GB594732A - An improved thermionic voltage regulator - Google Patents

Abstract

594,732. Automatic control systems for supply systems. BARTLETT, J. G. May 23, 1945, No. 12948. [Class 38 (iv)] Current; voltage.-In a thermionic voltage regulator, the output current when it tends to exceed the upper limiting value of the range within which a substantially constant output - voltage is maintained, is automatically restricted to substantially the limiting value by reducing the output voltage. In Fig. 2, the D.C. input to the device is applied to terminals 2, 3 and the output taken from terminals 4, 5. The conductance of the thermionic valve 10 is controlled by its grid, the negative potential of which, relative to the anode is a function of the current flowing in resistor 9, which carries the anode currents of both thermionic valves 1 and 7. The current in valve 7 is controlled by its associated grid, the voltage of which is related to the D.C. output voltage between terminals 4, 5 while the anode current of valve 1 is related to the regulator output current which flows through resistor 13 and which biasses valve 1 accordingly. The cathodes of valves 1 and 7 are held at fixed datum voltages relative to terminal 5 by constant voltage discharge tubes 14 and 8. As the output current increases, the output voltage is maintained constant in a known manner by valve 7 until the current limit is reached when the voltage across resistor 13 approaches the voltage across tube 14. At this point valve 1 conducts and assumes control of the 'regulation and reduces the regulator output voltage as the output current tends to increase further. With terminals 4, 5 short-circuited, the valve 10 " cuts off " due to the action of resistor 15. In Fig. 3, the thermionic valves 1, 7 and 10 function similarly to the correspondingly numbered valves in Fig. 2. The load current passes from terminal 4 to terminal 27 through parallel connected resistor 19 and windings 20, 21 of saturating transformer 22, the third winding 23 of which is supplied with high voltage A.C. from terminals 3 and 24. The inductance of winding 23 is an inverse function of the D.C. output current and as the A.C. current flowing through it is maintained substantially constant by the high-valued resistor 25, the A.C. voltage developed across it is a function of its inductance and hence is inversely proportional to the D.C. output current. This voltage is rectified by diode 26 and then applied as negative bias to thermionic valve I, the anode current of which flows through resistor 9 and exercises control of the output voltage through the grid of valve 10. Normally, the valve 1 is " cut off " by the negative bias developed by diode 26 but at a predetermined output current this is exceeded by the positive bias due to the potential drop across discharge tube 8, and the valve 1 conducts to reduce the regulator output voltage and to maintain the current at the limiting value. By means of tapped shunt 19, full scale deflection of meter 18 can be made to correspond to different output currents and windings 20, 21 may be wound with wire of low-temperature-resistance coefficient to minimize the overall temperature coefficient of the meter. In a modification of Fig. 3, valve 1 may be replaced by a grid-controlled gas-filled discharge tube which may be rendered conducting if the output current becomes excessive and will hold the output voltage at zero until the tube is deionized. In another arrangement, Fig. 1 (not shown), the valve 1 is biassed by a separate source, but in this arrangement valve 10 cannot be cut off.