Digital input for a programmable logic controller
AssigneeMaxim Integrated Products, Inc.
InventorDouglas S. Smith
Life of this patent
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Abstract
A digital input includes a galvanically isolated section having an integrating capacitor coupled to a high voltage signal input by at least one current-limiting resistor, a relaxation oscillator coupled across the integrating capacitor, and an electronic switch controlled by the relaxation oscillator. An optical isolator has an input side and an output side, wherein the input side is coupled across the integrating capacitor by the switch, and a low voltage section includes a decoder having an input coupled to the output side of the optical isolator and having a low voltage signal output.
Claims20
A digital input detection circuit comprising:
- (a) a galvanically isolated section including
- (i) an integrating capacitor coupled to a high voltage signal input by at least one current-limiting resistor,
- (ii) a relaxation oscillator coupled across the integrating capacitor, and
- (iii) an electronic switch controlled by the relaxation oscillator;
- (b) an optical isolator having an input side and an output side, wherein the input side is coupled across the integrating capacitor by the switch;
- and
- (c) a low voltage section including a decoder having an input coupled to the output side of the optical isolator and having a low voltage signal output;
- whereby the optical isolator provides galvanic isolation between the galvanically isolated section and the low voltage section.
A self-powered analog-to-digital converter with galvanic isolation comprising:
- an integrating capacitor coupled to a high voltage signal input by at least one current-limiting resistor;
- an encoder powered by a voltage developed across the integrating capacitor and operative to develop a serialized signal representative of the high voltage signal;
- and
- an isolator having an input coupled to an output of the serial encoder.
A multichannel interface comprising:
- (a) a plurality of high voltage input channels each including:
- (i) an integrating capacitor coupled to a high voltage signal input by at least one current-limiting resistor,
- (ii) a relaxation oscillator coupled across the integrating capacitor, and
- (iii) an electronic switch controlled by the relaxation oscillator;
- (b) a plurality of optical isolators each having an input side and an output side, wherein the input side of each optical isolator is coupled to one of the plurality of high voltage input channels;
- and
- (c) a plurality of low voltage output channels each including a decoder having an input coupled one of the optical isolators and having a low voltage channel output.
Dependencies are inferred from the claim text.