Ground fault circuit interrupter control circuit

A ground fault circuit interrupter (GFCI) control circuit for providing an indicator or trip at the end of life. A GFCI with a monitor circuit added, in addition to common functions, is intended to automatically detect and indicate an abnormity of the circuit. Once any abnormity occurs to the elemental parts, the control circuit will indicate the malfunction or trip directly and stop the flow of electricity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a ground fault circuit interrupter (GFCI) control circuit, which is intended to give an indicator or trip at the end of life.

2. Description of the Related Art

Conventional ground fault circuit interrupters (GFCIs) trip only in the event of a ground fault and are incapable of detecting a malfunction of the circuits themselves. Thus, GFCIs will not trip against the unwanted affects of electric leakage if the circuits themselves are damaged, thus putting people and property in danger.

SUMMARY OF THE INVENTION

In view of the above, an object of the present invention is to provide a ground fault circuit interrupter (GFCI) control circuit with a life-end indicator, which will give an indictor in advance of failure of the GFCIs or trip the GFCI directly in the event of an abnormity.

A technical solution in accordance with an embodiment of the present invention for solving its technical problem is as follows:main input lines1H and2N pass through an inductor L1; a capacitor C1and a capacitor C2are connected in serial and then connected in parallel with the inductor L1; a common node between the capacitor C1and the capacitor C2is connected to a negative end of a power supply via a resistor R5; one end of the inductor L1is connected to a pin1of a Single-Chip Microcomputer (SCM) IC1via a capacitor C5and a resistor R6connected in serial, and the other end of the inductor L1is connected to a pin3of the SCM IC1for detecting electric leakage; a pin5of the SCM IC1is connected to a resistor R14and connected to ground via a capacitor C10, for driving a silicon controlled rectifier SCR2; the silicon controlled rectifier SCR2is connected in serial with diodes D5, D6, D7and D8and a tripping relay RELAY-2; a power pin6of the SCM IC1is connected to a resistor R11and a cathode of a Zener diode D3; an anode of the Zener diode D3is connected to an anode of a diode D9in serial; a cathode of the diode D9is connected to ground via an anode of a light-emitting diode D2; the power pin6of the SCM IC1is connected to a cathode of a Zener diode D10; an anode of the Zener diode D10is connected in serial with a resistor R13; another end of the resistor R13is connected to a base of a transistor Q1, whose emitter is connected to the negative end of the power supply and the collector is connected to the anode of the light-emitting diode D2via a resistor R10; a reset circuit is connected to the main power supply and connected in serial with S2via a capacitor C7and a resistor R8connected in parallel; another end of S2is connected to a control pin of a silicon controlled rectifier SCR1; the control pin of the silicon controlled rectifier SCR1is connected in parallel with a resistor R9and a capacitor C6to form an instant trigger circuit; the silicon controlled rectifier SCR1is connected with a self-holding relay RELAY-1.

An anode of the silicon controlled rectifier SCR2is connected to a positive end of a bridge rectifier comprising the diodes D5, D6, D7and D8; a cathode of the silicon controlled rectifier SCR2is connected to a negative end of the bridge rectifier comprising the diodes D5, D6, D7and D8; an AC input of the rectifying bridge is connected in serial with the tripping relay RELAY-2; another end of the tripping relay RELAY-2is connected to a phase line of the power supply.

An end of an output phase line is connected with an anode of a light-emitting diode D1; a cathode of the light-emitting diode D1is connected in serial with a resistor R4; another end of the resistor R4is connected to an anode of a diode D4; a cathode of the diode D4is connected to a neutral power supply line.

