EP0661912B1 - Battery operated electric unit - Google Patents

Description

State of the art

The invention is based on a battery-operated electrical Device according to the genus of the main claim. Electrostatic discharge (ESD) can disrupt the function of electrical devices or even destroy electrical circuit parts in the device. This danger exists, for example, when touching an electrically charged one Body, for example a plastic, or the human Body with the electrical device. It is known that in particular integrated circuits are particularly sensitive to ESD. This Sensitivity increases with the degree of integration. For stationary and wired devices are already protective measures known that derive an applied overvoltage. A protective function can only offer these measures if a removal of the Charging to an earth line is possible. This is usually the case with stationary and wired devices. With the known However, it is not possible to take portable devices effectively protect against electrostatic discharge.

From US-A-4 138 711 is a printed circuit board with semiconductor components known, which is connected to input contacts on the circuit board are. A switching device designed as a bridge switch bridges all contacts before inserting a plug. When inserting the plug, the bridge switch is in transferred to a non-bridging state before the mating connections of the connector touch the input contacts. With this However, an arrangement is made when contacting one with an overvoltage overvoltage without ESD protection transferred to the components.

Devices for ESD protection against accidental contact with input contacts a circuit board with one of the input contacts Inserting a plug-bridging bridge switch also known from EP-A-0 501 749 and US-A-4 179 178.

DE-U-91 10 657 is a test socket with an upstream one Working electrode and one arranged inside the test socket contact isolated from the working electrode. The working electrode is connected to an earth line via which electrical Charges can drain against earth potential. When introducing a However, the mating connector contacts the mating connector not necessarily the working electrode, so that a sufficient ESD protection is not guaranteed. In addition, the arrangement is not Can be used in portable devices.

From NL-A-7 007 727 is a socket with a safety device known. By several arranged in a line Contacts are accidentally inserted into the outlet introduced contact for personal protection first with the neutral conductor and then in connection with the live contact brought. An earth line is mandatory for this.

The battery-operated electrical device according to the invention with the characteristic Features of claim 1 or claim 5 has in contrast the advantage that both stationary and portable devices are effective are protected against ESD. It is also described by the here Features a malfunction of the device functions by ESD difficult. There is no connection to a stationary protective conductor necessary. The protection also works for any electrical device charged bodies as well as for electrically charged plug contacts, which are connected to the device.

The measures listed in the subclaims are advantageous Further developments and improvements of the in claims 1 and 5 specified electrical device possible.

Switching to the essentially non-conductive state after expiration a delay time is advantageous in that the Delay time a certain period of time is made available in which equipotential bonding between the plug and the reference contact can take place. So the potential difference between the reference contact and the plug connector minimal.

The electrically conductive connection of each connector of the electrical Component with the reference contact via a switching means has the advantage that even if several connections are exposed to ESD, there are no harmful effects Potential differences between the connections and the reference contact can build up, reducing the risk of harm to the electrical components or subcircuits connected to these connections and thus the electrical device is reduced by ESD.

The switching device is designed with an electrically conductive contact pin In this respect represents an advantageous embodiment of the invention electrical device as the functions of electrical conductive connection and switching together from the contact pin are executable.

Another advantage is that the contact element electrically conductively connected to the reference contact via a switching means is because the structural design of the connector and the associated recess simplified.

Another advantage is that the switching means from the plug can be actuated, as this enables automatic switching is.

The formation of the switching means as a semiconductor switch brings the Advantage with it that the switching means is realized in a simple form which is also particularly low-wear.

The switching device is designed as a reed switch an advantageous embodiment, since contactless switching of the switching means is possible. In addition, the electrically conductive connection between the input contact and the Reference contact only when approaching one equipped with a magnet Counter connection and not accidentally e.g. mechanical release through another electrically charged body.

Another advantage is if the electrical device has a additional input contact for permanent connection with the reference contact has, since such a looping through the reference potential of the reference contact to the further electrical device having the counter connection is possible.

