Discharge lamp ballast, lighting unit, and vehicle

A discharge lamp ballast, comprising:

• a DC power supply;
• a DC-DC converter that converts a voltage of the DC power supply by operation of a switching element based on a PWM signal and outputs DC power;
• and
• an inverter that inverts the DC power into AC power having a lower frequency than a switching frequency of the DC-DC converter, thereby lighting a discharge lamp by the AC power of the inverter,
• a PWM ON-width controller that increases the ON time of the switching element starting from an edge of an AC oscillator signal received from an AC oscillator,
• a PWM signal generator that generates the PWM signal, and controls the switching element in the DC-DC converter to increase an ON-width of the PWM signal immediately before a polarity of the AC oscillator is reversed, such that the ON-width of the PWM signal is increased from a start of a polarity reversal, to increase the DC power in a period, and
• an inverter driving signal generator that causes the polarity of the AC power of the inverter to be reversed in synchronism with an operation of the switching element immediately after the PWM ON-width controller increases the ON-width of the PWM signal.