Method and apparatus for variable current control of a negative resistance device such as a fluorescent lamp

摘要

A fluorescent lamp is adjusted in illumination intensity by controlling the DC current in the lamp during each alternate direct current flow through the lamp. The magnitude of the current applied to the lamp is set each time the direction of current through the lamp is switched, and the current change between switch times is limited. Inductors are used as current change limiting devices so that in each direction of current flow through the lamp, the current can not rapidly change. The amount of current is set, and the direction of current flow is switched when a current monitor detects that the current through one of the inductors is equal to the current desired for the operating point of the lamp. In this way, uniform selectable illumination levels may be achieved even though the lamp is operating in the negative resistance portion of its resistance characteristic.