With its advantages of energy saving, long service life and rich color combination, LED has become one of the fastest growing semiconductor fields. In recent years, the annual compound growth rate (CAGR) is as high as 20%. It is expected that the global LED market will be even more in 2012. It will reach $11.4 billion and the prospects are very impressive.
Typical LED drivers on the market include two types, linear drivers and switch drivers; and further subdivided, there are three types, switching regulators, linear regulators, and resistive drivers. These three drivers are suitable for different levels of current applications, see Figure 1. High-current applications with currents greater than 500 mA use switching regulators because linear drivers are limited to their own structure and cannot provide such large currents. In low-current applications with currents below 200 mA, linear regulators are often used. Resistive drivers; in medium current applications from 200 to 500 mA, either linear regulators or switching regulators are available.
Figure 1: LED driver for different current ranges
Switching regulators offer high performance and excellent brightness control. The linear regulator structure is simple, easy to design, provides steady current and overcurrent protection, has an external current set point, and has no electromagnetic compatibility (EMC) problems. Resistive drivers use a simple discrete component such as a resistor to limit the LED string current. This is an economical LED driver solution that is equally easy to design and has no EMC issues.
ON Semiconductor offers a wide selection of switching regulators and linear regulators for different LED applications. And customers on the market also need a driver that is more economical than switching regulators and common linear regulators, but much more powerful than resistive drivers. In this case, ON Semiconductor is using it. The patented self-biasing transistor (SBT) technology, combined with its superior process control capabilities, introduces a new LED driver solution, the Discrete Linear Constant Current Regulator (CCR), which fills this market gap. Further enriched ON Semiconductor's broad lineup of LED driver products.
Low current LED application and driver comparison
The new linear constant current regulators are suitable for low current LED applications from 20 mA to 200 mA. As in automotive applications, the current requirements for combined taillights are typically only tens of milliamperes (mA). In addition, in commercial and industrial applications such as Kanban text circuits and backlit display cards, the input voltage is typically as high as 30 Vdc and the LED current is between 20 mA and 150 mA. In buildings such as decorative lighting, work lights, landscape lighting, counter lighting, and general lighting applications, the input voltage is typically 12 to 48 Vac or 120/220 Vac, and the LED current is only between 20 and 100 mA. In addition, LEDs such as refrigerators and washing machines also use LEDs for small LCD screen backlights or alternative lighting bulbs. Such applications also require low current LED drivers.
In low-current LED applications, the resistive driver, although low in cost and simple in structure, has a low forward current under low voltage conditions, which causes LED brightness to be insufficient and under transient conditions such as load dump. The LED may be damaged. In addition, this solution requires proper LED coding, high resistance inventory, and low performance.
Compared to resistive drivers, linear constant current regulators provide regulated current, provide constant brightness over a wide voltage range, protect LEDs from overdrive at high input voltages, and provide higher output at low input voltages. brightness. Thanks to its constant current characteristics, customers can reduce or eliminate the coding costs of different LEDs from different suppliers, resulting in lower total system cost.
Figure 2: CCR combines a resistor driver with a linear regulator to fill the gap
We can verify the performance comparison of the two drivers through actual tests, as shown in Figure 3. The test compares the combined taillights implemented with these two drivers, where the CCR is a 25 mA constant current component. As can be seen from the figure, at the same 9 V input voltage, the CCR has a higher current than the resistive driver, making the LED brighter. At the same voltage input of 13 V, the brightness is the same. After the voltage is higher than 13 V, the current of the CCR gradually flows to 25 mA, while the current of the resistive driver rises, which may cause the LED to overdrive and damage the LED. In addition, CCR provides a current accuracy of ±10%, which fully meets the application requirements, while the resistance type current accuracy is only ±50%, which is a far cry.
Figure 3: Comparison of VI curves between a resistive driver and a linear constant current regulator with a regulated current of 25 mA
Simple, economical and robust linear constant current regulator based on patented SBT technology ON Semiconductor's linear constant current regulator is based on ON Semiconductor's patented self-biased transistor (SBT) technology, which provides a degree of Integration, combined with ON Semiconductor's superior process control capabilities, provides simple, economical and Robust LED driver solutions for low current applications.
