Over the past fifteen years, LED lighting has progressed from disruptive technology to the incumbent solution. Seldom do we see a technology advance so rapidly and make such an immediate impact as Solid State Lighting (SSL) has.
Early SSL solutions targeted applications where reliable LED products could justify the heavy price premium placed on them. Applications such as commercial transportation (safety) or applications where the cost of replacing a luminaire far outweighed the cost of the product.
The next hurdle for SSL adoption was to manufacture a product that could compete with incandescent and fluorescent lighting within the general lighting industry. This obstacle was purely about cost and lumens per watt. Thanks to economies of scale, incentive programs, moving LED components onto inexpensive and larger wafers, and cost-effective single-stage driver designs occurred relatively quickly.
Currently, we find ourselves in the middle of the next phase of the adoption of SSL products. This phase encompasses all previous challenges but has the added criteria of demanding quality lighting and intelligence.
Quality lighting is referred to in the industry by a few common names and phrases, such as Human Centric Lighting (HCL). HCL focuses on artificial lighting in such a way as to not disrupt, confuse your body’s natural rhythm, and in some cases, enhance your performance (sleep or work) by adjusting the light type. Many other factors contribute to “Quality of Light”, such as ripple and light flicker, dimming range and type (linear vs. logarithmic), consistency of dimming between luminaires etc.
Light modulation limitations are currently in place with California Title-24, Energy Star, and other lighting standards. Light modulation is described as a repetitive change in magnitude over time, or modulation, of the luminous flux of a light source. The magnitude (high to low) and the modulation’s frequency are the two pertinent variables describing the severity of the modulation – more significant changes (high-low) and lower frequencies being the most detrimental to neurological problems, fatigue, headaches etc. One may not visibly see the light source’s modulation, flicker/flutter, but its effects may be felt. IEEE-1789, a standard that addresses light modulation, is becoming the dominant standard for light modulation limitations within lighting products. It will be a requirement in some form over the next couple of years.
Cost, quality lighting, challenging regulations, such as DLC, California Title 24, FCC, and additional market needs for intelligent lighting have created a challenge for LED electronics driver designers. How do we meet all requirements while keeping the solutions competitive?
Global regulations related to Power Factor (PF), Harmonic Distortion (iTHD), EMI signature, safety, reliability, and efficiency are becoming more stringent.
To resolve the design challenges described above, the industry has two paths to choose from concerning LED driver controller architecture:
The most common approach is to use analog controllers that are developed specifically for LED lighting applications. Careful consideration is taken when defining the controller’s features and what features are to be left out. Given the cost constraints, it’s critical to include only what is necessary.
There is a known comfort using simple analog controllers, but there is little flexibility, and older analog controllers are struggling to meet today’s lighting-specific design requirements.
The micro-controller based solutions are becoming more common today. The micro-controller based systems often contain an AC/DC Analog controller, paired with a micro-controller focusing on the quality of light requirements. First adopted by lighting manufactures whose customers required exceptional dimming, color-point control, and other requirements related to the quality of light.
Microcontrollers are undoubtedly flexible, but the design effort related to software development, revision control, and time to market, along with additional manufacturing and BoM cost, drives designers away from committing to this path.
There are pros-cons to each path.
There is a third option that Infineon Technologies has developed worth exploring. Infineon has developed a family of Digital LED driver controllers that are simple to use but paired with a user interface allowing the designer to modify settings with a simple click of a mouse.
The XDPL AC/DC controllers are a series of controllers that behave and operate similarly to traditional analog controllers but allow optimization and configurability of a micro-controller without the hassle of code development.
The XDPL products are available as a single-stage PFC/Flyback with 1% dimming (XDPL8210), a single IC that controls a separate PFC power stage and a Flyback converter (XDPL8221), and an IC that is a single stage PFC/Flyback with a constant-voltage (CV) output, with features addressing the LED SSL market (XDPL8219).
The XDPL-series of controllers are evaluated similarly to any traditional analog controller. Evaluation boards are ordered, AC power is applied to them with a LED array attached to the output. Common architecture principles still apply, transformer design, sizing of components, etc. The value of the devices is realized when the engineer optimizes the solution for production or changes need to be made to the design to ensure safety/regulatory compliance.
With traditional PWM controllers, when updates, revisions, or upgrades to an LED driver were necessary, revision(s) of PCBs, changes to the BOM, and compliance testing would all need to be performed.
With the XDPL-series, most of the optimization and changes are possible by adjusting parameters with the user interface for the device. A single click of the mouse can optimize parameters specific to protections, feedback loop control, and electrical compliance. It only takes a few minutes on the bench to realize the potential of editing critical parameters and watching the results in real-time to experience this approach’s added value.
Manufacturers of digitally controlled power conversion ICs stray too far from their analog roots and develop controllers that engineers with analog power conversion backgrounds do not evaluate quickly and efficiently.
As critical as the digital architecture is to performance, the interface ease of use is critical to allow all types of engineers to realize the benefit of digital controllers.
Set up needed to the XDPL-series evaluation
Power supply design principles apply with the XDPL as they usually will with a conventional analog AC/DC development. Transformer, inductor, power MOSFET, and diode selection are no different.
The engineer enters driver electrical parameters such as primary inductance, turns-ratio, output voltage, and current into the user interface “Hardware Configuration” window. A few critical surrounding component values determined during the design phase are also noted within the interface.
The XDPL converters use a three-pin UART control for communication, and a small connector is required on the PCB.
The evaluation board is connected to AC power and connected via a UART and computer USB via an interface module.
The Hardware Configuration is loaded into the permanent memory of the XDPL controller, and power is applied.
At this time in the driver development, optimization via the user interface is possible. Edits can be made and stored in the XDPL temporary memory, and the engineer can observe the results. The process of editing parameters and following the outcome can be done endlessly and quickly.
Once a configuration is settled upon that meets all the user’s needs, this configuration can be permanently written to the XDPL-device. Once this occurs, the UART – USB connection is no longer required, and the converter would operate as any other PWM controller.
Today’s lighting requirements have forced the industry to explore better suited AC/DC power conversion controllers allowing for precise system optimization. Infineon’s XDPL AC/DC LED drivers, coupled with a graphical user interface (GUI) that allows all engineers to explore the benefits of digital control, has achieved a proper balance that bridges the two worlds.
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