データシートサーチシステム |
|
SB340 データシート(PDF) 5 Page - Fairchild Semiconductor |
|
SB340 データシート(HTML) 5 Page - Fairchild Semiconductor |
5 / 12 page AN-9719 APPLICATION NOTE © 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.0.0 • 11/2/10 5 Figure 9. Output Voltage Reflected to the Primary As can be seen in Equation 5, the voltage stress across MOSFET can be reduced by reducing VRO. However, this increases the voltage stresses on the rectifier diodes in the secondary side, as shown in Equation 6. Therefore, VRO should be determined by a balance between the voltage stresses of MOSFET and diode. Especially for low output voltage applications, the rectifier diode forward-voltage drop is a dominant factor determining the power supply efficiency. Therefore, the reflected output voltage should be determined such that rectifier diode forward voltage can be minimized. Table 2 shows the forward-voltage drop for Schottky diodes with different voltage rating. The actual drain voltage and diode voltage rise above the nominal voltage is due to the leakage inductance of the transformer as shown in Figure 9. It is typical to set VRO such that VDS NOM and VDONOM are 70~80% of voltage ratings of MOSFET and diode, respectively. Table 2. Diode Forward-Voltage Drop for Different Voltage Ratings (3A Schottky Diode) Part Name VRRM VF SB320 20V 0.5V SB330 30V SB340 40V SB350 50V 0.74V SB360 60V SB380 80V 0.85V SB3100 100V (Design Example) As can be seen in Table 2, it is recommended to use rectifier diode with 100V voltage rating to maximize efficiency. Assuming that the nominal voltages of MOSFET and diode are less than 80% of their voltage rating, the reflected output voltage is given as: · 373 · 12 0.85 12 0.8 · 100 80 373 · 12 0.85 68 70.5 0.8 · 700 560 560 373 187 By determining as 74V, 74 74 79 0.48 373 74 447 · 373 · 12 0.85 74 12 76.8 [STEP-4] Determine the Transformer Primary-Side Inductance (LM) The transformer primary-side inductance is determined for the minimum input voltage and nominal-load condition. With the DMAX from Step-3, the primary-side inductance (LM) of the transformer is obtained as: · 2· · · (7) where fSW is the switching frequency and KRF is the ripple factor at minimum input voltage and nominal load condition, defined as shown in Figure 10. For DCM operation, KRF = 1, and, for CCM operation, KRF < 1. The ripple factor is closely related to the transformer size and the RMS value of the MOSFET current. Even though the conduction loss in the MOSFET can be reduced by reducing the ripple factor, too small a ripple factor forces an increase in transformer size. When designing the flyback converter to operate in CCM, it is reasonable to set KRF = 0.25-0.5 for the universal input range and KRF = 0.4-0.8 for the European input range. |
同様の部品番号 - SB340 |
|
同様の説明 - SB340 |
|
|
リンク URL |
プライバシーポリシー |
ALLDATASHEET.JP |
ALLDATASHEETはお客様のビジネスに役立ちますか? [ DONATE ] |
Alldatasheetは | 広告 | お問い合わせ | プライバシーポリシー | リンク交換 | メーカーリスト All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |