Maggie Nadjmi , Product Manager, SL Power Electronics
The main value propositions for LEDs over traditional lighting are twofold: Long life expectancy that translates to saving money on replacement costs, and higher illumination using less energy to lower electricity bills. Due to the solid state nature of LEDs that require electronic circuits to emit light, the thermal stress on supporting components such as electrolytic capacitors is a major area of concern for reliability and life of 50,000 hours or more. High efficiency circuit design can reduce the heat generated in the LED driver, however operating in temperatures well above 50°C requires the use of quality electrolytic capacitors to support the reliability and long life potential of LED lighting.
An important consideration for LED lighting is regulatory testing. The last thing a designer wants is a call from the regulatory testing agency stating that the product was unable to pass the required standards.
A likely discussion scenario might be: “Add an EMI filter,” one person suggests; “put EMI cores on the input wires.” Meanwhile, the cost of the fixtures starts climbing and what seemed to be a nice off-the-shelf inexpensive power supply requires costly modifications to perform. After spending thousands of dollars to obtain the required certification from the regulatory agency, the customer asks about the life expectancy of the fixture. The salesperson replies, “The LEDs have more than 50,000 hours of life.”=
Next, the customer probes and asks about the driver. The marketing manager enters the conversation by providing information on Mean Time Between Failures (MTBF) on the driver. “MTBF is not life expectancy,” the customer tells the marketing manager. “Most MTBFs are calculated based on the components’ count and provide just one part of information on reliability and life expectancy,” she adds.
Does this scenario sound familiar to you? If it does, next time you are searching the web for a power supply that meets power and output voltage, consider going further and look for a power supply that is dedicated to LED applications. See if it lists EN55015 for EMI compliance, has adequate life expectancy to match up with expensive LEDs in your fixture, and then move on to other requirements.
Criteria may include: Low leakage current for Canada, meets IEC61000-3-2 class C for the European market and can withstand temperatures of over 50°C, as heat generated by LEDs can raise the thermal profile within the fixture, putting thermal stress on electrolytic capacitors in the driver. Also, if the capacitor is not designed efficiently, this could deter the long life expectancy of the LED fixture.
Higher power efficiency will reduce the wasted heat generated by the supply. In addition, with adequate thermal design and high temperature electrolytic capacitors rated at 105°C and more than 10,000 hours’ life are the critical components in selecting an LED driver. With these factors in place, customers can expect minimum life expectancy of 50,000 hours for the LED fixture.
It’s important to know that the standby wattage requirement can be increased to 1 watt if the LED lighting fixture has intelligence built into it. To meet the power factor of 0.9, the driver needs a power factor correction stage. This requires additional components and complexity of design that can be addressed with an electronics designer with experience in power conversion and magnetic design. Low-cost drivers often claim to meet power factor requirements at full power, but as loading is dropped through dimming of the light emitted by the LED, these drivers will have a much lower power factor than 0.9.
This will disqualify the fixture from meeting the requirements. Adding metaloxide varistors (MOVs) is the simplest way to meet transient protection. Operating at -20°C temperature will be a challenge for the power designer and not all commercially available supplies can comply.
For obtaining Energy Star certification and to avoid costly delays in product launches, the right selection of the driver will save precious time. In addition, Energy Star assures high-quality LED lighting fixtures for this rapidly changing market.
The ability to control the illumination based on area occupancy is a growing field in the LED lighting market. For example, there are cost reductions that can be achieved by lighting only specific areas that are being occupied in a building or parking structure. Since an LED is an electronic device, limiting the current can achieve the desired outcome in dimming the light and saving energy and cost.
Controlling illumination offers an opportunity for the LED driver manufacturer to influence lighting design in its early stages. How? by providing flexibility in sensing and reporting critical information via wired or wireless antennas and receivers. With new technology offered, this can also be done via the AC line.
The communication protocol is varied by application-specific LED fixtures. Area lighting uses DALI commands, while in entertainment lighting, DMX-512 is widely employed. Remote Device Monitoring or RDM is the next step up for wireless control in architectural lighting.
No matter what the protocol is, an intelligent driver will be the future for powering LED light fixtures.