Two wire air gap off power supply

• US 5,856,905 A
• Filed: 08/08/1997
• Issued: 01/05/1999
• Est. Priority Date: 02/02/1995
• Status: Expired due to Term

• Current Assignee: Hubbell, Inc.
• Original Assignee: Hubbell, Inc.
• Inventors: Eckel, David Philip, Batko, Thomas James
• Primary Examiner(s): Elmore, Reba I.
• Assistant Examiner(s): Garland, Steven R.
• Application Number:
  US08/908,969
• Time in Patent Office: 515 Days
• Field of Search: 364/140.01-140.1, 364/141, 364/146, 361/191, 361/209, 361/160, 361/195, 361/170, 361/93, 361/187, 307/125, 307/130, 307/131, 307/138, 307/114, 307/157, 307/140, 307/116, 307/141.8, 307/113, 363/126, 702/64
• US Class Current: 361/187
• CPC Class Codes: H01H 47/007 with galvanic isolation between controlling and controlled circuit, e.g. transformer relay

Abstract

A power supply circuit is provided for selectively connecting and disconnecting a load from an alternating current power source having neutral and line conductors which comprises a transformer having a primary winding connected to the load and a secondary winding, a relay connected at one terminal thereof to the primary winding and connected at another terminal thereof to the line conductor, a control circuit connected to the relay and operable to open and close the relay, the relay being operable to provide power to the load when closed and to disconnect the line conductor from the primary winding when open, a rectifier circuit connected in parallel with the secondary winding, and an air gap switching mechanism connected to the relay and the control circuit and operable to open the relay when the air gap switching mechanism is activated.

Claims

1. A power supply circuit for selectively connecting and disconnecting a load from an alternating current power source having neutral and line conductors, said load being connected to said neutral conductor and to said power supply circuit via a load conductor, said power supply circuit comprising:

a transformer having a primary winding connected to said load and a secondary winding;

a relay connected at one terminal thereof to said primary winding and connected at another terminal thereof to one of said line conductor and said load conductor;

a control circuit connected to said relay and operable to open and close said relay, said relay being operable to complete and interrupt a current path along said line conductor, said primary winding and said load conductor when closed and open, respectively;

a first rectifier circuit connected in parallel with said secondary winding; and

an air gap switching mechanism connected to said control circuit, said control circuit being operable to detect a change in voltage across said secondary winding when said air gap switching mechanism is activated and to open said relay.

2. A power supply circuit for selectively connecting and disconnecting a load from an alternating current power source having neutral and line conductors, said load being connected to said neutral conductor and to said power supply circuit via a load conductor, said power supply circuit comprising:

a transformer having a primary winding connected to said load and a secondary winding;

a relay connected at one terminal thereof to said primary winding and connected at another terminal thereof to one of said line conductor and said load conductor;

a control circuit connected to said relay and operable to open and close said relay, said relay being operable to complete and interrupt a current path along said line conductor, said primary winding and said load conductor when closed and open, respectively;

a first rectifier circuit connected in parallel with said secondary winding;

a resistor connected to said first rectifier circuit;

a capacitor connected to said resistor;

a switch connected in parallel with said resistor and having substantially less impedance when closed than said resistor; and

a processor circuit to selectively close said switch to generate a pulse signal to charge said capacitor.

3. A power supply circuit as claimed in claim 2, wherein said processor circuit is programmable to generate said pulse signal in accordance with at least one of a group of conditions consisting of a fixed duty cycle, a varying duty cycle, random intervals, and following operations of said relay.

4. A power supply circuit as claimed in claim 2, further comprising an indicator, said processor circuit being programmable to generate said pulse signal in response to operation of said indicator.

5. A power supply circuit as claimed in claim 2, wherein said processor circuit is programmable to generate said pulse signal to operate said relay.

6. A power supply circuit as claimed in claim 2, further comprising an air gap switch connected to at least one of said line conductor and said neutral conductor and operable to interrupt the current path from said power source to said load when open, said processor circuit being programmable to generate said pulse signal to operate said air gap switch.

7. A power supply circuit for selectively connecting and disconnecting a load from an alternating current power source having neutral and line conductors, said load being connected to said neutral conductor and to said power supply circuit via a load conductor, said power supply circuit comprising:

a transformer having a primary winding connected to said load and a secondary winding;

a relay connected at one terminal thereof to said primary winding and connected at another terminal thereof to one of said line conductor and said load conductor;

a control circuit connected to said relay and operable to open and close said relay, said relay being operable to complete and interrupt a current path along said line conductor, said primary winding and said load conductor when closed and open, respectively;

a first rectifier circuit connected in parallel with said relay; and

a second rectifier circuit connected in parallel with said secondary winding.

8. A power supply circuit as claimed in claim 7, wherein said control circuit comprises:

a resistor connected to said first rectifier circuit;

a capacitor connected to said resistor;

a switch connected in parallel with said resistor and having substantially less impedance when closed than said resistor; and

a processor circuit to selectively close said switch to generate a pulse signal to charge said capacitor.

9. A power supply circuit as claimed in claim 8, wherein said processor circuit is programmable to generate said pulse signal in accordance with at least one of a group of conditions consisting of a fixed duty cycle, a varying duty cycle, random intervals, and following operations of said relay.

10. A power supply circuit as claimed in claim 8, further comprising an indicator, said processor circuit being programmable to generate said pulse signal in response to operation of said indicator.

11. A power supply circuit as claimed in claim 8, wherein said processor circuit is programmable to generate said pulse signal to operate said relay.

12. A power supply circuit as claimed in claim 8, further comprising an air gap switch connected to at least one of said line conductor and said load conductor and operable to interrupt the current path from said power source to said load when open, said processor circuit being programmable to generate said pulse signal to operate said air gap switch.

