DE2533577A1 - DEVICE FOR MONITORING ELECTRICAL VOLTAGE - Google Patents

Description

BREMEN

PATENTANWÄLTE DIPL.-ING. HANS MEISSNER DIPL.-ING. ERICH BOLTE

D 28 BREMEN,

Sievogtstrasse 21 Federal Republic of Germany

Telephone 0421 34 2019 Telegrams: PATMEIS BREMEN

Our sign 2913

SOCIETE INTERNATIONALE DE MECANIQUE INDUSTRIELLE 37, rue Notre-Dame, LUXEMBOURG

Device for monitoring an electrical voltage

The invention relates to a device for monitoring an electrical voltage, i.e. a device that displays or Contains control devices that respond at least when a predetermined limit voltage is exceeded.

There are already devices for monitoring a voltage range in which two Zener diodes are present, their breakdown voltages correspond to the limits of the voltage range to be monitored. These devices cannot be adjusted and therefore need a correctly specified Zener diode for each voltage limit to be monitored. Further, Since the characteristic values of the Zener diodes supplied by the manufacturers are subject to scatter, such a device is only from inferior accuracy.

509887/0813

Models sent in will be destroyed after 2 months, if not reclaimed. Oral agreements, especially by telephone, require a written one Confirmation. - The invoiced costs are due without deduction on the redemption date. - In the event of late payment, bank interest will be charged

Jurisdiction and place of performance Bremen. Bremer Bank, Bremen, No. 2310028 · Die Sparkasse In Bremen, No. 1045855 · AIIg. Deutsche Credlt-Anstalt, Bremen, No. 202 598 · Postal checking account: Hamburg 33952-202

One object of the invention is to provide a device for monitoring specify an electrical voltage that does not have the disadvantages mentioned and designed as an integrated circuit can be.

A solvent for this object is given by claim 1.

In an advantageous embodiment of the invention, the base of the control transistor is connected to the collector of a second control transistor, the emitter of which is connected to the negative connection terminal of the device and the base of which is connected via a second Zener diode to a second adjustable voltage divider which is connected to the two connection terminals of the device. tied together. The second voltage divider is set in such a way that the second Zener diode becomes conductive when the voltage at the connection terminals of the device has a second predetermined value E ₀ , which is greater

¹ >

as E, exceeds. The interposition of a zener diode between the control transistor and the voltage divider has the advantage that it creates a threshold for free tripping given is.

Preferably, in terms of the design, they are more integrated Circuit the Zener diodes transistors that are connected as reverse diodes, which also has the advantage that the Temperature drift of the threshold of the control transistors compensated will if one. selects identical transistors as zener diodes.

In an advantageous embodiment of the invention, there are Voltage divider consisting of a fixed resistor connected to the positive terminal and an adjustable resistor, which is connected to the negative terminal, with the corresponding Zener diodes at the junction of the two Resistors are connected.

In a further development of the invention, the power transistor is provided in the form of a Darlington circuit.

Such an arrangement has the advantage that a current gain is obtained which is higher than that of a single transistor, and consequently the heat energy emitted as a result decreased.

There is also a two-stage amplifier chain between the collector of the first control transistor and the base of the Darlington pair .

This embodiment is particularly good for training as Integrated circuit is suitable because the integrated transistors have smaller voltage amplifications than individual transistors. The amplification chain is necessary in order to either block or saturate the exclusive states with weak transistors for the Darlington pair.

Furthermore, a common coupling branch, which consists of a resistor consists, the emitter of the first transistor, which forms the Zener diode, with the collector of the first transistor of the amplifier chain tied together. A second negative feedback branch, which consists of a resistor, becomes the emitter of the second Transistor which forms the Zener diode, connected to the collector of the first control transistor.

The switching is improved by the negative feedback circuit and self-oscillations are thereby suppressed, so that one receives a free transition from the blocked to the conductive state.

The device also contains a capacitor which is connected in parallel to the two connecting terminals.

With this capacitor, the time constant of the device is increased and the device is thereby opposed to the effect made insensitive to signals of short duration, such as interference.

In a suitable configuration, the device is with exception the display device and the capacitor as hybrid,

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INSPECTED

25 3 3-77

integrated circuit formed, the adjustable resistors in the form of thin or thick layers or as a plated circuit element. The rest of the circuit is designed as an integrated circuit.

