Switching circuit having two external connection terminals for detecting a magnetic field

Abstract

The switching circuit (100) comprises a first and a second external connection terminal (102a, 102b) configured to be electrically connected to an external device (200). There is an electromagnetic sensor (104) configured to detect the intensity of a magnetic field, and comprising: a first power supply terminal (106a) electrically connected to the first external connection terminal (102a), a second power supply terminal (106b) electrically connected to the second external connection terminal (102b), and an output terminal (106o) configured to generate an electric control signal (Vo) as a function of the intensity of the detected magnetic field. There are a first and a second short-circuiting module (108, 110) electrically connected in series between the external connection terminals (102a, 102b). Each one of the short-circuiting modules (108, 100) is electrically controlled separately from the other one, and in such a way as to assume a closed condition and an open condition in which it respectively allows or prevents a flow of current through it. There is a delay circuit (112) electrically connected to the output terminal (106o) and configured to receive as input the electric control signal (Vo) and to output a delayed electric control signal (Vs). The first short-circuiting module (108) is electrically connected between the first external connection terminal (102a) and the second short-circuiting module (110), and is controlled as a function of the electric control signal (Vo). The second short-circuiting module (110) is electrically connected between the first short-circuiting module (108) and the second external connection terminal (102b), and is controlled by the delayed electric control signal (Vs).

Description

[0001] Switching circuit having two external connection terminals for detecting a magnetic field

[0002] DESCRIPTION

[0003] Technical field

[0004] The present invention relates to a switching circuit for detecting a magnetic field.

[0005] Technical background

[0006] In general, switching circuits are known which are configured to provide an electric signal in response to a variation in a magnetic field, and which can be applied to external devices used for detecting and measuring pulses, e . g. in rotary meters and / or measuring systems, particularly flow meters . In such applications, the external connection terminals of the switching circuit are typically connected to a processing unit, such as a microprocessor or a motherboard of a device .

[0007] Several types of switching circuits are known which can be used for the above mentioned applications .

[0008] One example is shown in Figure 1, and concerns a switching circuit 10 based on a per se known commutator or Reed sensor 12 to be connected to the terminals of an external device of the above-mentioned type, designated as a whole as 200 (e . g. used for detecting / measuring electric pulses) . Reed sensors are electromechanical sensors widely used for converting magnetic field variations into electric signals . Generally, Reed sensor-based switching circuits have a simple two-terminal configuration.

[0009] However, such switching circuits suffer from a few drawbacks . As a matter of fact, the Reed sensor employed inthe switching circuit is affected by reliability problems due to its mechanical fragility.

[0010] This has led to increased adoption of switching circuits making use of electronic commutators or sensors (e . g. Halleffect commutators or sensors, or magnetoresistors) to obtain an electric signal in response to a variation in a near magnetic field.

[0011] Nevertheless, switching circuits based on electronic sensors are also subj ect to a number of drawbacks . In particular, in their standard configuration, electronic sensors typically have three terminals, as opposed to Reed sensors, which are normally equipped with only two terminals . This makes it difficult to use circuits equipped with electronic sensors as a direct replacement for circuits incorporating Reed sensors . It is necessary, in fact, to make adaptations and modifications in the existing external devices for pulse detection and measurement, originally designed for switching circuits with Reed sensors .

[0012] In light of the above, switching circuits have been specifically conceived which are equipped with electronic sensors having two external connection terminals, thus being compatible with existing external detecting / measuring devices originally designed for use with circuits incorporating Reed sensors .

[0013] However, prior-art circuit solutions using electronic sensors with two external connection terminals suffer from significant limitations, particularly as concerns voltagelevel management and static short-circuit conditions .

[0014] Some of such circuit solutions are illustrated by way of example in Figures 2 and 3. In such circuit solutions, designated as a whole as 10' , the electronic sensor 12' can - through its internal circuit - act directly upon, andselectively connect, the two external connection terminals, as shown in Figure 2. As an alternative, as shown in Figure 3, the electronic sensor 12' can connect the output terminal to a further short-circuiting module or element 14' , which in turn can, under certain conditions, electrically connect the first external connection terminal to the second external connection terminal, thereby short-circuiting them. However, in the magnetic field condition in which the two external connection terminals are short-circuited, the power supply to the electronic sensor will no longer be available, resulting in incorrect operation of the latter .

