mode choke on separate layers or maintain ≥5 mm spacing to avoid magnetic coupling that cancels the filtering effect.
- Partition high-voltage and low-voltage ground planes; avoid routing across plane splits beneath the choke.
- With proper chassis grounding, a metal shield can above the choke further suppress radiated emissions.
Why Choose Dongguan Chaorong Electronics
As a specialized manufacturer of electronic magnetic components, Dongguan Chaorong Electronics Co., Ltd. offers automotive-grade customization for the SQ/UC flat wire common mode choke series — including custom inductance development, reinforced insulation design, special pin-out configurations and potting processes. Our EMI test laboratory and reliability verification platform provide CISPR 25 conducted/radiated test reports, AEC-Q200 qualification data and PPAP documentation packages, helping customers complete automotive design-ins efficiently.
We are committed to customer-driven, high-quality and cost-effective automotive magnetic component solutions, and look forward to working with you.