EV Charging System Design with Rohm SiC
Electric vehicle charging systems require high-efficiency power conversion to minimize charging time and maximize energy transfer. This guide covers the design of onboard chargers (OBC), DC-DC converters, and DC fast charging systems using Rohm SiC power devices.
Onboard Charger (OBC) Design: The OBC converts AC grid power to DC for charging the EV battery. A typical 11kW OBC uses a PFC stage followed by an isolated DC-DC converter. Rohm SiC MOSFETs enable efficiency above 98% while reducing system size and weight.
PFC Stage Design: The boost PFC stage uses 650V SiC MOSFETs (SCT3022AL) for 400V systems or 1200V devices (SCT3080KL) for 800V systems. SiC SBDs (SCH2080KE) in the bridge rectifier eliminate reverse recovery losses.
DC-DC Converter Design: The LLC resonant converter provides isolation and voltage conversion. Use SiC MOSFETs on the primary side for high-frequency operation (100-300kHz), enabling smaller magnetics. Synchronous rectification on the secondary side uses SiC SBDs for efficiency.
DC Fast Charging: For DC fast charging stations (50-350kW), Rohm SiC power modules (BSM series) provide the power density and efficiency required. The full SiC modules minimize losses and enable compact designs.
Thermal Management: EV charging systems operate in harsh environments. Design for maximum ambient temperatures of 85°C with adequate margin. Use thermal simulation to optimize heatsink design and airflow.
EMI Considerations: High-frequency switching generates EMI. Follow proper PCB layout guidelines, use shielding where necessary, and design EMI filters for conducted and radiated emissions compliance.
Protection Features: Implement comprehensive protection including overcurrent, overvoltage, overtemperature, and short-circuit protection. Use isolated gate drivers with desaturation detection for robust SiC protection.
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Frequently Asked Questions
1. What Rohm devices are recommended for 11kW OBC designs?
Rohm 11kW OBC recommendations: (1) PFC stage - SCT3022AL (650V, 400V systems) or SCT3080KL (1200V, 800V systems). (2) PFC diodes - SCH2080KE SiC SBDs for bridge rectifier. (3) DC-DC primary - SCT3022AL or SCT3040KL depending on current. (4) SR diodes - SCH2080KE for synchronous rectification. (5) Gate drivers - BM6104FV with isolation. (6) Power modules - BSM120D12P2C005 for integrated solutions. Contact BeiLuo FAE for detailed BOM recommendations.
2. How do I achieve 98% efficiency in OBC applications?
Achieving 98% OBC efficiency: (1) Use SiC MOSFETs for all switching stages. (2) Optimize gate drive - fast switching with proper damping. (3) Use SiC SBDs - zero reverse recovery. (4) Design magnetics properly - low-loss cores, litz wire. (5) Optimize switching frequency - 100-150kHz sweet spot. (6) Minimize PCB losses - heavy copper, proper layout. (7) Use synchronous rectification - Schottky diodes on secondary. (8) Thermal design - keep devices cool for lower Rds(on). Each percentage matters - 98% vs 95% means 150W less heat to dissipate in an 11kW system.