issue 1 - august 2007 1 www.zetex.com ? zetex semiconductors plc 2007 DN84 zxsc400 driving 3w high power leds ray liu, applications engineer, zetex semiconductors description this design note shows the zxsc400 driving a singl e 3w led. the input voltage ranges from 1.8v to 3.6v with constant output current of 700ma down to 2.6v with an overall 80% of efficiency. figure 1 shows typical constant current solution with zxsc400 driving one 3w led. the input voltage range allows the use of two alkaline batteries or one lithium ion cell (cr123a) for portable flashlight applications. q1 and q2 forms a pseudo darlington pair which provide enough current gain for a switching current up to 1.5a. in order to provide better switch off performance, a schottky diode, d2, is used to drain the base current from the base of q1 dire ctly. in order to achieve higher efficiency, current monitor u2 is used to provide a low voltage drop led current sensing through the low ohmic resistor, r2. the led current is converted to 300mv feedback voltage through r3. figure 1 schematic diagram q2 d2 q1 d1 v in = 1.8v to 3v d1 c3 c2 l1 r1 r5 r4 u1 v cc stdn gnd v drive i sense v fb zxsc400 zxct1009 v sense- v sense+ i out r6 r3 r2 u2 c1 c1
DN84 www.zetex.com 2 issue 1 - august 2007 ? zetex semiconductors plc 2007 ref. value part number manufacturer comments u1 zxsc400e6 zetex led driver in sot23-6 u2 zxct1009 zetex current monitor in sot23 q1 zxtn25012efh zetex low sat npn in sot23 q2 zxtn25012efl zetex low sat npn in sot23 d1 zhcs2000 zetex 2a schottky in sot23 d2 zhcs400 zetex 400ma schottky l1 15 h 744 561 15 wurth electronik isat = 3a dcr=60m r1 20m 1% generic generic 0805 size low ohmic r2 50m 1% generic generic 0805 size low ohmic r3 820 1% generic generic 0805 size r4 82 5% generic generic 0805 size r5 4.7 5% generic generic 0805 size r6 10 5% generic generic 0805 size c1 22 f 10v 10% generic generic 1206 size x7r/x5r c2 4.7 f 10v 10% generic generic 1206 size x7r/x5r c3 0.22 f 16v 10% generic generic c4 330pf/10v generic generic 0805 size table 1 bill of materials
DN84 issue 1 - august 2007 3 www.zetex.com ? zetex semiconductors plc 2007 typical operating characteristics (for typical application circuit where t amb = 25c unless otherwise stated) figure 2 performance graphs input voltage vs efficiency 50 60 70 80 90 100 1.8 2 2.2 2.4 2.6 2.8 3 input voltage (v) efficiency (%) input voltage vs output current 0.0 0.2 0.4 0.6 0.8 1.0 1.8 2 2.2 2.4 2.6 2.8 3 input voltage (v) output current (a) input voltage vs input current 0.0 0.4 0.8 1.2 1.6 1.8 2 2.2 2.4 2.6 2.8 3 input voltage (v) input current (a) input voltage vs output voltage 0 1 2 3 4 1.8 2 2.2 2.4 2.6 2.8 3 input voltage (v) output voltage (v)
DN84 www.zetex.com 4 issue 1 - august 2007 ? zetex semiconductors plc 2007 zetex sales offices europe zetex gmbh kustermannpark balanstra?e 59 d-81541 mnchen germany telefon: (49) 89 45 49 49 0 fax: (49) 89 45 49 49 49 europe.sales@zetex.com americas zetex inc 700 veterans memorial highway hauppauge, ny 11788 usa telephone: (1) 631 360 2222 fax: (1) 631 360 8222 usa.sales@zetex.com asia pacific zetex (asia ltd) 3701-04 metroplaza tower 1 hing fong road, kwai fong hong kong telephone: (852) 26100 611 fax: (852) 24250 494 asia.sales@zetex.com corporate headquarters zetex semiconductors plc zetex technology park, chadderton oldham, ol9 9ll united kingdom telephone: (44) 161 622 4444 fax: (44) 161 622 4446 hq@zetex.com ? 2007 published by zetex semiconductors plc definitions product change zetex semiconductors reserves the right to alter, without notice, specifications, design, price or conditions of supply of any product or service. customers are solely responsible for obtaining th e latest relevant information before placing orders. applications disclaimer the circuits in this design/application note are offered as desi gn ideas. it is the responsibility of the user to ensure that t he circuit is fit for the user?s application and meets with the user?s requirements. no representation or warranty is given and no liability whatsoev er is assumed by zetex with respect to the accuracy or use of such in formation, or infringement of patents or other intellectual prop erty rights arising from such use or otherwise. zetex does not assume