STABILIZED DC POWER SUPPLY

PURPOSE:To make the operation of a whole circuit smoother, by installing a serial control circuit composed of serial control transistors to the rear step of a positive feedback type differential amplifier circuit. CONSTITUTION:A high frequency pulse outputted from a pulse width modulator circuit IC is inputted into the primary winding N1 of a high frequency transformer T through a switching transistor Tr1. The boosted pulse voltage is inputted into a current limiting circuit III after it is rectified and smoothed at a rectifier circuit IV and smoothing circuits L and C. The output of the circuit III is stabilized through a serial control circuit IIand a regulated voltage E0 is obtained from the output terminal of the circuit II. Moreover, a positive feedback type differential amplifier I is connected with a negative feedback route starting from the output terminal and ending at the serial control circuit II and amplifies the difference between a reference voltage and output voltage. Therefore, when the output voltage E0 increases, electric currents flowing through a transistor Tr2', whose control voltage is a both-ends voltage V1 flowing through a resistance R15, increase and another electric current flowing through another transistor Tr2 decreases and, as a result, increase of the output voltage V0 is suppressed.