The Driver Circuit and Focusing Lens Designed for the Laser Range-Finder

Abstract

This paper has partitioned the laser range-finder into two parts: one is the laser diode (LD) driver circuit and the other is the focusing lens. The LD’s surface temperature rise will affect the LD’s light-power simultaneously when an LD works in a steady current. For this reason, we designed a driver circuit to control the LD’s light power to be effective and so as to freely adjust the LD’s brightness. There are three parts in driver circuit: the regulated power circuits, the regulated current circuit, and the limited current circuit. This investigation used a power meter to measure the LD’s power which was relative to the surface temperature. Then the experimental results were compared with the PSpice simulation, and the differences between the result and the simulation were eventually analyzed. The limited current circuit is an important part in our systems because the LD is easily damaged when active current is unstable. Similarly, the surface temperature would be raised after the LD is working for a while which results in the circuit failure. If the LD has worked for a very long time, the heat generated in the circuit should be taken care of. Therefore, we added an automatic power control circuit (APC) into the LD driver circuit in order to reduce the impact of heat. The emitted distance of laser beam could be up to 10 meters with adjusted focusing lens. The laser spot was extended into an ellipse before focusing laser beams. Therefore, we had to put a focal lens to shape the the laser spot into a circular spot. During this experiment, the LD did not work directly without installing the heat sink. Otherwise, the high temperature would damage LD immediately.