A device for driving a light-emitting element via three transistors includes a driving circuit, a negative voltage circuit, and a protection circuit. The driving circuit has a first transistor and a second transistor for producing a first signal. The negative voltage circuit electrically connected to the driving circuit for transforming the first signal into a second signal to be transmitted to the light-emitting element, and the light-emitting element is driven in response to an operating voltage resulted from the voltage of the second signal and a power voltage. The protection circuit includes a third transistor having two terminals connected to the light-emitting element and the third terminal connected to a base of an NPN transistor for controlling the operating voltage so as to stabilize an output of the light-emitting element.

A process and circuit arrangement for regulating the luminous power of a laser diode in an optoelectronic point-by-point or line recording device for recording information on a recording material. A deviation is determined by comparing a luminous power set value to a measured luminous power real value. A fast regulator generates a regulating current based on the deviation. A slow regulator with storage capabilities generates a working point regulating current that determines the working point on a laser diode characteristic curve and that is added to the regulating current to provide the driving current of the laser diode. The luminous power set value and the slow regulator are used during the switching-on periods of the laser diodes at the beginning of the recording periods and during preliminary periods that precede the recording periods. The working point regulating current corrects the working point of the laser diode during the preliminary periods and is kept constant during the subsequent recording periods. Oscillations of the luminous power that may occur during the recording periods are only regulated by the fast regulator.

An apparatus and method for detecting beam power generated by a plurality of light sources, using a single device. The apparatus includes a light-receiving unit that receives the beam power generated by one of a plurality of light sources, and an amplifying unit that selects a gain, amplifies the beam power received by the light-receiving unit according to the selected gain, and outputs the beam power amplified as a detected beam power. According to the apparatus and method, received beam power (or amplification gain) is amplified by a gain determined according to the characteristics of the respective light sources. Thus, it is possible to provide the detected beam power in consideration of a sufficient dynamic range for the each light source, thereby realizing effective APC.

An optical output controller including a light source emitting light, a light receiving unit receiving some of the emitted light and converting the received light into a current signal, and an automatic power controlling unit receiving the current of the light receiving unit and controlling an optical power output of the light source in accordance with the received current, wherein the automatic power controlling unit includes a resistance circuit section having a variable resistor of which one end is connected to an output end of the light receiving unit, a resistor connected in parallel with the variable resistor, and a load resistor connected in series to the variable resistor and a node providing a predetermined voltage, and a comparison circuit section controlling a driving current of the light source by comparing an output current of the resistance circuit section with a predetermined signal.