Energy-efficient 28 V, 3.3 A LED street light driver design

Foreword: With the continuous improvement of LED in almost every aspect of performance and cost, LED lighting is being used in an increasingly wide range of applications, among which LED street lights are a focus of the industry. This article will introduce a 28 V, 3.3 A offline high power factor LED driver design for applications such as LED street lights. This design is based on the NCL30001 LED driver and the NCS1002 constant voltage constant current controller. It is powered by 90 to 265 V AC voltage and provides a maximum output power of 90 W. It has a high power factor and meets the relevant harmonic content standards. Wide modulation (PWM) dimming.

Single-segment topology LED driver + secondary CVCC controller combination

The NCL30001 is a single-segment topology LED driver solution with flexible features that are ideal for new LED lighting products. This off-line LED driver with single-stage integrated power factor correction (PFC) and isolated step-down AC-DC (AC-DC) power conversion eliminates the need for dedicated PFC boost sections, reducing component count and reducing solution costs. In conjunction with improving the total energy efficiency of LED power systems, it is used in applications such as LED street lights, low ceiling lights, exterior wall lights and building lighting.

The NCL30001 operates in continuous conduction mode (CCM), which integrates PFC and isolated DC-DC conversion circuitry and provides constant current to directly drive the LEDs. It is equivalent to integrating the AC-DC conversion with the LED driver two-part circuit, all located in the lighting fixture, eliminating the linear or DC-DC converter integrated in the LED strip. This monolithic solution has fewer power conversion segments, reduces component usage (such as optical components, LEDs, electronic components, and printed circuit boards), reduces system cost, and supports higher overall energy efficiency of LED power supplies. Of course, this solution has higher power density and may not be suitable for all area lighting applications. Its optical pattern may be more suitable for lower power LEDs. Typical applications include LED street lights, exterior wall lights, wall washers and refrigerator cabinets. Lighting, etc.

Other specifications of the NCL30001 controller include high voltage start-up circuitry, voltage feedforward for improved loop response, input undervoltage detection, internal overload timer, latch input, and high precision multipliers that reduce input line harmonics. ON Semiconductor also offers an isolated single-segment power factor correction LED driver evaluation board for applications requiring direct current output from 40 W to 100 W power range. The current can be adjusted from 0.7 A to 1.5 A for a wider range of high power, high brightness LEDs.

The NCS1002 is a secondary-side constant voltage constant current (CVCC) controller suitable for regional lighting applications such as LED street lights. With the NCL30001 controller, it can also design a high-efficiency, dimming-enabled LED driver demonstration board.

90 W demo board based on NCL30001 and NCS1002

The 90 W constant voltage constant current demo board accepts an extended universal input voltage of 90 to 265 Vac (305 Vacable for component replacement), a constant current output range of 0.7 A to 1.5 A and a constant output of 30 V to 55 V Voltage range (selectable by resistor divider), maximum output power 90 W, support for 50 to 1,000 Hz dimming control, and 6-pin interface for optional dimming card for analog current regulation / dual Intelligent dimming applications such as brightness level digital dimming. In addition, the demo board offers a wide range of protection features such as short circuit protection, open circuit protection, over temperature protection, over current protection and over voltage protection. Tests show that the demo board is more than 87% efficient at 50 W output power, 1,000 mA output voltage / 48 V forward voltage drop, and power factor greater than 0.9 at 50% to 100% load, while complying with IEC61000- 3-2 Class C equipment harmonic content standard.

Figure 1: Demo board top view

Since this design can have comparable power levels to the standard NCL30001 evaluation board (50V2A), the circuit principle changes in the design of the transformer and the constant current/constant voltage secondary side control circuit based on the NCS1002. Figure 2 shows the primary side circuit. This design of the flyback transformer is derived from the original design of the secondary winding to meet the new maximum voltage and current requirements. The inductance required for the primary winding is substantially the same as the overall structure. The 277 VAC input can be used to vary the “X” and “Y” capacitors of the EMI input filter with the appropriate voltage rating.

Figure 2: Primary Side Schematic of the NCL30001 CVCC 90 W Demo Board

The NCL30001 continuous conduction mode power factor corrected single-stage flyback controller enables constant current LED drivers for area lighting applications such as overhead, tunnel, parking, and road lighting. This special design is optimized for LEDs that require more than 3A drive capability, such as Luminus Devices' CSM360 and SST90. This design can support up to 8 SST90 series or 2 CSM360 devices. The CSM360 LED has a nominal forward voltage of 12.8 V at a drive current of 3.2 A, which can produce 1600-3900 lumens depending on color temperature and luminous flux.

The secondary side control circuit is shown in Figure 3. In this design, the output voltage is determined by a resistivity, and the output current is also set based on a resistivity. Therefore, only two resistors need to be changed: one is the output voltage divider R34 and the other is R32, which is part of the current setting circuit. In addition, the output current is higher due to the lower output voltage, which increases the output capacitance and lowers the rated voltage of the capacitor.

Figure 3: Secondary side schematic

to sum up

The 90 W LED driver design for LED street light applications provides high power factor, meets IEC61000-3-2 Class C equipment harmonic content standards, and can be used with PWM dimming.