DE102022117765A1 - METHOD AND DEVICE FOR PROTECTING ONE OR MORE ELECTRICAL LOADS IN THE EVENT OF SHORT CIRCUIT - Google Patents

Abstract

A method for protecting an electrical load (L), which can be connected to an electrical energy source (B) via a switch (S), in the event of a short circuit in the load (L), comprises: connecting the load (L) to the electrical energy source (B) by first turning on the switch (S), detecting an output current (IA) of the switch (S), turning off the switch (S) when the output current (IA) exceeds an overcurrent threshold (IA_S) and/or a predetermined period of time ( TD) has elapsed since the switch (S) was first switched on, detecting an output voltage (UA) of the switch (S), determining an output voltage difference (ΔUA) of the output voltage (UA) between a predetermined first point in time (T1) and one after the first Time (T1) lying predetermined second time (T2), second switching on of the switch (S), if the output voltage difference (ΔUA) is negative and has an absolute value that is smaller than an upper output voltage gsdifferential threshold value (ΔUA_S1) and/or the switch (S) has been switched off after the predetermined period of time (TD) and the detected output current (IA) has not exceeded the overcurrent threshold value (IA_S) since the first switch-on until at least the switch-off.

Description

The present invention relates to a method and a device for protecting one or more electrical loads in the event of a short circuit in the one or more loads.

Modern electronic systems are designed with a high degree of integration in order to be powerful and offer a variety of functions. It also uses different supply voltages to support different types of loads for their proper operation. One of the most important requirements is minimal system downtime in the event of transient abnormal events such as overload, overvoltage or short circuit. Therefore, protective devices such as fuses or, more recently, so-called e-fuses or electronic fuses are used to deal with inrush currents, overload, overcurrent, short circuits and overvoltages and to protect the sensitive loads for reliable system operation. The main requirement is to reduce the fault currents to within the limits and bring the system back to the active state as soon as the fault is corrected without the need for manual intervention.

Fuses are traditionally viewed as protective devices used to isolate overload or short circuit faults from the main system. Although these fuses provide protection, the fault current must be much higher than the fuse rating, with response times ranging from milliseconds to seconds. This makes it extremely difficult to predict the exact overcurrent level at which the fuse will blow. Conservative fuse rating selection can result in fuse tripping during inrush current events. Also, once the fuse blows during an overload event, it must be physically replaced, increasing system downtime and maintenance costs. On the other hand, PTC resistors provide resettable overcurrent protection and, unlike a fuse, can avoid physical tampering. However, because they are actuated by the heating effect of an overcurrent load, their response time is limited to a few milliseconds. Also, the on-resistance of PTC fuses increases after each reset, raising concerns about repeatable performance over time.

The best way to avoid system failures is to detect, respond to, and correct potentially harmful conditions as quickly as possible. Since the operation of fuses and PTC resistors depends on heating (temperature), many system designers prefer to use the current as an indicator to ensure effective circuit protection. Both fuses and PTC resistors cover many of the protection requirements such as B. inrush current control, overvoltage, reverse current and reverse polarity protection, which are required in modern electronic systems.

Another aspect to consider is the system's response to a short circuit, depending on the type of electrical load in which the short circuit occurs. In the automotive sector, for example, short circuits can occur as a result of a marten bite, insulation damaged by an accident or damage to the insulation due to incorrect handling or the effects of age. These causes can occur both when an electronic safety device is switched off and when driving is active. The loads can be roughly divided into resistive, inductive and capacitive loads, which react differently to a short circuit and an inrush current (also known as inrush current). A protective device, i.e. a safety device in general, should be able to be manufactured as independently as possible from its use for a later load and should also be independent of it later in its operation. The type of input impedance and the magnitude of the input impedance cannot be deduced from the rated current of the fuse.

Ohmic loads do not result in increased currents either when switched on or when switched off. Inductive loads try to keep the current flowing when switched off. In contrast, with capacitive loads, especially with ideal capacitances, the impedances are low, so that the inrush current of a capacitive load differs only slightly in the case of a short circuit from the case without a short circuit, particularly when switching on at the beginning. This proves to be critical in the case of a rapid switch-on process. In a motor vehicle, for example, the input capacitance is charged during active driving, so that a distinction or determination of a case of a capacitive load is not necessary here. After a voltage-free parking (e.g. overnight in the garage), however, the distinction must be made.

1 shows a diagram with a current curve in the event of a short circuit (solid line) and a current curve with a normal inrush current (inrush) (dashed line).

The normal switch-on current surge can be uncritical, for example in motor vehicles, since the switch-on process there typically takes place before the start of a journey and is completed before the journey; the short-circuit current, on the other hand, is critical. However, since both current curves are approximately the same at the beginning, as described above, only after a certain time (this depends on the current gradient (capacitance, series resistance, line inductance); typical range 20 to 50 µs; in terms of current technology in the range »100A) can a differentiation between the critical short-circuit case and the normal inrush current. A fuse should trip in the event of an overload (overcurrent). In addition, the fuse should be designed in such a way that it only triggers in the event of a short circuit, but not in the event of an uncritical inrush current. However, this contradicts the desire for rapid tripping of the fuse.

Conventionally, therefore, at least one component (switch or additional resistor) is also required or used in electronic fuses, which has a much higher power loss capacity or heat capacity than is necessary in normal operation. This leads to increased costs.

When protecting loads using a total current measurement, as with multi-channel modules, in which all loads or channels are switched off if an overcurrent occurs in just one channel or load, the individual current of a branch or load can be measured, for example the switch voltage can be determined, but the entire system or module has no information about the channel or load in which the short circuit occurs or has occurred. This means that the electronic fuse switches off all channels in the event of a total current error such as exceeding a threshold value. This means that all channels that do not have an error or short circuit are also switched off.

However, this requires that all channels that do not have an error are switched on again as promptly or quickly as possible. In a normal connection procedure in the motor vehicle sector, this takes several milliseconds, which means that load modules can possibly go into reset and then switching back on again requires several milliseconds. It is therefore desirable for the time span for switching on or switching on in the motor vehicle electronics to be less than 100 μs, for example.

The object of the invention is therefore to provide a method and a device for protecting a load in the event of a short circuit, which can react to a short circuit more quickly and cost-effectively. The object is achieved by a method having the features of claim 1 and by a device having the features of claims 13 and 14, respectively.

In addition, it is an object of the invention to provide a method and a device for protecting a plurality of electrical loads in the event of a short circuit in at least one of the loads using a total current measurement, which can react more quickly and cost-effectively to a short circuit. The object is achieved by a method having the features of claim 15 and by a device having the features of claims 24 and 25, respectively.

The dependent claims are directed to advantageous developments of the invention.

According to the invention, a method is provided for protecting an electrical load, which can be connected to an electrical energy source via a switch, in the event of a short circuit in the load, the method comprising: connecting the load to the electrical energy source by first switching on the switch, detecting an output current of the switch, turning off the switch when the output current exceeds an overcurrent threshold value and/or a predetermined period of time has elapsed since the switch was turned on, detecting an output voltage of the switch, determining an output voltage difference of the output voltage between a predetermined first point in time and a predetermined point in time lying after the first point in time second point in time, second switching on of the switch when the output voltage difference is negative and has an absolute value that is less than an upper output voltage difference threshold value, and/or the switch after the vo has been switched off for a certain period of time and the measured output current has not exceeded the overcurrent threshold value since the switch was first switched on until at least when the switch was switched off.

In this case, the electrical energy source preferably corresponds to an energy source of a system in which the load is used or is intended to be used. In a vehicle, this can be a vehicle battery with the usual outputs of, for example, 12 volts or 24 volts DC voltage.

According to the invention, a short test sequence that is almost irrelevant to the load is carried out right at the beginning when the current is still low (see area of the arrow in 1 ), detected whether with a non-critical current flow (dashed line in 1 ) such as a non-critical inrush current (inrush current) or with a critical current flow such as a short circuit (solid line in 1 ) is to be expected.