[0015] In order to overcome this problem, as known in the industry, other examples of this type of circuit solution have been conceived - one of which is shown in Figure 4, designated as a whole as 10111. Such circuit solutions adopt short-circuiting elements 14111to which further components and elements are added which make it possible to decouple the power supply of the electronic sensor 12111, e . g . by means of a capacitor 16111and a diode 18111.

[0016] Nevertheless, such circuit solutions suffer from a few limitations and drawbacks as well, particularly when the external configuration of the magnetic field leads to a prolonged short-circuited condition of the external connection terminals . In some applications (e . g. the above-mentioned counting of pulses generated by a rotating magnet) , there is a range of usable frequencies of the generated electric signal that are associated with minimum and maximum durations of the short-circuit condition; however, at lower frequencies or in stationary conditions, the short circuit may last longer than the duration for which the capacitor has been sized, so that the above-mentioned problemsconcerning the power supply to the electronic sensor will still arise .

[0017] In order to overcome the above-mentioned limitations and drawbacks, a circuit solution made in accordance with patent publication EP 3 419 173 Al and illustrated in Figure 5, designated as a whole as 10IV, can be used. According to this circuit solution, which also includes a capacitor 16IVand a diode 18IV, the short-circuiting module 14IVis not operated directly by the electronic sensor 12IV, but through a pulse generator circuit 20IVgenerating pulses at the edges of the electric signal outputted by the electronic sensor 12IV: positive pulses at the rising edge and negative pulses at the falling edge .

[0018] While the switching circuit described in said patent publication EP 3 419 173 Al uses a pulse generator system for improved operation, it still has a number of limitations and drawbacks .

[0019] Summary of the invention

[0020] It is one obj ect of the present invention to overcome the limitations and drawbacks of the switching circuits made in accordance with the prior art .

[0021] In particular, the invention provides a switching circuit equipped with an electronic sensor and having two external connection terminals, which can offer one or more of the following advantages :

[0022] • ensuring a continuous power supply to the electronic sensor with which it is associated, even in prolonged short-circuit conditions;

[0023] • preventing any operation anomalies due to static or long-lasting signals; and• ensuring compatibility with existing external detection devices to which circuits equipped with Reed sensors were originally applied.

[0024] According to the present invention, this and other obj ects are achieved through a switching circuit having the technical features set out in the appended independent claim.

[0025] In particular, a switching circuit is provided which includes a pair of short-circuiting modules connected in series between the external connection terminals . The first short-circuiting module is controlled as a function of an electric control signal generated by an electromagnetic sensor . The second short-circuiting module is controlled by a delayed electric control signal, which is obtained by introducing a delay into the electric control signal . The electric control signal coming from the electromagnetic sensor immediately triggers the activation of the first short-circuiting module, while the second short-circuiting module inhibits a short circuit across the external connection terminals, particularly when quasi-static magnetic fields are generated. This provides flexible control over the operating conditions, preventing prolonged short circuits . In comparison with the solution described in EP 3 419 173 Al, the use of a pair of short-circuiting modules makes for reduced energy consumption and more stable operation even in quasi-static conditions or in the presence of extremely low operating frequencies .

[0026] It is understood that the appended claims are an integral part of the technical teachings provided in the following detailed description of the present invention. In particular, the appended dependent claims define some preferred embodiments of the present invention that include some optional technical features .Another advantage lies in the fact that the proposed configuration of the switching circuit provides dynamic control, making it possible to handle at best any static or dynamic condition, thereby improving the reliability and life of the system.

[0027] Another advantage lies in improved performance, since the switching circuit guarantees fast response times for the edges of the output signal, thus avoiding any delay or phaseshifting .

[0028] Yet another advantage lies in energetic efficiency, since the proposed architecture reduces the total consumption in comparison with prior-art solutions like, for example, the one described in EP 3 419 173 Al .

[0029] Further features and advantages of the present invention will become apparent in light of the following detailed description, provided herein merely as a nonlimiting example and referring, in particular, to the annexed drawings as summarized below.

[0030] Brief description of the drawings

[0031] Figure 1 schematically shows a switching circuit comprising a Reed sensor, made in accordance with the prior art .

