| 摘要 |
PURPOSE:To prevent the lowering in the voltage of a condenser, by directly applying a peak hold prohibiting signal to the second input terminal of a differential amplifying circuit. CONSTITUTION:When a signal A is at an L-level, the title circuit achieves peak hold function. That is, when a signal B is inputted as positive voltage, a Tr (transistor) 20 is transferred to an ON-side and Tr21 to an OFF-side and the collector currents of Tr23, 24 increase. By this mechanism, Tr30 is turned ON and a condenser 29 is charged and, when the voltage of the condenser 29 rises, the emitter potential of Tr27 rises and Tr21 is transferred to an ON- side while Tr20 to an OFF-state and Tr30 is turned OFF. When the signal B changes to a negative side, Tr20 is more turned OFF and Tr21 is more turned ON and Tr27 is driven by the voltage of the condenser 29 and Tr21 is further transferred to an ON-side and the voltage of a signal C is kept constant. In this case, because Tr21 is saturated to increase a base current and VBE of Tr27 increases and Tr26 prevents the potential drop of the signal C, a collector current is supplied to Tr21. Next, when the signal A comes to an H-level, the discharge of the condenser is stopped.
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