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[/ 1. The maximum duty cycle Dmax of the MOSFET switch is as follows: Vor is the reflected voltage from the secondary side to the primary side. When the input is AC220V, the reflected voltage is 135V. VminDC is the minimum voltage after rectification. DC voltage, VDS is the voltage between the D and S poles when the MOSFET power tube is turned on, generally 10V. 2. Transformer original The peak current IPK of the side winding is as follows: η is the conversion efficiency of the transformer, Po is the output rated power, in W. /image/20190404/20190404115626_24708.jpg[/img]
3. The primary inductance LP of the transformer is as shown above: Ts is the period of the switching tube (s), and the unit of LP is H. 4. Transformer The air gap lg is as above: Ae is the effective cross-sectional area of the core (cm2), △B is the change value of the working magnetic induction intensity of the core (T), Lp is in H, IPK is in A, and lg is in mm. 5. Transformer core formula. The flyback converter power is usually small. Generally, ferrite core is used as the transformer core. Its power capacity AP is as follows: AQ is the core window area, unit is cm2. Ae is the effective cross-sectional area of the core, in cm2. Po is the nominal output power of the transformer, in W. fs is the switching frequency of the switch tube, Bm is the maximum magnetic induction intensity of the core, in T. δ is The current density of the coil wire is usually 200-300A/cm2. η is the conversion efficiency of the transformer, and Km is the window filling factor, which is generally 0.2-0.4. KC is the filling factor of the core, which is 1.0 for ferrite. Select a core with a slightly larger margin based on the AP value obtained. Generally, try to choose a core with a larger window length to width ratio, so that the core window is effectively used. The coefficient is higher and the leakage inductance can be reduced. ]
6. The number of primary turns NP of the transformer is as shown in the above formula: △B is the change value of the working magnetic induction intensity of the core (T), Ae is in cm2, and Ts is in s. 7. Transformer The number of side turns NS is as shown above: VD is the forward voltage drop of the rectifier diode on the secondary side of the transformer. /20190404/20190404115811_15298.jpg[/img]
8. The minimum voltage stress UDS of the switch tube is as shown in the above formula: Generally, a MOSFET with a breakdown voltage between DS that is slightly larger than the value calculated by formula (9) is selected. Power tube. 9. Winding copper The consumption PCU is as follows: The resistance values of the primary and secondary windings can be calculated by the formula for the winding resistance value R. When calculating the copper consumption of the primary winding, the current is calculated using the primary peak current IPK; when calculating the copper consumption of the secondary winding , the current is calculated using the output current Io. 10. The core loss depends on the operating frequency, the working magnetic induction intensity, the circuit working state and the performance of the selected core material. For a bipolar switching transformer, the core loss PC is as follows: ]
Pb is the core loss per unit mass at the operating frequency and working magnetic induction intensity (W/kg), and Gc is the core mass (Kg). In the half area of the hysteresis loop, its core loss is about half of that of the bipolar switching transformer. The total transformer loss is the sum of the total copper loss and the core loss. /color]
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