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5 Important Factors When Buying LED Drivers
5 Important Factors When Buying LED Drivers
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5 Important Factors When Buying LED Drivers

WILMINGTON, Mass.--(BUSINESS WIRE)--Jul 31, 2017--Osram, a leading global lighting and technology company, today announced its OPTOTRONIC?Dual-Mode Programmable Emergency LED Driver, the market's first programmable single-driver solution for emergency Solid State Lighting fixtures, which offers the ability to program and customize the light output in both normal and emergency operations.A separate snap-on battery pack with harness, available in slim, linear and compact options, powers emergency lighting in the event of an outage and provides up to 18W in back-up mode. The complete solution reduces the number of components required per emergency luminaire, substantially simplifies in-fixture wiring, and enables OEMs to better tailor their fixtures to application requirements while reducing the number of SKUs they must inventory.

Industry's First Dual-Mode LED Driver with Programmable Emergency Light Levels Offers OEMs Greater Flexibility, Simplifies Manufacturing (Photo: Business Wire)

"Emergency lighting luminaires typically require a dedicated emergency driver, a dedicated LED driver and numerous wiring connections, creating a complex manufacturing process and often compatibility issues for OEMs," said Tom Shottes, Head of Osram Digital Systems, Americas Region. "Osram's new OPTOTRONIC? Programmable CE Emergency LED Driver combines the emergency and standard LED drivers into one solution, addressing key issues experienced by OEMs. The ability to program and tailor the light output in both standard and emergency mode offers additional value and flexibility in designing emergency lighting fixtures."

The National Fire Protection Association's code has a minimum requirement of one foot candle of light on the ground for at least 90 minutes to allow people to safely and efficiently exit a building in the event of an emergency. A programmable emergency driver solution enables OEMs to support customers with tailored and optimized emergency led driver accessories, irrespective of the building architecture, space and lighting plans.

The lamp inrush current on switching LEDs has become an area of concern in the lighting industry. 'Inrush current' of the LED drivers refers to the input current of short duration that flows into the LED driver, during the initial start-up, to charge the capacitors on the input side. Typically, this is a short duration current, whose amplitude is much greater than the operating or steady-state current. The inrush current is due to the EMC filter on the input and bulk capacitor on the boost circuit this is inherent to the LED technology.

The figure shows the nature of the inrush current and its peak, IMAX. T50 is the time duration in which the inrush current pulse is equal to 50% of IMAX. It shows an example of inrush current (IMAX) and T50 times for a typical LED driver.

If there are a number of LED drivers in an LED Luminaire, and if there are a number of such LED Luminaires on one circuit, the max peak inrush current and it's duration may be additive. However, it is not an exact mathematical calculation; i.e. for "N" drivers connected in parallel does not equal exact "N" times the inrush current for one driver or N times the T50 time for one driver. It depends on the impedance of each driver and the line impedance.

The line impedance has a significant effect on the peak and duration of the inrush current. Transformer type and size, wire size, length of runs, and other devices in the circuit path are a few things that could lead to high impedance.

The inrush current and the duration of the LED driver differs from manufacturer to manufacturer and from model to model. As this current duration is very small, sophisticated instruments with very high sampling rates need to be used for exact calculations. The inrush current also depends on the exact moment of switching, during the alternating cycle.

For a typical 150W, 0.7A LED driver, Philips Model 9137012116, used in various CREE luminaires, the inrush current is stated as 130Amp for 165 Micro Seconds. It is suggested that up to 7 -10 of these drivers be used / per 20A C curve MCB, however it will depend on the individual circuit impedance.

For a typical 220W, 1.05A LED driver, CREE Model LE098X01 used in CREE High Output Edge luminaires, the inrush current is stated as 80 Amp for 1000uS (1mS). It is suggested that up to 6 – 8 of these drivers be used /per 20A C curve MCB, however, it will depend on the individual circuit impedance.

A general recommendation is to use C curve circuit breaker with the highest current rating that is allowed by the circuit cable size. The MCB used needs to have sufficient clearing time for the inrush current to clear, without creating the nuisance tripping on power up. This will give protection from a short circuit and prevent overheating of wiring and connections. MCBs operate by tripping open on detection of an overload or short circuit condition. The tripping point relates to the magnitude of electrical energy being passed – and this in turn depends significantly on both the inrush current peak value and its time duration. Accordingly, an MCB could be tripped either by a high peak of short duration, or a lower peak of longer duration. In either case, the objective is to ensure that the MCB trips before passing excessive energy, yet does not trip and cause lighting blackouts, when it does not need to.

