| 摘要 |
A discharge lamp ballast circuit has a snubber circuit to perform a soft switching when the MOS transistor is turned off. The snubber circuit has, for example, a capacitor that resonates with a reactance of the fly-back transformer and enables a zero voltage switching. Before a breakdown of a discharge lamp, a control circuit drives the MOS transistor in a non-zero voltage switching manner by turning on the MOS transistor just after a peak voltage. The non-zero voltage switching increases an output voltage of the fly-back transformer. After the breakdown of the discharge lamp, the control circuit turns on the MOS transistor in the zero voltage switching manner to perform the soft switching. As a result, it is possible to reduce switching loss during a lighting of the discharge lamp and to supply sufficient voltage in the lighting preparation period.
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