Choose the right LED driver power solution for different power applications

In recent years, the high brightness light emitting diode (HB-LED) market has developed rapidly. The LED light efficiency has been increasing, and the average cost per lumen of light output has continued to decline, which has led to the continuous expansion of its application range. In addition to its dominant position in applications such as portable device backlighting with a screen size of less than 4 inches and large display screens in sports stadiums, it has also penetrated into the automotive, medium and large size liquid crystal display (LCD) backlighting and general lighting markets, and has a very promising development prospect.

Taking the general lighting market such as replacement of light bulbs and fluorescent tubes, recessed lights, street lights and parking lights, work lights (desk lamps, cabinet lighting), landscape lighting, billboard text circuits, and building lighting as an example, it is estimated that the current application ratio of LED lighting (or solid-state lighting, English abbreviation SSL) is less than 1%, and the market size (SAM) of LED drivers and related discrete devices in 2008 was only about US$688 million. It is expected that the market size will grow to US$1.308 billion by 2012, with an annual compound growth rate of up to 17.4%. Therefore, LED general lighting has become a hot market.

This article aims to explore the requirements of different power ranges and different power supply applications in the LED general lighting market, as well as applicable LED drivers and related components, to help lighting design engineers choose the right component solutions and speed up the listing process.

Requirements and solutions for AC-DC powered LED general lighting applications
of different powers The power supply topologies suitable for AC-DC LED lighting applications of different powers are different. For example, in applications with power below 80 W, the flyback topology is the standard choice; while in applications that require high energy efficiency, the resonant half-bridge dual inductor plus single capacitor (HB LLC) is the first choice. ON Semiconductor provides AC-DC LED lighting solutions covering a wide power range. Table 1 lists several typical ON Semiconductor AC-DC LED lighting solutions.

From the perspective of application power levels, AC-DC powered LED general lighting applications include low power, medium power and high power. Low power applications usually have a power range of 1 to 12 W, medium power covers a range of 8 to 40 W, and high power applications often have a power of more than 40 W.

1) 1 W to 8 W LED general lighting application requirements and solutions
In terms of 1 W to 8 W low-power LED general lighting, typical applications include G13, GU10, PAR16, PAR20 and recessed lights. The input voltage range of this type of application is between 90 and 264 V AC, the constant current output current includes 350 mA and 700 mA, the energy efficiency requirement is 80%, and protection features such as short-circuit protection and overvoltage protection are required.

In such applications, ON Semiconductor's NCP1015 self-powered monolithic switch control IC can be used. This device integrates a fixed frequency (65/100/130 kHz) current mode controller and a 700 V high-voltage MOSFET, providing all the features required to build a robust and low-cost power supply, such as soft start, frequency jittering, short-circuit protection, cycle skipping, maximum peak current set point, and dynamic self-power function (no auxiliary winding required).

It is worth mentioning that NCP1015 can be used in both isolated and non-isolated solutions in 1 W to 8 W LED lighting applications to meet different application requirements of customers. The cost of these two solutions is similar. However, the isolated solution uses a transformer to achieve electrical isolation. The solution contains a simple feedback circuit and a clamping circuit for load open circuit and fault protection. It is highly safe and more suitable for applications that require safety certification. The non-isolated solution uses a tapped inductor to isolate the AC signal, which can increase the duty cycle of the MOSFET and improve the system energy efficiency and circuit performance.

The above-mentioned isolated and non-isolated solutions based on NCP1015 do not contain PFC, but ON Semiconductor also provides NCP1015/NCP1014 solutions with PFC to provide customers with more choices. [page]

2) 8W to 25W LED General Lighting Application Requirements and Solutions: No PFC vs. PFC
In 8W-25W AC-DC LED lighting applications, we need to consider two situations. One is that the application does not require power factor correction (PFC). On the other hand, the U.S. Department of Energy (DOE) "Energy Star" solid-state lighting (SSL) specification stipulates that power factor correction (PFC) must be mandatory for any power level. This standard applies to a series of specific products, such as recessed lights, cabinet lights, and table lamps, among which the LED driver power factor must be greater than 0.7 for residential applications and greater than 0.9 for commercial applications. However, this standard is a voluntary standard, and you can choose not to comply or comply. Therefore, another situation to consider is the requirement of PFC.

In the 8 W to 25 W AC-DC LED lighting that does not require PFC, typical applications include PAR30, PAR38 and recessed lights. In such applications, the input voltage requirement is 85~135 Vac or 185~264 Vac (or universal input), the energy efficiency requirement is greater than 80%, and protection features such as short-circuit protection and open-circuit protection are provided. The constant current output current is 350 mA, 700 mA and 1 A. Accordingly, ON Semiconductor's NCP1028 or NCP1351 can be used, as shown in Figure 2.

