Surge protection device

A surge protection device comprising:

• a pulse controlled switch being a pulse relay, adapted to connect in series to a power line loop and having:
• an excitation coil having a forward control terminal and a reverse control terminal;
• and
• two switch contacts controlled by the excitation coil and adapted to connect in series to or disconnect from the power line loop;
• a pulse generation circuit having:
• an input terminal adapted to connect to the power line loop and located in a front end of the pulse controlled switch;
• an output terminal connected to the forward control terminal of the excitation coil of the pulse controlled switch;
• a control button;
• a first transistor being a PNP transistor, wherein an emitter of the first transistor is adapted to connect to the power line loop, and a collector of the first transistor is connected to the forward control terminal of the excitation coil;
• and
• a second transistor being an NPN transistor, wherein a collector of the second transistor is connected to a base of the first transistor, and a base of the second transistor is adapted to connect to the power line loop through the control button;
• and
• an abnormal voltage detection circuit having:
• at least one detection input terminal adapted to connect to the power line loop and located in a back-end of the pulse controlled switch;
• an output terminal connected to the reverse control terminal of the excitation coil of the pulse controlled switch;
• a detection input unit having multiple first diodes connected in series with one another and having:
• multiple detection input terminals adapted to connect to the power line loop;
• and
• an output terminal;
• a reverse loop control unit having a second diode, a first resistor and a third transistor connected in series between the forward control terminal of the excitation coil and the power line loop, wherein a base of the third transistor is connected to the output terminal of the detection input unit, and an emitter of the third transistor is grounded;
• and
• a surge-filtering unit having a third diode, a second resistor, a capacitor and a first zener diode, wherein an input terminal of the surge-filtering unit is connected to the output terminal of the detection input unit, and a node connected in series between the second resistor and the capacitor is connected to the base of the third transistor of the reverse loop control unit through the first zener diode;
• wherein
• when the control button is pressed, a pulse is transmitted to the base of the second transistor, when the second transistor is turned on, the first transistor is turned on and a current passing through the first transistor sends another pulse to the forward control terminal of the excitation coil to close the two switch contacts of the pulse controlled switch and connect the switch contacts to the power line loop;
• and
• when the abnormal voltage detection circuit detects an abnormal voltage occurring on the power line loop, a pulse generated by the abnormal voltage detection circuit is sent to the reverse control terminal of the excitation coil to control the two switch contacts of the pulse controlled switch to be open and disconnected from the power line loop.