[0032] Figures 2 to 5 schematically show a plurality of switching circuits, each one comprising an electronic sensor, e . g. a Hall-effect sensor, and having two external connection terminals . Such switching circuits are made in accordance with the prior art .

[0033] Figure 6 is a schematic representation of a switching circuit having two external connection terminals and an electronic sensor made in accordance with an illustrative embodiment of the present invention.Figure 7 is a schematic representation, more detailed than Figure 6, of a switching circuit having two external connection terminals and an electronic sensor .

[0034] Figures 8 and 9 are Cartesian diagrams representing in two different operating conditions, as a function of time, the voltage pattern of the electric voltage signal at the output terminal of a switching circuit made in accordance with Figures 6 and 7 .

[0035] Figure 10 is a switching circuit diagram that is similar to the one shown in Figure 7, but in which the switching circuit is made in accordance with a further embodiment of the present invention.

[0036] For completeness ' sake, the following is a list of alphanumerical references used herein to identify parts, elements and components illustrated in the above-summarized drawings .

[0037] 100. Switching circuit

[0038] 102a . First external connection terminal

[0039] 102b . Second external connection terminal

[0040] 104. Electromagnetic sensor

[0041] 105. Capacitor

[0042] 106a . First power supply terminal

[0043] 106b . Second power supply terminal

[0044] 106o . Output terminal

[0045] 107. Diode

[0046] 108. First short-circuiting module

[0047] 109. Intermediate resistor

[0048] 110. Second short-circuiting module

[0049] 112. Delay circuit

[0050] 114. First transistor

[0051] 114e . Emitter of first transistor

[0052] 114c . Collector of first transistor114b . Base of first transistor

[0053] 116. Second transistor

[0054] 116e . Emitter of second transistor

[0055] 116c . Collector of second transistor

[0056] 116b . Base of second transistor

[0057] 120. RC circuit

[0058] 122. Resistor of RC circuit

[0059] 124. Capacitor of RC circuit

[0060] 126. Further resistor of RC circuit

[0061] 130. Conditioning circuit

[0062] 132. Conditioning transistor

[0063] 132e . Emitter of conditioning transistor

[0064] 132c . Collector of conditioning transistor

[0065] 132b . Base of conditioning transistor

[0066] 134. Conditioning resistor

[0067] 200. External device

[0068] Vo. Electric control signal

[0069] Vs. Delayed electric control signal

[0070] Detailed description of the invention

[0071] With reference to Figures 6 and 7, there is shown, designated as a whole as 100, a switching circuit made in accordance with an illustrative embodiment of the present invention. Switching circuit 100 is designed to detect a magnetic field, and is intended for application, without however being limited thereto, to external devices used for detecting and measuring pulses, e . g. in rotary meters and / or measuring systems, e . g. flow meters .

[0072] Switching circuit 100 comprises a first and a second external connection terminal 102a, 102b . External connection terminals 102a, 102b are configured to be electrically connected to an external device 200, e . g. selected among devices of the type mentioned in the previous paragraph. Inparticular, first external connection terminal 102a is positive, and second external connection terminal 102b is negative .

[0073] In addition, switching circuit 100 comprises an electromagnetic sensor 104 configured to detect the intensity of a magnetic field. In the embodiment illustrated herein, electromagnetic sensor 104 is of the electronic type, e . g. a Hall-effect sensor or a magnetoresistor .

[0074] In the embodiment illustrated herein, switching circuit 100 optionally comprises electric storage means, in particular a capacitor 105, electrically connected across external connection terminals 102a and 102b, in particular through the interposition of a diode 107. More specifically, diode 107 is electrically connected between first connection terminal 102a and the electric storage means, which in the illustrated example consists of capacitor 105.

[0075] Electromagnetic sensor 104 comprises three terminals 106a, 106b and 106o . In more detail, electromagnetic sensor 104 comprises a first power supply terminal 106a, electrically connected to first external connection terminal 102a, and a second power supply terminal 106b, electrically connected to second external connection terminal 102b. In particular, first power supply terminal 106a is positive, and second power supply terminal 106b is negative . In addition, electromagnetic sensor 104 comprises an output terminal 106o configured to generate an electric control signal Vo as a function of the intensity of the detected magnetic field. In the switching circuit 100 shown in Figures 6 and 7, output terminal 106o is located at the point identified by letter 0.

[0076] Furthermore, in the embodiment illustrated herein, switching circuit 100 optionally comprises a diode 107electrically connected between first external connection terminal 102a and first power supply terminal 106a . In particular, diode 107 has its cathode electrically connected to first external connection terminal 102a and its anode connected to power supply terminal 106a .

[0077] Switching circuit 100 further comprises a pair of shortcircuiting modules 108, 110 configured to mutually cooperate in order to electrically connect in series the external connection terminals 102a, 102b . In Figures 6 and 7, short-circuiting modules 108, 110 are situated in switching circuit 100 at the points identified by letters A and B . As will be further described below, each one of shortcircuiting modules 108, 110 can be electrically controlled separately from the other, and in such a way as to assume a respective open condition and closed condition. In the respective closed condition, current is allowed to flow through the respective short-circuiting module 108 or 110. Conversely, in the respective open condition, current is prevented from flowing through the respective shortcircuiting module 108 or 110.

[0078] Switching circuit 100 further comprises a delay circuit 112 electrically connected to output terminal 106o and configured to receive as input the electric control signal Vo. Delay circuit 112 is also configured to output a delayed electric control signal Vs, which has a delayed time pattern in comparison with the electric control signal Vo. In the switching circuit 100 shown in Figures 6 and 7, delay circuit 112 is located at the point identified by letter S .

[0079] In particular, first short-circuiting module 108 and second short-circuiting module 110 have opposite switching characteristics, so that, in the absence of a magnetic field, one of the modules is in the open condition OFF and the othermodule is in the closed condition ON. In other words, shortcircuiting modules 108 and 110 are designed to assume opposite states, the control signal being the same .

[0080] First short-circuiting module 108 is electrically connected between first external connection terminal 102a and second short-circuiting module 110. Furthermore, first short-circuiting module 108 is controlled as a function of the electric control signal Vo.

[0081] Second short-circuiting module 110 is electrically connected between first short-circuiting module 108 and second external connection terminal 102b . Furthermore, second short-circuiting module 110 is controlled by the delayed electric control signal Vs .

[0082] Preferably, first short-circuiting module 108 comprises a first electronic commutator, e . g. a first transistor 114. As an alternative, the first electronic commutator may be of a type other than first transistor 114, e . g. a MOSFET .

[0083] Preferably, the first electronic commutator comprises a pair of power terminals - consisting of, in the embodiment illustrated in Figure 7, emitter 114e and collector 114c of first transistor 114 - which electrically connect in series first external connection terminal 102a and second shortcircuiting module 110. Furthermore, the first electronic commutator comprises a control terminal - consisting of, in the embodiment illustrated in Figure 7, base 114b of first transistor 114 - which is configured to regulate the flow of electric current across the power terminals - in particular, emitter 114e and collector 114c - as a function of the electric control signal Vo.

[0084] Preferably, the control terminal of the first electronic commutator - i . e . base 114b of first transistor 114 in the embodiment illustrated in Figure 7 - iselectrically connected in series with output terminal 106o of electromagnetic sensor 104.

[0085] Preferably, first short-circuiting module 108 further comprises an intermediate resistor 109 electrically interposed in series between output terminal 106o and the control terminal of the first electronic commutator - i . e . base 114b of first transistor 114.

[0086] Preferably, first transistor 114 has one of its power terminals, selected between emitter 114e and collector 114c, connected to first external connection terminal 102a . The other power terminal, selected between emitter 114e and collector 114c, is electrically connected to second shortcircuiting module 110.

[0087] Specifically, first transistor 114 is of the bipolar junction type, in particular the PNP type .

[0088] In the embodiment illustrated herein, emitter 114e is electrically connected to first external connection terminal 102a, while collector 114c is electrically connected to second short-circuiting module 110.

[0089] In the embodiment illustrated herein, base 114b of first transistor 114 is connected to output terminal 106o . Preferably, intermediate resistor 109 is interposed in series between output terminal 106o and base 114b .

[0090] Preferably, second short-circuiting module 110 is a second electronic commutator, e . g. a second transistor 116.

