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Typical scheme and Application Analysis: linear LED driver

among many lighting applications, linear LED driver is the preferred scheme with a large range of traditional industries in our province, because they are relatively simple and easy to design, and enable led to be driven with accurate current stabilization current, regardless of the change of led forward voltage drop or input voltage. Since drives are linear, they must match the power dissipation requirements of the application. Ansenmey Semiconductor provides a wide range of linear LED driver schemes with current range from 10 Ma to 1 A, including a novel linear constant current regulator (CCR) scheme and many other linear driver schemes

linear CCR for low current LED driving and application examples

in many low current LED applications with current lower than 350 Ma, such as automobile combined tail lights, neon red light replacement, traffic signal lights, large display backlight, building decorative lights and indicators, ordinary linear regulators or resistors can be used to provide LED driving solutions. The resistor is used to limit the current of the LED string. It is the lowest cost scheme, easy to design, and has no electromagnetic compatibility problems. However, when using resistors, the forward current of the LED is determined by the voltage. Under low voltage conditions, the forward current is low, which will lead to insufficient brightness of the LED, and the LED may be damaged under transient conditions such as sudden load drop. The resistance scheme also has the lowest energy efficiency, which is not conducive to energy saving, especially in applications that emphasize high and low energy consumption. In addition, the resistance scheme also has led thermal runaway and screening problems. The linear voltage regulator scheme provides better current stabilization accuracy (± 2%), supports over-power self-regulation, and has no EMI problem. This scheme has low energy efficiency and moderate cost

customers need a drive scheme that is more economical than ordinary linear regulators, but has much higher performance than resistors. By using the patent pending self bias transistor (SBT) technology and combining its strong process control ability, ansenmey semiconductor has introduced a novel LED driving scheme - nsi45 series linear constant current regulator (CCR). Compared with the resistance, the linear CCR has constant brightness over a wide voltage range, protects the LED from overdrive at high input voltage, and provides higher brightness at low input voltage. Thanks to its constant current characteristic, customers can reduce or eliminate the coding cost of different LEDs provided by different suppliers and reduce the total system cost. CCR also has no EMI problem. It is packaged with high power density and has passed aec-q101 certification in the automotive industry

the CCR of ansenmey semiconductor includes two types: two terminal fixed output and three terminal adjustable output. The current levels cover 10 to 350 Ma and 20 to 160 Ma respectively. The maximum anode cathode voltage VAK is 50 V and 45 V respectively. High VAK voltage helps suppress surges and protect LEDs. This series of CCRs have no voltage offset before current flow, and their fast on/off characteristics provide wide range and accurate pulse width modulation (PWM) dimming capability. There is no "plug and play" device like CCR in the market. Other devices need a minimum voltage of 0.5 V to be turned on, instead of being turned on immediately like CCR (see Figure 1 on the left). CCR can provide accurate PWM dimming with external bipolar transistor (BJT) (see Figure 1 on the right). The typical PWM dimming frequency is 0.1 to 3 kHz. There is no color drift in the dimming process, because the LED is always conducted with optimized current

figure 1:comparison of ireg VIN curve between 25 mA CCR and competitive devices (left); Example of CCR dimming application (right)

ccr has a negative temperature coefficient (NTC) feature to protect the LED from thermal runaway under extreme voltage and operating temperature. CCR is easy to design and suitable for high side and low side applications (see Figure 2a). It does not need external components. It is very simple and suitable for a wider range of applications; In comparison, some suppliers provide functions or performance similar to that of ansenmey semiconductor CCR that can be analyzed in terms of the functions and characteristics of this experimental machine, but require additional external components, cannot be configured as high-end or low-end drivers, different packaging or poor thermal reliability

figure 2:ccr can be flexibly used for high-end or low-end drive, and can also drive multiple strings of LEDs.

ccr can also be used to drive multiple strings of LEDs (see figures 2B and 2C). It can also be used for both high-end and low-end. Figure 2B shows an application example of a single CCR driving multiple strings of LEDs. This configuration has the lowest cost, but the forward voltage drop of different LEDs must match. If one string of LEDs fails, the current of other strings of LEDs increases, increasing the risk of failure. In this configuration, more power is dissipated in a single CCR package. Figure 2C shows that multiple CCRs drive multiple strings of LEDs. This configuration has the best protection performance. There is no need to match the LEDs. The failure of one string of LEDs has no impact on other strings, and the power is dissipated in multiple CCR packages

Figure 3: connect multiple CCRs in parallel to provide greater current and drive single string and multi string LEDs.

