This application note is intended to provide high-level, generic guidelines regarding the selection of LED drivers suitable for use with Violumas UV LED products. Furthermore, applicable LED parameters, LED driver concepts, and safety regulations for the North American market are briefly explained.
While this application note provides the basics for selecting a suitable power supply for use with Violumas UV LED products, it is not meant to replace fundamental engineering knowledge and is rather intended to be used as a first guide for selection of a suitable power supply. The documentation is not geared towards providing detailed information on regulations and safety certifications for different countries and does not provide information on application-specific requirements. Please contact the Violumas team for resources on thermal management solutions.
This resource is intended for product developers using Violumas UV LED products. Product designers are solely responsible for (1) selecting the appropriate Violumas products, (2) validating and testing the power supplies depending on the application, and (3) ensuring that the applicable standards and safety requirements are met. Violumas cannot be held responsible for any damages caused by following these
guidelines since this document provides generic, high-level guidelines for driver selection (independent of the application).
The power supply, also known as a driver, is one of the most important components of an LED system. LEDs are DC devices and so cannot be operated using AC wall-power. The LED power supply converts the AC wall-power to a DC signal and in most cases steps down the voltage/current to meet specific LED device and system requirements.
The selection of an optimal power supply is vital to obtain the desired optical output, suitable lifetimes, and the desired reliability from the LEDs. Using the incorrect power supply can not only damage your LED product but can also be a source of dangerous hazards. Hence, the power supply should be chosen with utmost caution, keeping in mind the specific characteristics, which closely match the requirements of the application and the LEDs being used.
In this document, we provide a general guideline to select power supplies for Violumas products. A standard PSU by Meanwell has been chosen as a reference to study the required parameters.
In order to select a suitable driver(s) for your LEDs, you need to obtain the datasheet(s) of the LED product(s) of interest. In the case of a custom product, please check in with the Violumas technical support team to obtain information regarding a suitable driver.
A. Forward Voltage: This parameter is specified in the electro-optical characteristics of the LED product and is defined as the voltage required to turn on the LED. While the parameter may be represented as a single value and not a range, it is important to also know about the binning differences and the range of forward voltages available for a particular bin. In addition, the operating voltage may vary slightly depending on the drive current. The forward voltage in the datasheet should match the output voltage required from the power supply.
Figure 1: Electro-optical characteristics of a Violumas LED
B. Driving Current: The optical output of an LED is directly proportional to the driving current chosen (as shown in Figure 2 below). This would be the minimum output current required from the power supply (in the case of a single LED product) and would determine the intensity of the light. Hence, this may be varied on the basis of the application.
Figure 2: Relative radiant flux as a function of the driving current for a UV LED
C. LED Arrays: In many cases LEDs may be configured in series or parallel arrays to meet application requirements. Information on the series/parallel combinations of LED products is important if a combination of products is required to be driven by the same PSU. Voltages are to be added in series and currents should be added when LEDs are connected in parallel. The total voltage and current requirements for a module need to be known to power up the module.
Figure 3: Different LED array formats define the voltage/current requirements
D. Power Requirements: Once the forward voltage and current are known, the output power requirements for the power supply can be calculated.
As the majority of our products are designed for specific illumination requirements, Violumas recommends the use of constant current drivers with LED products. Constant current drivers support limited voltage ranges and proper driver selection should be ensured for a given COB. If a constant voltage driver is used instead and the current is not regulated, as the LED temperature increases when powered ON, the LED forward voltage would decrease accordingly. This would mean that the LED would draw more current, implying a further increase in temperature. This continual increase in the driving current would result in additional heat generation leading to a thermal runaway fault resulting in premature failures and lower lifetimes. Hence,
the preferred method of driving Violumas LEDs is by using a constant current LED driver. A constant current driver controls and maintains the set current without over driving the LEDs and preventing thermal runaway, even if there is a change in temperature.
The driver specifications provided here assume that a constant current driver is being used.
Figure 4: Input parameters from a Meanwell power supply.
It should also be noted that the PSU may be derated below certain input voltages as shown in the static characteristics in Figure
5. This should be kept in mind if input AC voltage fluctuations are anticipated.
Figure 5: Load characteristics over the input voltage range from a Meanwell power supply
Figure 6: Output characteristics of a constant current driver
Figure 7: Ingress protection rating chart.
B. Ambient and Case Temperature: It is important to note the temperature ratings if the PSU is going to be used in extreme temperature conditions as the load % as well as the driver lifetime can vary depending on temperature. For example, in Figure 8, the performance characteristics for a Meanwell driver vary depending on the input wall voltage. The lifetime drops to 50% of the value when case temperature is increased to 80 deg. C.
Figure 8: Performance and lifetime dependence of drivers at different temperatures
C. Certifications: All LED drivers require basic agency safety certifications from UL and/or CSA, as well as FCC or equivalent EMI/RFI certification. In Japan, devices are required to meet PSE, and in Europe the certification requirement is TUV.
If the application requires intensity control, a power supply with a dimming control would be needed. Many PSU manufacturers such as Meanwell offer several options for dimming
control as shown. Depending on the driver type (Type A, Type B, or Type AB), various dimming options are available.
Meanwell’s Type A PSU provides an in-built potentiometer option for controlling current as well as the voltage (within the specified adjustable range).
Type B PSU requires external controlling devices to control the current. Three different ways are possible as shown in Figure 9.
Type AB provides both the in-built potentiometer as well as an external control option.
Please check with the Violumas team on what can be offered for dimming control for your application.
Figure 9: Different ways to dim a Type B Meanwell PSU
Violumas proudly offers a wide variety of standard products as well as customized solutions that are tailored to meet your specifications.
