Patent ID: 7953132

Claim:
A laser driver circuit which supplies a laser diode with a current so as to drive the laser diode, the laser driver circuit comprising a current supply circuit for supplying the laser diode with the current, wherein the current supply circuit comprises: a voltage-to-current converter circuit for converting an input voltage to the current so as to generate the current; a current output line which is connected to the voltage-to-current converter circuit, and which outputs the current generated by the voltage-to-current converter circuit; a current supply line which is connected to the laser diode, and which supplies the laser diode with the current generated by the voltage-to-current converter circuit; a ground line connected to the ground; and a current path switch for selectively connecting either the current supply line or the ground line to the current output line, wherein the current which is output from the voltage-to-current converter circuit, and which is running through the current output line, the current path switch and the current supply line is supplied to the laser diode so as to drive the laser diode, wherein the laser driver circuit further comprises a current output prevention circuit for preventing the voltage-to-current converter circuit from generating the current and preventing the current from being output from the current output line, when the current output line and the ground line are connected by the current path switch, wherein the current supply circuit further comprises a voltage input line which is connected to the voltage-to-current converter circuit, and which inputs a voltage to the voltage-to-current converter circuit, wherein the current output prevention circuit further comprises a voltage input switch for switching between connection and disconnection of the voltage input line, wherein by disconnecting the voltage input line using the voltage input switch so that the voltage is not input to the voltage-to-current converter circuit, the current output prevention circuit prevents the voltage-to-current converter circuit from generating the current, wherein when the period during which the current output line is connected to the ground line by the current path switch is longer than the sum of a current fall time and a current rise time, the current output prevention circuit disconnects the voltage input line using the voltage input switch so that the voltage is not input to the voltage-to-current converter circuit, wherein the current fall time is a period during which the current to be output from the current output line decays to zero, when the voltage input line has been disconnected by the voltage input switch, and wherein the current rise time is a period during which the current to be output from the current output line rises from zero level to the steady-state current level, when the voltage input line has been connected by the voltage input switch.