“Energy efficiency is especially important for low power applications due to total LED efficacy requirements and thermal constraints; in many cases, even lower power applications require power factor correction and harmonic handling; in space-constrained applications, especially bulb replacement applications , requires high driving power density; overall power supply reliability is very important to the life of the entire lamp; wide input power supply voltage range should support up to 277 Vac; compatible with TRIAC dimming and other requirements. In addition, LED general lighting must meet evolving standards and safety regulations, such as “Energy Star” and IEC requirements.
Energy efficiency is especially important for low power applications due to total LED efficacy requirements and thermal constraints; in many cases, even lower power applications require power factor correction and harmonic handling; in space-constrained applications, especially bulb replacement applications , requires high driving power density; overall power supply reliability is very important to the life of the entire lamp; wide input power supply voltage range should support up to 277 Vac; compatible with TRIAC dimming and other requirements. In addition, LED general lighting must meet evolving standards and safety regulations, such as “Energy Star” and IEC requirements.
Depending on the application requirements (size, energy efficiency, power factor, power, drive current), there are several topologies for driving LEDs from AC mains. ON semiconductor offers a variety of power solutions for various lighting applications.
Figure 1: Different AC mains powered LED driver topologies
ON Semiconductor LED General Lighting AC-DC Solutions
1) Power factor correction scheme
The 160 W power factor correction (PFC) boost solution using ON Semiconductor’s NCP1611 or NCP1612 adopts a non-isolated boost topology, and the light-load energy efficiency is higher than that of the traditional CrM PFC; no additional components are required, and the reliability and safety are high. The scheme adopts Current Controlled Frequency Flyback (CCFF) CrM, with boost or bypass diode short circuit protection, pin open/short circuit protection, optimized transient response, soft overvoltage protection, input undervoltage detection, low total harmonics Distortion configuration, thermal shutdown, and more.
Such PFC solutions also include NCP1607, NCP1608, NCP1615 and NCP1654 (non-isolated boost); NCL30000 (isolated single-stage flyback, non-isolated buck); NCL30001 (isolated single-stage flyback); NCL30002 (non-isolated buck) ; NCL30060 (single-stage flyback or buck).
Taking NCL30000 as an example, the “average current regulation” topology can choose two configurations, one is a buck configuration (including tapped Inductor buck configuration); the other is a buck-boost configuration, the inductor is not connected in series with the LED string , the input current waveform or distortion is independent of the output voltage drop. It can perform primary thyristor dimming, suitable for isolated and non-isolated solutions, and the energy efficiency of isolated solutions is 80-85%.
2) Primary-side control offline scheme
Primary side regulation (PSR) is also called primary side control. The primary-side controlled offline LED driver does not use an optocoupler and features a precision LED current regulation accuracy of ±1% (typ), a wide VCC range, high-efficiency quasi-resonant control, a robust combination of protection features, and a wide operating temperature range (-40 to +125°C); supports flyback and buck-boost topologies, with a power factor of about 0.9 with passive PFC input; this series can be used in LED bulb replacement, offline LED drivers, downlights, indoor/outdoor accent lighting and Task lights and LED Electronic controls.
Figure 2: Primary-Side Control Offline Scheme
Available devices are NCL30080A/B, NCL30081A/B, NCL30082A/B and NCL30083A/B (passive PFC control); NCL30085A/B, NCL30086A/B, NCL30087A/B and NCL30088A/B (active PFC control). Its dimming control includes non-dimming, 3-step/5-step dimming, analog/digital, triac/trailing edge trigger dimming, etc.
3) AC-DC switching regulator
ON Semiconductor’s switching regulators for isolated flyback and non-isolated converters include NCP1010, NCP1011, NCP1012, NCP1014/15, NCP1027/28, NCP1072/5, NCP1076 and more. These devices are current mode, with peak current limits from 100 mA to 800 mA. These solutions integrate MOS transistors, suitable for isolated and non-isolated applications, support secondary PWM dimming, analog dimming or dual brightness level dimming, energy efficiency Up to 75-80%.
4) High power factor boost scheme for high voltage LED strings
High-voltage multi-junction LEDs are becoming more common, as suppliers tend to better optimize LEDs to improve overall system efficacy and introduce more specialized LEDs. These LEDs have forward voltages of up to 24 to 200 V per package, Can be optimized for spot lighting, omnidirectional lighting or linear lighting. To achieve this goal with low component count and standard off-the-shelf inductors, the NCP1075 monolithic high-voltage switching regulator and high-precision NCP4328A constant current/constant voltage controller are used in the circuit.
