Intelligent LED lighting requires innovative control and dimming

Foreword

Lighting is vital to our modern life. Whether it is used to illuminate homes, offices, public buildings, or to provide security or just to create an atmosphere. In fact, about 25% of the energy in a typical building is used for lighting, making it one of the most important energy uses on Earth.

Coupled with the incredible efficiency of incandescent lighting solutions, energy costs are increasing at an alarming rate. It's easy to find that we are wasting a lot of world resources and paying a high price for it.

As a result, governments are seeking to regulate lighting through new energy efficiency regulations, and new technologies such as LEDs are becoming mainstream, expected to save up to 40% of energy used for lighting.

However, as designers and consumers begin to look for more energy efficient and innovative lighting solutions, there is a need to develop newer technologies to meet current and future market needs. In order to maximize its potential, smart lighting requires a more sophisticated and innovative approach.

ON Semiconductor is addressing the lighting industry's challenges of efficient power conversion and effective dimming, while looking for next-generation technologies that offer greater energy efficiency and other advantages.

Lighting designers face challenges

The government's need to strengthen control and consumer demand has made modern lighting designers face more and more challenges. Organizations such as ENERGY STAR and the European Commission are concerned not only with the energy efficiency of electronic devices (including lighting), but also with their standby power consumption, as this may be an important source of energy consumption for a long time. In the smart lighting solution, this challenge becomes even more difficult, because the power supply must remain "on" to search for signals from the controller, so the current is constantly being drawn. Currently, the ENERGY STAR regulations allow for a standby power consumption of 0.5W, but agencies such as the California Energy Commission (CEC) plan to reduce this number to 0.2W by 2019, which will further escalate the challenge.

As lighting has shifted from incandescent to LED technology, dimming has changed. More complex pulse width modulation (PWM) technology is gradually replacing simple resistive or TRIAC-based dimming, which requires designers to adopt different methods.

LEDs are a low-voltage technology, which means they can't be driven directly from the mains like incandescent lamps, but instead require a power supply that provides constant voltage (CV) or constant current (CC) power depending on the LED application. The power supply has a substantial impact on the overall performance and energy efficiency of the lighting solution, so at least a rigorous review is required like the LED itself.

There are many different lighting solutions on the market today, ranging in power from a few watts to a few hundred watts. Therefore, the design of its drive power is also varied. At lower power levels (typically below 10W), single-stage conversion topologies are the most popular solution.

Due to the increasing use of versatile solid-state lighting, the space occupied by LEDs and associated power supplies is being squeezed smaller and smaller, which means that efficiency is critical, thereby reducing the generation of waste heat. It is the lowest and is able to reliably install and operate the lighting solution in a small, usually enclosed space.

An important reason for the rapid development of LED lighting solutions is the decline in the price of LEDs themselves. As a result, installers and consumers don't just want LED power supplies to achieve better performance in a smaller space, but they also expect to see similar price cuts (which means designers need to reduce component count and lower overall BoM costs). .

Modern lighting power conversion method

Lighting in the 25W - 100W range for offices, factories and homes is one of the fastest growing market segments, with the two-stage approach being the most common solution. In many applications, a flyback power factor corrector (PFC) is used and a power supply in the form of a step-down DC-DC converter is provided.

This method is especially suitable for solutions with dimming requirements. It also easily turns off the LEDs in standby mode and allows simple control of multiple LED strings for a more complex lighting solution.

ON Semiconductor recently introduced an integrated solution for this type of application, enabling the design of high-performance lighting power supplies with two IC products and a small number of external components.

The FL7740 is a single-stage CV primary-side regulation (PSR) controller that provides CV regulation (±3%) with built-in dynamics (including fast response time) to overshoot and under line and load transients The ripple is minimized to within 10% of the output voltage.

The controller supports a wide range of AC input from 80V AC to 382V AC for utility power applications anywhere in the world. It delivers up to 100W of power while consuming only 0.15W in standby mode - easily surpassing all regulatory requirements. At the same time, it also implements a “continuous power-on” operation that is critical to intelligent lighting solutions.

The built-in PFC stage achieves 0.9 at full load and THD is 10%. In the case of half load, the optional PF optimizer is used, while the value of 0.9 PF remains the same. This ensures that input interference is kept to a minimum over a wide load range, making the FL7740 widely available.

This advanced controller includes a range of protection features critical to the safe operation of the lighting system: overload protection, output diode short circuit protection, sense resistor short/open circuit protection, and VDD and VS overvoltage protection.

The FL7760 buck ("Buck") controller operating in continuous current mode (CCM) provides a second stage of conversion. The device operates over a wide 8V to 60V input range while supporting wide analog and PWM dimming and consumes only 150μA.

Importantly, the FL7760's PWM dimming covers all 1-100% of the output range, although under certain operating conditions, undesirable stroboscopic and audible noise may occur due to the PWM operating frequency. The analog dimming range is 5-100%, which is a significant improvement over the prior art compared to the current 15-100%. In general, analog dimming is favored because it has no PWM defects, and the FL7760 makes it the viable option for the first time.

One of the significant advantages of dimming below 5% of the analog threshold is that the FL7760 combines analog and PWM to provide mixed dimming, which seamlessly combines both to provide full-range dimming. There are no stroboscopic and audible noise problems.

Like the FL7740, the FL7760 offers a variety of protection features including thermal shutdown and overcurrent protection.

to sum up

LED lighting is increasingly popular for its low power consumption, versatility, and inherent compatibility with intelligent lighting solutions, so designers are increasingly demanding performance, especially for low standby power. And the ability to provide a wide range of dimming.

Semiconductor devices such as ON Semiconductor's FL7740 / FL7760 combination meet these performance challenges and provide a compact, low component count solution that delivers state-of-the-art lighting power solutions at competitive cost.

Reverse Conducting Thyristor(RCT)

Reverse Conducting Thyristor(RCT) is also called Reverse- appreciation Thyristor.The characteristic is that a diode is connected in reverse parallel between the anode and cathode of thyristor, so that the transmitting junction of anode and cathode is short-circuited.As a result of this special circuit structure, it has high voltage resistance, high temperature resistance, short turn-off time, low switching voltage and other good performance.For example, the turn-off time of the reverse thyristor is only a few microseconds, and the working frequency is dozens of KHZ, which is better than the fast thyristor (FSCR).This device is suitable for switching power supply and UPS uninterrupted power supply. One RCT can replace one thyristor and one continuous current diode respectively.

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