[0091] Preferably, the second electronic commutator comprises a pair of further power terminals - consisting of, in the embodiment illustrated in Figure 7, a further emitter 116e and a further collector 116c of second transistor 116 - which electrically connect in series first short-circuiting module 108 and second external connection terminal 102b . Furthermore, the second electronic commutator comprises afurther control terminal - consisting of, in the embodiment illustrated in Figure 7, a further base 116b of second transistor 116 - which is configured to regulate, as a function of the delayed electric control signal Vs, the flow of electric current across the further power terminals - in particular, between the further emitter 116e and the further collector 116c .

[0092] Preferably, the further control terminal of the second electronic commutator - i . e . the further base 116b of second transistor 116 in the embodiment illustrated in Figure 7 -is electrically connected in series with output terminal 106o of electromagnetic sensor 104.

[0093] Preferably, second short-circuiting module 110 comprises also a further intermediate resistor 126 electrically interposed in series between output terminal 106o and the further control terminal of said second electronic commutator - i . e . the further base 116b of second transistor 116 in the illustrated embodiment .

[0094] Preferably, the further intermediate resistor 126 is electrically interposed in series between delay circuit 112 and the further control terminal of the second electronic commutator - i . e . the further base 116b of second transistor 116 in the illustrated embodiment .

[0095] Preferably, second transistor 116 has one of the further power terminals - selected between the further emitter 116e and the further collector 116c - electrically connected to first short-circuiting module 108, and the other one of the further power terminals - selected between the further emitter 116e and the further collector 116c - electrically connected to second external connection terminal 102b .

[0096] Specifically, second transistor 116 is of the bipolar junction type, in particular the NPN type .In the embodiment illustrated herein, collector 116c is electrically connected to first short-circuiting module 108, in particular to collector 114c of first transistor 114, and emitter 116e is electrically connected to second external connection terminal 102b .

[0097] In the embodiment illustrated herein, base 116b of second transistor 116 is electrically connected to the output of delay circuit 112.

[0098] Preferably, delay circuit 112 is an RC circuit 120. In the embodiment illustrated herein, delay circuit 112 has its input connected to output terminal 106o and its output connected to second short-circuiting module 110, particularly to the further control terminal of the second electronic commutator - more particularly to the further base 116c of second transistor 116.

[0099] In the embodiment illustrated herein, RC circuit 120 comprises a resistor 122 connected in series to output terminal 106o, and a capacitor 124 connected in series to resistor 122 .

[0100] In light of the above description, according to a preferred aspect of the present invention, the configuration of the electronic commutators of the first short-circuiting module and the second short-circuiting module may include :

[0101] a power terminal (e . g. emitter 114e) of the first electronic commutator (e . g. first transistor 114 ) electrically connected in series to first external connection terminal 102a;

[0102] the other power terminal (e . g. collector 114c) of the first electronic commutator (e . g. first transistor 114 ) electrically connected in series to a further power terminal (e . g. the further collector 116c) of the second electronic commutator (e . g. second transistor 116) ; andthe other further power terminal (e . g. the further emitter 116e) of the second electronic commutator (e . g. second transistor 116) electrically connected in series to second external connection terminal 102b .

[0103] With reference to Figures 8 and 9, the following will describe an exemplary mode of operation of a switching circuit in accordance with the embodiment shown in Figures 6 and 7 .

[0104] Each one of Figures 8 and 9 represents the time-based voltage pattern of three different electric signals detected through switching circuit 100. In more detail, observing such figures from top to bottom:

[0105] the first signal, designated as V (out) , is the output voltage of switching circuit 100, in particular measured across the external connection terminals 102a, 102b;

[0106] the second signal is the delayed electric control signal Vs, showing the pattern of the voltage outputted by delay circuit 112 and inputted to second short-circuiting module 110, in particular measured across base 116b of second transistor 116 and second external connection terminal 102b, and

[0107] the third signal is the electric control signal Vo, showing the pattern of the voltage outputted by electromagnetic sensor 104 and inputted to first shortcircuiting module 108, in particular measured across output terminal 106o and second external connection terminal 102b .

[0108] In the Cartesian diagrams of Figure 8, shown herein by way of non-limiting example, when electromagnetic sensor 104 does not detect the presence of a magnetic field, the electric control signal Vo is "inactive" with a high voltage level . In this case, first short-circuiting module 108 -including the first electronic commutator, e . g. firsttransistor 114 - will be inhibited into the respective open condition (OFF) . Conversely, when electromagnetic sensor 104 detects the presence of a magnetic field, the electric control signal Vo is "active" with a low voltage level . In this case, first short-circuiting module 108 will be set into the respective closed condition (ON) .