The predetermined period of time is preferably in a range from 1 to 100 μs. In the case of a capacitive load, such a short switch-on pulse causes its capacitor to be charged very quickly (for example in the case of a MOSFET with minimal charging resistance and switching resistance R _DSon ). After switching off, the capacitance or the capacitor then discharges via the internal load (resistances), which differs from the short-circuit load (especially with voltages in the range below the minimum functional voltage, most system modules are switched off, so that the internal load resulting from the current consumption of the control electronics).

The overcurrent threshold value is preferably defined in such a way that the switch is switched off when the output current exceeds the overcurrent threshold value no later than 100 μs, more preferably after 10 μs, after the first switch-on.

The overcurrent threshold value is preferably at least 70% of the nominal current or rated current of the load. Even in the event of an overcurrent shutdown, this occurs within a short time, i.e. within, for example, the above range of the predetermined time period of 1 to 100 µs.

The first point in time is preferably equal to the point in time at which the switch is switched off or is after the point in time at which the switch is switched off. The first point in time is advantageously as close as possible after the switch has been switched off, when a usable voltage value can be determined. The implementation of the method according to the invention can thus be accelerated.

The second point in time is preferably in a range from 100 to 1000 μs after the first point in time. It also applies here that the second point in time is as early as possible and realizable after the first point in time in order to be able to determine the voltage gradient as quickly as possible but also reliably.

Preferably, the upper output voltage difference threshold is set depending on the output voltage after the switch is turned off. This allows the upper output voltage difference threshold to still be adjusted or adjusted on retry passes.

Preferably, an initial value of the upper output voltage difference threshold is in a range of 100 to 200 mV/s.

The load is preferably a vehicle load, in particular a motor vehicle load. In addition to motor vehicles such as automobiles, the broader term vehicle also includes two-wheelers, airplanes, ships and possibly rail vehicles.

The method according to the invention is preferably carried out at the beginning of a switch-on process of the load for its operation. In a motor vehicle, for example, the process of switching on the load typically takes place before the start of a journey, so that brief current peaks (higher inrush current) are not relevant to safety, since the process of switching on is completed before the actual start. This also applies to other corresponding systems in which the switch-on process is completed before actual operation.

Preferably, when the output current has exceeded the overcurrent threshold after the switch is first turned on and the output voltage difference is negative, the load is determined to be a capacitive load.

Preferably, when the switch is first switched on, a switch-on pulse is generated which, given a capacitive load as the load, causes the output current (IA) to exceed the overcurrent threshold value. The overcurrent threshold value should be exceeded as quickly as possible so that the switch for the method according to the invention is switched off again quickly and the further evaluation of the voltage(s) and possibly the current can therefore take place quickly.

Furthermore, according to the invention, a method for protecting a plurality of electrical loads, which can be connected to an electrical energy source via respective switches, is created in the event of a short circuit in at least one of the loads, with a sum of the respective currents of the loads being recorded as a total current, and with if the total current exceeds a predetermined total current threshold value, the switches are switched off. The method has: After the switches have been switched off due to the total current threshold value being exceeded by the total current, for at least a first switch from the switches which is assigned to a capacitive load from the loads, detecting an output voltage of the first switch during a predetermined detection period after the Turning off the first switch when the output voltage during the predetermined detection time period is or becomes less than a predetermined voltage threshold value, maintaining the off state of the first switch, and if the output voltage during the predetermined detection time period is or becomes not less than the predetermined voltage threshold value, turning on the first switch after the predetermined detection time period has elapsed. If there are several capacitive loads, these or their voltages can preferably be checked individually in parallel during the detection period. The expression “during” thus includes in particular that the voltage threshold value is not undershot during the entire acquisition time period, but only occurs at some point in the acquisition time period, since the capacity needs some time to be discharged, even if this occurs relatively quickly.

The electric power source may correspond to the electric power source mentioned above.

Preferably, after the switch has been switched off due to the total current threshold value being exceeded by the total current for at least one second switch from the switches, which is assigned to an ohmic or inductive load from the loads, the second switch is switched on and a current flowing through the second switch is determined, and if the detected current exceeds an overcurrent threshold, the second switch is (finally) turned off.

The switching on of the second switch, the determination of the current flowing through the second switch and the switching off of the second switch are preferably carried out sequentially, i.e. one after the other, for several or all of the second switches, more preferably after the predetermined detection time period has elapsed, so that the resistive and inductive loads are checked after checking the capacitive loads.

The detection period can begin when the switches are switched off because the total current exceeds a predetermined total current threshold value and is less than or equal to 100 μs, preferably less than or equal to 20 μs. It is more preferably in a range from 10 to 20 μs. A rapid measurement of the output voltage in this time range is possible, particularly in automotive engineering.

Preferably, the predetermined voltage threshold is equal to or less than 5 volts, more preferably equal to or less than 3 volts. If, for example, the output voltage of the capacitive load or the corresponding switch occurs within 10 to 20 μs after switching off, the output voltage in the motor vehicle electronics is typically in a range between 3 and 5 volts if there is no short circuit. On the other hand, if the output voltage is less than 3 volts within the detection period, it can be assumed that there is a short circuit in this capacitive load.

If the output voltage is less than the predetermined voltage threshold value during the predetermined detection period, corresponding first error information can be stored in association with the capacitive load associated with the first switch, and if the determined current of a resistive or inductive load exceeds an overcurrent threshold value, corresponding second error information can be stored Error information can be stored in association with the resistive or inductive load associated with the second switch. This information can then be read later in the workshop, for example, and used for repairs.

Information on a respective type of the respective loads can be stored in advance, and this information can then be referred to when it is to be determined according to the invention at which load a short circuit has occurred in order to deactivate it permanently and at which load no short circuit has occurred or error has occurred in order to reactivate it. The determination and storage of the type of the respective loads can take place, for example, in advance, for example in a switch-on phase, according to the above inventive method for protecting an electrical load, in which a switch-off according to the total current measurement has not yet taken place. In actual further operation, the shutdown can be carried out according to the total current measurement and then subsequent checking of the individual loads with regard to the occurrence of a short circuit.

• 1 ein Funktionsdiagramm zur Erläuterung der Stromverläufe bei einem Einschaltstromstoß und einem Kurzschluss einer kapazitiven Last;
• 2A ein elektrisches Schaltbild zur Simulation von Stromverläufen bei einer kapazitiven Last;
• 2B ein Diagramm der Verläufe der Gate-Spannung bzw. Eingangsspannung des Schalters, des Laststroms und der Lastspannung bei einer kapazitiven Last ohne Kurzschluss zu 2A;
• 2C ein Diagramm der Verläufe der Gate-Spannung bzw. Eingangsspannung des Schalters, des Laststroms und der Lastspannung bei einer kapazitiven Last mit Kurzschluss zu 2A;
• 3A ein elektrisches Schaltbild zur Simulation von Stromverläufen bei einer ohmschen Last;
• 3B ein Diagramm der Verläufe der Gate-Spannung bzw. Eingangsspannung des Schalters, des Laststroms und der Lastspannung bei einer ohmschen Last ohne Kurzschluss zu 3A;
• 3C ein Diagramm der Verläufe der Gate-Spannung bzw. Eingangsspannung des Schalters, des Laststroms und der Lastspannung bei einer ohmschen Last mit Kurzschluss zu 3A;
• 4A ein elektrisches Schaltbild zur Simulation von Stromverläufen bei einer induktiven Last;
• 4B ein Diagramm der Verläufe der Gate-Spannung bzw. Eingangsspannung des Schalters, des Laststroms und der Lastspannung bei einer induktiven Last ohne Kurzschluss zu 4A;
• 4C ein Diagramm der Verläufe der Gate-Spannung bzw. Eingangsspannung des Schalters, des Laststroms und der Lastspannung bei einer induktiven Last mit Kurzschluss zu 4A;
• 5 ein Blockschaltbild eines beispielhaften Systems zum Schützen einer Last, in dem die erfindungsgemäße Schutzvorrichtung verwendet wird;
• 6A den ersten Teil eines Flussdiagrams einer ersten Ausführungsform eines erfindungsgemäßen Verfahrens zum Schützen einer Last bei einem Kurzschluss;
• 6B den zweiten Teil des Flussdiagrams der ersten Ausführungsform des erfindungsgemäßen Verfahrens zum Schützen einer Last bei einem Kurzschluss;
• 7A den ersten Teil eines Flussdiagrams einer zweiten Ausführungsform eines erfindungsgemäßen Verfahrens zum Schützen einer Last bei einem Kurzschluss;
• 7B den zweiten Teil des Flussdiagrams der zweiten Ausführungsform des erfindungsgemäßen Verfahrens zum Schützen einer Last bei einem Kurzschluss;
• 8 ein Teil eines Flussdiagrams einer dritten Ausführungsform des erfindungsgemäßen Verfahrens zum Schützen einer Last bei einem Kurzschluss;
• 9 ein Diagramm zur Erläuterung eines Moduls mit Summenstromabschaltung bei einem Kurzschluss in mindestens einer Last;
• 10 einen ersten Teil eines Flussdiagramms eines erfindungsgemäßen Verfahrens zum Schützen mehrerer Lasten bei einem Kurzschluss gemäß einer vierten Ausführungsform; und
• 11 einen zweiten Teil des Flussdiagramms des erfindungsgemäßen Verfahrens zum Schützen mehrerer Lasten bei einem Kurzschluss gemäß der vierten Ausführungsform.

