米6体育平台手机版

ZHCSQ75C June 2022 – March 2023 UCC28C50-Q1 , UCC28C51-Q1 , UCC28C52-Q1 , UCC28C53-Q1 , UCC28C54-Q1 , UCC28C55-Q1 , UCC28C56H-Q1 , UCC28C56L-Q1 , UCC28C57H-Q1 , UCC28C57L-Q1 , UCC28C58-Q1 , UCC28C59-Q1

PRODUCTION DATA

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机械数据 (封装 | 引脚)

D|8
- MSOI002K

散热焊盘机械数据 (封装 | 引脚)

订购信息

zhcsq75c_oa

9.2.2.1 Primary-to-Secondary Turns Ratio of the Flyback Transformer (NPS)

To start, we need to estimate the forward voltage (V_F) of the output Schottky diode and the on-time of the MOSFET (t_{ON_EST})

Equation 8.

V_{F} = 0.5 V

Equation 4.

t_{O N_E S T} = \frac{D_{V I N_M I N}}{f_{S W}} = \frac{0.80}{42.5 k H z} = 18.8 µ s

Next, estimate the transformer primary-to-secondary turns ratio

Equation 5.

N_{P S} = \frac{V_{I N_M I N} \times t_{O N_E S T}}{(\frac{1}{f_{S W}} - t_{O N_E S T}) \times (V_{O U T} + V_{F})} = \frac{40 V \times 18.8 µ s}{(\frac{1}{42.5 k H z} - 18.8 µ s) \times (15 V + 0.5 V)} = 10.3

Calculate the reverse withstand voltage of output rectifier diode during t_{ON_EST}

Equation 6.

V_{S E C_R E V} = V_{O U T} + \frac{V_{I N_M A X}}{N_{P S}} = 15 V + \frac{1000 V}{10.3} = 112 V

Calculate the (expected) drain-to-source voltage of the MOSFET during the off time

Equation 7.

V_{D S_O F F} = V_{I N_M A X} + (V_{O U T} + V_{F}) \times N_{P S} = 1000 V + (15 V + 0.5 V) \times 10.3 = 1160 V

The switching MOSFET and output rectifier generally experience voltage ringing due to transformer leakage and parasitic capacitance. Based on V_{SEC_REV}, a 200V-rated Schottky diode is chosen, so the secondary RC snubber can damp the voltage spike and ringing with reduced snubber power loss. Based on V_{DS_OFF}, a 1.7kV-rated SiC MOSFET is chosen, so a higher breakdown voltage of the primary TVS diode clamping circuit can clamp the switching voltage stress caused by the transformer leakage with reduced clamping power loss. If V_{DS_OFF} is too high, the turns ratio can be reduced by decreasing D_{VIN_MIN}, but V_{SEC_REV} will increase. Deciding which component voltage is more critical and iterate again if necessary.