A current source generating a charging current and a supply voltage by charging a capacitor with the charging current. The current source has a conversion circuit converting a line voltage into a second voltage, a current generation circuit generating the charging current based on the second voltage, and a control circuit controlling the current generation circuit based on the supply voltage. The charging current is controlled to be at a first current value when the supply voltage is lower than a first threshold voltage, the charging current is controlled to be at a second current value when the supply voltage is higher than a second threshold voltage. The first threshold voltage is lower than the second threshold voltage, and the first current value is lower than the second current value.