Preferred embodiments of the invention are described below with reference to the drawings. Show it:

• 1 a functional diagram to explain the current curves in the event of an inrush current and a short circuit of a capacitive load;
• 2A an electrical circuit diagram for simulating current curves with a capacitive load;
• 2 B a diagram of the curves of the gate voltage or input voltage of the switch, the load current and the load voltage to a capacitive load without a short circuit 2A ;
• 2C a diagram of the curves of the gate voltage or input voltage of the switch, the load current and the load voltage for a capacitive load with a short circuit 2A ;
• 3A an electrical circuit diagram for simulating current curves with a resistive load;
• 3B a diagram of the curves of the gate voltage or input voltage of the switch, the load current and the load voltage for a resistive load without a short circuit 3A ;
• 3C a diagram of the curves of the gate voltage or input voltage of the switch, the load current and the load voltage for a resistive load with a short circuit 3A ;
• 4A an electrical circuit diagram for simulating current curves with an inductive load;
• 4B a diagram of the curves of the gate voltage or input voltage of the switch, the load current and the load voltage for an inductive load without a short circuit 4A ;
• 4C a diagram of the curves of the gate voltage or input voltage of the switch, the load current and the load voltage for an inductive load with a short circuit 4A ;
• 5 Figure 12 is a block diagram of an exemplary system for protecting a load using the protection device of the present invention;
• 6A the first part of a flow chart of a first embodiment of a method according to the invention for protecting a load in the event of a short circuit;
• 6B the second part of the flow chart of the first embodiment of the method according to the invention for protecting a load in the event of a short circuit;
• 7A the first part of a flow chart of a second embodiment of a method according to the invention for protecting a load in the event of a short circuit;
• 7B the second part of the flow chart of the second embodiment of the method according to the invention for protecting a load in the event of a short circuit;
• 8th a part of a flow chart of a third embodiment of the method according to the invention for protecting a load in the event of a short circuit;
• 9 a diagram to explain a module with total current shutdown in the event of a short circuit in at least one load;
• 10 a first part of a flowchart of an inventive method for protecting multiple loads in the event of a short circuit according to a fourth embodiment; and
• 11 a second part of the flowchart of the inventive method for protecting multiple loads in the event of a short circuit according to the fourth embodiment.

First, typical current and voltage curves of ohmic, inductive and capacitive loads in the case of a short circuit and in the case without a short circuit are described using a simulation. Capacitive loads include, for example, cooling fan electronics, brushless DC motors, PWM controllers for DC motors and capacitive input filters. All modules that reduce the input voltage internally by switching them on and off must be equipped with such a capacitive input filter for reasons of electromagnetic compatibility (EMC). A resistive load is, for example, a PTC heater, i.e. a diesel auxiliary heater or an interior heater in a motor vehicle. An example of an inductive load is an uncontrolled solenoid valve.

2A shows a circuit diagram for simulating a capacitive load, which has a field effect transistor as switch M1, a voltage source V1 connected to the source connection of the field effect transistor, a further voltage source V2 with a parallel-connected capacitance C1, which are connected to the gate connection of the field effect transistor, a resistor R1 connected to the emitter terminal of the field effect transistor and a capacitance C2 as a capacitive load and a resistor R2 connected in parallel thereto.

The following values, among others, were used to simulate the capacitive load without a short circuit: R2 = 10 kΩ; R1 = 1mΩ; C2 = 3000uF.

2 B 12 shows the simulation result for a capacitive load without a short circuit, where the solid line shows the voltage UA, the dashed line shows the current IA and the alternate long and short dashed line shows the gate voltage V-gate. The abscissa indicates time, and the ordinate indicates voltage in volts on the left and current in amperes on the right. At the time TE (here 10 µs) a voltage pulse (here 23 V) was applied to switch M1 (see alternate long and short dashed line) to turn it on, and at time TA (here 20µs) the voltage was set to zero to turn switch M1 off.

The current IA or I(R1) and the voltage UA increase abruptly and drop almost abruptly, i.e. immediately, after the switch M1 has been switched off, but not to zero. The voltage UA at time T1 (here 30 µs) is equal to UA(T1) = 2000 mV and at time T2 (here 190 µs) is equal to UA(T2) = 1999.99 mV. Thus, for the gradient of the voltage UA after the switch is turned off, which can be expressed, for example, by the difference of the two voltages, i.e. ΔUA = UA(T1) - UA(T2), ΔUA = -10 µV / 160 µs = - 0.0625V/s. Also note the negative sign of the gradient ΔUA. The current IA is always zero when switched off.

• - Stromgradient und Stromamplitude IA sind sehr hoch;
• - „Spannung UA während Einschaltung“ ist abhängig von der Kapazität und dem Ladewiderstand (Leitungswiderstände, Schalter-Widerstand, Leitungsinduktivitäten);
• - je geringer die Ladewiderstände, desto größer die Amplitude „UA während Einschaltung“;
• - je größer die Kapazität, desto geringer die Amplitude „UA während Einschaltung“, und desto geringer der Spannungsgradient „ΔUA nach Abschaltung“.

The following general characteristics can be derived:

• - Current gradient and current amplitude IA are very high;
• - "Voltage UA during switch-on" depends on the capacity and the charging resistance (line resistance, switch resistance, line inductance);
• - the lower the charging resistances, the larger the amplitude "UA during switching on";
• - the larger the capacitance, the smaller the amplitude "UA during switch-on", and the smaller the voltage gradient "ΔUA after switch-off".

With relevant capacitive loads, i.e. with an input capacitance > 100 µF, the current will typically generate an overcurrent condition with a low-impedance vehicle electrical system. This leads to the switching off of the switch (e.g. MOSFET). Alternatively, the short switch-on can also be time-controlled in the typical time range of 1 to 1000 µs. Both cases are characterized by a very high, short-term power consumption.

2C shows that 2 B Corresponding simulation result for a capacitive load with short circuit, whereby R2 = 10mS2 was used here in the simulation. With the otherwise closed 2 B Under the same conditions, the voltage drops immediately after switching off, but does not reach zero immediately or quickly. Here the voltage is UA(T1) = 442 mV and the voltage UA(T2) = 76 mV, so that the gradient or the difference between the two voltages is not equal to zero, i.e. ΔUA = UA(T1) - UA(T2) applies. = -316mV / 160µs = -1.975V/s. It was also noted that the gradient has a negative sign. The current IA is always zero when switched off. Compared to the case in 2 B However, the amount or absolute value of the voltage gradient ΔUA is noticeably larger.

