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al1788 document number: ds39401 rev. 1 - 2 1 of 13 www.diodes.com october 2017 ? diodes incorporated al1788 new product low standby power pfc controller description t he al1788 is a high performance ac/dc power factor corre ction (pfc) controller targeting at led lighting applications. based on primary side regulation (psr) implementation, al1788 does not require opto-coupler and any secondary feedback circuit to save overall bom cost. it operat es at quasi-resona nt ( qr ) mode where mosfet is turned on at the valley of the drain voltage, which minimizes switchin g loss to result in high efficiency. with either flyback or buck topology, al1788 system su pports high efficiency, high power factor (pf>0.9) and low total harmonic distortion (thd < 20 %) for universal input at wide loading range (50% loading to 100% loading) the al1 788 features low start-up current, low operation current and low standby power . it has rich protection features including over voltage protection (ovp), short circuit protection (scp), over cur rent protection (ocp) and over temperature p ro tection (otp). the al1 788 is available in sot26 (sc74r) package for the controller. features ? psr implementation based on flyback and buck topology ? universal ac voltage input for constant voltage (cv) regulation ? valley detection for primary mosfet switch to achieve low switching loss and high efficiency ? high pf (>0.9) and low thd (<20%) for wide loading range (50% to full loading) ? internal protections: ? under voltage lockout (uvlo) ? over voltage protection (ovp) ? over current protection (ocp) ? output short protection (osp) ? over-temperature protection (otp): thermal shutdown and auto thermal recovery ? low standby power ? low system bom cost ? controller with external mosfet ? totally lead-free & fully rohs compliant (notes 1 & 2) ? halogen and antimony free. green device (note 3) pin assignments top view 1 2 3 6 4 out comp gnd 5 vcc fb cs applications ? general led lighting ? smart connected led light bulbs ? smart connected led tubes, panel lights, troffers, and c eiling lights ? high pfc and low thd power supply notes: 1. no purposely added lead. fully eu directive 2002/95/ec (rohs) & 20 11/65/eu (rohs 2) compliant. 2. see http://www.diodes.com/quality/lead_free.html for more information ab out diodes incorporateds definitions of halogen - and antimony-free, "green", and lead-free. 3. halogen- and antimony- free "green products are defined as those which contain < 900ppm bromine, <900ppm chlorine (<1500ppm total br + cl) and <1000ppm antimony compounds.
al1788 document number: ds39401 rev. 1 - 2 2 of 13 www.diodes.com october 2017 ? diodes incorporated al1788 new product typical applications circuit f1 vr1 r7 r5 r6 d1 aux c3 vcc fb comp c4 gnd cs l1 c1 c2 r10 c5 q1 d2 r cs d3 c6 out r12 u1 al1788 t1 db1 r2 c7 figure 1. al1788 controller flyback application f1 vr1 l1 c1 c2 r7 q1 r12 r5 r6 d2 l2 c6 r1 d1 r2 c4 u1 al1788 out vcc gnd comp cs fb db1 r cs c3 c7 figure 2. al1788 controller buck application
al1788 document number: ds39401 rev. 1 - 2 3 of 13 www.diodes.com october 2017 ? diodes incorporated al1788 new product pin descriptions pin name p in number descriptions cs 1 primary current sensing gnd 2 ground comp 3 loop compensation pin fb 4 voltage sensing feedback vcc 5 power supply out 6 gate driver output functional block diagram cs fb vcc out gnd leading edge blanking output control valley detector output over voltage protection + + - - + + - - sawtooth generator v cs_cl pwm control logic over temperature protection under voltage lockout vcc over voltage protection v clamp comp 1 2 3 6 4 5 figure 3. al1788 controller functional block diagram