Among them, NCP1028 is an enhanced monolithic switch control IC that provides 800 mA peak current, as well as over-power protection, built-in slope compensation and input undervoltage protection. It is suitable for providing output power of several watts to 15 W in applications with universal wide power input. In addition to the non-PFC solution based on NCP1028, ON Semiconductor now also provides a PFC solution based on NCP1028. NCP1351 is a fixed on-time, variable off-time pulse width modulation (PWM) controller suitable for cost-critical low-power offline flyback switching power supply applications. This device supports frequency retracement and also has features such as latch input, natural frequency jitter, negative current sensing and an extended power supply voltage range.

In terms of 8 W to 25 W AC-DC LED lighting that requires PFC, typical applications are also PAR30, PAR38 and recessed lights. The input voltage specification of this type of application is 90 to 264 Vac, the energy efficiency requirement is 80%, and it supports 350 mA, 700 mA and 1 A constant current output, provides short circuit and overvoltage protection, and the power factor requirement is higher than 0.9. This type of application is suitable for ON Semiconductor's NCL30000 single-stage power factor correction LED driver. The single-stage topology saves a dedicated PFC boost stage, reduces the number of components, and helps reduce the total system cost. The NCL30000 provides a power factor higher than 0.9 and meets the IEC Class C harmonic content requirements. This device can directly drive LEDs with precise constant current output control, with an efficiency higher than 80% at lower output powers of 5 to 15 W, a typical efficiency higher than 83%, and supports existing dimming schemes such as TRIAC.

3) Requirements and solutions for 50 W to 200 W LED general lighting applications
AC-DC LED applications with power above 50 W are widely used in street lighting and high-power area lighting. Different LED solutions can be used for the power range of 50 W-150 W or 100 W -200 W. Assume that its input voltage specification is 90--264 Vac, the power factor is higher than 0.9, the energy efficiency is greater than 85%, short circuit and overvoltage protection are provided, and constant current output of 350 mA, 700 mA and 1 A is provided. Such applications can adopt the following different solutions to meet different needs:
NCL30001: single-stage PFC LED driver;
NCP1607+NCP1377: CrM PFC+ QR PWM;
NCP1607+NCP1397 or NCP1392/3: CrM PFC+ LLC PWM.

[page]

Take NCL30001 as an example, which is a current continuous mode (CCM) controller for single-stage power factor correction LED drivers in the power range of 40 W to 150 W. This device supports adjustable switching frequency from 20 to 250 kHz, supports frequency jitter and voltage feedforward, includes input undervoltage and overload timers, provides high energy efficiency and high power factor and strong protection features. Figure 4 is a typical application circuit diagram of NCL30001.

It is worth mentioning that in recent years, the industry has shown a growing interest in ultra-high-efficiency LED lighting topologies, expecting to provide energy efficiency above 90% at relatively low power levels (<50 W). This energy efficiency target is even higher than the "Energy Star" 2.0 version external power supply energy efficiency requirements (energy efficiency above 87% when the power does not exceed 49 W). To achieve such high energy efficiency, new topologies need to be adopted, such as switching from a flyback topology to a resonant half-bridge topology, so as to give full play to the advantages of zero voltage switching (ZVS). Fortunately, ON Semiconductor has already begun to develop high-efficiency half-bridge solutions that can be used for LED driver power supplies, such as the NCP1396 and its upgraded version, the NCP1397 high-performance resonant mode controller. The NCP1397 has built-in high-end and low-end drivers, supports adjustable and precise minimum frequencies, provides extremely high energy efficiency, and has a variety of fault protection features.

Requirements and solutions for general lighting applications
of DC-DC-powered LEDs with different powers For DC-DC-powered LED lighting applications, the discussion can also be carried out according to different power ranges.
4) 1 W-3 W DC-DC LED buck applications
Typical 1 W-3 W DC-DC LED buck lighting applications include MR11/MR16, automotive lighting, solar power supply, etc. The input voltage of this type of application is 5 to 28 Vdc, supports 350 mA and 700 mA constant current output, the frequency is 500 kHz to 2 MHz, the energy efficiency is not less than 90%, and the operating temperature range is -40℃ to 125℃. In this type of application, the CAT4201 buck LED driver from ON Semiconductor can be used. This device has a patented switch control architecture that can drive 7 series LEDs (at 24 V input), with an energy efficiency of up to 94%, and provides protection features such as LED open circuit protection, current limiting and overheating protection.

5) 1 W-30 W DC-DC LED buck applications
Typical 1 W-30W DC-DC LED buck applications include secondary-side DC-DC LED drivers in MR16 spotlights and street lighting. In such applications, the input voltage range is 7 to 120 Vdc, the output voltage range is 6 to 110 Vdc, and it supports 350 mA, 700 mA or 1 A constant current output, with an energy efficiency of not less than 90%. Such applications can use ON Semiconductor's NCL30100 buck LED driver, which has an external switching MOSFET, provides flexible input voltage and output current design, and has an energy efficiency of more than 95%. The application circuit diagram is shown in Figure 6(a).