The energy efficiency of this solution is higher than 90%, it has a fast startup time of 20 ms, LED open circuit protection, can use existing inductors, power factor is higher than 0.95, and the power capacity is higher than 10 W when using NCP1075, the application is mainly LED bulbs and Lamps, low-power light sources and lamps, Electronic controls and LED drivers.
Figure 3: High Power Factor Boost Scheme for High Voltage LED Strings
5) AC-DC switch controller
Switching controllers for isolated and non-isolated buck, buck/boost converters are the fixed frequency NCP1200, NCP1203, NCP1218, NCP1219, NCP1230, NCP1234/6, NCP1237/8, NCP1250/1/3; Resonant NCP1207A, NCP1308, NCP1337/38, NCP1377, NCP1379/80 and NCP1336. Switching controllers for non-isolated buck converters are LV5011MD, LV5012MD, LV5026MC, LV5029MD, NCL30002 and NCL30105. There are also resonant half-bridge converters Switch controller NCP1392/3, NCP1398 and switch combination controller NCL30051 and NCL30030.
Figure 4: AC-DC switch controller LED drive scheme using NCL30030
6) Offline Buck LED Driver
The NCL30002 is an energy efficient CrM control method supporting high power factor or low ripple buck topologies with 485 mV peak current sensing accuracy ±2% (typ), startup current as low as 24 μA (typ); maximum Vcc up to 20 Vdc; with 500 mA source/800 mA sink MOSFET gate driver; wide operating temperature range -40 to +125°C. Applications include LED bulb (including small candle light) replacement, recessed lighting, interior/exterior accent lighting, and task lighting.
Figure 5: Small Design Using NCL30002
7) Non-isolated offline buck controller
The LV5026MC is a non-isolated off-line buck controller that supports different dimming controls (TRIAC, analog and PWM), selectable switching frequency (50 kHz or 70 kHz), low noise switching system; with short circuit protection, soft start and built-in TRIAC stabilization function. Applications include wall lights, task lights, step lights and LED bulb replacement.
Figure 6: Non-isolated offline buck controller
8) Dimmable LED Driver
The LV5026MC, LV5029MD, LV5011MD, and LV5012MD in the LV50xx are all dimmable LED drivers. Take LV5011MD and LV5012MD as an example, both of them have a switching frequency of 70 kHz, which can improve the power factor, and have the functions of external adjustment of the reference voltage, overvoltage protection, and thermal shutdown. The difference between the two is the dimming mode, which can be used for small dimmable LED bulbs, offline LED drivers, and downlights.
Figure 7: Dimmable LED Driver
9) Constant Current Regulator (CCR) for Non-Isolated Linear LED Driver Topology
One is the low-current LED string driver CCR NSIC2020 (120 V, 20 mA), the current remains constant when the AC voltage rises, and there is no delay in turning on after reaching the LED threshold voltage. The LED brightness is high at low voltage, which can prevent the LED from being subjected to voltage. surge effects. The other is for low-cost T5 LED tube, using CCR NSIC2050 (120 V, 50 mA) LED driver, which can directly AC drive LED, no leakage current, and steady current can protect LED.
Figure 8: Low-Cost T5 LED Tube Circuit
10) LED power supplies for street and area lighting
Instead of high-intensity discharge lamps (HID) or high-pressure sodium lamps (HPS), large LED arrays are used. Depending on the end product, LEDs can be configured in different configurations. One way is to convert the AC input voltage to a DC regulated output and power multiple parallel LED strips. Another approach is to provide constant current to drive the LEDs directly, eliminating the need for a linear or DC-DC conversion section built into the strip.
Figure 9a: Method 1 – Convert AC Input Voltage to DC Regulated Output
The second method is designed to match the “Energy Star” version 1.1 light source specification, and features include: Universal input range 90 – 265 Vac (change element to support 305 Vac); maximum output power 60 W (change element NCL30051 to support up to 250 W power); power factor PF greater than 0.9 (50-100% load, with dimming); harmonic content complies with IEC61000-3-2 class C standard; Iout = 1000 mA/Vf = 35 to 45 V, the energy efficiency is greater than 90 %; constant current output current range 0.7 – 1.5 A; output voltage range 35 – 50 V; output open circuit and short circuit protection, over temperature protection, over current protection – automatic recovery, over voltage protection – input (OVP large voltage) and other protection features .
Figure 9b: Method 2 – Provides constant current to drive LEDs directly
ON Semiconductor leverages its core expertise and strengths in power management, energy-efficient power supplies and packaging to provide control and drive devices that meet various regulatory requirements for LED lighting applications, especially general lighting. These solutions use unique LED driver power architectures, analog and dimming techniques, flyback converters, and non-isolated topologies for a variety of general lighting applications, providing a wealth of options for implementing these devices.