Specifically, the dual end of this component is very easy to design, suitable for high-side and low-side applications, and requires no external components, very simple. Its economy is mainly reflected in eliminating LED coding, reducing inventory costs, and protecting LEDs, reducing replacement and maintenance costs. ON Semiconductor also plans to introduce a linear constant current regulator with three-terminal adjustable output. Their structure is shown in Table 1.
It is worth mentioning that ON Semiconductor's linear constant current regulator supports 120/220 Vac power supply. For buildings and general lighting applications, the electrical input after 120/220 Vac AC is only required for bridge rectification. After the input voltage is subtracted from the total voltage of the LED string, the remaining voltage does not exceed the maximum anode-cathode voltage VAK of the linear constant current regulator 45 V. This also shows its easy-to-design features.
In terms of ruggedness, this series of components from ON Semiconductor is outstanding. For example, it is designed with a negative temperature coefficient (NTC) to protect the LED from thermal runaway at extreme voltages and operating temperatures. For example, the SOT-223 surface mount package measures 7.0 mm x 6.5 mm x 1.6 mm and dissipates 630 mW of power on a 500 mm long/less than 29 gram copper plate at 85 °C. Ideal for extreme thermal work environments. In addition, these components are certified to the rigorous AEC101 automotive standard for demanding automotive applications. These components are also subject to switching transients and voltage spikes and have a good electrostatic discharge (ESD) rated pulse rating of 1.8 kV. In addition, these components are environmentally friendly, use halogen-free mold compounds, and meet the lead-free RoHS directive.
ON Semiconductor's first NSI45 series of 10 dual-ended linear constant current regulators were introduced in May 2009. These components provide ±10% and ±15% steady-state steady current (Ireg) tolerances with a voltage rating of 45. V, operating temperature range -40 ° C to 85 ° C, maximum junction temperature of 150 ° C, providing 20 mA, 25 mA and 30 mA components and other options, in SOD-123 and SOT223 packages, the target market includes internal and automotive applications External LED lighting, xenon lamp replacement for commercial signage applications, traffic signals, etc., and screen backlighting, flat panel AC lighting, work and decorative lights, landscape and outdoor lighting in buildings and general lighting applications.
Table 1: Dual- and three-terminal linear constant current regulators that ON Semiconductor has introduced and planned
Table 1 lists the main parameters of ON Semiconductor's NSI450 series linear constant current regulators, including dual-ended components such as the NSI450XXT1G (SOT123 package, 20/25 /30 mA), NSI450XXZT1G (SOT223 package, 25/30). mA), available in existing samples and in volume production; also available in three-terminal components such as the NSI450XXZT1G (SOT223 package, 30 to 80 mA adjustable) and NSI450XXT1G (D-PAK package, 80 to 150 mA adjustable), to be released in 2009 Samples were provided in the third quarter of the year and were mass produced in the fourth quarter.
to sum up:
As the world's leading provider of high-performance, high-performance silicon solutions, ON Semiconductor has a proven track record of delivering more than 32 billion components per year through manufacturing facilities around the world, with advanced process and technical capabilities. ON Semiconductor is also familiar with its customers, has established extensive and in-depth relationships with a wide range of international and local customers, and serves customers with design support centers around the world. ON Semiconductor's broad portfolio of products and solutions spans standard products, proprietary solutions, proprietary standard products and custom ASIC solutions, as well as automotive, computer and game consoles, portable consumer products, media and entertainment, and industrial Markets for applications such as medical, high-voltage communications, military and aerospace.
All of the above applications in ON Semiconductor's services involve LED lighting/backlighting. And ON Semiconductor uses a wide range of technologies to provide solutions for a wide range of LED lighting applications, leveraging the core strengths of high-performance power solutions. ON Semiconductor's new simple, economical and rugged linear constant current regulator solution for low current LED lighting applications broadens ON Semiconductor's existing LED drivers including switching regulators and common linear regulators The product lineup is ideal for automotive interior/external lighting, commercial signage and building LED lighting applications.
(Editor: Zeng Cong)
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