Edn overcome the challenges of driving parallel led strings. What you can do is give each system each own driver and supply all the drivers together with a pcm modulated signal maybe dmx. Another led driver circuit based on the mp3302 led driver ic. In the formula we simply change the total forward voltage as show below. The up side of these large drivers with multiple parallel strings is you still have a class ii fixture and can use the bjb solderless connectors. The led strings are connected to internal current sources where the current level is set with an external resistor. Parallel components have the same voltage across them but fluctuating currents. There are two ways to supply a led system module or luminaire. Led driver ics system knowhow applications flexibilitiy st position. Using constant current drivers with parallel led strips.
Driving a large number of leds with a constant current can be done with either a lengthy series connection or by driving multiple strings in. It balances the current provided by the supply in a preset ratio for each active led string, where an active string is a fully turned on led string, regardless of the number of strings connected to. Due to regulatory requirements especially in class ii environments there is always a limitation on how many leds can be connected in series. The fan5607 constantcurrent parallel led driver from fair child semiconductor provides analog andor pulsewidthmodulation brightness control for lcd back lighting in ultraportable applications. The simplest way to drive parallel strings is with a fixed voltage source and a series currentsetting resistor.
The led driver will deliver a constant current at a voltage that is the average of the combined forward voltages of each string. Drives from one to two parallel led strings at up to 38 v at 25 ma per string. Parallel connections will always give you the most even and consistent lighting output due to less voltage drop with less serial connections. As you can see there is a drastic difference in the voltage and current needed to operate each of these circuits. When that is the case i usually test them cautiously with batteries starting at 1. The lm3466 integrates a linear led driver for lighting systems which consist of multiple led strings powered by a constant current power supply. Bcr linear led driver ics are the best choice when you need to drive led strings supplied by a dc voltage source. Led load can simulate any of these configurations by programming the correct values for vo, vd and rd. My plan is to wire up both 2 channels of 2 vesta strips, 4 channels total in parallel to that driver which in theory would drive each channel at 750ma, within max spec of 1a. Dimming is possible by by passing the current to a led string with a simple switch. Multiple strings of seriesconnected leds can be placed in parallel and driven by multioutput constantcurrent drivers to limit the drive voltage. How to connect multiple leds together tutorial youtube.
Driving an led with or without a resistor tinkerlog. Using one is very important in preventing damage to your leds as the forward voltage v f. The issues and solutions you may encounter when driving multiple led strings from a constant current source. Driving multiple led strings connecting the leds as two strings of five wired in parallel requires a higher current 700ma constant current source but only 16. Led strips are long and come in a series in the nonengineering sense, as in one after the other, but in reality they are made up of many parallel branches, comprised of 3 leds each for led strips rated at 12v or 6 leds each in a 24v led strip. Maxims continually expanding portfolio includes products covering the full range of efficient switchmode topologies stepdown, stepup, sepic as well as some linear led drivers. An object of the present disclosure is to provide an efficient led driver for parallel strings of series connected leds. Below you will see two circuits using five leds 16014451nd. For example, the lpc35700 driver will output 700ma at all times, regardless of how many leds are attached to the driver assuming youre running one string in series off the driver, as opposed to say multiple parallel strings. For 36 leds four strings with an lt3517 for each string may do.
Us20080001547a1 driving parallel strings of series. Currentlimiting devices in each led string are recommended when using a constant voltage driver. Thus a low cost buck converter running from 24vdc can be used. My original supply is directly from car battery which gives a spike of 9v16v. A currentmode stepup controller drives up to six parallel strings of multiple seriesconnected leds. An led driver is an electrical device that regulates power to an led or a string of leds. The three ps of led driver selection power electronics. The total current is the sum of currents through each led. Suppose we want to drive an led string with 400 ma. This means the supply that i need to give to the driver should be 8. The eup2990 regulates the current in each led string to the programmed value. After doing some research mostly here ive landed on the 75w thomas research products cc led driver with bridgelux vesta 2ft strips.
Led driver circuit with lm317t for parallel strings. Multistring led driver with accurate current matching and. Led solutions for lcd backlighting mouser electronics. Lm3466 multistring led current balancer for use with. Think of a parallel connection as each 1020ft section of your led lights running independently back to the power supply rather than linking them in a single series.
A common current the circuit needs open circuit protection. Option a is the baseline, each string is driven separately. Lm36922h highly efficient dualstring white led driver datasheet rev. Constant current paralling controller for midpower leds kit lti.
If one string fails figure 2b, the driver still produces 1. The led calculator will display the resistance value, draw a small schematic and show you the color code of the nearest lower and higher. A unique dynamic current equalizing control scheme enables communication between each lm3466 led driver to divide current equally or ratiometrically amongst multiple active led strings. The switching frequency is programmable by an external frequency setting resistor. In certain embodiments, these leds can comprise combinations of red, blue. I am using a design i found on the net, its a current mirror, but also has protection for open circuits so that one string doesnt get all the current if the other string opens. The result of driving led strings rather than an individual. National semiconductors new highbrightness led driver. If you would attach an led to a 5 volt power supply directly, you would burn it instantly.
