Diode Laser Power Supply and Controller


High power diode lasers are becoming more and more available on the open market. The circuitry required to operate and control them are rather complex though. Not only a stable current source is required for the laser diode (or array of diodes), but the temperature of the diode must also be controlled, in order to keep the wavelength constant (or indeed make it adjustable.) For this reason, the diodes are manufactured onto peltier cooling devices with embedded temperature feedback sensors.

The peltier coolers in turn requires stable bipolar current sources, and temperature feedback circuitry. We have been involved for over two years in the development of a diode laser system for a medical application. This did not only entail the diode power supply development, but the total instrument control system, which makes use of a PC104 computer with digital and analogue IO cards.

This system of which 2 prototypes were built have recently successfully undergone all of the EMI and safety standard tests required for CE certification of a medical instrument. Furthermore, the instruments have been used in successful clinical trials by the Department of ophthalmology of the medical school of the University of Pretoria.
 

In the first phase of the development, we made use of commercially available current controllers, which we had to feed with linear power supplies. Although the system worked well, the efficiency of these circuits are very poor. Furthermore, the large transformers and massive heat sinks required, makes the instrument very heavy (16kg) to carry. Therefore, we have developed switch mode circuitry for all the power requirements of the laser system. This has increased the efficiency dramatically and reduced the weight by half. Furthermore, the system can now make use of a car battery as an alternate power source.