[0109] Still with reference to Figure 8, let us now consider the pattern of the corresponding delayed electric control signal Vs . When the electric control signal Vo switches from the "inactive" state with a high voltage level to the "active" state with a low voltage level, the voltage level of the delayed electric control signal Vs starts decreasing gradually, remaining however "active" above the activation threshold value, designated as TV, of second shortcircuiting module 110. In this case, second short-circuiting module 110 - which includes the second electronic commutator, e . g. second transistor 116 - will remain conductive in the respective closed condition (ON) .

[0110] In the mode of operation illustrated in Figure 8, the second short-circuiting module 110 always remains conductive - even during the "active" transient with a low voltage level of the electric control signal Vo. Thus, first shortcircuiting module 108 alone can control the short-circuiting - in particular designated as C . C . in Figure 8 - of the external connection terminals 102a, 102b .

[0111] Let us now consider the case shown in Figure 9, wherein - unlike Figure 8 - there is a quasi-static condition of the external magnetic field, in which the electric control signal Vo stays "active" with a low voltage level for a long time . In this case, the delayed electric control signal Vs falls below the activation threshold value TV of second short-circuit module 110, and thus becomes "inactive" with a lowvoltage level . This prevents the short-circuit condition C .C . of the external connection terminals 102a, 102b, thereby avoiding the above-described problems .

[0112] Since in the normal operating frequency range the shortcircuiting of the external connection terminals 102a, 102b essentially only occurs through first short-circuiting module 108 (because second short-circuiting module 110 remains conductive) , the signal V (out) can "imitate" the behaviour of the electric control signal Vo; in particular, the rising and falling edges of the signal V (out) can be steep, thus preventing anomalies in the operation of external device 200 and of the circuits connected downstream of the application through the external connection terminals 102a, 102b .

[0113] Furthermore, as will be apparent to a person skilled in the art, delay circuit 120 can be appropriately sized to have second short-circuiting module 110 intervene - i . e . inhibit the short circuit - only outside the range of f requencies / durations that may be useful for a specific application. As an alternative, delay circuit 120 may be sized in such a way that switching circuit 100 will be able to operate in a "mixed" mode, in which the switching circuit will operate as described, substantially following the signal V (out) , at higher frequencies, whereas at lower frequencies it will intervene to limit the short-circuit duration .

[0114] With reference to Figure 10, there is shown a switching circuit designed in accordance with a further embodiment of the present invention.

[0115] Those parts and elements which are similar to - or which perform the same function as - those of the above-described embodiment, illustrated in Figure 7, have been assigned thesame reference numerals . For simplicity, the description of such parts and elements will not be repeated below, and reference should be made to the above description of the preceding embodiment .

[0116] In brief, in the embodiment illustrated in Figure 10 first transistor 114 is of the NPN type - as opposed to the PNP-type transistor employed in the embodiment illustrated in Figure 7. Therefore, the embodiment shown in Figure 10 uses a first short-circuiting module 108 having an inverse "logic" compared with the one of the diagram shown in Figure 9. In more detail, with "inactive" Vo, in order to inhibit first short-circuiting module 108 it is necessary to invert the signal in first transistor 114, which in this case is not a PNP transistor, but an NPN transistor .

[0117] Unlike the embodiment previously described herein with particular reference to Figure 7, in the embodiment shown in Figure 10 a signal conditioning circuit 130 is interposed in series between output terminal 106o and base 114b . In particular, conditioning circuit 130 is configured to output (to base 114b) a conditioned electric control signal Vc determined as a function of the electric control signal Vo received as input ( from output terminal 106o) . Preferably, the conditioned electric control signal Vc obtained from conditioning circuit 130 has a pattern which is substantially the opposite of that of the electric control signal Vo.

