Due to the rapid development in backlight and lighting and other related applications, LED technology, which is based on energy saving, environmental protection and long life, is returning to the ranks of hotspot technology. Although the industry still needs to overcome some technical challenges to improve existing technologies, major semiconductor manufacturers have all launched their own unique solutions.
Face many challenges
For many engineers who have just come into contact with LED technology, how to reduce their footprint in the system and increase the brightness as much as possible is the first problem they face when choosing an LED solution provider. However, as LED technology is still in its infancy, suppliers need to overcome many challenges.
Shone Tran, product marketing manager for Cypress's EZ-Color, believes that device binning, temperature, color calibration, and signal communication may be four major challenges facing semiconductor solution providers for all high-power LED designs. . However, there are some subtle differences in the specific market segments. For example, color calibration, temperature, and signal communication are the most urgent problems to be solved in LED backlights. In automotive lighting, the importance of temperature and color control technology is even higher. As for general lighting, no matter whether it is in terms of aspects, it still needs further development. The perfection.
Tran's views on different market segments are consistent with the opinions of Jiang Jialiang, marketing manager of the power management department in Asia Pacific of ON Semiconductor. The difference is that the latter believes that the cost issue is the most important factor in LED backlighting and general lighting. As for automotive lighting, he pointed out: "The existing solutions must also be continuously strengthened in terms of reliability (such as the ability to withstand harsh ambient temperatures)."
Jiang Jialiang stated that if LED technology wants to make more progress in the field of general lighting, it must consider how to more easily replace existing halogen sources such as halogen lamps and spotlights. "For example, assembling LEDs and conversion circuits into small fixtures," said Timon Rupp, director of LED marketing at OSRAM Opto Semiconductors. OSRAM Opto Semiconductors is currently focusing on the automotive and general lighting markets. Its close relationship with OSRAM, a lighting manufacturer, has made its experience of terminal demand deeper than other suppliers. "LED technology is trying to compete with traditional light sources in the field of general lighting." Rupp said, "The most important challenge for semiconductor suppliers is how to achieve breakthroughs in system integration, such as providing easier to move consumers from traditional light sources. The so-called 'turnkey' or 'plug and play' solution for this emerging technology."
Compared with other respondents, Wu Zhimin, marketing manager of National Semiconductor Asia-Pacific power management products, has to be more specific. "In a backlighting scheme that drives multiple LED strings, current matching between strings is a major challenge. Regardless of LCD TVs or automotive applications, there is a high requirement for contrast," said Wu Zhimin. In addition, he also pointed out that because of the wide application of LEDs in the general lighting field, suppliers must also be able to provide various drivers with a full range of input voltages.
"White LED drivers must be able to supply enough current and voltage for a particular LED configuration and have a conversion topology that meets the input voltage range and the required output voltage and current requirements," said Tony Armstrong, product marketing manager, Linear Power Products Group. . He pointed out that an excellent LED driver must have some or all of the following characteristics: wide output voltage range; high efficiency conversion; tightly regulated LED current matching; low noise, constant frequency operation; independent current and dimming control Compact size, small footprint, and minimal external components.
The main solution
EZ-Color is a flash-based programmable LED driver developed by Cypress last summer for high-brightness (HB) LED smart lighting systems. It can control up to 16 HB-LEDs (CY8CLED16), which is 4 to 5 more than competing products of the same type. In order to speed up the development of the designer as much as possible, the company also provided two design tools called PSoC Express and PSoC Designer. Targeted to entry-level users and embedded design experts who have not previously had any experience in embedded design. The provided evaluation kit (CY3261A-RGB) also provides an interactive graphical interface for quick color mixing via CIE diagrams or direct control of individual HB-LEDs. EZ-Color also has CY8CLED04 and CY8CLED08 which can control 4 and 8 LEDs respectively. It is reported that based on EZ-Color HB-LED driver, the company is also developing an optical feedback solution, which will use color sensors for closed-loop color accuracy compensation.
For high-end mobile flash applications, Osram Opto Semiconductors has developed the CERAMOS and OSLUX product lines. The company also offers OSTAR Lighting for automotive headlamps (OSTAR Lighting) and general lighting products. In particular, the OSTAR Headlamp, which has passed automotive safety certification and has begun sampling, was introduced. It does not use a lens, but with an improved converter and Thinfilm technology enhancements, it achieved peak brightness and power consumption of 620lm and 12W at an operating current of 700mA, and typical brightness values ​​of up to 500lm are also the previous generation products. This is twice as high as any LED currently available. The compact package allows it to be connected to small optics, saving space and giving designers more room for their own use. The company will begin mass production of this product by the end of 2008.
