Direct Drive® LED Circuitry

About

INDO Lighting is leading the way in Direct Drive® solutions for street lighting and outdoor lighting applications, improving reliability of LED products and ensuring that the longevity of the product lives up to user’s expectations. Why Direct Drive®? Typical LED assemblies, making use of a traditional, separate “LED driver” can fail early due to failures of the LED driver, meaning that although the LEDs are able to boast a 20+ year life, the system often requires maintenance after a much shorter period. But why is this? Why is it that the LED driver is notoriously unreliable in an industry where products are expected to have a maintenance free period in excess of 10 years?  One key reason is the use of “wet” electrolytic capacitors. A wet electrolytic capacitor is a component that stores charge, and is often used in two parts of the circuit – in the “input” section, part of the “power factor correction circuit” and in the “output” section, where capacitance is required to smooth the light output. The structure of the component is such that it contains a liquid (the electrolyte), and over time this liquid can escape from the component causing failure. Depending on the position of the component in the circuit, this failure can result in a catastrophic failure of the LED driver, rendering the luminaire useless. Increased complexity is also partly to blame. Reliability of a system, or circuit, is determined by the reliability of its component parts; the more complex the system becomes the more opportunities there are for failure. In other words, more failure modes are being introduced, ultimately reducing the reliability of the system. What is Direct Drive®? Direct Drive® is a technology which improves the reliability and longevity of life of LED circuits. There are no unreliable capacitors in the design whatsoever. The unique circuit design was first used by INDO lamp retrofit products in 2010 and have been operating with great success since; failures in the field total less than 0.1%. The MTBF of lamp retrofits using this technology has been calculated at over 500,000 hours by independent consultants working to MIL-HDBK-217. How does it work? Traditional LED luminaires commonly make use of single die LEDs, each with a forward voltage of around 3V, arranged in series to form “strings” with a higher forward voltage. An LED driver is typically used to power an array of LEDs with a forward voltage of between 12V and 120V. White LEDs are created using blue LEDs and a phosphor coating. It is for physical reasons relating to the energies required for blue light that the forward voltage of a single die white LED is around 3V. Within the semiconductor material of the diode there is an n-p junction which is formed by dopants, and it is this that sets a “band gap energy”. Multi-die LEDs can be used to increase this forward voltage, allowing for a significantly lower drive current (around 15-20mA), to be used to achieve the same LED power output as a single die LED driven at 350mA (P = V*I). A multi-die LED is a single LED chip which contains multiple light emitting diodes in series. Unlike a COB, these individual diodes are connected by miniature tracks which are formed in the production of the semiconductor, rather than using less reliable physical bonded wires. The LED chips used in the Direct Drive® technology are protected by multiple patents, and are supplied by a globally leading manufacturer both in terms of intellectual property and revenue. System configuration Chip voltage (Vf) Drive Current (mA) Power (W) Traditional 3V 350mA 1.05W Direct Drive® 60V 17.5mA 1.05W Using a high voltage multi-die LED chip allows for much higher system forward voltages to be achieved, which can then be driven directly from the mains supply, which peaks at over 320V. Paramount quality is achieved through innovative design, working only with component manufacturers of the highest quality, and through expertise in manufacture, most of which is carried out in the UK.  Using this method not only results in a huge improvement in reliability and service life, but higher power conversion efficiencies can be achieved.