GB1570764A

GB1570764A - Circuit for monitoring electrical loads

Info

Publication number: GB1570764A
Application number: GB5377/77A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1976-02-10
Filing date: 1977-02-09
Publication date: 1980-07-09
Also published as: DE2605114C2; DE2605114A1; SE408876B; SE7701432L

Description

(54) A CIRCUIT FOR MONITORING ELECTRICAL LOADS (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 loads, in particular bulbs of a motor vehicle.

In one such proposed circuit each consumer or consumer group i.e. load, to be monitored is connected in series with a switch and a low-resistance measuring resistor, the voltage tapped between the consumer or consumer group and the measuring resistor or between the switch and the measuring resistor being supplied to a threshold value switch of an electronic switching device whose output is coupled to a signal generator, preferably a warning light, and which is held in its blocked state when intact consumers are switched on but conducts if a consumer fails.

In such a circuit, the voltage drop of each measuring resistor associated with a consumer or consumer group is supplied to a threshold value switch. The measuring resistor and the threshold value switch are so tuned to one another that with intact consumers the voltage drop at the measuring resistor keeps the threshold value switch blocked so that no signal arises at its output to switch on the warning light.

If there is a current interruption at the consumer-e.g. a bulb burns out-, a voltage drop no longer arises at the measuring resistor. Thus, the threshold value switch is switched into its other state so that a signal is produced at its output which then switches on the warning light by means of the controllable semiconductor. The warning light goes out as soon as the consumer is disconnected or as soon as the fault is eliminated.

The disadvantage of this solution is that, for example, a defect in the switch of the monitored consumer is not indicated. For example, monitoring of the brake light bulbs of a motor vehicle is important for road safety but such monitoring is incomplete if the functioning of the brake light switch is not also monitored. Another disadvantage of the circuit is that a defect in the warning light is not noticed so that monitoring of the electrical consumers may be discontinued unbeknown to the driver of the vehicle.

An aim of the invention is to outline a circuit in which both the functioning of the switch of the consumers to be monitored and the functioning of the warning light may be checked by the driver of the vehicle.

According to the present invention there is provided a circuit for energising from a supply voltage, one or more electrical loads connected in parallel via a switch, said circuit comprising a switch, a measuring resistor and said loads, all connected in series, a threshold circuit being adapted to, in use, remain in a bolcked state when every load is switched on and is working normally and to conduct if a load fails, and whose output is coupled to an indicator via a signal storage circuit, the storage circuit having a resetting input which is connected by a differentiating circuit to the switch and is adapted to control the indicator through a semiconductor device, and a testing key so connected that when operated the input of the threshold circuit is connected to the supply voltage.

If a fuse for the consumer i.e. load, is located before the switch, it is particularly advantageous if only the measuring resistor and the switch are bypassed by the testing key.

The invention is described further, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a diagram of a circuit for monitoring a brake light system of a motor vehicle, and Fig. 2 is a diagram of the circuit shown in Fig. 1 having additional monitoring stages for a fuse element and for other consumers.

In the circuit shown in Figs. 1 and 2, a supply line 10 is to be connected to the power supply of a motor vehicle. In Fig. 1, this supply line 10 is connected by a brake light switch 11 to a line 12 to which two parallel-connected loads i.e. brake light bulbs 13a and 13b, each of 5W, are connected. For monitoring these bulbs a measuring resistor 14 of 150 mn is provided in the line 12, the voltage drop across this measuring resistor being supplied through the tapping 15 to a threshold value switch 16. The output of the threshold value switch 16 is connected to the setting input S of a signal accumulator 17 whose output Q is connected to the control input of a semiconductor 18. The switching path of this semiconductor 18 is connected in series with a warning light 19 which is connected to the supply line 10 and serves as a signal generator. The signal accumulator 17 is also provided with a resetting input R which is connected by a differentiating member 20 to the clippings of the brake light switch 11. A testing key 21 is connected in parallel with the brake light switch all and the therefore series-connected measuring resistor 14.

The mode of operation of this circuit is described in detail as follows. To monitor the warning light, 19, the testing key 21 is actuated by the driver for a short time, for example before driving commences. The positive potential of the supply line 10 therefore passes through the testing key 21 and the tapping 15 to the input of the threshold value switch 16. The input signal thereby produced at the threshold value switch 16 also switches it over for a short time so that a signal appears temporarily at its output and runs in the setting input S of the signal accumulator 17. As a result, a lasting signal is produced at the output Q of the signal accumulator 17 which makes the semiconductor 18 current-conductive. The warning light 19 must therefore light up during and after actuation of the testing key 21. If the warning light does not light up, there is either a defect in the control circuit or a defect in the warning light 19.

