Electronic drive circuit for multi-laser thermal printer

Abstract

There is disclosed an automatically adjustable electronic drive circuit for a multi-laser thermal-printer to insure uniformity in printing by all of the lasers. Each circuit includes a semi-conductor diode laser, a power transistor for driving the laser, a light sensor, a current sensor, a digitally adjustable potentiometer bias level unit, a dual input power amplifier for driving the power transistor, and two D/A converters for applying threshold and enable (full-on) signal levels to the inputs of the power amplifier. A first data feedback loop from a laser current monitor through an external central processor unit (CPU) to one of the D/A converters sets the threshold drive current to the laser. A second data feedback loop from the light sensor through the CPU and the adjustable bias unit to the second D/A converter establishes the level of the enable drive current to the laser to obtain a precisely calibrated full-on light power output of the laser. This circuit is periodically re-calibrated such that the laser light power output level remains constant for a given data command throughout the service life of the laser in spite of ageing. All of the light power output levels for the multiple lasers in the printer are calibrated to the same light power output level (within a narrow range) for a given data command.