Low Power DC and PWM Operation of Halogen Bulbs 2006-01-0713
Halogen light sources for automotive forward lighting applications are designed for a nominal DC voltage and power, typically in the range of 13 volts and 55 to 65 watts. However some applications attempt multifunctional use, such as a high beam – day time running lamp (DRL) combination, by regulating the power. This can be done by pulse width modulation (PWM) or by simply lowering the applied DC voltage. More advanced applications, such as smart headlamps or advanced forward lighting systems, might also operate the bulb only for a short period of time. This can have a similar effect as PWM. In either case the halogen bulb will perform differently than at the DC design voltage. The valid power or voltage ranges do not only depend on the light source itself, but strongly on environmental conditions. Thermal management and external temperatures of the system can influence or prevent the halogen cycle activation and cause problems, such as bulb wall blackening. This study will report on the effects of low average power operation and try to quantify these effects to give design guidelines for low power or advanced switching halogen applications.