초록 ▼

A controller such as a programmable logic controller (PLC) is coupled to a load such as a contactor or motor starter through an interface that operates over a range of DC or AC voltage and couples a Start output of the controller to the load through a low current switch such as an opto-relay. The in

A controller such as a programmable logic controller (PLC) is coupled to a load such as a contactor or motor starter through an interface that operates over a range of DC or AC voltage and couples a Start output of the controller to the load through a low current switch such as an opto-relay. The interface has a charging circuit coupled to the controller output, with a switching transistor, a load resistor and a capacitor in series. The low current switch is operated from accumulated charge in the capacitor and couples power to the load device. Charging of the capacitor to a threshold switches off of the transistor for an interval timed by a one-shot, during which the low current switch remains activated due to current draining from the capacitor. In an AC embodiment with a triac controller output, the capacitor continues to power the low current switch for the remainder of the positive AC half cycle, regardless of the triac, which may cease conduction due to lack of sufficient loading. The circuit substantially reduces the current dissipation of an interface between a PLC and a motor starter or contactor. The interface can include optically isolated signalling in both directions, including feed back of contact status and trip indications to inputs of the PLC.

대표청구항 ▼

An interface device for coupling between an output of a controlling device, the output carrying a Start command signal, and an input of a controlled device responsive to the Start command signal, comprising: a load resistor and a capacitor in series with one another to define a charging circuit in p

An interface device for coupling between an output of a controlling device, the output carrying a Start command signal, and an input of a controlled device responsive to the Start command signal, comprising: a load resistor and a capacitor in series with one another to define a charging circuit in parallel with the output carrying the Start command signal; a switching circuit coupled in series with the charging circuit, the switching circuit having a switching transistor operable to charge the capacitor from the Start command signal when the Start command signal is present and the switching transistor is conducting; a comparator coupled to the switching transistor and to the capacitor, the comparator being operable to switch the switching transistor off when the capacitor charges to a predetermined voltage and thereby to decouple the capacitor from further charging by the charging circuit; and, an output circuit coupled in parallel with the capacitor, the output circuit being operable to activate the controlled device from a voltage on the capacitor, for a period following switching off of the switching circuit; whereby loading of the output of the controlling device is minimized.