• - Stromgradient und Stromamplitude IA sind sehr hoch;
• - „Spannung UA während Einschaltung“ ist abhängig von der Kapazität und dem Ladewiderstand (Leitungswiderstände, Schalter-Widerstand, Leitungsinduktivitäten);
• - je geringer die Ladewiderstände, desto größer die Amplitude „UA während Einschaltung“;
• - je größer die Kapazität, desto geringer die Amplitude „UA während Einschaltung“, und desto geringer der Spannungsgradient „ΔUA nach Abschaltung“.

The following general characteristics can be derived:

• - Current gradient and current amplitude IA are very high;
• - "Voltage UA during switch-on" depends on the capacity and the charging resistance (line resistance, switch resistance, line inductance);
• - the lower the charging resistances, the larger the amplitude "UA during switching on";
• - the larger the capacitance, the smaller the amplitude "UA during switch-on", and the smaller the voltage gradient "ΔUA after switch-off".

Since, for example, most loads have capacitive input filters in automotive electronics, how based on the 2 B and 2C As can be seen, such an input capacitance is discharged slowly by a normal load current, but comparatively quickly by a short circuit.

3A shows a 2A Corresponding circuit diagram for simulating an ohmic load, in which case the capacitance C2 is not present or connected, but the resistor R2 forms the ohmic load.

3B shows that 2 B Corresponding simulation result for a resistive load without a short circuit. The following values, among others, were used to simulate the ohmic load without a short circuit: R2 = 1 Ω, R1 = 1 mΩ. Otherwise, the same values of the parameters as in the 2A , 2 B , 2C used.

The current IA and the voltage UA increase abruptly accordingly and drop back to zero almost abruptly, i.e. immediately, after the switch M1 has been switched off. The voltage UA at time T1 (here 30 µs) and at time T2 (here 190 µs) is equal to zero. Thus, the gradient of the voltage UA, which can be expressed, for example, by the difference between the two voltages, i.e. ΔUA = UA(T1)-UA(T2), is also zero. The current IA is always zero when switched off.

• - Die Spannung UA und der Strom IA haben einen identischen Verlauf;
• - die Spannung UA hat direkt nach der Abschaltung einen Spannungsgradienten und einen Absolutwert von 0V;
• - es wird keine Überstrombedingung erreicht.

The following general characteristics can be derived:

• - The voltage UA and the current IA have an identical course;
• - the voltage UA has a voltage gradient and an absolute value of 0V immediately after switching off;
• - no overcurrent condition is reached.

3C shows that 3B Corresponding simulation result for an ohmic load with short circuit, whereby R2 = 10 mΩ was used here in the simulation. With the otherwise closed 3B Under the same conditions, the voltage immediately falls back to zero after switching off, but does not reach zero immediately or quickly. Thus, the gradient of the voltage UA, which can be expressed, for example, by the difference between the two voltages, ie ΔUA=UA(T1)−UA(T2), is also zero. The current IA is always zero when switched off. However, while the switch is on, the voltage UA is lower than in the case of 3B due to the smaller value of the resistor R2 simulating the short circuit.

• - Die Spannung UA und der Strom IA haben einen identischen Verlauf;
• - die Spannung UA hat direkt während des eingeschalteten Zustands eine geringere Amplitude;
• - die Spannung UA hat direkt nach der Abschaltung einen Spannungsgradienten und einen Absolutwert von 0 V.

The following general characteristics can be derived:

• - The voltage UA and the current IA have an identical course;
• - the voltage UA has a lower amplitude directly during the switched-on state;
• - the voltage UA has a voltage gradient and an absolute value of 0 V immediately after switching off.

4A shows a 2A and 3A Corresponding circuit diagram for simulating an inductive load, in which case the capacitance C2 is not present or connected, but instead an inductance L3 is connected with a parallel diode D1, which represents the inductive load.

4B shows that 2 B and 3B Corresponding simulation result for an inductive load without a short circuit. The following values were used for the simulation of the inductive load without a short circuit: R2 = 10 kΩ, R1 = 1 mΩ; L3 = 100µH. Otherwise, the same values of the parameters as in the 2A , 2 B , 2C used.

The voltage UA rises abruptly and, after the switch M1 has been switched off, drops again almost abruptly, i.e. immediately, but falls below zero, i.e. is negative. The voltage UA at time T1 (here 30 µs) is UA(T1) = -844 mV, and voltage at time T2 (here 190 µs) is UA(T2) = -790 mV. Thus the gradient of the voltage UA, which can be expressed for example by the difference of the two voltages, i.e. ΔUA = UA(T1) - UA(T2), is positive. The current IA is zero when the switch is off and increases continuously while the switch is on.

• - Der Strom IA hat einen geringen Stromgradienten;
• - die Spannung UA hat eine sehr hohe Amplitude, nahezu Eingangsspannungsniveau;
• - keine Überstrombedingung während der Einschaltphase;
• - die Spannung UA hat direkt nach der Abschaltung einen positiven Spannungsgradienten und einen negativen Absolutwert.

The following general characteristics can be derived:

• - The current IA has a low current gradient;
• - the voltage UA has a very high amplitude, close to the input voltage level;
• - no overcurrent condition during start-up phase;
• - The voltage UA has a positive voltage gradient and a negative absolute value immediately after switching off.

4C shows that 4B Corresponding simulation result for an inductive load with a short circuit, whereby R2 = 10 mΩ was used here in the simulation. With the otherwise closed 4B under the same conditions, the voltage immediately falls back to zero after switching off. The gradient of the voltage UA, which can be expressed for example by the difference between the two voltages, ie ΔUA = UA(T1) - UA(T2), is therefore also the same zero. The current IA is always zero when switched off.

• - Die Spannung UA und der Strom IA haben einen identischen Verlauf;
• - die Spannung UA hat während des eingeschalteten Zustands eine geringere Amplitude;
• - Überstrombedingung während der Einschaltphase;
• - die Spannung UA hat direkt nach der Abschaltung einen Spannungsgradienten und einen Absolutwert von 0 V.

The following general characteristics can be derived:

• - The voltage UA and the current IA have an identical course;
• - the voltage UA has a lower amplitude during the switched-on state;
• - Overcurrent condition during power-up phase;
• - the voltage UA has a voltage gradient and an absolute value of 0 V immediately after switching off.

Based on the above findings, a critical short circuit can now be detected at the beginning of switching on a load and the load can be switched off accordingly.

5 FIG. 12 represents a circuit diagram of a system in which the method and the device according to the invention are used by way of example. A power supply or electrical energy source B (which supplies a voltage UB) such as a battery, a generator or the like is connected to the input of a switch S and a monitor Processing unit or electronic control device SE and connected to a load L in order to supply them with electrical energy. The electronic control device receives the output current IA and the output voltage UA of the switch S from current or voltage sensors, which are not shown. However, the electronic control device SE can itself also have appropriate sensors for detecting the output current IA and/or the output voltage UA. That is to say, it is not relevant how the electronic control device SE obtains information about the output current IA and the output voltage UA as long as it is able to obtain or determine this information in some way. The output current IA can also be replaced by or correspond to an input current of the load. Similarly, the output voltage UA can be replaced by or equal to the input voltage of the load.

The electronic control device SE outputs a signal for driving the switch S, which is switched on or off according to the signal. This signal can be equivalent to a gate voltage if, for example, a field effect transistor is used as a switch. A control of a switch, which can be a semiconductor switch such as a field effect transistor or a bipolar transistor, is familiar to the person skilled in the art and is therefore not explained in more detail here. It is only important that the switch can be switched on and off depending on the signal from the electronic control device.