In a further step the functioning of the brake light switch 11 may also be checked in that this switch is temporarily actuated.

As a result of actuation, the voltage of the supply line 10 passes to the differentiating member 20 at whose output a short pulse arises which runs into the resetting input R of the signal accumulator 17 and clears it. The semiconductor 18 is therefore then made blocked and - the warning light 19 is consequently extinguished if the brake light switch 11 is operating correctly and the bulbs 13a and 13b are intact. In the case of a defect in the brake light switch 11, no voltage pulse would be produced at the differentiating member 20 to clear the accumulator 17-i.e. in the case of a defect in the brake light switch, the warning light 19 would still be lit and would indicate the defect.

The mode of operation of the circuit is now described for the case where a brake light bulb 13a or 13b burns out. In this case, when the brake light switch 11 is actuated, only half the current flows in the line 12 and thus in the measuring resistor 14 as would flow if the brake light bulbs were intact. Consequently the voltage drop at the measuring resistor is only half as great. The threshold value switch 16 is so adjusted that its threshold voltage is still exceeded so that a signal is produced at its output, passes into the setting input of the signal accumulator 17 and switches the latter over. Since a short voltage pulse is only produced at the resetting input of the signal accumulator 17 on closure of the brake light switch 11 but the signal at the setting input remains for a longer period, when a brake light bulb fails the accumulator 17 cannot be reset until the defective bulb is replaced. The signal therefore remains at the output Q of the accumulator so that the semiconductor 18 is held in its current-conductive state and the warning light 19 remains switched on. Since the supply line 10 is generally connected by an ignition switch (not shown) to the vehicle battery, the warning light 19 indicating a defect in the brake light bulbs 13a or 13b may only be extinguished by switching off the ignition switch.

Fig. 2 shows an extended circuit for monitoring several consumers, the circuit design of the signal accumulator 17 for monitoring the brake light system of a motor vehicle being shown in detail. The brake light bulbs 13a and 13b here are connected by the measuring resistor 14, the brake light switch 11 and a fuse 30 to the supply line 10 which is connected, for example, by an ignition switch (not shown' to the positive pole of the power supply of a motor vehicle. In this example, the differentiating member 20 comprises a capacitor 31 and a resistor 32 connected between its output and earth. The signal accumulator 17 basically comprises two complementary transistors 33 and 34 of which the first is an NPN-conducting input transistor 33. The input transistor 33 is connected to the supply line 10 by a collector resistor 35 and by another seriesconnected resistor 36 and a fuse 37. It is connected on the emitter side by another resistor 38 to earth and its base is connected to the setting input S of the accumulator 17. The second transistor 34 is a PNP-conducting output transistor which is connected on the emitter side to the supply line 10 by a tapping 39 of a voltage divider, formed by two seriesconnected resistors 40 and 41, and by the fuse 37. Its collector terminal forms the accumulator output Q. The base of the two transistors 33 and 34 is connected in the form of a holding circuit by a resistor 42 and 43 respectively to the collector of the other transistor. The output of the threshold value switch 16 is connected by the setting input S directly to the base of the input transistor 33. Furthermore, the capacitor 31 of the differentiating member 20 is connected by the resetting input R and by a diode 44 to the base resistor 43 of the output transistor 34. To keep the output transistor 34 in its blocked state when the supply voltage is connected, the collector resistor 36 of the input transistor 33 is bypassed by a capacitor 45.

Since the fuse 30 for the brake light bulbs 13a and 13b is disposed before the brake light switch 11, an additional control member 50 was provided to monitor this fuse, it basically comprising a voltage divider connected by a line 55 to the clippings of the fuse 30 and two series-connected resistors 51 and 52. The output transistor 34 of the signal accumulator 17 is also used advantageously here to monitor the fuse 30 in that its base is connected by a diode 53 to the tapping 54 of the voltage divider 51,52.

