Circuit Arrangements For The Indication Of Lamp Failure

Abstract

An electric warning system for a pair of parallel-connected lamps includes a warning lamp in series with a thyristor across the system input terminals. A resistor is connected in a first series circuit with the lamps and in a second series circuit with a transistor and a capacitor across the input terminals. The transistor is biased to cut-off by means of second and third resistors in series across the input terminals. The circuit components are arranged so that failure of either lamp turns the transistor "on" to charge the capacitor. The capacitor voltage is coupled to the thyristor control electrode to trigger the thyristor "on" when a given capacitor voltage level is achieved. A switch is provided in the circuit so as to remove the input voltage from all of the circuit components except the thyristor and the warning lamp.

Description

BACKGROUND OF THE INVENTION

This invention relates to a circuit arrangement for the direct current supply of a first lamp, particularly a motorcar lamp, and for signaling the failure of said first lamp with the aid of an auxiliary lamp. In a circuit of this type, an input terminal of the circuit arrangement is connected to one end of a diagonal of an electric bridge and the other input terminal is connected to the other end of said bridge diagonal, a resistor being provided in three limbs of the bridge and the fourth limb of the bridge comprising at least the first lamp. The ends of the other bridge diagonal are connected to a main electrode--respectively the base--of a transistor, the other main electrode of which is connected through a subsequent circuit element to the negative input terminal.

A circuit arrangement of the kind described above is shown, for example, in British Pat. No. 947,491 (see, for example, FIG. 1 of said patent specification). A drawback of this known circuit arrangement is that when two parallel-arranged main lamps instead of one main lamp are used, the failure of one of these main lamps does not lead to satisfactory signaling by the auxiliary warning lamp. In fact, if one starts from two parallel-arranged main lamps and if upon failure of one of the lamps the base of the said transistor would receive a voltage such that this transistor becomes conducting, the auxiliary lamp in the known circuit starts to draw current so that the voltage of the emitter of the relevant transistor also becomes more negative which in turn would lead to the transistor becoming non-conducting. A satisfactory lighting up of the warning lamp and hence a satisfactory signaling of the fault (the failure of one of the main lamps) is thus not achieved with this arrangement.

Groups of two parallel-arranged lamps are frequently used, particularly for motorcar lighting. Consider, for example, the two stop lights, or the two headlights on the front side of the car, or the blinkers of the vehicle. In the interest of road safety, it is of paramount importance that a motorcar driver know whether all of these lamps systems are functioning in the correct manner and that he receive a timely signal when one of these lamps has failed. This is of course of paramount importance in so far as the stop lights are concerned.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a simple circuit for the case of two or more parallel-arranged lamps which circuit signals the failure of one of these lamps.

A circuit arrangement according to the invention for the direct current supply of a first lamp, particularly a motorcar lamp, and for signalling the failure of said first lamp with the aid of an auxiliary lamp, an input terminal of the circuit arrangement being connected to one end of a diagonal of an electric bridge and the other input terminal being connected to the other end of said bridge diagonal, a resistor being provided in three limbs of the bridge and the fourth limb of the bridge comprising at least the first lamp, the ends of the other bridge diagonal being connected to a main electrode--respectively the base of a transistor, the other main electrode of which is connected through a subsequent circuit element to the negative input terminal is characterized in that a second lamp is arranged parallel to the first lamp and that the subsequent circuit element which is connected to the transistor includes at least a capacitor, a junction between this transistor and the capacitor being connected to the control electrode of a thyristor, the input terminals of the circuit arrangement being also connected by means of a series arrangement of the auxiliary lamp and the thyristor, all this in such a manner that in the presence of a voltage across the input terminals, but in case of a first lamp not functioning, the emitter-base voltage of the transistor is sufficient to render this transistor conducting and thereby ignite the auxiliary lamp through the thyristor.

An advantage of this circuit arrangement is that when--due to the failure of one of the main lamps--the voltage across the resistor which is series-arranged with these lamps is reduced, and the resultant emitter-base voltage of the transistor is sufficient to make this transistor conduct, the said capacitor is charged through this transistor. Namely the transistor current by which this is effected need only be very low for this current need not flow through the warning lamp. The result thereof is that this auxiliary current does not bring about a great variation in the potential across the resistor which is series-arranged with the main lamp so that the transistor remains conducting for some time. If the capacitor has obtained such a charge that the trigger voltage of the thyristor has been reached the connection of the input terminals through the warning lamp and the thyristor is closed so that the warning lamp lights up. The fault is then signaled.

A circuit arrangement according to the invention might be used, for example, in a stationary signaling device or for the lighting of a vehicle.

In a special embodiment of the circuit arrangement according to the invention wherein the first lamp and the second lamp are motorcar lamps, these two lamps are motorcar stop lamps.

