flyback-design(0628)电子电路详解.pptVIP

AGENDA VT Balance Operation of Flyback Coverter How Flyback transformer store energy? DCM(Discontinous Current Mode) flyback CCM (Continuous Current Mode) flyback Advantage of CCM DCM/CCM Boundary Component selection Current mode vs. voltage mode converter Design a Transformer Primary Mosfet Secondary gate driver Mosfet Snubber Output Capacitor Input capacitor Current sense resistor Loop compensation Photo coupler Slope Compensation for Current Mode Some Idioms may confuse you Why choose Flyback Converter? T RL _ + Vref _ R S + Q Vin Vo Ve Vg OP AMP Comparator Feedback Loop of Current Mode Rs Ip Ip*Rs Design a Transformer Decide the turns ratio Decide the maximum duty cycle 2. Decide the inductance 3. Choose a magnetic core 4. Calculate primary turns 5. Calculate secondary turns wire diameter Skin effect 6. Design the winding sequence Design A Transformer 1. Turn Ratio : VT Balance : T D 50% for current mode NP Ns Design A Transformer 2. Calaculate the inductance : T Lm Vin Ns Np Im I,offset I,offset 3. Choose a Magnetic Core --- EFD20 4. Calculate Primary Turns --- Np B: flux density : Gauss Ae: effective Area of magnetic core : mm^2 B 2000 Gauss 2000Gauss Ip,peak Ip 5. Calculate Ns wire diameter Ns= NP*N Skin effect + + + + + + + + + + + + + + + S It is better, the diameter of wire 2*S The diameter of wire vs. Current D: diameter of Wire If D2*s, divide I into 2 or multiple, then recalculate the D Electrical Characteristics ? Inductance(pin 4-6)：110uH. ? 6-5 19Ts, Φ=0.3mm 10,11,12 - 7,8,9 7Ts, Φ=0.37mm*3 5-4 19Ts Φ=0.3mm* Hipot @ 1500Vdc for 1 second. Pins (46) to pins (10,11,12 7,8,9), also windings to core. ? Turns ratio: Pins (4-6)：(10,11,12 – 7,8,9,)：(1-3) = 1：0.19 ? Magnetic Core: EFD20 Output Power: 15W Vin: 36-75V Topology: Flyback Switching Frequency: 240KHz 6 4 5 5 7,8,9 10,11,12 Np1 Ns Np2 6. Winding sequence Np2 Ns Np1 Insulate