Solid state over-voltage and under-voltage detector

Claim 1

A CIRCUIT FOR MONITORING A POSITIVE SUPPLY VOLTAGE FOR OVERVOLTAGE AND A NEGATIVE SUPPLY VOLTAGE FOR UNDERVOLTAGE WHERE THE TWO SUPPLY VOLTAGES HAVE A COMMON REFERENCE POTENTIAL COMPRISING (A) A TERMINAL FOR THE COMMON REFERENCE POTENTIAL AND A TERMINAL FOR EACH OF THE SUPPLY VOLTAGES, (B) UNDERVOLTAGE RESPONSIVE MEANS FOR THE SUPPLY VOLTAGE OF NEGATIVE POLARITY INCLUDING A FIRST RESISTANCE CONNECTED AT ONE END TO THE POSITIVE TERMINAL AND A FIRST ZENER DIODE CONNECTED BETWEEN THE OTHER END OF THE RESISTANCE AND THE NEGATIVE TERMINAL FOR HOLDING THE INJUNCTION BETWEEN THE FIRST RESISTANCE AND THE FIRST ZENER DIODE AT A CONSTANT POTENTIAL LOWER THAN THE SUPPLY VOLTAGE ON THE NEGATIVE TERMINAL, (C) OVERVOLTAGE RESPONSIVE MEANS FOR THE SUPPLY VOLTAGE OF POSITIVE POLARITY INCLUDING A SECOND RESISTANCE CONNECTED AT ONE END TO THE NEGATIVE TERMINAL AND A SECOND ZENER DIODE CONNECTED BETWEEN THE OTHER END OF THE SECOND RESISTANCE AND THE POSITIVE TERMINAL FOR HOLDING THE JUNCTION BETWEEN THE SECOND RESISTANCE AND SECOND ZENER DIODE AT A CONSTANT POTENTIAL BELOW THE SUPPLY VOLTAGE ON THE POSITIVE TERMINAL, (D) A VOLTAGE DIVIDER CONNECTED ACROSS THE SECOND ZENER DIODE AND HAVING AN OUTPUT TAP FOR PROVIDING A POTENTIAL THAT IS HIGHER THAN THE POTENTIAL AT THE JUNCTION OF THE SECOND ZENER DIODE AND RESISTANCE BY A SMALL FRACTION OF THE POTENTIAL ACROSS THE SECOND ZENER DIODE, AND (E) A DIODE BETWEEN THE OUTPUT TAP AND THE JUNCTION BETWEEN THE FIRST RESISTANCE AND THE FIRST ZENER DIODE FOR PERMITTING CURRENT FLOW THERETHROUGH WHEN THERE IS PREDETERMINED UNDERVOLTAGE ON THE NEGATIVE TERMINAL, (F) WHEREBY PREDETERMINED OVERVOLTAGE ON THE POSITIVE TERMINAL AND PREDETERMINED UNDERVOLTAGE ON THE NEGATIVE TERMINAL CAUSES SUFFICIENT VOLTAGE RISE AT THE OUTPUT TAP FOR THE USE IN OPERATING AN INDICATOR.