The United States has just released a model LM3433 DC/DC synchronous buck constant-current regulator not long ago, which can provide stable negative current for high power HB-LEDs of projectors and rear projection TVs. Since multiple LED anodes are allowed to be directly connected to the ground, this greatly improves the ability of the circuit to dissipate heat. In addition, the PWM dimming control frequency of over 40 kHz has also led to the realization of digital color temperature control, interference cancellation, field sequential illumination, and brightness control. Due to the fixed on-time, the device does not need to add output capacitance. The company will soon also market a LM3431 3-channel constant current LED driver integrated with a boost controller for automotive and LCD TV backlight applications. It can provide high precision constant current for 3 LED strings (up to 10 LEDs per string). The maximum output current is 150mA, and it can drive 6 LED strings after proper expansion. In order to reduce the voltage drop and increase the efficiency, the LM3431 also uses a cathode feedback voltage regulator control circuit. With PWM dimming, the maximum dimming frequency is 25kHz, and the contrast ratio is 100:1. After further reducing the dimming frequency, the contrast ratio can exceed 1,000:1.
LED applications are diverse and suppliers need to provide a variety of different circuit topologies to achieve optimal program cost and performance in a specific application. Based on this idea, ON Semiconductor has used its LED drivers to increase switching frequency, adopt low-loss topologies, and charge pumps. For example, the NCP1216, based on its experience in charger solutions, can be easily used to build solutions with or without security isolation. As a PWM controller, an external MOSFET can be used for some backlight applications from 10 watts to tens of watts. In addition, the NXP101X series with a built-in MOSFET is ideally suited for smaller applications such as spotlights due to its compact package. The low-voltage DC-DC switching regulator NCP3065 can be used for simple step-down or step-up configurations of LED lamps. In addition, the single-stage PFC controller NCP1651 is also a good choice if PFC and power conversion are needed at the same time.
Linear is also a major supplier to the LED driver market. The LT3595 is the company’s latest high-performance LED driver for large-size TFT-LCD backlighting applications. Up to 160 (16×10) 50mA LEDs can be driven on 16 independent channels. The dimming of each channel can be achieved with a single PWM pin, with a dimming range of 5,000:1 and a circuit matching degree of 16% between 16 channels. The LT3595 also features open-circuit detection and thermal protection. Since all power switches, Schottky diodes, and compensation components are integrated, converter board area and component costs are greatly reduced.
The LTC3212 is another new addition to Linear's RGB LEDs for portable display and lighting applications. It can drive up to 3mA (up to 2.7V to 5.5V input voltage) with a current of up to 25mA. Since only three small capacitors and one to three programming resistors are required, a slim and complete RGB or white LED current controller and power solution can be constructed, which makes it particularly suitable for small battery-powered devices. Its multi-mode charge pump performs low-noise, constant-frequency operation to minimize ripple. Designers can use three separate resistors to set the LED current source, which in turn controls the dimming operation and brightness of the LED. When all 3 RGB LEDs are set to ON, the white mode optimizes the red, green, and blue LED current ratios to achieve optimal white light.
Face many challenges
For many engineers who have just come into contact with LED technology, how to reduce their footprint in the system and increase the brightness as much as possible is the first problem they face when choosing an LED solution provider. However, as LED technology is still in its infancy, suppliers need to overcome many challenges.
Shone Tran, product marketing manager for Cypress's EZ-Color, believes that device binning, temperature, color calibration, and signal communication may be four major challenges facing semiconductor solution providers for all high-power LED designs. . However, there are some subtle differences in the specific market segments. For example, color calibration, temperature, and signal communication are the most urgent problems to be solved in LED backlights. In automotive lighting, the importance of temperature and color control technology is even higher. As for general lighting, no matter whether it is in terms of aspects, it still needs further development. The perfection.
Tran's views on different market segments are consistent with the opinions of Jiang Jialiang, marketing manager of the power management department in Asia Pacific of ON Semiconductor. The difference is that the latter believes that the cost issue is the most important factor in LED backlighting and general lighting. As for automotive lighting, he pointed out: "The existing solutions must also be continuously strengthened in terms of reliability (such as the ability to withstand harsh ambient temperatures)."
Jiang Jialiang stated that if LED technology wants to make more progress in the field of general lighting, it must consider how to more easily replace existing halogen sources such as halogen lamps and spotlights. "For example, assembling LEDs and conversion circuits into small fixtures," said Timon Rupp, director of LED marketing at OSRAM Opto Semiconductors. OSRAM Opto Semiconductors is currently focusing on the automotive and general lighting markets. Its close relationship with OSRAM, a lighting manufacturer, has made its experience of terminal demand deeper than other suppliers. "LED technology is trying to compete with traditional light sources in the field of general lighting." Rupp said, "The most important challenge for semiconductor suppliers is how to achieve breakthroughs in system integration, such as providing easier to move consumers from traditional light sources. The so-called 'turnkey' or 'plug and play' solution for this emerging technology."
Compared with other respondents, Wu Zhimin, marketing manager of National Semiconductor Asia-Pacific power management products, has to be more specific. "In a backlighting scheme that drives multiple LED strings, current matching between strings is a major challenge. Regardless of LCD TVs or automotive applications, there is a high requirement for contrast," said Wu Zhimin. In addition, he also pointed out that because of the wide application of LEDs in the general lighting field, suppliers must also be able to provide various drivers with a full range of input voltages.
