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Selecting The Perfect Magnetic Cores For SMPS Transformers

Selecting The Perfect Magnetic Cores For SMPS TransformersSMPS Transformers are efficient transformers used in switch mode power supplies to transfer power to commercial and industrial electronic networks. They are usually preferred because of their ability to provide a regulated output voltage to electrical networks. When you are designing these transformers, selecting the right type of magnetic cores is crucial to ensure their performance. The choice of these cores depends on three characteristics of the transformers, namely, power requirements, frequency, and switching topology. 

In this blog, we are going to explore SMPS transformers, their types, and how you can select the ideal core material for them. 

What are SMPS Transformers?

SMPS Transformers are used to convert Alternating Current (AC) mains power into Direct Current (DC) output voltage. When the power is switched on, the AC is filtered through a capacitor and converted from AC voltage to unregulated DC voltage. Then, the SMPS transformer converts the unregulated DC Voltage into regulated DC voltage at varying voltage levels using a regulator. 

Common applications of SMPS transformers are:

  • Power sourcing equipment
  • Communication devices
  • Medical devices
  • Commercial power supplies
  • Audio-visual products
  • Security systems

Types of SMPS Transformer

1. Isolated Transformer 

Isolated SMPS transformers are those that are isolated from the other part of the circuit that it is powering. They are used to separate switches and output. The secondary winding of these SMPS helps to store energy. They are of 2 types:

  • Flyback Converter
  • Forward Converter

2. Non-Isolated Transformer

Non-Isolated SMPS transformers are those that do not have an isolated input and output circuitry. They are preferred when there is a minor change in the voltage levels. They help to step up or step down voltages as a DC-DC Converter. They are of 3 types:

  • Buck Converter (Step-Down)
  • Boost Converter (Step-Up)
  • Buck-Boost Converter (Step-Down/Step-Up)

How to select ideal cores for SMPS Transformers?

#1 Core Type

When you are designing these transformers, selecting the right type of magnetic cores is crucial to ensure their performance. The choice of these cores depends on three characteristics of the transformers: 

  • Power requirements
  • Frequency
  • Switching topology

Ferrite cores are the right choice for high-frequency transformer applications. If you are operating your electronic component below 500 kHz, you must have a transformer core with a high permeability ranging from 2000 to 2500. However, the permeability varies depending on the temperature rise and flux density.   

#2 Core Shape

You must select the right core shape to minimize the core losses in the high-frequency SMPS transformer. Along with this, the window configuration is another crucial aspect to check in the core shapes. 

To keep the AC winding resistance to lower levels, the winding area of the windings must be wider enough. This increases the winding breadth and reduces the number of winding layers. 

You can check out below shapes of ferrite cores to choose from depending on their properties.

1. EFD & EPC cores 

These cores have excellent space utilization quality, hence they are ideal for low-profile transformers.

2. EE & EF cores 

These cores are manufactured with simple bobbin winding either- vertical or horizontal. If you want a minimal footprint, you can choose vertical bobbins. 

3. ETD & EER cores 

These cores have a round center post and wider winding areas. This makes them ideal for high power designs and multiple outputs. 

4. PQ cores 

These cores have dimensions to provide an optimized volume ratio of winding & surface areas. They have a few hotspots as compared to other cores. They take minimal turns as compared to E cores. Besides, they take less PC board space. 

5. POT cores 

These cores provide lowest leakage inductance and high Q factor. They maintain their AL values using a complex gapping process. They can achieve high inductances using small cores, so they are commonly used for SMPS transformers. 

#3 Core Size

Selecting the suitable core size for your SMPS transformer design is another crucial aspect.

The core area can be measured by multiplying the core cross-section area by the window area used for the winding. This technique is used to initially estimate the core size for an application. 

The power handling capacity of the core does not align with its volume or area. Here, the surface area reducing the heat does not increase in the volume of heat production. Therefore, a large transformer operates at a lower power density. 

#4 Core Losses

In transformers, core losses occur due to alternating magnetic flux in the core. When it happens, the operating flux density is to be estimated to determine the core loss. The losses must be minimal for an efficient performance of the transformer.


A proper selection of the right magnetic cores will help you ensure less heat generation, less power wastage, and enhance the efficiency of your SMPS transformer. 

At Alisha Coils & Transformers, you can get help for finding the right materials for your requirements. They are a reliable manufacturer of high-quality SMPS transformers in India using state-of-the-art technology. You can reach out to their team for any queries or samples required.