When designing the contact pin with a contact means that by means of a spring element to one connected to the reference contact Conductor piece is pressed, there is the advantage of a particularly simple and reliable implementation of ESD protection.

drawing

Es zeigend Figur 1 ein elektrisches Gerät mit einer Vorrichtung zum ESD-Schutz in einer ersten Ausführungsform,

Figur 2 ein elektrisches Gerät mit einer Vorrichtung zum ESD-Schutz in einer zweiten Ausführungsform,

Figur 3 ein elektrisches Gerät mit externer Stromversorgung in einer ersten Ausführungsform,

Figur 4 ein elektrisches Gerät mit externer Stromversorgung in einer zweiten Ausführungsform,

Figur 5a ein elektrisches Gerät mit externer Stromversorgung in einer dritten Ausführungsform, Figur 5b einen Stiftkontakt

Figur 6 ein elektrisches Gerät mit externer Stromversorgung mit verschiebbaren Kontaktstiften.

Embodiments of the invention are shown in the drawing and explained in more detail in the following description.

1 shows an electrical device with a device for ESD protection in a first embodiment,

FIG. 2 shows an electrical device with a device for ESD protection in a second embodiment,

FIG. 3 shows an electrical device with an external power supply in a first embodiment,

FIG. 4 shows an electrical device with an external power supply in a second embodiment,

5a shows an electrical device with an external power supply in a third embodiment, FIG. 5b shows a pin contact

Figure 6 shows an electrical device with an external power supply with sliding contact pins.

Description of the embodiments

An electrical device 26 with a housing 1 is shown in FIG. Inside the housing 1 there is a power supply 3, to the positive pole of which a first connecting line 13 and to the negative pole of which a second connecting line 12 are connected. The two connecting lines 12, 13 lead to a circuit 2, likewise located in the housing 1, which comprises a plurality of electrical subcircuits n ₀ , n ₁ , ... n _i . Each of these electrical subcircuits n ₀ , n ₁ , ... n _i is connected to a third connecting line 12 ', which is connected to the second connecting line 12 at the circuit input of the circuit 2. On the second connecting line 12 there is a reference contact 7, to which a first connecting line 8 ′ and a second connecting line 8 are connected. The first connecting line 8 ′ leads to an equalizing contact 22 located on the outside of the housing 1. The second connecting line 8 leads via a switching means 19 to an output line 9, which leads from a circuit output of the circuit 2 to an input contact 4 located on the outside of the housing 1 leads. The input contact 4 is surrounded by a coupling piece 29 for receiving a plug 25.

The plug means 25 comprises a connector housing 18, which on its Front one corresponding to the input contact 4 Has counter terminal 11. On the outside, the housing 1 also a recess 10 through which an actuation of the as Opener trained switching means 19 is possible. The switching means 19 has an angled probe arm 20, which in the recess 10 over the switching means 19 fits.

The third connecting line 12 'is preferably a line which connects all the electrical subcircuits n ₀ , n ₁ , ... n _{i to} one another. Such a line is usually already present in the circuit 2, since it is common in circuit design that a circuit ground is led through the circuit. The compensating contact 22 is constantly connected to the reference contact 7 via the first connecting line 8 '. Charges that reach the compensation contact 22 when handling the housing 1 by touching an electrically charged body, for example a human body part, thus flow to the reference contact 7, so that this has approximately the same potential as the compensation contact 22. This reduces the risk to the electrical device 26 from ESD, since the reference contact 7 and also the third connecting line 12 'connected to it are also at almost the same potential as the compensating contact 22 and the electrically charged body. Touching an electrically charged body with a circuit part of the electrical device 26 or electrical contacts accessible from the outside can therefore not trigger an electrical discharge in the direction of the reference contact 7. The compensation contact 22 is preferably attached at an exposed location on the outside of the surface of the housing 1 and can be of any shape (eg wire mesh, metal surface, decorative strips, etc.) and size.

