AN109. Push-Pull Converter Design Using a CoreMaster E2000Q Core. By Colonel Wm. T. McLyman. Figure 1 Single output push-pull converter.

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1 age 1 of 6 AN109 ush-ull Converter Design Using a CoreMaster E000Q Core By Colonel Wm. T. McLyman The single output push-pull converter is shown in Fig.1. Figure 1 ingle output push-pull converter. ush-ull Converter Transformer Design pecification 1. Input voltage nominal V nom 8 V. Input voltage minimum V min V 3. Input voltage maximum V max 3 V. Output voltage V O 5 V 5. Output current I O 10 A 6. Output circuitry Center tapped 7. Frequency f100 khz 8. Regulation α 0.5 % 9. Efficiency η 98 % 10. Operating flux density B m 0.1T 11. Window utilization K U Diode voltage drop V d 1 V 13. Duty ratio D max Temperature rise T r 5 C At this point, select a wire so that the relationship between the ac resistance and the dc resistance is 1. RAC 1 R DC

2 age of 6 The skin depth in cm is: 6.6 δ f 6.6 δ [cm] 100,000 Then, the wire diameter is: Wire diameter δ Wire diameter [cm] Then, the bare wire area A W is: πd AW A W [cm ] From the Wire Table, number 6 has a bare wire area of centimeters. This will be the minimum wire size used in this design. If the design requires more wire area to meet the specification, then, the design will use a multifilar of #6. Listed Below are #7 and #8, just in case #6 requires too much rounding off. Wire AWG Bare Area Area Ins. Bare/Ins. µω/cm # # # tep No. 1. Calculate the transformer output power, O. I V + V ( ) ( ) O O O d O [W] tep No.. Calculate the total apparent power, t. t O + η 1.1 t [W] 0.98 tep No. 3. Calculate the electrical conditions, K e K 0.15 K f B 10 e f m K f for square wave K e tep No.. Calculate the core geometry, K g. t Kg α K , K g 3,00 1 e [cm ]

3 age 3 of 6 tep No. 5. elect from the data sheet a E000Q core comparable in core geometry, K g Core number TEA011Q Manufacturer CMI Magnetic material E 000Q Magnetic path length, ML 5.11 cm Core weight, W tfe 9.5 g Mean length turn, MLT 3. cm Iron area, A c 0. cm Window area, W a cm Area product, A p 0.08 cm Core geometry, K g cm 5 urface area, A t.9 cm tep No. 6. Calculate the number of primary turns N using Faradays Law. V( MIN) 10 Np f A B K c AC f 1 10 N 5 [turns] 100, tep No. 7. Calculate the current density J using a window utilization, K u 0.. t 10 J f A B K K AC u f J 100, tep No. 8. Calculate the input current, I in. O IIN V η IN 51 [A/cm ] 60 I IN.55 [A] 0.98 tep No. 9. Calculate the primary bare wire area, A wp(b) IIN DMAX Awp( B) J A wpb ( ) [cm ] 51 tep No. 10. Calculate the required number of primary np. Using the area of a #6 wire. Awp( B) np # np.7 use tep No. 11. Calculate the primary new µω/cm from the number 6AWG. µ Ω/ cm newµ Ω / cm np 135 newµω / cm 8 3

4 age of 6 tep No. 1. Calculate the primary winding resistance, R p. 6 R MLT N µ Ω 10 cm 6 R [ Ω] tep No. 13. Calculate the primary copper loss,. I R rms [W] tep No. 1. Calculate the number of secondary turns, N. N V α N 1+ VMIN 100 V VO + Vd V [V] N use 6 [turns] 100 tep No. 15. Calculate the secondary bare wire area, A ws. IO DMAX Aws J A wsb ( ) [cm ] 51 tep No. 16. Calculate the required number of secondary strands, ns. Aws( B) ns # ns use tep No. 17. Calculate the secondary new mw per centimeter using number 6 AWG. µ Ω/ cm ( new) µ Ω / cm N 135 ( new) µω / cm tep No. 18. Calculate the secondary resistance, R s. µ Ω 6 R MLT N 10 cm 6 R s [ Ω] tep No. 19. Calculate the secondary copper loss,. I R [W] tep No. 0. Calculate the total copper loss, cu. + CU [W] CU

5 age 5 of 6 tep No. 1. Calculate the transformer regulation, α. CU α 100% O 0.51 α % 60 tep No.. Calculate the milliwatts per gram, mw/g mw / g f BAC mw / g , tep No. 3. Calculate the core loss, Fe. 3 mw / g W 10 Fe ( ) Fe tep No.. Calculate the total loss, Σ. Σ Cu Fe Σ [W] tep No. 5. Calculate the watt density, Ψ. Σ Ψ A 0.61 Ψ.9 tep No. 6. Calculate the temperature rise, T r. T 50 Ψ r tfe [W] t 0.07 [W/cm ] 0.86 T r tep No. 7. Calculate the total window utilization K U [ C] KU Ku + Ku N A K u K us K u N ws W α N n Aw W α K u K u

6 age 6 of 6 BIBLIOGRAHY Colonel William T. McLyman, Transformer and Inductor Design Handbook, econd Edition, Marcel Dekker Inc., New York, Colonel William T. McLyman, Magnetic Core election for Transformers and Inductors, econd Edition, Marcel Dekker Inc., 1997 Colonel William T. McLyman, Designing Magnetic Components for High Frequency, dc-dc Converters, Kg Magnetics, Inc., For information regarding the above Books and Companion oftware for Windows 95', 98' and NT, contact: Kg Magnetics, Inc. 38 West ierra Madre Blvd, uite J ierra Madre, Ca. 910 hone: (66) , FAX: (66) Web age: sheasso@pacbell.net