поискавой системы для электроныых деталей |
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SB320 датащи(PDF) 10 Page - Fairchild Semiconductor |
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SB320 датащи(HTML) 10 Page - Fairchild Semiconductor |
10 / 12 page AN-9719 APPLICATION NOTE © 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.0.0 • 11/2/10 10 4. Printed Circuit Board Layout High-frequency switching current / voltage makes printed circuit board layout a very important design task. Good PCB layout minimizes excessive EMI and helps the power supply survive during surge/ESD tests. 4.1 Guidelines To get better EMI performance and reduce line-frequency ripple, the output of the bridge rectifier should be connected to capacitor CDC first, then to the switching circuits. The high-frequency current loop is in CDC – Transformer – Drain pin – CDC. The area enclosed by this current loop should be as small as possible. Keep the traces (especially 2→1 in Figure 17) short, direct, and wide. High-voltage traces related the drain and RCD snubber should be kept far away from control circuits to prevent unnecessary interference. As indicated by 2, the ground of control circuits should be connected first, then route other traces. As indicated by 3, the area enclosed by the transformer auxiliary winding, DDD and CDD should also be kept small. Place CDD close to the controller for good decoupling. GND2→3→1 are suggestions for ESD tests where the earth ground is not available on the power supply. In the ESD discharge path, the charge goes from the secondary, through the transformer stray capacitance, to GND3, then GND1, and back to mains. It should be noted that control circuits should not be placed on the discharge path. Point discharge for common-mode choke (see Figure 17) can decrease high-frequency impedance and increase ESD immunity. Should a Y-cap between primary and secondary be required, connect this Y-cap to the positive terminal of CDC. If this Y-cap is connected to primary ground, it should be connected to the negative terminal of CDC (GND1) directly. Point discharge of this Y-cap also helps for ESD. In addition, the creepage distance between these two pointed ends should be at least 5mm according to safety requirements. Figure 17. Layout Considerations |
Аналогичный номер детали - SB320 |
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Аналогичное описание - SB320 |
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