Improvements in or relating to circuit arrangements for safeguarding transistors

摘要

928,584. Automatic voltage control systems. PHILIPS ELECTRICAL INDUSTRIES Ltd. April 20, 1960 [April 23, 1959], No. 13837/60. Class 38 (4). [Also in Group XL (c)] Junction transistors connected as cascaded emitter followers in a voltage stabilizer are protected from an excessive collector voltage supply by connecting a Zener diode between collector and base of the first transistor. The voltage stabilizer shown comprises input terminals 10 for the unregulated supply and output terminals 11 for the regulated supply. A portion of the output voltage derived from a potentiometer 16 is compared in a comparator 14, 15 with the voltage developed across a Zener diode circuit 12. The resulting variations at the collector of transistor 15 are fed through emitter follower stages 18, 19 and 20 to control transistors 21, 22 &c. connected in series with the supply so as to stabilize the output voltage. An excess input voltage will cause the Zener diode 30 to break down and so protect the transistor 18 by limiting the collector base voltage. Transistors 19-22 being connected in the emitter follower fashion to transistor 18 are also protected against over voltage. Transistors 13 and 14 are protected against the over voltage by providing a series transistor 23 in their common collector circuit. Excessive rise in voltage across terminals 10 will cause potentiometer 25 to apply a sufficient voltage to the emitter of transistor 13 to cut the transistor off. The voltages then applied by potentiometers 25 and 24 to transistors 14 and 23 are such that the maximum permissible collector base voltage of transistors 13 and 14 is not exceeded. A capacitor 31 is provided to prevent oscillation in the circuit.