The present invention relates to a device for breaking the supply of current to a mains connected electronic apparatus having at least two different normal alternative current consumption levels due to the equipment current consumption deviating from one of these consumption levels, wherein the device includes a current breaker which is connected in series with the current consumption line of the equipment.

It is well known that a strong indication of a malfunction in electronic equipment which is normally mains connected is when the equipment current consumption/power consumption begins to deviate from a normal consumption level. In this regard it has been realized that when a malfunction occurs, it is important to quickly cut-off the supply of current to the equipment in order to prevent subsequent events in the form of smoke, fire, short-circuiting, etc. , that may occur should the malfunction be allowed to continue. It is also known to connect-up the equipment current supply line through the medium of a current breaker provided with a window discriminator which accepts a current consumption/power consumption within given window limits, and which therewith permits the current breaker to conduct current to the equipment provided that consumption lies within the window, whereas the discriminator is constructed to otherwise cause the current breaker to isolate the equipment from the mains/current source.

Such window discriminator controlled current breakers are well known to the art; c.f. EP-A2 3,074,417, DE-A1 6,924,419 and US-A 3,934,239.

However, the use of a known circuit breaker construction in the case of electronic equipment whose power consumption markedly varies or which have two or more different normal alternative current consumption levels, is not convenient

because it is necessary to make the circuit breaker window so wide as to make it impossible to detect in a meaningful way deviations from the window limits that are significant with regard to malfunctions. For instance, the window discriminator is unable to detect a malfunction in the form of overcurrent or excess current occurring from a region in the vicinity of the bottom limit of the window, or to detect an "undercurrent" on the basis of a current level in the vicinity of the upper limit of the window.

The object of the present invention is to provide a device which will safeguard against fires or other consequential damage to mains connected electronic equipment that has at least two different normal alternative current consumption levels, when the current consumption/power consumption of the equipment deviates significantly from one of the alternative normal power levels/current consumption levels.

The invention is defined in the following Claim 1.

Further developments of the invention are set forth in the dependent Claims.

The invention is based on the concept of providing for connection between the mains supply and the electronic equipment a current breaker which has at least two window discriminators, one for each alternative normal equipment power consumption level/equipment current consumption level, said window discriminators being adapted so that the differ- ent equipment current consumption levels will each lie within a respective window, wherein the discriminators are adapted to trigger activation of the current breaker, i.e. to cause the current breaker to break the supply of current to the equipment, when the equipment current consumption does not lie within any one of the windows.

Naturally, the inventive device may include more than two

windows, so that it can be used with equipment that has more than two normal current consumption levels. In order to enable the inventive device to be adapted to different equipment having mutually different normal current consump- tion levels and different permitted variations in normal current consumption at respective levels, the inventive device may be provided with adjustment means for setting the limits of the different discriminator windows and therewith adapt the device to the respective current consumption levels of a given piece of equipment.

When the inventive device shall be used with equipment having a first current consumption level which corresponds to an equipment stand-by state, and a second current consumption level which corresponds to an operational state of the equipment, the discriminator window of the device may have preset magnitudes for the first and the second levels, and the operating devices may be adapted to permit respective windows to be displaced so as to cover respective current consumption levels of the equipment concerned. The device may also include an exposed light-emitting diode which lights up when a discriminator window covers the instantaneous power consumption of the equipment.

The device may also be provided with a conventional resetting device which enables the circuit breaker to be reset manually after having been released.

The device may advantageously be formed by a housing unit which carries an electrical contact for connection to a mains outlet, and which includes a socket connection for a plug contact on a mains connecting cable belonging to the equip¬ ment.

According to preferred embodiments, the window discriminators of the device may be adapted generally for adjustment to a stand-by level and to an operational level of current

consumption of conventional remote control equipment, such as a TV-set.

The control devices activated by the window discriminators will conveniently have a time delay function which will allow the equipment current consumption to be reset to the differ¬ ent levels without releasing the current breaker, within a predetermined permitted resetting time.

The discriminators are suitably connected to a circuit which will prevent the circuit breaker being triggered or released when the level of current consumed by the equipment lies within the setting of a discriminator window.

It will be understood that the inventive device finds general use with current-consuming equipment that have at least two different current consumption levels, wherein the levels can be considered to have typical variation limits so that a clear indication of a malfunction will lie in the extent to which current consumption within the limits of said current consumption level deviates from said level limits.

The invention is well suited for use with TV-sets that have a stand-by function.

The inventive device can also be used beneficially with music and audio systems. However, because the amount of current consumed by such systems when in an operating state will vary markedly in relation to a mean power level, it is necessary to make the window correspondingly large or to take other appropriate measures.