The compensation contact 22 is preferably close as the housing 1 completely enclosing metal jacket. Just like the compensating contact 22 is the input contact 4 via the switching means 19 and the second connecting line 8 is connected to the reference contact 7. Charges that reach the input contact also flow to the reference contact 7, whereby the potential difference between the Input contact 4 and the reference contact 7 is minimized. In principle becomes an electrically charged body with the reference contact 7 electrically connected. When connecting the connector 25 to the input contact 4, e.g. to connect the electrical Device 26 with any other electrical device, such as printers, Charger, programming device, alarm transmitter, signal transmitter, remote control device, etc., the counter terminal 11 first reaches an electrically conductive one Contact with the input contact 4. This allows on the mating connector 11 charges located on the input contact 4 and thus also to Reference contact 7 arrive. The counter terminal 11 is with resilient contact tongues equipped when hitting the input contact 4 yield elastically, while the plug 25 for a safe coupling inserted into the housing 1 deeper into the coupling piece 29 becomes. Only when the plug 25 is fully inserted into the coupling piece 29 is, the probe arm 20 causes an intervention in the recess 10 an opening of the switching means 19. By opening the switching means 19, the input contact 4 is separated from the reference contact 7, whereby the input contact 4 its actual function for the circuit 2 can exercise. However, since the input contact 4 has almost the same potential shows how the reference contact 7 is damaged in the circuit 2 due to a potential difference between input contact 4 and Reference contact 7 almost impossible.

Since the plug 25 has the counter terminal 11, this is with the input contact 4 electrically connected. The condition, that the plug 25 is electrically conductively connected to the reference contact 7 must be before an electrically conductive connection between Counter terminal 11 and input contact 4 is created by the arrangement in Figure 1 automatically fulfilled.

As an alternative to the embodiment shown in FIG. 1, instead of the counter terminal 11 and the input contact 4 with elastic Contact tongues should be provided when the input contact meets 4 and give counter-connection 11. The input contact 4 and accordingly the counter terminal 11 can have multiple contacts, i.e. be multi-pole. The probe arm 20 is also by the design one of the contacts as a mechanically longer pin contact replaceable in input contact 4 or mating connector 11. By the bigger one mechanical length is then ensured that this compared to the other, Shorter contacts of the input contact 4 or counter terminal 11 leads ahead and when touching the electrically conductive switching means 19 establishes an electrically conductive connection to the reference contact 7. A deeper insertion of the plug 25 into the housing 1 causes then preferably opening the switching means 19 before one electrically conductive connection of the other contacts of the input contact 4 with the contacts of the counter terminal 11. Provided the relative Position between the input contact 4 and the counter terminal 11 to each other by other means such as the housing 1 and the connector 25 common enclosing container is secured, the coupling piece 29 also omitted. The plug 25 can also be connected to the device 26 be attachable accessory, on the outside of the counter connector 11 is arranged. A suitable reference contact is e.g. a metal layer in a multilayer circuit board.

FIG. 2 shows a further embodiment of that shown in FIG. 1 electrical device 26 shown. The same numbers denote here same elements. The embodiment shown here differs differs from that shown in FIG. 1 by the following features: The second connecting line 8 does not lead via the switching means 19 to the output line 9, but directly to one on the outside of the Housing 1 attached contact element 6. The contact element 6 is attached to the inlet opening of a recess 27, at the The bottom of the input contact 4 is. The recess 27 serves instead of the coupling piece 29 from Figure 1 for receiving the plug 25. The top of the input contact 4 is at a depth x from the inlet opening of the recess 27. The plug 25 has here again a connector housing 18 on the front the counter terminal 11 is arranged with resilient contact tongues. Furthermore the mating connector 11 has a side resilient contact tab 28 on that when inserting the plug 25 into the one in the housing 1 Indentation 27 touches the contact element 6, slides along it and when the plug 25 is fully inserted, no more contact to the contact element 6. During the side resilient contact tab 28 slides along the contact element 6, the counter-connection arrives 11 in electrically conductive contact with the input contact 4. This electrically conductive contact is maintained when the connector 25 is fully inserted into the recess 27.

