Abstract: The invention provides a transient voltage detecting circuit for detecting changes of voltage in an electronic system which has a first power supply (VDD), a second power supply (VDD), a third power supply (VDD), a fourth power supply (VDD), a first ground (GND), and a second ground (GND). The voltage of the first VDD is substantially equal to that of the second VDD. The voltage of the third VDD is substantially equal to that of the fourth VDD. The voltage of the first GND is substantially equal to that of the second GND. The circuit according to the invention can detect a positive or negative transient voltage once that occurs at the first VDD, the second VDD, the third VDD, or the fourth VDD.