The HY5630 TEC controller consists of a thermistor bridge amplifier, a window comparator, an integrator/gain stage and a voltage-to-current converter power drive stage. This is illustrated in the simplified schematic diagram for the HY5630 in Figure 1. The thermistor bridge precisely measures the temperature of a device attached to a Thermoelectric Cooler (TEC). The bridge is balanced when the thermistor value is equal to the value of the temperature set resistor (Rs). When power is first applied to the TEC, the temperature of the device attached to the TEC is higher than the desired set temperature. The resistance of the thermistor is therefore less than the temperature set resis-