1 MHz Switchmode Transformer

West Coast Magnetics' 402 series high frequency transformers are intended for use in switch mode power supplies including push/pull, flyback, and forward converter circuits. Output power as high as 257 watts can be achieved in push/pull circuits. All sizes are based on low proÞle E-core geometry and two sizes are offered in surface mount packaging. West Coast Magnetics stocks core material which will accommodate a range of operating frequencies from 10 kHz to 3 MHz.

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Design Constants

Size Code	Al frequency > 500 kHz a.	Al frequency ≤ 500 kHz a.	Al single gap	Al double gap	Ae core area (mm²)	le magnetic path length (mm)	Ve core volume (mm³)	Wa bobbin winding area (mm²)	WaAc core area x winding area (mm⁴)	Bobbin window width (mm)	Bobbin window height (mm)	Mean length per turn (mm)
EFD-15	400	850	70	135	15	34	510	17.1	257	8.9	1.93	27
EFD-20	650	1200	70	135	31	47	1460	28.1	871	13.4	2.1	38
EFD-25	1000	2000	80	155	58	57	3300	42.5	2465	16.7	2.55	48
EFD-30	1050	2150	80	155	69	68	4700	54.1	3733	20.4	2.65	52

Power Curve Assumptions:

Push/Pull circuit topology
Bobbin Window area utilization = 40%
Flux density (B) chosen so that core losses at all Frequencies are 100 mW/cm³.

a. Al measured for ungapped cores. nH/T² ± 25%

output frequency

Output Power vs Frequency of Operation (Watts)

Size Code	50 kHz	100 kHz	250 kHz	500 kHz	1000 kHz	2000 kHz	3000 kHz
EFD 15	6.8	9.3	14	16	25	20	17
EFD 20	20	27	42	47	72	59	49
EFD 25	49	67	104	117	180	147	121
EFD 30	70	96	149	169	257	210	173

schematics

Part Views and Dimensions

EFD 15 and EFD 20	EFD 25 and EFD 30
click image to enlarge	click image to enlarge

Size/Code	A	B	C	D	E	F	I	J	K	L
EFD 15	.894/22.7	.736/18.7	.657/16.7	.039/1.0	.315/8.0	.012/0.3	.110/2.8	.150/3.75	.811/20.6	.079/2.0
EFD 20	1.091/27.7	.933/23.7	.854/21.7	.039/1.0	.406/10.3	.012/0.3	.110/2.8	.150/3.75	1.01/25.6	.079/2.0

Size/Code	A	C	D	E	F	G	J	K	L
EFD 25	1.024/26.0	1.024/26.0	.031/0.8	.511/13.0	.071/1.8	.138/3.5	.197/5.0	.886/22.5	.052/1.3
EFD 30	1.220/31.0	1.220/31.0	.031/0.8	.511/13.0	.071/1.8	.138/3.5	.197/5.0	1.083/27.5	.052/1.3

Note: All materials of construction minimum Class B 130 degrees C rated.

Dimensions: Inches/mm

notes

Notes:

Reduce power rating in Table above by 50% for forward and flyback converter topologies.
Final sizing of the transformer will depend on a number of interrelated variables. The data in the above table should be considered a starting point only.
If safety agency is required, the final size may be significantly
larger than the data in the table would indicate.