Circuit for controlling the power supply of an electrical device, as well as an electrical device with a circuit

Description

[0001] The invention relates to a circuit for controlling the power supply of an electrical device, which is configured to control a connection between a circuit input and a circuit output. The invention also relates to an electrical device with such a circuit.

[0002] Particularly in devices with two or more power supply paths, the ability for the device itself to switch off the power sources can be advantageous in certain cases. For example, there are devices in motor vehicles that are connected to the vehicle battery and also have an internal battery. As long as voltage is available from the vehicle battery, it is used to power the device. Only when the voltage from the vehicle battery is insufficient is the internal battery used to power the electrical device.

[0003] With such devices, it is usually necessary to protect the internal battery from deep discharge. To do this, the device should be disconnected from the battery and switched off if the vehicle battery voltage is insufficient and the voltage of the internal battery drops too low. As soon as sufficient voltage is available again from the vehicle battery, the device should start automatically.

[0004] A circuit designed for controlling the power supply as described above is known, for example, from DE 10 2009 013 232 A1. The circuit disclosed therein includes a switching component connected between the circuit input and the circuit output, and in addition to its connections to the circuit input and output, it has a switching input for controlling the switching component. Furthermore, the circuit disclosed therein includes a control circuit via which the switching input of the switching component is controlled. However, the circuit disclosed in the aforementioned publication also consumes current when it disconnects the connection between the circuit input and the circuit output, i.e., when it is precisely intended to prevent current consumption as completely as possible in order to avoid deep discharge.

[0005] DE 10 2006 028 708 A1 discloses a circuit arrangement for undervoltage detection of a power source with a transistor switch and at least one further switching element. The circuit arrangement is characterized in that the transistor switch and the further switching element have low resistance in an operating state of the circuit arrangement and the transistor switch blocks the further switching element from interrupting the power supply when a supply voltage of the power source falls below a defined voltage value.

[0006] Further devices for protecting batteries are described in US 3,409,802 A and US 4,005,344 A.

[0007] The publication IBM Technical Disclosure Bulletin Vol. 37 No. 09 September 1994 "Hot-Plug Protection Circuit" discloses a circuit for preventing high current surges and low voltage dips at a low-voltage source.

[0008] The object of the invention is to propose, based on DE 10 2009 013 232 A1, a circuit designed to control the connection between the circuit input and the circuit output, which only requires current when the circuit input is connected to the circuit output. A further object of the invention is to propose an electrical device with such a circuit.

[0009] These tasks are solved by an electrical device according to claim 1. Advantageous further developments and embodiments result from the features of the dependent claims.

[0010] As is known from the prior art, the circuit of the device comprises a switching component that is connected to the circuit input and the circuit output and has a switching input. The switching component is configured to switch between conduction and interruption depending on a control signal applied to the switching input.

[0011] Furthermore, the circuit includes a control circuit that serves to output a control signal to the switching input. The control circuit is designed such that – provided a required supply voltage is supplied to it – it switches the switching component to conduct when the voltage applied to the circuit input is above a reference value, and to open when the voltage applied to the circuit input is below the reference value.

[0012] According to the invention, the control circuit is connected to the circuit output in such a way that the voltage supply to the control circuit is dependent on the voltage at the circuit output. If the switch component is open, the control circuit is therefore not supplied with the required supply voltage to perform the comparison of voltage and reference value or to control the switch component. This ensures that the circuit only consumes a relevant amount of current when the voltage is above the reference value, i.e., when there is no risk of deep discharge.

[0013] Additionally, the circuit includes a startup circuit connected to the circuit input. This startup circuit is designed to switch the circuit component on, depending on a voltage rise at the circuit input, even if no supply voltage is applied to the control circuit. The startup circuit thus serves to supply the control circuit with the necessary voltage for comparing the voltage and the reference value when, due to a voltage rise at the circuit input, the voltage might have risen above the reference value. This ensures that the circuit can start operating when an energy storage device connected to the circuit input is replaced, even though the control circuit only receives a supply voltage when the switching component is on. The startup circuit therefore serves as a bootstrapping circuit.The process involves the brief activation of a more complex, power-consuming circuit (the control circuit) by a simple and energy-efficient circuit (the start circuit), whereby the more complex circuit remains active after the brief activation (by drawing its supply voltage depending on the voltage at the circuit output and controlling the switching component via the control circuit). The start circuit preferably consumes no current, at least when the voltage at the circuit input is constant.

