| 摘要 |
1,040,642. SCR switching circuits. STANDARD TELEPHONES & CABLES Ltd. Jan. 31, 1964 [Feb. 4, 1963], No. 4206/64. Heading H3T. A control circuit comprises a linear impedance in series with two semi-conductor devices which can exist in high and low conductance states, one of these being triggered into a high conductance state by an input signal at an auxiliary electrode, and means responsive to the current through the circuit to develop output signals. In Fig. 1 the impedance is a resistor 20 and the semi-conductor devices are an SCR 16 and a four-layer diode 18 respectively. The devices 18, 16, 32, 34 are non-conducting, and capacitor 24 is charged, until an input pulse 10 arrives which is large enough to overcome the threshold bias across the diodes 32, 34. When a large enough pulse arrives, the SCR 16 fires, and the voltage across the four-layer diode 18 is sufficient to cause that to conduct also. Capacitor 24 then discharges through the four devices and the pulse transformer 22 to provide an output at the secondary. Positive feedback through capacitor 44 ensures rapid switching. When capacitor 24 has discharged to a certain point, the current supplied by this and by resistor 20 is no longer sufficient to maintain conduction in the devices 16, 18 and the circuit reverts to its former condition. The holding current of the diode 18 should be higher than that of the SCR. Within certain limits of desired output pulse frequency and width the transformer 22 may be replaced by a resistor. The circuit may be used to drive a counter to operate a stepping relay and servomotor in a tracking radar which detects a predetermined relationship between transmitted pulses from a aircraft and reply pulses from a ground station. |
