Conversion circuit between fluorescent ballast and LED
A tubular LED lamp designed for connection to a high frequency ballast. An electrically conductive screen is provided with an electrical connection between an internal node, such as an internal LED ground, and the screen. This provides a low impedance path5 for leakage currents which bypasses the LED string and thus prevents glow.
1. A tubular LED lamp, comprising:
an LED arrangement electrically connected between a voltage bus and an internal ground;
a driver circuit for driving the LED arrangement, wherein the driver circuit is adapted for connection to a high frequency ballast;
an electrically conductive screen enclosed within an electrically insulating outer cover; and
an electrical connection between a node of the LED arrangement and the screen for preventing glow of the LED arrangement when the tubular LED lamp is in an off state.
2. A lamp as claimed in claim 1 , wherein the electrical connection is between the internal ground and the screen.
3. A lamp as claimed in claim 1 , wherein the screen comprises a heatsink.
4. A lamp as claimed in claim 1 , wherein the electrical connection between the node and the screen comprises a solder pad.
5. A lamp as claimed in claim 4 , wherein the electrical connection between the node and the screen comprises a plurality of solder pads at multiple positions along the LED arrangement.
6. A lamp as claimed in claim 1 , wherein the driver circuit comprises a dimming unit for providing a dimmable drive signal to the LED arrangement; and wherein the lamp further comprises a wireless receiver for receiving a command to implement said dimmable drive signal within the lamp itself.
7. A lamp as claimed in claim 1 , comprising an outer casing, wherein the screen is electrically isolated from the outer casing.
8. A lamp as claimed in claim 7 , wherein the outer casing is electrically insulating, and wherein the screen is mounted to the outer casing using screws which are sunk in recesses of at least 5 mm depth.
9. A lamp as claimed in claim 1 , wherein the LED arrangement comprises an elongate printed circuit board on which a series string of LEDs is arranged.
10. A lamp as claimed in claim 1 , wherein the driver circuit comprises:
a filament emulation circuit;
a pin safety and startup circuit;
a rectifier;
an output capacitor at the output of the rectifier; and
an LED driver.
11. A lighting installation comprising:
a fluorescent ballast; and
a lamp as claimed in claim 1 .
12. A lighting installation as claimed in claim 11 , wherein the fluorescent ballast comprises a half-bridge resonant converter.
13. A method of preventing glow from a tubular LED which is driven by a fluorescent ballast, wherein the method is for preventing glow when the tubular LED is driven to an off state, the method comprising:
coupling a node of an LED arrangement of the tubular LED to an electrically conductive screen; and,
electrically isolating the screen from an outer housing of the lamp.
14. A method as claimed in claim 13 , comprising forming the coupling by providing an electrical connection between an internal ground and the screen.