"White LED drivers must be able to supply enough current and voltage for a particular LED configuration and have a conversion topology that meets the input voltage range and the required output voltage and current requirements," said Tony Armstrong, product marketing manager, Linear Power Products Group. . He pointed out that an excellent LED driver must have some or all of the following characteristics: wide output voltage range; high efficiency conversion; tightly regulated LED current matching; low noise, constant frequency operation; independent current and dimming control Compact size, small footprint, and minimal external components.
The main solution
EZ-Color is a flash-based programmable LED driver developed by Cypress last summer for high-brightness (HB) LED smart lighting systems. It can control up to 16 HB-LEDs (CY8CLED16), which is 4 to 5 more than competing products of the same type. In order to speed up the development of the designer as much as possible, the company also provided two design tools called PSoC Express and PSoC Designer. Targeted to entry-level users and embedded design experts who have not previously had any experience in embedded design. The provided evaluation kit (CY3261A-RGB) also provides an interactive graphical interface for quick color mixing via CIE diagrams or direct control of individual HB-LEDs. EZ-Color also has CY8CLED04 and CY8CLED08 which can control 4 and 8 LEDs respectively. It is reported that based on EZ-Color HB-LED driver, the company is also developing an optical feedback solution, which will use color sensors for closed-loop color accuracy compensation.
For high-end mobile flash applications, Osram Opto Semiconductors has developed the CERAMOS and OSLUX product lines. The company also offers OSTAR Lighting for automotive headlamps (OSTAR Lighting) and general lighting products. In particular, the OSTAR Headlamp, which has passed automotive safety certification and has begun sampling, was introduced. It does not use a lens, but with an improved converter and Thinfilm technology enhancements, it achieved peak brightness and power consumption of 620lm and 12W at an operating current of 700mA, and typical brightness values ​​of up to 500lm are also the previous generation products. This is twice as high as any LED currently available. The compact package allows it to be connected to small optics, saving space and giving designers more room for their own use. The company will begin mass production of this product by the end of 2008.
The United States has just released a model LM3433 DC/DC synchronous buck constant-current regulator not long ago, which can provide stable negative current for high power HB-LEDs of projectors and rear projection TVs. Since multiple LED anodes are allowed to be directly connected to the ground, this greatly improves the ability of the circuit to dissipate heat. In addition, the PWM dimming control frequency of over 40 kHz has also led to the realization of digital color temperature control, interference cancellation, field sequential illumination, and brightness control. Due to the fixed on-time, the device does not need to add output capacitance. The company will soon also market a LM3431 3-channel constant current LED driver integrated with a boost controller for automotive and LCD TV backlight applications. It can provide high precision constant current for 3 LED strings (up to 10 LEDs per string). The maximum output current is 150mA, and it can drive 6 LED strings after proper expansion. In order to reduce the voltage drop and increase the efficiency, the LM3431 also uses a cathode feedback voltage regulator control circuit. With PWM dimming, the maximum dimming frequency is 25kHz, and the contrast ratio is 100:1. After further reducing the dimming frequency, the contrast ratio can exceed 1,000:1.
LED applications are diverse and suppliers need to provide a variety of different circuit topologies to achieve optimal program cost and performance in a specific application. Based on this idea, ON Semiconductor has used its LED drivers to increase switching frequency, adopt low-loss topologies, and charge pumps. For example, the NCP1216, based on its experience in charger solutions, can be easily used to build solutions with or without security isolation. As a PWM controller, an external MOSFET can be used for some backlight applications from 10 watts to tens of watts. In addition, the NXP101X series with a built-in MOSFET is ideally suited for smaller applications such as spotlights due to its compact package. The low-voltage DC-DC switching regulator NCP3065 can be used for simple step-down or step-up configurations of LED lamps. In addition, the single-stage PFC controller NCP1651 is also a good choice if PFC and power conversion are needed at the same time.
Linear is also a major supplier to the LED driver market. The LT3595 is the company’s latest high-performance LED driver for large-size TFT-LCD backlighting applications. Up to 160 (16×10) 50mA LEDs can be driven on 16 independent channels. The dimming of each channel can be achieved with a single PWM pin, with a dimming range of 5,000:1 and a circuit matching degree of 16% between 16 channels. The LT3595 also features open-circuit detection and thermal protection. Since all power switches, Schottky diodes, and compensation components are integrated, converter board area and component costs are greatly reduced.
The LTC3212 is another new addition to Linear's RGB LEDs for portable display and lighting applications. It can drive up to 3mA (up to 2.7V to 5.5V input voltage) with a current of up to 25mA. Since only three small capacitors and one to three programming resistors are required, a slim and complete RGB or white LED current controller and power solution can be constructed, which makes it particularly suitable for small battery-powered devices. Its multi-mode charge pump performs low-noise, constant-frequency operation to minimize ripple. Designers can use three separate resistors to set the LED current source, which in turn controls the dimming operation and brightness of the LED. When all 3 RGB LEDs are set to ON, the white mode optimizes the red, green, and blue LED current ratios to achieve optimal white light.
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