Sourc­ing Mantra

LED driv­ers: The en­gines be­hind LED light­ing sys­tems

Electronics Bazaar - - Contents - By Baishakhi Dutta

The LED bal­last or driver plays a key role in de­ter­min­ing the life of a prod­uct. The con­stant pres­sure to re­duce chip sizes and in­crease lu­mens per watt has forced man­u­fac­tur­ers to come up with mod­i­fied driv­ers equipped with the lat­est tech­nolo­gies. Driv­ers ac­count for nearly 20 per cent of the to­tal cost of the com­po­nents used in an LED light. With LEDs mov­ing into var­i­ous ap­pli­ca­tion ar­eas, their driv­ers need to be more ef­fi­cient and cost-ef­fec­tive.

The In­dian LED light­ing mar­ket gen­er­ated a rev­enue of US$ 168.6 mil­lion in the last few years and is ex­pected to grow at a CAGR of 38 per cent in the up­com­ing years. Cur­rently, the LED driver mar­ket com­prises both im­ports and lo­cally man­u­fac­tured prod­ucts. Do­mes­tic com­pa­nies, how­ever, are set­ting up plants to man­u­fac­ture driv­ers. But the miss­ing link in the In­dian ecosys­tem is lo­cal IP ca­pa­bil­i­ties, though de­sign reg­is­tra­tions are be­ing en­cour­aged.

Types of LED driv­ers

The three types of LED driv­ers are:

• Con­stant cur­rent (350mA, 700mA or 1A) driv­ers

• Con­stant volt­age (10V, 12V or 24V) driv­ers

• AC LED driv­ers

Con­stant cur­rent driv­ers fix the cur­rent, and can vary the volt­age. How­ever, this de­pends on the load of the LED. Con­stant volt­age driv­ers, on the other hand, re­quire a fixed volt­age. The LED loads are added in par­al­lel across the out­put of the driver un­til max­i­mum out­put cur­rents are reached. AC LED driv­ers are ac­tu­ally no-min­i­mum load trans­form­ers, which means that they could tech­ni­cally op­er­ate low-volt­age halo­gen or in­can­des­cent bulbs as well.

The pur­pose of LED driv­ers

LEDs re­quire driv­ers for two pur­poses:

• LEDs are de­signed to run on low volt­age (12-24V), di­rect cur­rent elec­tric­ity. How­ever, most places sup­ply a higher volt­age (120V-277V), AC elec­tric­ity. An LED driver rec­ti­fies higher volt­age, al­ter­nat­ing cur­rent to low volt­age, di­rect cur­rent.

• Driv­ers also pro­tect LEDs from volt­age or cur­rent fluc­tu­a­tions. A change in volt­age could cause a change in the cur­rent be­ing sup­plied to the LEDs. The LED light out­put is pro­por­tional to its cur­rent sup­ply, and LEDs are rated to op­er­ate within a cer­tain cur­rent range (mea­sured in amps). There­fore, too much or too lit­tle cur­rent can cause light out­put to vary or de­grade faster due to higher tem­per­a­tures within the LED.

In­ter­nal vs ex­ter­nal driv­ers

Ev­ery LED light source re­quires a driver. How­ever, some LEDs, par­tic­u­larly those de­signed for house­hold use, con­tain in­ter­nal driv­ers rather than sep­a­rate, ex­ter­nal driv­ers. House­hold bulbs usu­ally in­clude an in­ter­nal driver be­cause it makes re­plac­ing old in­can­des­cent or CFL bulbs eas­ier. These in­clude LED bulbs with stan­dard screw-in or plug-in bases or those that spec­ify a line­volt­age (120 volts) in­put on their datasheet.

LEDs that typ­i­cally re­quire an ex­ter­nal driver in­clude cove lights, down­lights, and tape lights, as well as cer­tain fixtures, pan­els, and out­door-rated lights. These bulbs are of­ten used for com­mer­cial, out­door, or road­way light­ing pur­poses. They typ­i­cally re­quire a sep­a­rate driver be­cause it is sim­pler and cheaper to re­place the driver than the LEDs.

Some­times, LEDs come equipped with a sep­a­rate driver. Oth­er­wise, the man­u­fac­turer’s datasheets will spec­ify whether or not an LED re­quires a sep­a­rate driver, along with the type of driver it re­quires, if nec­es­sary.

