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

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

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.