any le gal responsibility or will not be held legally liable (whether in contract, tort (including negligence), breach of statutory duty, restricti on or otherwise) for any damages, loss of profit, business, con tract, opportunity or consequential loss in the use of th ese circuit applications, under any circumstances. life support zetex products are specifically not authorized for use as critic al components in life support devices or systems without the ex press written approval of the chief executive officer of zetex semiconductors plc. as used herein: a. life support devices or systems are devices or systems which: 1. are intended to implant into the body or 2. support or sustain life and whose failure to perform when proper ly used in accordance with instructions for use provided in t he labelling can be reasonably expected to result in significant injury to the user. b. a critical component is any component in a life support devi ce or system whose failure to pe rform can be reasonably expected to cause the failure of the life support device or to affect its safety or effectiveness. reproduction the product specifications contained in this publication are issu ed to provide outline information only which (unless agreed by the company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the pr oducts or services concerned. terms and conditions all products are sold subjects to zetex? terms and conditions of sale, and this disclaimer (save in the event of a conflict bet ween the two when the terms of the contract shall prevail) according to region, supplied at the time of order acknowledgement. for the latest information on technology, delivery terms and condi tions and prices, please contact your nearest zetex sales off ice . quality of product zetex is an iso 9001 and ts16949 certified semiconductor manufacturer. to ensure quality of service and products we strongly advise the purchase of parts dire ctly from zetex semiconductors or one of our regionally authorized distributors. for a complete listing of authorized distributors please visit: www.zetex.com/salesnetwork zetex semiconductors does not warrant or accept any liability whatsoever in respect of any parts purchased through unauthorized sales channels. esd (electrostatic discharge) semiconductor devices are susceptible to damage by esd. suitab le precautions should be taken when handling and transporting dev ices. the possible damage to devices depends on the circumstances of the handling and transporting, and the nature of the device. the extent of damage can vary from immediate functional or parametric malfunc tion to degradation of function or performance in use over ti me. devices suspected of being affected should be replaced. green compliance zetex semiconductors is committed to envir onmental excellence in all aspects of its operations which includes meeting or exce eding regulatory requirements with respect to the use of hazardous s ubstances. numerous successful programs have been implemented to reduce the use of hazardous substances and/or emissions. all zetex components are compliant with the ro hs directive, and through this it is supporting its customers in their compliance with weee and elv directives. product status key: ?preview? future device intended for production at some point. samples may be available ?active? product status recommended for new designs ?last time buy (ltb)? device will be discontinued and last time buy period and delivery is in effect ?not recommended for new designs? device is still in production to support existing designs and production ?obsolete? production ha s been discontinued datasheet status key: ?draft version? this term denotes a very early datasheet ver sion and contains highly provisional information, which may change in any manner without notice. ?provisional version? this term denotes a pre-release datasheet. it provides a clear indication of anticipated performance. however, changes to the test conditions and specif ications may occur, at any time and without notice. ?issue? this term denotes an issued datasheet cont aining finalized specifications. however, changes to specifications may occur, at any time and without notice.
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