The New Constant Current High Power LED Driver!

By Carl Schramm,
Development / Manager Technical Support, , RECOM Development Ltd. & Co KG,

The introduction of the light bulb in the 19th Century might have excited just as much attention then as the application of high brightness white LED technologies to lighting systems today. Besides the much better illumination efficiency, which will lead to considerable energy savings and reduction of greenhouse gasses, the white LED has several additional technical advantages over the light bulb. However, to operate these high brightness LEDs, an adaptor or driver is required to match it to commonly available power supplies. For AC supplies, there are already several products available on the market and now for DC supplies, the DC-DC power-specialist RECOM has recently developed a driver that ideally matches the needs of this new illumination technology.

The probably most well known and useful technical quality of the white LED is the lifespan of 50,000 to 100,000 hours, which corresponds to approximately 5 to 10 years of continuous operation. Alone this fact already makes LED technology interesting. In addition, the compact size and robustness against vibration will permit completely new areas of application and will make some technologies, like for example fibre optic lighting systems as cold light sources, superfluous. The minimum lifetime of 50,000 hours will give LED lighting technology an innovation thrust as conventional light bulbs have a lifespan of only 1000 hours and halogen lamps a lifespan of approximately 2000 hours. This means that a LED lamp lives 25 to 50 times longer than a filament lamp.
If one takes a commercial lighting application such as a shop where no permanent maintenance personnel are on the staff, any defective lamp must be exchanged by a technical specialist. This activity must calculated with a working time of 15 minutes to clear a space under the lamp and to put up a ladder and estimated expenses of 40€/h plus travelling costs, so that each lamp exchange incurs an expense of approximately 10€. Therefore, the savings in switching over to LED technology amounts to 250€ to 500€ in maintenance costs alone without even taking the reduction of running costs into account. An alternative to LED lighting is the energy saving lamp (compact fluorescent), but although it has a lifetime of up to 8,000 hours, it also contains mercury which makes it less eco-friendly and contains a built-in electronic ballast which must be also discarded when the lamp fails, so making it un-recyclable.
Multiple high brightness LEDs should be powered with a constant current supply of 350mA, 500mA or 700mA, depending on the type, if they are to be run at the optimum operating conditions to generate a uniform brightness and colour of light. This constant current module can be either incorporated in the LED lamp or mounted separately so that it can be just as easily installed or exchanged as any other conventional light fitting. However, these LED driver modules must have some particular qualities to be universally applicable.

What qualities are required in a LED driver?

Although LEDs are eight times more efficient than filament lamps, they still can get very warm due to internal heat dissipation and ohmic resistances within the device. If a LED driver is mounted close to a group of LED lamps, it must be able to cope with the high ambient temperature. Indeed, environmental temperatures of over +80°C are no rarity. RECOM has succeeded in developing the RCD-24-0.35 constant current driver to meet these environmental demands. With an efficiency of up to 98%, the internal power losses within the driver are so low that it can be used in ambient temperatures of up to +85°C at full load.
This achievement has been made possible by the application of a non-isolated, buck regulator topology, with such extremely high efficiency that almost no energy is lost during the conversion. Furthermore, this topology enables a very compact construction within a case size of only 22.1 x 12.6 x 8.5mm (LxWxH). Versions for pcb through-hole mounting and with flying leads are already available and RECOM is currently working on a surface mount version.

However, the excellent conversion efficiency does not alone suffice to meet all of the demands of LED illumination technology, as the driver must also be as reliable as the LED lamp itself. The design lifespan of up to 100.000 hours at +85°C represented a real challenge with the development of this driver. Specifically for this purpose, RECOM has built an environment and reliability testing facility in order to optimize the products of the RCD driver family to meet this requirement. This laboratory will conduct HALT testing, which uses different forms of environmental stresses such as high and low temperatures, rapid temperature changes, random wide bandwidth vibration and power cycling to uncover any material or process weaknesses and to be able to create meaningful forecasts about the product lifespan.
Not to be overlooked is the fact that the RCD driver family has been designed to be very simple in its application. It requires no setting up or adjustment and meets the standards for EMC, EMI and component safety without the need for any external components. The converters are also manufactured from UL-94V0 materials to meet the requirements for fire safety.

Picture 1: LED-Driver

Summary of the driver specification:

Consequently, the RECOM LED driver can be used in a wide variety of DC supply applications such as fork lift trucks, traffic lights, railway signalling, aircraft interior illumination, hazardous environments, buses and other industrial and transport uses. The module has an on/off control pin, with which the converter can not only be powered down but also dimmed by applying a pulse width modulated (PWM) signal with a frequency anywhere between 10Hz to1000Hz.. RECOM therefore has introduced a very advantageous "Ready-to-Go" solution that can be installed without any fuss or external components.