Patent ID: 7638902

Claim:
A dual-power supplying system, comprising: a first voltage output circuit loop with an output transformer, which receives a first power source and supplies, in turn, a first output voltage through the output transformer to an output terminal; a second voltage output circuit loop, which receives a second output voltage from a second power source and selectively supplies the second output voltage to the output terminal; and a circuit loop switching control circuit, which comprises an induction coil coupled with the output transformer to detect the first output voltage of the first voltage output circuit loop, and a switching element connected in series to the second voltage output circuit loop, the switching element having an open-circuit condition and a closed-circuit condition, which are switched by a switching driving signal generated by the induction coil of the circuit loop switching control circuit; wherein when the first power source is supplied through the first voltage output circuit loop to the output terminal, the induction coil of the circuit loop switching control circuit generates the switching driving signal to switch the switching element of the circuit loop switching control circuit to the open-circuit condition thereby cutting off the second voltage output circuit loop; and wherein when the first voltage output circuit loop fails to supply the first power source to the output terminal, the switching element is set in the closed-circuit condition to allow the second power source to be supplied through the second voltage output circuit loop to the output terminal.