PURPOSE: To supply a constant voltage at all times by a method wherein a capacitor is connected between a positive pole terminal, in which a rectifying and smoothing circuit and a voltage stabilizing circuit are connected to the output unit of a low voltage side between two sets of secondary side output windings, and the positive pole terminal of the rectifying and smoothing circuit of high voltage side.

CONSTITUTION: The output of the secondary side winding 251 of an output transformer 25 in a power source device 20 is set so as to be higher tban the output of another secondary side winding 252. Normally, the power source device 20 is controlled through negative feedback by a signal from the output signal generating unit 30 of the first output unit 28 of high voltage side whereby the output of the first output unit 28 is made constant. The output of the second output unit 33 of low voltage side is made constant in some degree through the negative feedback and the output, rectified and smoothed in a rectifying and smoothing circuit 34, is supplied to a load 36 through a voltage stabilizing circuit 35. When a load 32 is fluctuated and the output of the output signal generating unit 30 becomes high, the output of the winding 252 is reduced through negative feedback control. The output voltage of the rectifying and smoothing circuit 34 tries to be reduced, however, the output voltage is maintained at a normal value by the discharging of a capacitor 37. According to this method, a constant voltage is supplied to the load at all times.