“Square pegs in round holes.” This aptly describes the task engineers face when trying to develop the perfect lighting solution. As if it were not difficult enough to match LEDs with suitable LED drivers and embedding them in a suitable thermal environment, builders of “smart homes” now demand a multitude of intelligent lighting solutions, posing new challenges to lighting designers.
“Smart lighting” is the buzz word, and lamps are now expected to do much more than just brighten up a room when a switch is pressed. Lighting is now expected to adapt itself automatically to the needs of people, generating the perfect ambience for any activity, or putting goods and persons into the right light. These new smart solutions must also be energy-efficient, as consumers want to reduce their carbon footprint.
To meet all these objectives, engineers and designers are resorting to a number of innovative technologies and approaches.
Control systems for modern lighting solutions
When it comes to lighting control, there are two schools of thought. One group swears by wired systems, while the other prefers wireless solutions. Both options obviously have their advantages and disadvantages.
Wired systems, such as DALI, DMX, or KNX, are often perceived as outdated. The DALI interface was, for instance, standardized in the 1980s. Given the relatively high wiring costs, these solutions are not really suitable for retrofitting into existing buildings.
On the other hand, the technology has proven very reliable, and can easily be installed by any electrician, as all that is required in most cases are two additional control wires. In addition, they are very resistant to interference.
Wired lighting control systems are therefore still the preferred solution for new buildings. Luminaires can be integrated directly into the building automation system (e.g. KNX), or installed with standardised gateways (e.g. DALI). Wired systems are normally programmed through a system controller that automatically searches for connected devices and assigns addresses during the commissioning process. This allows for easy configuration in groups, irrespective of the actual wiring. System components can also be serviced and replaced without the need for time-consuming reprogramming.
Wireless systems on the other hand are currently experiencing a real boom given the trend towards the Internet of Things (IoT).
Systems like WiFi, Bluetooth and ZigBee are predestined for retrofitting, as they do not require any additional wiring apart from a power line. By choosing suitable gateways, they can also be integrated into existing installations.
Virtually all wireless technologies use Carrier Sense Multiple Access (CSMA) to communicate within the same frequency band. With CSMA, each network subscriber checks first whether the channel is free before sending a command. To prevent one device from continuously blocking the channel, the maximum transmission time of a data packet is limited. This ensures that all devices in the network can eventually send out their commands.
With the arrival of IoT, the number of devices in networks has grown substantially. Sometimes, this has made wireless systems overly complicated for users. Let’s examine a typical example: A user is streaming a film via their home WiFi system to a tablet, while switching on the living room light with a wireless switch. As both applications use the same frequency band, the switch signal must wait until there is a free slot, and the light might not come on for several seconds. On the other hand, the streamed video image might become distorted the moment the light switch is pressed. This is not exactly what consumers expect from state-of-the art technology.
LED drivers – the underestimated core component
LED drivers need to be compatible with as many systems as possible. In addition, manufacturers face the challenge that a new LED model is brought to the market nearly every week. Unfortunately, these new products often come with custom current/voltage combinations. Manufacturers of LED drivers thus face the problem that virtually every LED model requires a special LED driver. Developing matching LED drivers for each and every new product in the market is obviously not sustainable, as only large production volumes can keep prices down. What is required is a universal solution.
When looking at the problem from a different angle, we can see that such a solution might just be within our grasp. How about a LED driver that does not produce a constant current (CC) or constant voltage (CV), but adapts the output to the connected LED? To achieve this, we need to further develop the principle of constant power.
Conventional LED drivers are controlled on the basis of the measured secondary side current (CC) or voltage (CV). These measurements are fed back to the primary side control IC that actuates the primary switcher.
Modern measuring technology, however, allows for accurate measurement of the actual LED characteristics. To use this information, we need a secondary side sensing circuit that measures the voltage relative to a variable output current (calibration) once the device is commissioned. After linearizing certain characteristic sections, the microprocessor can then control the secondary side buck-boost converter in such a way that the LED is always operated at its optimum. Such a system would allow for the separate control of any type of LED within a preset performance range.
As always, there’s trouble in the details, especially when it comes to thermal drift or special and unique LED characteristics. The new technology would, however, put an end to the current practice where the LED driver is chosen solely based on the LED current and the forward bias voltage. Apart from all the new options for lighting designers, this approach would also have massive advantages for manufacturers, and drive down prices.
To take things one step further, it would even be possible to share the above calibration data with other LED drivers through the previously mentioned interfaces, producing a self-learning system. The operating modes of the LEDs could be changed on the spot, as required. At the push of a smartphone or tablet button, the LED could, for instance, be set to optimum brightness or optimum lifetime mode.
This technology is still in its infancy but there will come a time when it will become the only way forward for LED driver manufacturers.
