Temperature controller design for laser system based photodynamic therapy devices

With the development of technology, many electronic circuits are being developed and reduced to serve specific work areas. The most basic problem encountered in this denominator is the problem of heating. For this reason, the heat load on the power consumptions of the elements used in the electronic circuits. Designed systems must be operated at certain temperatures to ensure stable and correct operation. The temperature ranges needed for device systems to operate steadily and accurately can vary according to the disciplines of operation. The main purpose of this work is to ensure that devices with precise operating characteristics at specific temperature values can operate in the narrow temperature range they need. In this study, Intense M5215 laser diode thermal load is selected for photodynamic therapy as application and it is ensured that it is kept constant in long working time at the desired temperature range. Four different prototypes have been implemented to fix the laser diode to a certain temperature value. Each prototype was designed by eliminating the problems of the previous prototype and the final analogue temperature control circuit design was implemented in the fourth prototype. The analog circuit senses the temperature value of the thermal load through the temperature sensor and transfers the temperature information to the microprocessor. During the operation period of the system, the error rate is calculated by comparing the desired temperature value with the current temperature by the PID controller. The PID controller generates the PWM signal with this error rate information, enabling the thermoelectric material to be driven in a gradual manner. It has been shown that the temperature controller can control up to 5.3 A at a room temperature of 24 ° C and a maximum thermal load of 27.5 W at a maximum value of 8.1 V. With temperature stability, the light quality produced by the laser diode has been recorded as a result of long-term experiments and has been shown to have a much shorter residence time compared to the requirements of the laser systems used in the literature. Class D amplifier filters were used, which were much cheaper than the equivalent temperature controllers with the use of DC-DC converters.