Here too, when inserting the plug-in means 25, a first becomes electrically conductive connection between the counter terminal 11 and the Reference contact 7 via the second connecting line 8 and the contact element 6 manufactured. A charge balance between the reference contact 7 and the counter terminal 11 is therefore initially possible.

Then the input contact 4 and the counter terminal 11 touch and in the further consequence of the movement of the plug 25, the electrically conductive connection between the counter terminal 11 and the Contact element 6 interrupted. As a result, none remains here significant potential difference between the input contact 4 and the reference contact 7, which creates the ESD risk for those at the input contact 4 connected circuit 2 is reduced. The depth is x selected in an advantageous manner so that the lateral resilient Contact lobe 28 with plug-in means fully inserted into the recess 27 25 no longer touches the contact element 6 and discharges an electrically charged body only on the contact element 6 and can not be done on the inclusion 4. Alternatively, the interruption the electrically conductive connection between the reference contact 7 and the Counter terminal 11 also via a circuit mechanism analogous to FIG. 1 done, the choice of depth x no longer according to the above Criterion must take place.

Figure 3 shows an electrical device 26 to which the power supply 3, which is located in an external housing 1 ', can be connected. The numbering from FIGS. 1 and 2 is also in this figure maintained, the following differences compared to FIG. 1 are present: The connecting lines 12, 13 lead from the Power supply 3 away from the external housing 1 'and into it Housing 1 into the circuit located therein 2. Die Connection lines 12, 13 are between the housings 1, 1 ' interrupted and by means of plugs and couplings e.g. in the form of Pins and contact surfaces can be coupled together. In front of the switching device 19, a delay element 15 is additionally connected, which in the Recess 10, in which the probe arm 20 of the plug 25 engages, is arranged. In addition, the two connecting lines 12 and 13th connected within the housing 1 via an additional switch 14.

The additional switch 14 causes the line input of the first Connection line 13 on the housing 1 for connecting the power supply 3 remains connected to the reference contact 7 until the power supply 3 is connected. Charging the first connection line compared to the reference contact 7 is therefore not possible. The electric conductive connection of the first connecting line 13 with the reference contact 7 causes an electrically conductive connection of an electrically charged body, which extends from the housing 1 end of the first Line 13 touches, with the reference point 7. It will assumed that the electrically charged body is not that in the external Housing 1 is arranged power supply 3, but for example a inadvertently the end of the first connecting line starting from the housing 1 13 touching electrically charged body part. In this Case does not have to open the additional switch 14, in contrast to Case of connecting the power supply 3. Coupling the external Housing 1 'to the housing 1 causes a housing extension Open the additional switch 14 before all four coupling points in the Touch connecting lines 12, 13. The additional switch 14 must be on everyone Open case before connecting the power supply 3, otherwise a short circuit would result. Thus happens when the first one is connected Connection line 13 in contrast to the switching means 19 an opening of the Switch 14 before an electrically conductive connection in the first Connection line 13 takes place and not afterwards. The connection of the power supply 3 thus ensures that the first connecting line is touched 13 not by an electrically charged body more can be done. So here is an electrically conductive connection built between the counter terminal 11 and the input contact 4.

The formulation that an electrically conductive connection is "built up" is in the sense of the invention thus either that a electrically conductive connection exists, as shown in Figure 1 or that the contact to be protected is endangered by touch is prevented with an electrically charged body, as in the example the first connecting line 13 shown in Figure 5a. That was delayed Switching off the switching means 19 by means of the delay element 15 after the actuation by the probe arm 20 causes enough time to Charge compensation for the charge on the plug 25 is present between the input contact 4 and the reference contact 7.

