EPC-TDK issues 8 standard sizes of RM-configured cores in execution versions with standard height and low height (low profile). Configuration of RM (Rectangular Module) ferrite cores was developed due to a necessity to create ferrite magnetic circuits of modular type having frames with pins being integrated into a construction with a purpose to increase a productivity on installing over a printed circuit board. Geometrical dimensions of RM-configured ferrite cores were designed according to requirements for compact accommodation on printed circuit board. So, for example, RM6 designation corresponds with a core that occupies (together with a frame) 6 x 6 squares (with a side of 2.54 mm) on printed circuit board.
Most widely used applications of RM ferrite cores are:
High-stability precision inductances featuring a high reactance factor and operating in wide temperature range (ferrites of K1, M33, N48 materials).- Small-sized wideband matching transformers (ferrites of N30, T38, T66, T57 materials).
- Compact transformers and chokes of power electronics for single-ended and push-pull pulse power supplies (made from power ferrite materials N41, N51, N87, N97) operating in a frequency range of up to 500 kHz.
tarting from 90th years of XX century, RM-configured ferrite cores found a wide application in Russia and became most frequently used configuration of ferrite cores utilized in new developments of advanced design engineers in Russia.
History of RM cores (KV cores) in USSR and Russia
Epcos RM ferrite cores without gap
Geometrical Dimensions
Geometrical dimensions of RM ferrite cores issued by Epcos AG:
| Standard Size | A [mm] | D1 [mm] | D2 [mm] | D3 [mm] | h1 [mm] | h2 [mm] |
| RM 4 | 9,8-0,4 | 8,0+0,3 | 3,9-0,2 | 2,0+0,1 | 10,5-0,2 | 7,0+0,4 |
| RM 5 | 12,3-0,5 | 10,2+0,4 | 4,9-0,2 | 2,0+0,1 | 10,5-0,2 | 6,3+0,4 |
| RM 6 | 14,7-0,6 | 12,4+0,5 | 6,4-0,2 | 3,0+0,1 | 12,5-0,2 | 8,0+0,4 |
| RM 7 | 17,2-0,7 | 14,75+0,65 | 7,25-0,3 | 3,0+0,1 | 13,5-0,2 | 8,4+0,5 |
| RM 8 | 19,7-0,8 | 17,0+0,6 | 8,55-0,3 | 4,4+0,2 | 16,5-0,2 | 10,8+0,4 |
| RM 10 | 24,7-1,1 | 21,2+0,9 | 10,9-0,4 | 5,4+0,2 | 18,7-0,2 | 12,4+0,6 |
| RM 12 | 29,8-1,2 | 25,0+1,0 | 12,8-0,4 | - | 24,6-0,2 | 16,8+0,6 |
| RM 14 | 34,8-1,3 | 29,0+1,2 | 15,0-0,6 | - | 30,2-0,2 | 20,8+0,6 |
Frames, Mounting Brackets, Trimming Cores
Bobbins, clamps, adjusting screw recommended for a use with RM-configured ferrite cores of Epcos AG.
Epcos AGproposes a wide nomenclature of winding bobbins and clamps for signal and power applications using a surface and three-dimensional mounting. To adjust inductance coils into a resonance, standard series of ferrite trimming tube cores pressed into plastic bushes is issued.
Information on a standard range of winding accessories that are issued by TDC-EPC for RM-configured ferrite cores may be accessed by opening an appropriate pdf file from the table given.
Lepcos Company recommends also to use together with RM-configured ferrite cores produced by Epcos AG, additional range of products RM cores bobbins and clamp of other firms, which were to be acknowledged as good products with regard to their quality and more than 10-year experience of their use by leading manufacturers of radio-electronic industry in Russia.
Example of Assembling a Set on RM Ferrite Cores
Low Height Profile Ferrite Cores
To obtain low height profile transformers and chokes based on IEC recommendations, Epcos AG developed a standard series of low profile RM cores having a reduced height.
| Standard Size | A [mm] | D1 [mm] | D2 [mm] | h1 [mm] | h2 [mm] |
| RM 4 LP | 9,8-0,4 | 8,0+0,3 | 3,9-0,2 | 7,8-0,2 | 4,3+0,4 |
| RM 5 LP | 12,3-0,5 | 10,2+0,4 | 4,9-0,2 | 7,8-0,2 | 3,6+0,4 |
| RM 6 LP | 14,7-0,6 | 12,4+0,5 | 6,4-0,2 | 9,0-0,2 | 4,5+0,4 |
| RM 7 LP | 17,2-0,7 | 14,75+0,65 | 7,25-0,3 | 9,8-0,2 | 4,7+0,5 |
| RM 8 LP | 19,7-0,8 | 17,0+0,6 | 8,55-0,3 | 11,6-0,2 | 5,9+0,4 |
| RM 10 LP | 24,7-1,1 | 21,2+0,9 | 10,9-0,4 | 13,0-0,2 | 6,7+0,4 |
| RM 12 LP | 29,8-1,2 | 24,9+1,1 | 12,8-0,4 | 16,8-0,2 | 9,0+0,5 |
| RM 14 LP | 34,8 -1,3 | 29,0+1,0 | 15,0-0,5 | 20,5-0,2 | 11,1+0,6 |
Information on a standard range of winding accessories that are issued by TDC-EPC for RM-configured ferrite cores may be accessed by opening an appropriate pdf file from the table given above.
LEPCOS Co. recommends also to use with RM-configured (Low profile) ferrite cores made by Epcos AG additional nomenclature list of low-cost winding frames and brackets issued by other companies.
Designation in Design Documentation
Measurement unit — set
N87 RM10 A=400 нГн B65813-J400-A87
B65813 — standard size code for RM10 ferrite core
J400 — gap value is selected to provide value of AL=400 nH*
A87 — P-configured core is made from N87 material. Value variation for AL is ±3%
A, C, D — execution in version with an aperture matching with central kernel providing a possibility to use a trimming core.
F, N — execution in version with plastic bush (for trimmer) pressed into an aperture matching with central kernel of ferrite cup.
E, J — P core construction has not an aperture in central kernel
P — execution with reduced height (Low profile).
Additional Information
To decrease losses on transportation and storage, it is recommended (as possible) to order ferrite cores, bobbins and clamps of RM-configured cores in multiples of amounts contained in factory package. Information on number of cores in standard factory package is given in this page.