6) 1 W-20 W DC-DC LED boost applications
Typical 3 W-20 W DC-DC LED boost applications are common in DC-DC LED drivers. The input voltage of this type of application is 5 to 28 Vdc, supports 350 mA or 700 mA constant current output, and the energy efficiency is not less than 90%. This type of application can use ON Semiconductor's NCP3065/NCP3066 LED driver. NCP3065/NCP3066 can be configured as buck, boost, single-ended primary inductor converter (SEPIC) and inverter modes, and provides a corresponding automotive application version, namely NCV3065/NCV3066. Figure 6(b) shows the boost configuration LED application circuit diagram of NCP3066.

7) 1 W-3 W flashlight LED boost/buck applications
1 W-3 W flashlight LED applications include both boost and buck types. The input voltage range for boost applications is 1 to 2.5 Vdc, and the operating frequency is up to 1.2 MHz; the input voltage range for buck applications is 4 to 5.5 Vdc, and the frequency is up to 1.7 MHz. Both types of applications need to support 350 mA or 600 mA constant current output, and the energy efficiency is higher than 90%. In 1-3 W flashlight boost LED applications, ON Semiconductor's NCP1421 boost DC-DC converter can be used. In flashlight buck LED applications with the same power range, ON Semiconductor's NCP1529 low-voltage buck converter can be used. The application circuit diagrams are shown in Figure 7(a) and Figure 7(b), respectively.

[page]

Linear constant current regulators especially suitable for low current LED lighting applications
The previous article discussed the requirements of LED applications in different power ranges and the suitable driving power supply solutions according to different power supply types. However, looking at different LED lighting applications, it can be found that there is a category of applications that focus on low current applications, such as commercial and industrial signage, automotive parking lights and taillights, and architectural and decorative lighting. Common driving solutions for such low current LED applications include low voltage drop linear regulators and resistors. These two driving solutions have their own advantages and disadvantages.

Fortunately, ON Semiconductor has introduced a new low-current LED drive solution, the NSI45 series of two-terminal and three-terminal linear constant current regulators (CCRs), using patent-pending self-biased transistor (SBT) technology combined with its own superior process control capabilities. This solution is simpler and lower cost than a linear regulator, but its performance is greatly improved compared to the resistor solution, filling the market gap. The NSI45 series offers many advantages, such as maintaining constant brightness over a wide voltage range, protecting LEDs from overdrive when the input voltage is high, making LEDs brighter when the input voltage is low, helping to reduce or eliminate LED coding inventory, and helping to reduce total system cost, etc., making it very suitable for low-current LED current applications.

Other products and solutions in LED lighting applications
As we all know, LED lighting systems are relatively complex, involving different areas such as optics, electricity and heat. As the leading supplier of high-performance, energy-efficient silicon solutions for green electronic products, ON Semiconductor provides complete LED lighting solutions, including communication, light sensors, MOSFETs, rectifiers, protection, filters and thermal management products in addition to driver power supplies, see Figure 8.

For example, applications such as LED ambient light and street light intensity control, LED backlight intensity control, and display white balance control require extremely low-power ambient light sensors and require the light sensors to support accurate low-light level operation, especially in the presence of light filtering. In such applications, ON Semiconductor provides an optoelectronic product portfolio that includes light sensors, LED drivers, and high-speed I2C interfaces. The light sensor products include NOA1211 (analog output), NOA1302 (digital output), and NOA1305 (digital output). The operating current of these light sensors is extremely low, only 58 μA, 550 μA, and 115 μA respectively at 100 lumens of light output.

In addition, in order to reduce the subsequent maintenance costs, applications such as LED street lights can add protection devices to the application, such as the NUD4700 from ON Semiconductor, which provides bypass current when an LED open-circuit fault condition occurs to ensure the normal operation of other LEDs. If heat dissipation is properly handled, it can also support currents greater than 1 A. In addition, under the trend of smart grids, engineers can also use products such as ON Semiconductor's AMIS-30585 and AMIS-49587 power line carrier (PLC) modems and NCS5650 PLC line drivers in LED networked street light applications. In addition, ON Semiconductor's BC858CDXV6T1G bipolar junction transistor (BJT) can also be used for low-energy constant current sensing in LED lighting applications.

Summary:
With the emergence of cost-effective, ultra-high brightness LEDs, solid-state lighting has developed rapidly in recent years. Accordingly, lighting design engineers need to choose different LED driver power solutions based on the power supply, lamps, power range and LED configuration. From a system perspective, ON Semiconductor provides high-reliability products that take into account multiple factors such as electricity, heat and light, including a wide range of AC-DC and DC-DC powered high-efficiency LED driver solutions, as well as light sensors, filtering, protection and networking products, to provide customers with complete LED lighting solutions.

As a leading global supplier of high-performance, energy-efficient silicon solutions, ON Semiconductor provides LED lighting driver and PFC solutions covering a power range of 1 to hundreds of watts. Regardless of whether the LED lighting application uses an AC-DC power supply, a DC-DC power supply or a battery used in an LED flashlight, it meets customers' different requirements for low cost, high cost performance, high energy efficiency or the choice of whether to add PFC.