CST25 Current Sense Transformers Triad Magnetics CST25 Current Sense Transformers are ideal for monitoring currents in high-frequency applications such as switch-mode power supplies, LED lighting, etc. The CST25 components are offered with a built-in sense winding, allowing for ease of use. These fully encapsulated current sense transformers allow for a high isolation voltage of 4000VAC between primary and secondary windings. There are five different popular turn ratios available.