In addition to the advantage of miniaturization, this form of training the disadvantage avoided due to the scatter of the characteristic values of the individual components in relation to those specified by the manufacturer Values is given.

To set up the circuit, you build it in and place a changeable supply voltage. The adjustable resistors are set to such values that the Zener diodes only become conductive when the supply voltage exceeds the specified values mentioned.

It is an object of the invention to provide an embodiment the device described above with two thresholds E and E, which are particularly good for monitoring the voltage of a Motor vehicle battery is suitable. In the following it is assumed that the load resistance is formed by an indicator lamp which is arranged on the instrument panel of a vehicle. The invention however, is in no way specific to this particular embodiment limited, since the load resistance is just as well formed by a control device or a display device of another type can be.

The problem of monitoring the voltage of a battery arises in the following way.

At first, when the ignition is switched on, the engine does not run so that the battery has its open-circuit voltage. The lamp that the already forms mentioned display device should light up.

If the engine is running, the lamp must go out as soon as the speed increases of the engine is sufficient to charge the battery. This corresponds to a higher voltage than the rest voltage.

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When working, you have to avoid abnormally high voltages, otherwise the battery can be destroyed. This results in there is an upper limit for the voltage from which the lamp should shine in order to warn the driver of the vehicle.

If the voltage drops, for example when stopping when the motor is running slowly, a lower limit must be set which corresponds to a real discharge of the battery, i.e. a limit that is below the open-circuit voltage, thus by the Illumination of the lamp causes a real warning to the driver of the vehicle. This lower limit is necessarily different from that The upper limit defined above is different, since it is above the open-circuit voltage of the battery. As a result, one must Provide two lower limits, one which is above the open-circuit voltage of the battery and at which the lamp goes out when the The voltage rises and another which is below the rest voltage and at which the lamp lights up when the voltage drops.

The present invention therefore also relates to a device of the type mentioned, in which, in addition to the upper threshold, two lower thresholds, which are different from one another, instead of a single one lower threshold are present.

For this purpose, the base of the first control transistor is equipped with a third adjustable voltage divider via a third Zener diode connected, wherein the third voltage divider is set so that the third Zener diode is conductive when the voltage to the Terminals of the device a third predetermined value E, which is less than E, falls below. The collector of the first The control transistor is connected to the base of an intermediate transistor, the collector of which is connected on the one hand to the base of the power transistor and on the other hand is connected to the base of a transistor, the collector of which is connected to the setting point of the third Voltage divider is connected, all these transistors are connected to the negative terminal via their Emittei ^.

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üie third threshold device, created by the third zener diode, which is associated with the third voltage divider and connected to the base
of the first control transistor is connected, occurs for the first threshold device when the voltage is the
Value E, which is chosen above the open circuit voltage of the battery
is, falls below and remains switched through when the voltage falls below the value E, whereby the lamp remains extinguished. The voltage must fall below the voltage E_, which is selected below the open-circuit voltage, so that the third threshold device blocks, whereby the lamp is switched on.

It is also known that the charging conditions of a battery change with temperature. In particular, the lower the temperature, the greater the charging current that a battery can withstand
is. As a result, the voltage applied can be significantly higher in the cold without having to worry about damaging the battery. It is desirable at least as a result
to vary one of the thresholds mentioned in such a way that it decreases as the temperature increases. This is a preferred one
Embodiment of the invention at least one of the voltage dividers
connected to the negative terminal via a zener diode, the
is identical to the Zener diode, which is assigned to the voltage divider and connected in the same direction. The dem
The zener diode assigned to the voltage divider is connected to the set point of the voltage divider via a diode chain.

The interconnection of the diode chain results in a precisely defined one Temperature drift when you consider the number of diodes in the chain and the Everyone knows drift. As a result, the threshold sinks to which the voluntary temperature drift is applied, with a given slope as the temperature rises.

Furthermore, the Zener diode, which is connected between the voltage divider and the negative terminal *, compensates for the temperature drift
and the spread of the threshold of the zener diode associated with the voltage divider, since the two zener diodes interrelate
are identical and connected in the same way. This is

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important to have a defined variation depending on the To reach temperature, since the Zener diodes have relatively significant scatter.