It is also conceivable within the scope of the invention to couple several different pieces of electronic equipment to the mains network through the medium of one single inventive device, wherein the protection afforded these pieces of equipment will be effective when the device is designed to

embrace each of the different power levels of the combination with an intrinsic discriminator window of sufficiently small size.

The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings, in which

Fig. 1 is a detailed circuit diagram of an inventive device; and

Fig. 2 illustrates schematically the outer configuration of an inventive device.

Referring first to Fig. 2, the embodiment illustrated in this Figure is based on a protective circuit breaker generally referenced A and available commercially from and manufactured by Marelko, Gothenburg, Sweden, under the trade designation Marelko M-01B, power supply & breaker.

In accordance with the invention, the circuit breaker A (Marelko M-01B) has been supplemented with the illustrated circuits and components, which for the sake of clarity have been shown outside the "wall" A of the fundamental circuit breaker. The components have been identified with convention¬ al signs and symbols.

Referring again to Fig. 2, the circuit breaker A is supple¬ mented with setting knobs VR1 and VR2, a light-emitting diode LED and a switch SI. The actual circuit breaker A also includes a male electrical contact IN and a female electrical contact OUT.

The operator may connect the IN side of the device to a wall socket and the electrical connection cable of, e.g., a remote controlled TV-set to the OUT side.

When the television set is now switched on to a stand-by state, the switch SI is manually pressed-in at the same time, so as to prevent the circuit breaker unit A from immediately breaking the current supply or from breaking the current supply after a short space of time has lapsed. With the switch SI pressed in, the operator turns the knob VR1 until the light emitting diode LED lights up. The idling current supplied to the television set in its stand-by state will now lie within a discriminator window and the circuit breaker unit A will automatically break the supply of current to the television set should the current consumed by the television set in its stand-by state deviates from the set window value.

The operator can now adjust the television set to its operational state, with the switch SI being held pressed-in and the knob VR2 turned until the light-emitting diode lights up, so that the current consumed by the television set in its operational state also lies within a predetermined window.

The circuit defines time constants which prevent the circuit breaker A from momentarily breaking the supply of current should the current consumption momentarily deviate from a discriminator window. The circuit is also designed to accept when the connected equipment, for instance the television set, is disconnected, for instance through its main switch. This is achieved in the exemplifying embodiment of Fig. 2, by coupling in R14. Illumination of the light-emitting diode LED indicates that current is available from the current breaker A.

The aforementioned time constants, which after a short period of time would cause the circuit breaker relays to break the current supply, are defined, e.g., by C4, C6, R15-C9, R21- C10, and others. These time constants are neutralized by closing the switch SI and holding the switch closed while setting the windows with the aid of the knobs VR1, VR2.

The consumption currents to be measured are isolated from the network and converted to appropriate relative measuring voltages in the current transformer Tl, which is essentially loaded by C2, R5, R7.

This load can be accepted when no absolute values are required.

When the absolute values of the measuring signal are low, particularly in the lower current regions, it is necessary to amplify the AC signal in order to obtain a correct DC signal. This is effected in ICla and b.

The amplification in ICla for the "low" current region is substantially greater than in the operational amplifier IClb, which is otherwise identically coupled. As a result, the two rectifying couplings C3-D1-D2-C4 and C5-D3-D4-C6 deliver DC measuring signals which lie well within the available dynamic range of the chosen, permitted "current windows", even at supply voltages as low as 5V.

These measuring voltages are delivered to the operational amplifiers IC2a, b, c and d, used as comparators. IC2 is coupled to function as two mutually independent window discriminators. IC2a and IC2b form "low" window discrimin¬ ators and IC2c and IC2d form a "high" window discriminator. Since these circuits are identical to each other, only IC2a and b will be discussed.

The negative input on IC2a is connected to the positive input on IC2b via R10-R12. The measuring signal is applied to the junction node between RIO and R12, and is loaded with Rll to earth.

A fixed voltage, although adjustable via VR1, is applied from R16-R18 to the negative input on IC2b and, via the hysteresis resistance R9, to the positive input on IC2a. The hysteresis

function is balanced by R8.

As a result, the outputs of the two operational amplifiers will pass to a high state only when the value of the measur- ing signal lies within the hysteresis of the value set by the setting knob VR1. In this regard, none of the diodes D5 or D6 will load the line which is high via R13. The high signal which reaches the positive input on IClc via D7 and R19 is then higher than the signal which reaches the negative input via R14, since this signal is limited by ZDl, despite the occurrence of a saturated signal o OCla. The pin 8 of the integrated circuit IClc therewith goes high. The positive input on ICld goes high, via R29, and the light-emitting diode LED lights up. At the same time, the power unit M-01B is commanded to hold the relays drawn, i.e. the circuit closed, via R20, Dll, R23.

TR1 together with Rl and the time constant R21-V10 short- circuit momentarily the +5V supply and herewith ensure that Tyl is extinguished.