[0014] In a particularly preferred embodiment, the start circuit can be configured as a delay circuit designed to output a voltage applied to the circuit input, or changes in the voltage applied to the circuit input, in a delayed and / or smoothed manner. In particular, a low-pass filter can be used as the delay circuit, or the delay circuit can include a low-pass filter. Due to the delayed output, a voltage difference arises between the voltage at the circuit input and the voltage delayed or smoothed by the delay circuit when the voltage at the circuit input changes. This voltage difference can be used to switch the switching component.

[0015] In a particularly preferred embodiment, the control circuit and the delay circuit are configured such that the delayed and / or smoothed voltage is applied to the switching input of the switch component at least temporarily (preferably at least when the circuit was previously not supplied with a voltage and is newly supplied with a voltage). In such embodiments, the switch component is configured to switch depending on a voltage difference between the circuit input and the switching input.

[0016] Such switching behavior of the switching component is particularly possible when a transistor, preferably a MOSFET (especially a P-channel MOSFET), is used as the switching component. A MOSFET that conducts when its gate is not supplied with voltage is particularly preferred; that is, it conducts when the voltage at the circuit input (or at the source terminal of the MOSFET) is greater than the voltage at the switching input (or at the gate terminal of the MOSFET) by at least an amount that depends on the choice of MOSFET.

[0017] The control circuit includes a comparator circuit that compares a voltage dependent on the voltage applied to the switch input with a reference value. In particular, the voltage at the circuit output can be compared with the reference value. A microcontroller can be used as the comparator circuit, preferably having an integrated analog-to-digital converter or being connected to an external comparator.

[0018] According to the invention, the control circuit comprises a logic circuit connected to the starter circuit. The logic circuit serves to output a control signal that depends, at least temporarily, on the output signal of the starter circuit. Overall, the control signal is thus influenced, at least temporarily, by both the starter circuit and the comparator circuit. Particularly preferably, the logic circuit can be configured to temporarily output or forward the output signal of the starter circuit as a control signal. Specifically, whether or not the output signal of the starter circuit is forwarded to the control input by the logic circuit can depend on a signal from the comparator circuit.

[0019] Particularly preferably, the logic circuit can be configured to connect the switching input of the switch component to a potential, preferably a fixed potential, when the control circuit (preferably the comparator circuit of the control circuit) detects a voltage at the circuit input that is above the reference value. This potential is suitable for switching the switch component to conduction and corresponds, at least temporarily, to the control signal. The logic circuit can also be configured to supply the output signal of the start circuit to the switch component as a control signal when the control circuit or the comparator circuit either detects a voltage below the reference value or fails to perform a comparison due to an insufficient voltage supply.This output signal, as already mentioned, only switches the switching component to conduction when the voltage at the circuit input increases; otherwise, it switches the switching component to open circuit. A logic circuit configured as described above.

[0020] The circuit comprises a switching element—specifically, a transistor—where the switching element has an input, an output, and a control input for controlling the connection between the input and the output, i.e., for switching the switching element to conduct or break. The input of the switching element is connected to the potential, and the output is connected to the start circuit and the switching input. Thus, depending on the switching state of the switching element, the switching input of the switching element receives either the potential or an output signal from the start circuit. To control the logic circuit based on the result of the aforementioned comparison of voltage and reference value, the control input of the switching element is connected to the comparison circuit.