An advantage of this special embodiment is that a motorcar driver is timely informed of a fault in the brake signaling system. In a number of cases this may lead to the prevention of serious traffic accidents.

It is feasible that a switch is incorporated in the circuit which switch is arranged in series with the main lamps as well as with the auxiliary lamp. In that case signaling can only take place if also the voltage on the bridge including the main lamps is present.

In a further embodiment of the circuit arrangement wherein a switch is provided between one of the input terminals and the electric bridge, one end of the series arrangement of the auxiliary lamp and the thyristor is connected to a point between the switch and the said input terminal.

An advantage of the latter embodiment is that a failure possibly signaled during the voltage present on the bridge also remains indicated by a burning auxiliary warning lamp after the electric bridge has been switched off. In fact, if during operation one of the main lamps is out of order, this will lead to the thyristor arranged in series with the warning lamp becoming conducting. As a result this lamp lights up. However, if the switch is opened, all main lamps which may still be operating will be extinguished, but the auxiliary lamp continues to operate because the current flowing through the thyristor is only interrupted when this current drops below the holding value. The circuit arrangement is proportioned in such a manner that the current flowing through the warning lamp is greater than this holding current value and in that case the auxiliary lamp will continue to operate even when the switch is opened, and hence the signaling of the fault will be continued.

The two last-mentioned embodiments of the circuit arrangement are preferably used in combination in a motorcar, the switch being coupled to the brake of the car.

An advantage thereof is that the warning lamp lights up when a fault is revealed in one of the stop lights during a braking procedure, which warning lamp continues to operate also when the driver has released the brake. In such a system attention is thus drawn for a longer period to the presence of a fault in one of the vital parts of the signaling system of his vehicle.

It is possible to guard each group of two parallel arranged lamps by means of an arrangement according to the invention in a vehicle of, for example, in a system for guarding a panel of signaling lamps.

In a further advantageous embodiment of the circuit arrangement, wherein more than one group of parallel-arranged lamps is present, all these groups of lamps are included in bridge circuits which are substantially the same as those for the group of the first and the second lamp and wherein two limbs of all these bridges are common, these two limbs being provided with resistors and wherein a diode is present for each group of lamps which diode connects the junctions of the remaining limbs to a main electrode of the transistor in such a manner that a failure of one out of the total number of lamps is indicated by the ignition of the auxiliary lamp.

An advantage of the latter embodiment is that a great number of groups of lamps can be guarded with the aid of one warning lamp.

It is evident that in a system according to the invention the warning lamp lights up not only when one of the main lamps fails, but also when both main lamps fail. In fact, when the two lamps do not light up the voltage drop across the resistor series arranged with these lamps is zero and also in that case the emitter-base voltage is certainly sufficient to render the transistor conducting. In the foregoing discussion reference was always made to two parallel arranged auxiliary lamps. However, it is alternatively feasible that this number is more than two and that the resistor which is series-arranged with these lamps is proportioned in such a manner that the voltage across this resistor is sufficient to render the said transistor conducting and thus to signal the fault when only one of the lamps from this group has failed.

BRIEF DESCRIPTION OF THE DRAWING

In order that the invention may be readily carried into effect, a few embodiments thereof will now be described in detail, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 shows a circuit diagram of a circuit arrangement according to the invention;

FIG. 2 shows a further circuit diagram of a circuit arrangement according to the invention; and