You can of course use this voluntarily obtained temperature drift also apply to the two-threshold device described first.

Embodiments of the invention are given below with reference to of the drawings.

Figure 1 shows the circuit of an embodiment of the invention, where there are two thresholds.

Figure 2 shows the circuit of another embodiment, the is suitable for voltage monitoring of a vehicle battery, this embodiment being three Has sleepers.

Figure 3-A- shows the status of the indicator lamp as a function of

the voltage applied to the terminals at low temperatures, with the lamp as the load resistance is used, and where the state is the switched-on state and the state 0 is the corresponds to the switched-off state of the lamp.

FIG. 3B corresponds to the illustration in FIG. 3-A- at ambient temperature.

FIG. 3C corresponds to the illustration of FIG. 3A with increased

Temperatures.

According to Figure 1, terminals A and B are the positive and negative Connection terminals of the circuit whose voltage you want to monitor. Denoted at 14 is a resistor which is an indicator lamp can be.

The circuit includes a first control device, which follows Way is formed. Between the positive and the negative terminal, a voltage divider is connected, which consists of a Fixed resistor 3 and an adjustable resistor 1 are formed

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is. The connection point of resistors 1 and 3 is with the Base of a control transistor 5 via a transistor 15 ι the with the transistor 5 is identical, connected. The transistor 15 is connected with a reverse diode so that one to one Zener diode equivalent circuit is formed, i.e. that the emitter of the transistor 15 with the connection point of the resistors 1 and 3 is connected, while its base and its collector are connected to the base of the transistor 5 and via a Resistor 17 are connected to the negative terminal of the device. The emitter of transistor 5 is negative Terminal of the device and its collector is connected to the positive terminal via a load resistor 7.

The resistor 1, which with the resistor 3 is a voltage divider forms is set so that the voltage threshold of the Zener diode (about 7V) formed by transistor 15, is achieved when the voltage between the terminals A and B exceeds a certain value E, for example 12.5V. The Zener diode is then conductive and the transistor 5 also changes from the blocked state to the conductive one.

The breakdown of the potential threshold of the Zener diode allows a free switchover, and since the transistor 5 oppositely connected transistor 15 is formed, which is identical to that, the temperature drift of the threshold of the transistor 5 in a sufficient manner by the temperature drift of the transistor 15 compensated.

The device has in the same way a second control device which has a voltage divider, which consists of a fixed resistor 4 which is connected to the positive terminal and an adjustable resistor 2 which is connected to the negative terminal. There is also a control transistor, the base of which is connected to the connection point of the resistors 2 and k via a Zener diode which is formed by a transistor 16 which is identical to the transistor 6.

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2533F.77

The transistors 16 and 6 are inverted diodes with each other switched. The base and collector of transistor 16 are connected to the negative terminal via a resistor 18.

The resistor 2 is set in such a way that the voltage which the Zener diode formed from the transistor 16 (approximately 7V) is conductive makes, is achieved when the voltage at the terminals A and B exceeds a predetermined value E, for example 16 V. The Zener diode is then conductive and the transistor 6 becomes conductive.

The device also includes one with the collector of the transistor 5 connected chain of voltage amplifiers, which is formed from two transistors 11 and 12, the emitter of which with the negative Terminal and its collectors are connected to the positive terminal via load resistors 21 and 22. The collector of transistor 5 acts on the base of transistor 11, the collector of which is connected to the base of the transistor 12.

There is also a Darlington circuit, which consists of transistors 9 and 19, and serves as a current amplifier. The Darlington circuit is connected to the collector of transistor 12 via the base of transistor 19. The emitter of transistor 19 is connected to the base of transistor 9, the emitter of which is connected to the negative terminal. The collectors of the transistors 9 and 19 are connected to the lamp lh .

The advantage of designing the power amplifier as a Darlington pair is that the saturation voltage decreases collector-emitter with respect to a single transistor is. As a result, the Joule heat emitted becomes also decreased.

The voltage amplifier chain formed from transistors 11 and 12 allows only the locked or saturated for states

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2533R77

to obtain the Darlington pair with transistors of very short duration. The integrated translators have voltage amplifications, which are much smaller than those of individual transistors (on the order of 60 - 80 compared to 3OO - 500), so that additional reinforcement is necessary.

