Filter circuit for eliminating inrush current, DC coil control circuit, and electromagnetic contactor

A DC coil control circuit for controlling a current flowing through an actuator coil of an electromagnetic contactor or relay, wherein the DC coil control circuit comprises:

• a first input terminal to be connected with a direct current voltage of a first polarity;
• a second input terminal to be connected with a direct current voltage of a second polarity, wherein the first polarity is positive with respect to the second polarity;
• a first output terminal to be connected with a first terminal of the actuator coil;
• a second output terminal to be connected to a second terminal of the actuator coil;
• a first diode having an anode and a cathode, wherein the cathode of the first diode is connected to said first output terminal and to said first input terminal and the anode of the first diode is connected to an intermediate node;
• a second diode having an anode and a cathode, wherein the anode of the second diode is connected to said second output terminal and the cathode of the second diode is connected to the intermediate node;
• a filter capacitor which is connected between said second input terminal and the intermediate node, wherein the filter capacitor is charged via the actuator coil and the second diode when the direct current voltage is applied across the first input terminal and the second input terminal, such that the actuator coil reduces a capacitive inrush current associated with charging the filter capacitor;
• a switching device connected in parallel to the filter capacitor and the second diode between said second input terminal and said second output terminal, the switching device having a control input terminal for receiving a control signal that controls opening and closing of the switching device;
• and
• a control unit that is operable for generating said control signal.

A method of actuating an electromagnetic contactor, the electromagnetic contactor including a movable magnetic core assembly, an actuator coil for magnetically actuating the magnetic core assembly, a fixed magnetic core, and at least one fixed contact element, wherein the actuator coil is connected with a DC coil control circuit for controlling a current flowing through the actuator coil, the method comprising the steps of:

• controlling a switch to open and close in response to a control signal;
• and
• suppressing a capacitive inrush current during startup by using the actuator coil as a part of an input filter circuit, wherein:
• the input filter circuit includes a first diode having an anode and a cathode, wherein the cathode of the first diode is connected to a first terminal of the actuator coil and to a first DC input terminal and the anode of the first diode is connected to an intermediate node,
• a second diode having an anode and a cathode, wherein the anode of the second diode is connected to a second terminal of the actuator coil and the cathode of the second diode is connected to the intermediate node,
• a filter capacitor which is connected between a second DC input terminal and the intermediate node wherein a polarity of DC voltage present at the first DC input terminal is positive with respect to a polarity of DC voltage present at the second DC input terminal, and
• the switch is connected in parallel to the filter capacitor and the second diode between the second DC input terminal and the second terminal of the actuator coil.