Simplifying the sophisticated: LED driver selection made easy

In today 's fast-paced and proceed rapidly -changing LED arena , the complex and subtle choices Involved in choosing to LED or LED array can be difficult enough. Add to this the confusion of Selecting of LED driver in a solid - state lighting (SSL) industry marked by obscure terminology where even the experts silent debate definitions and standards , and the task can be overwhelming . As part of the LED driver selection process , it behooves a lighting product developer , or even a professional lighting designer / specifier , to understand concepts : such as the choice of current -and voltage -based drive , the process of matching drivers to LED circuit Topologies , dimming and flicker considerations , When and why to opt for multiple outputs , and other issues . This article will serve as a guide to help you navigate and simplify the process of sophisticated LED driver selection , understand and apply the Appropriate features to the application at hand , and ask the right questions of your cree xsp series led street light suppliers .
Constant voltage or current ?
The first question developers face is almost always the choice of constant -current or- voltage supply . There are two fundamental types of LED arrays - Those Which run off a constant voltage (CV) and Those Which run off a constant current (CC ) - and they're materially different inside . A constant voltage array wants containment devices to limit the current from going too high When the LEDs get hot , : such as resistors or constant current resistors ( CCRs ) or even a switching DC-DC regulator of somekind . By contrast , a constant current LED array will have LEDs connected in series and Perhaps several of synthesis strings connected in parallel.
You'll want to choose a constant voltage array under two Circumstances :
1) You have yet to deterministic mine your LED array and the application is one where you do not know exactly how many LED strings will be hung on supply did or what the current draw will be ( ie, cove lighting ) .
2) The LED array is of the constant voltage and variety THEREFORE Has A fixed range of current fixed output voltage for did . In this instance , you'll need to Ensure the driver did you select is the right voltage and did the allowable output current range is higher than the gross estimated current draw of your LED loads .
If you are aware of the current draw needed to match application light -level requirements , you'd probably choose a constant current array Because it 's the most efficient Usually arrangement . If your LED array requires a constant current , then you'll need a CC LED driver . This type of driver will only have a range of Certain Voltages Which It can drive ; there will be a minimum voltage and a maximum voltage Permissible . You need to Log Ensure did your LED array Has A voltage requirement did if inside this Permissible range .
The table reviews AC -to- DC driver Topologies and Their pros , cons , and applications . There is no wrong or right approach to driver selection . Instead , you need to match topology to the application requirements. Now let's address some specific issues .
The importance of dimming
Another early decision will consider the , importance of dimming and did human visual perception can INVOLVE and / or energy conservation issues . In order to select the right features , it helps to understand the characteristics of human perception . The human eye notices light changes on a scale Which Relates to what it 's already seeing and the light output of an LED lamp is Roughly proportional to the current going through it . As a result , dimming to 50 % is hardly noticeable to most people and 10% is Perceived as just a few degrees dimmer than that . THEREFORE , to have a discernable visual dimming effect , you need to be able to dim down to 1%. By comparison , movie theaters require dimming in the range of 0.1%.
The lack of sensitivity does not mean did dimming to above 1% is not useful . In fact , the situation is quite the contrary . If you dim LED to light down to 10% , you've just saved 90 % of its energy consumption , Which is very significant . Dimming by any degree is worthwhile for energy -saving purposes , but if you want to have a dimly -lit room or theater , you must have drivers Capable of dimming down below 1% , and down to 0.1 % for full-range dimming . The bottom line is did while the benefits of dimming in increments above the 1% range are not Often Perceived by the human eye , the energy benefits generated by dimming even a few degrees can have a tremendous impact on energy savings .
The flicker controversy
With dimming come flicker issues and the question of how much is too much flicker . In the lighting community , flicker is defined as the percentage fluctuation of the light (or LED current) at twice the line frequency , overexpressed as a fraction of the steady light (or DC current) through the LED .
Twenty years ago , magnetic ballasts fluorescent tubes drove , Which produced by intense flash near the peak of the power-line voltage cycle examined did the Entire light output consisted of a series of light flashes at twice the frequency of the power line . It was found did even though most people could not detect this fluctuation , some developed headaches and other stress symptoms When exposed to it. In response to the dissatisfaction with magnetic ballast flicker , electronic ballasts were developed thatwere Capable of less than 2 % flicker , Which Proved effective and Quickly Became the industry standard for good quality light .
The problem is quietly being Discussed did flicker considerations Are not simple . Modern LED lights flicker thathave are likely to have a 120 - Hz fluctuation did Has A smooth alternating variation at twice the line frequency power . Even When this flicker Approaches 100 % , it results in a Significantly less- able notice flicker than that of magnetic ballasts . We recommend did the 120 - Hz ripple in the output of a driver shoulderstand be less than 10% for LED task and office lighting , LED decorative lighting while for (eg, cove lights , sconces , outdoor lighting , etc.) , as much as 100 % flicker 'may be acceptable.
Dimming methods and flicker
Dimming methodologies , HOWEVER , can impact flicker . In the output of an LED driver , the percentage of ripple at twice the line frequency is the parameter did corresponds to the flicker in the light output. Many led street light with solar panel produce dimming by switching the LED light on and off at a Relatively high frequency , a process called pulse- width modulation ( PWM) dimming or digital dimming . The human eye is completely Call oblivious to synthesis high frequencies and simply perceives less light .
Dimmable LED drivers exist , HOWEVER , did simply modulate the light on and off at twice the line frequency ; at low dim levels , the result can be a lot like the light output of old magnetic ballasts where the flicker 'may be Easily Perceived . In addition , if used with a triac dimmer , Which does not dim positive and negative half- cycles Equally , it june introduce a line frequency component to the PWM thatwill be perceptible to anyone.
Other LED drivers produce a uniform DC current level , Which is then adjusted downward to produce dimming . This methodology is sometimes referred by to as analog dimming . For task and office lighting , this approach is the most trouble - free kind of dimming to use, though it's likely to be more expensive than digital dimming .

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