GB2174258A - Circuit for preventing unauthorised use of electrical equipment - Google Patents

Abstract

The circuit has an electrical power input 13, 14 and a security (e.g. key operated) electrical switch 23 for switching between two positions, in one position connecting the power input direct to an electrical output 16 and in a second position connecting the power input via a current limiting device 28 to the output 16 which forms the sole power supply for the electrical equipment. The circuit may be used with a video recorder or computer, so that in the second position of the switch a clock will continue to operate but any attempted use of the video recorder or computer, requiring on increased load current, is prevented by the device 28. The device 28 may be a thermal switch or may limit the current without disconnecting the load. The circuit may be built into the equipment, or into a power socket or plug (Figs. 1 to 3). <IMAGE>

Description

SPECIFICATION Power supply control apparatus The present invention relates to power supply control apparatus.

In many cases it is desirable to control access to electrical equipment.

A particular problem arises in the use of video television recorders. There has been considerable concern and publicity regarding the protection of juveniles against the use of video cassette machines in the absence of their parents. Many types of video cassettes are available which are not suitable for juvenile viewing and in the absence of their parents juveniles have been known to use a video cassette recorder to replay cassettes of an unsuitable nature.

The use of some kind of key switch or key pad operated switch on the video recorder itself would be of some use but really is no more useful than locking the video recorder away in a locked cupboard in the parents' absence. The problem of such an arrangement is that interruption of the power supply affects the timing mechanism of the video recorder so that it is necessary to reset this timing mechanism every time the video recorder is switched back on.

The present invention relates to a power supply control apparatus for electrical equipment such as a video cassette recorder, although it is applicable to other pieces of electrical equipment, comprising an electrical power input means, a current limiting device, a security electrical switch for switching between two positions, in one position connecting the electrical power input direct to an electrical output and in a second position connecting the electrical power input to an input of the current limiting device the current limiting device being connected to the electrical output means, and the electrical output means being connected to the electrical equipment and forming the sole power supply therefor.

Thus by such an arrangement, the use of the current limiting device, may allow a limited current to pass from the power supply to the electrical equipment in use which may be sufficient to operate, for example, the timing mechanism of the electrical equipment, but insufficient to allow the proper operation of the electrical equipment.

The power supply control apparatus may be in the form of a plug which may be wired to the end of the wire from the electrical equipment and may be simply inserted in a power socket or may be built into the electrical equipment itself.

The current limiting device may comprise a thermal cut-out switch or other device which allows only a limited current to flow therethrough.

A preferred arrangement of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure l is a front perspective view of the power supply control apparatus according to the invention, Figure 2 is a rear perspective view of the power supply control apparatus according to the invention, Figure 3 is a view of the apparatus of Figs.

1 and 2 in pieces, and, Figure 4 is a circuit diagram of the apparatus of Fig. 1.

Referring to Figs. 1 and 2 the power supply control apparatus 10 is in the form of a plug 11 which may be plugged into an electrical socket (not shown) by means of pins 12, 13, 14 (pin 12 being a plastic pin for opening the shutters on the socket) and is connected by means of an electrical lead 16 to the electrical equipment 17 which may be a video recorder.

The power supply control apparatus 10 comprises a housing 1 7 from the rear face of which extend the pins 12, 13, 14 and on the front housing is mounted a key hole 18 provided in a circular mounting 19, the key hole itself being rotatable between two positions, in one of which it aligns with a first indication 21 marked "video" and in the second position in which it aligns with an indication 22 marked "clock".

Fig. 4 illustrates a circuit diagram of the power supply control apparatus 10. It will be seen that the pin 14, is connected to the neutral line of the power supply directly through to a respective wires within the output lead 16.

However the live pin 13 is connected inside the housing 17 to a key switch (not shown) operated by means of the key hole 18 and when the key hole 18 is aligned with the indicator 21 ("video") the key switch switches the live pin 13 to a line 27 and when the key hole 18 is aligned with the indication 22 ("clock") the live pin 13 is connected to the line 26. The line 26 is connected to a current limiting device in the form of a thermal switch 28 and the output of the thermal switch 28 comprising a line 29 is connected, together with line 27 direct to the live wire within the output lead 16.

Fig. 3 shows the power supply control apparatus 10 when taken apart, the rear face of the housing 17 being removable from the remainder of the housing.

The thermal switch 28 may be of a type having a characteristic such that at a current level passing through line 13 less than approximately 90 mA the switch 28 remains closed, but at higher currents the switch 28 opens.

In use of the power supply control apparatus the apparatus 10 may be inserted into an electrical supply in the form of the electrical socket so that power is supplied to the live pin 13. We will assume that the apparatus 10 is connected to electrical apparatus 20 in the form of a video recorder. A video cassette recorder includes a clock circuit which requires about 65 mA to operate the clock and drive motors which require more than 100 mA to drive them.

Let us assume that the key hole 18 is aligned with indication 21 so that power is supplied from the pin 13 direct to the video recorder direct through line 27. In this position the video recorder 20 may be operated normally as sufficient current to drive the motors and others parts of the video recorder may be drawn through the apparatus 10 from the pin 13 to the video recorder 20 (although a fuse 31 may be incorporated in the apparatus 10 so as to limit the current to, for example, 13 amps to prevent damage to the video recorder 20).

If, however, the person holding the key to a key 25 hole 18 (normally the parent) wishes to limit the operation of the video recorder 20, then the key 25 may be inserted into the key hole 18 and the key hole 78 aligned with the indication 22. This connects the thermal switch 28 into the circuit. The key 25 is then removed in this position. The thermal switch 28 allows the passage of sufficient current from the pin 13 to operate the clock. If, however, the video recorder is switched on and a cassette inserted so as to operate the video recorder then sufficient current will pass through the thermal switch 28 such that the thermal switch 28 will switch off and cut connection between the live pin 13 and the video recorder 20.

It is thus not possible to operate the video recorder whilst the key hole 18 is aligned with the indication 22.

In this way parents can limit the use of the video recorder by their children or other persons whilst they are absent.

Clearly there are other uses for a similar arrangement, for example with computers or other electrical equipment to which access should be restricted but which should be normally continuously connected to the electrical supply, for example to maintain a clock circuit in operation.

Although the power supply control apparatus 10 has been described in the form of a separate unit wired to the electrical equipment such as video recorder 20 similar apparatus may be incorporated in the electrical equipment itself. Thus the video recorder may include in its power supply circuit a key switch 23 and thermal switch 28 and other components arranged so as to limit unauthorised usage of the video recorder without the key.

Furthermore a current limiting device which limits the current to, say, 90 mA, without cutting out may be used in place of the thermal switch 28.

The invention is not restricted to the details of the foregoing examples.

Claims (5)

1. A power supply control apparatus for electrical apparatus, the power supply control apparatus comprising an electrical power input means, a current limiting device, a security electrical switch for switching between two positions, in one position connecting the electrical power input direct to an electrical output and in a second position connecting the electrical power input to an input of the current limiting device, the current limiting device being connected to the electrical output means, and the electrical output means being connected to the electrical equipment and forming the sole power supply therefor.

2. Apparatus as claimed in Claim 1 in which the power supply control apparatus includes a plug which is wired to the end of the wire from the electrical equipment.

3. Apparatus as claimed in Claim 1 or Claim 2 in which the current limiting device comprises a thermal cut-out switch which allows only a limited current to flow therethrough.

4. Apparatus as claimed in any of Claims 1 to 3 in which the security electrical switch includes a keyioperated lock.

5. Apparatus as claimed in Claim 1 substantially as hereinbefore described with reference to the accompanying drawings.