mt 793 0 maximizing ic performance single stage, high pfc, ac - dc led driver mt 7930 rev. 1. 30 www.maxictech.com copyright ? 20 1 1 maxic technology corporation page 1 d escription MT7930 is a single - stage primary side control ac - dc led driver with high power factor . with maxic patent pending technology, the led current can be regulated accurately through sensing the primary side information with few external components w ithout the need of an opto - coupler. MT7930 integrates power factor correction function and works in dcm and constant off time mode. a s mall harmonic current emission (thd) is achieved. MT7930 is also implemented with various protection s , such as over - cur rent protection ( ocp ) , over - voltage protection ( ovp ) , short - circuit protection ( scp ) and over - temperature protection ( otp ) , etc, to ensure a reliable system. features ? wide input voltage range from ac 85 v to ac 265 v ? highly accurate constant led current (+/ - 3%) ? up to 5 0w power d rivability . ? primary - side current sensing and regulation without an opto - coupler ? leading edge blanking (leb) technique ? cycle - by - cycle current limiting ? under - v oltage lockout (uvlo) protection ? vdd and o utput over voltage protection ? adjustable constant current and output power setting ? power on s oft - star t ? available in sop8 package application s ? ac/dc led driver applications ? general purpose constant current source ? signal and decorative led lighting ? e14/e27/par30/par38/gu10 led lamp typi cal application circuit
mt 793 0 maximizing ic performance single stage, high pfc, ac - dc led driver mt 7930 rev. 1. 30 www.maxictech.com copyright ? 20 1 1 maxic technology corporation page 2 absolute maximum rat ings stp, vdd , drv voltage - 0.3v to 2 5 v all other pins voltage - 0.3v to 6 v storage temperature - 55c to 150c junction temperature (tj) 150 c recommended operating conditions supply voltage 7.2 v to 18 v op erating temperature - 4 0c to 10 5c thermal resistance case to ambient (r c a ) 128 c/w pin configurations p in description name pin no. description d rv 1 gate drive output for power n - mosfet. gnd 2 ground . tm 3 test pin . al ways tie to ground. comp 4 internal ea s output. connect a capacitor to ground for frequency compensation . stp 5 start - up pin. the mt793 0 is softly started through stp pin . dsen 6 the voltage feedback from auxiliary winding. connected to a resistor divi der from auxiliary winding reflecting output voltage. vdd 7 power supply. cs 8 current sense pin .
mt 793 0 maximizing ic performance single stage, high pfc, ac - dc led driver mt 7930 rev. 1. 30 www.maxictech.com copyright ? 20 1 1 maxic technology corporation page 3 electrical character istics ( t est conditions: v dd = 12 v, t a =25c unless otherwise stated .) symbol parameter conditions min typ max unit start - up (stp pin, vdd pin) i start start up current 2 5 50 a dd v dd pin ramp down 6.0 7.2 8.5 v v st art start - up voltage v dd pin ramp up 1 5 .5 18 .5 20 v supply current i q quiescent current no switching 1.2 ma i cc operating current fs =70khz 3 ma control loop v fb primary current sense voltage 392 4 00 408 m v v comph upper limit of comp 2.1 2.2 2.4 v t off off time of drv 10 11 12 us scp short circuit protection threshold at dsen pin 190 200 210 mv ovp1 over voltage protection t hreshold at dsen 3.04 3.2 3.36 v ovp2 over voltage protection threshold at vdd pin 18. 2 19.2 23.5 v current sense (cs pin) leb leading edge blanking of cs 300 ns ocp over current protection at cs pin 2.2 2.4 v thermal protection otp over tempe rature protection 150 drive stage (drv pin) t r rising time cl=1nf, drv pin falls from v dd to 0v 50 f falling time cl=1nf, drv pin rises from 0v to v dd 30 note : guaranteed by design.
mt 793 0 maximizing ic performance single stage, high pfc, ac - dc led driver mt 7930 rev. 1. 30 www.maxictech.com copyright ? 20 1 1 maxic technology corporation page 4 block diagram application informat ion MT7930 is a primary - side controller for ac - dc led driver. the led current can be accuratel y regulated through sensing the primary side information to realize real curre nt control. MT7930 integrates power factor correction function to eliminate pollution to the ac line and works in dcm and constant off time mode. real current control with m axic proprietary technique , MT7930 accurately regulate led current through sensin g the primary side information. t he led current can be easily set as following (refer to the application circuit in page 1) : w here n p i s primary winding , n s i s secondary winding ; v fb (=400mv) is the internal voltage reference and r s i s an external current sensing resistor (rs is r4 in page1 application circuit) . start up during start - up proce ss , vdd is charged through a start - up resistor. a s vdd reaches 18 .5 v, the control logic starts to work , and the gate drive begins to switch . a soft - start function is implemented to prevent the transformer from enter ing into ccm (continuous current mode) as show in fig. 1 . the power supply is taken over by the auxiliary winding once the voltage of this winding is high enough. after MT7930 control logic starts to work, stp pin is clamped to lower than vdd voltage about 0.2v. MT7930 will shut down if vdd goes below 7.2v (uvlo threshold voltage ). s fb s p led r v n n 2 1 94 . 0 i ? ? ?
