AMD_POW_AN1632

AN112 Page 1 of 6 www.coremaster.com AN112 Single Ended Regulation only, Mag-Amp Design Using a CoreMaster E1000S Core By Colonel Wm. T. McLyman The Single Ended Forward Converter and Mag-Amp are shown in Figure 1. Figure 1. Single ended forward converter with mag-amp. Single Ended Forward Converter Mag-Amp Design Output Specification 1. Secondary voltage maximum VSmax = 16 V 2. Output voltage VO = 5 V 3. Output current IO = 2.5 A 4. Overwind OW=20% 5. Frequency f=100 kHz 6. Maximum duty ratio Dmax = 0.5 7. Operating flux density @100°C BAC = 0.25 T 8. Window utilization KU =0.2 9. Current density J=300 A/cm2 10. Control Regulation only 11. Magnetic material E1000S 12. Diode voltage drop Vd = 1 V AN112 Page 2 of 6 www.coremaster.com Select a wire so that the relationship between the AC resistance and the DC resistance is 1: 1AC DC R R = The skin depth in cm is: 6.62 f d = 6.62 0.0209 [cm] 100,000 d = = AN112 Page 3 of 6 www.coremaster.com Then, the wire diameter is: Wire diameter = 2d Wire diameter = 2 0.0209= 0.0418 [cm]× Then, the bare wire area AW is: 2 4W D A p = 2 23.1416 0.04180.00137[cm ] 4W A × = = From the Wire Table, number 26 has a bare wire area of 0.001280 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 #26. Listed Below are #27 and #28, just in case #26 requires too much rounding off. Wire AWG Bare Area Area Ins. Bare/Ins. mW/�cm #26 0.00128 0.001603 0.798 1345 #27 0.001021 0.001313 0.778 1687 #28 0.000804 0.000105 0.765 2142 Step No. 1 Calculate the total period, T. 1 T f = 61 10 10 [s] 100,000 T -= = × Step No. 2 Calculate the maximum transistor on time, ton. on MAXt TD= 610 10 0.5 5 [ s]ont m -= × × = Step No. 3 Calculate the required pulse width, tpw. ( ) onpw O d MAX t t V V V = + × ( ) 55 1 1.875 [ s] 16pw t m= + × = Step No. 4 Calculate the mag-amp required micro-seconds, tma. ( )ma on pwt t t= - ( )5 1.875 3.125 [ s]mat m= - = Step No. 5 Calculate the mag-amp control and clamp voltage, Vc. 10 5 [ s] 2 2off T t m= = = maxs ma C off V t V t × = 16 3.125 10 [V] 5C V × = = AN112 Page 4 of 6 www.coremaster.com Step No. 6 Calculate the rms gate current, Ig(rms). ( )g rms O MAXI I D= × ( ) 2.5 0.5 1.77 [A]g rmsI = × = Step No. 7 Calculate the gate wire area, A w(B). ( ) grms w B I A J = 2 ( ) 1.77 0.0059 [cm ] 300w B A = = Step No. 8 Calculate the mag-amp apparent power, Pt. ( ) (max)t g rms s wP I V O= × × 1.77 16 1.2 34 [W]tP = × × = Step No. 9 Calculate the required mag-amp core area product, Ap. 410 2 t ma P ac u P t A B J K × × = × × × 6 4 434 3.125 10 100.0354 [cm ] 2 0.25 300 0.2P A -× × × = = × × × Step No. 10 Select from the data sheet a mag-amp core comparable in area product Ap. Core number TCM0232 Manufacturer CMI Magnetic material E 1000S Magnetic path length, MPL 3.5 cm Core weight, Wtfe 2.9 g Copper weight, Wtcu 2.4 g Mean length turn, MLT 2.0 cm Iron area, Ac 0.108 cm 2 Window area, Wa 0.232 cm 2 Area product, Ap 0.03584 cm 4 Core geometry, Kg 0.000777 cm 5 Surface area, At 10.4 cm 2 Step No. 11 Calculate the number of gate turns, Ng. 4 (max) 10 2 S w ma g c m V O t N A B × × × = × × 6 416 1.2 3.125 10 10 11 [turns] 2 0.108 0.25g N -× × × × = = × × Step No. 12 Calculate the required number of gate strands, Sg, and the new mW/cm #26 wg g A NS = 0.0059 4.61 use 4 0.00128P NSg = = / 1345 / 336 4g cm new cm S m m W W = = = AN112 Page 5 of 6 www.coremaster.com Step No. 13 Calculate the gate winding resistance, Rg. 610g gR MLT N cm m -Wæ ö= × ×ç ÷ è ø 62.0 11 336 10 0.00739 [ ]PR -= × × × = W Step No. 14 Calculate the gate copper loss, Pg. 2 g g gP I R= 21.77 0.00739 0.0231 [W]gP = × = Step No. 15 Calculate the window utilization, KU. ( )g w B g u a N A NS K W × × = 11 0.00128 4 0.169 0.332u K × × = = Step No. 16 Calculate the watts per kilogram, WK . 7 1.934 2.2494.154 10 acWK f B -= × × × × 7 1.934 2.2494.154 10 100,000 0.25 84.9 [W/kg] or [mW/g]WK -= × × × = Step No. 17 Calculate the core loss, PFe. ( ) 3/ 10Fe tfeP mW g W -= × × 384.9 2.9 10 0.246 [W]FeP -= × × = Step No. 18 Calculate the total loss, PS. Cu FeP P PS = + 0.246 0.0231 0.269 [W]PS = + = Step No. 19 Calculate the watt density, Y. t P A SY = 20.269 0.0259 [W/cm ] 10.4 Y = = Step No. 20 Calculate the temperature rise, Tr. 0.826450rT = × Y 0.826450 0.0259 22 [ C]rT = × = o Step No. 21 Calculate the magnetizing force in Oersteds, Hc. 2.2 0.019c m WK H B f = × × 84.9 2.2 0.0818 [Oe] 0.019 0.25 100,000c H = = × × AN112 Page 6 of 6 www.coremaster.com Step No. 22 Calculate the control or magnetizing current, Ic. mI 1.256 c g H MPL N × = × m 0.0808 2.0 I 0.0117 [A] 1.256 11 × = = × BIBLIOGRAPHY Colonel William T. McLyman, Transformer and Inductor Design Handbook, Second Edition, Marcel Dekker Inc., New York, 1988. Colonel William T. McLyman, Magnetic Core Selection for Transformers and Inductors, Second Edition, Marcel Dekker Inc., 1997 Colonel William T. McLyman, Designing Magnetic Components for High Frequency, dc-dc Converters, Kg Magnetics, Inc., 1993. For information regarding the above Books and Companion Software for Windows 95', 98' and NT, contact: Kg Magnetics, Inc. 38 West Sierra Madre Blvd, Suite J Sierra Madre, Ca. 91024 Phone: (626) 836-7233, FAX: (626) 836-7263 Web Page: www.kgmagnetics.com Email: sheasso@pacbell.net