Patent ID: 6963170
Filing Date: 2005-11-08
Classification: H05B

Abstract:
1. A lamp comprising an electrically driven light source and a monitor circuit, both mounted by a lamp housing to form a single unit, the lamp having power supply terminals for connection of the light source to a power supply, the monitor circuit comprising: a first resistor; a second resistor, the second resistor having a resistance greater than the resistance of the first resistor; a first solid state switching device having an input and an output, the first resistor, the second resistor and the input of the first solid state switching device connected in series across the terminals of the power supply, the first resistor and the light source connected in series across the first and second terminals of the power supply to illuminate the light source, a first terminal of the light source connected to a first terminal of the first resistor, a second terminal of the light source connected to the second terminal of the power supply, a second terminal of the first resistor connected to the first terminal of the power supply, a state of the output of the first solid state switching device responsive to a value of the voltage across the first resistor; a third resistor; and a second solid state switching device having an input and an output, the output of the first solid state switching device, the third resistor, and the input of the second solid state switching device connected in series across the first terminal of the power supply and the first terminal of the light source, the common connection between the series connected first and second resistors connected to a common connection between the series connected input of the second solid state switching device and the first terminal of the light source, the output of the first solid state switching device controlling the input of the second solid state switching device, the input of the second solid state switching device controlling the output of the second solid state switching device.