Light-emitting device, driving method of light-emitting device, light-emitting chip, print head and image forming apparatus

A light-emitting device comprising:

• a plurality of light-emitting chips each having a plurality of light-emitting elements;
• an enable signal supply unit that transmits an enable signal in common to the light-emitting chips belonging to each of M (M is an integer of two or more) groups into which the plurality of light-emitting chips are divided, the enable signal selecting a light-emitting element as a target for lighting up from the light-emitting elements set as a control target;
• a write signal supply unit that transmits a write signal in common to light-emitting chips belonging to each of N (N is an integer of two or more) classes into which the light-emitting chips in each of the M groups are classified, the write signal selecting the light-emitting element as the target for lighting up from the light-emitting elements set as the control target;
• and
• a light-up signal supply unit that transmits a light-up signal in common to the light-emitting chips belonging to each of the M groups, the light-up signal supplying power for lighting up the light-emitting element selected by the enable signal and selected by the write signal.

A light-emitting chip comprising:

• a plurality of light-emitting elements;
• a plurality of transfer elements that are provided corresponding to the plurality of light-emitting elements, respectively, and sequentially set the plurality of light-emitting elements one by one as a control target for lighting up or not lighting up;
• and
• N control terminals (N is an integer of two or more) that each receive a designation signal to control light-on or light-off of each of the plurality of light-emitting elements, separately.

A print head comprising:

• an exposure unit that exposes an image carrier to form an electrostatic latent image;
• and
• an optical unit that focuses light emitted by the exposure unit on the image carrier,
• the exposure unit including:
• a plurality of light-emitting chips each having a plurality of light-emitting elements, and each being designated, as a control target for lighting up or not lighting up, by two to Q designation signals (Q is an integer of two or more);
• and
• a selection signal generating part that selectively transmits P selection signals (P is an integer of three or more where P>Q) as the designation signals to designate each of the plurality of light-emitting elements as the control target, the designation signals for each of the plurality of light-emitting chips including a combination of two to Q selection signals taken from the P selection signals.

An image forming apparatus comprising:

• a charging unit that charges an image carrier;
• an exposure unit that exposes the image carrier to form an electrostatic latent image;
• an optical unit that focuses light emitted by the exposure unit on the image carrier;
• a developing unit that develops the electrostatic latent image formed on the image carrier;
• and
• a transfer unit that transfers an image developed on the image carrier to a transferred body,
• the exposure unit including:
• a plurality of light-emitting chips each having a plurality of light-emitting elements, and each being designated, as a control target for lighting up or not lighting up, by two to Q designation signals (Q is an integer of two or more);
• and
• a selection signal generating part that selectively transmits P selection signals (P is an integer of three or more where P>Q) as the designation signals to designate each of the plurality of light-emitting elements as the control target, the designation signals for each of the plurality of light-emitting chips including a combination of two to Q selection signals taken from the P selection signals.