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ACT412 Fiches technique(PDF) 11 Page - Active-Semi, Inc |
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ACT412 Fiches technique(HTML) 11 Page - Active-Semi, Inc |
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11 / 17 page ![]() ACT412 Rev 1, 30-Oct-13 Innovative PowerTM - 11 - www.active-semi.com Copyright © 2013 Active-Semi, Inc. Active-Semi Proprietary―For Authorized Recipients and Customers ActivePSR TM is a trademark of Active-Semi. TYPICAL APPLICATION CONT’D An EE16 core is selected for the transformer. From the manufacture’s catalogue recommendation, the core with an effective area AE is 19.2mm 2 .The turn of the primary winding is: The turns of secondary and auxiliary winding can be derived accordingly: Determining the value of the current sense resistor (R9) uses the peak current in the design. Since the ACT412 internal current limit is set to 1V, the design of the current sense resistor is given by: The voltage feedback resistors are selected according to frequency at full load. The design frequency at full load is given by: The design Vo is given by: Where k is IC constant and K=0.0000065, then we can get the value: When selecting the output capacitor, a low ESR electrolytic capacitor is recommended to minimize ripple from the current ripple. The approximate equation for the output capacitance value is given by: Two 330µF electrolytic capacitors are used to keep the ripple small. In fact, consider of transformer production, we scale down the turn ratio and inductance. PCB Layout Guideline Good PCB layout is critical to have optimal performance. Decoupling capacitor (C4) and feedback resistor (R5/R6) should be placed close to VDD and FB pin respectively. There are two main power path loops. One is formed by C1/C2, primary winding, Mosfet transistor and current sense resistor (R9). The other is secondary winding, rectifier D8 and output capacitors (C5/C6). Keep these loop areas as small as possible. Connecting high current ground returns, the input capacitor ground lead, and the ACT412 GND pin to a single point (star ground configuration). T 95 10 3000 2 . 19 00073 . 0 75 . 0 B A L I N 10 max E max _ p lim P = × × × = × × ≥ − (13) mA 750 mA 375 2 I 2 I FL _ p lim ≈ × = × = (14) T 24 17 4 . 1 N N N N T 17 53 . 5 / 95 N N / N N s S A A S p p s ≈ × = × = ≈ = = (15) Ω . 3 . 1 75 . 0 1 I V R lim CS CS ≈ = = (16) sw _ f cs cs p D O 2 fb 1 fb 2 fb 1 fb s p s K R V L V V R R R R N N f × × + × + × × = (17) D FB a s 2 fb 1 fb o V V N N ) R R 1 ( V − × × + = (18) K 9 . 6 R , K 3 . 45 R 2 fb 1 fb = = (19) F 327 mV 50 k 110 8 . 1 V f I C RIPPLE sw OUT OUT μ = × = × = (20) mH 5 . 0 L , T 17 N , T 12 N , T 68 N p A s p = = = = (21) |
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