Technical Insights | The High- and Low-Voltage Energy Hub in Electric Vehicles: Understanding Bidirectional Onboard DC/DC Technology and Its Applications
News Update
June 15, 2026
Technical Insights | The High- and Low-Voltage Energy Hub in Electric Vehicles: Understanding Bidirectional Onboard DC/DC Technology and Its Applications
Electric vehicles typically use two separate power systems: a high-voltage traction battery and a low-voltage battery system. The onboard DC/DC converter is the key component that connects these two voltage platforms.
Compared with a conventional unidirectional DC/DC converter, a bidirectional DC/DC converter enables energy to flow in both directions. It also provides the hardware foundation for emergency energy transfer, vehicle-to-vehicle charging, and temporary range extension.
This article provides a technical overview based on the Formitek 7 kW bidirectional DC/DC converter, model XEV320D48D07K0DNW.
Unidirectional DC/DC vs. Bidirectional DC/DC
Key Differences
Unidirectional DC/DC Converter
A unidirectional DC/DC converter only supports high-voltage-to-low-voltage conversion.
Its function is relatively limited: it supplies power to the vehicle's low-voltage battery system during charging or normal vehicle operation, but it cannot transfer energy in the reverse direction.
As a result, it does not support emergency power recovery, reverse energy transfer, or vehicle-to-vehicle charging.
Bidirectional DC/DC Converter
A bidirectional DC/DC converter supports both step-down and step-up conversion between the high- and low-voltage systems.
Energy can flow in either direction, allowing the converter to support both routine low-voltage power supply and emergency energy-transfer applications.
It is increasingly becoming a key solution for modern 48 V vehicle electrical architectures and vehicle-to-vehicle energy transfer.
Two Operating Modes of a Bidirectional DC/DC Converter
Forward Step-Down Mode
Under normal operating conditions, when the vehicle is connected to a DC fast-charging station, the converter steps the high-voltage DC supply down to 48 V.
The low-voltage output charges the vehicle's low-voltage battery pack and ensures the stable operation of onboard low-voltage electrical systems.
The low-voltage output can be adjusted between 40 V and 55 V. The entire charging process is controlled by the battery management system, which automatically reduces the charging current as the battery approaches full charge.
Reverse Step-Up Mode
When no charging station is available, the converter can step the 48 V low-voltage supply up to the traction-battery voltage range of 240-360 V.
This mode enables several practical functions:
• Emergency self-recovery: The low-voltage battery supplies limited energy back to the traction battery, providing temporary additional driving range.
• Vehicle-to-vehicle charging: Two battery electric vehicles can be connected to transfer energy between them, helping a vehicle that has run out of power before reaching a charging station.
• Automatic voltage tracking: When the voltage difference is less than 5 V, the converter can automatically connect to the main power circuit, allowing smoother and more stable energy transfer.
Formitek 7 kW Bidirectional DC/DC Converter
Key Specifications
• Rated power: 7 kW
• Bidirectional conversion efficiency: ≥97%
• Low-voltage side: 40-55 V, maximum output current 150 A
• High-voltage side: 240-360 V, maximum output current 30 A
• Output response time: ≤200 ms
• Dynamic load recovery time: ≤5 ms
• Cooling method: Passive cooling with no additional liquid-cooling system required
• Design focus: Compact integration and stable onboard operation
Automotive-Grade Design Standards
Comprehensive Safety Protection
As a high-voltage onboard component, safety is a central design requirement.
The converter incorporates multiple protection mechanisms across both the high- and low-voltage sides:
• High- and low-voltage overvoltage protection
• Undervoltage protection
• Overcurrent protection
• Short-circuit protection
• Automatic shutdown in the event of a fault
• Automatic recovery after normal operating conditions is restored
The product also features multi-stage overtemperature protection. Output power is reduced when the temperature enters a high-temperature range, while the system shuts down completely if the temperature exceeds the safety threshold.This helps prevent overheating and thermal failure.
Additional protective functions include:
• Reverse battery connection protection
• Dedicated hardware fault protection
• Output lockout following critical hardware faults
• Rapid discharge of residual input voltage
• Reduction of residual voltage to below 5 V within five seconds
• Insulation and grounding performance designed to comply with applicable electric-vehicle standards
• Electric-shock protection suitable for high-voltage vehicle systems
Intelligent Control Capabilities
The converter is equipped with a CAN communication system, an essential feature for original-equipment vehicle integration.
Key capabilities include:
• Real-time communication with the vehicle control unit and battery management system
• Exchange of voltage, current, operating status, and fault information
• CAN-based online firmware updates
• Parameter calibration for different vehicle platforms
• Support for both hardware and communication-based wake-up modes
• Automatic shutdown after the main power supply is switched off
• Extremely low standby power consumption
Environmental Performance and Reliability
The product is designed to operate reliably under demanding automotive conditions.
Key environmental and durability specifications include:
• Operating temperature: -40°C to 65°C
• Reliable performance in both high- and low-temperature environments
• Protection, vibration, mechanical shock, and drop testing in accordance with automotive industry requirements
• IP67-rated connectors
• Connector insertion and removal durability of at least 5,000 cycles
• Strong resistance to complex and uneven road conditions
• Design life: Eight years or 120,000 kilometres
These features allow the converter to meet the long-term operating requirements of passenger vehicles and other electric mobility platforms.
Main Applications of Bidirectional DC/DC Converters
Original Equipment Vehicle Integration
Suitable for battery electric passenger vehicles and light commercial vehicles using a 48 V low-voltage architecture.
Vehicle Modification and Range Extension
Applicable to electric vehicle retrofit projects, range-support systems, and expanded power supply for parked vehicles.
Emergency Roadside Assistance
Enables vehicle-to-vehicle energy transfer during maintenance or emergency recovery, potentially reducing the need for towing in some situations.
Specialized Electric Vehicles
Suitable for electric construction vehicles, sightseeing vehicles, refrigerated vehicles, and other purpose-built electric platforms.
Energy Storage and Microgrids
The converter can also serve as a key energy-management component in:
• Refrigerated trucks
• Mobile air-conditioning equipment
• High-power mobile electrical systems
• Photovoltaic energy storage
• Wind-energy storage
• Distributed energy systems
• Microgrid applications
2026 Industry Outlook
Bidirectional onboard DC/DC converters are becoming increasingly important as electric vehicles continue to evolve and 48 V low-voltage architectures become more widely adopted.
Compared with conventional unidirectional products, bidirectional converters offer greater flexibility, more efficient energy management, and support for emergency energy transfer.
As demand grows for vehicle-to-vehicle charging, emergency energy recovery, and more precise control of onboard electrical systems, high-power bidirectional DC/DC converters with high efficiency, advanced safety protection, and CAN communication are expected to become increasingly important components in future battery electric vehicles.
