Design Resources

Inrush Current Protection

Powertronix - Inrush Current ProtectionToroidal transformers’ excellent magnetic properties can occasionally lead to high inrush current when the transformer is turned on. The inrush current could be as high as 30 – 90 times the operating current of the transformer during first cycle.

For low power transformers (<300 VA) nuisance power loss due to blown fuses can be avoided by using fuses with slow characteristics. For higher-power toroidal transformers, we recommend using POWERTRONIX Low Inrush Transformers or use of Inrush Limiting Circuitry. Typical Inrush current graph for a toroidal transformer is shown below.