Light source drive circuit, optical scanning apparatus, semiconductor drive circuit, and image forming apparatus

Abstract

A light source drive circuit which drives a light source is disclosed, including a drive current generating unit which generates a drive current, the driving current including a predetermined current for obtaining a predetermined light amount from the light source; and first and second overshoot currents which are applied to the predetermined current in synchronization thereto; and a control unit which sets, to the drive current generating unit, a value of the first overshoot current to a fixed value, and a value of the second overshoot current in accordance with a light amount output from the light source.

1 . A semiconductor laser drive circuit which drives and modulates a semiconductor laser, comprising:
 a current source which supplies a drive current for driving and lighting the semiconductor laser;   a first overshoot current source which supplies a current at a time of a rise of the drive current; and   a second overshoot current source which supplies a current at the time of the rise of the drive current, wherein a time in which the first overshoot current source supplies the current is a time which is shorter than a time in which the semiconductor laser responds to the drive current; and   a time in which the second overshoot current source supplies the current is longer than the time in which the first overshoot current source supplies the current and is shorter than the time in which the semiconductor laser responds to the drive current.   
     
     
         2 . The semiconductor laser drive circuit as claimed in  claim 1 , wherein the first overshoot current source and the second overshoot current source provide a power supply simultaneously with a timing at which the current source supplies the drive current. 
     
     
         3 . The semiconductor laser drive circuit as claimed in  claim 2 , wherein a signal of an addition current in which the current supplied by the first overshoot current source and the current supplied by the second overshoot current source are added is a signal in which a signal of the drive current or a delayed signal of the drive current is differentiated at a predetermined change point. 
     
     
         4 . The semiconductor laser drive circuit as claimed in  claim 1 , wherein the current source includes a transistor which performs a voltage-to-current conversion; and,
 to an emitter or a source of the transistor,   a first capacitor as the first overshoot current source is connected and   a resistor and a second capacitor are serially connected as the second overshoot current source.   
     
     
         5 . The semiconductor laser drive circuit as claimed in  claim 4 , wherein the resistor is a variable resistor, and
 the first capacitor and the second capacitors are variable capacitors.   
     
     
         6 . The semiconductor laser drive circuit as claimed in  claim 1 , wherein the semiconductor laser is a VCSEL. 
     
     
         7 . The semiconductor laser drive circuit as claimed in  claim 1 , wherein the semiconductor laser is a red laser or a red laser array. 
     
     
         8 . An image forming apparatus, comprising:
 a semiconductor laser whose output is modulated by an image modulation signal; and   a scanning unit which scans a rotating photosensitive body with a light of the semiconductor laser, wherein   an electrostatic latent image is formed onto the rotating photosensitive body in accordance with the image modulation signal, and wherein   the semiconductor laser is driven by the semiconductor laser drive circuit as claimed in  claim 1 .