GB1571056A - Circuit for monitoring electrical consumers - Google Patents

Description

(54) A CIRCUIT FOR MONITORING ELECTRICAL CONSUMERS (71) We, ROBERT BOSCH GMBH, a German Company, of Postfach 50, 7 Stuttgart 1, Federal Republic of Germany, do hereby declare-the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a circuit for monitoring electrical consumers, in particular bulbs of a motor vehicle, whereby each consumer group or each consumer to be monitored is connected in series to a low-resistance measuring resistor and to a switch and the voltage tapped at the measuring resistor is supplied to an electronic switching device in whose output a signal generator, in particular a warning light, is located and which is held in its blocked state when intact consumers are switched on but is made current-conductive when a consumer breaks down.

In a circuit proposed in German Offenlegungsschrift 21 47 681, a tapping between each consumer and its associated measuring resistor is supplied to the emitter of a transistor whose collector is connected to the control electrode of a semi-conductor which switches the signal generator. The base of the transistor is biassed in such a manner that, in the case of an intact consumer, the potential supplied to tthe collector is not sufficient tto make the transistor current-conductive. If the consumer breaks down, the potential increases, the transistor becomes current-conductive and therefore in turn makes the above-mentioned semiconductor current-conductive so that the signal generator indicates a defect.

The disadvantage of this solution is that, to switch the transistor over, the emitter potential must be raised by a sufficiently high amount which is only possible if there is a complete interruption at the consumer. The circuit is therefore unsuitable for monitoring bulb pairs of a motor vehicle which are to be monitored by means of a common measuring resistor. If one bulb failed, the current flowing through the measuring resistor would certainly be reduced in this case.

However, since the measuring resistor must be kept as low-resistance as possible, the potential tapped at it would not be enough for a complete switching over of the transistor or the semi-conductor for the signal generator even with a reduced supply voltage, e.g. with a weakly charged accumulator battery. Thus, a separate measuring resistor has to be provided for each consumer.

An aim of the invention is to outline a circuit with which it is possible even with voltage fluctuations to monitor several consumers at a common measuring resistor and which with the minimum circuit outlay ensures reliable response of the switching device even in the case of partial or complete failure of a monitored consumer.

According to the present invention there is provided a circuit for monitoring electrical consumers comprising a low-resistance measuring resistor and a switch connectible in series to a consumer or consumer group and arranged such that the voltage tapped at the rneasuring resistor in use, is supplied through a diode to the control path of a first semi-conductor whose switching path is connected in parallel with the control path of a second semi conductor, at least the switching patn ot tie first semiconductor being connected to the tapping of a voltage divider which is con nected on the one hand to earth and is con nectible on the other hand to the switch of the consumer or consumer group to be moni- tored and the second semi-conductor lying with its switching path in the control circuit of a control semi-conductor whose switching path is connected in series with a signal generator for indicating when a consumer breaks down, and is connectible to a supply voltage.

In this circuit, the common resistor in the switching path of the first and second semiconductor in cooperation with the remaining circuit has the effect that switching-over of the output is effected independently of the operating voltage at a reduction of the receiving current by a fixed percentage.

The switching sensitivity is improved by the two semi-conductors acting as signal amplifiers to such an extent that even bulbs connected in pairs may be monitored at one measuring resistor.

The invention is described further by way of example with reference to the accompanying drawings in which: Fig. 1 is a circuit for monitoring a pair of bulbs having a switching device with a control semi-conductor which is controlled by a switching stage, and Fig. 2 is a circuit for monitoring several pairs of bulbs by a switching device in which several switching stages control a common control semi-conductor.

In the circuit shown in Fig. I, a supply line 10 is connected to the positive pole of the power supply of a motor vehicle. The supply line 10 is connected by a switch 11 to a receiving line 12 to which two bulbs 13a and 13b, which are connected in parallel, are connected by a common fuse 14. A switching device 15 is provided for monitoring the bulbs and has a measuring resistor 16 of 150 m a which lies in the receiving line 12 and whose voltage drop when the bulbs 13 of 15W are switched on is used to control the switching device. The voltage potential at a tapping 17 between the measuring resistor 16 and the bulbs 13 is supplied through a resistor 18 and a diode 19 connected in series taerewith to the base of a first PNP-transistor 20. The switching path of this transistor 20 lies parallel to the control path of a second PNP-transistor 21 in that the emitters of both transistors are directly connected to one another and in that the collector of the first transistor 20 is connected to the base of the second transistor 21.

