Modules - Beriled

Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | SubscribeqMqM | Next PageqqM qMMQmagsTHE WORLD’S NEWSSTAND ®strategically speaking | DRIVER MARKETconstant, high-current sources, which areunusual in electronics and create unusualchallenges for product engineers. Moreover,the designs are complex and unique to everyLED product. The end-product features areconstantly evolving: from keypads to touchscreens,from one type of edge-lighting toanother, and so forth. And, there is a wide varietyof supply arrangements that obscure thelandscape for observers: from conventionalsuppliers to contract manufacturers to widespreaduse of chip foundries to manufacturersof custom ICs for specialized driver designs.Fig. 4 shows some examples of LED drivercircuits driven from a DC voltage. Thestrings of LEDs, shown in the figure as singlediodes, require at least some current control.A common design uses only a resistor tolimit the current (Fig. 4a). This approach issimple and inexpensive, and is common invehicle lighting, but is inadequate for applicationsdemanding precise control and uniformity,such as backlights or signs. Substitutinga linear regulator (not shown) for thecurrent-limiting resistor improves the currentcontrol. Ganging multiple regulators inparallel into an IC can reduce the componentcount and improve reliability (Fig. 4b).Controlling the input rail voltage is normallyconsidered the task of the system’spower supply, but many LED applicationsrequire a voltage conversion to match theLED load. An IC may be dedicated for thatpurpose (Fig. 4c). For example, LED backlightscan operate with strings of up to 10 ormore LEDs in series, with a total string voltageof 60V or more.FIG. 2. An LED driveris the electrical circuit,minus the LEDs. The drivermay include one or more driver ICs,or none. The driver at left from ROALElectronics and the driver IC at right fromTI both serve LED lighting.3. IC integration and customizationVoltage conversion creates another option: theconverter IC may be combined with a currentregulatingfunction on the same chip (Fig. 4d).The choice to integrate voltage conversionand current regulation depends on many factors,such as the need for reduced componentcount, current requirements, and so forth.LED driver ICs are especially vexingbecause of the ways that multiple functionsor components can be integrated onto onechip. For example, in a handset the LED flashand backlight functions can be managedwith multiple ICs, or they can be integratedinto a single IC, or they can be managed withyet other handset functions in a general-purpose-power-managementIC (PMIC). We considera PMIC to be in a category apart, not anLED driver IC, if it includes management ofbattery recharging and voltage regulationfor other functions. The trend toward PMICstherefore shifts some of the sales of LED driverICs to suppliers of PMICs.The trend toward integration also offersan opportunity for chipmakers that useBCD (bipolar-CMOS-DMOS)processes to fabricate LEDdriver ICs that enable highvoltageoperation. BCD allowsfor integration of diverse circuitelements – such as lowvoltageanalog and high-voltagepower transistors – on thesame chip. It is a high-margingrowth opportunity for thefoundries and chip suppliersthat can do it.Customers must alsochoose between customASICs (application-specificICs) that form a perfect fitfor their application versusoff-the-shelf products thatleverage non-recurring engineeringcosts. Customerscommonly veer between custom and standardproducts depending on many changingdemands in their product cycles.4. Potentially disruptive AC-LEDsNovel AC-LED products have the potentialto complicate the driver market. Inits purest form, the AC-LED eliminatesthe driver, using the diode features of theLED to replace conventional diodes. Otherdesigns use some basic components to limitthe current, but sparingly. If highly successful,the AC-LED could make some LED lightingproducts – such as replacement bulbs– more competitive and greatly expand theLED-lighting market. Such a move could begood for both the LED industry and the endDriverVoltageconverter(External)programmablemicrocontrollerLED(Integrated)current controllerFIG. 3. The driver (dotted rectangle) in this simplifi edcircuit includes a voltage converter and a currentcontrollingelement. The programmable microcontrolleris not part of the driver. It is external to the LEDproduct, and may include such features as timing,dimming, and color control.users, but would displace potential driversales for those products.However, we expect that AC-LEDs will havean impact only in certain product segments.In replacement bulbs, the pressure to innovateis so high that the AC-LED is just one of severalnovel solutions, and there is no room forolder, less-innovative designs. Consequently,58 NOVEMBER/DECEMBER 2011 LEDsmagazine.comPrevious Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | SubscribeqMqM qMM MQmags| Next Page q qTHE WORLD’S NEWSSTAND ®