[0021] In some embodiments, the start circuit includes a storage element. In such embodiments, the control signal output by the logic circuit corresponds to the potential when the potential is connected to the switching input, i.e., when the switching element is in the conducting state. While the switching input, or output side of the start circuit, is connected to the potential, the storage element is discharged. If the comparator circuit detects a voltage that is too low and accordingly switches the switching element to the blocking state (i.e., when the potential is not connected to the switching input), the control signal corresponds to a voltage of the storage element and thus to the output signal of the start circuit. Meanwhile, the storage element is charged via the voltage at the circuit input.Because the memory element is initially charged after the switching element is switched to the off position, so that the voltage at the switching input of the switch component changes only with a delay, short-term voltage fluctuations at the circuit input do not directly lead to the interruption of the connection between the circuit input and the circuit output. Unintentional interruption of this connection, for example due to a voltage fluctuation, is thus reliably prevented. Preferably, the capacity of the memory element is selected such that the switch component only switches to the off position between one millisecond and one second (especially preferably between 100 and 500 milliseconds) after the voltage has dropped below the reference value.

[0022] In some implementations, the comparator circuit can also be configured to pulse the switching input to the potential when it detects a voltage above the reference value. This means that it is not strictly necessary for the switching element to be continuously open when the voltage is above the reference value. Because the control signal corresponds to the voltage of the storage element when the switching element is in the off state, and thus blocking the switching element does not directly trigger the output of a control signal to switch the switching element to the off state, the switching element remains reliably open even with a pulsed signal from the comparator circuit, as long as the voltage applied to the circuit input is above the reference value.

[0023] According to the invention, the circuit comprises limiting means for limiting an inrush current. The inrush current is limited by at least temporarily reducing the conductivity of the switching component depending on a voltage at the circuit output and / or circuit input. The limiting means are configured to supply the switching input of the switching component with a coupling signal of the voltage of the circuit output and / or circuit input. For this purpose, the limiting means can include corresponding coupling means that can be connected either between the circuit input and the switching input or between the circuit output and the switching input. The coupling means are preferably configured such that the generated coupling signal is significantly shorter than the duration that the start circuit switches the switching component on, regardless of whether the voltage supplied to the circuit is above or below the reference value.

[0024] Preferably, the coupling element can be designed as a capacitor or at least include a capacitor. The feedback signal then arises because the electrode of the capacitor facing the circuit input or output is charged, causing the electrode facing the switching input to strive for an opposite charge as its most energetically favorable state. This results in a voltage spike. The capacitor thus transmits the voltage increase at the circuit input or output to the switching input of the switching component and therefore acts as a differentiator. Any other type of differentiator can also be used instead of a capacitor to generate a feedback signal. However, devices other than a differentiator can also be used to generate a feedback signal. For example, an operational amplifier could be used for this purpose.This would then be connected with one of its inputs to the circuit input or circuit output, and with its output to the switching input of the switch component.

[0025] Particularly preferred is the absence of any resistive load connected in parallel to the switch component, at least when the switch component is open-circuit. The start circuit connected to the circuit input thus preferably represents a pure AC voltage load, not a resistive load, at least when the switch component is open-circuit (or when the start circuit is not connected to the potential on the output side). The resistance of the start circuit is preferably frequency-dependent. For DC voltages, the resistance is preferably essentially infinite, so that no current flows when the voltage at the circuit input remains constant and below the reference value. The essentially infinite resistance to a constant voltage at the circuit input reliably prevents current consumption when the circuit input is disconnected from the circuit output.limited to situations where the voltage applied to the circuit input changes.

[0026] The circuit may additionally include a voltage regulator or limiter that regulates a voltage supplied to the control circuit via the power supply input and / or prevents overvoltage. Furthermore, the electrical device includes an energy storage device, namely an internal battery, a connection for an external power supply, and a power path switch that is connected to both the energy storage device and the external power supply connection and selectively connects either the energy storage device or the external power supply connection to the circuit input. The power path switch may have additional inputs connected to further power sources. This selective connection can be made, in particular, depending on the voltage of the energy storage device or an applied signal.

[0027] The energy storage device and the external power supply connection (and, if applicable, the other inputs) can be treated with different priorities. Specifically, the external power supply connection can be connected to the circuit input whenever the voltage at the external power supply connection is sufficiently high. Only when the voltage at the external power supply connection is too low will the energy storage device be connected to the circuit input, ensuring that the energy storage device is only used when there is insufficient voltage at the external power supply connection.

