Isolated Fuse Fail Indicator

This circuit uses standard components and shows a method of indicating the fuse status of mains powered equipment while providing electrical isolation from the mains supply.A standard miniature low power mains transformer (e.g. with an output of around 6 V at 1.5 VA) is used as a ‘sense’ transformer with its primary winding (230 V) connected across the equipment’s input fuse so that when the fuse blows, mains voltage is applied to the transformer and a 6 V ac output voltage appears at the secondary winding.