| 摘要 |
1,026,983. Protecting transistor circuits. E. K. COLE Ltd. July 28, 1964 [Aug. 9, 1963], No. 31450/63. Heading H3T. [Also in Divisions G3 and H2] In a static inverter the semi-conductor switching devices are protected from current overloads by a sensing circuit which reduces the conduction angle of the devices and at the same time utilizes a predominant harmonic of the inverter fundamental frequency present in the output current waveform to operate a cut-out in the load circuit. Under normal load conditions voltage feedback from across the load R 2 to a regulating stage 2 maintains a constant output voltage by varying the conduction angle of the semi-conductor devices in the inverter output stage 3, and a filter circuit L 1 , C 1 connected across an output transformer T 1 and resonant at the fundamental frequency results in the current through the load comprising mainly the fundamental frequency. An output current control circuit comprising C 2 , D 1 , D 2 , R 1 and a current transformer T 2 generates a control potential which is applied to the regulating stage 2 and which is arranged to override the output voltage feedback for output currents above a predetermined threshold value. Under short-circuit load conditions an inductance L 2 (whose impedance at the fundamental frequency is low compared with R 2 ) is effectively in shunt with L 1 and C 1 and its value is chosen so that the combination L 1 , L 2 , C 1 resonates at a predominant harmonic of the fundamental frequency. The values of C 2 , R 1 and the turns ratio of T 2 may be chosen to favour the production of this harmonic under short-circuit load conditions. With a large harmonic content in the output waveform due to resonance of the combination L 1 , L 2 , C 1 the RMS current through the fuse 8 is higher than for a predominantly fundamental output and is sufficient to operate the fuse 8. In various modifications the inverter may be provided with more than one output, T 2 may be connected on the load side of T 1 , L 1 may form part of T 1 , L 1 , C 1 may be connected across the inverter side of T 1 , or T 1 may be omitted altogether. |