In general, the energy input of a slow switch-on process does not differ or differs only slightly from that of a fast switch-on. With a capacitive load, for example, the charging resistance for the capacitance consists of the series connection of the resistances Ri (internal resistance of the electrical energy source; ohmic-inductive, actually Zi) and the resistance of the switch S (with MOSFET as a switch, this is R _DS ). The power distribution depends on the ratio R _DS / Ri. This loading process takes place in the essential time domain with R _DS =R _DSon . This makes the ratio R _DS / Ri very small; the main part of the power loss occurs in the area of the supply line and only a small part in the area of the switch. Since the supply system has a much higher heat capacity and is in the range >10mQ, cheaper switches (in the R _DSon 1mΩ range) with a very low heat capacity can be used.

As described above, the load L is of the capacitive, ohmic or inductive type, with mixed forms also being possible and thus when the type is named, the dominant type is mentioned or meant.

The switch S and the electronic control device SE together form a protective device according to the invention, which can also be referred to as an electronic fuse. As described above, the current and/or voltage sensor may or may not be part of the protection device.

With reference to the 6A and 6B a first embodiment of the invention is described below. Initially, the switch S is turned on in step S1. Then, in step S2, it is checked whether the current IA is equal to or greater than an overcurrent threshold value IA_S. This overcurrent threshold value IA_S is used to check whether a current flows through the load that is greater than a current that usually flows or is expected to flow during operation of the load. The overcurrent threshold value IA_S can also be exceeded in the event of an inrush current (inrush current) and, for example during operation of the load, results in the load being switched off or disconnected from the power supply or energy supply. The overcurrent threshold value IA_S is preferably at least 70% of the nominal current or nominal current of the load, but can also more preferably be at least 95% of the nominal current or nominal current of the load, and is even more preferably greater than the nominal current of the load or is selected in such a way that the load and the system in which the load is used are not damaged or faulty, as is also usually the case in the prior art, a corresponding safety fuse is selected according to, for example, the area of application or the rated current of the load.

If the result of the check in step S2 is no, step S2 is repeated. Alternatively, you can go directly to the end of the flowchart ("End" in 6B ) can be jumped, so that then, for example, the normal operating process of the load can take place immediately afterwards. If the result of the check in step S2 is yes, the switch S is switched off again in step S3. A measurement of a time t is then started in step S4. This can be done via a built-in timer or in any other known way. Then in step S5 it is checked whether the measured time has reached a first time T1. This also implies that the measured time is greater than T1, depending on the accuracy of the time measurement, even if in the diagram of 6A only one query relative to t=T1 is shown. The first time T1 can also be present or determined when the current IA is being monitored or continuously measured after the current IA has been switched off of the switch has reached a stable value, for example if this has only changed by less than 1%, preferably less than 0.1%, between two current measurement times. The first point in time T1 is, for example, at most 100 ms after the switch has been switched off, which is practical in the automotive field. In other areas, the first point in time T1 can also be selected accordingly.

If the result of the check in step S5 is no, step S5 is repeated. If the result of the check in step S5 is yes, the value of the voltage UA(T1) of this point in time T1 is stored in step S6. However, this can also mean that part or all of the course of the voltage UA is recorded or stored since the switch was switched on. It is only important that the voltage UA(T1) can later be used for further evaluation and is available.

Then in step S7 it is checked whether the measured time has reached a second time T2. This also implies that the measured time is greater than T2, depending on the accuracy of the time measurement, even if in the diagram of 6A only one query relative to t=T2 is shown. The second time T2 is, for example, between 10 μs and 100 ms after the first time T1. However, the first time or the first point in time T1 and the second time or the second point in time T2 only have to be selected or specified in such a way that a reliable determination of the voltage gradient ΔUA is possible.

If the result of the check in step S7 is no, step S7 is repeated. If the result of the check in step S7 is yes, the value of the voltage UA(T2) of this point in time T2 is stored in step S8. However, this can also mean that part or all of the course of the voltage UA is recorded or stored since the switch was switched on. It is only important that the voltage UA(T2) can later be used for further evaluation and is available.

Then, in step S9, the difference ΔUA between the voltage UA(T2) at time T2 and the voltage UA(T1) at time T1 is determined. Then, in step S10, it is checked whether the voltage difference ΔUA is negative. Alternatively, it can also be checked in step S10 whether the amount or absolute value of the voltage difference is equal to or greater than a lower voltage difference threshold value ΔUA_S2. As a result, erroneous or inaccurate results with regard to the voltage difference ΔUA, which are very small and can also result from measurement inaccuracies or the like, can be ruled out. This contributes to increasing the reliability of the determination that there is a negative relevant voltage difference ΔUA. The lower voltage difference threshold value ΔUA_S2 is of course smaller than the upper voltage difference threshold value ΔUA_S1 described below.

In addition or as an alternative to a comparison of the absolute value of the voltage difference with the lower voltage difference threshold value ΔUA_S2 in step S10 or in a subsequent step, it can be checked whether the voltage UA is greater than zero after the switch has been switched off, preferably greater than a third voltage threshold value UA_S3 , which is for example in a range between 10 and 100mV. If the voltage UA after switching off is greater than zero or equal to or greater than the third voltage threshold UA_S3, it can be concluded that it is a capacitive load in a normal case, i.e. a non-critical case, so that in this case the switch can be switched on again (see step S12). This check using the third voltage threshold value UA_S3 can also take place instead of step S11. If the voltage UA after switching off is equal to zero or less than the third voltage threshold value UA_S3, step S13 is then proceeded to.

If the result of the check in step S10 is yes, i.e. if the voltage difference or the gradient is negative, it is checked in step S11 whether the amount or absolute value of the voltage difference ΔUA is equal to or greater than an upper voltage difference threshold value ΔUA_S1. If the result of the check in step S11 is yes, the switch-on process is regarded as non-critical and/or normal, and the switch S is switched on again in step S12. If the result of the check in step S10 or in step S11 is no, i.e. if the voltage difference or the gradient is below the upper threshold value and/or not negative, the switch-on process is considered critical or abnormal, and it is e.g Step S13 issued a corresponding error message. The output of an error message can be output for a driver or a maintenance person or it can only be stored in the system itself. However, the output of an error message is not an essential part of the invention. This also applies to the following description.

In particular, as discussed above, a short circuit on a capacitive load is critical and can result in damage to the load and/or the system. Such a critical situation can be recognized in that, as described above, the voltage gradient at a kapa zitive load is negative and relatively high after the switch has been turned off, ie exceeds the upper threshold value. An exemplary value for the upper threshold value ΔUA_S1 for the voltage difference or the voltage gradient is 200 mV/s. However, this only serves as a guide value and can, for example, be determined in advance by means of experiments for various loads and their nominal values. This only has to be suitable for detecting an abnormal case of a capacitive load compared to a normal case of the capacitive load, where the voltage gradient is also negative but smaller than in a critical or abnormal case.

The permissible voltage gradient or the upper threshold value ΔUA_S1 can also be determined as a function of the voltage UA directly after the switch has been switched off, for example within a period of 100 to 1000 μs. The higher the voltage UA immediately after switching off, the lower the capacitance, for example, and the greater the voltage gradient that occurs after switching off. Accordingly, the upper threshold value ΔUA_S1 can also be determined and/or adjusted.

In the 6B However, the routine shown can also be used, for example, by the in 7B routine shown and described below.

With reference to the 7A and 7B a second embodiment of the invention is described below. Here for the same steps as in the 6A and 6B the same step numbers or reference characters are used, and their description will not be repeated.

After step S1, the time measurement described above is started in step S4. Then, in step S21, the output current of the switch or the input current of the load or a comparable current IA is detected and stored or recorded. Thereafter, in step S22, it is checked whether a predetermined period of time TD has elapsed since the switch S was turned on. When this time TD has elapsed, the switch S is turned off in step S3. If the time has not elapsed, step S22 is performed again. Subsequently, the steps S5 to S10 as above based on the 6A and 6B carried out as described. In contrast to 6B However, if the result of the query in step S10 is no, ie if the voltage difference or the gradient is not negative, it is checked in step S23 whether the current IA during the switched-on state of the switch, ie during the time period TD, equal or has been greater than the above-mentioned current threshold value IA_S (see description of step S2). This may have been the case once or during part or all of the time period TD. As in step S2, this is used to check whether an overcurrent or impermissibly high current was present. If the result of the determination in step S23 is yes, that is, if an overcurrent has occurred within the time period TD, step S13 described above is executed. On the other hand, if the result of the determination in step S23 is no, the switch S is turned on again in step S24 since no trouble has occurred.

