Light power controlling apparatus

DETAILED DESCRIPTION Accordingly, an object of the present invention is to provide a light power controlling apparatus which operates stably against temperature change to produce a constant light power, has an invariable peak value of the modulated light against a great fluctuation of the duty ratio of the modulated signal waveform, and little power fluctuation at the start and end of modulation.
In the present invention, a semiconductor light emitter is driven by a forward current from a first current circuit, and emits light.
Part of the light emitted is received by a photosensor and converted into a corresponding electric signal.
The detected signal from the photosensor is compared with a desired value by an error amplifier.
The error amplifier produces a signal of a difference between the detected signal and the desired value.
The difference signal is integrated by an integrator and is fed as a feedback control signal to the first current circuit.
This signal is integrated by an integrator and is fed back as a feedback control signal to the first current circuit.
The first current circuit is connected in parallel with a first current circuit, via a modulating switching circuit.
A peak power at the time of modulation is set in the second current circuit.
The desired value is added to the product of a signal representing an averaged form factor of the modulating signal and the set value of the peak power.
The first current circuit is controlled by the signal representing the added value, thereby to attain a stabilization of the light power.