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november 2009 doc id 15559 rev 1 1/14 AN2961 application note steval-ill026v1 non-isolated 3 w offline led driver based on the viper22a-e introduction this application note describes the functioning of the steval-ill026v1 non-isolated 3 w offline led driver power supply designed using the viper22a-e low power offline smps primary switcher from stmicroelectronics. the circuit regulates the load current to 350 ma and generates about 10 v. the load is composed of three high-brightness (hb) leds, connected in series. the project does not provide safety isolation between the input and output. this document provides the power supply specific ation, circuit diagrams, the complete bill of materials, and reports the results of circuit testing. figure 1. steval-ill026v1 board photographs ! - v www.st.com
contents AN2961 2/14 doc id 15559 rev 1 contents 1 specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4 circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5 test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 6 conducted emission tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7 adapting the board for a 230 v input mains range . . . . . . . . . . . . . . . 12 8 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 AN2961 list of figures doc id 15559 rev 1 3/14 list of figures figure 1. steval-ill026v1 board photographs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 figure 2. steval-ill026v1 schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 figure 3. viper22a-e startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 figure 4. 110 v steady state operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 figure 5. led current regulation vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 figure 6. board efficiency vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 figure 7. conducted emissions at 230 vac 50 hz - line 1 peak detector . . . . . . . . . . . . . . . . . . . . . 11 figure 8. conducted emissions at 230 vac 50 hz - line 2 peak detector . . . . . . . . . . . . . . . . . . . . . 11 specification AN2961 4/14 doc id 15559 rev 1 1 specification the electronic lamp ballast electrical spec ifications are given in the table below. table 1. specification input parameters v in input voltage range 90 to 265 v rms f line line frequency 50/60 hz hb leds number 3 power / current 3 w / 350 ma AN2961 bill of material doc id 15559 rev 1 5/14 2 bill of material table 2. steval-ill026v1 bill of material type name value rated description c c1 22 f 50 v electrolytic c c3 2.2 f 450 v electrolytic c c4 470 nf 50 v ceramic c c5 22 f 50 v electrolytic c c6 470 nf 50 v ceramic c c7 470 nf 400 vdc polyester epcos b32561j6474k c c8 do not fit do not fit do not fit d d1 39 v zener diode d d2 stth1r06a 600 v stmicroelectronics d d3 bridge 600 v 500 ma rectifier bridge d d4 stth1r06a 600 v stmicroelectronics l l1 1 mh epcos b7818s1105j000 l l2 1 mh coilcraft mss1260-105klb q q1 bc557b pnp transistor q q2 bc547b npn transistor r r1 4.7 k smd resistor 0805 r r2 4.7 k smd resistor 0805 rr3 10 k smd resistor 0805 rr4 10 k smd resistor 0805 rr5 1.3 smd resistor 1206 r r6 6.8 k smd resistor 0805 r r7 10 1/2 w through hole resistor u ic1 viper22a-e stmicroelectronics electrical schematic AN2961 6/14 doc id 15559 rev 1 3 electrical schematic figure 2. steval-ill026v1 schematic diagram ! - v 5 . 5 . / p + ' 6 7 7 + 5 $ & |