FIG. 4 shows the electrical device 25 from FIG. 3 in a further embodiment, the same numbers denoting the same parts. In addition to the elements in FIG. 3, the external housing 1 'has an additional circuit 17 which has further electrical subcircuits m ₀ , m ₁ . The further electrical subcircuits m ₀ , m ₁ are also connected to the second connecting line 12 via a third connecting line 16 and a further reference contact 7 '. The additional circuit 17 also has outputs p ₁ , p ₂ , which are led out of the external housing 1 '. The housing 1 in turn has a plurality of inputs d _m , d ₀ , d ₁ , d ₂ , which are each connected to the circuit 2. Instead of the switching means 19, a second switching means s _{0 is provided} with a first switching line 31, via which the input d _{0 is} connected directly to the reference contact 7. Likewise, the input d _{1 is} connected directly to the reference contact 7 via a third switching means s ₁ and a second switching line 24, and the input d _{2 is} connected directly to the reference contact 7 via a fourth switching means s ₂ and a third switching line 23. The external housing 1 'has extensions 33, 34, 35 which fit into recesses in the housing 1 and which actuate the switching means s ₀ , s ₁ , s ₂ . The outputs p ₁ , p ₂ and the connecting lines 12, 13 end on the outside of the external housing in resilient contacts.

Through these connections, all inputs d _m , d ₀ , d ₁ , d _{2 are} connected to the reference contact 7 and thus there can be no significant potential difference between them and the reference contact 7. The inputs d _m , d ₀ , d ₁ , d ₂ are thus protected against potential differences resulting from contact with electrically charged bodies and damage caused thereby.

When the external housing 1 'is coupled to the outputs P ₁ , p ₂ and the connecting lines 12, 13, to the inputs d _m , d ₀ , d ₁ , d ₂ , the output p ₂ comes with the input d ₂ , the output p ₁ with the input d ₁ , the first connection line 13 with the input d ₀ and the second connection line 12 with the input dm in electrically conductive contact. The second switching means s ₀ is opened by one of the extensions 33, 34, 35 before the first connecting line 13 touches the associated input d ₀ , while the third and fourth switching means s ₁ , s ₂ only after contacting the outputs p ₁ , p _{2 can be} opened. This means that ESD protection can also be achieved for any arrangement of contacts between the electrical device 26 and its periphery.

FIG. 5a shows a further exemplary embodiment with a housing 1 and an associated external housing 1 'while retaining the previous numbering with the following differences: While the second connecting line 12 is connected to the reference contact 7 via the input d _m on the housing surface of the housing 1 the inputs d ₀ , d ₁ , d ₂ for connection to the first connecting line 13 or the outputs p ₁ , p ₂ in depressions 5 in the housing 1. The outputs p ₁ , p ₂ and the connecting lines 12, 13 have at their end pin contacts 36, 37, 38, 39 telescopically resiliently telescopically of equal length. The further housing 1 ′ is thus contacted first via the second connecting line 12 and only subsequently via the first connecting line 13 or the connections p ₁ , p ₂ . Thus, the spatial arrangement of the inputs d _m , d ₀ , d ₁ , d ₂ ensures that when the two housings 1, 1 'are brought together, the reference contact 7 is always used first to equalize the charge before the other contacts between the two Housing 1, 1 ', are connected. The input contact 4, which is configured here in FIG. 5 similarly to the input contact 4 in FIG. 2, has the contact element 6 at the input of the associated recess 27, which is connected to the reference contact via the switching means 19, which is designed here as a reed switch 7 is connected. The reed switch 19 enables contactless switching through the wall of the housing 1. The corresponding plug 25 is equipped with a switching magnet 30.

In the closed state, the switching means 19 only has to have a low volume resistance in order to limit the potential difference between the input contact 4 and the reference contact 7 to a level that is not dangerous for the circuit 2 and its electrical subcircuits n ₀ , n ₁ , ... n _i . An optical, mechanical, electrical or magnetic solution is equally provided as the actuating mechanism for the switching means 19. In addition, it is also expedient to combine the designs described above in order to obtain optimum protection against electrostatic discharge. It is also provided that the external housing 1 ′ with the additional circuit 17 is designed with an identical protective measure in order to obtain protection against ESD here too.

