The Best LED Drivers and Applications
The driver or transformer for LED lighting can vary in quality. We experiences unfortunately still many dubious drivers in the market, resulting in bad experience of the room or, in worst case, the LED light sources are not lit.
Since the LED technology was created back in the mid-1900s, there have been low-voltage DC components. It is within the last 10 years that there are LEDs that can be supplied directly to AC voltage e.g. 230VAC, but most of the LEDs are still powered by DC voltage. The installation can be done in series or in parallel. What is chosen depends to a greater extent on the need and desires of the installation.
In this blogpost we’ll discuss which types that exist and how the best drivers can be implemented in the projects.
What types of drivers are used?
Most LEDs must be supplied with a given voltage and fixed current. The higher the current, there more light is generated in the semiconductor, but too high current also means a lower energy efficiency and a shorter lifetime. It must therefore balance between the thermal properties of the cooling surface, the LED and of course the expected ambient temperature. The first thing to look at is always whether there is a constant current or a constant voltage.
The most unconditionally driver who is being used is the constant current driver. These drivers can supply the LEDs with typically 150mA - 1500mA and a varying voltage. Downlights, line luminaires, 60x60 panels are in most cases provided with such a driver. The second type holds a constant voltage e.g. 12V or 24VDC which can supply LED tapes or other lighting products. The types of lighting products are equipped with a resistor, without the LEDs would burn off.
However, the current varies depending on the load in the circuit being connected. It is alway possible to see the difference between the two types. Constant current driver has on the rating plate, e.g. 5-36VDC - where the second type has a constant voltage e .g. 12V or 24VDC.
Select the best driver for the solution
With the supplied current, the voltage can vary over one LED. The voltage is approx. at 2,6V - 3,2V. It is seen on a constant current driver that the voltage interval, as mentioned earlier, could be 5-36VDC. If 10 small in-ground up-lights are in a driveway, the voltage could be 28V. The example of 5-36VDC would work if otherwise the current matches the LEDs, which could be 250mA. Other considerations are the drivers’ physical size. There are waterproof drivers and drivers that should only be used for single LEDs.
At the same time there are drivers for e.g. street lighting that emits a high current, for example 1500mA. With a high current where the LED is not dedicated to this, the LED will overheat. For the same reason, always check which current the LEDs must be supplied with and the make sure the voltage matches too.
Light dimming with drivers
In addition to the driver that matches the given type and amounts of LEDs, the possibilities for dimming should be looked into more closely. Leading edge and Trailing are the two types where the high voltage side (230V) is dimmed. With these drivers, there may be some challenges if the dimmer is not tested with the given driver.
With several thousands of dimmers and drivers, test before installation, or obtain test report from the drivers’ manufacturer about which dimmers that driver is compatible with. However, DALI or 0-10V are some of the most stable light dimming options for LED lighting. If the lamps are to be controlled individually and more complexly, DALI will be the preferred choice. Analog dimming is a controlled voltage that is between 0-10V. Meaning, all the lamps are controlled at once, and can thus only be divided into zones if the installation is divided. To return to DALI, there exist several versions today. DALI version 8 tied up to several addresses which allow for variation of color temperature, light intensity and possibly more colors as red, green and blue.
Strobe effect or flicker?
Before we're talking about the subject, the effectiveness of a driver in question must be seen in continuation of dimming. Power Factor (PF) is expressed in percent and provides an excellent indication of how effective the driver is. Located on e.g. 90% is a good driver and vice versa is it less than 80%, in some cases it may be a less good driver. Other parameters such as harmonic currents (THD) generated by a given number of LED drivers are a matter of their own, but not forgetting this value must always be below THD 20%.
When the subject is drivers, flicker will be a sin not to mention. It is probably the biggest challenge the LED market is experiencing today. Although the human eye may not be able to detect the rapid flicker, it still exists in many more lamps than we expect. There are older standards within the maximum permissible flicker value (Flicker <20%). Because of the major challenges the LED technology experience, new standards will come in 2019 to ensure that the bad drivers with high flicker value do not enter the European market.
We are waiting for the standards but until they are published, we must all be wary of drivers with a high flicker value. The reason is simply a poor working environment that can result in headaches, neck pain and other tension in the body. The flicker value can now be measured and if the value is high it can be seen clearly if a camera is held up against the light. There are drivers close to 0%.