odule (BCM). The specific loads handled by the BCM also vary by manufacturer. Most of them cover things like power windows and door locks, windshield wipers, and lighting. The MCU-controlled BCM is made up of a mix of dc-dc converters, LDO regulators, LED drivers, and a variety of sensors and switches. Typical load voltages are in the 1.2- to 5-V range.
The BCM starts with the battery output that’s loaded with noise and transients. Some EMC filtering and battery-protection components prep the voltage for some regulators that generate the needed rail voltages. For small BCMs, an all-LDO architecture is used. The LDOs further clean and regulate the 12 V down to several lower-voltage buses. LDOs aren’t the most efficient of regulators, but with light loads they’re preferred. With loads greater than about 400 mA, the heat and inefficiency may make the LDO approach unacceptable.
Another approach is to use a combination buck switching regulator followed by LDOs. It’s more efficient. The buck regulator usually creates a 5-V bus; following LDOs make up any lower-voltage buses.
An alternative arrangement is to start with a buck converter followed by a boost converter and another buck regulator. The boost converter controls the voltage so that some loads can operate under cold-crank conditions and/or operate the engine start/stop feature implemented in many new vehicles. Under such conditions, the battery voltage drops drastically, so regulation is critical. Additional buck converters are also used to generate the other needed lower-voltage buses.
A good choice for the buck/boost approach is to use a SEPIC-type converter. The SEPIC is a combination buck/boost architecture that’s efficient and flexible. It can then be followed with additional converters or LDOs as needed (Fig. 3).
3. Here’s a simplified BCM automotive power supply using a SEPIC buck-boost converter.
EV Battery-Charging Solutions
EVs and HEVs both require battery-charging systems. Some of the chargers are internal to the vehicle while others are external, either at home or a commercial charging station. The only thing keeping EVs from completely dominating auto sales is the constant need for battery charging, the dearth of commercial charging stations, and the limited range of the vehicles themselves. Fast, reliable battery charging is the key to EV eventual success.
So, let’s take a look at onboard chargers, how they work, and why they’re used. Also discussed are charging stations and how they interact with onboard charger and EV battery-management systems (BMS).
All EVs and HEVs have an onboard charger for the main HV drive battery. It takes the ac from a home or commercial charging station and conditions it into dc to charge the battery. The charging station hardware is typically referred to as the electric-vehicle service equipment (EVSE). The other form of external charger is a dc source that connects directly to the HV battery and provides a rapid recharge.
Three classes or levels of vehicle charging have been defined by the Society of Automotive Engineers (SAE) (see table). Level 1 and 2 chargers are built into the vehicle itself. Level 3 chargers are defined primarily for public charging stations.
Other organizations also define charging-related standards. The International Electrotechnical Commission (IEC) defines four charging modes. In addition, four charger connection plugs have been specified. Added to all that are the many governmental safety codes/standards and regulations related to EMC, efficiency, and safety.
Figure 4 shows a generalized EVSE powering an onboard charger. The EVSE equipment conditions and controls the AC while communicating with the vehicle a CAN bus connection (COMMS). The onboard charger first performs power factor correction (PFC) on the ac to keep the input current in phase with the ac mains voltage to meet the power-factor requirements of the regulations. A DC-DC converter then develops the output to charge the battery.
4. The generic content of an EVSE Level 2 charger that supplies ac to the vehicle.
Figure 5 shows a Level 3 c