FIG. 3 shows a third circuit diagram of a circuit arrangement according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, the reference numerals 1 and 2 are connecting terminals which are intended to be connected to the battery of a motorcar. The reference numerals 3 and 4 denote two stop lamps of the motorcar. The terminals 1 is connected to an electric bridge one limb of which is formed by a resistor 5. A further limb of this bridge is formed by a resistor 6 which is series-arranged with the resistor 5, and a subsequent limb of the bridge is formed by a resistor 7. The resistor 7 is arranged between the lamps 3 and 4 at one end and the connecting terminal 1 at the other end. The lamps 3 and 4 together constitute a fourth limb of the bridge. This bridge is connected through a switch 8 to the negative input terminal 2 of the circuit arrangement. The switch 8 is mechanically coupled to the brake of the motor car. The negative terminal 2 is connected to the frame of the car. A junction of the resistors 5 and 6 is connected to the base of a transistor 9. This transistor is of the pnp-type. The emitter of the transistor 9 is connected to a junction between the resistor 7 and the lamps 3 and 4. The collector of the transistor 9 is connected through a subsequent resistor 10 and a capacitor 11 to a conductor 14 which connects the resistor 6 to the lamps 3 and 4. The conductor 14 is associated with the electric bridge. The conductor 14 is connected through the switch 8 to the terminal 2. A junction between the resistor 10 and the capacitor 11 is connected to the control electrode of a thyristor 12. An auxiliary lamp 13 is incorporated in series with this thyristor 12. This lamp is the warning lamp. The series arrangement of lamp 13 and thyristor 12 is connected at one end to a junction between the input terminal 1 and the resistor 7 and at the other end to the conductor 14. One end of a diagonal of the said electric bridge is formed by a junction of the resistors 5 and 7, and a further end of the same diagonal is formed by the part of the switch 8 facing the bridge. The ends of the other diagonal of the bridge are formed by the junction of the resistors 5 and 6, and the junction of the resistor 7 and the lamps 3 and 4. The resistors in the circuit of FIG. 1 are proportioned in such a manner that the voltage drop across the resistor 7 is so high that the emitter-base voltage of the transistor 9 is insufficient to render this transistor conducting when the two lamps 3 and 4 function in the closed condition of the switch 8. In that case the thyristor 12 will also be non-conducting and hence the lamp 13 is extinguished. However, if one of the two main lamps 3 or 4 fails, the voltage across resistor 7 (as a result of the reduced current flow) will decrease so that the emitter of the transistor 9 receives a more positive potential while the potential on its base remains the same so that this transistor 9 becomes conducting. As a result the capacitor 11 will be charged through the resistor 7 and the resistor 10. When this capacitor has received a given charge, the thyristor 12 will be rendered conducting thereby through the control electrode of this thyristor and the lamp 13 will light up. The lamp 13 is installed, for example, on the dashboard of the motorcar. Due to the lamp 13 lighting up the motorcar driver sees that there is something wrong with the stop-light system. In that case he can take timely steps to correct this fault.

The circuit of FIG. 2 largely corresponds to that of FIG. 1. An important difference is, however, that the switch 8 is replaced by a switch 18 which is provided between the input terminal 1 and the resistor 7. Furthermore the lamp 13 is connected to a point 19 which is located between the input terminal 1 and the above-mentioned switch 18. In the case of FIG. 2 the input terminal 2 is furthermore connected to the common conductor 14. Corresponding circuit elements in FIGS. 1 and 2 have the same reference numerals. In the circuit of FIG. 2 the switch 18 is also coupled to the brake of the motorcar. If during a braking procedure, there is a fault in one of the lamps 3 or 4, the auxiliary lamp 13 will light up in the same manner as described with reference to FIG. 1. However, when the motorcar driver releases the brake and hence the switch 18 is opened again, the current circuit of lamp 13 and thyristor 12 will remain closed because the current flowing through the thyristor does not fall below the holding current value. As a result the lamp 13 will continue to operate after braking so that the motorcar driver receives a continuous signal of a fault in the stop-light system. The lamp 13 (in the system of FIG. 2) will not be extinguished until the current from the battery to the different power consumption systems is interrupted, for example, by turning the ignition key of the vehicle.

The circuit of FIG. 3 includes an extension of the circuit of FIG. 2. Corresponding circuit elements in FIGS. 3 and 2 have the same reference numerals. FIG. 3 shows again two stoplamps 3 and 4. However, the circuit of FIG. 3 also includes a group of two other lamps, to wit, lamps 30 and 40. These are, for example, lamps constituting the main lighting of the motorcar (the headlights). In the citcuit of FIG. 3 the warning lamp 13 guards both the group of lamps 3, 4 and the group of lamps 30, 40. New elements in FIG. 3 are the resistor 70 which is arranged in series with the lamps 30 and 40 and a switch 180. The resistor 70 corresponds to the resistor 7 and the switch 180 corresponds to the switch 18. The switch 180 is arranged between the resistor 70 and the junction 19 of the circuit arrangement. In the case of FIG. 3 a diode 20 is provided between the emitter of the transistor 9 and the junction between the resistor 7 and the lamps 3 and 4. Similarly, a diode 200 is provided between the emitter of the transistor 9 and the junction between the resistor 70 and the lamps 30 and 40. The diodes 20 and 200 serve to prevent current in the stop-light system 3,4 from flowing over to the system of the motorcar head lamps 30, 40 and also serve to prevent an inverted flow of current. If, in the switched-on condition of the switch 18, a fault occurs in one of the lamps 3 or 4 (or in both lamps) the transistor 9 will become conducting in the manner already described with reference to FIG. 2, and hence the thyristor 12 will become conducting so that the lamp 13 lights up. Since the lamp 13 is again connected to a point 19 located between the input terminal 1 and the switch 18 the fault can remain signalized by the operating lamp 13 even when this switch is reopened. In the closed condition of the switch 180 a possible fault in the system of the lamps 30 and 40 can be passed on through the resistor 70 to the transistor 9, namely because in case of failure of one of the lamps 30 or 40 the potential difference across this resistor 70 is smaller than when both of the lamps 30 and 40 operate satisfactorily. If one of the lamps 30 or 40 is out of order, the emitter-base voltage of the transistor 9 is sufficient to render this transistor conducting and, in the same manner as described with reference to the other circuit, the capacitor 11 is charged and hence thyristor 12 is rendered conducting so that the lamp 13 lights up. Also in the case of the lamps 30 and 40 a possible fault of the lamps 30 or 40 continues to be signaled even after the switch 180 is reopened.

