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FAN6300A データシート(PDF) 3 Page - Fairchild Semiconductor |
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FAN6300A データシート(HTML) 3 Page - Fairchild Semiconductor |
3 / 13 page AN-6300 APPLICATION NOTE © 2009 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.0.2 • 5/21/10 3 Design Procedure for the Primary-Side Inductance of Transformer In this section, a design procedure is described using the schematic of Figure 1 as a reference. [a] Define the System Specifications Line voltage range (Vin,min and Vin,max) Maximum output power (Po). Output voltage (Vo) and maximum output current (Io) Estimated efficiency (η) The power conversion efficiency must be estimated to calculate the maximum input power. In the case of NB adaptor applications, the typical efficiency is 85%~90%. With the estimated efficiency, the maximum input power is given by: o in P P= η (1) [b] Estimate Reflected Output Voltage Figure 3 shows the typical waveforms of the drain voltage of quasi-resonant flyback converter. When the MOSFET is turned off, the DC link voltage (Vo), together with the output voltage (Vo) and the forward voltage drop of the Schottky diode (Vd) reflected to the primary, are imposed on the MOSFET. The maximum nominal voltage across the MOSFET (Vds) is: ds,max in,max o d VV + n V +V =( ) (2) where the turns ratio of primary to secondary side of transformer is defined as n and Vds is as specified in Equation 2. By increasing n, the capacitive switching loss and conduction loss of the MOSFET is reduced. However, this increases the voltage stress on the MOSFET as shown in Figure 3. Therefore, determine n by a trade-off between the voltage margin of the MOSFET and the efficiency. Typically, a turn-off voltage spike of Vds is considered as 100V, thus Vds,max is designed around 490~550V (75~85% of MOSFET rated voltage). [c] Determine the Transformer Primary-side Inductance (LP) Figure 4 shows the typical waveforms of MOSFET drain current (Ids), secondary diode current (Id), and the MOSFET drain voltage (Vds) of a QR converter. During tOFF, the current flows through the secondary side rectifier diode. When Id reduces to zero, Vds begins to drop by the resonance between the effective output capacitor of the MOSFET and the primary-side inductance (LP). To minimize the switching loss, the FAN6300/A/H is designed to turn on the MOSFET when Vds reaches its minimum voltage Vin-n(Vo+Vd). Vin + - Vo + - Coss Vds + - + - Vds Vin,max n(Vo+Vd) Vds 0V n(Vo+Vd) n(Vo+Vd) n(Vo+Vd) +- Vd n(Vo+Vd) n:1 Figure 3. Typical Waveform of MOSFET Drain Voltage for QR Operation Ids Id Vds Vin Vin+n(Vo+Vd) tON tOFF tF TS n(Vo+Vd) Vin-n(Vo+Vd) n(Vo+Vd) Iin Ids pk DTs Figure 4. Typical Waveform of QR Operation |
同様の部品番号 - FAN6300A |
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同様の説明 - FAN6300A |
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