3 On-Board Chargers/DC-DC Converters System Overview

An OBC/DC-DC system consists of three main stages: the OBC PFC stage, the OBC DC-DC stage, and the HV-LV DC-DC stage. Non-isolated gate drivers are primarily located in the OBC PFC stage and the secondary side of the HV-LV DC-DC side of the system due to the requirement of isolation in other parts of the system.

An OBC takes an AC voltage from the grid (commonly from a garage wall box charger or public xEV charging station plug) and converts it into DC voltage to charge the xEV’s batteries during the PFC stage. This voltage is regulated, maintained at a certain voltage, and power factor corrected to improve performance and efficiency.

There are multiple ways to implement a PFC stage on an xEV. A boost PFC is popular implementation which uses a high-efficiency gate driver like the UCC27614-Q1 to drive a FET. An interleaved boost PFC provides even higher efficiency at the tradeoff of complexity and additional components. Typically, a dual channel gate driver like the UCC27624-Q1 is used to accommodate for the additional FET used. To explore other PFC topologies like totem-pole or bridgeless, see Review of Different Power Factor Correction (PFC) Topologies' Gate Driver Needs. To learn more about the PFC design in xEVs, see Power Factor Correction design for On-Board Chargers in Electric Vehicles.

The OBC DC-DC converter stage takes the DC voltage from the PFC stage and converts it into a high-voltage battery, commonly 400V or 800V. These typically require isolation to prevent noise or voltage spikes on the high-voltage side from affecting the low-voltage side, so a gate driver like the UCC21550-Q1 can fulfill isolation requirements as well as high-voltage ratings.

The last section of the OBC/DC-DC subsystem is the high-voltage to low-voltage DC-DC conversion, typically stepping down that high-voltage battery to 12V or 48V for use in car outlets, motors, lighting, and other smaller components. In this stage, high power density, reliability, and efficiency are key factors to what components are chosen. Switching the FETs quickly in harsh environments is critical for a gate driver, and TI’s UCC27624-Q1 has 30V VDD absolute maximum and 5A/5A drive current for DC-DC converter needs.