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LED driver: Which one to choose?

2020-11-04

When commercially available LEDs were used as ordinary controls or displays, providing power supply to them was very simple and did not require any special solutions, except for the use of current-limiting resistors. However, since the first medium- and high-power components for illuminating a wide variety of rooms appeared on the market, the requirements for their power supply have changed significantly. In order to ensure the good performance and durability of these semiconductors and power them properly, it became necessary to use dedicated drivers.

LED driver: Which one to choose?

Why do we call these devices "drivers" and not just "power supplies"?

Because the driver designed to power the LEDs is not just an ordinary power supply as it is traditionally understood. This solution is based on the design that from the very beginning has embraced the specific properties of LEDs to ensure their optimal operation, durability, energy efficiency and protection against damage. A classic power supply would not be able to provide all of these functionalities, and to perform all of them it would have to be equipped with an electronic control system.

Are the commercially available drivers all similar?

Absolutely not. Different models of drivers may vary significantly, and the differences depend on the target applications. As an example, we can distinguish several macro-categories of applications, briefly describing their features that should be taken into account in relation to individual devices.

Home lighting

Generally, drivers designed to illuminate the interior of a house should meet the following requirements:

  • Small size
  • Affordable price
  • Medium to low power
  • High efficiency and reliability
  • Easy assembly
  • Simple and immediate brightness control (dimming)
  • Durability

Example solutions for this category of applications include e.g. drivers of LDC series with a power of 35 to 80W, which enable CP control of LEDs, at constant power.

In the case of applications intended for integration with home automation systems, apart from the solutions mentioned above, we can also indicate:

  • Availability of advanced interfaces, such as DALI or KNX
  • Possibility of wireless control

For example, the LCM-BLE series combines the functions of Bluetooth and Mesh Networking. The devices can be easily programmed and operated with a special application.

Road lighting

This is probably one of the most critical applications, as in this case LED lamps have to operate failure-free in harsh conditions. Therefore, the drivers that are used to power them should have the best possible features related to control, reliability and durability.

  • Wide range of operating temperatures
  • High efficiency and stability
  • Operation with constant power
  • Active power factor correction (Active PFC)
  • High degree of IP protection
  • Appliance class 2
  • Remote control option for the Smart City function,
  • Excellent price to performance ratio.

XLG-100-H-A Figure 1. Constant power driver XLG-100-H-A

Drivers from the XLG series – shown in Figure 1 – compact-sized, or from the ELG series with excellent price to performance ratio, or from the HLG series with high efficiency, will all be a very good choice for this type of applications.

For additional savings of energy, D2 versions of the ELG series (optionally for the HLG model) are equipped with the "Smart Timer Dimming" function.

What exactly is "Smart Timer Dimming"?

With this function, the dimming percentage can be varied over a 14 hour period, from 00:00 to 14:00, according to three default profiles (home lighting, road lighting or tunnel road lighting). Alternatively, the programming interface SDP-001 can be used, which enables the driver to be programmed with user-defined profiles.

Stage lighting

LED light sources are also a good choice in the creative sector, e.g. for theatres or music-halls, on modern stages, where their range of applications is exceptionally wide.

In the case of RGB solutions, drivers with the function of voltage adjustment (CV) from MEAN WELL can be used as highly stable power supplies for LED drivers in the DMX standard, thanks to their high scalability and a wide range of applications. However, in the case of high-power monochrome solutions (for example spotlights with a focused beam), we advise to use e.g. the HBG series drivers with a cylindrical shape, which is perfectly suited for this purpose.

Lighting for intensive crops

LED lighting used in the intensive cultivation of plants in greenhouses has replaced, due to its advantages, the previously used light sources, i.e. high-pressure sodium lamps. The main advantage of the change was that it became possible to use combinations of differently-coloured LED lamps to obtain appropriate shades of light, depending on the species of grown crops or their growth stages. Apart from their efficiency, reliability, insulation and protection, which already characterised the previous category, drivers intended for these applications should also have following features:

  • High output power
  • Wide range of control, also in the case of high voltage

LCM-40KN LED drivers from the LCM series by MEAN WELL

The devices from the HVGC series (Figure 7) are particularly suitable for applications in the agricultural sector, due to their special properties. In this field of application, the use of high power is common, so the possibility to connect 2 phases on a three-phase line (input 400 V AC) is extremely useful, as it has a positive effect on energy efficiency and a significant reduction of the input current. In these cases, the "Active PFC" system has proved to be particularly beneficial.

What is an active PFC system and what are its advantages?

