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We are an OEM lighting fixture manufacturer, we do not manufacture LED drivers. The question is when do you see driver efficiencies getting better than 90 percent? Our clients are lighting people used to fluorescent and HID systems with efficiencies of better than 95 percent and they are constantly dismayed to have us explain that the best efficiencies we see on drivers is about 87 percent, with a range of 77 to 85 percent being more typical. Barry Besmanoff, Litelab Corporation
Efficiencies of 87 to >90% are achievable at the 20W level for LEDs. The choice of LED VF and driver current as well as other features, high power factor, wide input range, physical size as well as power component selection (MOSFET, Output rectifier, Transformer) all come into play. In this specific case with the Philips Lumileds Luxeon S100 the nominal VF of 26V and 700 mA drive current impact the architectural choices.
As you indicated, an isolated topology is needed so an example isolated driver reference design would be NCL30060 is a switch mode power supply controller intended for low to medium power single stage power factor (PF) corrected LED Drivers which typically achieves ~ 88% at these operating conditions.
This particular design was intended for 90-305 Vac to cover global voltage range including the US 277 Vac requirement and achieve high power factor and low THD. The driver also has circuitry to support 1-10V dimming which consumes additional power. Optimizing this circuit for one input voltage range or removing dimming capability would improve the efficiency beyond this level. Lowering the switching frequency and increasing the size of the transformer would also reduce losses.
From my experience when looking at efficiency comparisons, it is more useful to convert these numbers into driver power losses. 87% efficiency at 20W power output translates into about 3W of total losses in the driver and wiring. Improving the efficiency to 90% requires a reduction in power dissipation of 25% which is significant and improving that to 92% would require a 40% reduction in total power losses.
By the way, switching from an isolated topology to a non-isolated power factor corrected buck like the NCL30002 buck power factor (PF) corrected LED driver at the same output voltage/current range would achieve typical efficiencies of over 90%. A higher forward voltage LED with a lower current would also allow efficiency gains as well.
Answered by: ON Semiconductor
2014-09-11 11:18:11.471