データシートサーチシステム |
|
FAN6747 データシート(PDF) 2 Page - Fairchild Semiconductor |
|
FAN6747 データシート(HTML) 2 Page - Fairchild Semiconductor |
2 / 12 page AN-6747 APPLICATION NOTE © 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.0.1 • 9/16/10 2 2. Design Considerations Flyback converters have two operation modes; continuous conduction mode (CCM) and discontinuous conduction mode (DCM). CCM and DCM each have advantages and disadvantages. In general, DCM provides better switching conditions for the rectifier diodes, since the diodes are operating at zero current just before becoming reverse biased and the reverse recovery loss is minimized. The transformer size can be reduced using DCM because the average energy storage is low compared to CCM. However, DCM causes high RMS current, which increases the conduction loss of the MOSFET severely for low line condition. Thus, especially for applications with peak load profile, such as printer and scanner; it is typical to design the converter such that the converter operates in CCM for low line and peak load condition to maximize efficiency. In this section, a design procedure is presented using the schematic of Figure 1 as a reference. An offline SMPS with 20W/32V nominal output power and 70W/32V peak output power has been selected as a design example. [STEP-1] Define the System Specifications Designing a power supply with peak load current profile, the following specifications should be determined first: Line voltage range (VLINE MIN and VLINEMAX) Line frequency (fL) Nominal output power (PNO) Peak output power (PPO) and its duration (tPO) Estimated efficiencies for nominal load ( ηN) and peak load ( ηP). The power conversion efficiency must be estimated to calculate the input powers for each condition. Typically, the efficiency at peak load condition is lower than that of nominal load since most of the components of power supply are selected for nominal load condition. If no reference data is available, set ηN = 0.7~0.75 and ηP = 0.65~0.7 for low-voltage output applications and ηN = 0.8~0.85 and ηP = 0.75~0.8 for high-voltage output applications. With the estimated efficiency, the input power for peak load condition is given by: P PO INP P P η = (1) The input power for nominal load condition is given by: N NO INN P P η = (2) (Design Example) The specifications of the target system are: VLINE MIN =90VRMS, VLINEMAX=264VRMS Line frequency (fL) = 60Hz Nominal output power (PNO) = 20W (32V/0.625A) Peak output power (PPO) = 70W (32V/2.187A) Peak load duration (tPO) < 100ms Estimated efficiency: ηN = 0.87 and ηP = 0.83 W 84 83 . 0 70 P P P PO INP = = η = W 23 87 . 0 20 P P N NO INN = = η = FAN6747 can be used for this application because the peak load duration is less than the OCP delay time of 220ms. [STEP-2] Determine the Input Capacitor (CIN) and the Input Voltage Range It is typical to select the input capacitor as 1.5~2 μF per watt of peak input power for universal input range (85-265VRMS) and 0.7~0.8 μF per watt of peak input power for European input range (195V-265VRMS). With the input capacitor chosen, the minimum input capacitor voltage at peak load condition is obtained as: ( ) () L IN CH INP 2 MIN LINE MIN INP f C D 1 P V 2 V • − • − • = (3) The minimum input capacitor voltage at nominal load condition is obtained as: ( ) () L IN CH INN 2 MIN LINE MIN INN f C D 1 P V 2 V • − • − • = (4) where D CH is the input capacitor charging duty ratio defined as shown in Figure 2, which is typically about 0.2. The maximum input capacitor voltage is given as: MAX LINE MAX IN V 2 V = (5) Figure 2. Input Capacitor Voltage Waveform |
同様の部品番号 - FAN6747 |
|
同様の説明 - FAN6747 |
|
|
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 |