Patent ID: 6600324
Filing Date: 2003-07-29
Classification: B61L,G01R,H05B

Abstract:
A cold filament detection circuit connected between first and second lines through which a voltage and current supply source supplies voltage and current to a light-emitting load, the voltage, and current supply source having a set up time during which no current is supplied to the light-emitting load, said cold filament detection circuit comprising:a) a resistor; b) a controllable switch member connected in series with the resistor between the first and second lines; responsive to the voltage on said first and second lines; and having a current-conductive junction established in response to the voltage on the first and second lines to thereby establish through said resistor a current path between said first and second lines; and c) a switch control unit responsive to the current supplied to the light-emitting load, connected to the controllable switch member, and having a switch-disabling circuit which prevents the current-conductive junction to establish as long as current is supplied to the light-emitting load; whereby, during the set up time no current is supplied to the light-emitting load and the current path is established through said resistor to emulate the impedance of an incandescent lamp, and when current is supplied to the light-emitting load, said switch-disabling circuit prevents said current-conductive junction to establish whereby said resistor is disconnected from between said first and second lines.