Electronic apparatus for biological research Electronic apparatus for biological research . electronicappara00dona Year: 1958 SOFT VALVES Thyratron switch—The criterion of a good 'on-off' switch is that when the switch is 'off' the resistance be extremely high and when the switch is 'on' the resistance be low, that is, that the potential difference across it be small Control voltage o+V + Output 1 Output 2 Output 3 k__^^. ^^^T Figure when it is passing the load current. The thyratron is a good electronically controlled switch {dvpoL—a door), for provided it is capable of passing the
Electronic apparatus for biological research Electronic apparatus for biological research . electronicappara00dona Year: 1958 SOFT VALVES Thyratron switch—The criterion of a good 'on-off' switch is that when the switch is 'off' the resistance be extremely high and when the switch is 'on' the resistance be low, that is, that the potential difference across it be small Control voltage o+V + Output 1 Output 2 Output 3 k__^^. ^^^T Figure when it is passing the load current. The thyratron is a good electronically controlled switch {dvpoL—a door), for provided it is capable of passing the load current the voltage dropped across it cannot exceed some 15 V, which is not much in apparatus commonly supplied with voltages of around 500. The usefulness of the thyratron in switching direct current supplies is somewhat reduced by its inability to switch 'off'. In Figure we have a direct voltage generator supplying some kind of load, an electromagnet or a motor or a lamp, perhaps, and the circuit can be made by removing a heavy negative bias from the thyratron grid. However it must be broken in some other way, perhaps manually with a push button. Depending on the applica- tion, this may or may not put the thyratron out of court. 'Off'button Jk 0 200-500 volts IT \ -rwmwiv- 0 350 volts tlr Ml Control potential Figure Control potential Figure If the supply is , then the grid can be used both for switching on and off. For example, in Figure the thyratron acts both as a switch and as a rectifier. If the grid is at cathode potential we have virtually a soft diode choke input rectifying circuit feeding + ripple to the load. When the upper generator terminal is negative the thyratron anode is negative with respect to the cathode and no conduction can occur. When A is positive the 130
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