GB1052813A - - Google Patents

Abstract

1,052,813. Converting. BARBER-COLMAN CO. March 2, 1964 [March 4, 1963], No. 8752/64. Heading H2F. [Also in Division G3] A temperature control system for an aircraft windshield supplying one or more complete cycles of A.C. power in given repetitive periods comprises a condition sensitive resistor 78 forming part of a bridge circuit 75-78 having a shunt diode 80 eliminating negative half cycles and connected to an A.C. supply 63 through a phase shifting capacitor 74, and a differential amplifier 67-71. When the bridge is balanced, transistors 67-68 conduct equally hence another transistor 66 is non-conducting. Unbalance of the bridge causes transistor 66 to conduct through a resistor 85 hence allowing a leading thyristor 61 to conduct on the next positive half cycle energizing a load 64 which through a rectifier 91 charges a capacitor 90, which on discharging through resistors 92, 93 fires trailing thyristor 62. During positive half cycles, a previously charged feedback capacitor 81 discharges through a resistor 84 and thyristor 61 until the base potential of transistor 68 drops to that of transistor 67 when conduction of thyristors 61, 62 ceases. Capacitor 81 will then recharge through rectifier 83 allowing the base potential of transistor 68 to rise and the thyristors again to conduct, thus the system works in a series of power cycles of a number of complete A.C. cycles on and a number off, the numbers depending on the relationship of the actual temperature to the desired temperature. In another arrangement (Fig. 1, not shown) only one thyristor is used and half cycles only are admitted to the load.