With the continuous improvement of LEDs in almost every aspect of performance and cost, LED lighting is being used in a wider and wider range of applications, among which LED street lights are a focus of attention in the industry. As the premier high-performance silicon solution supplier for energy-efficient Electronic products, ON semiconductor provides a wide range of drivers, voltage regulators/regulators for various LED lighting applications, as well as communications, light sensors, MOSFETs, rectifiers, protection , filters and thermal management products and other complete solutions. This article will describe a 28 V, 3.3 A offline high power factor LED driver design for applications such as LED street lighting. This design is based on ON Semiconductor’s NCL30001 LED driver and NCS1002 constant voltage and constant current controller, powered by 90 to 265 V AC voltage, providing a maximum output power of 90 W, with high power factor, while complying with relevant harmonic content standards, and Can cooperate with pulse width modulation (PWM) dimming.
Single-segment topology LED driver + secondary-side CVCC controller combination
The NCL30001 is a single-segment topology LED driver solution, and its flexible features are ideal for new LED lighting products. This offline LED driver with single-stage integrated power factor correction (PFC) and isolated step-down AC-to-DC (AC-DC) power conversion eliminates the need for a dedicated PFC boost stage, reducing component count and solution cost. In conjunction with improving the overall 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 circuits and provides constant current to directly drive LEDs. It is equivalent to integrating AC-DC conversion and LED driving circuits, both located in the lighting fixture, eliminating the need for linear or DC-DC converters integrated in LED strips. This integrated solution has fewer power conversion stages, reduces the number of components used (such as optical components, LEDs, electronic components and printed circuit boards, etc.), reduces system cost, and supports higher overall LED power efficiency. Of course, this solution has a 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 boxes. lighting etc.
Additional specification features of the NCL30001 controller include a high voltage start-up circuit, voltage feedforward to improve loop response, input undervoltage detection, an internal overload timer, latched inputs, and a high precision multiplier to reduce input line harmonics. ON Semiconductor also offers an isolated single-segment power factor corrected LED driver evaluation board for this device for applications in the 40 W to 100 W power range requiring direct constant current output. The current is adjustable from 0.7 A to 1.5 A to match a wider range of high-power, high-brightness LEDs.
NCS1002 is a secondary-side constant voltage and constant current (CVCC) controller, suitable for area lighting applications such as LED street lights. With the NCL30001 controller, a high-efficiency LED driver demo board with dimming function can be designed.
90 W demo board based on NCL30001 and NCS1002
To help engineers implement lighting designs as quickly as possible, ON Semiconductor also offers a 90 W constant voltage and constant current demo board that accepts an extended universal input voltage from 90 to 265 Vac (305 Vac with component replacement) and provides 0.7 A to 1.5 A constant current output range of A and a constant output voltage range of 30 V to 55 V (selectable by a resistive voltage divider), maximum output power of 90 W, support for 50 to 1,000 Hz dimming control, and includes an optional dimmer that can be connected to The 6-pin interface of the optical card is used for intelligent dimming applications such as analog current regulation/dual brightness level digital dimming. In addition, this demo board provides rich protection features such as short-circuit protection, open-circuit protection, over-temperature protection, over-current protection, and over-voltage protection. Tests have shown that the demo board is more than 87% energy efficient at 50 W output power, 1,000 mA output voltage / 48 V forward voltage drop, and has a power factor greater than 0.9 at 50% to 100% load, while complying with IEC61000- 3-2 Harmonic content standards for Class C equipment.
Figure 1: Demo board top view
Since this design can have power levels comparable 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. The flyback transformer of this design is derived from the secondary winding of the original design and can meet the new maximum voltage and current requirements. The required inductance and overall structure of the primary winding are essentially the same. The 277 VAC input can vary the “X” and “Y” capacitors of the EMI input filter with the appropriate voltage rating.
Figure 2: Schematic of the primary side of the NCL30001 CVCC 90 W demo board
Constant current LED drivers for area lighting applications such as overhead, tunnel, parking lot and road lighting can be implemented using the NCL30001 continuous conduction mode power factor corrected single stage flyback controller. This particular design is optimized for LEDs that require drive capabilities greater than 3A, such as the CSM360 and SST90 from Luminus Devices. This design can support up to 8 SST90s in series or 2 CSM360 devices. The CSM360 LED has a nominal forward voltage of 12.8 V at a drive current of 3.2A, 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, there are only two resistors to change: one is the output voltage divider R34 and the other is R32 which is part of the current setting circuit. Additionally, the higher output current due to the lower output voltage increases the output capacitance while reducing the voltage rating of the capacitor.
Figure 3: Secondary Side Schematic
Using this circuit, a 30 Vout LED driver CVCC secondary detection with PWM dimming input and optional dimming card can be implemented.
Energy-efficient lighting is becoming a focus of competition in the industry. This article focuses on ON Semiconductor’s 90 W LED driver design for LED street lighting applications, which provides high power factor, meets IEC61000-3-2 Class C equipment harmonic content standards, and is capable of PWM dimming. Customers take advantage of ON Semiconductor’s energy-efficient products and reference designs to accelerate time-to-market.
1. NCL30001, NCS1002: Up to 28 V, 3.3 A Constant Current Offline High PF LED Driver, ON Semiconductor, www.onsemi.cn/pub/Collateral/DN06068.PDF