Patent ID: 6972547

Claim:
A power supply for positive and negative output voltages, comprising: a switching power supply circuit having: a coil; a switch, series-connected with said coil, for switching energization of said coil by a voltage supplied from an input power supply to said coil; a rectifying and smoothing circuit for rectifying and smoothing a voltage at a series connection point between said coil and said switch and for outputting a resultant voltage as a positive output voltage; a positive output voltage detecting circuit for generating a positive output voltage detection voltage from the positive output voltage; and a control circuit for performing on-off switching of said switch so that the positive output voltage detection voltage is equal to a reference voltage; a negative output voltage setting circuit for generating a negative output voltage setting voltage, which is lower than the positive output voltage by a predetermined voltage; and a negative output voltage generating circuit for generating a negative output voltage, whose magnitude corresponds to that of the predetermined voltage, according to the voltage at the series connection point between said coil and said switch and to the negative output voltage setting voltage.