Current Sense Transformer Application Design Guidelines

The standard for precise current measurement in instrumentation and other high reliability equipment applications has been the current sense transformer. They are accurate, easy to implement, and reliable under harsh environmental and thermal conditions. In electronic systems applications such as switch-mode power supplies, current transformers are generally used for control, circuit-protection, and monitoring features. With the increasing availability of OTS (Off-The-Shelf) current transformers, a simple guideline can greatly help in the selection of proper and cost-effective components for many applications.

The Input Specifications
The selection of a current transformer must begin with the definition and verification of certain factors such as size, frequency, function, and the range of current being sampled – the accuracy and effectiveness will essentially be dependent on these parameters. Aside from the possibility of compromising the transformer’s accuracy, using a current transformer above the manufacturer’s rated current specification may saturate the transformer and may cause circuit failures due to an uncontrolled rise in operating temperature. On the other hand, a current transformer that is rated much higher than the “sample current” might be restrictively too large and expensive for its purpose. Typically, selecting a current-transformer that is rated approximately 30%

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