The circuit of Fig. 2 may also be used to monitor other consumers such as, for example, the rear light bulbs, the parking light bulbs or the number plate lighting of a motor vehicle. This being the case, the bulbs 60 to be monitored in a circuit are connected by a measuring resistor 61, a switch 62 and a fuse 63 to the supply line 10. Here, the input of another threshold value switch 16a is connected to the measuring resistor 61, the voltage supply of said switch being tapped before the measuring resistor 61. The output of the threshold value switch 1 6a is connected by a resistor 64 and a diode 65 disposed at the output of the signal accumulator 17 in parallel with the signal accumulator. Both outputs are jointly connected by another resistor 66 to the base of an NPN-conducting transistor 18a which is earthed on its emitter side and whose collector terminal is connected to the warning light 19, which is connected to the line 10, by a diode 67 and a resistor 68 which is connected in series to this diode.

The following is a detailed description of the mode of operation of the circuit shown in Fig. 2. When a voltage is applied to the supply line 10, it passes through the fuse 37 and the capacitor 45 and through the resistor 43 to the base of the output transistor 34 of the signal accumulator 17 and holds the latter blocked so that no signal is produced at the output Q. The transistor 1 8a therefore remains blocked and the warning light 19 remains dark.

To monitor the warning light 19 and the functioning of the brake light switch 11, the process described with reference to Fig.

1 then occurs in that the testing key 21 is actuated for a short time. As a result, a signal is produced at the output of the threshold value switch 16 and thus through the setting input S of the accumulator 17 at the base of the input transistor 33 so that this transistor becomes currentconducting. The collector potential is consequently reduced and therefore, through the resistors 35 and 43, also the base potential of the output transistor 34. By means of a suitably adjusted potential at the tapping 39 of the voltage divider 40,41, this reduction in the base potential causes the output transistor 34 to become currentconductive so that its collector potential is raised. This potential in turn passes through the resistor 42 to the base of the input transistor 33 and keeps the latter still current-conductive even after apening af the testing key 21. The signal thus set at the output Q of the accumulator 17 passes through the diode 65 and through the resistor 66 to the base of the transistor 18a and makes the latter current-conductive.

The warning light 19 must then light up and therefore indicate to the driver that the monitor circuit and the warning light itself are in order.

When the brake light switch 11 is actuated, the voltage is applied to the differentiating member 20 so that a voltage pulse passes through the resetting input R of the accumulator 17 and the diode 44 and the resistor 43 to the base of the output transistor 34 and changes the latter to its blocked state. As a result, the signal at the output Q is quenched and the input transistor 33 is therefore also triggered back intro its blocked state. The transistor 18a for the warning light 19 is consequently also blocked and the warning light 19 is extinguished. If, however, the warning light 19 does not go out, there is a defect in the brake light switch 11.

In the event of failure of one of the brake light bulbs 13a or 13b, a signal is likewise produced at the threshold value switch 16. Through this signal the input transistor 33 is again made currentconductive so that, through the resistors 35 and 43, the output transistor 34 is also made current-conductive. A signal is there fore produced at the output Q of the accumulator 17 which causes-as described above-the warning light 19 to be switched on.

The control member 50 for monitoring the fuse 30 remains ineffective in the abovedescribed examples of breakdown since the potential at the tapping 54 of the voltage divider 51,52 is so adjusted that the diode 53 is biassed in a blocking direction. If the fuse 30 blows, however, positive potential no longer passes through the line 55 to the voltage divider so that the earth potential becomes effective at the tapping 54.

The diode 53 then becomes conducting and, through the control path of the output transistor 34, a control current then flows through the diode 53 and the resistor 52 to earth. The output transistor 34 is therefore made current-conductive and is held in this state by the input transistor 33.

The signal thereby produced at the output Q of tie accumulator 17 switches the warning light 19 on and thereby indicates the defect in the fuse.

The bulbs 60 are monitored by the threshold value switch 1 6a independently of the monitoring of the brake light system of the motor vehicle. If one of these bulbs fails, the threshold value switch 16a responds when the switch 62 is closed and through the output transistor 64 and the base resistor 66 makes the transistor 18a current-conductive so that the warning light 19 lights up.

If other consumer circuits are to be monitored by the warning light 19, a corresponding measuring resistor must be provided in each consumer circuit for triggering a threshold value switch associated therewith. The outputs of the threshold value switches may be connected in parallel by resistors so that they may trigger the transistor 1 8a for the warning light 19 independently of one another.