al1788 document number: ds39401 rev. 1 - 2 4 of 13 www.diodes.com october 2017 ? diodes incorporated al1788 new product absolute maximum ratings (@ t a = +25c, unless otherwise specified.) (note 4) symbol parameter rating unit v in input voltage -0.3 to 30 v v cs voltage at cs -0.3 to 7 v v fb voltage at fb -0.3 to 7 v v comp voltage at comp -0.3 to 7 v t j junction temperature -40 to +150 c t st storage temperature range -65 to +150 c t lead lead temperature (soldering, 10 sec) + 26 0 c p d power dissipation (note 5) 0. 7 w ja thermal resistance junction- to -ambient ) (note 5) 16 0 c /w jc thermal resistance junction- to -case) (note 5) 36 c /w esd hbm human body model esd protection 2,000 v cdm charged device model esd protection 1,000 v notes: 4. stresses greater than those listed under absolute maximum ratings may c ause permanent damage to the device. these are stres s ratings only, and functional operation of the device at these or any other conditions beyond those indicated under recommended operating conditions is n ot implied. exposure to absolute maximum ratings for extended periods may affe ct device reliability. all voltages unless otherw ise stated and measured with respect to gnd. 5 . device mounted on 1"x1" fr-4 mrp substrate pc board, 2oz cooper, with minim um recommended pad layout . recommended operating conditions (@ t a = +25c, unless otherwise specified.) symbol parameter min max unit v cc input voltage at vcc 9 .0 25 v t j operating junction temperature - 40 + 125 c
al1788 document number: ds39401 rev. 1 - 2 5 of 13 www.diodes.com october 2017 ? diodes incorporated al1788 new product electrical characteristics (v cc =12v@t a = +25c , unless otherwise specified.) symbol parameter condition min typ max unit uvlo section v st startup threshold voltage - - 19 - v v opr_min minimal operating voltage after turn on 7.0 - 8 .5 v v cc_ovp v cc ovp voltage - - 30 - v standby current section i st startup current v cc = v st -0.5v, before start- up - 3 - ? a i cc_opr operating current static - no switching (v cs =0.6v) - 5 00 - ? a i cc_ovp shunt current in ovp mode v cc =1 5v after v cc >v cc_ovp triggered - 2.5 - ma drive output section v out_clamp output clamp voltage v cc =18v 12 13.5 15 v v ol output low level i gd_sink =20ma, v cc =12v - - 1 v t r output voltage rise time c l =1nf - 100 - ns t f output voltage fall time c l =1nf - 50 - ns t on_min minimum t on - - 0. 7 - ? s t on_max maximum t on - - 17 - ? s t off_min minimum t off - - 1. 2 - ? s t off_max maximum t off - - 40 - ? s f max maximum frequency - - 120 - kh z cs section v cs_ocp primary current ocp - - 0.5 - v comp section gm _comp comp transconductance - - 100 - ? a/v i max_comp_source comp maximum source current v fb =0 .8 v - 16 - ? a i max_comp_sink comp maximum sink current v fb =1.5v - 16 - ? a v comp_pro comp protection voltage - - 3.5 - v fb section v fb_cv fb cv threshold - 1.15 1.2 1.25 v v fb_ovp fb ovp threshold - - 1.35 - v over temperature protection section (note 6) t sh (note 7) shutdown temperature - - + 160 - c t hy temperature hysteresis - - + 30 - c notes: 6. the over temperature protection parameters are guaranteed by design. 7 . when the junction temperature reaches thermal shutdown temp erature (t sh ), al1788 enters thermal shutdown mode with hiccup restart until junction temperature drops below shutdown temperature minus te mperature hysteresis (t sh - t hy ). once junction temperature drops below (t sh - t hy ), al1788 restarts as in normal operation .
