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1. A laser diode drive circuit, connected to a laser diode, comprising:
a timing determination circuit to generate a timing signal in synchronization with an image data signal based on a light intensity of the laser diode; a power supply circuit connected to an anode of the laser diode and configured to receive the timing signal and supply a variable voltage to the laser diode, the power supply circuit comprising a reference voltage generator to output a variable reference voltage; a voltage setting circuit to generate a voltage setting signal to set the variable reference voltage; and a drive current control circuit connected to a cathode of the laser diode and configured to control a current of the laser diode, wherein the power supply circuit generates a start-up voltage which is equal to a sum of a maximum drive voltage of the laser diode and a predetermined first reference voltage, acquires a cathode voltage of the laser diode while the start-up voltage is generated, and generates the variable voltage which is less than the start up voltage and is controlled, based on the variable reference voltage output by the reference voltage generator and set in accordance with the voltage setting signal from the voltage setting circuit, the first reference voltage being a minimum cathode voltage of the laser diode necessary to supply a predetermined current to the laser diode by the drive current control circuit, wherein the timing signal generated by the timing determination circuit defines a time interval within which the cathode voltage of the laser diode, when changing from maxima to minima or from minima to maxima, converges within a predetermined range.
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