Schaltbarer elektrischer Stromkreis

摘要

1,108,945. Semi-conductor switching circuits. ENERGY CONVERSION DEVICES Inc. 9 April, 1965 [10 April, 1964], No. 15084/65. Addition to 1,070,412. Heading H3T. [Also in Divisions H1 and H2] A switchable A.C. circuit comprises a load and a series-connected pair of semi-conductor bodies or layers of the type described in Specification 1,109,102 which go conductive above an upper threshold value of applied voltage amplitude and revert to a non-conductive state when the amplitude falls below a lower threshold. The amplitude of the supply voltage is less than the sum of the upper threshold voltages of the layers and the control circuit, connected in parallel with one of the layers is designed to apply a voltage in excess of the upper threshold to the other layer to switch it on. The control circuit impedance is such that with the other layer conductive the voltage across the first layer exceeds the threshold to render it conductive thus short-circuiting the control circuit. Near the end of each half cycle the layers go non-conductive but conduction is re-established in the succeeding halfcycle providing the lower threshold voltage of the series layer is exceeded. In a typical circuit the control circuit consists of a mechanical switch in series with a resistor having a value intermediate the resistances of the parallel layer in its two states. Alternatively, in a circuit for controlling the value of a physical variable e.g. temperature or pressure by a heater or pump which consistitutes or is operated by a relay constituting the load, the circuit consists of a resistor controlled by the variable. For example a heater may be controlled by a resistor the value of which increases with temperature to reduce the voltage across the series layer below the threshold and thus open circuit the heater. When the temperature falls to a certain level the voltage across the series layer exceeds the upper threshold and the circuit is re-established. The sensitivity of the resistor and closeness of the upper and lower threshold voltages determine the precision of the temperature control. In alternative circuits e.g. that shown in Fig. 7, the control circuit consists of the secondaries of one or more control signal transformers and a resistor 2711 the value of which is such that both layers remain non- conductive in the absence of a control signal. When a suitable signal is applied by closing switch 30 or 301 the threshold voltage of the series layer, in this case the end of layer 10b is exceeded to close the load circuit. Instead of the OR control thus provided AND control may be obtained by connecting the transformer secondaries in series.