High current and power limiting circuit for I/O modules with internal output power support

An output circuit for an output module used in an industrial controller, wherein the output module includes a plurality of output terminals, the output circuit comprising:

• a plurality of isolation circuits, wherein each isolation circuit corresponds to one of the plurality of output terminals and each isolation circuit is configured to receive power from a power source at an input to the isolation circuit and to provide electrically isolated power from an output of the isolation circuit to the corresponding output terminal;
• a plurality of terminal control circuits, wherein each terminal control circuit corresponds to one of the plurality of output terminals and each terminal control circuit is operative to selectively connect the electrically isolated power from the corresponding isolation circuit to the corresponding output terminal;
• a plurality of switches, each switch connected between the output of one of the plurality of isolation circuits and the corresponding output terminal to selectively connect the output of the isolation circuit to the corresponding output terminal in one of three operating states, wherein the three operating states include an off operating state, an on operating state, and a current limited operating state;
• and
• a plurality of current limit circuits, wherein each current limit circuit corresponds to one of the plurality of output terminals and is operative to:
• output a control signal to the corresponding switch to select one of the three operating states, and
• vary a voltage of the control signal to limit a current conducted between the output of the isolation circuit and the corresponding terminal to a predefined threshold in the current limited operating state.

A method of limiting current in an output module used in an industrial controller, wherein the output module includes a plurality of output terminals, the method comprising the steps of:

• receiving a digital input signal for each of the plurality of output terminals, wherein each digital input signal defines a desired output state of the corresponding output terminal;
• receiving power from a power source at an input for a plurality of electrical isolation devices, wherein each electrical isolation device corresponds to one of the plurality of output terminals;
• selectively supplying power from an output of each of the plurality of electrical isolation devices to the corresponding output terminal, wherein a switching device receives the electrically isolated power from the output of the electrical isolation device and selectively supplies the power to the corresponding output terminal in one of three operating states responsive to the corresponding digital input signal, wherein the three operating states include an off operating state, an on operating state, and a current limited operating state;
• monitoring a current present at each of the plurality of output terminals in a terminal control circuit;
• outputting a control signal from a current limit circuit to the switching device to select one of the three operating states, and
• varying a voltage of the control signal to limit the current conducted between the output of the isolation circuit and the corresponding terminal to a predefined threshold with a current limit circuit in the current limited operating state.