PFC or "Power Factor Correction" or active power factor correction, is a very useful feature that eliminates one of the common problems with input states in less advanced drivers without this feature. Figure 3 shows the voltage (green) and current (red) waveforms connected with the AC input of the power supply of this type. The left side of the figure shows the waveform of the current consumed by the device without the active PFC system. If we take a closer look, we can see that the current waveform is not only shifted in relation to the voltage, but is also significantly distorted. This situation cannot be neglected, because it decreases the efficiency of the electrical installation (high currents in relation to the actually transmitted active power). Moreover, such a state is contrary to the law and is punished by energy companies by applying increased tariffs for businesses and industrial customers. The active PFC system used in MEAN WELL drivers, thanks to its continuous operation and the automatic adjustment function, enables a significant reduction of the current waveform distortion and of the shift between two signals (as shown in the right part of Figure 3), bringing the power factor to 0.9 or more, regardless of the load.

Voltage waveforms Figure 3. Voltage (green) and current (red) waveforms at the AC input of the driver without the power factor control system (left) and with the Active PFC system (right).

What are the standards for LED lighting power supplies?

Standard LED power supplies are usually current source (CC – constant current) or voltage source (CV – constant voltage) devices. The best way to find out which one you need is to read the technical specifications of used components, provided by the manufacturers.

Current source power supplies (CC – constant current)

LEDs (single or connected in series) are powered by a driver that constantly controls and adjusts the intensity of the current flowing through the semiconductor connectors. An example of this type of devices is the MEAN WELL family of low-pulsation current source drivers from the HVGC series, available with output currents of 350 mA to 7 A, able to maintain a wide voltage range, variable depending on the number of LEDs forming a circuit controlled by the driver.

Voltage source (CV – constant voltage) power supply

In this case, the driver precisely controls and adjusts the voltage reaching the LEDs that support this operating mode. The supplied current depends on the number of connected elements, while the integrated driver protection prevents the exceedance of power limits determined in the data sheet. The APV series from MEAN WELL is an example of the application of the "Constant Voltage" solution. It includes devices with output voltages of 5 V to 48 V, adjustable or constant, and currents of 0.3 A to 40 A.

LED power supply with a 40 A output? What does it do?

Safety standards for Hazardous Locations (HazLoc) stipulate, in principle, the use of low voltage sources. Also, the risk of creating sparks or electric arcs should be minimized. Therefore, designs of such installations prefer parallel connection of lighting devices as well as higher currents. It is to the detriment of efficiency, but to the benefit of the level of operational safety and maintenance of these installations.

The driver HLG-600H-12 is an example of a device adapted to this type of high-current CV applications.

Why is LED power supply such an important and decisive factor?

LEDs, like all semiconductors, are characterized by temperature drift. Depending on the temperature change, the voltage at the Vf connection of the components also changes. In order to control them properly, this phenomenon should always be taken into account. Let us give you a practical example: we assume that we need to power a circuit consisting of 50 LEDs connected in a series. By keeping the current of this series circuit constant at 0.35 A and stabilizing the connector’s temperature at 85°C, we will obtain a Vf value of 3.2 V for each LED (not counting any component tolerances) and a total voltage at the driver output of 160 V. Nevertheless, if we had to switch on the LED series circuit at an extremely low temperature, the situation at the output of the power supply would be very different.

Figure 4 shows the ratio of connector’s temperature to Vf (for the current value as given previously). We can see that at 0°C the diode's operating voltage is 3.6 V, which, when multiplied by 50 gives the final value of 180 V – this is the value the power supply should be able to provide, while keeping the current constant (in constant current applications) or reducing it proportionally (in constant power applications). One of the most important features of the appropriate driver is its wide operating range, ensuring stable operation of LEDs in an exceptionally wide temperature range, and the fact that it enables the LED series to be switched on also in low temperatures ("Cold Start" function).

Temperature to Vf ratio Figure 4. Temperature to Vf ratio

Cold Start? What is it?

In MEAN WELL drivers, this feature allows to modify the working conditions of the driver during cold switching on of the lighting system. In the previous example, we showed how a good driver responds to LEDs temperature changes, not only maintaining a certain current, but also monitoring if the total voltage does not exceed the limits of the system. Let us take the HLG-480H-C2100 model as a reference. The specifications in Figure 5 show that it can produce a maximum current of 2.1 A, with a maximum power of 481 W, and is able to effectively regulate the voltage (in the constant current mode) in the range from 114 V to 229 V.

Main technical data of the driver Figure 5. Main technical data of the HLG-480H-C2100 driver

Figure 6 shows a graph that illustrates the above-mentioned operating range of the driver (gray, the operating voltage range is shown on the X axis, the current range on the Y axis).

Operating range for the cold-start function Figure 6. Standard (gray) and extended (white) operating range for the cold-start function

During normal operation, once the system has been thermally stabilized, the V-I work ratio is always within this zone. When switched on at extremely low temperatures, MEAN WELL drivers temporarily "modify" these ranges, and increase the operating voltage by 20% while simultaneously reducing the generated current. This temporary compromise keeps the power supply operating in the white zone (shown in Figure 6), thus allowing the system to boot normally. After the LEDs are thermally stabilized, the standard parameters provided for in the device specification are restored.