The emitter terminaL of the first transistor is connected jointly with that of the second transistor through a resistor 22 and through the line 12 to the switch 11 of the bulbs 13 to be monitored. The collector of the second transistor 21 is connected by a resistor 23 to the base of an NPN-conductive control transistor 24 whose switching path is connected in series with a warning light 25 through a line 26 which is connected on the one hand to the supply line 10 and on the other hand through a diode 27 and a resistor 28 connected in series therewith to the collector terminal of the control transistor 24 whose emitter terminal is earthed. The emitter terminals of the first and second transistors 20 and 21 are jointly connected to earth by a variable resistor 29 and the collector terminal of the first transistor 20 is connected to earth by another resistor 30. Moreover, the base of the first transistor 20 is connected by a capacitor 31 to its collector and by another resistor 32 to earth. The first and second transistors 20, 21 are therefore connected on the emitter side, to a voltage divider formed by resistors 22 and 27. This voltage divider ensures that the variations in voltage in the supply system do not affect the sensitivity of the monitoring device, as is described hereinbelow.

The mode of operation of the monitoring device is such that when the switch 11 is opened the transistors 20 and 21 are blocked so that the base of the control transistors 24 does not receive any positive voltage potential.

The control transistor 24 is therefore also blocked and the warning light 25 remains disconnected.

When the switch 11 is closed and the bulbs 13a and 13b are intact, a current flows from the supply line 10 through the switch 11, the measuring resistor 16 and the fuse 14 to the two bulbs 13a and 13b and from there to earth. The voltage drop thereby arising at the measuring resistor 16 passes on the one hand through the resistor 22 to the emitter terminal of the first transistor 20 and on the other hand through the resistor 18 and the diode 19 to the base of this first transistor 20.

When the bulbs 13a and 13b are intact, the voltage drop at the measuring resistor 16 is so great that the first transistor 20 is switched through completely into its current-conductive state. As a result, the emitter to base section of the second transistor 21 is short-circuited so that this transistor remains blocked and therefore through the resistor 23 also holds the control transistor 24 blocked. Still the warning light 25 remains disconnected.

If there is a defect in a bulb, the current in the measuring resistor 16 is reduced to half and therefore also the voltage drop arising at it. The potential at the tapping 17 between the measuring resistor 16 and the bulbs 13 is consequently increased to such an extent that the first transistor 20 then blocks.

Through the resistor 30 connected to its collector, the earth potential then passes to the base of the second transistor 21 and switches it over completely into its currentconductive state. As a result, the positive potential at the switching path of this transistor 21 is then switched through the resistor 23 to the base of the control transistor 24 so that this transistor too is switched completely over into its current-conductive state. A signal current then flows through the warning light 25 by way of the line 26, the diode 27, the resistor 28 and the switching path of the control transistor 24. The warning light 25 lights up and indicates a defect in one of the moni tored bulbs.

In this manner both the two bulbs 13a and 13b and the fuse 14 are monitored. If the fuse 14 blows, the current is interrupted so that there is practically no longer any voltage drop at the measuring resistor 16. In this case too, the first transistor 20 is blocked so that the second transistor 21 is made currentconductive. Since this transistor lies in the control path of the control transistor 24, it also makes this transistor current-conductive so that even when the fuse 14 fails the warn ing light 25 lights up. The exact setting of the switching threshold is effected by adjustment of the resistor 29.

Whilst the monitoring device is sensitive to voltage fluctuations arising from the bulbs 13a and 13b, or fuse 14, burning out, the monitoring device is insensitive to variations in voltage in the vehicle supply system. This is due to the first and second transistors 20, 21 being connected in the emitter side, to a voltage divider formed by resistors 22 and 29. This arrangement results in variations in voltage in the vehicle supply system causing equally large variations in potential both at the base and at the emitter of first transistor 20. Thus these voltage fluctuations do not have any effect upon the monitoring device and it is thereby possible to determine the res ponse threshold of the transistor 20 so accurately that a plurality of lamps, con nected in parallel, can be monitored with only one measuring resistor 16. The same provision in the arrangement of Fig. 2, provides for the same facility.

In Fig. 2, baslcally the same circuit con struction is again provided for several con sumer groups in the switching device 15a. In so doing, the first and second transistors 20 and 21 are combined with the resistors 29, 30, the capacitor 31 and the resistor 32 into a switching stage in the form of a threshold value switch. In the first consumer circuit to be monitored, the right parking light bulb 41 and the right rear light bulb 42 are con nected in parallel and are connected by a fuse 43 to the measuring resistor 16a. The bulbs are either connected by an ignition switch 44 and a parking light switch 45 connected in series therewith through the receiving line 12a or they are switched by means of a light switch 46 arranged parallel thereto. The voltage drop at the measuring resistor 16a is supplied on the one hand through the resistor 22a and on the other hand through the resistor 18a to the diode 19a of the switching stage 40a connected in series therewith, said switching stages already mentioned-comprising the two tran sistors 20 and 21 described in Fig. 1.

