Ten AC-DC LED general lighting design solutions "comparison"

According to market research institutions, China's demand for LED general lighting will reach US$10 billion by 2015 and US$22 billion by 2020. It is an inevitable trend for LED lighting to gradually replace traditional lighting. However, LED general lighting has many challenges, such as power density, power factor correction (PFC), space constraints and reliability. ON Semiconductor is committed to providing a wide range of solutions for LED lighting, launching a variety of products that meet the latest LED lighting standards, including AC-DC  LED driver power solutions for general lighting.

　　General Lighting Challenges and AC Mains Powered LED Driver Topologies

　　Energy efficiency is particularly important for low-power applications due to the total LED light efficiency requirements and heat dissipation limitations; in many cases, even lower power applications require power factor correction and harmonic processing; in space-constrained applications, especially replacement bulb applications, high drive power density is required; overall power reliability is very important for the entire lamp life; wide input power voltage range should support up to 277 Vac; compatible with TRIAC dimming and other requirements. In addition, LED general lighting must also meet evolving standards and safety specifications, such as "Energy Star" and IEC requirements.

　　There are many topologies for driving LEDs from AC mains power, depending on the application requirements (size, efficiency, power factor, power, drive current). ON Semiconductor offers a variety of power solutions that can be used in a variety of lighting applications.

　　Figure 1: Different AC mains powered LED driver topologies

　　Ten different AC-DC solutions for LED general lighting

　　1) Power factor correction solution

　　The 160 W power factor correction (PFC) boost solution using ON Semiconductor's NCP1611 or NCP1612 adopts a non-isolated boost topology, with higher light load efficiency than traditional CrM PFC; no additional components are required, and the reliability and safety are high. The solution uses current-controlled frequency foldback (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 harmonic distortion configuration, overtemperature shutdown and other features.

　　This type of PFC solution also includes 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 stabilization" topology can choose two configurations, one is buck configuration (including tapped inductor buck configuration); the other is buck-boost configuration, the inductor is not connected in series with the LED string, and the input current waveform or distortion has nothing to do with the output voltage drop. It can perform primary thyristor dimming and is suitable for isolated and non-isolated solutions. The energy efficiency of the isolated solution is 80~85%.

　　2) Primary-side control offline solution

　　Primary-side current regulation (PSR) is also called primary-side control. Primary-side control offline LED drivers do not use optocouplers and have ±1% (typical) precision LED current regulation accuracy, wide VCC range, high-efficiency quasi-resonant control, a strong combination of protection features, and a wide operating temperature range (-40 to +125°C); support flyback and buck-boost topologies, with a power factor of about 0.9 with passive PFC input; this series can be used for LED bulb replacement, offline LED drivers , recessed lights, indoor/outdoor accent lighting and task lights, and LED electronic control devices.

　　Figure 2: Primary-side control offline solution

　　The 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 triggered 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, etc. These devices are all current mode, with peak current limit from 100 mA to 800 mA. These solutions integrate MOS tubes and are suitable for isolated and non-isolated applications. They support secondary PWM dimming, analog dimming or dual brightness level dimming, and have energy efficiency of up to 75~80%.

　　4) High power factor boost solution for high voltage LED strings

　　High-voltage multi-junction LEDs are becoming more common as suppliers tend to better optimize LEDs to improve the overall system efficacy and introduce more specialized LEDs. These LEDs have a forward voltage of 24 to 200 V per package and can be optimized for spot lighting, omnidirectional lighting, or linear lighting. To achieve this goal with a low component count and standard off-the-shelf inductors, the NCP1075 monolithic high-voltage switching regulator and the high-precision NCP4328A constant current/constant voltage controller are used in the circuit.

　　The solution has an efficiency of over 90%, a fast start-up time of 20 ms, LED open-circuit protection, can use existing inductors, a power factor of over 0.95, and a power capability of over 10 W when using NCP1075. Applications are mainly LED bulbs and tubes, low-power light sources and lamps, electronic control devices and LED drivers.

