High power direct current switching circuit

Claim 2

A DC power switching circuit, connecting a load to a DC power source, comprising: a normally open relay, having an energizing coil with a first end connected to a control input terminal and a second end, and having a pair of switching contacts, the first contact of said pair being connected to said load and the second contact of said pair being connected to said DC power source, said contacts closing from an open state after a first delay interval in response to an on-signal at said control input terminal; an SCR having its principal current conducting path connected between said load and said DC power source and having its control gate connected to said second end of said relay energizing coil, conducting current between said load and said power source during said first delay interval, thereby reducing the potential difference between said first and second contacts of said relay, preventing arcing between said relay contacts during the closure thereof; an FET having its principal current conducting path connected between said load and said DC power source and having a control gate; a timer having a control input connected to said control input terminal and an output connected to said gate of said FET, maintaining on said FET gate for a duration of a second delay interval in response to an off-signal at said control input terminal, said relay contacts opening from a closed state in response to said off-signal after a delay which is shorter in duration than said second delay interval; said SCR gate turning off substantially when said off-signal occurs and said timer turning on said FET substantially when said off-signal occurs, said FET device in response thereto conducting current between said load and said power source during said second delay interval, thereby reducing the potential difference between said first and second contacts of said relay, for preventing arcing between said relay contacts during the opening thereof.

Claim 3

A DC power switching circuit, connecting a load to a DC power source, comprising: a low voltage control section having a signal input for receiving an on/off signal; a first voltage level detector in said low voltage section, preventing the operation of said circuit if said on/off signal has an insufficient voltage magnitude; a high voltage switching section having a control input terminal connected to an output of said low voltage control section, switching high voltage DC power from said power source to said load in response to said on/off signal; a second voltage level detector in said high voltage section, preventing the operation of said circuit if said DC power source has an insufficient voltage magnitude; a normally open relay in said high voltage section, having an energizing coil with a first end connected to said control input terminal and a second end, and having a pair of switching contacts, the first contact of said pair being connected to said load and the second contact of said pair being connected to said DC power source, said contacts closing from an open state after a first delay interval in response to an on-signal at said control input terminal; an SCR in said high voltage section having its principal current conducting path connected between said load and said DC power source and having its control gate connected to said second end of said relay energizing coil, conducting current between said load and said power source during said first delay interval, thereby reducing the potential difference between said first and second contacts of said relay, preventing arcing between said relay contacts during the closure thereof; an FET in said high voltage section having its principal current conducting path connected between said load and said DC power source and having a control gate; a timer in said high voltage section having a control input connected to said control input terminal and an output connected to said gate of said FET, turning on said FET gate for a duration of a second delay interval in response to an off-signal at said control input terminal, said relay contacts opening from a closed state in response to said off-signal after a delay which is shorter in duration than said second delay interval; said SCR gate turning off substantially when said off-signal occurs and said timer turning on said FET substantially when said off-signal occurs, said FET device in response thereto conducting current between said load and said power source during said second delay interval, thereby reducing the potential difference between said first and second contacts of said relay, preventing arcing between said relay contacts during the opening thereof.

Claim 4

A DC power switching circuit, connecting a load to a DC power source, comprising: a low voltage control section having a signal input for receiving an on/off signal; a first voltage level detector in said low voltage section, preventing the operation of said circuit if said on/off signal has an insufficient voltage magnitude; a high voltage switching section having a control input terminal connected to an output of said low voltage control section, switching high voltage DC power from said power source to said load in response to said on/off signal; a second voltage level detector in said high voltage section, preventing the operation of said circuit if said DC power source has an insufficient voltage magnitude; a normally open relay in said high voltage section, having an energizing coil with a first end connected to said control input terminal and a second end, and having a pair of switching contacts, the first contact of said pair being connected to said load and the second contact of said pair being connected to said DC power source, said contacts closing from an open state after a first delay interval in response to an on-signal at said control input terminal; an SCR in said high voltage section having its principal current conducting path connected between said load and said DC power source and having its control gate connected to said second end of said relay energizing coil, conducting current between said load and said power source during said first delay interval, thereby reducing the potential difference between said first and second contacts of said relay, preventing arcing between said relay contacts during the closure thereof; an FET in said high voltage section having its principal current conducting path connected between said load and said DC power source and having a control gate; a timer in said high voltage section having a control input connected to said control input terminal and an output connected to said gate of said FET, turning on said FET gate for a duration of a second delay interval in response to an off-signal at said control input terminal, said relay contacts opening from a closed state in response to said off-signal after a delay which is shorter in duration than said second delay interval; said SCR gate turning off substantially when said off-signal occurs and said timer turning on said FET substantially when said off-signal occurs, said FET device in response thereto conducting current between said load and said power source during said second delay interval, thereby reducing the potential difference between said first and second contacts of said relay, preventing arcing between said relay contacts during the opening thereof.