in addition to driving single string or multi string LEDs with a single CCR, multiple CCRs can be connected in parallel to provide greater current and drive single string or multi string LEDs. Among them, the use of three terminal adjustable output CCR helps to meet the specific current setting requirements, and the energy consumption of adjustable resistance is less than 150 MW

ccr can be used in applications directly powered by AC power supply. After the AC mains input is rectified by the bridge type such as sticky soft rubber on the surface in contact with the sample, it is only necessary to ensure that the remaining voltage after subtracting the total LED string voltage from the input voltage does not exceed the VAK of CCR. CCR can also be used in T8 fluorescent tube LED alternative applications. CCR is used to drive LED T8 lamp tube (see Figure 4). Compared with fluorescent lamp with electronic ballast, it has lower input power, higher power factor, lower total harmonic distortion and higher optical output

figure 4:circuit diagram of nsi45090ddt4g CCR in the application of driving LED T8 lamp

ansenmey semiconductor's nsi45 series CCR includes 10, 15, 20, 25 or 30 Ma fixed output versions, 60 to 160 Ma adjustable output versions, and 20 to 160 Ma adjustable output versions certified by automotive standards. Ansenmey semiconductor also provides CCR sample kits and evaluation boards for customers to apply for trial use

linear LED drivers for addressable signs, building decorative lights and other applications

in addition to providing new low current LED drivers such as linear CCR, ansenmey semiconductor also provides a variety of other linear drivers for display screen drives, addressable signs, building decorative lights and other application fields

figure 5:cat4016 typical application circuit diagram

LED applications such as billboard signs, rolling banners, intelligent vehicle signs and sports scoreboards need to use multiple LEDs, usually including multiple strings of LEDs. The LED drive scheme is required to provide constant light output. The current matching accuracy between different channels should be high. Easy to use interfaces should be provided to control different LED channels, and reliable protection functions should be provided. Ansenmey semiconductor's solutions for such applications include constant current LED swab drivers such as cat4008 and cat4106. The former supports 8 channels and the latter supports 16 channels. The LED current range is 2 to 100 mA. This current is set by the external resistance

some building decoration lighting applications designed to create a high visual impact effect use high brightness LEDs. LED drivers are required to drive high brightness LEDs and have high-speed interfaces to support high data rates and ensure high data integrity. They also need to have ultra-low voltage drop to provide higher energy efficiency. LED drivers suitable for such applications include cat4101, cat4103 and cat4109

Figure 6: typical application circuit diagram of cat4103 and cat4109 RGB pixel LED drivers

among them, cat4101 is a 1 a high brightness linear LED driver, which does not require inductance, eliminates switching noise, minimizes the number of components, simplifies the design, and is aimed at building LED decoration lighting applications requiring high current. Cat4103 is a 3-channel serial programmable constant current RGB LED pixel driver. It is designed for high-end, multi-color and "intelligent" led building lighting applications. It has a high-speed serial interface, can support data rates up to 25 MHz, and provides fully buffered data output to ensure the highest data integrity in distributed (long-distance) and Daisy chain lighting systems. Cat4 must evaluate the proposed experimental standard 109. It is also a three channel RGB LED pixel driver, using a parallel interface. Each channel has a special pulse width modulation (PWM) control, which is very suitable for more conventional LED visual effect applications, such as color mixing and building key lighting

in addition, in the application of medium and large-size LCD TV, LED backlight is also accelerating the replacement of traditional CCFL backlight. Ansenmey semiconductor's cat4026 is a 6-channel linear LED driver for large panel LED backlight applications. Designers can use the ncp1397 half harmonic dual inductor plus single capacitor (LLC) resonant controller of ansenmey semiconductor and cat4026 side light LED linear driver in the LED backlight part of LCD TV to support the design of LED backlight LCD TV with circuit board height as low as 8 mm. Cat4026 supports 6 channels with a single IC, and is easy to be classified into up to 12 or 18 channels (2 or 3 controllers are used accordingly). The target energy efficiency is higher than 90%, and the typical energy efficiency is 94%. In addition, the driver also provides forward voltage monitoring function, which can limit the overall power consumption; It can also provide protection for different LED string faults such as LED open circuit and too many led short circuits

Figure 7: schematic diagram of 46 inch LED backlight LCD TV power supply with ncp1397 and cat4026 in the backlight part


as the leading supplier of high-performance silicon solutions for energy-efficient electronic products, ansenmey Semiconductor provides energy-efficient driver solutions for various LED lighting/backlight applications, including AC-DC led solutions, DC-DC led switching regulator solutions and different linear LED driver solutions. This paper focuses on different linear LED driver schemes of ansenmey semiconductor, including a novel linear CCR scheme for low current applications and a linear LED driver scheme for addressable signs and building decoration lighting applications. Customers can choose the appropriate ansenmey semiconductor linear LED driver scheme according to the actual application needs, shorten the design cycle and speed up the product launch process. (end)

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