GB1602364A

GB1602364A - Apparatus for the protection of an electrical installation

Info

Publication number: GB1602364A
Application number: GB8387/78A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1977-03-02
Filing date: 1978-03-02
Publication date: 1981-11-11
Also published as: FR2382789B1; DE2708981C2; FR2382789A1; DE2708981A1

Description

(54) APPARATUS FOR THE PROTECTION OF AN ELECTRICAL INSTALLATION (71) We, ROBERT BOSCH GmbH, a German company of 50, Postfach, Stuttgart, 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 present invention relates to apparatus for the protection of an electrical installation.

In the wiring system of vehicles, overvoltages may occur. These over-voltages are normally limited by the battery. If there are conductors between an interference source and the battery then, of course, considerably higher voltages can occur. However, a great danger exists when the driving generator is disconnected from the battery, be it due to accidental loosening of terminals or due to the fact that its current circuit is interrupted by mechanical actions. A similar effect is produced by the fact that, due to ageing (for example sulphating) the internal resistance of the battery increases considerably.

It is already well known to limit the voltage of such an electrical installation to safe values by means of zener diodes (Zdiodes), wherein the breakdown voltage of the Z-diodes must lie only slightly above the maximum operating voltage of the system.

When,itis desired to monitor all over-voltage conditions using one or more Z-diodes, then they must be capable of accepting the energy existing when the maximum possible generator current is switched off with a fully energised generator. However, Z-diodes for such peak energies are difficult to manufacture and are thus unacceptably expensive.

Thus, it has already been proposed to make the individual units of the vehicle wiring, such as for example the voltage regulator for the generator or its diodes, self-protective against voltage and to only protect individual loads separately, especially electronic apparatus, by means of small Z-diodes. Due to the increasing number of electronic loads, not only has this method an economical limit but also a physical limit. The Z-diode associated with loads receiving larger current may no longer be sufficiently decoupled from the wiring. The internal resistance ofthree-phase generators is, of course, substantially inductive so that resistors of 1 ohm and less connected in series with the apparatus are practically ineffective with regard to a decoupling of the following Z-diode.

The so-called over-voltage protective apparatus, an example of which is described in German OS 2 308 090, is offered 8s a further possibility for the protection of an electrical installation. With the aid of this, the generator is short-circuited on its field side as soon as the voltage in the wiring has exceeded a predetermined threshold value. A thyristor is preferably used for the short-circuiting. With this apparatus, the full generator current must still be accepted at very low voltages, however, the great disadvantage exists that over-voltage pulses of low energy content cause actuation of the over-voltage protective apparatus.

The present invention provides an apparatus for the protection of an electrical installation including a voltage source, the apparatus comprising voltage amplitude detecting means for detecting a voltage from the output of the voltage source in excess of a predetermined level, means for detecting a temperature of the voltage amplitude detecting means in excess of a threshold level, and semiconductor switching means arranged to be connected in parallel with said voltage source and arranged to respond when there is a voltage in excess of said predetermined level and an output from the temperature detecting means for shorting the output from the voltage source.

The apparatus to be described has the advantage that all over-voltage pulses of low energy content are accepted by small and cheap Z-diodes without damaging the wiring and the switching device only comes into operation on the occurrence of high overvoltages with high energy content. Thus, with the avoidance of high power and expensive Z-diodes, this arrangement nevertheless guarantees full protection for the electrical system and limits over-voltages which are low in energy without damaging the wiring, that is to say without shortcircuiting of the electrical voltage by actuation of switching device.

Three embodiments of the invention are illustrated in the drawing by way of example and are described in more detail in the following specification. Figure 1 shows, as a first embodiment, an over-voltage protective apparatus in an electrical installation which can be triggered by the temperature of a Zdiode, Figure 2 shows, as a second embodiment, the alternative triggering by the temperature of three Z-diodes, Figure 3 shows a third embodiment incorporating triggering by the over-voltage itself, Figure 4 shows an embodiment of an integrated Z-diode and Figure 5 shows a further embodiment of integrated Z-diodes.

In the first embodiment illustrated in Figure 1, an electrical system is illustrated as is used for example in a motor vehicle. An electrical battery 10 is charged through a supply line 11 by a generator 12, preferably a three-phase generator. A voltage regulator 13, preferably a transistor regulator, is likewise connected to the generator 12 through a regulator supply line 20. Such a regulator 13 is incorporated in every motor vehicle, thus sufficiently known and will therefore not be described in detail. All the loads in the electrical installation are represented symbolically by the load 14, which is likewise connected to the supply line 11. A Z-diode 160 is also connected between the supply line 11 and earth. An over-voltage protective device 15, is likewise connected to the regulator supply line 20.A voltage amplitude detecting means in the form of a Z-diode 16 is also connected to the said regulator supply line 20. A temperature sensor 17 applied to or in the Z-diode 16, such as a thermo element, is connected through a threshold value stage 18 to the control input to the over-voltage protective device 15. All components and units and connected to earth by means of a further connection.

