Patent ID: 7982626

Claim:
A detection and alarm circuit for detecting grounding status of an electronic device, comprising: a transformer comprising two input terminals connected to a ground terminal of the electronic device and ground, and a first and second output terminals; a rectifier comprising two input terminals connected to the first and second output terminals of the transformer, respectively, a first output terminal grounded, and a second output terminal; an alarm comprising a first terminal connected to the second output terminal of the rectifier, and a second terminal grounded; a first switch comprising a first terminal grounded via a first resistor and the alarm, a second terminal grounded, and a third terminal connected to a power supply via a second resistor; a second switch comprising a first control terminal connected to the third terminal of the first switch, a second control terminal grounded, a first controlled terminal connected to the ground terminal of the electronic device, and a second controlled terminal; and a light emitting diode (LED) comprising an anode connected to the power supply via a third resistor, and a cathode connected to the second controlled terminal of the second switch; wherein when the ground terminal of the electronic device is well grounded, the transformer and the rectifier do not operate, the alarm is not activated, the first terminal of the first switch is at low voltage level, the first switch is turned off, a current flows through the first and second control terminals of the second switch, the first and the second controlled terminals of the second switch are connected, and the LED emits light; when the ground terminal of the electronic device is not well grounded, the transformer converts an alternating current (AC) to a smaller AC voltage to provide to the rectifier, the rectifier is capable of converting the smaller AC voltage to a direct current (DC) voltage to provide to, and activate, the alarm, the first terminal of the first switch is at high voltage level, the first switch is turned on, no current flows through the first and second control terminals of the second switch, the first and second controlled terminals of the second switch are not connected, and the LED does not emit light.