Protected input/output circuitry for a programmable controller

In an input/output system of a programmable controller, an overcurrent protected output switching circuit, comprising:

• an insulated gate transistor (IGI) responsive to a command signal to be turned on and off for controlling electrical current flow to a connected load, said IGT having a main section for carrying a major portion of said load current and an emulation section for carrying a relatively small fractional portion of said load current;
• first circuit means responsive to the emulation portion of said load current to provide a signal indicative of the total load current;
• and
• second circuit means responsive to said load current signal for initiating said command turning the IGT off at a time which depends upon the occurrence of excessive current therethrough and the time duration and magnitude of said excessive current.

In a programmable control system, an input/output circuit capable of providing diagnostic information regarding its current loading conditions, such circuit comprising:

• an insulated gate transistor (IGT) responsive to a command signal to be turned on and off for controlling current flow to a connected load, said IGT having a main section for carrying a major portion of said load current and an emulation section for carrying a fractional portion of said load current;
• current sensing means adapted to be responsive to the fractional portion of said load current for provision of a load signal indicative of total load current;
• first circuit means responsive to said load signal to provide a first diagnostic signal indicative of whether the load current is above or below a first preselected value thereof;
• second circuit means responsive to said load signal to provide a second diagnostic signal indicative of whether the load current is above or below a second preselected value thereof, said second preselected value being greater in magnitude than said first preselected value;
• and
• third circuit means responsive to said load signal to provide a third diagnostic signal indicative of whether the load current is above or below a third preselected value thereof, said third preselected value being lesser in magnitude than said first preselected value.

For use in an input/output (I/O) system of a programmable controller, I/O control circuitry capable of providing diagnostic information indicative of its operating condition, comprising:

• switching means for controlling load current to a connected load, said switching means being responsive to be turned on and off by a command signal and having a main current section for carrying a major portion of the load current and a shunt current section for carrying a fractional portion of the load current;
• current sensing means responsive to said fractional portion of load current for providing a load current signal;
• first circuit means responsive to the load current signal for providing a set of signals indicative of the range of load current;
• second circuit means for providing a load signal indicative of the voltage level applied to said connected load;
• third circuit means for providing a line voltage signal indicative of the voltage level of a supplied operating voltage for such input/output circuitry;
• and
• encoding means responsive to said set of load current signals, said load voltage signal, and said line voltage signal for providing an encoded diagnostic signal having an encoded value which depends on said signals and which is indicative of said operating condition.