WHAT WE CLAIM IS: 1. A circuit for energising from a supply voltage, one or more electrical loads connected in parallel via a switch, said circuit comprising a switch, a measuring resistor and said loads, all connected in series, a threshold circuit being adapted to, in use, remain in a blocked state when every load is switched on and is working normally and to conduct if a load fails, and whose output is coupled to an indicator via a signal storage circuit, the storage circuit having a resetting input which is connected by a differentiating circuit to the switch and is adapted to control the indicator through a semiconductor device, and a testing key so connected that when operated the input of the threshold circuit is connected to the supply voltage.

2. A circuit as claimed in Claim 1, in which the measuring resistor and the consumer switch are bypassed by the testing key.

3. A circuit as claimed in Claim 1 or 2, in which the signal accumulator comprises two complementary transistors, one being an NPN-conducting input transistor whose collector is connected by a resistor to a supply line and whose emitter is connected by a resistor to a supply line and whose emitter is connected by another resistor to earth, and the other being a PNP-conducting output transistor whose emitter is connected by a voltage divider tapping to the supply line and whose collector forms the accumulator output, the base of each transistors being connected by a resistor to the collector of the other transistor.

4. A circuit as claimed in Claim 3, in which the output of the threshold value switch is connected to the base of the input transistor.

5. A circuit as claimed in Claim 4, in which a capacitor serving as a differentiating member is connected by a diode to the base resistor of the output transistor.

6. A circuit as claimed in any of Claims 3 to 5, in which the collector resistor of the input transistor is by-passed by a capacitor.

7. A circuit as claimed in any of Claims 3 to 6, in which, for monitoring a fuse disposed before the consumers switch, the.

base of the output transistor of the accumulator is connected by a diode to the tapping of a voltage divider which is connected to the clippings of the fuse to be monitored.

8. A circuit as claimed in any of Claims 1 to 7, in which the output of the accumulator is connected in parallel with the output of one or more threshold value switches for monitoring other consumers which are jointly connectible to the control input of a semiconductor whose switching path is connected in series with the signal generator.

9. A circuit arranged substantially as herein particularly described with reference to and as illustrated in Fig. 1 or Fig.

2 of the accmpanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. likewise produced at the threshold value switch 16. Through this signal the input transistor 33 is again made currentconductive so that, through the resistors 35 and 43, the output transistor 34 is also made current-conductive. A signal is there fore produced at the output Q of the accumulator 17 which causes-as described above-the warning light 19 to be switched on. The control member 50 for monitoring the fuse 30 remains ineffective in the abovedescribed examples of breakdown since the potential at the tapping 54 of the voltage divider 51,52 is so adjusted that the diode 53 is biassed in a blocking direction. If the fuse 30 blows, however, positive potential no longer passes through the line 55 to the voltage divider so that the earth potential becomes effective at the tapping 54. The diode 53 then becomes conducting and, through the control path of the output transistor 34, a control current then flows through the diode 53 and the resistor 52 to earth. The output transistor 34 is therefore made current-conductive and is held in this state by the input transistor 33. The signal thereby produced at the output Q of tie accumulator 17 switches the warning light 19 on and thereby indicates the defect in the fuse. The bulbs 60 are monitored by the threshold value switch 1 6a independently of the monitoring of the brake light system of the motor vehicle. If one of these bulbs fails, the threshold value switch 16a responds when the switch 62 is closed and through the output transistor 64 and the base resistor 66 makes the transistor 18a current-conductive so that the warning light 19 lights up. If other consumer circuits are to be monitored by the warning light 19, a corresponding measuring resistor must be provided in each consumer circuit for triggering a threshold value switch associated therewith. The outputs of the threshold value switches may be connected in parallel by resistors so that they may trigger the transistor 1 8a for the warning light 19 independently of one another. WHAT WE CLAIM IS:

1. A circuit for energising from a supply voltage, one or more electrical loads connected in parallel via a switch, said circuit comprising a switch, a measuring resistor and said loads, all connected in series, a threshold circuit being adapted to, in use, remain in a blocked state when every load is switched on and is working normally and to conduct if a load fails, and whose output is coupled to an indicator via a signal storage circuit, the storage circuit having a resetting input which is connected by a differentiating circuit to the switch and is adapted to control the indicator through a semiconductor device, and a testing key so connected that when operated the input of the threshold circuit is connected to the supply voltage.

2 of the accmpanying drawings.