LED general lighting (General Lighting) design engineers encounter many challenges, such as power density, power factor correction (PFC), space constraints and reliability. These LED lighting design challenges are similar to power supply design challenges. Specifically, LED general lighting has the following challenges: due to overall effecacy requirements and thermal constraints, energy efficiency is important even for low power applications; in many cases Lower power also requires power factor correction and harmonic handling; in space-constrained applications, especially when replacing light bulbs, the requirements for driving power density are high; overall power supply reliability is very important to improve overall lamp life ; Wide input supply voltage range should support up to 277 Vac; Compatible with legacy specific lighting requirements such as TRIAC dimming. In addition, LED general lighting must comply with the still evolving standards and safety regulations, such as the requirements of Energy Star in the United States and the International Electromechanical Commission (IEC) in the European Union.
ON semiconductor has been committed to providing a wealth of solutions for LED lighting, launching a variety of products that meet the latest LED lighting standards, including AC-DC power ICs, DC-DC drivers, CCR regulators, constant current and constant Voltage (CCCV) Controls, high voltage FETs, rectifiers, digital interfaces, ambient light sensors, protection, power line communication (PLC) modems, and more. This article mainly introduces the AC-DC power supply configuration and related circuits for LED lighting to help engineers meet the above challenges and design products that meet general lighting requirements.
ON Semiconductor LED Lighting Solution
Figure 1 shows the types of products that ON Semiconductor offers for LED general lighting.
Figure 1: Schematic diagram of ON Semiconductor’s LED lighting solution application
In ON Semiconductor’s AC-DC power supply configuration for LED lighting, NCP1010~NCP1015 are recommended for lighting applications from 1 to 10 W, and NCP1027/8 can be used for 1 to 15 W. These solutions integrate MOS transistors and are suitable for isolation And non-isolated applications, support secondary PWM dimming, analog dimming or dual brightness level dimming, energy efficiency up to 75-80%; 1 to 30 W applications can use LV5026, 5027, 5028, support isolation solutions, typical energy efficiency 85 %; 1 to 40 W is recommended to use NCL30000, which can perform primary thyristor dimming, suitable for isolation and non-isolation solutions, and the energy efficiency of isolation solutions is 80-85%. The NCL30001 is recommended for 40 to 150 W, which is a continuous conduction mode (CCM) control chip with a typical energy efficiency of 85-90% for the isolation scheme; the NCL30051 is recommended for higher power. Figure 2 is a comparison of the output power and energy efficiency of these schemes. The functions and features of these programs will be introduced in detail below.
Figure 2: Comparison of output power and efficiency for an AC-DC power supply configuration for LED lighting.
LV5026/27/28 Series LED Controllers for 1 to 30 W Power AC-DC Applications
This series is the LED controller of SANYO Semiconductor, a member company of ON Semiconductor – LV5026M, LV5028TT and LV5027T, of which LV5026M has TRIAC dimming, PWM dimming, analog dimming and power factor correction functions; LV5028TT only has TRIAC dimming and power factor correction functions Function. The LV5026/7/8 TRIAC dimming circuit is shown in Figure 3.
Figure 3: LV5026/7/8 TRIAC dimming circuit.
Taking the most versatile LV5026M as an example, it is a high-voltage LED controller compatible with different dimming. The dimming method is TRIAC, analog input or PWM input, and the switching frequency (50 kHz, open circuit 70 kHz) can be selected. The solution is a low-noise switching system, using 5-stage skip mode frequency, which can drive the switch in steps; its reference voltage can be selected (internal 0.605 V and external input voltage), with soft-start function and TRIAC stabilization function.
A PWM control architecture designed to reduce electromagnetic interference (EMI) offers advantages over competing products. It adopts 2-step drive, which can significantly reduce noise; 5-level frequency with non-constant period can effectively eliminate EMI peaks.
There are two ways of low power AC-DC LED power conversion, one is non-isolated step-down, which requires mechanical insulation; its design and circuit configuration are simple, the circuit board size is small, the number of components is small, the energy efficiency is high, and the bill of materials (BOM) The cost is also lower. The other is isolated flyback, which uses electrical (magnetic) isolation and is easy to meet safety requirements. The magnetic design is more complicated, suitable for higher power designs, and requires a larger circuit board size.
LV5026/7/8 are used for non-isolated A19 LED lamps, which can realize the following product features: adopting step gate driving method, with oscillation frequency slewing function, high gate capability driving circuit, externally adjustable reference voltage, support for various dimmers (TRIAC dimming, digital dimming and analog dimming); also supports soft-start, over-current protection, thermal shutdown, over-voltage protection, etc. The LV5027M/LV5028M are simplified versions of the LV5026M with fewer external components.
Figure 4: LV5026/7/8 for non-isolated A19 LED lamps.
NCL30100 Low Power Buck Solution for Applications requiring High Energy Efficiency and Space Constraints
The NCL30100 is an energy efficient, peak current controlled self-adjusting fixed off-time buck controller for low power and space constrained applications where space and energy efficiency are critical, such as MR16 LED lamps. The scheme features adjustable oscillation frequency, uses continuous conduction mode (CCM), can eliminate output capacitors, is more energy efficient, and provides natural LED open-circuit protection. Using the NCL30100 can take advantage of negative current sensing and reduce power losses with small inductors, enabling low cost, high energy efficiency (100 Vac Vo=36 V, >90% energy efficiency) and low component count applications.
Figure 5: NCL30100 single-voltage input step-down solution.
