COMPANY NEWS

Jul 20, 2026

Technical Insights | The High- and Low-Voltage Energy Hub of an EV: Understanding Onboard Bidirectional DC/DC Technology and Its Applications

News Update

June 15, 2026

Electric vehicles typically use two separate power systems: a high-voltage traction battery and a low-voltage battery pack. The onboard DC/DC converter is the key component that connects these two voltage platforms.

Unlike a conventional unidirectional DC/DC converter, a bidirectional DC/DC converter enables power to flow in both directions. It 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's 7 kW Bidirectional DC/DC Converter, model XEV320D48D07K0DNW.

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Unidirectional vs. Bidirectional DC/DC Converters

Key Differences

Unidirectional DC/DC Converter

A unidirectional DC/DC converter only supports high-voltage-to-low-voltage conversion. Its functionality is limited to supplying power to the low-voltage battery and electrical system while the vehicle is operating or charging.

It cannot transfer power in the reverse direction and therefore does not support emergency energy transfer, reverse charging, or vehicle-to-vehicle assistance.

Bidirectional DC/DC Converter

A bidirectional DC/DC converter supports both step-down and step-up conversion between the high-voltage and low-voltage systems.

Energy can flow freely in either direction, allowing the unit to support both normal vehicle operation and emergency power-transfer scenarios. It is becoming a mainstream solution for modern 48 V vehicle architectures and vehicle-to-vehicle, or V2V, charging applications.

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Two Operating Modes of a Bidirectional DC/DC Converter

Forward Step-Down Mode: Normal Operation

When the vehicle is connected to a DC charging station, the converter steps the high-voltage input down to 48 V to recharge the onboard low-voltage battery pack and maintain stable operation of the vehicle's low-voltage electrical systems.

The low-voltage output is adjustable from 40 to 55 V and is continuously managed by the battery management system, or BMS. Once the battery approaches full charge, the charging current is automatically reduced.

Reverse Step-Up Mode: Emergency Operation

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 to 360 V.

This enables several practical functions:

• Self-rescue and temporary range extension: The low-voltage battery can transfer energy back to the traction battery, providing limited emergency driving range.

• Vehicle-to-vehicle charging: Two electric vehicles can be connected for emergency energy transfer, helping a stranded vehicle recover from a depleted traction battery.

• Automatic voltage tracking: When the voltage difference is below 5 V, the converter can automatically connect to the main circuit, enabling smoother and more stable power transfer.

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Formitek's 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 of 150 A

• High-voltage side: 240-360 V, maximum output current of 30 A

• Output response time: ≤200 ms

• Dynamic load recovery time: ≤5 ms

• Cooling method: Passive cooling, with no additional liquid-cooling system required

• Integration: Designed for space-efficient onboard installation

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Automotive-Grade Design Standards

Comprehensive Safety Protection

As a high-voltage onboard component, safety is a central design requirement. The unit incorporates multiple protection mechanisms:

• Overvoltage, undervoltage, overcurrent, and short-circuit protection on both the high-voltage and low-voltage sides

• Automatic shutdown during a fault, with self-recovery once normal operating conditions are restored

• Multi-stage overtemperature protection, including power derating at elevated temperatures and complete shutdown under excessive-temperature conditions

• Reverse-battery-connection protection and dedicated hardware-fault protection

• Output lockout in the event of a hardware fault to prevent further safety risks

• Rapid discharge of residual input voltage to below 5 V within five seconds, improving service and maintenance safety

• Insulation and grounding performance designed to comply with applicable electric-vehicle safety standards

• Electric-shock protection suitable for automotive high-voltage systems

Intelligent Control and Communication

The converter is equipped with CAN communication, an important feature for OEM vehicle integration:

• Real-time communication with the vehicle control unit, or VCU, and the BMS

• Exchange of voltage, current, operating status, and fault information

• Support for online firmware updates and parameter calibration through CAN

• Flexible configuration for different vehicle platforms and operating requirements

• Support for both hardware-based and communication-based wake-up modes

• Automatic shutdown after the main power supply is disconnected

• Extremely low standby power consumption

Environmental Performance and Reliability

• Operating temperature: –40°C to 65°C

• Designed for reliable operation in both extremely cold and hot climates

• Ingress protection, vibration resistance, mechanical-shock resistance, and drop performance tested to automotive industry requirements

• IP67-rated waterproof connectors

• Connector mating durability of at least 5,000 cycles

• Suitable for demanding road and vehicle operating conditions

• Designed service life: 8 years or 120,000 km

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Main Applications of Bidirectional DC/DC Converters

OEM Vehicle Integration

Suitable for battery electric passenger vehicles and light commercial vehicles equipped with 48 V low-voltage electrical architectures.

Vehicle Conversion and Range Extension

Applicable to range-enhancement projects for older electric vehicles and the expansion of auxiliary or parked-vehicle power systems.

Emergency Roadside Assistance

Enables vehicle-to-vehicle energy transfer during repair and roadside-rescue situations, potentially reducing the need for towing.

Special-Purpose Vehicles

Suitable for electric construction vehicles, sightseeing vehicles, refrigerated vehicles, and other specialized electric platforms.

Energy Storage and Microgrids

Can be used as an energy-management component in mobile high-power equipment, refrigerated trucks, mobile air-conditioning systems, photovoltaic and wind-energy storage systems, and microgrid applications.

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2026 Industry Summary

By this point, you should have a clear understanding of onboard bidirectional DC/DC converter technology.

As electric vehicles continue to evolve and 48 V low-voltage architectures become more widely adopted, bidirectional DC/DC converters are gradually replacing traditional unidirectional solutions.

With increasing demand for vehicle-to-vehicle charging, emergency energy transfer, and more precise onboard energy management, high-power, high-efficiency, and highly reliable bidirectional DC/DC converters with CAN communication capability are expected to become essential components in next-generation electric vehicles.