[0118] Unlike the embodiment illustrated in Figure 7, in the embodiment shown in Figure 10 collector 114c is electrically connected to first external connection terminal 102a . Furthermore, emitter 114e is electrically connected to second short-circuiting module 110. In particular, as aforementioned, first transistor 114 is of the NPN type .In particular, conditioning circuit 130 comprises intermediate resistor 109, a conditioning electronic commutator - e . g. a conditioning transistor 132 - and a conditioning resistor 134, which are essentially configured to output the conditioned electric control signal Vc as a function of the electric control signal Vo received as input . In more detail, intermediate resistor 109 is electrically connected in series to output terminal 106o at one end, and electrically connected in series to base 132b of conditioning transistor 132 at the other end. Moreover, conditioning circuit 132 has its collector 132c electrically connected in series to conditioning resistor 134, while its emitter 132e is electrically connected in series to second external connection terminal 102b . Conditioning resistor 134 is also electrically connected, on the side opposite conditioning transistor 132, to first external connection terminal 102a, particularly through the interposition of diode 107. Furthermore, base 114b of first transistor 114 is electrically connected to the output of conditioning circuit 130, at a branch between conditioning resistor 134 and collector 132c .

[0119] Of course, without prejudice to the principle of the invention, the forms of embodiment and the implementation details may be extensively varied from those described and illustrated herein by way of non-limiting example, without however departing from the scope of the invention as set out in the appended claims .

Claims

CLAIMS1. Switching circuit ( 100) for detecting a magnetic field, comprising :a first and a second external connection terminal ( 102a, 102b) configured to be electrically connected to an external device (200) ;an electromagnetic sensor ( 104 ) configured to detect the intensity of a magnetic field, and comprisinga first power supply terminal ( 106a) electrically connected to said first external connection terminal ( 102a) , a second power supply terminal ( 106b) electrically connected to said second external connection terminal ( 102b) , andan output terminal ( 106o) configured to generate an electric control signal (Vo) as a function of the intensity of said detected magnetic field;said switching circuit being characterized in that it further comprises :a first and a second short-circuiting module ( 108, 110) configured to mutually co-operate in order to electrically connect in series said external connection terminals ( 102a, 102b) , each one of the short-circuiting modules ( 108, 110) being electrically controlled separately from the other, and in such a way as to assume a closed condition and an open condition in which it respectively allows or prevents current from flowing through it, anda delay circuit ( 112 ) electrically connected to said output terminal ( 106o) and configured to receive as input said electric control signal (Vo) and to output a delayed electric control signal (Vs) having a time pattern which is delayed in comparison with said electric control signal (Vo) ;in that said first short-circuiting module ( 108 ) is electrically connected between said first external connection terminal ( 102a) and said second short-circuiting module ( 110) , and is controlled as a function of said electric control signal (Vo) ; andin that said second short-circuiting module ( 110 ) is electrically connected between said first short-circuiting module ( 108 ) and said second external connection terminal ( 102b) , and is controlled by said delayed electric control signal (Vs) .

2. Circuit according to claim 1, wherein said first shortcircuiting module ( 108 ) and said second short-circuiting module ( 110) have opposite switching characteristics, so that, in the absence of a magnetic field, one of the modules is in the open condition and the other module is in the closed condition.

3. Circuit according to claim 1 or 2, wherein said first short-circuiting module ( 108 ) comprises a first electronic commutator ( 114 ) .

4. Circuit according to claim 3, wherein said first electronic commutator ( 114 ) comprises :a pair of power terminals ( 114e, 114c) that electrically connect in series the first external connection terminal ( 102a) and the second short-circuiting module ( 110) ; and a control terminal ( 114b) configured to regulate, as a function of said electric control signal (Vo) , the flow of electric current across said power terminals ( 114e, 114c) .