What is the "Flicker Free" function?

In standard-quality LED drivers, under operating conditions, when voltage approaches the regulated limits, a high level of low-frequency pulsation at the output of the first section of the power supply makes the operation dependent on the PWM controller, and consequently (despite its relatively high switching frequency) the "flickering" of the light produced by the LEDs is visible. This phenomenon is associated with the high value of the residual component of 100 Hz frequency, resulting from the first section. In the products from MEAN WELL, the solutions ensuring a low level of pulsation in the first section and a wide margin between the peak voltage and the maximum value regulated at the output guarantee the operation of the lighting system without flickering.

HVGC-1000A-L-AB Figure 7. The HVGC series by MEAN WELL, with high power and a wide range of applications

For example, the LDC series from MEAN WELL, which is especially appreciated in home lighting installations, has this feature.

How can the driver be powered?

Basically, the drivers can be powered with a wide spectrum of AC voltages, ranging (depending on the model) from 90 V to over 300 V. For the benefit of versatility, some versions can also be operated with a DC voltage of 110 V to 430 V, depending on the model.

What connections are placed at the driver input and output?

Normally, there are power input connections, AC or DC, and an output for LED. In more advanced models, apart from simple I/O connections, we can also find control inputs for adjusting (dimming) the light emitted by LEDs. In some cases, there is also an input for connecting a sensor of ambient temperature (NTC). The connection standards in most cases are 0-10V and DALI.

What is the "0-10 V" standard?

The 0-10 V signal control has been known for over twenty years and is one of the simplest, most widespread and proven analogue brightness control protocols for LED drivers and power supplies for lighting systems. The control input supports DC voltage, which can be from 0 V (corresponding to the output level = 0%, lights off) to 10V (output = 100%, full brightness). This system has many advantages, including:

  • Linearity of adjustment, from 0 to 100%
  • Safety (in the case of interruption of the controlling signal, the driver output is set to 100%)
  • Exceptional simplicity, requiring no complex control electronics

What is DALI?

DALI (Digital Addressable Lighting Interface) is a digital evolution of the 0-10V standard. It is a manufacturer-independent protocol, defined in the IEC62386 standard, which warrants the interoperability of control devices used in lighting installations. Digital control is definitely more universal than the analogue 0-10 V standard and enables controlling and addressing individually up to 64 devices, which can additionally be divided into 16 groups and 16 separate control scenarios. Moreover, its linear (BUS) as well as star topology enables significant reduction of cabling complexity.

I have a home automation system in a KNX standard: are there any LED drivers that can be connected?

Yes, for example the LCM-KN series MEAN WELL models. KNX is the first standard that can be used in building automation systems that meets the requirements of European (EN50090 - EN13321-1) and global (ISO/IEC 14543) standards. To manage the powers that are higher than those offered by the LCM series, you can use the KNX-DALI KDA-64 input, thus controlling other DALI-compatible drivers or actuators/dimmers from the KAA series

Can a PWM control signal be used at the input?

Of course. In models with this solution, lighting can also be controlled this way. The PWM (Pulse Width Modulation) control signal typically uses a constant voltage (10 V) power source that is then periodically interrupted for a period called a duty cycle lasting from 0 to 100% of the time interval used, as shown in Figure 8 (which shows three examples with values of 50, 75 and 25%).

Duty cycle Figure 8. Examples of 50, 75 and 25% duty cycle

The values obtained at the driver's output are proportional to the duty cycle of the input signal. Also, this type of (analogue) control has many advantages related to the simplicity of wiring and the use of the 0-10V standard, but it also has many limitations. Special digital converters can be installed for more versatility when using PWM control.

What interfaces can be used in this type of control?

The DALI-PWM DAP-04 converter from MEAN WELL allows you to overcome the limitations resulting from the use of PWM control, by accepting the input signal in accordance with DALI standards and generating four PWM signals on the output (separately addressable), thanks to which you can control the same number of drivers with PWM inputs with the Active-High or Active-Low logic. It is an exceptionally advantageous solution that facilitates the connection of LED drivers which do not enable digital control.

Are LED drivers adapted to work outdoors?

Of course, but not in all cases. The best way to check whether the product you are interested in is suitable for outdoor use (or in partially roofed rooms) is to find its IP protection level in the technical specification provided by the manufacturer. These IP codes are established by the International Standard IEC 60529 and they determine in detail the level of water resistance of electrical devices. However, it is always advisable to limit the conditions in which drivers are exposed to the elements and sunlight. If in doubt, please consult the MEAN WELL customer service. They will help you choose the product that is most suitable for your needs.

See the LED drivers in our catalogue

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