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E Cores: Specifications, Designing Decisions & Shapes

E Cores: Specifications, Designing Decisions & Shapes

E Cores are magnetic cores designed with round or rectangular center legs. They offer the benefit of easy winding, especially when thick winding wires are employed. They also provide low core losses even at high temperatures. The cores are designed with a specified air gap which makes them suitable for switching regulator inductors, flyback transformers, and power inductors.

This blog will make you informed about the specifications, designing, and major shapes of E cores, so that you can make the right selection for your applications. 

Specifications for E Cores

The AL Value capacity for E Cores is measured by considering optimized process parameters for all materials. These materials have an initial permeability between 2200 to 10,000. Then, the quantized AL Values have to be considered. These can still be seen in the lower tolerance ranges. Depending on the initial permeability of the cores, the tolerances can be higher or lower. 

E cores also lose their magnetic properties when kept at a specific curie temperature. Therefore, you must consider this while selecting the cores for your transformer or inductor. 

Leakage Flux

The shape of the cores has a direct impact on external leakage fields. E cores have a greater external leakage field because most of their core part surrounds the winding, as compared to toroidal cores where the winding surrounds the core. 

While choosing E cores for your applications, you must consider their external leakage. These cores shouldn’t be kept with metallic brackets as it would concentrate the leakage flux in the brackets, leading to an increase in core losses. 

Even when laying out the circuit board, the leakage field has to be checked. Those components that stray magnetic field can affect must be kept away from E Cores.  

Designing Process

The coil formers of E Cores are designed in a way to wound automatically. Then, half of each core along with its mounting assembly is fitted into the coil former. This allows fully automatic assembly in the cores. 

If coil formers are used for E Cores with rectangular shaped legs, then the winding height can help to evaluate the theoretical value. If thick wires are used, it leads to a rounding of the winding from layer to layer. In this scenario, you must get the planned winding design verified through a winding test.  

Different Shapes available in E Cores

E Cores are available in several shapes that can be used for transformers, inductors, and chokes. They include:

1. E Cores: 

These cores are used widely for featuring simple bobbin winding and easy assembly. However, they do not offer self-shielding. Common applications for these cores are power inductors, telecom inductors, differential inductors, broadband transformers, converter transformers, and inverter transformers.

Available sizes: EE1011, EE1306, EE1306B, EE1306C, EE1404, EE1605, & EE1608

2. EER Cores

These cores have a round center post, which leads to a shorter winding path length as compared to a square center post. Their design provides optimum efficiency, but less productivity. They can be an ideal choice for inductors and transformers. Common applications for these cores are differential inductors and power transformers. 

Available sizes: EER2811, EER2811A, EER2811B, EER3511, & EER3913

3. ETD Cores:

These cores also have a round center post along with a minimum winding resistance. The dimensions of ETD core can be optimized to boost their efficiency for various applications. However, they offer less productivity and are slightly expensive. Common applications for these cores are differential inductors and power transformers. 

Available sizes: ETD2910, ETD3411, ETD3411A, & ETD3913

4. EFD (EFF) Cores:

These cores are designed with cross-sectional areas as per the industry standards. They offer excellent space utilization but are little expensive. Common applications for these cores are compact transformers and inductors. 

Available sizes: EFF1505, EFF2007, EFF2309, EFF2509, & EFF3009

5. EP Cores:

These cores are built with a low profile and self-shielding feature. Their design offers maximum volume to surface ratio, but has lesser winding space. Common applications for these cores are differential inductors and telecom inductors.

Available sizes: EP7, EP10, EP13, EP15, & EP20

6. EPC/EFC Cores:

These cores are highly expensive than the standard E cores. They also offer excellent space utilization. Common applications for these cores are compact transformers. 

Available sizes: EFC2508

7. Planar (EI, EE Cores):

These cores are commonly used for gapped inductors where fringing losses have to be considered. The cores do not have any wasted space and are useful where low height space of the transformer is required. Common applications for these cores are differential inductors, and DC/DC and AC/DC converters. 

Available sizes: EE6415P, EE6420P, & EE1804P


E cores are an economical choice that offers the advantages of simple assembly or easy winding. They are produced using premium materials, making them ideal for various applications. If you are looking to buy Ferrite E Cores from a reliable source, you can reach out to us at Cosmo Ferrites. We provide ferrite cores in various dimensions and specifications to help you fulfill requirements for your applications.