Current mode restart circuit for a dc arc lamp

An illumination system for supplying uniform illumination of a transparent film in a film scanner, said illumination system comprising:

• means for providing uniform illumination of the film, said means provided with an input for receiving light;
• a dc arc lamp for directing light into the input of said uniform illumination means, said dc arc lamp subject to power variations that cause the lamp to extinguish;
• a power circuit for supplying the dc lamp with current, said current being a constant current value while the lamp is operating, said power circuit including a high current power supply and a current driver connected to an output of the power supply for supplying the constant current value;
• a current monitor connected to an the power circuit for monitoring the current supplied to the dc arc lamp and for providing a current sense signal corresponding to said supplied current;
• a comparator connected to receive the current sense signal and to provide a restart signal having a hysteresis characteristic, said restart signal activated when the current sense signal falls a first predetermined value below the constant current value indicating that the dc arc lamp has been extinguished and deactivated when the current sense signal rises above a second predetermined value greater than said first predetermined value, but still less than the constant current value;
• and
• an ignition circuit responsive to the restart signal for supplying the dc arc lamp with an ignition voltage to restart the lamp.