Linear LED drivers are the preferred solution for many lighting applications because they are relatively simple, easy to design, and enable LEDs to be driven with precise current flow regardless of LED forward voltage drop or input voltage. Since the drives are linear, they must match the power dissipation requirements of the application. ON Semiconductor offers a wide range of linear LED driver solutions with currents ranging from 10 mA to 1 A, including the novel Linear Constant Current Regulator (CCR) solution and many other linear driver solutions.
Linear CCR for low current LED drive and application examples
In many low-current LED applications with currents below 350 mA, such as automotive taillights, neon replacement, traffic lights, large display backlights, building lighting and indicators, etc., you can use a common linear regulator or It is a resistor to provide an LED drive solution. Resistor is used to limit the current of the LED string. It is the lowest cost solution, easy to design, and has no electromagnetic compatibility issues. However, when using a resistor, the LED forward current is determined by the voltage. Under low voltage conditions, the forward current is low, which causes the LED to be insufficiently bright, and the LED may be damaged under transient conditions such as load dump. The resistance scheme has the lowest energy efficiency and is not conducive to energy saving, which is particularly disadvantageous in applications that emphasize high and low energy consumption. In addition, the resistor scheme also has LED thermal runaway and screening problems. The linear regulator scheme provides better current regulation accuracy (±2%), supports over-power self-regulation, and has no EMI issues. This solution is less energy efficient and cost effective.
Customers need a drive that is more economical than ordinary linear regulators but has a much higher performance than resistors. Using its patented self-biased transistor (SBT) technology, ON Semiconductor has introduced a novel LED driver solution, the NSI45 Series Linear Constant Current Regulator (CCR), combined with its superior process control capabilities. Compared to resistors, linear CCRs have a constant brightness over a wide voltage range, protecting the LED from overdrive at high input voltages and providing higher brightness at low input voltages. Thanks to its constant current characteristics, customers can reduce or eliminate the coding costs of different LEDs from different suppliers and reduce the total system cost. CCR also has no EMI problems, is packaged in high power density, and is certified by the automotive industry AEC-Q101.
ON Semiconductor's CCR consists of two types of dual-ended fixed output and three-terminal adjustable output. The current ratings range from 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 to suppress surges and protect LEDs. These series of CCRs have no voltage offset before current flows, and their fast turn-on/turn characteristics provide a wide range and precise pulse width modulation (PWM) dimming capability. There are no "plug and play" devices on the market that are the same as CCR. Other devices require a minimum of 0.5 V to turn on, and do not turn on immediately like CCR (see Figure 1 left). CCR can provide accurate PWM dimming with an external bipolar junction transistor (BJT) (see Figure 1 to the right). The typical PWM dimming frequency is 0.1 to 3 kHz. There is no color drift during dimming because the LED is always optimized. The current is turned on.
Figure 1: Comparison of the ICR-Vin curve of a 25 mA CCR versus competing devices (left); CCR dimming application example (right).
CCR has a negative temperature coefficient (NTC) characteristic that protects the LED from thermal runaway at extreme voltages and operating temperatures. CCR is easy to design and is suitable for high-side and low-side applications (see Figure 2a). It requires no external components and is very simple for a wider range of applications. In comparison, some suppliers offer Similar to the functional or performance of ON Semiconductor CCR, but requires additional external components, can not be configured for high-end or low-end drivers, different packages or less thermal reliability.
Figure 2: CCR can be used flexibly for high-end or low-end drives, as well as driving multiple strings of LEDs.
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