Voltage or contact closure sensor

摘要

An external signal sensor uses a single sensing circuit to detect a DC voltage or an AC voltage or a contact closure. The circuit can sense different isolated signals with relatively low power consumption. According to various embodiments, an isolation transformer has a primary winding that is fed by an oscillator signal. A secondary winding of the isolation transformer is open when no contact closure or AC or DC voltage is present, but is closed when a contact closure is present or when an AC or DC voltage is present. When the secondary winding is open, a status signal at an output of the sensing circuit has a logical high value. When the secondary winding is closed, the status signal has a logical low value. In this way, the same sensing circuit can be used to detect either a contact closure or an AC or DC voltage.

主权项

1. A sensing circuit comprising:
an isolation transformer having a primary winding configured to receive an oscillator signal and a secondary winding, the isolation transformer configured to provide a first voltage to a common node of a voltage divider when the secondary winding is open and to provide a second voltage, higher than the first voltage, to the common node when the secondary winding is shorted when a contact closure is present across a first pair of terminals; a transistor arrangement configured to short the secondary winding when an alternating current (AC) or direct current (DC) signal is present across a second pair of terminals such that the second voltage is provided to the common node; and an inverter operatively coupled to the isolation transformer and configured to produce a logical high output signal when the first voltage is present at the common node and to produce a logical low output signal when the second voltage is present at the common node.