Importance

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Abstract

One or more superluminescent light emitting diodes (SLDS) are driven with an oscillatory square wave pulse drive signal Vd varying between OVDC and 1.8-3.2VDC at a frequency between 1Hz to 12Hz, preferably between 6Hz to 8Hz, and having a pulse duty cycle between 5% to 10%, preferably between 6% to 8%, to periodically forward bias the SLDs into illumination and produce a brilliant rapidly flashing light having high on-off contrast for enhanced visibility and perceptibility at a distance, thus being usable for battery-powered visual indicator and warning flasher applications. A low frequency oscillator stage generates an oscillatory square wave voltage signal Vo which drives a power driver stage to produce the correspondingly oscillating drive voltage signal Vd which is supplied to the SLDS. The frequency and duty cycle of the drive pulse signal Vd are chosen to produce enhanced SLD illumination brightness for high on-off contrast and to operate the SLD within its most efficient operating characteristics for long battery life. An exemplary circuit utilizes an asatable monovibrator employing two transistors operated in the saturation mode with positive feedback as the low frequency oscillator, and a third transistor is driven as a saturated switch by the oscillator output Vo and acts as a power driver stage to switch battery current supplied to the SLDs as the drive voltage Vd for flashing the SLDs on and off at the frequency and pulse duty cycle of Vo. The pulse on time and off time and thus the flash frequency and duty cycle are determined by RC time constants of feedback circuits in the oscillator stage and thus can be set by selecting appropriate component values.

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