Eliminating silver migration in EL lamps
View Patent ↗A net negative charge is used to eliminate silver migration in an EL lamp. An electrode containing silver, either the entire electrode, a bus bar on the electrode, or a contact area on the electrode, receives a net negative charge while the EL lamp is being driven with alternating current. The net negative charge can be provided by the driver itself or by a current source, such as a battery or a charged capacitor; or by asymmetric current means in the current path of the EL lamp, including the lamp itself.
1. A lighting system including an EL lamp having a first electrode, a second electrode, a dielectric layer and a phosphor layer between the first electrode and the second electrode, and a driver supplying alternating current to the lamp, characterized in that the first electrode contains silver particles, the second electrode does not contain silver particles, and the driver includes a bias circuit that produces a net negative charge on the first electrode.
2. The lighting system as set forth in claim 1 wherein said bias circuit is an source of direct current.
3. The lighting system as set forth in claim 1 wherein said bias circuit is an asymmetric conducting means in series with said EL lamp.
4. The lighting system as set forth in claim 1 wherein substantially the entire first electrode includes silver particles and is reflective.
5. A lighting system including an EL lamp having a first electrode, a second electrode, a dielectric layer and a phosphor layer between the first electrode and the second electrode, and a driver supplying alternating current to the lamp, characterized in that the first electrode includes a bus bar and the bus bar contains silver particles, the second electrode does not contain silver particles, and the driver includes a bias circuit that charges the EL lamp with net negative charge on the first electrode.
6. The lighting system as set forth in claim 5 wherein said bias circuit includes a source of direct current.
7. The lighting system as set forth in claim 5 wherein said bias circuit includes asymmetric conducting means in series with said EL lamp.
8. A lighting system including an EL lamp having a first electrode, a second electrode, a dielectric layer and a phosphor layer between the first electrode and the second electrode, and a driver supplying alternating current to the lamp, characterized in that the first electrode includes a contact area and the contact area contains silver particles, the second electrode does not contain silver particles, and the driver includes a bias circuit that charges the EL lamp with net negative charge on the first electrode.
9. The lighting system as set forth in claim 8 wherein said bias circuit includes a source of direct current.
10. The lighting system as set forth in claim 8 wherein said bias circuit includes asymmetric conducting means in series with said EL lamp.
11. A method for eliminating silver migration in an EL lamp having an electrode containing silver particles, said method comprising the steps of:
supplying alternating current to the EL lamp during operation; and providing a DC offset to the alternating current, thereby generating a net negative charge on the electrode.
12. The method as set forth in claim 11 wherein said providing step includes the step of:
coupling an asymmetric current means in series with the EL lamp.
13. The method as set forth in claim 11 wherein said providing step includes the step of:
adding direct current to the alternating current.