al1788 document number: ds39401 rev. 1 - 2 6 of 13 www.diodes.com october 2017 ? diodes incorporated al1788 new product typical performance characteristics (@t a =+25c, unless otherwise specified.) 12.0 14.0 16.0 18.0 20.0 22.0 -40 0 40 80 120 startup voltage (v) ambient temperature ( ) startup voltage vs. ambient temperature 4.0 5.0 6.0 7.0 8.0 9.0 10.0 - 40 0 40 80 120 minimum operating voltage (v) ambient temperature ( ) minimum operating voltaqge vs. ambient temperature 0.0 0.5 1.0 1.5 2.0 2.5 3.0 - 40 0 40 80 120 startup current ( ? a) ambient temperature ( ) startup current vs. ambient temperature 0 100 200 300 400 500 600 - 40 0 40 80 120 operating current ( ? a) ambient temperature ( ) operating current vs. ambient temperature 0.80 0.90 1.00 1.10 1.20 1.30 1.40 - 40 0 40 80 120 feedback voltage (v) ambient temperature ( ) v fb_cv vs. ambient temperature 0.42 0.44 0.46 0.48 0.50 0.52 -40 0 40 80 120 primary current limit voltage (v) ambient temperature ( ) current limit voltage vs. ambient temperature
al1788 document number: ds39401 rev. 1 - 2 7 of 13 www.diodes.com october 2017 ? diodes incorporated al1788 new product functional description and application information the al1788 is a high performance ac/dc power factor c orrection (pfc ) constant voltage controller targeting at led lighting appli cations. it operates with constant on time to achieve high power facto r. and i t adopts the quasi-resona nt ( qr ) mode valley switching method to reduce switching loss and improve emi performance. f1 vr1 r7 r5 r6 d1 aux c3 vcc fb comp c4 gnd cs l1 c1 c2 r10 c5 q1 d2 r cs d3 c6 out r12 u1 al1788 t1 db1 r2 c7 figure 4. al1788 controller flyback application start- up after ac supply is powered on, the capacitor c3 across v cc and gnd pin will be charged up by bus voltage through a start-up resistor r7. once v cc reaches v st , the internal blocks start to work. v cc will be supplied by v bus until the auxiliary winding of flyback transformer could supply enough energy to maintain v cc above v opr_ min . if v cc voltage is lower than v opr_ min , the switch will be turned off. to accelerate the start- up process, the comp voltage is internally pulled up and clam ped high, leading to large mosfet duty cycle and fast climbing up of the output voltage. when the fb voltage re aches the reference voltage v fb_cv , t he start-up process ends and the comp voltage turns to be modulated by the external compensation network . v cc v comp pwm v fb_cv internal comp v st external comp v fb figure 5. start up waveform
al1788 document number: ds39401 rev. 1 - 2 8 of 13 www.diodes.com october 2017 ? diodes incorporated al1788 new product functional description and application information (cont.) constant voltage operation as to constant-voltage (cv) operation mode, the al1788 detects the auxiliary winding voltage at fb pin to regulate th e output voltage. the auxiliary winding voltage is coupled with secondary side winding volt age, so the auxiliary winding voltage at d3 conduction time i s: where: v o is the output voltage v d is the output rectifier diode forward voltage drop n aux is the turns of auxiliary winding n s is turns of the secondary winding v fb_cv is the output voltage setting r 5 and r 6 that is shown as figure 4 divide reflected voltage. figure 6. auxiliary voltage waveform figure 6 shows the voltage waveform of the auxiliary winding. to accurately sample the divided auxiliary winding voltage, the al 1788 fb pin delays a t sample time before sampling. and t discharge is the demagnetization time for the transformer. load transition operation to obtain good load transition performance, the al1788 comp r egulation mechanism is optimized . when the load changes from heavy to light causing the fb voltage reaching v fb_ovp (typically 1.35v), the ic will pull down the comp voltage and enter the max-off-time mode, accelerating the discharge of the output voltage. when the load chan ges from light to heavy leading to the fb voltage touching 1 .0 v, the ic will charge up the comp voltage and raise the mosfet on time, quickening the increase of the output voltage. 1.35v v fb v cs v comp heavy load transition to light load max-off-time mode 0 v v fb v cs v comp light load transition to heavy load 1.0 v 0 v figure 7 . load transition waveform
