| 摘要 |
PURPOSE:To guarantee the safety of a load circuit by allowing a diode to clamp a base potential of a transistor (TR) inputted in a differential way so as to regulate an upper limit and a lower limit of a voltage impressed to the load circuit. CONSTITUTION:Cathodes of diodes 23, 30 are connected to inputs A, B of a power amplifier comprising TRs 21, 23, 28 and 29. Voltages V1, V2 of non- inverting/inverting phase corresponding to an input Vin are impressed to an input of the power amplifier so as to flow a current I1 or I2 controlled by a base current to the load circuit 26. When the input becomes negative in this case, the current I3 or I4 flows to the diode 23 or 30 so as to decrease the base potential of the TR22 or 29 from a common by a voltage drop's share of the diode. Thus, the emitter potential of the TR22 or 29 approaches nearly a common potential, allowing to regulate the voltage applied to the load circuit 26.
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