Patent ID: 7499479

Claim:
A laser diode driver circuit for driving a laser diode, comprising: a current source for generating a laser drive current which is used for driving the laser diode; a switch for switching the passage/non-passage of the laser drive current into the laser diode; an optical output power control circuit for controlling the magnitude of the laser drive current based on a monitoring result as to the optical output power of the laser diode such that the optical output power is equal to a predetermined value; and a switch control circuit for controlling the operation of the switch according to an input signal, wherein the switch control circuit switches the drive power to the switch in conjunction with the control of the magnitude of the laser drive current by the optical output power control circuit, wherein when the laser drive current is controlled to be large, the switch control circuit increases the drive power; and when the laser drive current is controlled to be small, the switch control circuit decreases the drive power, wherein the switch control circuit includes a plurality of buffer circuits between which electrical connection and disconnection are switchable; and the switch control circuit switches the drive power by changing the number of buffer circuits connected in parallel.