Figure 5b shows the structure of the pin contact 38, which consists of an outer Sleeve 42 with an end opening; in the sliding a pin 40 is supported which at its inner end in a base plate 45 merges with a spiral spring 41. The base plate 45 is surrounded by a slide ring 43 which the base plate 45 of the outer sleeve 42 insulated. The pin 40 is in the area of the front Opening from the outer sleeve 42 by means of an insulating bush 44 electrically isolated. The spiral spring 41 presses the base plate 45 against the end wall of the outer sleeve 42 so that an electrical conductive connection between the electrically conductive coil spring 41 over the pin 40 to the outer sleeve 42.

For the application according to the invention, the sleeve 42 is with the third connecting line 16 electrically connected. The coil spring 41 forms the line to the additional circuit 17. An indentation of pin 40 disconnects the connection that one before pressing Protection against electrostatic discharge.

Figure 6 shows an example of a configuration with contact pins. The following differences exist compared to the configuration according to FIG. 4:
Instead of the inputs d _m , d ₀ , d ₁ , d ₂ here contact pins k _m , k ₀ , k ₁ , k _{2 are} provided which protrude from the housing 1. The contact pin k _m is mechanically longer than the contact pins k ₀ , k ₁ , k ₂ and accordingly protrudes further from the housing 1 than this. The contact pins k _m , k ₀ , k ₁ , k ₂ are slidably mounted in the housing wall. They have disc-shaped contact means a _m , a ₀ , a ₁ , a ₂ lying within the housing 1 and rigidly connected to the contact pins k _m , k ₁ , k ₂ . The contact means a _m , a ₀ , a ₁ , a ₂ are supported against the housing wall and are pressed against the housing wall by spring elements f _m , f ₀ , f ₁ , f ₂ . Between the contact means a ₁ , a ₂ , the housing wall is provided with a conductor piece 32 which is electrically conductively connected to the reference contact 7 via the switching line 23, 24. The contact means a ₁ , a ₂ touch the conductor piece 32. A further conductor piece 31 corresponding to the first switching line 31 from FIG. 4 is arranged between the contact means a _m , a ₀ and forms an electrically conductive connection between the contact means a _m , a ₀ . The contact pin k _m is directly electrical with the reference contact 7 a _m , a ₀ . conductively connected. The external housing 1 'is provided with surface contacts y _m , y ₀ , y ₁ , y ₂ , which are connected to the connecting lines 12, 13 and the outputs p ₁ , p ₂ .

An approach of the external housing 1 'inevitably results in the surface contact y _m first coming into contact with the contact pin k _m . A charge adjustment takes place. The further movement of the external housing 1 'causes the switching means s _{0 to be} opened by the contact means a _m detaching from the further conductor piece 31. At the same time, the electrically conductive connection between the contact pin k ₀ and the reference contact 7 is also interrupted. A short circuit of the connecting lines 12, 13 is thus prevented. As soon as the further contacts y ₀ , y ₁ , y ₂ touch the respective contact pins k ₀ , k ₁ , k ₂ , charge matching to the reference contact 7 also takes place there. If the external housing 1 'is further approximated to the housing 1, the electrically conductive connections of the contact pins k ₁ , k ₂ to the reference contact 7 via the switching lines 23, 24 and the conductor piece 32 are also interrupted. Now the external housing 1 'is brought to the housing 1 in such a way that a functional connection is established, the connection being established while avoiding an ESD load. As an alternative to this, provision is also made for the switching line 23, 24 to be connected to the further conductor piece 31 instead of the reference contact 7. Then, when the contact pin k _{m is} pressed in, all the other contact pins k ₀ , k ₁ , k _{2 are} simultaneously electrically separated from the reference contact 7. Adequate ESD protection is also provided with this variant, since contact of the contact pins k ₀ , k ₁ , k ₂ with an electrically charged body is prevented by the spatial proximity of the housings 1, 1 'to one another. The length of the parts of the contact pins k _m , k ₀ , k ₁ , k ₂ projecting from the housing 1 expediently ranges from <1 cm.