The generator 12 is of a construction as is normally used in a motor vehicle. The three winding regions of a stator winding 120 in star connection, are connected to the regulator supply line 20 through three excitation diodes 121 to 123 and a terminal 124.

Furthermore, the stator winding 120 is connected to the supply line 11 through a first group of three main current diodes 125 to 127 and through a terminal 128. A third group of main current diodes 129 to 131 is connected between the stator winding 120 and earth. The armature winding 132 in the armature 133 is connected between earth and a terminal 134. A terminal 135 is connected to earth. The terminals 124, 134, 135 are connected to the regulator 13 in known manner.

The method of operation of the arrangement illustrated in Figure 1 is based on the fact that the minimum breakdown voltage of the Z-diodes 16, 160 is arranged above the maximum occurring operating voltage. Thus, over-voltage pulses which are poor in energy and act for a short time are limited by the Zdiode 16 or 160 to the breakdown voltage thereof. The over-voltage protective device 15 does not come into operation. On the other hand, when the over-voltage pulses are rich in energy and last a longer time, then the danger exists that, for example, the Z-diode 16 will be damaged by heating. For that reason, signals are transmitted from the temperature sensor 17 to a threshold value stage 18.At a particular threshold value, that is to say at a particular heating of the Z-diode 16, or of its junction, the threshold value stage 18 produces an output signal through which the voltage protective device 15 is actuated. A switch, preferably a thyristor 150, provided in the over-voltage protective device 15, becomes conductive and shortcircuits the generator voltage decoupled from the battery 10. The voltage on the anodecathode-voltage of the thyristor is thereby reduced, thus, for example, to 1 to 2 Volts. If the thyristor 150 has a hold current which is higher than the generator current, which can still be delivered under the predetermined conditions, then the thyristor 150 is blocked once again, the generator can be excited once again, and the voltage for the electrical installation is built up once again.

Instead of the junction temperature of the Z-diode 16, which is accessible with difficulty, the triggering can, for example, take place through the housing temperature of a Z-diode. Moreover, the triggering of the over-voltage protective device 15 can also be influenced or even be caused by the current through the Z-diode 16 (described in more detail in Figure 3) as well as by time integrals and/or differential quotients.

The triggering of the over-voltage protective device 15 can take place not only through the Z-diode 16--as describedbut also through other diodes provided in the electrical installation.

The second embodiment illustrated in Figure 2 shows the section of an electrical installation in which three Z-diodes 16, 160, 260 are provided. Three temperature sensors 17, 170, 270 are each associated through threshold value stages 18, 180, 280 with inputs to an OR-gate 19, the output from which is connected to the control input to the over-voltage protective device 15.

The three illustrated Z-diodes 16, 160, 260, as well as a further optional number of nonillustrated Z-diodes, can be connected to the supply line 11 and/or the regulator supply line 20 of the system, and even replace rectifier diodes in the generator 12 with advantage, especially the diodes 125 to 127, 129 to 131 in the main current circuit are suitable for that purpose. Preferably, one or both of the groups of three of the main current diodes 125 to 127 or 129 to 131 is replaced by Z-diodes. The diode 260 symbolises one such group of three main current diodes in the generator 12. Thus, the overvoltage generated by the generator may also be limited by Z-diodes 260 in the generator 12. The Z-diode 16 can be used in combination with Z-diodes in the main current circuit of the generator, even when a Z-diode 160 is connected between the supply line 11 and earth.Moreover, the minimum breakdown voltage of the Z-diode 160 connected to the supply line 11, must be at- least equal to the maximum breakdown voltage of the Z-diode 16 connected to the regulator supply line 20 in addition to the highest possible forward voltage from the diode group in the energisation current circuit of the three-phase generator 12, since otherwise the Z-diode 160 must accept the entire peak energy independent of whether it originates from the generator or from the wiring. Otherwise the Z-diode 160 would be ineffective.

If a number of Z-diodes (three Z-diodes 16, 160, 260 are illustrated in Figure 2) are provided for the protection of the electrical installation, then the junction temperature which reproduces the loading state of the Zdiode must be interrogated and the overvoltage protective device 15 is triggered through the threshold stages 18, 180, 280 as well as through the OR-gate 19, by that Zdiode which exceeds the load parameter associated with it in the first instance.

