COMPRISING SAID FILTER

DESCRIPTION

[TECHNICAL FIELD]

The present invention relates to a filter for electric noise suppression.

The present invention also relates to a household appliance equipped with said filter.

[PRIOR ART]

As it is known, household appliances are equipped, internally, with one or more electric loads that are suitably supplied in order to contribute to the execution of the functions to which the household appliance is responsible.

By way of example, the heating resistors present in the dishwasher and in washing machines may be considered, which have the task of heating the water used for the washing cycles .

A possible breakdown of said electric loads may cause, as it is known, an excessive current leakage to ground, causing uncontrolled overheating of the loads and/or of their components, that can cause fires.

According to the prior art, if the equipment is supplied by an electric power mains which is realised and maintained according to the standards of safety requirements, a circumstance such as that briefly described above should be avoided by the security system that is part of the electrical power mains itself which, following a differential detection on the phase and neutral lines, recognizes the occurrence of a dangerous situation and cuts off the power supply to the household appliance.

However, there are circumstances where, for various reasons, this security system does not intervene, or is entirely absent.

The prior art provides technical solutions that aim at solving the problem briefly described above.

These solutions, however, have a considerable structural complexity and entail high realisation costs.

[OBJECTS AND SUMMARY OF THE INVENTION]

It is an object of the present invention to provide a filter for electric noise suppression, and a household appliance equipped with said filter, that allow to overcome the drawbacks mentioned above.

In particular, it is an object of the present invention to provide a household appliance that is equipped with an additional safety system with respect to the system that each power mains network should provide by itself.

A further object of the present invention is to provide a household appliance that is equipped with an additional safety system which is easy to realise.

It is another object of the present invention to provide a household appliance that is equipped with a safety system that does not impose any constraint, both in the design and realisation phases, in terms of flexibility in the positioning of the electrical/electronic components.

A further object of the present invention is to provide a filter for electric noise suppression which also allows to perform an earth leakage current control in a simple and reliable manner.

These and other objects are substantially achieved through a filter for electric noise suppression, and a household appliance that is equipped with said filter, as defined in the appended claims.

The idea underlying the present invention consists in adding, to the common mode coil of the so-called machine filter, a further winding through which a main parameter representative of a possible earth leakage current can be detected.

In particular, according to a first aspect, the present invention relates to a filter for electric noise suppression, adapted for use in a household appliance, said filter comprising :

a first capacitor connectable across connection terminals of said household appliance and adapted to filter differential mode noise;

a second capacitor and a third capacitor, respectively connectable across a respective one of said connection terminals and a ground node, said second and third capacitors being adapted to filter common mode noise to ground;

- a common mode coil comprising two windings adapted to filter common mode noise;

wherein said common mode coil further comprises a detection winding configured for detecting a parameter representative of a leakage current flowing in a ground connection branch.

Preferably, said representative parameter is a voltage measured across said detection winding.

Preferably, the terminals of said winding are connected to the respective terminals of a termination resistor.

Preferably, said windings, adapted to filter common mode noise, can be connected between said terminals and said second and third capacitors.

According to another aspect, the present invention relates to a household appliance comprising at least one electric load connected to an electric power mains, said at least one electric load being associated with a ground connection branch, said household appliance further comprising:

a. said a filter for electric noise suppression;

b. a comparison module associated with said detection winding and configured for comparing said main parameter with a preset threshold; wherein said comparison module is also configured for disconnecting said at least one electric load from said power mains, if said main parameter turns out to be greater than said preset threshold.

Preferably, said comparison module is configured for disconnecting said at least one electric load from both a phase line and a neutral line of said power mains.

Preferably, said household appliance is provided with at least two connection terminals configured for being connected to the phase line and to the neutral line of said power mains, wherein the first capacitor of said filter is connected across said two connection terminals, wherein the second and third capacitors of said filter are connected across a respective one of said at least two connection terminals and a ground node.

Preferably, said at least one electric load is a plurality of electric loads, each one having a first connection to one of said connection terminals through a respective main switch, and a second connection to the other connection terminal.

Preferably, the second connections of said electric loads are connected to the respective terminal of said household appliance through a common switch.

Preferably, said comparison module is configured for opening said main switches and said common switch, if said main parameter exceeds said preset threshold.

[BRIEF DESCRIPTION OF THE DRAWINGS]

Other features and advantages will become more apparent from a detailed description of a preferred, but not exclusive, embodiment.

Such a description is given below with reference to the attached figures, which are also supplied by way of non- limiting example, wherein:

figure 1 shows a circuit diagram of a filter for electric noise suppression according to the present invention;

figure 2 shows a block diagram of a household appliance equipped with the filter of figure 1, wherein some elements have been deleted to improve readability.

[DETAILED DESCRIPTION OF THE INVENTION]

With reference to the attached figures, F indicates a filter for electric noise suppression according to the present invention, whereas the reference numeral 1 generally indicates a household appliance that is equipped with said filter.

Filter F (figure 1) is a so-called a "machine filter", i.e., a filter used for the suppression of electric noise incoming in the household appliance from the power mains, and electric noise injected in the power mains, from the household appliance itself.

The filter F preferably comprises a first capacitor CI in the class "X", which is connected between the two connection terminals Tl, T2.

The first capacitor CI has the task of suppressing the differential mode noise.

The filter F preferably comprises a second capacitor C2 and a third capacitor C3, both in the class "Y", respectively connected across the connection terminal Tl and ground, and across the connection terminal T2 and ground.

The second and third capacitors C2, C3 have the task of suppressing ground noise.

The filter F also includes a common mode coil B comprising two windings Bl, B2, adapted to filter common mode noise and wound on the same toroid T.

The winding Bl is positioned between the terminal Tl and the second capacitor C2.

