Patent ID: 7239046

Claim:
An electric power supply unit comprising: a first electric power supply circuit connected to a first power supply line; a second electric power supply circuit connected to a second power supply line; and a first amplifier having a power supply input supplied with an output voltage of the first electric power supply circuit; a second amplifier having a power supply input supplied with an output voltage of the second electric power supply circuit; and a voltage control circuit comprising: a first comparator that compares the output voltage of the first electric power supply circuit and a reference voltage value; a second comparator that compares the output voltage of the first electric power supply circuit and the output voltage of the second electric power supply circuit; a first control circuit that controls the output voltage of the first electric power supply circuit to be substantially constant based on an output of the first comparator; and a second control circuit that controls the output voltage of the second electric power supply circuit to be approximately equal to the output voltage of the first electric power supply circuit based on an output of the second comparator.