[0028] The electrical device can be configured, in particular, as a toll device or a tachograph. It is also advantageously conceivable that the toll device additionally has the functionality of a tachograph, or that the tachograph additionally has the functionality of a toll device. In particular, the electrical device can be an onboard unit of a vehicle.

[0029] When installed in a vehicle, the electrical device can be connected to the vehicle battery via its external power supply connection. Specifically, this connection can be made via the connection point designated as terminal 30 according to DIN 72552.

[0030] Exemplary embodiments of the invention are explained in more detail below with reference to schematic figures. These show: Fig. 1 a schematic representation of a switching arrangement according to the invention, according to an exemplary embodiment, Fig. 2 a representation of a circuit-technical implementation of the switching arrangement from Fig. 1 , Fig. 3 a section of the circuit from Fig. 2 with points marked within the circuit, Fig. 4 Voltage waveforms for a switching-on and switching-off process at the marked points from Fig. 3 For a microcontroller outputting a continuous signal, Fig. 5 shows voltage waveforms for a switch-on and switch-off process at the marked points. Fig. 3 In the case of a pulsed microcontroller, current and voltage waveforms at the marked points are shown in Fig. 6. Fig. 3 for a power-on process.

[0031] In Figure 1A switching arrangement 1 is shown, comprising a circuit 2 and a supply path switch 3 upstream of the circuit for connecting one of two energy sources 4, 5 to the circuit 2 and a consumer 6.

[0032] The first energy source 4 is designed as an internal battery and can be arranged in a housing together with the circuit 2, the supply path switch 3, and the load 6, so that these components together form an electrical device 7. In the present embodiment, this electrical device is a toll collection device. The second energy source 5 can, for example, be designed as a vehicle battery, which is connected to the device 7 via the terminal provided for connecting loads (usually referred to as "terminal 30").

[0033] The power supply path switch 3 is configured to connect the second power source 5 to the device 2 whenever it provides a sufficient output voltage. If, however, the output voltage of the second power source 5 falls below the voltage required to supply the circuit 2, the power supply path switch 3 connects the first power source 4 to the circuit 2. The output voltage of the power source selected by the power supply path switch 3 is thus connected to the input 8 of the circuit 2.

[0034] Circuit 2 comprises a switch 9, a start circuit 15, a control circuit 32 including a comparator circuit 16 and a logic circuit 12, and a protection circuit 18, which can, for example, be configured as overcurrent protection. Overvoltage protection can be integrated into the protection circuit 18. The protection circuit 18 can be connected downstream of the switch 9 as shown. Alternatively, the protection circuit can also be arranged upstream of the switch 9, as shown by the dashed lines. The protection circuit can directly implement overvoltage and / or overcurrent protection itself, or it can provide such protection by supplying a signal to the control input 11 of the switch 9 (as shown by the dashed lines). Additional overvoltage protection can also be provided between the switch 9 and the supply path switch 3.

[0035] The switch 9 connects input 8 to an output 10 of circuit 2 or disconnects input 8 from output 10. Whether the switch is blocked or open depends on the voltage applied to control input 11 of the switch 9 or on the control signal supplied to control input 11. Depending on the design of the switch 9, its switching state can also depend on the difference between the voltage applied to control input 11 and the voltage at input 8.

[0036] The control input 11 of the switch component 9 is connected to an output of the logic circuit 12, which is connected to the microcontroller 16 and the start circuit 15. The logic circuit 12 outputs a signal via its output 31, which depends on the voltages applied to its inputs 13 and 14.

[0037] The first input 13 of the logic circuit 12 is connected to the start circuit 15, which is designed as a delay circuit and forwards the voltage applied at input 8 to the circuit part 12 with a delay or smoothing.