13. A power supply circuit as claimed in claim 7, further comprising an air gap switch connected to at least one of said line conductor and said load conductor and operable to interrupt the current path from said power source to said load when open, and a voltage detection circuit connected in parallel with said secondary winding, said voltage detection circuit being operable to open said air gap switch when said relay is closed and said load is open.

14. A power supply circuit as claimed in claim 7, further comprising an air gap switch connected to at least one of said line conductor and said load conductor and operable to interrupt the current path from said power source to said load when open, and a voltage detection circuit connected in parallel with said first rectifier circuit, said voltage detection circuit being operable to open said air gap switch when said relay is open and said load is open.

15. A power supply circuit for selectively connecting and disconnecting a load from an alternating current power source having neutral and line conductors, said load being connected to said neutral conductor and to said power supply circuit via a load conductor, said power supply circuit comprising:

a transformer having a primary winding connected to said load and a secondary winding;

a relay connected at one terminal thereof to said line conductor and connected at another terminal thereof to said primary winding when closed and to said secondary winding when open; and

a first rectifier circuit connected in parallel with said secondary winding.

16. A power supply circuit for selectively connecting and disconnecting a load from an alternating current power source having neutral and line conductors, said load being connected to said neutral conductor and to said power supply circuit via a load conductor, said power supply circuit comprising:

a transformer having a primary winding connected to said load via a load conductor and a secondary winding;

a relay connected at one terminal thereof to said primary winding and connected at another terminal thereof to said line conductor;

a control circuit connected to said relay and operable to open and close said relay, said relay being operable to provide power to said load when closed and to disconnect at least one of said line conductor and said load conductor from said primary winding when open;

a first rectifier circuit connected in parallel with said secondary winding; and

an air gap switching mechanism connected to said relay and said control circuit, said control circuit being operable to detect a change in voltage across said secondary winding when said air gap switching mechanism is activated and to open said relay.

17. A power supply circuit for selectively connecting and disconnecting a load from an alternating current power source having neutral and line conductors, said load being connected to said neutral conductor and to said power supply circuit via a load conductor, said power supply circuit comprising:

a transformer having a primary winding connected to said load and a secondary winding;

a relay connected at one terminal thereof to said primary winding and connected at another terminal thereof to one of said line conductor and said load conductor;

a control circuit connected to said relay and operable to open and close said relay, said relay being operable to complete and interrupt a current path along said line conductor, said primary winding and said load conductor when closed and open, respectively;

a first rectifier circuit connected in parallel with said secondary winding;

an air gap switching mechanism connected to said control circuit and operable to open said relay when said air gap switching mechanism is activated, said control circuit comprising a processor circuit and an air gap detection circuit connected to said processor circuit, said air gap switching mechanism comprising a switch in series with said secondary winding and operable to connect and disconnect said air gap detection circuit to and from said secondary winding when switched to first and second positions, respectively.

18. A power supply circuit as claimed in claim 17, wherein said air gap detection circuit is operable to detect an increase in voltage when said switch is in said first position, said processor circuit being operable to open said relay in response thereto.

19. A power supply circuit as claimed in claim 17, wherein said switch is selected from the group consisting of a slide switch, a press button and a relay.

20. A power supply circuit for selectively connecting and disconnecting a load from an alternating current power source having neutral and line conductors, said load being connected to said neutral conductor and to said power supply circuit via a load conductor, said power supply circuit comprising:

a transformer having a primary winding connected to said load and a secondary winding;

a relay connected at one terminal thereof to said primary winding and connected at another terminal thereof to one of said line conductor and said load conductor;

a control circuit connected to said relay and operable to open and close said relay, said relay being operable to complete and interrupt a current path along said line conductor, said primary winding and said load conductor when closed and open, respectively;

a first rectifier circuit connected in parallel with said secondary winding;

an air gap switching mechanism connected to said control circuit and operable to open said relay when said air gap switching mechanism is activated, said control circuit comprising a processor circuit and an air gap detection circuit connected to said processor circuit, said air gap switching mechanism comprising a switch having a first set of contacts connected in series with said transformer, said transformer and said first set of contacts being connected in parallel with said first rectifier circuit, and a second set of contacts connected to said air gap detection circuit, said switch being operable to disconnect said transformer from said first rectifier circuit when said switch is in a first position, said air gap detection circuit being operable to detect a decrease in voltage and said processor circuit being operable to open said relay in response thereto.

21. A power supply circuit as claimed in claim 20, wherein said air gap detection circuit is operable to detect a decrease in voltage when said switch is in a second position connecting said transformer to said first rectifier circuit, said relay is closed and said load is open, and to open said relay in response to said detection.

22. A power supply circuit for selectively connecting and disconnecting a load from an alternating current power source having neutral and line conductors, said load being connected to said neutral conductor and to said power supply circuit via a load conductor, said power supply circuit comprising:

a transformer having a primary winding connected to said load and a secondary winding;

a relay connected at one terminal thereof to said primary winding and connected at another terminal thereof to one of said line conductor and said load conductor;

a control circuit connected to said relay and operable to open and close said relay, said relay being operable to complete and interrupt a current path along said line conductor, said primary winding and said load conductor when closed and open, respectively;

a first rectifier circuit connected in parallel with said secondary winding;

an air gap switching mechanism connected to said control circuit and operable to open said relay when said air gap switching mechanism is activated, said air gap switching mechanism comprising a switch in series with said secondary winding and being operable to connect and disconnect said first rectifier circuit to and from said secondary winding when closed and opened, respectively, and said control circuit being operable to detect a decrease in voltage and open said relay in response thereto.

23. A power supply circuit as claimed in claim 22, wherein said control circuit is operable to detect a decrease in voltage when said switch is closed, said relay is closed and said load is open, and to open said relay in response to said detection.