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Deliver Power More Efficiently with On-board and Off-board Charging Systems

Jack Lamar, Product Marketing Engineer
Mar 29, 2020
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Electric vehicles (EV) and hybrid electric vehicles (HEV) are rapidly overtaking the automotive market, and with these new vehicles comes an increased demand for on-board and off-board charging systems. However, these charging systems cannot depend on yesterday’s technology to meet today’s needs. They must be able to deliver power more efficiently while remaining small and generating as little heat as possible.

On-Board Charging Systems

An on-board charger, or OBC, serves one main purpose: to convert AC power from the grid to DC power stored in the high-voltage vehicle battery. This conversion is all happening inside the actual vehicle, or “on-board.” These OBC systems can vary in power level and charging speed (the higher the power delivered, the faster the battery charges). An additional potential feature of an OBC is to provide bi-directional power flow. This allows the vehicle to distribute power and not only consume it for internal functions. Bi-directional OBCs can be used for V2X power distribution. This can turn the EV into a mobile power bank to be used for grid balancing, “jump starting” EVs, and providing off-the-grid power in remote locations (e.g. camping). Designing for peak performance in the smallest size of both unidirectional and bidirectional OBCs can help ease consumer concerns of long charge times and environmental harm.

Figure 1: Unidirectional OBC
Figure 2 Bi-directional OBC

Off-Board Charging Systems

An off-board charging system takes incoming AC power and converts it to the DC power needed to charge the battery system. The term “off-board” refers to charging systems not native to the vehicle itself (e.g., public vehicle charging station). One critical performance aspect of an off-board charger is its ability to quickly recharge the vehicle. For example, some modern fast chargers can recharge 250 miles of range in less than 30 minutes.

Figure 3: Off-board charging

SiC for Charging Systems

One major factor in modern charging system designs is the choice of a power semiconductor. While older technologies make extensive use of Silicon (Si), engineers have discovered that Silicon Carbide (SiC) makes it possible for these charging systems — both on-board and off-board — to accomplish their jobs with less heat generation and reduced energy losses, while requiring less physical space. These smaller, lightweight SiC charging systems offer more driving range in less time at a lower cost, making them friendly to both the environment and economy.

Application Example: 650 V SiC MOSFETS for Bi-Directional On-Board Chargers

The use of SiC MOSFETs (and more specifically, 650 V SiC MOSFETs) is currently the only way to engineer successful bi-directional, on-board chargers without compromising critical design principles such as size, weight, and complexity. SiC MOSFETs run much cooler than Si superjunction (SJ) MOSFETs and require far less thermal management (smaller heat sinks). In turn, this leads to a lower system BOM cost.

Additionally, fewer components result in less opportunity for malfunction or breakage. Other benefits include the high-frequency operations SiC supports, yielding an overall reduction in the on-board charger’s size and weight.

SiC for Automotive Systems

Extreme temperatures and vibration and shock loadings are to be expected for EV/HEV devices. Therefore, automotive electronic systems must be especially rugged and reliable, which is why the Automotive Electronics Council certifies certain electronics — including SiC products — as automotive AEC-Q101 certified. According to the AEC, this means “a device is capable of passing the specified stress tests and thus can be expected to give a certain level of quality and reliability in the application.”

Wolfspeed Solutions for Automotive Systems

Wolfpseed is leading the charge when it comes to SiC power devices, including those integral to fast, efficient, compact charging systems for EVs and HEVs. With more than 25 years of experience with SiC devices, Wolfspeed offers silicon carbide technology with unrivaled performance and reliabilty.

Product and Reference Design Solutions

Blocking Voltage (V)
at 25°C (mΩ)
Current Rating
at 25°C (A)
650 V
120 A
650 V
120 A
650 V
37 A
650 V
36 A
650 V
37 A

Reference Designs

Explore Wolfspeed’s 650V SiC MOSFETs, companion parts, and reference designs to learn more about how SiC MOSFET technology from Wolfspeed can help you build better products that are up for the demands of today’s modern devices.


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