Surge-resistant relay switching circuit
First Claim
1. A switching circuit for switching power between a power source and a load, said switching circuit comprising:
- (a) first and second electrically controllable switches connected in series to electrically connect and disconnect said power source and said load;
(b) a third electrically controllable switch connected in parallel with said series connected first and second electrically controllable switches;
(c) control means connected to said first, second and third switches;
said control means being operable for sequentially closing said first, second and third switches in that order to connect said power source to said load;
(d) said control means being operable for thereafter opening said first and second switches and retaining said first and second switches open until an opening sequence is begun;
(e) said control means being further operable for reclosing said first switch and said second switch while said third switch remains closed to initiate an opening sequence;
(f) said control means being further operable for opening said third switch after reclosing said first and second switches during said opening sequence; and
(g) thereafter reopening said first and second switches.
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Accused Products
Abstract
In a relay switching panel, a switching circuit operates to selectively connect and disconnect resistive, capacitive and inductive loads to an AC power source with substantially no arcing. The switching circuit comprises a pair of relays, preferably connected in parallel, with one of such relays having a triac, connected in series therewith. With the relays open, an air gap isolates the power source and the load. In closing the relays in sequence, one relay provides a conductive path from the power source to the triac. After a suitable delay to allow the relay contacts to stabilize in the closed position, the triac is triggered to provide a conductive path from the power source to the load, and a large current surge flows to the load. After the current surge has subsided, the second relay is closed to provide a direct conductive path between the power source and the load. Next the first relay and the triac are removed from the circuit to ensure full conduction through the second relay. Another sequence of opening and closing the relays and the triac in a particular order can be employed to provide substantially arcless switching during turn off. As a result of this arrangement, the switching circuit is low cost, compact and reliable over an extended period of time.
164 Citations
26 Claims
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1. A switching circuit for switching power between a power source and a load, said switching circuit comprising:
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(a) first and second electrically controllable switches connected in series to electrically connect and disconnect said power source and said load; (b) a third electrically controllable switch connected in parallel with said series connected first and second electrically controllable switches; (c) control means connected to said first, second and third switches;
said control means being operable for sequentially closing said first, second and third switches in that order to connect said power source to said load;(d) said control means being operable for thereafter opening said first and second switches and retaining said first and second switches open until an opening sequence is begun; (e) said control means being further operable for reclosing said first switch and said second switch while said third switch remains closed to initiate an opening sequence; (f) said control means being further operable for opening said third switch after reclosing said first and second switches during said opening sequence; and (g) thereafter reopening said first and second switches. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A switching circuit for switching power between a power source and a load, said switching circuit comprising:
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(a) first and second electrically controllable switches connected in series to electrically connect and disconnect said power source and said load; (b) a third electrically controllable switch connected in parallel with said second electrically controllable switch; (c) control means connected to said first, second and third switches;
said control means being operable for sequentially closing said first, second and third switches in that order to connect said power source to said load;(d) said control means being operable for thereafter opening said second switch and retaining said second switch open until an opening sequence is begun; (e) said control means being further operable for reclosing said second switch while said first switch and said third switch remain closed to initiate an opening sequence; (f) said control means being further operable for opening said third switch after reclosing said second switch during said opening sequence; and (g) thereafter reopening said first and second switches. - View Dependent Claims (14, 15, 16)
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17. A method for switching power between a power source and a load, said method comprising the steps of:
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(a) providing a switching circuit comprising a first switch and a controllably conductive device connected in series with one another and connected in series with said power source and said load, and a second switch connected in parallel, with said series connected first switch and said controllably conductive device; (b) connecting said power source to said load by closing said first switch and waiting for a first predetermined time period and after said first predetermined time period, rendering said controllably conductive device conductive and waiting for a second predetermined time period and thereafter closing said second switch;
thereafter rendering said controllably conductive device nonconductive and opening said first switch until an opening sequence is begun;(c) and disconnecting said power source from said load by reclosing said first switch device and rendering said controllably conductive device conductive again to initiate an opening sequence, and opening said second switch and then rendering said controllably conductive device nonconductive again and reopening said first switch. - View Dependent Claims (18, 19, 20, 21, 22, 23)
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24. A method for disconnecting a load from a power source;
- said method comprising the steps of;
(a) providing a switching circuit comprising a first electrically controllable switch and a controllably conductive device in series with the load and a second electrically controllable switch in parallel with said first electrically controllable switch and said controllably conductive device;
said second electrically controllable switch being in the closed state when said load is connected to said power source;(b) disconnecting said power source from said load by closing said first electrically controllable switch and waiting for a predetermined period of time, and after said period of time rendering said controllably conductive device conductive and waiting for a second predetermined period of time; and
thereafter opening said second electrically controllable switch, then rendering said controllably conductive device nonconductive and opening said first electrically controllable switch. - View Dependent Claims (25, 26)
- said method comprising the steps of;
Specification