New Industry Products

Second-Generation DC-DC Converter to Power Auxiliary Loads in Medium- and Heavy-Duty Hybrid and Electric Vehicles

September 09, 2023 by Mike Falter

The 700DNG40-24-8 from Bel Fuse delivers up to 4 kW of power from the battery bus of industrial hybrid (HEV) and electric vehicles to power low-voltage accessories.

Bel Fuse has released their second-generation 700DNG40-24-8 4 kW, liquid-cooled, DC-DC converter designed to efficiently convert EV and hybrid (HEV) battery bus voltages to lower voltages for powering auxiliary loads. 


Hybrid EV (HEV) equipment

Hybrid EV (HEV) equipment. Image used courtesy of Bel Fuse

Weighing only 4.5 kg, the converter is smaller and lighter than the prior generation, contributing to extended vehicle ranges and operating times. The second-generation supply also supports a wider input voltage range, allowing it to accommodate battery bus voltages ranging from 450 to 900 VDC. 

With its high-power density, the 700DNG40-24-8 is well suited to the auxiliary load requirements of medium- and heavy-duty e-mobility platforms like construction, mining, trucking, marine, and ground support equipment.


700DNG40-24-8 DC-DC converter for heavy-duty e-mobility.

700DNG40-24-8 DC-DC converter for heavy-duty e-mobility. Image used courtesy of Bel Fuse

Powering Auxiliary Loads in an Industrial EV

In traditional internal-combustion engine (ICE) vehicles, an alternator is used to generate electric power directly from the rotation of the motor to power loads, such as lights and electronics, and to maintain a charge on the vehicle battery, which is primarily used to start the vehicle. 

In hybrid and electric vehicles, the alternator can be replaced by a DC-DC converter that converts power directly from the high-voltage, powertrain battery bus. 

From the battery bus (450 to 900 VDC), the 700DNG40-24-8 delivers up to 4 kW (143 ADC) of power through a single output at a nominal voltage of 28 VDC. The output is well regulated with a line regulation of +/- 0.28 VDC and a voltage drop of only 1.2 VDC over the full load current.

The 28 VDC output can be used to directly power vehicle auxiliary loads, or more commonly, to power downstream conversion circuitry that generates additional, lower-voltage rails.


Converter Features and Specifications

The converter is lightweight and compact, measuring 10.34 x 2.16 x 13.98 inches. A key performance feature is its high-power conversion efficiency, up to 95%. Higher efficiency means less power lost to heat and better use of the battery’s energy to extend a vehicle’s range and operating time between charges or refueling.  


700DNG40-24-8 mechanical drawing.

700DNG40-24-8 mechanical drawing. Image used courtesy of Bel Fuse


For heat that is lost during conversion and needs to be dissipated to the environment, the 700DNG40-24-8 uses a liquid cooling system that can handle up to 20 LPM of 50/50 propylene or ethylene glycol/water coolant.  

Along with extensive monitoring and safety features, such as over temperature, output overvoltage and over current protection, and reverse polarity protection, the 700DNG40-24-8 offers full galvanic isolation between the input and output.

For higher power applications, up to 8 units can be operated in parallel for a combined load capacity of 32 kW.

Constructing a High Voltage DC-DC Converter

For a high-power DC-DC converter, the input DC voltage is typically converted to AC using high-voltage switches such as SiC or IGBT  in an inverter configuration. The AC power is then isolated and down-converted through a transformer where it is rectified via MOSFET bridge back to DC and conditioned as needed to generate the regulated DC output.    

Transformer-isolated DC-DC converter topology.

Transformer-isolated DC-DC converter topology. Image used courtesy of MathWorks