5. Circuit according to claim 4, wherein the control terminal ( 114b) of the first electronic commutator ( 114 ) is electrically connected in series to said output terminal ( 106o) of the electromagnetic sensor ( 104 ) .6 . Circuit according to claim 5 , wherein said first shortcircuiting module ( 108 ) further comprises an intermediate resistor ( 109 ) electrically interposed in series between said output terminal ( 106o ) and the control terminal ( 114b ) of said first electronic commutator ( 114 ) .7 . Circuit according to any one of claims 3 to 6 , wherein said first electronic commutator is a first transistor ( 114 ) , wherein the power terminals are , respectively, an emitter ( 114e ) and a collector ( 114c ) , while the control terminal is a base ( 114b ) .8 . Circuit according to claim 7 , wherein said first transistor ( 114 ) hasone of the power terminals , selected between the emitter ( 114e ) and the collector ( 114c ) , electrically connected to the first external connection terminal ( 102a ) , andthe other one of the power terminals , selected between the emitter ( 114e ) and the collector ( 114c ) , electrically connected to the second short-circuiting module ( 110 ) .9 . Circuit according to claim 7 or 8 , wherein said first transistor ( 114 ) is of the bipolar j unction type .10 . Circuit according to claim 9 , wherein said first transistor ( 114 ) is of the PNP type .11 . Circuit according to claim 9 , wherein said first transistor is of the NPN type .12 . Circuit according to claim 11 , wherein said first shortcircuiting module ( 108 ) comprising a conditioning circuit ( 130 ) electrically connected in series to said output terminal ( 106o ) and configured to supply to the base ( 114b ) of said first transistor ( 114 ) a conditioned electric control signal (Vc) determined as a function of said electric control signal (Vo) .

13. Circuit according to claim 12, wherein said conditioned electric control signal (Vc) has a pattern which is substantially the opposite of the one of said electric control signal (Vo) .

14. Circuit according to any one of the preceding claims, wherein said second short-circuiting module ( 110) comprises a second electronic commutator ( 116) .

15. Circuit according to claim 14, wherein said second electronic commutator ( 116) comprises :a pair of further power terminals ( 116e, 116c) that electrically connect in series the first short-circuiting module ( 108 ) and the second external connection terminal ( 102b) ; anda further control terminal ( 116b) configured to regulate, as a function of said delayed electric control signal (Vs) , the flow of electric current across said further power terminals ( 116e, 116c) .

16. Circuit according to claim 15, wherein said further control terminal ( 116b) of the second electronic commutator ( 116) is electrically connected in series to said output terminal ( 106o) of the electromagnetic sensor ( 104 ) .

17. Circuit according to claim 16, wherein said second short-circuiting module ( 110) further comprises a further intermediate resistor ( 126) electrically interposed in series between said output terminal ( 106o) and said further control terminal ( 116b) of said second electronic commutator ( 116) .

18. Circuit according to claim 17, wherein said further intermediate resistor ( 126) is electrically interposed in series between said delay circuit ( 112 ) and said further control terminal ( 116b) of said second electronic commutator ( 116) .

19. Circuit according to any one of claims 14 to 18 , wherein said second electronic commutator is a second transistor ( 116 ) , wherein the power terminals are , respectively, a further emitter ( 116e ) and a further collector ( 116c ) , while the control terminal is a further base ( 116b ) .20 . Circuit according to claim 19 , wherein said second transistor ( 116 ) hasone of said further power terminals , selected between said further emitter ( 116e ) and said further collector ( 116c ) , electrically connected to the first short-circuiting module ( 108 ) , andthe other one of said further power terminals , selected between said further emitter ( 116e ) and said further collector ( 116c ) , electrically connected to the second external connection terminal ( 102b ) .21 . Circuit according to claim 19 or 20 , wherein said second transistor ( 116 ) is of the bipolar j unction type .22 . Circuit according to claim 21 , wherein said second transistor ( 116 ) is of the NPN type .23 . Circuit according to any one of the preceding claims , wherein said delay circuit ( 112 ) is an RC circuit ( 120 ) . 24 . Circuit according to claim 23 , wherein said RC circuit ( 120 ) has its input electrically connected to said output terminal ( 106o ) and its output electrically connected to said second short-circuiting module ( 110 ) .

25. Circuit according to claim 24 , wherein said RC circuit ( 120 ) comprisesa resistor ( 122 ) electrically connected in series to said output terminal ( 106o ) , anda capacitor ( 124 ) electrically connected in series to said resistor ( 122 ) .

26. Circuit according to any one of the preceding claims, wherein said electromagnetic sensor ( 104 ) is of the electronic type .

27. Circuit according to claim 26, wherein said electromagnetic sensor ( 104 ) is selected between a Halleffect sensor and a magnetoresistor .

28. Circuit according to any one of the preceding claims, further comprising electric storage means ( 105) electrically connected across said external connection terminals ( 102a, 102b) .

29. Circuit according to any one of the preceding claims, further comprising a diode ( 107 ) electrically connected between said first external connection terminal ( 102a) and said first power supply terminal ( 106a) .

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