| 摘要 |
1,230,696. Protecting transistor amplifiers by signal limiting; switching between amplitude limits. SIEMENS A.G. 6 May, 1969 [6 May, 1968], No. 23144/69. Heading H3T. An amplifier is protected against overvoltage by means of a field effect transistor connected to the input and controlled via a threshold device from the output. In Fig. 1 the amplifier 1 is of the chopper type and is protected by a field effect transistor which becomes conductive when the output exceeds positive and negative threshold values determined by circuit D. In Fig. (2), not shown, protection is effected by both series and shunt transistors and in Fig. 3 the protecting transistor is in a negative feedback path. In circuit D, when the input signal goes positive the base follows the signal more slowly than the emitter because of the potentiometer R6, R7 in the base circuit and a point is reached at which the transistor becomes conductive and so renders the field effect transistor conductive. For negative going signals a point is reached where the emitter potential is clamped but the base follows until transistor Tr conducts, again making the field effect transistor conduct. |
