High-frequency magnetic cores are common in switching power supplies. When faced with high-frequency magnetic cores of various shapes, can you explain their differences? The following is an analysis of how the shape of high-frequency transformer cores affects the operation of transformers, which we hope will be helpful.
A high-frequency transformer is a device that transforms AC voltage, current, and impedance. When an AC current flows through the primary coil, an AC magnetic flux is generated in the iron core (or magnetic core), inducing a voltage (or current) in the secondary coil. A transformer consists of an iron core (or magnetic core) and coils. The coils have two or more windings; the winding connected to the power supply is called the primary coil, and the remaining windings are called secondary coils. Transformer magnetic cores include pot-type cores, RM-type cores, E-type cores, EC, ETD, and EER-type cores, PQ-type cores, EP-type cores, toroidal cores, etc. So, how do these magnetic cores affect the operation of the transformer? The following is a detailed analysis.
1. Pot-shaped magnetic core
The frame and windings are almost entirely enclosed by the core, resulting in excellent EMI shielding. The dimensions of the can-shaped cores conform to IEC standards, ensuring excellent interchangeability during manufacturing. Simple frames (without pins) and PCB-mount frames (with pins) are available. Due to the can-shaped design, the cost is higher compared to other types of cores of the same size. Because its shape is not conducive to heat dissipation, it is not suitable for use in high-power transformer inductors.
2. RM type magnetic core
Compared to the can-type design, the two symmetrical sides of the can-type are cut off, which is more conducive to heat dissipation and large-size lead-out. Compared to the can-type design, it saves about 40% of the installation space. The frame is available in pinless and pin-type. It can be installed using a pair of clips. The RM type core can be made into a flat shape (suitable for current planar transformers or directly mounted on a printed circuit board with pre-designed windings). Although the shielding effect is not as good as the can-type design, it is still quite good.
3. E-type magnetic core
Compared to can-type magnetic cores, E-type magnetic cores are much cheaper, and their winding and assembly are relatively simple. This core shape is currently the most widely used, but its disadvantage is that it cannot provide self-shielding. E-type magnetic cores can be installed in different directions, and several can be stacked to apply higher power. This type of magnetic core can be made into a flat shape (which is a popular core shape for planar transformers). Pinless and pin-type frames are also available. Due to its excellent heat dissipation and ability to be stacked, this shape of magnetic core is generally used in high-power inductors and transformers.
4. EC, ETD and EER type magnetic cores
These core structures fall between the E-type and can-type cores. Like the E-type core, they provide ample space for large-section leads (suitable for the current trend of low-voltage, high-current switching power supplies); these core shapes also offer excellent heat dissipation; due to the cylindrical center post, the length of a single-turn winding is shortened by 11% compared to a cuboid core of the same cross-section, resulting in an 11% reduction in copper losses and enabling the core to provide higher output power; simultaneously, the cylindrical center post, compared to a cuboid center post, avoids the risk of damage to the winding wire insulation caused by the sharp edges of a cuboid during winding.
5. PQ type magnetic core
PQ-type magnetic cores are specifically designed for inductors and transformers used in switching power supplies. The PQ shape optimizes the ratio between core volume, surface area, and winding area; this design allows for maximum output power with minimal transformer size and weight, and occupies minimal PCB mounting space; it can be mounted using a single clip; this efficient design also results in a more uniform magnetic circuit cross-sectional area, thus leading to fewer hot spots compared to other core designs.
6. EP type magnetic core
The circular central pillar three-dimensional structure of the EP type magnetic core completely encloses the winding except for the end that contacts the PCB board, providing excellent shielding. This unique shape minimizes the impact of the air gap formed at the contact surface when assembling two magnetic cores and provides a larger volume and overall space utilization ratio.
7. Toroidal core
For manufacturers, toroidal cores are the most economical, costing the least among comparable cores; due to the use of a bobbin, additional and assembly costs are zero; they can be wound using a winding machine when suitable; and their shielding is also very good.
