R-Core Transformers
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Home »  Products »  Linear Transformers » R-Core Transformers

R-core Transformers are manufactured using unique rectangular cores with round cross section known as R-cores. The special feature of this transformer is that the core has no gaps and is continuous.

The other unique feature of R-cores is the use of Bobbins in two parts. The winding is done on special round bobbins on two parallel legs of the core. This ensures complete isolation between the two windings and satisfies safety standards. In comparison with EI Transformers of same capacity, the R-core transformer is compact (nearly 40% smaller) and has a low temperature elevation. Leakage flux of the R-core transformer is about 1/10th of conventional transformers which permits the equipment manufacturer to place the transformer close to critical electronic components. The balanced winding & low leakage flux ensures low noise of the transformers. This makes R-Core transformers suitable for use in noise sensitive equipment.

The R-core Transformers have found wide application in CRT display units, audio equipment, satellite receivers, bio-medical equipment, printers, photo-copier machines, weighing scales, etc.

Dimensions



R-cores A B C D E t F dia VA W(kgs.)
R-5
48
62
27
45
35
0.5
4.0
5-8
0.23
R-10
74
60
50
45
32
1.0
4.0
5-15
0.4
R-20
81
68
55
45
37
1.0
4.0
15-30
0.5
R-30
96
74
70
60
41
1.0
5.0
30-40
0.7
R-40
98
80
70
60
43
1.0
5.0
40-50
0.9
R-50
100
86
75
65
47
1.0
5.0
50-65
1.0
R-75
101
97
70
80
54
1.0
5.0
70-105
1.3
R-80
123
90
90
70
50
1.2
5.0
80-110
1.4
R-100
124
102
100
80
55
1.2
5.0
110-150
1.8
R-160
139
110
100
85
63
1.6
5.0
150-210
2.6
R-260
160
121
128
96
68
1.6
5.0
210-290
3.1
R-320
163
128
135
95
70
1.6
5.0
290-380
3.8
R-600
189
143
142
100
80
1.6
8.0
380-750
6.5
R-1000
225
172
180
140
99
2.3
8.0
750-1200
10.5
R-30L
121
65
95
50
39
1.0
4.0
30-45
0.9
R-80L
129
82
110
70
45
1.0
5.0
65-80
1.3

  • All dimensions are in mm.
  • E dimension of R-core Transformer may vary depending on the number of terminals.
  • Specifications may change without notice due to product modification.

PCB - Mounting




SIZE A B C D E F G No.of pins CAPACITY(VA)
R-5
45
45
17
14
5.25
3.0
5.75
12
0-8
R-10
75
65
40
15
6
3
6
12
8-15

Leakage Flux



  • The special characteristic of the R-core transformer is the ability of the two coils to mutually cancel each other's magnetic flux by means of balanced, symmetrical winding of the coils. With this winding method the leakage flux can be kept to a minimum amount. The key point is the exact balance of the two coils.
  • The R-core transformer has absolutely no gap in its magnetic paths. On the other hand, the EI-type has a magnetic gap in 6 locations, and the CI or the cut core type has 2 to 4 magnetic gaps. A great deal of leakage flux escapes from these magnetic gaps.
  • The R-core transformer makes a maximum use of the superior material properties of the Z-H grain-oriented silicon steel. As a result, the core's magnetic resistance is very low, and the cross section of the magnetic path is uniform. The exiting current of the R-core transformer is lower than the EI-type ensuring that the leakage flux is minimal and a higher percentage of the entire magnetic flux of the R-core transformer is being put to much more effective use.

Advantages


Reference R-core Transformer Toroid Transformer EI Transformer
Shape The Standard model is thin, small & light. Small transformer leads to higher copper loss. The Ideal shape is square. The transformer tends to be large & heavy.
Leakage flux With balanced winding canceling the leakage flux, the total amount of leakage flux is extremely small. As a result can be used even without shield. Winding is not balanced hence there is lot of leakage flux. To reduce the effect there is a need to provide shielding. There are gaps in the magnetic path and the winding is not balanced. As a result the leakage flux is very high which can affect sensitive electronic components if proper shielding is not provided.
Winding Winding is done on special machine resulting in evenly spaced winding. Balanced winding is an inherent constituent of the design. The winding is not evenly spaced. The density of turns on the inner edge is more and on the outer edge the wires are roughly spaced out. Thus the winding is not balanced. While the layers of turns are well laid out the winding is only on the center limb of the EI core. Thus it is not balanced.
Exiting Current The exiting current is minimal as all the magnetic paths are in alignment with the rolling direction of the steel and there is no gap in the core. The exiting current is less than that in EI Transformer, but the same is higher than that of R-core transformer due to lack of balancing of winding. More exiting current is required due to presence of magnetic gaps, the inability to use the effect of rolling direction of grain oriented steel, the variation in assembly operation, etc.
Insulation Double structure bobbins are used ensuring complete separation between primary & secondary winding. Thus, safety standards are easily met. The dielectric strength is more than adequate. The winding is done on the core without the use of bobbin. Thus difficulties are observed in meeting safety standards. Partition bobbins allow separation between Primary and Secondary bobbins but this is not complete. The dielectric strength is not as good as R-core transformer. Difficulties are observed in meeting safety standards.
Efficiency Very low losses result in better efficiency. Efficiency greater than 90% is generally observed in most designs. Efficiency is better than EI transformer but less compared to R-core transformer. More losses result in poor efficiency.
Heat Heat generation is minimal due to low Iron loss. The large surface area of the coil allows for better heat dissipation. The core is not exposed at any point. Thus the heat generated has no area for dissipation. Thus temperature rise is more. Due to iron loss the heat generation is more. Further as large part of the winding is covered inside the core there is poor heat dissipation.
Mounting Due to the thin design & lightness can be accommodated in available space of assembly. Can also be mounted vertically on the sides. Because of circular shape the length & width of the space should be identical. Usual cubic space takes more space in assembly.