The circuit arrangements described provide a simple and efficient means for signaling the failure of one or more lamps of the motorcar.

Claims

What is claimed is:

1. A direct current supply circuit for a first lamp comprising an auxiliary lamp for signaling a failure of the first lamp, a pair of input terminals adapted for connection to a source of DC current, means connecting one input terminal to one end of a diagonal of an electric bridge circuit and the other input terminal to the other end of said bridge diagonal, said bridge including a resistor in three legs of the bridge and the fourth leg of the bridge including at least the first lamp, means connecting the ends of the other bridge diagonal to a main electrode and to the base of a transistor, respectively, means connecting the other main electrode of the transistor through a capacitor to an input terminal, means connecting a junction between said transistor other main electrode and the capacitor to the control electrode of a thyristor, means connecting the auxiliary lamp and the thyristor in series across the input terminals, said bridge resistors being chosen so that with a voltage present across the input terminals and with said first lamp not functioning, the transistor base-emitter junction is forward biased so as to render the transistor conducting and thereby trigger on the thyristor to ignite the auxiliary lamp through the thyristor.

2. A circuit as claimed in claim 1, further comprising a second lamp connected in parallel with said first lamp and wherein the first lamp and the second lamp are motorcar lamps, said bridge resistors being chosen so that a failure of either of said first and second lamps will forward bias the transistor base-emitter junction to provide said trigger action.

3. A circuit as claimed in claim 1 further comprising a switch connected between one of the input terminals and the electric bridge, characterized in that one end of the series arrangement of the auxiliary lamp and the thyristor is connected to a point between the switch and the said input terminal so that said series arrangement is connected to the input terminals even in the open condition of the switch.

4. A circuit as claimed in claim 2 provided in a motorcar and further comprising a switch coupled to the brake of the motorcar and serially connected with the bridge circuit across said input terminals.

5. A circuit as claimed in claim 1 further comprising a second lamp and a second resistor connected in series therewith across the input terminals to form a second bridge circuit along with the two series legs of the first bridge circuit that include the resistors, first and second diodes, means connecting the first and second diodes between said transistor main electrode and the associated end of the bridge diagonal and the junction of said second lamp and the second resistor, respectively, so that a failure of any one of the main lamps will trigger the thyristor and thereby ignite the auxiliary lamp.

6. A circuit as claimed in claim 5 further comprising a third lamp connected in parallel with the first lamp and a fourth lamp connected in parallel with the second lamp whereby a failure of any one of the main lamps will trigger the thyristor and thereby ignite the auxiliary lamp.

7. A DC supply and indicating system for a first lamp comprising, a pair of input terminals adapted for connection to a source of DC current, an auxiliary lamp for signalling a failure in said first lamp, a thyristor connected in series with said auxiliary lamp directly across the input terminals, a first resistor connected in a first series circuit with said first lamp across said input terminals, a transistor and an impedance element connected in a second series circuit with said first resistor across the input terminals, means coupled to said input terminals and to the transistor for biasing the transistor into the cut-off state, means for coupling the voltage derived across said impedance element to the thyristor control electrode for controlling the ignition thereof, said derived voltage being of sufficient magnitude to trigger the thyristor into conduction upon a failure of said first lamp, and a switch connected in series with at least one of said first and second series circuits across the input terminals.

8. A system as claimed in claim 7 further comprising a second lamp connected in parallel with the first lamp, and wherein said biasing means is arranged to allow a substantial current to flow in said transistor upon the failure of either one of said first and second lamps thereby to derive said trigger voltage across said impedance element.

9. A system as claimed in claim 8 wherein said impedance element comprises a capacitor.

10. A system as claimed in claim 8 further comprising a first diode connected in series with said first resistor and said transistor, third and fourth lamps connected in parallel, a second resistor and a second diode, means connecting said second resistor and said parallel-connected third and fourth lamps in a third series circuit across the input terminals, and means connecting said second diode in series with said second resistor and said transistor.

11. A system as claimed in claim 7 for use in a motorcar and further comprising means for coupling said switch to the motorcar brake mechanism.