Regarding 8th a third embodiment of the invention will be described below. In the 8th You can follow the steps shown in the 6A or 7A steps shown are carried out. In this regard, reference is made to the above description of the first and second embodiment. However, the steps S31 and S32 shown in the figures with dashed lines are also carried out here, which are not necessary in the first and second embodiment.

In step S31 it is then checked whether the measured time has reached a predetermined time T0. This also means that the measured time is greater than T1, depending on the accuracy of the time measurement, even if the diagram only shows a query for t = T0. The time T0 is preferably a time immediately after the switch is turned off or a time in the immediate vicinity thereof. However, the time T0 can also be later, even between the time T1 and the time T2 or later, even if these are in 6A is before the time T1, as long as at this time an unequivocal detection of the voltage UA after the switch has been turned off is possible, which is negative in the case of an inductive load. However, if the voltage UA(T0) is also used to set or adjust the upper limit for the voltage gradient, i.e. ΔUA_S1, the time T0 should preferably be as close as possible after the switch has been turned off, in order to allow a quick determination or adjustment of the Allow threshold ΔUA_S1 for further evaluation. However, it is also conceivable that the time T0 lies between the times T1 and T2 or corresponds to one of these times.

When the measured time has reached the time T0 (step S31: yes), the voltage of that point in time is stored in step S32. Instead, however, the voltage profile of the voltage UA can generally be recorded since the switch was switched on or also later or earlier until the end of the method or earlier and stored for later use and evaluation. It is only important that the value of the voltage UA(T0) is available if it is for the white further evaluation or calculation is required. This also applies to all other voltage and current values in all embodiments.

An explanation of the follows 8th , using the same steps as in the 6B and 7B are denoted by the same step numbers and reference numerals, respectively, and the description thereof will not be repeated. If the result of the check in step S10 is yes, ie if the sign of the voltage difference ΔUA is negative, it is first determined in step S33 that it is a capacitive load and this result is saved so that it can be used for later evaluations and processes it can be accessed. Only then is step S11 described above carried out.

If the result in step S23 is yes, i.e. if an overcurrent has occurred while the switch was on, it is checked in step S37 whether the voltage during the switched-on state of the switch UA(Tein) was equal to or less than a first voltage threshold value UA_S1 . The first voltage threshold value UA_S1 is defined in such a way that a comparison with it can be used to determine whether the voltage UA was lower than in a normal case during the switched-on state of the switch S. In particular, the threshold value is equal to or smaller than 0 V. In this case, the threshold value can preferably be derived from the accuracy of the measuring system. The threshold can typically be -100 mV (or in a range around this value).

This case occurs when a resistive load is short-circuited, so that if the result in step S37 is positive, it is determined in the subsequent step S38 that the load is resistive and this result is stored for later possible use or evaluation . Then, in step S13 described above, an error message is output, which can also include the result that the load is resistive.

If, on the other hand, the result of the check in step S37 is negative, it is determined in the subsequent step S39 that an inductive load is involved, and the result is stored for possible later use or evaluation.

If the result of the determination in step S23 is no, i.e. if no overcurrent has occurred, to further identify the type of load (resistive load or inductive load), it is determined in step S34 whether the value of the voltage UA(T0) at the time T0 described above is less than a second voltage threshold UA_S2. The second voltage threshold value UA_S2 serves to check whether the voltage UA was or is negative after the switch was switched off, as is the case with an inductive load in a normal case. Thus, if the result of the determination in step S34 is yes, it is determined in step S35 that the load is an inductive load and this result is stored for possible later use or evaluation. Thereafter, the switch S is turned on again in step S24.

On the other hand, if the result of the determination in step S34 is no, it is determined in step S36 that the load is a resistive load and this result is stored for possible later use or evaluation. Thereafter, the switch S is turned on again in step S24.

In 8th However, the steps for determining or characterizing the load as a resistive or inductive load can also be omitted, so that only a characterization as a capacitive load (or no capacitive load) is carried out. This would lead, for example, to 6B and/or 7B step S33 is inserted after step S10.

It is pointed out that due to the wide load spectrum that is to be protected by a safety device according to the invention, as already indicated above, uniform parameterization for all loads or applications is difficult. The aim of the following parameterization example is the safe but also fast detection of short circuits, so that in the best case the short circuit is detected in a very short time or, if there is no short circuit, the load branch can be switched on very quickly. The minimum times are determined by the measurement system used and its uncertainty.

1. 1. Ermittlung der einzelnen Messzeit für sichere Spannungswerte (Datenblatt, Schaltungsanalyse der speziellen Last).
2. 2. Die minimale Beobachtungsdauer der Spannung UA sollte im Bereich von 5 - 10 Messzeiten aus Punkt 1 betragen.
3. 3. Der Beginn der Messung des Spannungsgradienten ist abhängig vom Spannungsverlauf nach einer Abschaltung. Der früheste Startzeitpunkt sollte dabei so gewählt werden, dass der Schalter S sicher komplett offen ist.
4. 4. Ermittlung des Spannungsgradienten (z.B. mit Oszilloskop) im GUT-Fall (kein Fehler).
5. 5. Ermittlung des Spannungsgradienten im SCHLECHT-Fall. Hier wird eine ohmsche Zusatzlast (R_Zusatz) zur Last parallelgeschaltet. Der Wert von R_Zusatz errechnet sich aus: R_Zusatz = Unom/Inom; Unom: nominale Betriebsspannung der abzusichernden Last; Inom: nominaler Abschaltstrom der abzusichernden Last.
6. 6. Den Grenzwert für die Unterscheidung Kurzschluss vs. Inrush-Current bzw. normalem Einschaltstrom kann dementsprechend (je nach Priorität „sicheres Einschalten“ oder „sicher im Fehlerfall nicht Einschalten“) im Bereich zwischen den unter Punkt 4 und Punkt 5 gemessenen Grenzen gewählt werden.
7. 7. Der typische Wert für die Messzeit (T2-T1) liegt im Bereich 100 bis 1000µs. Ist der Unterschied der beiden ermittelten Grenzen aus Punkt 4 und Punkt 5 zu gering, d.h. kann das Messsystem die Spannungsgradienten nicht sicher zuordnen, kann durch Verlängerung der Messzeit (T2-T1) das System sicherer gemacht werden. Durch die längere Messzeit, wird die Entladung ggf. erhöht und die Absolutspannungen entsprechend besser unterscheidbar; die Startprozedur wird dadurch verlängert. Liegt die Priorität auf der Zeitdauer der Startprozedur, kann durch einen sehr schnellen Schalter und eine sehr schnelle Messeinheit ggf. eine kürzere Messzeit (T2-T1) gewählt werden.