mt 793 0 maximizing ic performance single stage, high pfc, ac - dc led driver mt 7930 rev. 1. 30 www.maxictech.com copyright ? 20 1 1 maxic technology corporation page 5 fig.1 start up sequence power factor correction the primary side current increases linearly from zero to peak value, as sensed by the current sensing pin cs, during the external mosfet on - time. when the primary current reaches the threshold, MT7930 turns off the power mosfet immediately. after a constant off time, t off , MT7930 turns on the power mosfet ag ain. the peak current threshold is regulated by maxic proprietary technique and follows the rectified sinusoidal - shape of main line voltage. as a result, t he envelope of the inductor current is sinusoidal - shaped , high power factor is therefore achieved in this way . fig.2 power factor correctioin auxiliary sensing MT7930 features over - voltage protection (ovp), short - circuit protection (scp), and over - current protection (ocp) functions. those protections are triggered by sensing the auxiliary winding wa veform information, as the auxiliary winding voltage is proportional to the output voltage (secondary winding voltage) during the off time period. the auxiliary winding voltage is sampled by dsen pin, one le b (leading edge blanking) time right after drv si gnal is turned off. fig.3 auxiliary signal sensing over - v oltage protection MT7930 is implemented with two over - voltage protection schemes : (1) i f dsen p in s voltage is detected above 3.2v for three times (refer to auxilia ry sensing section) , MT7930 turns off the pwm switching signal , and vdd voltage gradually drops to uvlo threshold , and the system will be re - start ed . the threshold voltage of over - voltage protection v out_ov , can be easily defined as (refer to the applicati on circuit in page 1): where n s is the secondary winding, n a is auxiliary winding , v d 8 is th e forward bias of the secondary side rectifier diode. (2) i f vdd p in s voltage exceeds 19.2 v three t imes, MT7930 turns off the pwm switchin g signal , and vdd gradually drops to uvlo d r v a u x l e b t i m e d8 a s out_ov v n n ) r6 r5 (1 3.2 v ? ? ? ?
mt 793 0 maximizing ic performance single stage, high pfc, ac - dc led driver mt 7930 rev. 1. 30 www.maxictech.com copyright ? 20 1 1 maxic technology corporation page 6 threshold , and then the system will be re - start ed . i t is highly recommended to set up the vdd voltage between 12v and 16v by designed a proper n a to n s ratio of the transformer. short - c ircuit protection the short - circuit protection is triggered if the dsen pin voltage is detected below 200mv for a continuous time of 640us. the gate drive switching will be turned off , and a restart process will be kicked off when the vdd voltage drops below the uvlo threshold. this re - start process will repeat if the short - circuit condition continue s to exist. over - c urrent protection MT7930 immediately turn s off the power mosfet once the voltage at cs pin exceeds 2.2v . this cycle by cycle current limitation scheme prevents the rel evant components, such as p ower mosfet , transformer, etc. from damage .
mt 793 0 maximizing ic performance single stage, high pfc, ac - dc led driver mt 7930 rev. 1. 30 www.maxictech.com copyright ? 20 1 1 maxic technology corporation page 7 package information
mt 793 0 maximizing ic performance single stage, high pfc, ac - dc led driver mt 7930 rev. 1. 30 www.maxictech.com copyright ? 20 1 1 maxic technology corporation page 8 for detail products information and sample requests, please contact: maxic technology corporation (beijing office) 1006 crown plaza office tower, no106, zhichun road, hai dian district, beijing, china, 100086 tel: 86 - 10 - 62662828 fax: 86 - 10 - 62662951 maxic technology coporation (shenzhen office) 25bc , fortune plaza, futian district, shenzhen 518040 tel: 86 - 755 - 830 21778 fax: 86 - 755 - 83021336 maxic technology corporation ( suzhou office) b - 503, #3 chuangye park, 328 xinghu street, indurial park, suzhou, 215021 tel: 86 - 512 - 62958262 fax: 86 - 512 - 62958262 maxic technology corporation(hong kong office) rm d1, 7th floor, jianan commercial building, no. 49 - 51, suhong str., sheung wan, hong kong web: www.maxictech.com e - mail: sales@maxictech.com , info@maxictech.com
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