The winding B2 is positioned between the terminal T2 and the third capacitor C3. The common mode coil B also comprises a detection winding B3.

The detection winding B3 is wound on the same toroid T of the windings B1, B2.

The currents in the windings Bl, B2 generate a magnetic field in the toroid T; this magnetic field generates a corresponding current in the detection winding B3.

The detection winding B3 is configured for detecting a main parameter MP representative of a leakage current I flowing in a ground connection branch 10.

Preferably, the terminals of the detection winding B3 are connected to the respective terminals of a termination resistor RX .

The main parameter MP can be advantageously a voltage measured across said detection winding B3.

The Applicant considers that this voltage is representative of the imbalance between the phase line P and the neutral line N and is therefore correlated to earth leakage (represented by the connector E) .

By way of example, the household appliance 1 (figure 2) may be a dishwasher or a washing machine.

In general, the household appliance 1 is a household appliance wherein, for regulatory or security issues, at least one electric load is connected to ground.

In more detail, the household appliance 1 comprises at least an electric load L1-Ln.

By way of example, figure 2 shows a household appliance 1 comprising a plurality of electric loads Ll-Ln.

As mentioned above, the at least an electric load Ll-Ln is associated with a ground connection brand 10.

In particular, as shown by way of example in figure 2, the connections Yl-Yn coming from electric loads Ll-Ln are related to the ground node N, to which the second and third capacitors C2, C3 of the filter F are also connected; from the ground node N the connection branch 10 develops, wherein the leakage current I to be monitored may flow.

It should be noted that the filter F of figure 2 is the same filter F of figure 1; in figure 2 some elements have been deleted (e.g. windings Bl, B2) to improve readability. The elements not shown in the figure are to be considered in any case included also in the filter F of figure 2.

According to the invention, the household appliance 1 is equipped with a comparison module 40.

As will be apparent hereafter, through said comparison module 40 it is possible to disconnect said at least one electric load Ll-Ln from the power mains, should a leakage current, flowing in the branch 10, exceed a preset threshold.

In an advantageous embodiment, to this aim the comparison module 40 cooperates with at least the above- mentioned detection winding B3.

The comparison module 40 is configured to compare the main parameter MP detected by the detection winding B3 with a preset threshold.

The preset threshold can be defined both in hardware mode, i.e., by setting a reference voltage through appropriate circuit elements dimensioned in an appropriate way, and in the software mode, i.e., programming a threshold value in a microprocessor that implements said comparison module 40.

Preferably, a first terminal of the detection winding B3 is connected to a ground pin of the microprocessor, whereas the other terminal of the same detection winding B3 is connected to a converter A/D, which provides the digital data to the microprocessor. The preset threshold is a limit beyond which there is a real danger that can cause fires; the preset threshold preferably corresponds to a leakage current I comprised between 250 mA and 3A.

Therefore, in case the leakage current I exceeds safety values represented by said preset threshold, the comparison module 40 disconnects said at least one electric load Ll-Ln from the power mains.

In particular, the comparison module disconnects said at least one load Ll-Ln from both a phase line P, and a neutral line N of the power mains. In this way it is performed a protection with a so-called "bipolar" disconnection.

Preferably, the household appliance 1 has at least two connection terminals Tl, T2 configured for being connected to the phase line P and to the neutral line N of said power mains. The terminals Tl, T2 may be part of or be included in an electrical plug 50, connectable to a socket which is connected to a power mains.

Said socket has preferably a connection for the phase line P, a connection for the neutral line N and a connection for the earth line E.

The filter F described above is connected to the two connection terminals Tl, T2.

In particular, the winding Bl is positioned between the terminal Tl and the second capacitor C2, whereas the winding B2 is positioned between the terminal T2 and the third capacitor C3.

With reference to the embodiment schematically illustrated in Figure 2, the household appliance 1 comprises a plurality of electric loads Ll-Ln.

By way of example, the electric loads Ll-Ln may comprise one heating resistor R, one electric motor as a part of the household appliance 1, etc..

In general, the loads Ll-Ln are electric loads having at least one grounded metal part.

In the above example of an electric motor, the grounded metal part is represented by the sheet metal group forming part of the stator.

Preferably, each electric load Ll-Ln is connected to the ground connection branch 10 through a respective connection Yl-Yn.

The ground connections Yl-Yn of all electric loads Ll-Ln are thus afferent to the ground connection branch 10.

Preferably, each electric load Ll-Ln has a first connection Xl-Xn, through a respective main switch MSl-MSn, to one of said connection terminals Tl, T2, and a second connection Zl-Zn to the other connection terminal.

Preferably, the second connections Zl-Zn of the electric loads Ll-Ln are connected to the respective terminal Tl, T2 of the household appliance 1 through a common switch SX.

By way of example, figure 2 shows that the first connections Xl-Xn of the loads Ll-Ln are afferent to the second terminal T2, through the main switches MSl-MSn, whereas the second connections Zl-Zn are afferent to the first terminal Tl through the common switch SX.

When the comparison module 40 determines that the leakage current I flowing in the branch 10 has reached critical values (i.e., the main parameter MP has exceeded the preset threshold) , it opens both the main switches MSl-MSn, and the common switch SX.

The invention achieves important advantages.

First of all, the filter according to the present invention allows to implement additional controls on unwanted leakage currents, and sometimes extremely dangerous, in a particularly simple and economical manner.

The household appliance according to the present invention is thus equipped with an additional safety system with respect to the system that each power mains should provide .

Moreover, the safety circuit realised in the electrical household appliance is simple and economical.

In addition to the above, the safety system can be mounted inside the appliance according to the present invention with extreme flexibility, particularly with reference to the arrangement of the detection element .