Current state of the art are measuring cycles for currents and voltages in the range of 10 to 100 µs. The voltage gradient for capacitive loads is essentially determined by the capacitance value of the input capacitance and the initial discharge current. Since the initialization current is usually much smaller than the operating current and the input capacitance is designed for the operating current, the voltage gradients in error-free operation can be assumed to be < 100 to 200 mV/s. If the conditions in individual cases deviate from the standard conditions, the parameters can be adjusted according to the following parameterization recipe:

1. 1. Determination of the individual measuring time for safe voltage values (data sheet, circuit analysis of the special load).
2. 2. The minimum observation time of the voltage UA should be in the range of 5 - 10 measurement times from point 1.
3. 3. The beginning of the measurement of the voltage gradient depends on the voltage profile after a shutdown. The earliest start time should be selected so that the switch S is definitely completely open.
4. 4. Determination of the voltage gradient (eg with an oscilloscope) in the GOOD case (no error).
5. 5. Determination of the voltage gradient in the BAD case. Here, an additional ohmic load (R_Zusatz) is connected in parallel to the load. The value of R_Zusatz is calculated from: R_Zusatz = Unom/Inom; Unom: nominal operating voltage of the load to be protected; Inom: nominal breaking current of the load to be protected.
6. 6. The limit value for distinguishing short-circuit vs. inrush current or normal inrush current can be selected accordingly (depending on the priority "safe switching on" or "safe not switching on in the event of an error") in the range between the limits measured under point 4 and point 5 .
7. 7. The typical value for the measurement time (T2-T1) is in the range of 100 to 1000µs. If the difference between the two limits determined from points 4 and 5 is too small, ie the measuring system cannot reliably assign the voltage gradients, the system can be made safer by extending the measuring time (T2-T1). Due to the longer measuring time, the discharge may be increased and the absolute voltages can be distinguished more easily; the start-up procedure is thereby lengthened. If the priority is on the duration of the start procedure, a shorter measuring time (T2-T1) can be selected using a very fast switch and a very fast measuring unit.

It is evident from this that the method according to the invention can also be carried out repeatedly in order to get to know the load or the corresponding parameters in order to increase the accuracy. The results derived from the method according to the invention can be stored for further use and/or adjustment or correction. In the case of a motor vehicle, for example, this can already be carried out during or directly after manufacture or at a dealer.

The following is with reference to the 9 until 11 a fourth embodiment of the invention is described. In 9 are several loads L1 to Ln, ie a capacitive load L1, a resistive load L2, an inductive load L3 and other loads Ln, which can be capacitive, resistive and / or inductive loads, via respective associated switches S1 to Sn, for example a respective transistors M1 to Mn such as a MOSFET are connected to an electric power source B. With regard to the switches S1 to Sn, reference is made to the description of the switch S above. That is, each switch S1 to Sn can be a respective switch S described above. With regard to the loads L1 to Ln, reference is made to the description of the load L above. That is, each load L1 to Ln can be a respective load L described above. The switches S1 to Sn are individually controlled, ie switched on and off, by an electronic control device SE'. The respective voltages across the loads L1 to Ln or the respective output voltages U1 to Un of the switches S1 to Sn are tapped from the electronic control device SE' or input into it. Corresponding voltage sensors or voltage measuring devices are contained in the electronic control device SE', but can also be present partially or completely outside the electronic control device SE' for measuring the output voltages U1 to Un. Alternatively, the output voltages U1 to Un can also be determined differently, for example indirectly via a respective current measurement of the currents I1 to In of the loads L1 to Ln.

In addition, the electronic control device SE' receives the total current IS from the currents of the switches S1 to Sn, which can be regarded as equivalent to the load currents I1 to In. The electronic control device SE' switches all switches on or off when the total current IS exceeds a predetermined total current threshold value. The technology or procedure of an electronic fuse with total current measurement and corresponding shutdown is known and is therefore not explained in detail. The electronic control device SE' can be the same as the control device SE described above with extended functionality or can be a different control device.

Based on 10 and 11 an exemplary sequence of a method according to the fourth embodiment, which is carried out by the electronic control unit SE′, is described below. At the beginning it is assumed that the type of loads, at least the capacitive loads, is known and that the corresponding information from the electronic Control unit SE' can be accessed. During the operation of the loads L1 to Ln, in step S41 (see 10 ) the total current IS is determined, for example measured, and compared with a safety threshold value or total current threshold value IS_S. If the total current IS is not greater than the total current threshold value IS_S, step S41 is repeated. If the total current IS is greater than the total current threshold value IS_S, all switches S1 to Sn are switched off in step S42. Then in step S43 for the capacitive loads, in this example at least the load L1, it is checked whether their voltage U1 or the output voltage of their associated switch S1 is less than a voltage threshold value U_S. The voltage threshold value U_S can be set appropriately for the load, the switch and/or the area of application and is designed in such a way that a short circuit can be detected when the voltage threshold value is exceeded. With regard to possible values, reference is made to the explanations above.

If, in step S43, the output voltage U1 is not equal to or greater than the voltage threshold value US_S, there is a short circuit in the corresponding capacitive load L1, and corresponding error information is stored in step S45 for later use. However, step S45 can also be omitted.

If, in step S43, the output voltage U1 is equal to or greater than the voltage threshold value U_S, a check is carried out in step S44 to determine whether the determination period has elapsed. The determination period should be as short as possible, but also long enough to be able to measure the output voltage and evaluate it with regard to a short circuit. The determination period can be in a range from 10 to 20 μs, for example. If the determination time has not elapsed, it returns to step S43. When the determination period has elapsed, the corresponding switch S1 is switched on again in step S46 since there is no short circuit in this capacitive load L1. Corresponding information that there is no short circuit in the capacitive load L1 can then also be stored here. The process for the capacitive loads is thus ended.

In addition, if there are resistive and/or inductive loads to be checked, after the determination period has elapsed, step S44 advances to step S51 ( 11 ) passed, in which a (selected) inductive or ohmic switch S2, S3 is turned on. Then in step S52 it is checked whether the current I2, I3 flowing through the switch or the corresponding load exceeds an overcurrent threshold value IS_S. This check can be done very quickly, since if there is a short circuit after power-up, the current will rise quickly and exceed the overcurrent threshold. It can be sufficient, for example, a period of 10 microseconds, as for example based on the time between TE and TA in the 2 until 4 is shown.

If the overcurrent threshold value IS_S is exceeded within the above time period for checking a short circuit, the corresponding switch is switched off in step S53 and corresponding error information is stored in step S54 for later use. Step S54 can also be omitted, can be performed before step S53 or in parallel therewith. Step S55 is then carried out, in which it is queried whether all ohmic and/or inductive loads to be checked have been checked. Step S55 is also carried out directly after step S52 if the overcurrent threshold value IS_S is not exceeded within the above short-circuit checking period. Corresponding information that there is no short circuit in the load can then also be stored here.

If all resistive and/or inductive loads to be checked have not yet been checked in step S55, a return is made to step S51 and the procedure for a next (selected) resistive or inductive load is carried out. On the other hand, if all the resistive and/or inductive loads to be checked have been checked, the procedure ends.

The procedure in 10 can also be ended after step S46 or S45 without going to the procedure in 11 (S51) is progressed (see dashed line after step S46 in 10 ). This can also depend on whether or not there are resistive and/or inductive loads to be checked.

Claims (25)

