a zener diode 82 and a resistor 84 connected in parallel between the source terminal and the gate terminal of fet 80 further to the operation of the present invention which was described above with reference to fig1 when the dc voltage is applied to input terminals 24 and 28 with the positive polarity applied to input terminal 24 for cooling purposes diode network 32 applies the dc voltage to voltage regulator 38 with the plus polarity being applied on lead 40 digital temperature sensor 50 provides a digital signal to the programmable control means 44 which is indicative of the temperature where the temperature sensor 50 is located if the signal from the temperature sensor 50 indicates to the programmable control means 44 that power needs to be applied to the thermoelectric assembly 16 to bring the temperature down to the desired set point temperature programmable control means 44 will complete the circuit through led 57 via lead 60 which will result in diode network 20 and phototransistor 59 providing continuity between leads 66 and 68 with the plus dc voltage being on lead 26 zener diode 72 places the plus dc voltage on lead 66 and the gate terminal of fet 70 which results in the provision of continuity between the source and drain terminals of fet 70 and places the plus dc voltage on output terminal 12 the plus dc voltage is also placed on lead 68 and the gate terminal of fet 80 through diode network 20 and phototransistor 59 fet 80 then provides continuity between the source and drain terminals of fet 80 and places the negative polarity of the dc voltage.