Low Power Offline Buck Solution NCP1015
The NCP1015 monolithic switching power supply IC can meet the AC 85-265 Vac wide voltage input range, and is suitable for low-power offline step-down LED lighting design with output power within 10 W. This device provides rich features such as soft-start, frequency jittering, short-circuit protection, skip period, maximum peak current setting, and dynamic self-supply (DSS), which not only improves energy efficiency, but also enhances reliability. Adding a Resistor between C8 and the 1st pin of IC can improve energy efficiency and is suitable for small current and high voltage output.
Figure 6: NCP1015 buck scheme.
Medium and low power AC-DC solution NCL30000 suitable for both buck and buck-boost configurations
Using the “average current regulation” topology of the NCL30000, two configurations can be selected, one is a step-down configuration (including a tapped Inductor step-down configuration). Its inductance is connected in series with the LED string, and current flows only when the input voltage is greater than the output voltage drop; the performance of power factor (PF) and input current total harmonic distortion (THDi%) depends on the ratio of output voltage drop to input voltage (VF/ Vin), the higher the ratio, the lower the PF, and the higher the ratio, the higher the THDi.
The other is a buck-boost configuration, where the Inductor is not in series with the LED string, and the input current waveform or distortion is independent of the output voltage drop; inherent LED fault protection provides protection when the mosfet is shorted; the LED forward voltage drop can be higher than or lower than the input voltage; the MOSFET switching voltage stress is the sum of the input voltage and the output voltage drop (Vin+Vout).
Buck topology works by allowing current to flow only when input voltage exceeds LED forward voltage drop (VF); utilizes critical conduction mode (CrM) and constant on-time operation to provide high power factor; direct sensing of LEDs current; low loop bandwidth supports high power factor operation; MOSFET current equals LED peak current; MOSFET voltage stress equals peak line voltage.
Figure 7 is the application circuit of the NCL30000 high power factor step-down solution. When the line needs to be dimmed, the maximum on-time can be adjusted according to the line and load power; it is compatible with TRIAC or trailing edge (Transistor) dimmers; At line voltage (120 Vac or 230 Vac), phase-cut dimming is available to optimize the EMI filter design, reduce the value of the X Capacitor, and minimize peak current.
Figure 7: NCL30000 high power factor step-down solution application circuit.
Introduced below are two AC-DC isolated power supply configuration examples based on NCL30000.
1) AC dimmable A19 LED lamp supporting thermal reversal: input voltage 90 to 135 Vac, 5 W rated output power (10 V @ 500 mA), can drive 3 LEDs in series; isolated thermal reversal, temperature Linearly reduces output current when rising; power factor > 0.96, energy efficiency > 77%; meets the requirements of “Energy Star” version 1.1 integral LED lamps; compatible with TRIAC and Transistor dimmers.
Figure 8: Thermal Reverse AC Dimmable A19 LED Lamp.
2) AC dimmable PAR30 LED lamp: can be used for lamps with input voltage of 115 V/230 V, 11 W rated output power (24.5 V @ 450 mA), driving 8 LEDs in series/3 series-parallel; isolated; power Factor>0.96, energy efficiency>83%, according to the requirements of “Energy Star” version 1.1 integral LED lamps; compatible with TRIAC and Transistor dimmers.
Figure 9: AC dimmable PAR30 LED light.
NCL30001 solution for medium and high power AC-DC LED lighting applications
The NCL30001 Power Factor Corrected (PFC) Dimmable LED Driver is suitable for medium to high power applications (power up to 90 W) such as architectural decorative lighting. There are three supported dimming methods: 1-10 V analog voltage input (1 V = minimum, 10 V is the value at 100% on); two-level two-level analog dimming; and PWM dimming (dimming Frequency range 350 Hz to 3 kHz, dimming range > 10:1). Protection features include: output open-circuit and short-circuit protection, over-temperature protection, over-current protection, over-voltage protection and over-temperature reversal.
Figure 10: NCL30001 is used for architectural decorative lighting.
NCL30051 solution for high-power architectural decorative lighting applications
The NCL30051 is a dedicated LED power integrated circuit (IC) capable of providing constant voltage for step-down DC-DC converters/LED drivers such as the NCL30160. The device integrates a critical conduction mode (CrM) PFC controller with a half-bridge resonant controller, and built-in 600 V driver, optimized for offline power applications, and has all the required energy-efficient, small form factor designs characteristic. The NCL30051 can be used for architectural decorative lighting applications up to 100 W, and can support up to 250 W with modified components. The dimming methods supported by the NCL30051 include 1-10 V analog voltage input (1 V = minimum, 10 V is the value at 100% on), two-level two-level analog dimming, and PWM dimming (frequency range 100 to 300 Hz, dimming range >10:1). Protection features include: output open-circuit and short-circuit protection, over-temperature protection, over-current protection, and over-voltage protection.
Figure 11: NCL30051 is used for high power architectural decorative light.
In addition, ON Semiconductor’s GreenPoint® design simulation tool allows designers to select products, determine design requirements, automatically generate designs (circuit diagrams), simulation and verification, bill of materials (BOM) and reports, and download in just a few steps The report is a series of processes such as PDF file, saving disk and sharing, so as to realize fast, easy-to-use and efficient LED product development.
ON Semiconductor leverages its core expertise and strengths in energy-efficient power supplies and packaging to provide control and drive components for LED lighting applications, especially general lighting, that meet various regulatory requirements. These solutions use unique LED drive power architectures, analog and dimming technologies, flyback converters and non-isolated topologies, combined with a wide range of applications, providing more options for implementing a variety of general lighting equipment.