CONSTANT VOLTAGE POWER SUPPLY CIRCUIT

PURPOSE:To expand a current supply area by using plural normal transistors (TRs) having low allowable power consumption to constitute a constant voltage power supply circuit. CONSTITUTION:About -21V voltage is applied to the base of a TR Q2 through a Zener diode 1 and a resistor 2. When a load is connected to an output terminal P, output current is made to flow to the terminal P, but the TRs Q2, Q5 operate like Darlington connection in a small output current range A and the output current is made to flow from the load to the power supply (-48V) through a ground, resistors 4, 5, a TR Q5, and the output terminal P. When the output current is increased and included in a range B, the interval of the collector and emitter of the TR Q5 is extremely reduced and shorted and the base-emitter almost acts as a diode, so that the output current is supplied to the load through the a parallel circuit consisting of the TR Q2 and the resistor 5.