The third embodiment illustrated in Figure 3 once again shows substantially the same construction consisting of the Z-diode 16, the temperature sensor 17, the threshold value stage 18 and the over-voltage protective device 15. To distinguish from the previous arrangement, the input to a further threshold value stage 24 is connected to the regulator supply line 20. Moreover, a delay device 21 is connected between the output from the threshold value stage 24 and the control input to the over-voltage protective device 15. Moreover, both the temperature sensor 17 and a current measuring device 22 are connected to the inputs to an OR-gate 23 the output from which is likewise connected to the control input to the over-voltage protective device 15 through the threshold value stage 18.Moreover, the output from the OR-gate 23 is not only connected to a control input to the threshold value stage 24 for varying the threshold value but also to a control input to the delay device 21 for varying the delay time. The. current measuring device 22 is connected in series with the Z-diode 16.

The method of operation of the components 24, 21 of the third embodiment illustrated in Figure 3 is based on the fact that as well as the junction temperature of the Zdiode 16, the voltage applied to the regulator supply line 20 can be used for triggering the over-voltage protective device 15. The threshold value for the voltage beyond which a triggering of the over-voltage device must take place, must be, on the one hand, higher than the normally occurring maximum operating voltage, but, on the other hand, be lower than the minimum possible breakdown voltage of the Z-diode 16.In order not to damage the Z-diode on the one hand, but not to interfere unnecessarily with the vehicle wiring on the other hand, the triggering of the over-voltage protective device is so delayed by the delay device 21 on exceeding the threshold value of the threshold stage 24, that, the maximum attainable junction temperature of the Z-diode 16 or of further Zdiodes provided in the installation, lies sufficiently far below the destruction limit under all operating conditions. This delay time to be set depends, among other things on the maximum peak energy to be accepted by a Z-diode and may be determined, for example, from the maximum generator current, the maximum breakdown voltage of the Zdiode and the junction temperature of the Zdiode as well as a size of the Z-diode determined by constructional requirements.

When the delay time has passed and an overvoltage still exists, the over-voltage protective device 15 become operative.

With the Z-diode 160 at the supply line 11 and with the Z-diodes in the main current circuit of the generator 12, the voltages applied thereat correspondingly serve as parameters for triggering the over-voltage protective device 15.

Various values characterising the loading condition of the Z-diode 16 should not in any case be exceeded, since an excess would result in the destruction of the Z-diode. Thus, these parameters trigger the over-voltage protective device 15 directly through the threshold value stage 18 or a plurality, not shown, of further threshold stages whilst bypassing the components 24 and 21. In the embodiment illustrated, this direct triggering takes place on exceeding a maximum permissible current through the Z-diode 16 and on exceeding a maximum permissible junction temperature.In addition, further parameters are, for example, firstly the exceeding of a maximum permissible velocity of variation of the breakdown voltage of the Z-diode dU/dt and/or the exceeding of a maximum permissible voltage at the regulator supply line 20 as occurs with a defective Z-diode 16 and which must, of course, be substantially higher than the threshold value of the threshold value stage 24. In Figure 3, two such parameters are combined by an ORgate. However, in this connection, an AND combination is also conceivable if the spontaneous triggering of the over-voltage protective device is only to occur when two parameters exceed their limit value simultaneously.

In the third embodiment, not only is a variation of the threshold value of the threshold value stage 24 provided by parameters of the system, but also in the delay time of the delay stage 21. Moreover, an especially advantageous coupling is the control of the delay time by thejunction temperature or the more easily accessible housing temperature.

If this temperature is already very high then an over-voltage pulse poor in energy is sufficient to bring the Z-diode 16 up to its destruction limit. Thus, the delay time of the delay device 21 is preferably made shorter at a higher temperature than at a lower temperature. The same applies to the current flowing through the Z-diode 16 the value of which likewise indicates an approximation of the destruction limit. An effect similar to the shortening of the delay time is provided in the third embodiment also by a reduction in the threshold voltage by the two described parameters.For controlling the threshold value of the threshold value stage 24 and the delay time of the delay element 21, it is also of advantage to connect a non-linear circuit element in front of the control inputs so that the values of the delay time and threshold value can be produced more than proportionally with an increasing influence on the Z-diode 16.