　　Figure 3: High power factor boost solution for high voltage LED strings

　　5) AC-DC switching controller

　　The switch controllers for isolated and non-isolated buck and buck/boost converters include fixed-frequency NCP1200, NCP1203, NCP1218, NCP1219, NCP1230, NCP1234/6, NCP1237/8, NCP1250/1/3; and quasi-resonant NCP1207A, NCP1308, NCP1337/38, NCP1377, NCP1379/80 and NCP1336. The switch controllers for non-isolated buck converters include LV5011MD, LV5012MD, LV5026MC, LV5029MD, NCL30002 and NCL30105. In addition, there are switch controllers NCP1392/3 and NCP1398 for resonant half-bridge converters and switch combination controllers NCL30051 and NCL30030.

　　Figure 4: AC-DC switch controller LED drive solution using NCL30030

　　6) Offline Buck LED Driver

　　NCL30002 is a high-efficiency CrM control method that supports high power factor or low ripple buck topology, with 485 mV peak current sensing accuracy ±2% (typical), startup current as low as 24 μA (typical); maximum Vcc up to 20 Vdc; with 500 mA source/800 mA sink MOSFET gate driver; wide operating temperature range -40 to +125℃. Its applications include LED bulb (including small candle lamp) replacement, recessed lights, indoor/outdoor accent lighting and task lights.

　　Figure 5: Small design using NCL30002

　　7) Non-isolated Offline Buck Controller

　　The LV5026MC is a non-isolated offline buck controller that supports different dimming controls (TRIAC, analog and PWM), selectable switching frequency (50 kHz or 70 kHz), low noise switching system; short circuit protection, soft start and built-in TRIAC stabilization. Applications include wall lamps, task lamps, step lamps 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 . Taking LV5011MD and LV5012MD as examples, both have a switching frequency of 70 kHz, which can improve the power factor, and have externally adjustable reference voltage, overvoltage protection, and overheating shutdown functions. The difference between the two lies in the dimming mode, and both can be used for small dimmable LED bulbs, offline LED drivers, and recessed lights.

　　Figure 7: Dimmable LED driver

　　9) Constant Current Regulator (CCR) for Non-Isolated Linear LED Driver Topology

　　One is a low-current LED string driver CCR NSIC2020 (120 V, 20 mA), which keeps the current constant when the AC voltage rises, turns on without delay after reaching the LED threshold voltage, and has high LED brightness at low voltage, which can prevent the LED from being affected by voltage surges. The other is used for low-cost T5 LED tubes, using CCR NSIC2050 (120 V, 50 mA) LED driver, which can directly drive the LED with AC, without leakage current, and the steady current can protect the LED.

　　Figure 8: Low-cost T5 LED tube circuit 10) 　　LED power supply for street and area lighting

　　To replace 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 structures. One method is to convert the AC input voltage to a DC regulated output and power multiple parallel LED light strips. Another method is to provide a regulated constant current to drive the LED directly, eliminating the linear or DC-DC conversion stage built into the light strip.

　　Figure 9a: Method 1 - Converting AC input voltage to DC regulated output

　　The second method is designed to comply with the Energy Star 1.1 version of the light source specification, and its features include: universal input range of 90 - 265 Vac (changing components can support 305 Vac); maximum output power of 60 W (changing the component NCL30051 to support up to 250 W); power factor PF greater than 0.9 (50-100% load, with dimming); harmonic content complies with IEC61000-3-2 class C standard; energy efficiency greater than 90% under the condition of Iout = 1000 mA/Vf = 35 to 45 V; constant current output current range of 0.7~1.5 A; output voltage range of 35 - 50 V; output open 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 - Providing a regulated constant current to directly drive the LED

　　Summarize

　　ON Semiconductor uses its core expertise and advantages in power management, high-efficiency power supplies and packaging to provide control and driver devices that meet various regulatory requirements for LED lighting applications, especially general lighting. These solutions use unique LED driver power architecture, analog and dimming technology, flyback converters and non-isolated topologies, which are suitable for various general lighting applications and provide a wealth of options for the implementation of these devices.