Heating device and image forming apparatus

An image forming apparatus comprising:

• a heating device including,
• a heat generating unit that generates heat in response to energization of an alternating-current power supply,
• a zero-crossing signal generating circuit that generates a zero-crossing signal in synchronization with a zero-crossing time of the alternating-current power supply,
• an energization regulating unit that regulates an energization period of the heat generating unit by the alternating-current power supply based on the zero-crossing signal,
• a voltage change rate detecting unit that detects whether a rate of voltage change of the alternating-current power supply at the zero-crossing time is equal to or larger than a predetermined value,
• a switching unit that is provided between the alternating-current power supply and the heat generating unit, the switching unit switching on and off a connection between the alternating-current power supply and the heat generating unit, and
• an energization disabling unit that disables energization of the heat generating unit by the alternating-current power supply by controlling the switching unit when the rate of voltage change is equal to or larger than the predetermined value;
• and
• an image forming unit that forms images on a recording medium in accordance with image data, the images being fixed to the recording medium by the heating device,
• wherein the energization regulating unit is provided downstream of the switching unit with respect to the alternating-current power supply and is connected in series with the heat generating unit,
• wherein when it is detected that the rate of voltage change is equal to or larger than the predetermined value before the heat generating unit is energized and when the switching unit is in an ON state, the energization disabling unit disables energization of the heat generating unit by disabling the energization regulating unit from starting an operation of regulating the energization period,
• wherein when it is detected that the rate of voltage change is equal to or larger than the predetermined value after the heat generating unit is energized, the energization disabling unit disables energization of the heat generating unit by switching the switching unit from the ON state to an OFF state,
• wherein the alternating-current power supply of the zero-crossing signal generating circuit is taken from between the switching unit and the heat generating unit,
• wherein the image forming apparatus is configured to operate in a sleep mode where the heat generating unit is not energized, and
• wherein, when operating in the sleep mode, the voltage change rate detecting unit does not detect whether the rate of voltage change of the alternating-current power supply at the zero-crossing time is equal to or larger than the predetermined value.