a digital data detector is part of the primary side control electronics in a high voltage integrated circuit for regulating a power supply secondary side output potential ; the detector output is responsive to the transitions of digital error data received from the supply secondary side via an electrically - isolated data transmission means . only the transition edges are utilized by the detector , so that any non - linearity after each transition of the transmission means is immaterial . if the isolation device is a pulse transformer , the transformer core can be of relatively small volume , as full - pulse reproduction is unimportant and pulse saturation is tolerable . a multiplexer allows the primary side control electronics to initiate power supply operation ; control is switched to the secondary side responsive to signal edges therefrom being detected by the digital data detector .