How To Test A Switch Mode Power Supply Transformer?

Switch Mode Power Supply (SMPS) transformers are flexible and used in a variety of industries like aerospace, biomedical, telecommunications, and automation controls. The major applications for these transformers include converters, inverters, switching regulators, low power isolation power supplies, high Q filters, and RFI filters. With so many applications using these transformers, it is important that you test your transformers periodically so as to avoid any faults or breakdowns.


However, testing a SMPS transformer is different from testing a linear transformer, because both these types of power supplies operate differently on distinctive principles, depending upon their distinguished characteristics and designs. Because the SMPS transformer’s pass transistor continually swaps between low and high dissipation, testing it cannot be as simple as attaching probes and examining the power. There are multiple tests that are specific to SMPS transformers to check their power and functionality, which are listed below.

Winding resistance

This test helps to analyze the suitability and standard of the wires used; whether the correct wire has been used or not, and whether or not the wire is up to the required standard. Also, whether or not the winding has been properly installed within the transformer can be checked.

Turns ratio and phasing

This test verifies the polarity of the windings, along with checking for the accuracy of the turns of the winding.

Insulation resistance

This test checks the resistance of the non-safety insulation between the screens and windings of the transformer.


This test can be performed on any SMPS transformer – with or without air gaps. In case of transformers with air gaps, the gap between the winding and core is checked for mutual inductance. While, in the case of transformers without air gaps, the core faces are checked for contamination and tightness. If not, the respective measures of thorough cleaning and fitting are taken.

Current and inductance leakage

As the name suggests, this test checks for current leakage within the transformer. Moreover, the windings are also checked to ensure that they are properly positioned on the bobbin.


This test checks the safety isolation at the core, safety screen, and both primary and secondary windings.

Q factor

This test checks for any wires that have been shorted during transformer assembly.

In order to prevent situations of shutdowns or over voltage, you must perform the above mentioned tests on your SMPS transformer. If all these tests are passed, then the transformer is ready for use. However, if you buy your transformer from a renowned SMPS transformer manufacturer in India like Miracle Electronics, you need not worry about any tests as all their transformers are always tested before being shipped to the customers. Moreover, all their transformers are RoHS and REACH compliant. Available product variants at Miracle Electronics include UU transformers, EE transformers, EI transformers, toroid ferrite core transformers, and pot core transformers. In addition, you can also get other inclusions like TEX E wires, sleeves, connectors, L clamps, U brackets, ferrite cores, and class B / F/ H insulation.


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