Posts Tagged ‘Solid State Lighting’

Light Install

November 23, 2017

Advertisements

DC Power Devices in PV Installations

February 20, 2011

The design of PV systems tied to the AC grid requires a DC-AC inverter to convert DC from the solar panel to AC power, for use by AC-powered devices or to feed-in to the utility’s AC grid, the latter operation also requiring power conditioners. The DC-AC conversion process is less than 100% efficient. The losses are similar to ones imposed by step-down transformers and vary by equipment nameplate efficiency.

To maximize the power harvested, one may use DC devices as possible, avoiding the loss inherent in the inverter. Solid state lighting (SSL) including LED offers such an opportunity, increasing the systemic energy efficiency by both providing greater Lm/W over incandescent and fluorescent sources and by capturing the energy lost through the inverter to the AC portion of the distribution system.

The number of available DC devices in buildings is limited, typically elevators and SSL, and equipment such as lifts and cranes in industrial applications, including boat lifts. Distribution with the above strategy is also made somewhat more complex. Consequently a cost-benefit analysis should be undertaken for any particular building project or retrofit.

LED Links

July 14, 2009

2497773629_a9bdb04219

* President Obama meets with Cree CEO to discuss LED lighting.

* DOE-sponsored workshop on Solid State Lighting opened today in the windy city.

* Seoul Semiconductor P4 Series Natural White LED achieves a Color Rating Index of 93.

* USA companies Microchip and National Semiconductor provide the Driver Integrated Circuits for Seoul Semiconductor P4 Series LED.

* NYSERDA is making US$10 million available to energy efficient lighting manufacturers to expand production in NYS.

* The NYS Bridge Authority has lit the Mid-Hudson Bridge with RGB LED.

* Texas bans lighting designers, deems architects and engineers only ones qualified to provide lighting services.

ARMSTRONG

Lance maintained his third place standing, 0:08 behind, finishing today’s stage within the peloton. Tomorrow the Tour heads back to the flats after two mountain stages. The lights of Paris are 12 stages away.

bp1523

B&W photo courtesy Arquitecto Moises Levi

An LED Driver Design for High Currents

June 9, 2009

blockHigh-brightness LEDs are being used in luminaires for commercial downlighting, and industrial, architectural, exterior, and emergency lighting.

To produce more lumens, some LED designs require forward currents to increase. Typical LED forward currents range from 350 mA to 1000 mA; a few of the latest LED require up to 3000 mA.

To address this high current approaching 3 Amps, some driver solutions are utilizing innovative switching.

The majority of LED driver solutions available are based on standard voltage-regulator, using a fixed frequency, current-mode-control buck converter. Control schemes tend to be complex, often having two loops: an outer-loop to regulate the current control and an inner-loop to provide the peak current control. This control technique typically requires external compensation components.

Brightness control is difficult to achieve. Most solutions rely on pulse width modulation frequencies in excess of 200 Hz to avoid flicker. A good dynamic range for brightness control requires the ability to modulate to duty cycles as low as 10%. With a 200 Hz signal, this means the driver has to support the ability to turn on and off in a period of 0.1 × 1/200 seconds = 0.5 ms. As some driver solutions have a soft-start feature in the region of several ms, this can restrict the dynamic control range.

The voltage in the current-control loop can be as high as 1.2 V, which has a large impact on the power dissipation. When driving a single LED with a forward voltage (Vf) of 3.5V, the efficiency drops by 34%, even before other losses are considered.

The diagram shows a circuit built around a driver designed for driving high-current LEDs. With a simplified control scheme, the component count includes two resistors, two capacitors, one Schottky diode, and the power inductor (L). An output capacitor is not required because the peak-to-peak current ripple can be as low as 10% of the maximum LED current. This meets the majority of high bay LED lighting applications.

The design uses an inner-loop that controls the current by sensing the voltage developed across the sense resistor (R2) during the recirculation diode (D) conduction phase. No outerloop is required, removing the need for external compensation components.

Soft-start is not used in the design, so expect the life expectancy of the driver will be less than drivers that do provide soft-start, and as such the driver design is best deployed in applications not requiring repeated starting or on-off switching.

Portions excerpted from a whitepaper by Peter Tod