On the other hand, two stages are necessary in the amplifier chain in order to make the transistor jjvxn conductive State of the transistor preceding the Darlington pair or vice versa.

The operation of the device is as follows. The resistors 1 and 2 have been set in the manner described. If the voltage between the terminals A and B is below E ₁ (12.5V), the Zener diode formed by the transistor 15 is in the blocked state, whereby the transistor 5 is also blocked. The collector of transistor 5 and, as a result, also the base of transistor 19 are at an increased potential, which is state 1. As a result, the Darlington circuit is conductive and the lamp 14 lights up.

If the voltage between terminals A and B is E (12.5V), the Zener diode becomes conductive, as does transistor 5 and the voltage at its collector goes to 0 (State θ). It follows that the Darlington pair is locked and the lamp 14 goes out.

As long as the voltage between the connections A and B does not exceed the value E_ (i6v), the Zener diode, which is formed by the transistor 16, remains in the blocked state, as does the transistor 6. The Zener diode formed by the transistor 15 remains conductive and the lamp 14 remains dark.

If the voltage between the terminals A and B exceeds the value E n (16v), the Zener diode formed by the transistor 16 becomes conductive, as does the transistor 6. The voltage that forms at the emitter of the transistor 15> which forms the Zener diode ,

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2 5 3 3: ϊ 7 7

attacks, falls, so that as a result the Zener diode is blocked State goes over, just like transistor 5. The potential at the collector of transistor 5 goes into state 1, whereby the Darlington circuit becomes conductive and the lamp 14 lights up.

The device thus makes it possible to monitor that the voltage between the terminals A and B remains within the predetermined range which is limited _{by the values E and E 2.}

The device therefore has the advantage that no tight tolerances are necessary for the individual components. The resistances 1 and 2 are set once when the circuit is installed. It is then of little importance that a certain spread of the threshold voltages of the Zener diodes is present in relation to the voltage values specified by the manufacturer, since the setting in the finished circuit \.

The device also contains a negative feedback branch, which consists of a resistor 8 and the emitter of transistor 16, which forms the Zener diode, connects to the collector of the control transistor 5. There is also a second negative feedback branch, which is formed from a resistor 8 ', which is the emitter of the the Zener diode forming transistor 15 with the collector of the amplifying transistor 11 connects.

The negative feedback amplifies the states whether it is blocked or not conductive of the Zener diodes 15 and 16 and creates a freer transition from blocked to conductive state. When the Zener diode 15 is blocked, so is the transistor 5 and the transistor 11 is conductive. As a result, that is up to its collector State 0 before and the voltage at the input of the Zener diode 15 is lowered because the negative feedback has the role of one with the set point of the voltage divider and the resistor connected to the negative terminal plays.

In contrast to this, when the Zener diode 15 is conductive, the

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Collector of transistor 11 has an increased potential and the negative feedback amplifies the input voltage of the zener diode.

The mode of operation is the same for the branch of the Zener diode 16. When this is blocked, it is also the transistor 6. The transistor 5 is conductive and its collector shows the state o. The negative feedback tries the input voltage of the Zener diode 16, as has already been explained to reduce. When this becomes conductive, so will transistor 6 and transistor 5 is locked. Its collector has an increased potential. The negative feedback amplifies the input voltage of the Zener diode 16 and the Transition to the conductive state.

Of course, the negative feedback branches are connected in such a way that they do not act at the same time, since the control transistors 5 and 6 are each in opposite states. Incidentally, the hysteresis resulting from the branches is negligible, since it does not exceed 50 mV.

The device also has a low inductance capacitor 10 connected in parallel with terminals A and B. is to increase the time constant of the device. This makes it possible that the device against the influence of Interference signals (whose peak voltages can assume high values and damage the components) is not exposed, because these signals have a short duration which is below the response time of the device.

With the exception of the lamp 1h and the capacitor 10, the device described can be designed in the form of a hybrid circuit in which the adjustable resistors can be formed from thin or thick layers or in a plated form. The connections to the heart of the integrated circuit are made by gold wires soldered by thermocompression. The adjustable resistors 1 and 2 are set to the desired value by removing material, both

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253357?

for example by means of a sand or laser beam.

