Low-cost temperature stabilization in APD photo sensors by means a high frequency switching DC/T converter

APD-type photo sensors are widely used in several applications when a low level of light must be measured such as phosphorescence; fluorescence measurements. In such applications, Avalanche Photo Diodes must work in the avalanche region of APD in order to achieve high light-current gain. But the curve is extremely sensitive and, so the gain changes in temperature. Under these conditions, an small change in the temperature of diode can introduce errors and increases the uncertainty because changes in output current can be produced by changes in the input signal (light) or changes in the gain of APD (due to temperature). The total uncertainty could seem too small to be taking into account but a variation of temperature less than 0.001 p.u. will introduce notable drift in output signal. Moreover, this effect is not only an offset in output signal because small thermal oscillations or sustained changes in room temperature can add to output signal as a perturbation of low or medium frequency. In this paper, a new low-cost solution (DC/T converter) is presented. This system uses the cooling capability of Peltier cells and the reliability of high frequency switching power regulators in order to guarantee a low and extremely constant temperature in an APD. In next sections, principles of operation, system blocks and experimental results will be discussed. A DC/T converter uses a power source (dc source) as input and a regulator controls the power introduced into the thermal transducer. The output variable is the temperature and, consequently, a feedback loop must be placed to inform regulator and to hold the desired value of temperature.