al1788 document number: ds39401 rev. 1 - 2 9 of 13 www.diodes.com october 2017 ? diodes incorporated al1788 new product functional description and application information (cont.) protections 1. output-open protection (vcc_ovp; vfb_ovp) the output voltage is reflected by the voltage on transformers au xiliary winding. both fb pin and v cc pin of ic have ovp function. when there is a rapid line and load transient, the outpu t voltage may exceed the regulated value. if v fb exceeds v fb _ ovp , the ovp will be triggered, and then al1788 increases the off time to reduce output voltage. if v cc exceeds v cc _ ovp the ovp will be triggered, the switch will be turned off a nd v cc will be discharged. once v cc is below v opr_ min , the ic will shut down and power on again by bus voltage through start up resistor. 2. output short protection (osp) when the output is shorted, the output voltage is cla mped to zero. the output voltage of the auxiliary winding, w hich is proportional to the secondary winding, will drop down too. once v cc is below v opr_ min , the ic will shut down and power on again by the bus v oltage through the startup resistor. 3. over current protection (ocp) al1 788 has a built- in cycle- by -cycle ocp of primary induct or current. when cs pin voltage reaches the voltage v cs_ocp , the switch will be turn ed off until the next switch period. the maximum peak curren t (i peak (max) ) of the inductor can be calculated as below: where : v cs_ocp means primary current clamp voltage that is 0.5v r cs is current sense resister shown as figure 4 4 . over temperature protection (otp) the al1788 has built-in otp function. when the junction tempera ture goes up to shut down temperature, the otp will be triggered, the switch will be shutdown. until the junction temperature falls to the recovery temperature, the al1788 will be restarted. operation parameters design 1. setting the current sense resistor the current sense resistance can be calculated as following : where : i o_mean is the mean output current k cs =1.5 r cs is current sense resister which is shown as figure 4 v cs_ocp means primary current clamp voltage that is equal to 0.5v n ps is the turns ratio of flyback transformer
al1788 document number: ds39401 rev. 1 - 2 10 of 13 www.diodes.com october 2017 ? diodes incorporated al1788 new product functional description and application information (cont.) 2. setting transformer selection (t1) n ps is limited by the electrical stress of the switch mosfet, ca n be calculated by below formula. where : v mos_ds is the breakdown voltage of the switch mosfet v in_max is the maximum rated input voltage v s is the overshoot voltage clamped by rcd snubber during off time v o is the output voltage v d is the forward voltage of secondary diode n ps is the turn ratio of flyback transformer; for boundary conduction mode and constant on time metho d, the peak current of primary inductance can be calc ulated as below. where : v in _ rms is the rate input voltage i p is the primary inductance current n ps is the turn ratio of flyback transformer i o_mean is the mean output current v o is the output voltage; the switching frequency is not constant for al1 788 due to qr operation. to set the minimum switching frequency f min at the crest of the minimum ac input, primary inductance can be obtained by below formula. where : v in_rms is the rate input voltage i p is the primary inductance current n ps is the turn ratio of flyback transformer i o_mean is the mean output current; v o is the output voltage f min is the minimum switching frequency at the crest of the mi nimum ac input according to the f araday s law, the winding number of the inductance can be calculated by: where : a e is the core effective area b m is the maximum magnetic flux density
al1788 document number: ds39401 rev. 1 - 2 11 of 13 www.diodes.com october 2017 ? diodes incorporated al1788 new product ordering information al1788 x - x product name package packing w6 : sot26 (sc74r) w6 : sot26 (sc74r) 7: 7" tape & reel 7: 7" tape & reel part number package code packaging 7 tape and reel quantity part number suffix al1788 w6 -7 w6 sot26 (sc74r) (note 8) 3,000/tape & reel -7 note : 8 . for packaging details, go to our website at https://www.diodes.com/design/support/packaging/diodes-packaging/. marking information sot26 (sc74r) 1 2 3 6 7 4 xx y w x xx : identification code y : year 0~9 x : internal code ( top view ) 5 w : week : a~z : 1~26 week; a~z : 27~52 week; z represents 52 and 53 week part number package identification code al1788 w6 -7 sot26 (sc74r) a8