The embodiment according to FIG. 2 is described below, especially for monitoring the voltage of a vehicle battery suitable is.

The components of the device according to FIG. 2, which correspond to those of the device according to FIG. 1, have the same, however Reference numbers increased by a value of 100.

The connections (+) and (-) are the battery connections whose voltage you want to monitor. 114 with an indicator lamp is designated .

The circuit includes a first threshold device connected to the base of a transistor 105. This facility has a voltage divider formed by the fixed resistor 103 and the adjustable resistor 101. This voltage divider is connected between the connections (+) and (-). One connection of a zener diode 115 is to the connection point of resistors 101 and 103 are connected via a chain of diodes 133. The other terminal is connected to the base of the transistor 105 via a diode 120. The diode 120 can be used in a simple Way an exact compensation of the temperature drift can be made. Another zener diode 134 is between the resistor 101 and the negative terminal. Their meaning and that of the diode chain 133 will be described in more detail. Of the Resistor 101 is set so that the threshold device switches when the voltage between terminals (+) and (-) exceeds a value E which is selected above the open-circuit voltage of the battery. This is generally 12V and one selects, for example, 13.5V for the value E.

The device has a second threshold device, which in the same way consists of resistors forming a voltage divider 102 and 104, formed from a Zener diode 116 and the diode 121 and is connected to the base of a transistor 106. Of the

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Resistor 102 is set so that the switching voltage of the second device at a voltage E between the terminals: which is above the value E, for example 16V.

The apparatus also includes third threshold means connected to the base of transistor 105 and through which Resistors 122 and 123, the zener diode 124 and the diode 125 is formed. The third device switches based on the appropriate Setting of the resistor 122 when the voltage between the terminals falls below a value E, which is below the open-circuit voltage the battery must lie. For example, it can reach 11.5V to get voted. In the following, thresholds E, E, E are used as “the designated first, second and third threshold means.

It should be noted that in the practical implementation, as in the device according to FIG. 1, the Zener diodes 115> 116, 124 and 134 and diodes 120, 121, 125 and 133 by transistors which are connected with reverse diode or direct diode. This also applies to the Zener diodes to which is referred to below so that the device can be designed as an integrated circuit.

The adjustable resistors are made for the same reason thin, thick or plated layers are produced and adjusted to their desired value by removing material, for example brought by a sand or laser beam.

The transistors 105 and IO6 are connected to a common emitter, while their bases are connected to the negative terminal via resistors 117 and 118, respectively. Further is the collector of transistor 106 is connected to the base of transistor 105.

The collector of transistor 105 is on the one hand with the positive Connection through a resistor 107 and on the other hand to the base

Β0Θ887 / 08Ί3

of transistor 126 connected. The collector of this transistor 126 is via a current generator or a current inverter 127, which is formed from three transistors, on the one hand with the base of transistor 128 and on the other hand with the base of the Transistor 119 connected, which with transistor 109 is a Darlington pair forms, which serves as a current amplifier.

The collector of transistor 128 is to the junction point of the resistors 122 and 123 belonging to the threshold E connected and thus, when the transistor 128 is conductive, the state 0 is present at its collector and the threshold E n is present Dimensions .

The operation of the device as a function of the voltage changes at its connections is described below. For a better illustration, the method of operation is shown schematically in the table. The table shows the states (blocked = 0, conductive = 1) which the thresholds E ₁ , E and E ~ the transistors 106, 105 »128 and the lamp 114 assume as a function of the voltage at the connections.

The transistors 126, 127, 119 and 109 are not in the table indicated because they are always in the same state as transistor 128.

If the voltage is below E, all thresholds are blocked, in particular the threshold E. As a result, the transistor 105 is blocked and its collector has the state 1, so that transistor 126 is conductive. As a result, the Current generator 127 conductive, and therefore also transistor 128 and the Darlington circuit, which consists of transistors 119 and 109 is formed. The collector of transistor 109 is in state 0, so that lamp 114 lights up.

Furthermore, since transistor 128 is conductive, its collector is in state 0 and threshold E is at ground.