The control circuit of the present invention provides the following advantages. In normal cases, the control circuit can trip reliably upon occurrence of electric leakage. In case of standby, i.e. when no electric leakage occurs, if the GFCI itself encounters an abnormity, the control circuit can generate an indication with the light-emitting diodes so that people can discover the abnormity as soon as possible, or the control circuit can directly trip, in order to reduce occurrences of accidents that may cause injury or death or damage to equipment, due to failure of tripping upon occurrence of electric leakage caused by the malfunction of the GFCI itself.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

As shown inFIG. 1, according to the present invention, main input lines1H and2N pass through an inductor L1. A capacitor C1and a capacitor C2are connected in serial and then connected in parallel with the inductor L1. A common node between the capacitor C1and the capacitor C2is connected to a negative end of a power supply via a resistor R5. One end of the inductor L1is connected to a pin1of a Single-Chip Microcomputer (referred to as “SCM” hereinafter) IC1via a capacitor C5and a resistor R6connected in serial. The SCM IC1may be, for example, RV4145 or 54123. The other end of the inductor L1is connected to a pin3of the SCM IC1for detecting electric leakage. A pin5of the SCM IC1is connected to a resistor R14and connected to ground via C10, for driving a silicon controlled rectifier SCR2. The silicon controlled rectifier SCR2is connected in serial with diodes D5, D6, D7and D8and a tripping relay RELAY-2. A power pin6of the SCM IC1is connected to a resistor R11and a cathode of a Zener diode D3. An anode of the Zener diode D3is connected to an anode of a diode D9in serial. A cathode of the diode D9is connected to ground via an anode of a light-emitting diode D2. The power pin6of the SCM IC1is connected to a cathode of a Zener diode D10. An anode of the Zener diode D10is connected in serial with a resistor R13. The other end of the resistor R13is connected to a base of a transistor Q1, whose emitter is connected to the negative end of the power supply and collector is connected to the anode of the light-emitting diode D2via a resistor R10. A reset circuit is connected to the main power supply and connected in serial with S2via a capacitor C7and a resistor R8connected in parallel. Another end of S2is connected to a control pin of a silicon controlled rectifier SCR1. The control pin of the silicon controlled rectifier SCR1is connected in parallel with a resistor R9and a capacitor C6to form an instant trigger circuit. The silicon controlled rectifier SCR1is connected with a self-holding relay RELAY-1. An anode of the silicon controlled rectifier SCR2is connected to a positive end of a bridge rectifier consisting of the diodes D5, D6, D7and D8. A cathode of the silicon controlled rectifier SCR2is connected to a negative end of the bridge rectifier consisting of the diodes D5, D6, D7and D8. An AC input of the rectifying bridge is connected in serial with the tripping relay RELAY-2. The other end of the tripping relay RELAY-2is connected to a phase line of the power supply. An end of an output phase line is connected with an anode of a light-emitting diode D1. A cathode of the light-emitting diode D1is connected in serial with a resistor R4. The other end of the resistor R4is connected to an anode of a diode D4. A cathode of the diode D4is connected to a neutral power supply line.

In connecting, an AC power supply is delivered via connection terminals and the two main input lines1H and2N that pass through the inductors L1and L2, controlled by a main contact, and then provided to loads via output terminals. In case of standby, the input line1H, a fuse F1, the coil RELAY-2, the diodes D5, D6, D7and D8for rectifying, and 2N constitute a loop for outputting a DC power supply, the voltage of which is reduced by a resistor R12and then supplied to the IC1. The inductors L1and L2, the resistors R6and R7, the capacitors C1, C2, C3, C4and C5, and IC1together constitute an electric leakage detection circuit. Upon the occurrence of electric leakage, an inductive current will be generated in L1, causing variations at the input terminals1and3of IC1and generating an output at the pin5, such that the silicon controlled rectifier SCR2is driven to power the tripping coil RELAY-2, and the main contact is disconnected.

An abnormity monitoring circuit includes four parts: 1) a part for monitoring electric leakage or a short of the leakage current detecting elements C1and C2; 2) a part for monitoring over-voltage of the power supply of IC1; 3) a part for monitoring under voltage of the power supply of IC1; and 4) a part for giving an indicator or tripping when either one or both of SCR1and SCR2are broken down.

