INPUT DETECTING CIRCUIT USED FOR ELECTRIC-LEAKAGE PROTECTION DEVICES WITH SELF-DIAGNOSTIC FUCNTION

Abstract

An input detecting circuit for an electric-leakage protection device with self-diagnostic function includes an analog electric-leakage unit, a magnetic electric-leakage induction ring, an operational amplifier, and an inverse feedback circuit. The inverse feedback circuit includes a first resistance and a second circuit unit shunted with the first resistance. The second circuit unit includes a second resistance and a unidirectional break-over unit connected in series with the second resistance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the structure scheme of an input detecting circuit used for a kind of electric-leakage protection device with self-diagnostic function in accordance with an embodiment of this invention.

FIG. 2 is the structure scheme of a negative feedback circuit for an input detecting circuit used for a kind of electric-leakage protection device with self-diagnostic function in accordance with an embodiment of this invention.

FIG. 3 is the structure scheme of a negative feedback circuit for an input detecting circuit used for a kind of electric-leakage protection device with self-diagnostic function in accordance with an embodiment of this invention.

FIG. 4 is the structure scheme of a negative feedback circuit for an input detecting circuit used for a kind of electric-leakage protection device with self-diagnostic function in accordance with an embodiment of this invention.

FIG. 5 is the structure scheme for one concrete example of a negative feedback circuit for an input detecting circuit used for a kind of electric-leakage protection device with self-diagnostic function in accordance with an embodiment of this invention.

DETAILED DESCRIPTION OF EMBODIMENTS

As FIG. 1 shows, an input detecting circuit used for an electric-leakage protection device with self-diagnostic function is provided, containing emulation electric-leakage unit 101, magnetic leakage current detecting ring 102 and amplifying circuit 103. The characteristic lies in that it also has a negative feedback circuit 104.

One end of the above-mentioned emulation electric-leakage unit 101 is connected with a forward current, while the other end is connected with a backward current. A unidirectional leakage current produced by that emulation electric-leakage unit 101 will be superimposed on the actual leakage current.

The input current of the electric-leakage detecting circuit is induced by the magnetic leakage current detecting ring 102 after it passes through the forward and backward currents, and outputs the induced current to the amplifying circuit 103.

The amplifying circuit 103 is connected with the magnetic leakage current detecting ring 102, and then outputs the input forward and backward leakage currents after amplifying the currents.

One end of the negative feedback circuit 104 is connected with the input end of a negative terminal of the amplifying circuit 103, while the other end is connected with the output end of the amplifying circuit 103. The negative feedback circuit 104 contains the first resistance R₁, and the second resistance R₂ paralleled with the first resistance.

The second circuit unit contains the second resistance R₂, and a unidirectional conductive unit 1041 connected in series with the second resistance.

The conductive unit 1041contains several unidirectional conductive elements including diode(s) (as shown in FIG. 2), or diode(s) of BC (base and collector) junction of triode(s) (as shown in FIG. 3), or diode(s) of BE (base and emitter) junction of triode(s) (as shown in FIG. 4).

The resistance value of the negative feedback circuit 104 may vary with the forward current or backward current; thus causing different feedback amounts.

As shown in FIG. 5, when the direction of the emulation leakage current is the same as that of the backward current, thus the forward current at output end is I_f=I_lm. And the backward current is I_r=I_lm+I_dm. Due to different forward and backward resistance properties in the negative feedback circuit, when the forward current is input to the operational amplifier, the feedback amount is decided by the forward resistance R_f=R₁, thus the output voltage of the operational amplifier V_f=−I_f*R_f, i.e., V_f=−I_lm*R₁. When the backward current is input to the operational amplifier, the feedback amount is decided by the backward resistance R_r=R₁*R₂/(R₁+*R₂), thus the output voltage of O.A V_f=−I_r*R_r, i.e., V_f=−(I_lm+I_dm)*[R₁*R₂/(R₁+*R₂)]. If the forward electric-leakage sensitivity is half of the backward electric-leakage sensitivity, then take R₁=R₂, the forward and backward electric-leakage sensitivity is just compensated to reach the aim of providing the same magnitude to forward and backward outputs.

The described and other embodiments of the invention offer a detecting circuit used for an electric-leakage protection device with self-diagnostic function which can solve the problem of un-uniform sensitivity of forward and backward electric-leakage caused due to the addition of an emulation leakage current for unidirectional detection to the ground fault electric-leakage protection device with self-diagnostic function, and enables such GFCI electric-leakage protection with self-diagnostic function to comply with the same forward and backward electric-leakage sensitivity required by the UL standard.

Claims

1. An input detecting circuit for an electric-leakage protection device with self-diagnostic function, comprising: an emulation electric-leakage unit,a magnetic leakage current detecting ring,an amplifying circuit, anda negative feedback circuit; wherein

2. An input detecting circuit as set forth in claim 1, wherein one end of said emulation electric-leakage unit is connected with a forward current, while the other end is connected with a backward current, and the emulation electric-leakage unit is adapted to produce a unidirectional emulation leakage current, which is superimposed to the actual leakage current.

3. An input detecting circuit as set forth in claim 1, wherein said magnetic leakage current detecting ring passes through the forward and backward currents, the input current of the electric-leakage detecting circuit will be induced and output that current to said amplifying circuit.

4. An input detecting circuit as set forth in claim 1, wherein said amplifying circuit is connected with the magnetic-electric-leakage induction ring, and outputs the input forward and backward leakage currents after amplifying the currents.

5. An input detecting circuit as set forth in claim 1, wherein said at least one unidirectional conductive element comprises diodes.

6. An input detecting circuit as set forth in claim 1, wherein said at least one unidirectional conductive element comprises diodes of BC (base and collector) junction of triodes.

7. An input detecting circuit as set forth in claim 1, wherein said at least one unidirectional conductive element comprises diodes of BE (base and emitter) junction of triodes.