Patent ID: 7414820
Filing Date: 2008-08-19
Classification: H02H

Abstract:
1. A protective apparatus for preventing an electrical device from being electrically damaged, the device is connected to an AC circuit via the protective apparatus, the circuit comprising a live line, a neutral line, and an earth line, the protective apparatus comprising; a detector connected between the neutral line and the earth line, the detector comprising a rectifier-filter circuit, a detection circuit, and an isolating circuit connected in series, the detector converting an abnormal AC voltage between the neutral line and the earth line, when a misconnection occurs, to a stable DC voltage; and a controller connected between the live line and the neutral line, the controller receiving and driven by the stable DC voltage of the detector, the controller allowing power to the device in a normal working state and disconnecting from the device when the misconnection occurs between the live line and the neutral line, the controller comprising a field-effect transistor having a control terminal receiving a start voltage, a power terminal, and a ground terminal, a winding with an iron core, and a switch, the ground terminal connected to ground via the winding, the switch attracted by the iron of the winding when the transistor is turned on to disconnect the live line and the neutral line; wherein the detector further comprises a voltage grading circuit, the voltage grading circuit comprises a first resistor and a second resistor connected in series between the neutral line and the earth line; wherein the rectifier-filter circuit comprises a diode, a capacitor, and a tantalum capacitor, an anode of the diode is connected to a node between the first and second resistors, a cathode of the diode is connected to a cathode of the tantalum capacitor, an anode of the tantalum capacitor is grounded, the capacitor is connected in parallel to the tantalum capacitor; wherein the rectifier-filter circuit further comprises a Zener diode, an anode of the Zener diode is grounded, a cathode of the Zener diode is connected to the cathode of the tantalum capacitor; and wherein the detection circuit comprises a third resistor, a forth resistor, a fifth resistor, a first transistor, a second transistor, one end of the third resistor is connected to the cathode of the diode, the forth resistor is connected to the other end of the third resistor and the earth line, a base of the first transistor is connected to a node between the third and forth resistors, an emitter of the first transistor is grounded, the fifth resistor is connected between a collector of the first transistor and a base of the second transistor, an emitter of the second transistor is connected to the cathode of the diode.