A DOB LED light is an LED lighting system (either an LED bulb or an LED luminaire) that incorporates a light engine with an integrated on-board driver. DOB is short for "driver-on-board". In conventional LED lighting systems the driver is typically separated from the LED assembly and fabricated on an FR4 printed circuit board (PCB). This configuration is based on the consideration that LED drivers have been dominantly designed as switching mode power supplies. SMPS drivers typically make use of bulky, expensive and unreliable reactive components such as inductors and capacitors. The use of reactive components necessitates a dedicated FR4 board which provide adequate routing layers for component interconnects. In an integrated lighting system, the considerable volume of a typical SMPS driver creates a need for an adequate space within the lighting system in order to accommodate the driver circuit. Furthermore, reactive components such as electrolytic capacitors are temperature sensitive. Remote mounting can alleviate these components of thermal stresses otherwise imposed by the LEDs.
A DOB lighting system uses only solid state driver components which are available in surface-mount packages capable of being assembled on circuit boards with a single-sided copper construction. This makes it possible to mount driver components a metal-core printed circuit board (MCPCB) where LEDs are mounted. Typically, the driver is designed as a linear power supply. Since there is no high frequency switching, electromagnetic interference (EMI) is practically absent in linear power supplies. The complete absence of EMI radiation allows linear power supplies to be designed with a significantly reduced parts count. The small circuit parts count and small form factor of circuit components contribute a small footprint of the driver, which introduces minimal impact on the LED assembly when it comes to photometric performance. The drive current is regulated by small driver ICs without using electrolytic capacitors. The weakest component with the shortest life expectancy determines the life of the driver. The removal of electrolytic capacitors translates to significantly improved driver reliability.
DOB light engines, however, have their limitations. Linear supplies are inherently inefficient. The headroom voltage is dissipated as heat which introduces an additional thermal load to the co-located LEDs. Absence of flicker is important for any lighting system but can be challenging to DOB lighting systems because of the presence of large ripples in the DC current provided to LEDs. The LEDs in a DOB light engine are not only stressed by the additional thermal load introduced by the driver, but are also subject to electrical overstresses because the driver has limited ability of absorbing voltage surges that may be present on the AC line. The output circuit is not galvanically isolated from the mains. In this case, all metal contacts must be properly isolated to provide protection against electric shock.
A DOB lighting system uses only solid state driver components which are available in surface-mount packages capable of being assembled on circuit boards with a single-sided copper construction. This makes it possible to mount driver components a metal-core printed circuit board (MCPCB) where LEDs are mounted. Typically, the driver is designed as a linear power supply. Since there is no high frequency switching, electromagnetic interference (EMI) is practically absent in linear power supplies. The complete absence of EMI radiation allows linear power supplies to be designed with a significantly reduced parts count. The small circuit parts count and small form factor of circuit components contribute a small footprint of the driver, which introduces minimal impact on the LED assembly when it comes to photometric performance. The drive current is regulated by small driver ICs without using electrolytic capacitors. The weakest component with the shortest life expectancy determines the life of the driver. The removal of electrolytic capacitors translates to significantly improved driver reliability.
DOB light engines, however, have their limitations. Linear supplies are inherently inefficient. The headroom voltage is dissipated as heat which introduces an additional thermal load to the co-located LEDs. Absence of flicker is important for any lighting system but can be challenging to DOB lighting systems because of the presence of large ripples in the DC current provided to LEDs. The LEDs in a DOB light engine are not only stressed by the additional thermal load introduced by the driver, but are also subject to electrical overstresses because the driver has limited ability of absorbing voltage surges that may be present on the AC line. The output circuit is not galvanically isolated from the mains. In this case, all metal contacts must be properly isolated to provide protection against electric shock.
