Patent ID: 8179057

Claim:
An electronic ballast for a discharge lamp, comprising: a power conversion circuit including an inverter circuit and a resonant circuit, the power conversion circuit being configured to convert DC voltage from a DC power supply circuit into AC voltage with the inverter circuit to apply the AC voltage across a load circuit including at least the discharge lamp via the resonant circuit; a drive circuit configured to adjust an operating frequency of the inverter circuit in accordance with a control signal; and a frequency control circuit configured to supply the control signal to the drive circuit to sweep the operating frequency of the inverter circuit from a start frequency to an end frequency and thereby to increase load voltage that is the AC voltage applied across the load circuit, wherein the electronic ballast further comprises: a predictive circuit configured to predict a resonance frequency of the combination of the resonant circuit and the load circuit after ignition of the discharge lamp, the resonance frequency being predicted based on an input signal representing the load voltage in the period of time from the start of sweep of the operating frequency through a time point immediately after ignition of the discharge lamp; and a correction circuit configured to change said end frequency to the resonance frequency.