In a second receiving circuit, the left park ing light bulb 51 and the left rear light bulb 22 are connected in parallel and are connected by a common fuse 53 to the measuring resistor 16b to the receiving line 12b. The voltage drop at the measuring resistor 16b is supplied in this case on the one hand through the resistor 22b and on the other hand through the resistor 18b to the diode 19b of another switching stage 40b connected in series there with. In the third consumer circuit, two number plate lights 61 are connected in parallel and are connected to a measuring resistor 16c. In this consumer circuit there is a fuse 63 before the switching contact of the light switch 46 to which the receiving line 12c of the number plate lights 61 is connected.

The switching stage 40c associated with this consumer circuit is again connected by a resistor 22c on the one hand and by a resistor 1 sic and a series-connected diode 1 9c to the ends of the measuring resistor 16c. In the last consumer circuit, failure of the fuse 63 is not simultaneously monitored by the switching stage 40c. Here, monitoring is effected by a separate control circuit. This control circuit comprises a PNP-transistor 64 whose emitter is connected to the tapping of a voltage divider comprising two series-connected resistors 65 and 66 which lies between the supply line 10a and earth and which therefore supplies a fixed emitter potential to the transistor 64. The base of the transistor 64 is connected to the tapping of another voltage divider whose two resistors 67 and 68 are connected behind the fuse 63 and on the.ather hand also to earth.

The outputs of the three switching stages 40a, 40b, 40c are each connected by an out put resistor 23a, 23b and 23c in parallel to one another and to the switching path of the transistor 64, and they are jointly connected by the resistor 23 to the base of the control transistor 24. In this case too, the warning light 25 is connected in series with the diode 27, the resistor 28 and the switching path of the control transistor 24. The warning light is directly connected to the supply line 10a whilst the emitter terminal of the control transistor 24 is earthed.

The mode of operation of the circuit shown in Fig. 2 is-like that of Fig. 1-such that with intact connected bulbs the control tran sistor 24 is blocked so that the warning light 25 is disconnected since at the output of the switching stages 40a, 40b and 40c no signal is produced which can make the control transistor 24 current-conductive. However, if, for example, the right rear light bulb 42 in the first consumer circuit fails, the voltage drop at the measuring resistor 16a is reduced and the first transisistor, which was previously biassed in its conductive state, of the switching stage 40a becomes blocked. Consequently, the second transistor of the switching stage 40a is made current-conductive. At the output of this switching stage 40a therefore a switching signal is produced which passes through the resistor 23a and the resistor 23 to the base of the control transistor 42 and makes the latter current-conductive. A signal current then flows through the warning light 25, the diode 27, the resistor 28 and the switching path of the control transistor 24 to earth. The warning light lights up and indicates the defect in one of the monitored bulbs.

In the case of a defect in the second or third consumer circuit, if the consumer cir cuit is connected, the same process is re peated accordingly at the control stage 40b or 40c with the result that a signal voltage passes through the relevant output resistor 23b or 23c and the resistor 23 to the base of the control transistor 24 and makes the latter current-conductive for connection of the warning light. The warning light goes out, however, as soon as the consumer circuit is disconnected.

In the case of a healthy fuse 63, a specific potential also lies across the base of the transistor 64. This potential is so dimensioned that the transistor 64 is controlled completely into its blocked state. If there is a defect in the fuse 63, the power-supply voltage no longer reaches the voltage divider 67, 68 and the base of the transistor 64 then receives through the resistor 68 almost earth potential.

As a result, the transistor 64 is made completely conductive. The potential at its collector is then increased so that the control transistor 24 is also switched through. The warning light 25 then indicates the defect in the fuse by lighting up.

WHAT WE CLAIM IS:- 1. A circuit for monitoring electrical consumers comprising a low-resistance measuring resistor and a switch connectible in series to a consumer or consumer group and arranged such that the voltage tapped at the measuring resistor in use is supplied through a diode to the control path of a first semi-conductor whose switching path is connected in parallel with the control path of a second semiconductor, at least the switching path of the first semi-conductor being connected to the tapping of a voltage divider which is connected on the one hand to earth and is connectible on the other hand to the switch of the consumer or consumer group to be monitored and the second semi-conductor lying with its switching path in the control circuit of a control semi-conductor whose switching path is connected in series with a signal generator for indicating when a consumer breaks down and is connectible to supply voltage.