The arrangements according to Figure 2 and Figure 3 are especially simple to produce when the Z-diodes 16, 160, 260 and the overvoltage protective device 15 as well as the further components which are used are integrated into one unit. In this case, it is of especial advantage, as illustrated in Figure 4, to replace one Z-diode 16 by a voltage amplitude detecting means in the forms of one or more inversely operating transistors 161 to 164. Since the breakdown voltage of an individual inversely operating transistor is generally too low, this series circuit is usually necessary. Moreover, each collector may be connected to an emitter of the following transistor. Moreover, the emitter of a final transistor 161 is connected to the regulator supply line 20 or some other line and the collector of the other final transistor 164 is connected to earth.Furthermore, leakage resistors 165 to 168 can be connected respectively between the base and the collector of such an inverse operating transistor.

Another integrated circuit instruction for the voltage amplitude detecting means is shown in Figure 5. The integrated circuit is formed on the substrate 25 into which is diffused the highly doped conductive surface of reversed polarity 26. Then, the weakly doped epitaxial layer 27 of the same polarity as the conductive layer 26 is applied to the said substrate 25. Finally, the reiatively highly doped so-called insulation diffusion 28 which has the same polarity as the substrate 25, and the highly doped connection diffusion 29, which has the same polarity as the conductive layer 26 and which permits the latter to be connected to the upper surface with very low resistance, is diffused therein. The customary insulating surface layer consisting of silicon dioxide is provided with the reference numeral 30.The metallizing 31 forms the connection for the conductive layer 26 and the metallizing 32 the connection for the insulating fusion 28. All these strip-like metallizing of the same polarity 31 or 32 are connected to one another in a manner not shown and lead to terminals. A PN-transition is formed between the insulating diffusion 28 and the conductive layer 26.

The doping gradient determining the breakdown voltage is normally or subordinate importance to the functioning of the integrated circuit so that the desired breakdown voltage of the thus produced Z-diode may also be directly introduced. Beyond this, a plurality of Z-diodes may also be connected in series. If, as is usual, the substrate 25 is Pconductive, then the metallizing 31 is the cathode of the Z-diode and the metallizing 32 is the anode of the Z-diode. The arrangements illustrated in Figures 4 and 5 can obviously be made complementary.

WHAT WE CLAIM IS: 1. Apparatus for the protection of an electrical installation including a voltage source, the apparatus comprising voltage amplitude detecting means for detecting a voltage from the output of the voltage source in excess of a predetermined level, means for detecting a temperature of the voltage amplitude detecting means in excess of a threshold level, and semiconductor switching means arranged to be connected in parallel with said voltage source and arranged to respond when there is a voltage in excess of said predetermined level and an output from the temperature detecting means for shorting the output from the voltage source.

2. Apparatus according to claims 1 wherein said voltage amplitude detecting means comprises a zener diode.

3. Apparatus according to claim 1 or 2 and including further detecting means arranged to detect a voltage applied to a component of the electrical installation.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. dU/dt and/or the exceeding of a maximum permissible voltage at the regulator supply line 20 as occurs with a defective Z-diode 16 and which must, of course, be substantially higher than the threshold value of the threshold value stage 24. In Figure 3, two such parameters are combined by an ORgate. However, in this connection, an AND combination is also conceivable if the spontaneous triggering of the over-voltage protective device is only to occur when two parameters exceed their limit value simultaneously. In the third embodiment, not only is a variation of the threshold value of the threshold value stage 24 provided by parameters of the system, but also in the delay time of the delay stage 21. Moreover, an especially advantageous coupling is the control of the delay time by thejunction temperature or the more easily accessible housing temperature. If this temperature is already very high then an over-voltage pulse poor in energy is sufficient to bring the Z-diode 16 up to its destruction limit. Thus, the delay time of the delay device 21 is preferably made shorter at a higher temperature than at a lower temperature. The same applies to the current flowing through the Z-diode 16 the value of which likewise indicates an approximation of the destruction limit. An effect similar to the shortening of the delay time is provided in the third embodiment also by a reduction in the threshold voltage by the two described parameters.For controlling the threshold value of the threshold value stage 24 and the delay time of the delay element 21, it is also of advantage to connect a non-linear circuit element in front of the control inputs so that the values of the delay time and threshold value can be produced more than proportionally with an increasing influence on the Z-diode 16. The arrangements according to Figure 2 and Figure 3 are especially simple to produce when the Z-diodes 16, 160, 260 and the overvoltage protective device 15 as well as the further components which are used are integrated into one unit. In this case, it is of especial advantage, as illustrated in Figure 4, to replace one Z-diode 16 by a voltage amplitude detecting means in the forms of one or more inversely operating transistors 161 to 164. Since the breakdown voltage of an individual inversely operating transistor is generally too low, this series circuit is usually necessary. Moreover, each collector may be connected to an emitter of the following transistor. Moreover, the emitter of a final transistor 161 is connected to the regulator supply line 20 or some other line and the collector of the other final transistor 164 is connected to earth.Furthermore, leakage resistors 165 to 168 can be connected respectively between the base and the collector of such an inverse operating transistor. Another integrated circuit instruction for the voltage amplitude detecting means is shown in Figure 5. The integrated circuit is formed on the substrate 25 into which is diffused the highly doped conductive surface of reversed polarity 26. Then, the weakly doped epitaxial layer 27 of the same polarity as the conductive layer 26 is applied to the said substrate 25. Finally, the reiatively highly doped so-called insulation diffusion 28 which has the same polarity as the substrate 25, and the highly doped connection diffusion 29, which has the same polarity as the conductive layer 26 and which permits the latter to be connected to the upper surface with very low resistance, is diffused therein. The customary insulating surface layer consisting of silicon dioxide is provided with the reference numeral 30.The metallizing 31 forms the connection for the conductive layer 26 and the metallizing 32 the connection for the insulating fusion 28. All these strip-like metallizing of the same polarity 31 or 32 are connected to one another in a manner not shown and lead to terminals. A PN-transition is formed between the insulating diffusion 28 and the conductive layer 26. The doping gradient determining the breakdown voltage is normally or subordinate importance to the functioning of the integrated circuit so that the desired breakdown voltage of the thus produced Z-diode may also be directly introduced. Beyond this, a plurality of Z-diodes may also be connected in series. If, as is usual, the substrate 25 is Pconductive, then the metallizing 31 is the cathode of the Z-diode and the metallizing 32 is the anode of the Z-diode. The arrangements illustrated in Figures 4 and 5 can obviously be made complementary. WHAT WE CLAIM IS:

