Abstract: A power supply circuit which ceases the supply of power to an external device if the ground connection of the external device is broken includes a connector module, a test module, and a switch module. The connector module connects to the external device. The test module tests the connection between the connector module and the external device and can output a first or a second signal. The switch module is connected between the test module and the connector module, when the switch module receives the first signal from the test module, the switch module permits a connection between the connector module and power supply. When the switch module receives the second signal from the test module, the switch module disconnects the connector module from the power supply.

Abstract: A frequency adjustment system includes a phase-locked loop (PLL) circuit, an adjusting circuit, and a voltage regulator module (VRM). The PLL circuit outputs a trigger signal when a communication frequency of a chip changes. The adjusting circuit adjusts a clock frequency of the adjusting circuit to receive communication data. The adjusting circuit further outputs a control signal to the VRM. The VRM outputs a voltage according to the control signal.

Abstract: A power supply circuit includes a load, a chargeable battery, a discharging circuit, a charging circuit, an adapter, and a control circuit. When the adapter operates normally, the control circuit measures a voltage of the chargeable battery, and controls the charging circuit to charge the chargeable battery when the voltage of the chargeable battery is less than a preset value. The control circuit measures a charging current and a temperature of the chargeable battery, and regulates the charging current through the charging circuit according to the measured charging current and temperature. The adapter provides a voltage to the load through the discharging circuit. When the adapter is powered off, the control circuit does not sense a voltage a voltage from the adapter. The control circuit controls the chargeable battery to power the load through the discharging circuit.