Patent ID: 8733659

Claim:
An arrangement for regulating output power of a laser beam emitted by a laser that has an internal semiconductor laser diode and an internal semiconductor monitor photodiode, in an electro-optical reader for reading targets, comprising: a feedback circuit configure to receive electrical signal from the monitor photodiode and to adjust the output power in response to the electrical signal received from the monitor photodiode, for maintaining substantially constant the output power of the laser beam during normal operation; a disabling circuit for periodically and momentarily disabling the feedback circuit; a drive circuit for driving the laser diode with a drive current when the feedback circuit is disabled, and for concomitantly generating an output voltage of the monitor photodiode; a current modification circuit for periodically and momentarily modifying the drive current passing through the laser diode by a predetermined current with a concomitant change in the output voltage of the monitor photodiode when the feedback circuit is disabled; and a control circuit for monitoring the change in the output voltage of the monitor photodiode, for determining whether the change in the output voltage of the monitor photodiode is sufficient to indicate an over-power condition, and for interrupting power to the laser diode when the over-power condition is indicated.