GENERATING CIRCUIT FOR SWITCHING CONTROL SIGNAL

摘要

PURPOSE:To manage with only one control signal input terminal for switching types of noise reduction, by putting a circuit in three kinds of operation in accordance with a ternary input signal. CONSTITUTION:The reference voltage VREF developed at a connection point J2 is equal to the potential obtained by dividing a power voltage through resistances R1 and R2. The base potential of a transistor (TR) Q1 is a voltage VREF+VBE the voltage VBE of a diode D1 higher than the voltage VREF. The base potential of a TRQ3 is a voltage VREF-3VBE the 3VREF of three diodes lower than the VREF. A switching control signal VS is supplied to the base terminal of a TRQ2. When the VS is nearly equal to the power voltage, the base potential of the TRQ2 is VREF+2VBE and higher than the base potential of the TRQ1, so the TRQ1 turns off and the TRQ2 turns on to generate a control signal (c), placing a noise reduction circuit in mode (c). When the VS is as high as the VREF, the TRQ1 turns on and the TRQ2 turns off to generate a control signal (b).