Self-regenerative, latching, semiconductor voltage selection circuit

1,009,340. Automatic character reading. GENERAL PRECISION Inc. April 24, 1962 [April 24, 1961], No. 15604/62. Heading G4R. [Also in Divisions G1 and H3] A circuit for selecting, upon interrogation, a single extreme value (greatest or least) from a group of simultaneously applied input voltages each on a separate input lead 101-104 comprises for each input lead a thyristor Q5-Q2 (self-latching transistor switch) the input lead being connected to the base and an output lead 201-204 to the collector, and current control means for supplying a predetermined amount of current to a common terminal to which all the emitters are connected, the current being cut off when an interrogation pulse is applied. The interrogation pulse is applied at terminal 199 to cut off transistor Q1 which normally acts as a current source for the thyristors Q2-Q5, the current passing through resistor R2 to hold the voltage at the emitters of the thyristors Q2-Q5 accurately at a preset voltage. When the transistor Q1 is cut off, this current ceases and current through resistor R4 to terminal 126 pulls the emitters towards the - 10 volt level. In this condition all the thyristors Q2-Q5 are cut off. At the end of the interrogation pulse the transistor Q1 conducts again and the voltage applied to the emitters rises rapidly towards +10 volts. As this voltage becomes more positive than any of the input voltages the corresponding thyristor Q2-Q5 will conduct preventing any further rise in the emitter voltage through current drawn through one of the resistors R7, R10, R13 or R16 so that none of the other thyristors can conduct. The conducting thyristors stays conducting until the next interrogation pulse.