OUTPUT LIMIT SYSTEM

PURPOSE:To decrease the collector loss of an output transistor (TR) to fluctuation of a load, by limiting the amplitude of an output voltage in response to the change in power supply voltage. CONSTITUTION:When a power supply voltage drops and an input voltage of a comparator A1 attains a reference value or below, an output of the comparator A1 turns to negative. Thus, TRsQ4 and Q5 are turned off. The base voltage of TRsQ1 and Q2 is a voltage division of power supply voltage by resistors R3, R4 and R5. Then, the collector voltage of the TRQ1 is the sum of a base voltage, a VBE and a forward voltage of a diode D1. The collector voltage of the TRQ2 is the subtraction of the base voltage of the TRQ2 from the VBE and a forward voltage of a diode D2. Thus, a large current flows to an output stage and a power supply voltage is decreased, then the amplitude of the output voltage at a terminals 2 can be limited automatically.