1. Apparatus for the protection of an electrical installation including a voltage source, the apparatus comprising voltage amplitude detecting means for detecting a voltage from the output of the voltage source in excess of a predetermined level, means for detecting a temperature of the voltage amplitude detecting means in excess of a threshold level, and semiconductor switching means arranged to be connected in parallel with said voltage source and arranged to respond when there is a voltage in excess of said predetermined level and an output from the temperature detecting means for shorting the output from the voltage source.

4. Apparatus according to claim 1 or 2

and including further detecting means arranged to detect the current flowing through a zener diode.

5. Apparatus according to any one of the preceding claims wherein at least two zener diodes are provided each with a measuring device for the temperature, and the signals corresponding to the temperatures are transmitted through threshold value stages to the inputs to an OR-gate, the output signal from which is arranged to activate the switching means.

6. Apparatus according to claim 5 wherein at least one zener diode is provided with a measuring device for measuring the current in the blocking direction of the diode and the signals corresponding to the current and the temperature are transmitted to the inputs to an OR-gate, the output signal from which is arranged to activate the switching means.

7. Apparatus according to claim 6 and comprising a delay device connected to the output of the voltage threshold device for delaying activation of the switching means thereby. Apparatus according to claim 7 wherein the delay time of the delay device is adjustable.

8. Apparatus according to claim 1 and comprising a voltage threshold device for activating the switching means, said threshold device being arranged to be connected to the supply voltage for the electrical installation, and wherein the voltage amplitude detecting means comprises a zener diode whose breakdown voltage is higher than the supply voltage.

9. Apparatus according to any one of the preceding claims wherein the installation comprises a voltage regulator, the voltage amplitude detecting means comprising a zener diode arranged to be connected to the regulator supply line, and wherein a furtherzenerdiode is arranged to be connected to the voltage supply line to a load, the maximum breakdown voltage of the first-mentioned diode being lower than the minimum breakdown voltage of the further diode.

10. Apparatus according to any one of the preceding claims wherein the voltage source comprises a three-phase generator, and the apparatus comprises at least three zener diodes of a group of diodes arranged to be in the main current circuit of the threephase generator.

I 1. Apparatus according to claim 10 wherein the break-down voltages of the three diodes are lower than those of the other diodes of the group, which other diodes are arranged externally of the generator.

12. Apparatus according to any one of the preceding claims wherein the voltage amplitude detecting means is integrated together with the switching device into a single unit.

13. Apparatus according to claim 12 wherein said voltage amplitude detecting means comprises at least one inversely operated transistor.

14. Apparatus according to claim 12 wherein said voltage amplitude detecting means comprises a zener diode formed by a pn-transition between a conductive layer diffusion and the insulation diffusion.

15. Apparatus for the protection of an electrical installation substantially as hereinbefore described with reference to the accompanying drawings.

16. An electrical installation including apparatus according to claim 15.