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does not include core loss make ls very large 1000x

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Unformatted text preview:   Typically 1-5% of total inductance –  Larger for gapped cores (due to fringing) –  Can be reduced by ‘interleaving’ windings •  Can be reflected to primary or secondary –  Just one leakage inductance Model with Leakage Inductance SPICE Model of a Transformer * Transformer Model! * Does not include core loss! * Make Ls very large (1000x Lm)! * N:1 primary:secondary
 * Lx is leakage Lm is magnetizing inductance! .subckt xfrmr PP PN SP SN! RP PP X {Rs*N*N}! LM X Y {Lm}! LP X Y {N*N*Ls}! LX Y PN {Lx}! LS SP Z {Ls}! RS Z SN {Rs}! K LP LS 1! .ends! Transformer Design Procedure •  (Does not apply to flyback transformer) •  Repeat the following steps 1.  Select core based on power to be handled 2.  Compute Np = VT/BA 3.  Compute winding and core loss •  Distribute window area to windings to balance current density 4.  Adjust B to balance losses 5.  Repeat with different core if required •  Co-optimize with switching losses to get best overall system Transformer Specification Nratio Vp Tp Imax F P 2:1 170 5 10 100 <10 Turns Ratio V Primary Voltage uS Primary Pulse Width A Primary Current kHz Frequency W Total Power First iteration Spec Nr V t Imax Bmax f 2 170 Volts 5.00E- 06 s 10 Amps 0.1 T 1.00E+05 Hz Constants pi mu0 Rw Aw 3.1416 1.26E- 06 8.40E- 02 Ohms/m 24AWG 2.00E- 01 mm^2 24AWG Turns ra*o - primary to secondary Primary voltage Primary pulse width Max current Max flux density Opera*ng Frequency Core Data Part E41/17/12 Ac 1.49E- 04 m^2 Lc 7.70E- 02 m Vc 1.15E- 05 m^3 AL 5.37E- 06 H OD 28.6 mm ID 12.5 m^2 H 20.8 mm W 12 mm Aw 1.68E+02 mm^2 Lturn 8.21E- 02 m Core Loss Data Pc pcb pcf 80 kW/m^3 Core loss at 0.1T 100kHz 2.50 Exponent for B field scaling 1.65 Exponent for f scaling Derived V*t Np Ns L 8.50E- 04 V- s 57 Turns 29 Turns 1.75E- 02 H Windings Kw Kwp Awp Nw Ns Ls Rp Pp Pw 0.7 0.35 5.88E+01 mm^2 294 Turns 5 Strands 4.68E+00 m 7.87E- 02 Ohms 7.87 W 15.74 W Core Loss Pc 0.92 W Total Loss Pt 16.66 Primary turns Secondary turns Primary magne*zing inductance Fill factor Window frac*on for primary Area for primary Number of wires that will fit Parallel strands per turn Length of each strand Core loss Copper loss too high – and not balanced with core loss Optimize B field Spec Nr V t Imax f 2 170 Volts 5.00E- 06 s 10 Amps 1.00E+05 Hz Constants pi mu0 Rw Aw 3.1416 1.26E- 06...
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