As input contact 4 in the sense of the invention, both input and Output contacts of the electrical device 26 can be seen.

Claims (12)

1. Battery-operated electrical appliance having at least one input contact exposed to the risk of static charging, characterized in that the input contact (4) is connected by a switch means (19) for electrical conduction to a reference contact (7) of the electrical appliance, which contact is situated on a connection lead (12) of the current supply unit (3) of the electrical appliance (26), and in that the switch means (19) passes over to a substantially non-conductive state as soon as an electrically conductive connection has been made between the input contact (4) and a corresponding co-acting connection (11) of a plug means (25).
2. Battery-operated electrical appliance according to Claim 1, characterized in that the switch means (19) passes over to the substantially non-conductive state only at the end of a delay time after the electrically conductive connection between the input contact (4) and the corresponding co-acting connection (11) of the plug means (25) has been made.
3. Battery-operated electrical appliance according to Claim 1 or 2, characterized in that each input contact (4) of the electrical appliance (26) has switch means (19).
4. Battery-operated electrical appliance according to one of Claims 1 to 3, characterized in that the switch means (19) has an electrically conductive contact pin (k_m, k₀, k₁, k₂) which is connected for electrical conduction to the reference contact (7), and in that this connection can be broken by translatory or rotary movement of the contact pin (k_m, k₀, k₁, k₂).
5. Battery-operated electrical appliance having at least one input contact exposed to the risk of static charging, characterized in that the input contact (4) is arranged in a depression (27) on the electrical appliance (26), and in that a contact element which spatially precedes the input contact (4) is provided, said contact element being connected for electrical conduction to a reference contact (7) of the electrical appliance and which is situated on a connection lead (12) of the current supply unit (3) of the electrical appliance (26), and in that the contact element (6) is arranged such that an electrically conductive connection between the input contact (4) and a corresponding co-acting connection (11) of a plug means (25) is possible only after the co-acting connection (11) has made contact with the contact element (6).
6. Battery-operated electrical appliance according to Claim 5, characterized in that the contact element (6) is connected for electrical conduction to the reference contact (7) with the aid of a switch means (19) which passes over to a substantially non-conductive state as soon as an electrically conductive connection has been made between the contact elements (6) and the co-acting connection (11).
7. Battery-operated electrical appliance according to Claim 6, characterized in that the switch means (19) passes over to the substantially non-conductive state only at the end of a delay time after the electrically conductive connection between the contact element (6) and the co-acting connection (11) of the plug means (25) has been made.
8. Battery-operated electrical appliance according to one of Claims 1 to 7, characterized in that the switch means (19) can be operated by the plug means (25).
9. Battery-operated electrical appliance according to one of Claims 1 to 8, characterized in that the switch means (19) has a semiconductor switch.
10. Battery-operated electrical appliance according to one of Claims 1 to 9, characterized in that the switch means (19) has a reed switch, and in that the plug means (25) has a switch magnet (30) cooperating with the reed switch in the plugged-in state.
11. Battery-operated electrical appliance according to one of Claims 1 to 10, characterized in that at least one additional input contact (k_m) is provided, which is continuously connected for electrical conduction to the reference contact (7).
12. Battery-operated electrical appliance according to Claim 4, characterized in that the contact pin (k_m, k₀, k₁, k₂) is mounted for axial movement in a casing wall of the electrical appliance (26), and in that the contact pin (k_m, k₀, k₁, k₂) is connected for electrical conduction and mechanically rigidly to a contact means (a_m, a₀, a₁, a₂) which is pressed by the spring force of a spring element (f_m, f₀, f₁, f₂) to a conductor element (32) which is arranged on the casing (1) and is connected for electrical conduction to the reference contact (7).

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