Voltage selecting circuit, voltage providing circuit utilizing the voltage selecting circuit, and signal delaying system utilizing the voltage providing circuit

A voltage providing circuit, comprising:

• a first voltage providing circuit, for providing a first voltage;
• a switch element, for receiving the first voltage;
• a second voltage providing circuit, for providing a second voltage;
• a control circuit, for controlling the switch element and the second voltage providing circuit, wherein in a first mode, the control circuit turns off the switch element for allowing a target apparatus to receive the second voltage, and in a second mode, the control circuit turns on the switch element, and stops the second voltage providing circuit from providing the second voltage to therefore provide the first voltage to the target apparatus;
• and
• an adjusting circuit, coupled to the first voltage providing circuit and the second voltage providing circuit, for providing a reference voltage to the first voltage providing circuit for altering the first voltage, according to the first voltage and the second voltage, thereby making the first voltage substantially equal to the second voltage.