Cree SA19-08127MDFD-12DE26 LED bulb

The Cree SA19-08127MDFD-12DE26 bulb is rated at 9.5w and 815 lumens light output equivalent to a 60W incandescent bulb. There are 14 upward facing LEDs mounted on an aluminum-backed PCB which is crimped to an aluminum heat sink disk. A white plastic cylinder is clipped to the heat sink/PCB assembly inside a ring of 10 LEDs and surrounding the remaining 4 LEDs to reflect light to the side for more uniform illumination. The heat sink/PCB assembly is pressed into an additional aluminum heat sink within the A19 base. The entire base is filled with potting compound in which the power conversion PCB is embedded.

A double sided printed circuit board inside the A19 base provides AC to DC conversion. On one side most of the board larger through-hole components such as inductors and capacitors are located. On the other side the surface mounted components and output electrolytic capacitor are located. The semiconductor content of this power conversion board consists of a diode bridge, a diodes, a high-voltage power MOSFET and a Silergy SSL5251 controller in an 8-pin package. The AC to DC conversion circuit connects to the LED assembly via a 2-pin connector.

The circuit is a non-isolated buck-boost converter that generates a DC voltage for driving the LEDs from the full wave rectified 120 volt AC input. The rectified AC is not directly filtered to an intermediate DC voltage because this would require a large capacitor. Instead, the full wave rectified AC voltage varying from 0 to approximately 170 volts peak is fed through a passive LC filter to block high frequencies and provided directly to the switching regulator consisting of an inductor, diode, a large electrolytic output capacitor, high voltage MOSFET and the controller IC. The high voltage MOSFET limits the voltage applied to the controller IC so that the switching transistor within the IC does not have to withstand the full peak line voltage. The gate of the MOSFET is biased the constant DC supply voltage Vcc regulated by the controller IC. The use of an external high voltage MOSFET allows the controller IC to be manufactured with a lower cost technology.  Transient protection is provided by a 270v varistor and a fuse at the AC input.

A polar coordinate graph shows the light intensity of the Cree SA19-08127MDFD-12DE26 at 4 different power levels adjusted with a triac dimmer. 0 degrees is the top of the bulb and 180 degrees is the base of the bulb where the light is completely blocked. Full power intensity is at a maximum of 4500 lux at 0 degrees and begins to fall off rapidly at +/-90 degrees. Integrating over the entire surface gives a total light output of 620 lumens, short of the rated 815 lumens. However a 60W incandescent light bulb provided only 400 lumens under the same measurement conditions so there is probably a significant calibration error. Power consumption was measured at 10.3 watts, exceeding the rated power consumption. Energy efficiency of the bulb can be calculated by converting lumens to watts on the basis of the photopic luminosity function (683 lumens/watt) which approximates the range of wavelengths visible to the human eye at normal intensities. The Cree SA19-08127MDFD-12DE26 efficiency in converting electrical power to optical power at visible wavelengths is calculated at 8.8% under full power. For comparison the 60W incandescent bulb is calculated at only 1.0% efficiency.


2017.08.21