| 摘要 |
1480301 Transistor amplifiers INTERNATIONAL STANDARD ELECTRIC CORP 29 July 1975 [5 Aug 1974] 31667/75 Heading H3T An amplifier, e.g. for a telephone microphone M, which is insensitive to the polarity of the D.C. supply, comprises first and second multistage amplifiers connected generally in parallel, corresponding transistors in each amplifier being complementary to each other, the amplifier which operates depending on the supply polarity, and biasing means being provided responsive to the operation of one amplifier to disable the other. Transistors SC1, SC3, SC5 form the first amplifier and SC2, SC4, SC6 the second. When SC1 &c. is operating SC2 &c. is biased off by the collector-base leakage current of SC6, which holds SC4 off. A transistor SC7 provides regulating means for operation over a range of supply currents, the collector current of SC7 increasing if the supply current through R17 increases because the base-emitter voltage of SC7 depends on the voltage between the points E and B. With low currents through R11, R14, diode D3 does not conduct, but with sufficient current D3 clamps the voltage across R14, and the voltage across R11 controls SC7. Conversely, when SC2 &c. is operating SC3 is biased off by the leakage current of SC5, and SC8 with R12, R15 and D4 regulate the supply current. Diodes D1, D2 temperature compens sate SC1, SC2 respectively, and mirror across the microphone M the voltage drops across R7, R8. Positive feedback to shape the frequency response is provided by C4, R16. |