Whenever you use parallel strings we highly recommend the use of resistors and fuses. Here are a few bullet points for reference about a parallel circuit. These long led strings are commonly found in streetlights and parking garage lights. Connecting multiple leds to a constant current led driver in parallel should be avoided where possibleconstant current led drivers are. How a circuit is wired will determine the voltage and current needed to properly operate the circuit. Current distribution in parallel led strings ee publishers. Also, some care is required with led drivers capable of delivering many amps of current. A complete fixture can be constructed by repeating the strings in parallel. Infineon bcrs are suitable for driving currents from 10 250ma driving current, making the ideal solution for low and mid power leds. Is it safe to drive multiple strings of leds in parallel. If your led has a nominal power of 10w and load voltage of 35v, then.
Dimmable drivers on the other hand have variable current levels. The max8790 is a highefficiency driver for white light emitting diodes leds. Driving parallel strings of leds pose additional design challenges over single strings, such as tolerating voltage imbalance, current regulation methods, minimizing power dissipation and fault conditions. Max8790 sixstrin white led driver ith active current. Drivers u1 and u2 max16803 are good for automotive use because they have a high inputvoltage range, excellent thermal qualities, and the.
The highpower led string drivers use internal current control mosfets to sink up to 100ma per string, and can drive 16 parallel strings of 10 white leds each, for a total of 160 white leds per device. Therefore, one of the first decisions a designer must make is whether to drive the leds in series, in parallel, or as a parallel array of strings. The simplest way to drive parallel strings is with a. I am making an led driver circuit which will drive 2 strings of leds connected in parallel. One of the standard practices to overcome this issue is to have multiple parallel strings of series leds driven from a single constant current cc source. The disadvantage of connecting many strings in parallel is that a driver capable of delivering several amps will be required and this would be expensive or hard to find.
They are configured as either inductorless charge pump or switching regulatorbased led drivers that support driving white leds in series, parallel. How to calculate and connect leds in series and parallel. Come back for more led information and projects in the future. Connecting led strips in series vs parallel waveform. Avoid connecting multiple leds to a constant current led driver in. Another constraint is minimising the number of wires running from the light to the driver. The led driver can provide a common voltage, or the target led current might vary with the intended number of leds used within strings. In this case the leds are connected in parallel so that the same voltage is applied to each of them, which presents the disadvantage of the losses associated with the circuit of equalization resistance necessary, as we shall see below. Well they can but its usually not a good idea to parallel leds directly.
When many strings of leds are used in series, the most efficient way to drive them is with a constantcurrent power supply, which connects the leds directly across the terminals of the power supply. System solutions technology integration and innovation excellent technical support stmicroelectronics, datapoint and darnell 2008 isupply 2010. Led university led grow lights, drivers, heatsinks and. Highbrightness led drivers are integrated circuits that are optimized to efficiently drive strings of highbrightness leds. The lt3517 may be used with 30 vin and a string of 9 leds. Also, it will send more current into the parallel strings, which increases their temperature and will damage them if the current is. Instead, the current is what becomes split among the leds in a parallel circuit. Current mirror for parallel leds all about circuits. Designing led lighting systems for optimal light output. Balancing led current in parallel string eeweb community. Led driver ic analog devices has a very broad line of led driver ics for automotive, display backlighting, handheld, and general highpower lighting applications. If a buck topology is desired, the led array can be broken down into parallel strings such that the led string voltages are less than the minimum input voltage. Led series current limiting resistor calculator useful when designing circuits with a single led or series parallel led arrays for both the common smallcurrent 20ma leds and the more expensive, high power leds with currents up to a few amperes.
It is a crucial piece to an led circuit and to operate without one will result in system failure. In contrast, when a single driver is used for leds all wired in parallel, the driver needs to be a lowvoltage, highercurrent source, but such sources tend to be inefficient in dcdc conversion compared to highervoltage ones. To obtain optimum efficiency, a constant current, or cc, drivers with a narrow output voltage and current provide the best answer. Dont let electrical circuits and wiring led components sound daunting or. Article library supplying high voltage for led strings supplying high voltage for led strings by bill schweber. In a dcdriven circuit shown in figure 2a, the 24v dc constant current driver sends 1. It is designed for large liquid crystal displays lcds that employ an array of leds as the light source. Many beginners ask why leds cant be wired in parallel to share a common currentlimiting resistor as shown in figure 1. If your driver outputs 36v, then every single cob that you have hooked up to it in parallel will have that same 36v across it. Im designing a circuit to power high power leds, instead of individual drivers and i want to power several in series parallel.
Overcome the challenges of driving parallel led strings edn. The proposed multistring led driver is implemented in a 5 v 0. This circuit can drive 9 parallel strings of three white leds in series and can be operated from a 3v dc supply and it is suitable for single cell applications. For high power leds linear controller ics with external power stage allow for great flexibility. No worries, we can still make a string of these 2 leds and put it in parallel with the remaining 33 strings. Its a constant current driver with very little heat loss. Using the example shown with a ma output driver, each led would receive 333ma. Lm36922h data sheet, product information and support. Thats the point where the current limiting resistor comes in. Large parallel strings of leds electrical engineering. The led array configuration can be arranged to allow for a desired driver topology. It is possible to place more then one module in parallel to a driver.