20.1 Lighting Controls

Controlling lamps with power electronics offers many advantages and a few disadvantages over conventional switches or relays. An important advantage includes easier diagnostics compared to the classical mechanical switch or relay approach, while a significant disadvantage includes the higher cost of the electronics. Because some lights, such as headlamps, turn signals, and brake lamps are safety related, a method to test the integrity of these lamps is an advantageous feature. The power electronic design can not only turn lights on or off, but it can vary the light's intensity and detect abnormal conditions such as open or shorted lamps. The cost tradeoff issue becomes more interesting when the power electronics load control is connected onto a data bus or multiplexed network (see Chap. 26).

The typical automotive lamp can range from small-wattage panel lamps to large 60-W or higher headlamps (refer to SAE ref HS-34/93 for auto lamp standards). Tungsten and halogen types prevail for many vehicular lamp designs. The prime difference between standard tungsten nonhalogen and halogen lamps is in light efficiency. Halogen types produce about 20 percent more light for each watt of energy consumed. Other types of lamps, such as light-emitting diodes (LEDs), fluorescents, or gas discharge, are somewhat adaptable for vehicular applications. The power electronics operating requirements vary for each lamp technology category.