Twelve white OSRAM advanced power TOPLEDs per headlight power the daytime running lights on the Audi A4.

On a per vehicle basis, hybrids certainly contain the greatest amount of new power semiconductors. However, other vehicle applications for power semiconductors continue to grow based on high-volume usage. Some applications such as ignition systems use high-voltage insulated gate bipolar transistors (IGBTs). However, the majority are low-voltage systems that use power MOSFETs. In addition to cost reduction, other key characteristics that customers are looking for include improved reliability, integration of additional features, application-specific design, packaging and more.

Since the ignition system is present on all internal combustion engine vehicles, it represents the highest volume high-voltage vehicle load. IGBTs are the primary technology for firing the ignition coil in the United States, Europe and Japan. Low cost is the primary driving force for this application but not the only one. According to Gary Wagner, director of body electronics and smart switches, Fairchild Semiconductor, other factors include “the trends toward multifuel, the continuing need to improve fuel economy and emissions, as well as extending the ignition capabilities to emerging markets and some of the lower-value vehicles that may not have had the more sophisticated electronics associated with them.”

Wagner believes that coil on plug and technologies such as pencil coils have somewhat stabilized and become more mainstream. With this level of acceptance, the current trend is to add more intelligence to the drivers and to combine the driver to the switch that is mounted on the coil. For Fairchild, this means adding current sense capabilities as well as adding a control die in a multi-die configuration, typically side by side in a TO-247-type package. “These parts are in development right now,” said Wagner.

One of the high-voltage applications that is still emerging, or in the transition phase, is injector drivers. Direct injection with piezoelectric injectors for either gasoline or diesel engines is considered essential to meet stricter emission standards and could be required for future CAFE goals since it allows finer metering of the fuel than solenoid injectors. With direct injection and turbocharging, a six-cylinder engine can outperform a V-8 or a four-cylinder can outperform a six-cylinder. “This technology allows fun driving capability along with the fuel economy,” said Jim Spangler, field applications engineer, ON Semiconductor.

In high-pressure, direct-diesel injection, higher voltages are required to further atomize the fuel to get better burning and 150 V is a common voltage requirement. “In some cases, we are actually using small IGBTs as opposed to FETs for some of the even higher-voltage applications,” said Jim Gillberg, director of applications and strategic marketing, Fairchild Semiconductor.

“Many times customers that are asking for high-voltage boost converter circuits, the application is injector drivers,” said ON Semiconductor's Spangler. In some in-stances, the customers are reevaluating capacitive discharge circuits for spark discharge ignition, but more often than not, the target application is high-voltage injectors. Figure 1 shows one of the approaches used to drive high-voltage injectors.

ON Semiconductor supplies the UC3843BVD control IC and MBR-B20200 diodes used in the boost converter to develop the high voltage for the piezo drive circuit. In addition, the company's NCV7513 or NCV7517 are used as the pre-driver from the MCU to select the proper injector. MURS360 or MURD660 Ultra-Fast diodes are used for recirculation diodes.

Figure 2. Melexis integrated MLX81100 provides complete circuitry for driving simple N-Channel MOSFETs.

It turns out that either IGBTs or FETs can drive the injectors. The choice depends somewhat upon the voltage. The higher the voltage, the more likely that the driver is an IGBT. However, if the system designer has not used IGBTs, they may be inclined to use power MOSFETs. With newer trench devices in the higher-voltage range, the MOSFET's size is reduced making it even more attractive.

Another high-voltage application is high-intensity discharge (HID) lamps. Small 300 to 600 V IGBTs are frequently used for these lamps. The application requires 175 °C operation temperature even though the housing mounts in the airflow at the front of the engine. One of the available products is Fairchild's FGD3N60LSD, an IGBT that can also be used for piezo-injectors. Housed in a DPAK, the unit has 600 V breakdown rating and conducts a continuous forward current of 3 A at a case temperature of 100 °C.

The power device in HID applications requires driver circuitry as well. IXYS' Micronix subsidiary recently introduced a full-bridge high-voltage integrated circuit (HVIC) for HID lighting applications. The MX6895 addresses low-cost, high-volume automotive Xenon headlight applications. Operating with an output supply voltage of -80 to -550 V with control inputs from 3.3 to 12 V, the MX6895 driver requires no external boost-related components. Features include soft turn-on level translators to minimize electromagnetic interference (EMI) effects when directly driving a MOSFET bridge network.