al1788 document number: ds39401 rev. 1 - 2 12 of 13 www.diodes.com october 2017 ? diodes incorporated al1788 new product package outline dimensions (all dimensions in mm.) please see http://www.diodes.com/package-outlines.html for the latest version. sot26 (sc74r) sot26 (sc74r) dim min max typ a1 0.013 0.10 0.05 a2 1.00 1.30 1.10 a3 0.70 0.80 0.75 b 0.35 0.50 0.38 c 0.10 0.20 0.15 d 2.90 3.10 3.00 e - - 0.95 e1 - - 1.90 e 2.70 3.00 2.80 e1 1.50 1.70 1.60 l 0.35 0.55 0.40 a - - 8 a1 - - 7 all dimensions in mm suggested pad layout please see http://www.diodes.com/package-outlines.html for the latest version. sot26 (sc74r) dimensions value (in mm) c 2.40 c1 0.95 g 1.60 x 0.55 y 0.80 y1 3.20 a1 d e e1 e b a2 a1 seating plane l c a e1 a3 c1 y1 g x y c
al1788 document number: ds39401 rev. 1 - 2 13 of 13 www.diodes.com october 2017 ? diodes incorporated al1788 new product important notice diodes incorporated makes no warranty of any kind, expres s or implied, with regards to this document, including, but not limited to, the implied warranties of me rchantability and fitness for a particular purpose (and their equivalents under the laws of any jurisdiction). diodes incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, correct ions or other changes without further notice to this document and any produ ct described herein. diodes incorporated does not assume any liability arising out of the application or use of this document or any product des cribed herein; neither does diodes incorporated convey a ny license under its patent or trademark rights, nor the rights of others. any custom er or user of this document or products described her ein in such applications shall assume all risks of such use and will agree to hold diodes incorpo rated and all the companies whose products are repres ented on diodes incorporated website, harmless against all damages. diodes incorporated does not warrant or accept any lia bility whatsoever in respect of any products purchased through unauthorized sales channel. should customers purchase or use diodes incorporated prod ucts for any unintended or unauthorized application, cus tomers shall indemnify and hold diodes incorporated and its representatives harmless against all claims, damages, expenses, and attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized applicati on. products described herein may be covered by one or more united states, international or foreign patents pending. pro duct names and markings noted herein may also be covered by one or more unite d states, international or foreign trademarks. this document is written in english but may be translated in to multiple languages for reference. only the english vers ion of this document is the final and determinative format released by diodes incorporat ed. life support diodes incorporated products are specifically not auth orized for use as critical components in life support dev ices or systems without the express written approval of the chief executive officer of diodes i ncorporated. as used herein: a. life support devices or systems are devices or sy stems which: 1. are intended to implant into the body, or 2. support or sustain life and whose failure to perfor m when properly used in accordance with instructions for u se provided in the labeling can be reasonably expected to result in signi ficant injury to the user. b. a critical component is any component in a life sup port device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or to affect i ts safety or effectiveness. customers represent that they have all necessary exp ertise in the safety and regulatory ramifications of their lif e support devices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concern ing their products and any use of diodes incorporated products in such safety-criti cal, life support devices or systems, notwithstanding any devices- or systems-related information or support that may be provided by diodes incorpo rated. further, customers must fully indemnify diodes incor porated and its representatives against any damages arising out of the u se of diodes incorporated products in such safety-critic al, life support devices or systems. copyright ? 2017, diodes incorporated www.diodes.c om

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