No abstract

APD-@pe photo sensors are widely used in several applications when a low level of light must be measured such as phosphorescence, fluorescence measurements. In such appliartions, Avalanche Photo Diodes must work in the avalanche region of APD in order to achieve high lighkurrent gain. But the curve is atremely sensitive an4 so the gain changes in temperature. Under these conditions, an small change in the temperature of diode can introduce errors and increases the uncertain@ because changes in output current can beproduced by changes in the input signal (lighi) or changes in the gain of APD (due to temperature). The total uncertain@ could seem too small to be taking into account but a variation of temperature less than 0.001 p.u will introduce notable driift in output signaL Momover, this egect is not only an ofiset in output signal because smdl thermal oscillations or sue rained changes in room temperature can add to output signal as a perturbation of low or medium f i u e n q y . I n this paper, a new low-eost solution (DCm converter) is ptesented This system uses the cooling capability of Peltier ceuS andthe relbbiliw of high frequency switching power regulators in order to guarantee a IOW and atremely constant temperature in an APD. In n& sections, principles of operation, system blocks and aperimental results will be dixussed A D C ' converter uses a power source (de source) as input and a regulator controk the power introduced into the thermal trane ducer. The output variable i s the temperature and, consequent&, a feedback loop must be placed to inform regulator and to hold the desired value of temperature Kevwords-Photo sensors, temperature, light measurement