Please see below, a typical MCB tripping curve showing the amount of time required for a circuit breaker to trip, at a given overcurrent level. These curves differ from manufacturer to manufacturer and from type to type. Typically, the B type MCB curve has the operating range of 3 to 5 In, C type has 5 to 10In and D type has 10-14 In.

LED drivers (also known as LED power supplies) are similar to ballasts for fluorescent lamps or transformers for low-voltage bulbs: they provide LEDs with the correct power supply to function and perform at their best. If you read our previous article on whether or not your LED requires a driver, you'll already know that all LEDs require a driver and that the question you should really be asking is whether or not your LED requires an external driver. You'll also know that there are two main kinds of external LED drivers, constant-current and constant-voltage, and that the driver you need depends on whether or not your LED light source already includes a constant-current driver within the light (if so, you would need a constant-voltage driver; if not, you need a separate constant-current driver). Now that you're certain your LED light requires an external driver as well as what type, it's time to narrow down to the specs you need to consider when making a purchasing decision. Here are five factors that will help you make the right selection.

First, consider the voltage requirements of your light. If your 4W UL emergency led driver, use a 12-volt driver; if it uses 24 volts, use a 24-volt driver, etc. When choosing a driver for a constant-current LED, you must also consider the LED's current output, which is measured in amps or milliamps. In short, make sure your driver will achieve power outputs within your light's specified ranges: consider both voltage and current range for a constant-current driver, and simply voltage range for a constant-voltage driver.

Input Voltage / Current

Next, consider the voltage supply of the location you'll be using your light. Your driver must accept the input voltage of the place you're using your light so it can properly step it down to the right output voltage. Conventional homes supply a standard of 120 volts, and most commercial or industrial enterprises supply 277 volts, though it's best to check with an electrician if you're not sure. Most drivers accept a wide range of input voltages. Again, when choosing a driver for a constant-current LED, you must consider the LED's current input as well.

Max Wattage

Lastly, consider the wattage requirements of your light. Choose a driver with a max wattage higher than the wattage of your light. Do not pair a driver with a light that exceeds the driver's maximum wattage or with a light that uses less than 50% of the driver's maximum wattage.

2. Dimming

Both constant-current and constant-voltage LEDs and drivers can be made with a dimming capability, though both must specify that they are dimmable in the product datasheet for that assertion to be made. If the specs don't mention dimming at all, it is safe to assume that the product is not dimmable, and the same goes for household LEDs with internal drivers. Dimmable external drivers often require an external dimmer or other dimming control devices specified on the product datasheet to work.

3. Safety

IP Ratings

IP ratings tell users the environmental protection that a driver's enclosure provides. The first number specifies protection against solid objects, and the second number specifies protection against water elements. For example, according to the chart below, a driver with an IP67 rating is protected against dust and temporary immersion in water.

UL Listed Emergency LED Driver, meaning output is considered safe to contact and no major safety protection is required at the LED / luminaire level. There is no risk of fire or electric shock. These drivers operate using less than 60 volts (dry) and 30 volts (wet), less than 5 amps, and less than 100 watts. Although safer, these limitations pose restrictions on the number of LEDs a Class 2 driver can operate.

UL Class 1 drivers have output ranges outside UL Class 2 designations. UL Class 1 drivers have a high-voltage output and safety protection is required within the fixture. Although there are less safety precautions, a Class 1 driver can accommodate more LEDs, making it more efficient than a Class 2 driver.

4. Efficiency

Another key characteristic to choosing LED drivers is efficiency. Efficiency, expressed as a percentage, tells you how much of the input power the driver can actually use to power the LED. Typical efficiencies are between 80-85%, but UL Class 1 drivers that can operate more LEDs are usually more efficient.

5. Power Factor

The last major characteristic to consider is your driver's power factor. Power factor tells you how much of a real power load the driver puts on the electrical network. The range for power factor is between -1 and 1. The closer to 1 the power factor is, the more efficient the driver is. A conventional standard for power factor is 0.9 or above. If power factor isn't mentioned in a driver specification, it implies that the device has a low power factor, below 0.9.

Still have questions about choosing a driver? Let us know in comment or drop us a line on Facebook, Twitter, LinkedIn, or Pinterest!

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