2. A circuit as claimed in claim 1, in which the first and second semi-conductors form a switching stage whose output is connected by a resistor in parallel with other switching stages which are jointly connected in series with the control path of the control semiconductor.

3. A circuit as claimed in claim 1 or 2 in which the first and second semi-conductors are PNP-transistors and the control semiconductor is an NPN-transistor.

4. A circuit as claimed in claim 3, in which the emitter terminals of the first and second transistors are connected to one another and the collector terminal of the first transistor is connected by a resistor to earth.

5. A circuit as claimed in claim 4, in which the base of the first transistor is connected on the one hand by a resistor to earth and is connectible on the other hand by the diode and another resistor connected in series there with between the measuring resistor and the consumer or consumer group to be monitored.

6. A circuit as claimed in any of claims 3 to 5 in which the signal generator comprises a warning light lying in the collector circuit of the control transistor.

7. A circuit as claimed in claim 1, including consumers in the form of two bulbs connected in parallel and having a common preconnected fuse connected in series with measuring resistor.

8. A circuit as claimed in claim 2 in which a fuse of the consumer or consumers group is disposed before the measuring resistor and, for monitoring the fuse, there is connected to its tailings a voltage divider which is connected to the tapping by the base of another transistor, the switching path of the transistor being connected on the emitter side to the tapping of another voltage divider connected to the supply voltage and being connected on the collector side in parallel to the outputs of the switching stages to the control path of the control semi-conductor.

9. A circuit for monitoring electrical consumers, arranged substantially as herein particularly described with reference to and as illustrated in Fig 1; or Fig. 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. the control transistor 24 and makes the latter current-conductive for connection of the warning light. The warning light goes out, however, as soon as the consumer circuit is disconnected. In the case of a healthy fuse 63, a specific potential also lies across the base of the transistor 64. This potential is so dimensioned that the transistor 64 is controlled completely into its blocked state. If there is a defect in the fuse 63, the power-supply voltage no longer reaches the voltage divider 67, 68 and the base of the transistor 64 then receives through the resistor 68 almost earth potential. As a result, the transistor 64 is made completely conductive. The potential at its collector is then increased so that the control transistor 24 is also switched through. The warning light 25 then indicates the defect in the fuse by lighting up. WHAT WE CLAIM IS:-

1. A circuit for monitoring electrical consumers comprising a low-resistance measuring resistor and a switch connectible in series to a consumer or consumer group and arranged such that the voltage tapped at the measuring resistor in use is supplied through a diode to the control path of a first semi-conductor whose switching path is connected in parallel with the control path of a second semiconductor, at least the switching path of the first semi-conductor being connected to the tapping of a voltage divider which is connected on the one hand to earth and is connectible on the other hand to the switch of the consumer or consumer group to be monitored and the second semi-conductor lying with its switching path in the control circuit of a control semi-conductor whose switching path is connected in series with a signal generator for indicating when a consumer breaks down and is connectible to supply voltage.

2. A circuit as claimed in claim 1, in which the first and second semi-conductors form a switching stage whose output is connected by a resistor in parallel with other switching stages which are jointly connected in series with the control path of the control semiconductor.

3. A circuit as claimed in claim 1 or 2 in which the first and second semi-conductors are PNP-transistors and the control semiconductor is an NPN-transistor.

4. A circuit as claimed in claim 3, in which the emitter terminals of the first and second transistors are connected to one another and the collector terminal of the first transistor is connected by a resistor to earth.

5. A circuit as claimed in claim 4, in which the base of the first transistor is connected on the one hand by a resistor to earth and is connectible on the other hand by the diode and another resistor connected in series there with between the measuring resistor and the consumer or consumer group to be monitored.

6. A circuit as claimed in any of claims 3 to 5 in which the signal generator comprises a warning light lying in the collector circuit of the control transistor.

7. A circuit as claimed in claim 1, including consumers in the form of two bulbs connected in parallel and having a common preconnected fuse connected in series with measuring resistor.

8. A circuit as claimed in claim 2 in which a fuse of the consumer or consumers group is disposed before the measuring resistor and, for monitoring the fuse, there is connected to its tailings a voltage divider which is connected to the tapping by the base of another transistor, the switching path of the transistor being connected on the emitter side to the tapping of another voltage divider connected to the supply voltage and being connected on the collector side in parallel to the outputs of the switching stages to the control path of the control semi-conductor.

9. A circuit for monitoring electrical consumers, arranged substantially as herein particularly described with reference to and as illustrated in Fig 1; or Fig. 2 of the accompanying drawings.