A method for protecting an electrical load (L), which can be connected to an electrical energy source (B) via a switch (S), in the event of a short circuit in the load (L), the method comprising: connecting the load (L) to the electrical Energy source (B) by first turning on the switch (S), detecting an output current (IA) of the switch (S), turning off the switch (S) when the output current (IA) exceeds an overcurrent threshold (IA_S) and/or a predetermined period of time (TD) has elapsed since the switch (S) was first turned on, detecting an output voltage (UA) of the switch (S), determining an output voltage difference (ΔUA) of the output voltage (UA) between a predetermined first point in time (T1) and a predetermined second point in time (T2) after the first point in time (T1), second switching on of the switch (S) when the output voltage difference (ΔUA) is negative and has an absolute value that is less than an upper output voltage difference threshold value (ΔUA_S1) and/or the switch (S) was switched off after the predetermined time period (TD) and the detected Output current (IA) has not exceeded the overcurrent threshold value (IA_S) from initial power-on until at least power-off. procedure after claim 2 , wherein the predetermined period of time (TD) is in a range of 1 to 100 µs. procedure after claim 1 or 2 , wherein the overcurrent threshold value (IA_S) is set such that the switch (S) is switched off by exceeding the overcurrent threshold value (IA_S) by the output current (IA) no later than 100 μs after the first switch-on. Procedure according to one of Claims 1 until 3 , where the overcurrent threshold (IA_S) is at least 70% of the nominal current of the load (L). Procedure according to one of Claims 1 until 4 , wherein the first point in time (T1) is equal to the point in time (TA) at which the switch (S) is switched off or is after the point in time (TA) at which the switch (S) is switched off. Procedure according to one of Claims 1 until 5 , the second point in time (T2) being in a range from 100 to 1000 μs after the first point in time (T1). Procedure according to one of Claims 1 until 6 , wherein the upper output voltage difference threshold value (ΔUA_S1) is set as a function of the output voltage (UA) after the switch (S) has been switched off. Procedure according to one of Claims 1 until 7 , wherein an initial value of the upper output voltage difference threshold (ΔUA_S1) is in a range of 100 to 200 mV/s. Procedure according to one of Claims 1 until 8th , wherein the load (L) is a vehicle load, in particular a motor vehicle load. Procedure according to one of Claims 1 until 9 , which is carried out at the beginning of a switch-on process of the load (L) for its operation. Procedure according to one of Claims 1 until 10 , wherein if the output current (IA) has exceeded the overcurrent threshold (IA_S) after the switch (S) is first turned on and the output voltage difference (ΔUA) is negative, it is determined that the load (L) is a capacitive load. Procedure according to one of Claims 1 until 11 , With the first switching on of the switch (S), a switch-on pulse is generated which, with a capacitive load as the load (L), causes the output current (IA) to exceed the overcurrent threshold value (IA_S). Device for protecting an electrical load (L), which connects the load (L) to an electrical energy source (B) and disconnects the connection in the event of a short circuit of the load (L), the device comprising: a switch (S) which, when switched on, connects the load (L) to the electrical energy source (B), a current sensor for detecting an output current (IA) of the switch (S), a voltage sensor for detecting an output voltage (UA) of the switch (S), and an electronic control device (SE), which is connected to the switch (S), the current sensor and the voltage sensor, wherein the electronic control device (SE) is designed, turn on the switch (S) first and then turn off the switch (S) when the output current (IA) exceeds an overcurrent threshold (IA_S) and/or a predetermined time period (TD) has elapsed since the switch (S) was first turned on, to determine an output voltage difference (ΔUA) of the output voltage (UA) between a predetermined first point in time (T1) and a predetermined second point in time (T2) after the first point in time (T1), and turn the switch (S) back on when the output voltage difference (ΔUA) is negative and has an absolute value that is less than an upper output voltage difference threshold (ΔUA_S1), and/or the switch (S) has been switched off after the predetermined period of time (TD) and the detected output current (IA) has not exceeded the overcurrent threshold value (IA_S) since the first switch-on at least until the switch is switched off. Device for protecting an electrical load (L) in the event of a short circuit in the load (L) with a switch (S) which can be switched between the load (L) and an electrical energy source (B), the device being designed according to a method one of the Claims 1 until 12 to perform. A method for protecting a plurality of electrical loads (L1 to Ln), which can be connected to an electrical energy source (B) via respective switches (S1 to Sn), in the event of a short circuit of at least one of the loads (L1 to Ln), with a sum of respective currents (11 to In) of the loads (L1 to Ln) is detected as a total current (IS), and wherein if the total current (IS) exceeds a predetermined total current threshold value, the switches (S1 to Sn) are switched off, the method comprising : after switching off the switches (S1 to Sn) due to the total current threshold being exceeded by the total current (IS), for at least one first switch (S1) from the switches (S1 to Sn), which is assigned to a capacitive load (L1) from the loads (L1 to Ln), Detection of an output voltage (U1) of the first switch (S1) during a predetermined detection period after the first switch (S1) has been switched off, if the output voltage (U1) is or becomes less than a predetermined voltage threshold value during the predetermined detection period, maintaining the switched-off state of the first switch (S1), if the output voltage (U1) is not or will not be less than the predetermined voltage threshold value during the predetermined detection time period, switching on the first switch (S1) after the predetermined detection time period has expired. Method for protecting multiple electrical loads (L1 to Ln). claim 15 , which also has: after the switches (S1 to Sn) have been switched off because the total current threshold value has been exceeded by the total current (IS), for at least one second switch (S2, S3) from the switches (S1 to Sn), which has a resistive or inductive load (L2, L3) from the loads (L1 to Ln), switching on the second switch (S2, S3) and determining a current (I2, I3) flowing through the second switch (S2, S3), and switching off the second switch (S2, S3) when the determined current (I2, I3) exceeds an overcurrent threshold value. Method for protecting multiple electrical loads (L1 to Ln). Claim 16 , wherein the switching on of the second switch (S2, S3), the determination of the current (I2, I3) flowing through the second switch (S2, S3) and the switching off of the second switch (S2, S3) are carried out sequentially for several or all of the second Switch (S2, S3) is carried out. Method for protecting multiple electrical loads (L1 to Ln). Claim 16 or 17 , wherein the second switch (S2, S3) is switched on, the current (I2, I3) flowing through the second switch (S2, S3) is determined and the second switch (S2, S3) is switched off after the predetermined detection time period has elapsed . Method for protecting a plurality of electrical loads (L1 to Ln) according to any one of Claims 15 until 18 , wherein the predetermined acquisition period is less than or equal to 100 µs, preferably less than or equal to 20 µs. Method for protecting a plurality of electrical loads (L1 to Ln) according to any one of Claims 15 until 19 , wherein the predetermined voltage threshold is equal to or less than 5 volts, preferably equal to or less than 3 volts. Method for protecting a plurality of electrical loads (L1 to Ln) according to any one of Claims 15 until 20 , wherein, if the output voltage (U1) is less than the predetermined voltage threshold value during the predetermined detection time period, a corresponding first item of error information in association with the capacitive load (L1) associated with the first switch (S1) is stored. Method for protecting a plurality of electrical loads (L1 to Ln) according to any one of Claims 15 until 21 , wherein if the determined current (I2, I3) exceeds an overcurrent threshold value, corresponding second error information is stored in association with the ohmic or inductive load (L2, L3) associated with the second switch (S2, S3). Method for protecting a plurality of electrical loads (L1 to Ln) according to any one of Claims 15 until 22 , wherein information on a respective kind of the respective loads (L1 to Ln) is stored in advance and this information is referred to. Device for protecting a plurality of electrical loads (L1 to Ln), which connects the load (L1 to Ln) to an electrical energy source (B) and disconnects in the event of a short circuit of one or more of the loads (L1 to Ln), wherein the Device comprises: for each of the loads (L1 to Ln) a switch (S1 to Sn) which when switched on is tet, the load (L1 to Ln) with the electrical energy source (B) connects, and a voltage sensor for detecting an output voltage (U1 to Un) of the switch (S), an electronic control device (SE '), with the respective switches (S1 to Sn) and contains the respective voltage sensors or is connected to the respective voltage sensors, wherein the electronic control device (SE) is designed to calculate a sum of respective currents (11 to In) of the loads (L1 to Ln) as a sum current (IS) and, if the total current (IS) exceeds a predetermined total current threshold value, to switch off the switches (S1 to Sn), after switching off the switches (S1 to Sn) due to the total current threshold value being exceeded by the total current (IS), for at least one first switch (S1) from the switches (S1 to Sn), which is assigned to a capacitive load (L1) from the loads (L1 to Ln), an output voltage (U1) of the er first switch (S1) during a predetermined detection time period after the first switch (S1) has been switched off via the associated voltage sensor, if the output voltage (U1) is or becomes less than a predetermined voltage threshold value during the predetermined detection time period, the off state of the first switch ( S1) to maintain if the output voltage (U1) is not less than the predetermined voltage threshold value during the predetermined detection time period or becomes, to turn on the first switch (S1) again after the predetermined detection time period has expired. Device for protecting a plurality of electrical loads (L1 to Ln) in the event of a short circuit of at least one of the loads (L1 to Ln) with switches (S1 to Sn) associated with the respective loads (L1 to Ln), the respective switches (S1 to Sn) between the corresponding loads (L1 to Ln) and an electrical energy source (B) are switchable, wherein the device is designed, a method according to one of Claims 15 until 23 to perform.

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