Either electric leakage or short of C1and C2will cause the inputs of IC1varying, resulting in an output from IC1, such that the tripping coil is powered and the main contact is disconnected. D3, D9, R11and D2together constitute a power supply over-voltage monitoring circuit, wherein D2is lighted when the power supply voltage is higher than a set value, indicating an abnormal operation. D10, R13and Q1together constitute a power supply under voltage monitoring circuit, wherein D2is lighted when the power supply voltage is lower than a set value, indicating an abnormal operation of the GFCI. The breakdown of the reset silicon controlled rectifier SCR1or the tripping silicon controlled rectifier SCR2will cause the coil to overheat, such that F1will melt and the light-emitting diode D2will light, indicating an abnormal operation. When SCR2is broken down, the tripping coil is powered, the main contact is disconnected, and the loads are cut off. The output indicating lamp D1turns off. In any case, if the main contact is disconnected, the output indicating lamp D1will turn off. The detailed analysis is provided as follows.

Situation 1. In case of monitoring electric leakage and short of the leakage current detecting elements C1and C2:C1and C2are connected in series, with un-common ends connected to the detection coil L1in parallel, equal to the situation that a capacitor with a capacity of half the capacity of C1and C2is connected with L1in parallel. The common end of C1and C2is connected to the negative end of the power supply via the resistor R5with large resistance. When electric leakage occurs at either or both of the capacitors C1and C2, signals at the inputs of IC1will vary and the voltage decrease, such that a control signal is output from the pin5of IC1. As a result, SCR2and the tripping coil are powered, the main contact is disconnected to cut off the loads, and D1turns off.

Situation 2. In case of the power supply over-voltage of IC1:R11and the cathode of D3are connected in series. The anode of D3and the anode of D9are connected in series. The other terminal of R11is connected to the power pin6of IC1. The cathode of D9is connected to the anode of the light-emitting diode D2. The cathode of the light-emitting diode D2is connected to the negative end of the power supply. When the supply voltage exceeds a rating value of D3, D9, D2connected in series (which may be specific to IC), the light-emitting diode D2is lighted. Because R10is connected with the transistor Q1in series, even Q1turns on at this time, D2can be lighted properly, indicating an abnormity of the power supply of IC1.

Situation 3. In case of the power supply under voltage of IC1:The cathode of D10is connected to the power pin of IC1, while the anode thereof is connected with the resistor R13in series. The other terminal of the resistor R13is connected to the base of the transistor for driving the transistor. If the supply power is in a normal state, i.e. higher than a sum of a voltage drop across D10and a voltage between the base and emitter of the transistor (0.7V), the transistor Q1turns on, to keep the voltage across the light-emitting diode D2at about 0.3V, such that D2will not illuminate. If the power supply voltage is too low, i.e. lower than the sum of the voltage drop across D10and the voltage drop between the base and emitter of the transistor (0.7V), the transistor Q1will turn off, and the power is supplied through R2, R2and R10to the anode of the light-emitting diode D2, such that the light-emitting diode D2will illuminate. Because of inverse connection of D9, current will not flow through D9, D3, R11, and the pin6of IC1to ground, indicating that the power supply voltage of IC1is too low.

Situation 4. In case of breakdown of either or both of SCR1and SCR2:An indication is generated and tripping is performed. Breakdown of either or both of the elemental components SCR1and SCR2will cause the reset coil RELAY-1and/or the tripping coil RELAY-2to be powered for a long time, such that the coil will be overheated and the fuse F1will melt, preventing the accident from escalating and preventing a potential fire from occurring. Meanwhile, because no current flows through the coil, the resistor R16is connected in series in the whole main circuit, causing the power supplied to IC1to significantly decrease. As analyzed in situation 3, the light-emitting diode D2is lighted, indicating abnormity of the GFCI. However, only when SCR2is broken down, the GFCI trips, the main contact is disconnected, and the loads are cut off. In case that RELAY-2is continuously powered and heated, the fuse F1is melted and the light-emitting diode D2is illuminated.

The above embodiments are provided for the purpose of example only, and are not intended to limit the present invention. It is to be understood by those skilled in the art that there may be various modifications or replacements to the embodiments without departing from the scope and spirit of the present invention, and they shall fall into the scope defined by the appended claims.