Power supply switching apparatus with protection function for supplying power to an electronic circuit via an external power source or an internal power supply source

摘要

A power supply switching apparatus for electronic equipment including a first control circuit connected to a battery. The first control circuit monitors a power supply voltage of the battery to output a first control signal when the power supply voltage of the battery is lower than a first predetermined voltage. The first control circuit also outputs a second control signal when the power supply voltage of the battery is higher than a second predetermined voltage. A second control circuit monitors whether power is supplied from an external power supply to the electronic equipment, to generate a third control signal when the power is not supplied from the external power supply. The second control circuit generates the third control signal regardless of whether the second control signal is present, when power is supllied from the external power supply. A switching circiut section supplies power from the battery to the internal circuit when the first and third control signals are not present. The switching circuit section disconnects the battery from the internal circuit in response to the first or third control signal.