509887/0813

If the voltage exceeds the value E ", the threshold E" become conductive, but since it is grounded because of the conductive transistor, it does not matter and the lamp 114 remains switched on.

When the voltage exceeds the value E, the threshold becomes E conductive and therefore also the transistor 105

Its collector goes to state 0, transistor 126 goes into the locked state, as does the current generator 127> transistor 128 and the Darlington pair. Consequently the lamp 1 1 ^ J- does not light up.

Incidentally, since the transistor 128 is blocked, it is located Collector in state 1. This allows current to pass through threshold E " flow and this is effectively conductive, since the voltage is above E and therefore all the more above E. The stream that flows through the threshold E, adds to that through the Threshold E current flowing to indicate the information.

When the voltage rises above the fourth E, the threshold becomes E conductive, and thus also the transistor 106. The voltage acting on the base of the transistor 105 thus falls to the Saturation voltage collector-emitter of transistor 106, the is well below the threshold voltage of transistor 105. It follows that that of the thresholds E and E, the conductive remain, incoming current flows through transistor 106 to ground. Under these conditions, transistor 105 goes into FIG blocked state and the transistor 126 becomes conductive, as well as the transistor 128 and the Dariington circuit. the Lamp 114 lights up.

Furthermore, since transistor 128 is conductive, its collector is in state 0 and threshold E comes to ground.

If the voltage now drops again, there will be a change

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γ ι ^ r π ^Γ /

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tion of the state for a voltage E ¹ which is slightly different from the voltage E due to the hysteresis caused by the temperature drift of the transistor 106

By changing the state, the circuit is brought into the state described for one above voltage E, wherein the transistor 105 returns to the conductive state and the transistors 126, 128 and the Darlington circuit are blocked will. The threshold E_ works again because the collector of transistor 128 is in state 1. The lamp 114 goes out.

When the voltage drops below E, one gets one of the different state described above, because, since the transistor 128 is blocked, the threshold E remains conductive and the Threshold E takes over, which is now blocked in order to keep transistor 105 in the conductive state. As a result, the Lamp 114 dark.

The voltage must fall below the value E so that the threshold E Is blocked. No current flows through transistor 105, transistor 126 is conductive, as is transistor 128 and the Darlington circuit. The lamp 114 lights up. Furthermore, since the Transistor 128 is conductive, the threshold E "reaches ground, which confirms the information. The cycle can then start again.

Thus, as shown for example in Figure 3B, in the sense of the voltage increase, the lamp 114 remains lit up to the voltage E, then it goes out and lights up again when the voltage exceeds the value E. Now in the sense of falling voltage, the lamp goes out when the voltage falls below it of the value E ', which differs only slightly from the value E, and remains dark when the voltage is below the value E falls to only light up again when the tension falls below the value E ".

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The device according to the invention perfectly matches that problem of voltage monitoring of a vehicle battery explained above.

At the beginning with the ignition switched on, the voltage at the connections is the open-circuit voltage of the battery (l2V), below E ₁ (13.5V): The lamp 114 lights up.

If the engine is running, the battery will be charged as soon as sufficient Speed is reached. The voltage exceeds the value E, so that the lamp goes out.

With the engine running, if the voltage gets too high, it will exceed E (e.g. l6v) and the lamp will come on to warn the driver.

When the engine is running slowly, the voltage drops, but the lamp 114 lights up only when the voltage falls below the value E_, which, as already mentioned, is below the no-load voltage and has been set to, for example, 11.5V. Consequently the warning corresponds to a real discharge of the battery and is absolutely necessary. In such a case the vehicle driver becomes caused by the warning to reduce electricity consumption, for example by switching off the heating, the Fog lights etc.

Of course, if the alternator fails, the battery voltage immediately drops below the value E, which means that the Lamp lights up.

It has already been mentioned above that a battery can withstand a considerably higher voltage when it is cold than when it is warm and it is for this reason that a diode chain 133 has been provided between the connection point of the resistors 101 and 103 and the Zener diode. By following the chain of diodes I33 a temperature drift of the threshold E ₁ is generated, which is accurately determined and the impact by reducing the voltage E ₁ when

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the temperature increases. This change in voltage E ₁ is shown in FIGS. 3A, 3B and 3C. FIG. 3A corresponds to low temperatures (of approximately -3O ° C.), FIG. 3B corresponds to the ambient temperature (+ 20 ° C.) and FIG. 3C corresponds to elevated temperatures (+ 80 ° C.), these temperatures being perceived by the device.

