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AN-9737 Datasheet(PDF) 4 Page - Fairchild Semiconductor |
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AN-9737 Datasheet(HTML) 4 Page - Fairchild Semiconductor |
4 / 11 page AN-9737 APPLICATION NOTE © 2011 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.0.0 • 4/13/11 4 0136 . 0 ) 5 . 0 ( 00003108 . 0 ) 0004608 . 0 ( ) ( 2 2 = = = α e g K ENG K [cm 5] Step 13. See Table 2 for core size. To prevent core saturation, select a little big core after comparing two Kg values: calculate value at Step 12 vs. the existing value in Table 2. The PQ-42016 has a little bit big Kg value (0.01327) in Table 2 with 2500 permeability (µi). Step 14. Calculate the current density, J.: 265 ) 4 . 0 )( 2484 . 0 ( 35 . 0 10 ) 0004608 . 0 ( 2 10 ) ( 2 4 4 = × = × = u P m K A B ENG J [A/cm 2] Step 15. Calculate the required wire area. AW(B): 001207 . 0 265 32 . 0 ) ( = = = J I A rms B W [cm 2] Step 16. Calculate the number of turns, N: 93 . 141 001207 . 0 4 . 0 4283 . 0 ) ( = × = = B w u a A K W N [T] N=141.93; use 142 turns. Step 17. Calculate the required gap, lg: 0489 . 0 35 . 0 10 ) 96 . 0 )( 142 ( 4 . 0 10 ) )( ( 4 . 0 4 4 = × = ∆ × ∆ = − − π π m g B I N l [cm] Step 18. Calculate the new turns using a gap from Step 15. 153 . 83 ) 58 . 0 ( 4 . 0 ) 10 )( 2500 74 . 3 0489 . 0 ( 10 1 ) ( 4 . 0 ) ( 8 3 = + × = + = − π π µ c i g A MPL l L N [T] N=83.153; use 83[T]. where i is permeability of selected core material and MPL is Magnetic Path Length of selected core. Step 19. Calculate the fringing flux, F: 238 . 1 ) 0489 . 0 ) 001 . 1 ( 2 ln 58 . 0 0489 . 0 1 ( ) 2 ln 1 ( = + = + = g c g l G A l F where G is window height of selected core. Step 20. Calculate the new turns, Nnew: 6 . 73 ) 238 . 1 )( 58 . 0 )( 4 . 0 ( 10 1 0489 . 0 ) 10 ( ) )( 4 . 0 ( 5 8 = × × = = − π π F A L l N c g [T] Nnew=73.6; use 74. Step 21. Calculate the AC flux density in Tesla, BAC: 113 . 0 0489 . 0 ) 10 )( 238 . 1 )( 2 96 . 0 )( 74 )( 4 . 0 ( ) 10 ( ) 2 ( ) 4 . 0 ( 4 4 = = = − − π π g PK ac l F I N B [T] Step 22. Calculate the new wire size, AW(B) : 002315 . 0 74 4 . 0 4283 . 0 ) ( = × = = new u a B W N K W A [A/cm 2] Step 23. Calculate the skin depth at expected operating frequency at low input voltage. The skin depth is the radius of the wire. 02960 . 0 10 50 62 . 6 62 . 6 3 = × = = f γ [cm] Step 24.Calculate the required wire area under considering skin depth : 0027535 . 0 ) ( 2 = = r Wire A π [cm 2] Step 25. Select a wire size with the required area from Table 4. If the area is not within 10% of the required area, then go to the next smallest size. AWG=#23 AW(B)=0.00259[cm 2] µ /cm=666 Step 26. Calculate the required number of primary strands, Snp: 8938 . 0 00259 . 0 002315 . 0 ) ( = = = A B w np Wire A S This means that the selected wire from the Step 25, AWG23, is enough or has enough margins for supplying the primary- side current on the flyback converter. Step 27. Calculate the secondary and auxiliary turns, Ns Naux: 05 . 27 ) 35 . 0 )( 90 2 ( ) 35 . 0 1 )( 1 24 ( 74 ) ( ) 1 )( ( max max = × − + = − + = D V D V V N N p d o p s Ns=27.05; use 27. 31 . 17 ) 35 . 0 )( 90 2 ( ) 35 . 0 1 )( 1 15 ( 74 ) ( ) 1 )( ( max max = × − + = − + = D V D V V N N p d o p aux Naux=17.31; use 17. Step 28. Calculate the secondary peak current, Ispk: 153 . 2 35 . 0 1 ) 7 . 0 ( 2 ) 1 ( 2 max = − = − = D I I o spk [A] Step 29. Calculate the secondary rms current, Isrms: 0021 . 1 3 ) 35 . 0 1 ( 153 . 2 3 ) 1 ( max = − = − = D I I spk srms [A] Step 30. Calculate the secondary wire area, Asw(B): 003781 . 0 265 0021 . 1 ) ( = = = J I A rms B SW [cm 2] Step 31. Select a wire size with the required area from Table 4. If the area is not within 10% of the required area, go to the next smallest size. |
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