Electronic operations counter for a voltage regulator controller

Abstract

A voltage regulator controller of a step-type voltage regulator monitors its own power supply and saves the regulators operations count to a non-volatile memory, only when it is determined that a power failure is imminent. The controller counts the number of tap changes in the voltage regulator transformer by monitoring an 'operations counter' signal from the regulator's tap changer mechanism. When a tap change is detected, the controller increments an electronically stored count value. The electronically stored count value is maintained exactly, even when the power to the device is lost. In order to determine whether a power failure is imminent, the controller monitors the AC supply voltage using a zero-crossing detector circuit. The zero crossing detector circuit produces transitions corresponding to transition in the AC power waveform. The zero crossing circuit stops producing transition when the AC voltage falls below a predetermined threshold. A monitoring program determines when the zero-crossing detector has stopped producing transitions and causes the control program to initial a power down sequence. The power down sequence provides an orderly shut down of the microprocessor program tasks and finishes by storing the value of the operations counter to a non-volatile memory. The power supply maintains its level for a significant time after the AC voltage waveform drops below the predetermined threshold. This gives the microprocessor time to detect that zero transitions have ceased and to store the operations counter value.