The life­time of an LED driver

The driver’s life­time should be an im­por­tant pa­ram­e­ter that buy­ers and in­vestors should con­sider. The longevity of an LED driver is de­ter­mined by the life­time of the in­di­vid­ual elec­tronic com­po­nents in­side it. The weak link is usu­ally the elec­trolytic ca­pac­i­tors, which are typ­i­cally gels that act like lit­tle bat­ter­ies.

The prob­lem arises when these ca­pac­i­tors grad­u­ally evap­o­rate over the com­po­nent’s life­cy­cle, be­cause of the tem­per­a­ture in­side the driver — which, in turn, cor­re­lates with the ex­ter­nal tem­per­a­ture on the driver case. Higher op­er­at­ing tem­per­a­tures speed up ca­pac­i­tor evap­o­ra­tion and, hence, shorten its life.

There is a small cir­cle called the hotspot or ‘Tc point’ on the la­bel of most LED driv­ers, which sig­ni­fies the hottest point on its sur­face dur­ing op­er­a­tion. Us­ing the driver close to this lim­it­ing tem­per­a­ture or Tc point mark short­ens its op­er­at­ing life­time. Op­er­at­ing at a lower tem­per­a­ture en­sures bet­ter dura­bil­ity.

What’s new in the mar­ket

Cur­rently, the LED mar­ket has bal­lasts with a ca­pac­ity rang­ing from 3W to 120W and above. The ca­pac­ity shift de­pends on the wattage of the LED in which the bal­last is be­ing used. At present, there is a con­stant need to re­duce chip sizes and in­crease the lu­mens per watt; so man­u­fac­tur­ers are con­tin­u­ously work­ing on the driv­ers to meet these chal­lenges, thus help­ing to re­duce the cost of the fi­nal prod­uct.

One tech­nol­ogy to watch for is Light Fidelity (Li-Fi) as it has been get­ting a lot of at­ten­tion lately. This bidi­rec­tional, high-speed and fully net­worked wire­less com­mu­ni­ca­tion tech­nol­ogy uses LEDs.

What the fu­ture holds

The lat­est de­vel­op­ment in the LED driver mar­ket is the en­try of AC-powered LEDs. These avoid the use of ACDC con­vert­ers and can be powered di­rectly from the AC mains with min­i­mal driver tech­nol­ogy. The fu­ture of LED driv­ers should log­i­cally lie in the de­vel­op­ment of in­no­va­tive driv­ing tech­niques for AC LEDs.


With LED sys­tems gain­ing promi­nence, the need for stan­dards be­comes crit­i­cal. Presently, the stan­dards

that are im­por­tant in­clude En­ergy Star, IEC stan­dards, UL and RoHS.

IS stan­dards have been re­leased, but have not been made manda­tory. How­ever, they will soon be ap­pli­ca­ble. This will help to bring qual­ity prod­ucts to the con­sumers and curb im­ports, which is a ma­jor worry for the in­dus­try at present.

The im­por­tance of se­lect­ing the right LED driver

Cur­rent can only flow in one di­rec­tion through an LED (diode). The in­ter­nal op­er­a­tions that go on in an LED de­pend on the quan­tity of cur­rent flow­ing through it. Due to the di­rect cor­re­la­tion be­tween cur­rent in­ten­sity and the ac­tions per­formed, an in­crease in op­er­a­tions will lead to a rise in cur­rent flow, which in turn, will in­crease the in­ter­nal tem­per­a­ture. This in­ter­nal tem­per­a­ture needs to be within spec­i­fied lim­its. If these lim­its are crossed, the LED de­vice will mal­func­tion or fail. This limit/thresh­old is kept in check by LED driv­ers. In case the LED driver is not able to con­tain the cur­rent flow within the lim­its spec­i­fied, over­pow­er­ing of the de­vice will ren­der the de­vice use­less or per­ma­nently dam­aged.

In case the LED driver does not re­ceive the nec­es­sary amount of volt­age for its op­er­a­tions, ei­ther the LED will not glow at all due to volt­age short­age, or even if it does, it may flicker or ap­pear com­par­a­tively dim­mer than usual. At times, it may also get dam­aged due to volt­age in­con­sis­tency. So, cau­tious­ness is re­quired.

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