Electronic ballast with load shed circuit

Abstract

An electronic ballast () for powering at least one gas discharge lamp () includes a current-fed resonant inverter () and a load shed circuit (). Inverter () ordinarily powers the lamp at a first level. When a load shed command is sent by the electric utility and received by an associated load shed receiver within the ballast (), load shed circuit () causes the inverter to reduce the lamp power from the first level to a second level. Preferably, load shed circuit () includes an isolation circuit () and a bidirectional switch () that is coupled in parallel with a return ballasting capacitor () within inverter (). In the absence of a load shed command, bidirectional switch () effectively shunts return ballasting capacitor (), which causes the lamp to be powered at the first level. In response to a load shed command, bidirectional switch () ceases to shunt return ballasting capacitor (), thereby causing the lamp power to be reduced to the second level.