If, for example, each diode 133 has a temperature drift of -1.5 mV / C, with k diodes a drift of the diode chain of -6 mV / C is obtained, to which the drift of the base-emitter connection of transistor 105, for example -1 , 5 mV / ° C, must be added in order to obtain the total drift, which here is -7> 5 mV / C.

On the other hand, the temperature drift and the spread of the threshold of the Zener diode 115 compensates, since these two Zener diodes are identical to one another and are connected in the same way are so that one can get an exact temperature drift on this Way receives.

In the device shown, the desired temperature drift acts on the threshold E, but it can also act in the same way on the thresholds Έ or E or on several of the thresholds, as required.

The intended use of the device makes it efficient Fault protection necessary, on the one hand an unwanted Functioning of the device (for example, the lighting of the lamp in the event of interference voltages) must prevent and on the other hand the Device must protect against destruction due to overvoltages.

To light up the lamp by switching the transistor A capacitor 129 is to be used to prevent 105 due to interference voltages resulting from overvoltages of short duration between the base of transistor 105 and the negative terminal switched. This capacitor results in a time constant

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which slows down and prevents the response of transistor 105, that it switches when brief overvoltages occur.

Furthermore, the device must be protected against increased overvoltages that can reach several 100 volts in a vehicle. For this purpose, a row of Zener diodes 130 is between the negative connection and a resistor 131 »the one with the positive Connection is connected, switched. The chain of zener diodes 130 cuts the voltage above its threshold, thus avoiding the destruction of the components. In the illustrated Embodiment, the chain contains, for example, three Zener diodes, each of which has a threshold of 7V, so as a result the chain cuts above 3 x 7 = 21 V. The resistance 131 absorbs the resulting voltage drop and limits the intensity, which is necessary in order to destroy the Zener diodes to avoid.

To the Darlington pair, made up of transistors 119 and 109 is formed to protect which is not protected by the foregoing arrangement, Zener diodes 132 are in series between the Base of transistor 109 and lamp 114 switched. In the event of an overvoltage is the transistor IO9 by switching of the chain of Zener diodes 132 conductive and causes the lighting up of lamp 114. Its resistance increase following its lighting up limits the intensity and protects the Darlington pair against too high an intensity with which one runs the risk of being gets destroyed.

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TABEL

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connection
tension Condition of the components SchwlS ₂ 106 3ChWLE ₁ 105 T ¹ 1 128: ■ 1 Schv.'l. E- 4th 1 114 h ■
^E 1 1
^E 2: 0 0 0 0 0 1 0 0 Al * 0 0 0 ι Oil
V. 1 ^Et * l 0 t ° 1 1 0 1 Et 1 Al

ro

OO

* Al = lit Et = extinguished

ro

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Claims (19)

- 22 claims Λ
l.) i Device for monitoring an electrical voltage with a working resistor belonging to a display or control device and one terminal of which is connected to the positive terminal of the device, with a power transistor, the collector of which is connected to the other terminal of this working resistor and its Emitter is connected to the negative terminal of the device, and to a control transistor whose collector is connected on the one hand to the base of the power transistor and on the other hand to the positive terminal of the device, its emitter being connected to the negative terminal and its base to a point, whose potential depends on the voltage between the terminals of the device, characterized in that the base of the control transistor (5 »105) is connected via a Zener diode (15> 115) to an adjustable voltage divider (1,3} 101, ΙΟ3) which is connected between the two connections (A, B) of the device , wherein the voltage divider is set so that the Zener diode (15> 115) is conductive when the voltage at the terminals of the device exceeds a predetermined fourth E. 2.) Device according to claim 1, characterized in that the base of the control transistor (5 »1O5) is connected to the collector of a second control transistor (6,106), whose emitter is connected to the negative terminal and whose base is connected via a second Zener diode (16,116) is connected to a second adjustable voltage divider (2,4; 102,1θ4) which is connected between the two terminals of the device, wherein the second voltage divider is set so that the second Zener diode is conductive when the voltage at the terminals of the Device a second predetermined value E ₁ which is greater than E exceeds. 509887/081 3 3 ^ 577 3.) Device according to one of claims 1 and 2, characterized characterized in that the zener diodes are transistors connected with reverse diodes. k.) Device according to one of claims 1-3 »characterized in that the voltage dividers (1,3» 2,4; 101,103,102,10 * 0 consist of a fixed resistor (3, k ; 103 , 1 Ok) and an adjustable resistor (1,2; 101,102) connected to the negative terminal, the corresponding Zener diodes (15,16; 115 »116) being connected to the junction of the two resistors. 5.) Device according to one of claims 1-4, characterized in that the power transistor (9> 19 5 109 j 1 19) is designed as ^a Darlington circuit. 6.) Device according to one of claims 15, characterized gekennze ichne t that the collector of the second control transistor (6) is connected to the base of the first control transistor (5) over the latter associated Zener diode (15). 7.) Device according to one of the preceding claims 1-6, characterized in that an amplifier chain with two stages (11,12) between the collector of the first control transistor (5) and the base of the Darlington pair is arranged. 8.) Device according to one of claims 1 - 7> characterized in that a negative feedback branch from a resistor 8 'the first Zener diode (15) with the collector of the first transistor (11) of the amplifier chain connects, and that a second negative feedback branch from a resistor (8) the second Zener diode (16) with the Collector of the first control transistor (5) connects. 509887/0813 9.) Device according to one of claims 1-8, characterized characterized in that the device includes a capacitor (io) in parallel with the two Connections is switched. 10.) Device according to one of claims 1-5> characterized in that the base of the first control transistor (105) is connected via a third Zener diode (124) to a third adjustable voltage divider (122,123), the third voltage divider being so set is that the third Zener diode is conductive when the voltage at the terminals of the device falls _{below a third predetermined value E, which is smaller than the value E 1} , and that the collector of the first control transistor (105) with the base of an intermediate transistor ( 126), whose collector is connected on the one hand to the base of the power transistor (127) and on the other hand to the base of a transistor (128) whose collector is connected to the set point of the third voltage divider, all transistors with their emitters to the negative terminal are connected. 11.) Device according to claim 10, characterized in that that the intermediate transistor (126) is connected to the base of the power transistor (127) and that of the transistor is that via a current generator (127) or a current inventor with the third voltage divider (122,123) is connected. 12.) Device according to one of claims 10 and 11, characterized in that each of the Zener diodes (116, 115, 124) is assigned a diode (121, 120, 125). 13 ·) Device according to claim 12, characterized gekennzeich.-n e t that the diode transistors are directly connected diodes. 14.) Device according to one of claims 10-13, characterized 509'8: 87 / O813 ο c ς q ς 7 £. J ν / ■ »■ - 25 - mark that a capacitor (129) between the base of the first control transistor (105) and the negative terminal of the device is connected. 15 ·) Device according to one of claims 10-14, characterized in that a chain of in series switched Zener diodes (130) between the negative Connection of the device and a resistor (131)> connected to the positive terminal is switched. 16.) Device according to one of claims 10-15, characterized denote that a chain of Zener diodes (132) connected in series between the base of the second transistor (109) of the Darlington circuit and the load resistor (ii4) is connected. 17 ·) Device according to one of claims 1 - 16, characterized in that at least one (101,103) the voltage divider via a zener diode (13 ^) with the the Zener diode (i15) assigned to the voltage divider is identical and connected in the same way, wherein the zener diode (115) assigned to the voltage divider is connected to the set point of the voltage divider via a chain of diodes (133). 18.) Device according to one of claims 1 - 17, characterized in that it, with the exception of the Working resistance (114) and the capacitor (1O; 129) is designed as a hybrid circuit, the adjustable resistors as thin or thick layers or as a plated circuit, and that the remainder of the circuit is in the form of an integrated Circuit has. 19.) Method for setting the device according to one of claims 1 - 18, characterized in that 509887/0813 that the circuit is built in and with an adjustable Voltage is supplied, and that the adjustable resistors are set to such values that the Zener diodes assigned to the corresponding voltage dividers only change their state when the supply voltage reached the corresponding specified values. 509887/0813