[0038] The second input 14, however, is connected to the microcontroller 16. If the microcontroller has been supplied with a voltage for a sufficient period to begin operation, it compares the voltage at output 10 with a reference value and outputs a signal via its output 17. The signal depends on whether the voltage at output 10 is above or below the reference value. Alternatively, a comparator circuit connected upstream of the microcontroller 16 can compare the voltage at output 10 with the reference value and output a signal corresponding to the result of this comparison to the microcontroller 16. The microcontroller then outputs a corresponding signal via its output 17, as in embodiments where the microcontroller performs the comparison itself.A comparator circuit upstream of the microcontroller can, for example, be integrated into a voltage regulator that provides the supply voltage for the microcontroller.

[0039] The reference value is chosen such that if the voltage falls below this value, the energy sources 4 and 5 connected to circuit 2 will no longer supply a sufficient voltage, thus risking deep discharge of the energy source. Conversely, a voltage at output 10 above the reference value ensures that the energy source 4 or 5 connected to circuit 2 outputs a sufficient voltage, indicating that the respective energy source is still adequately charged. As long as the microcontroller 16 is not yet supplied with a power supply and therefore cannot yet begin operation, it outputs a voltage of 0 volts. If it detects that the voltage at output 10 is too low, it also outputs a voltage of 0 volts.If, however, it detects that the voltage at output 10 exceeds the reference value, it outputs a voltage other than 0 volts (continuously or pulsed, depending on the design of the microcontroller 16).

[0040] If the microcontroller outputs a voltage other than 0 volts, the logic circuit 12 supplies a control signal to the switching input 11, which switches the switch component to conduction. Conversely, if the microcontroller supplies a voltage of 0 volts to the logic circuit 12, the logic circuit 12 outputs a signal from the start circuit 15 to the switching input 11.

[0041] As mentioned previously, the switch 9 is activated depending on the voltage at the circuit input and / or the voltage difference between the voltage at circuit input 8 and the voltage at switching input 11. In one possible embodiment, the switch 9 is activated when the voltage at circuit input 8 is sufficiently higher than the voltage at switching input 11 and is deactivated when the voltage difference is too small. In another possible embodiment, the switch 9 is activated as long as the voltage at switching input 11 is below a predetermined value and is deactivated as soon as it exceeds this predetermined value. The required voltage difference between switching input 11 and circuit input 8, or the required voltage at switching input 11 for the switch to activate, depends on the specific switch 9 chosen.By selecting the switch component 11 and designing the start circuit 15 (especially with regard to its delay or smoothing effect), the time window can be determined for which the switch component 9 switches on independently of the voltage at the circuit output 10 and independently of the function of the microcontroller 16 when the voltage at the circuit input 8 suddenly increases.

[0042] This preferably ensures that when a new energy source 4 or 5 is connected to the circuit 2 (provided the voltage of the energy source is sufficiently high), the switch 9 initially switches on, since the start circuit 15 still outputs a low voltage in the corresponding time range. Therefore, in this time range, the voltage at the switch input 11 is low and the voltage difference between the voltage at the circuit input 8 and the voltage at the switch input 11 is high. Thus, when a new energy source 4 or 5 is connected, the voltage required to supply the microcontroller 16 is allowed to pass through the switch 9 until the microcontroller can check whether the voltage at the circuit output 10, and thus the voltage of the energy source 4 or 5 connected to the circuit 2, is above or below the reference value.This temporary activation of the microcontroller when the voltage at the circuit input increases is also known as bootstrapping.

[0043] In addition to the components described in more detail so far, circuit 2 also includes the protection circuit 18 mentioned at the beginning, whose sole function is to protect the microcontroller 16 and the consumer 6.

[0044] A specific circuit design of the in Fig. 1 The schematically illustrated circuit arrangement 1 is in Figure 2The circuit is illustrated in this configuration. In this circuit design, a MOSFET is used as the switching component 9. As can be seen, the start circuit 15, designed as a delay circuit, is formed by a resistor 21 and a capacitor 22 connected to ground, i.e., by a low-pass filter. The logic circuit 12 includes a transistor 19, whose collector forms the input 13 of the logic circuit and is simultaneously connected to the switching input 11 of the switching component 9. When the transistor 19 is off, the voltage across the capacitor of the start circuit 15 is present at the output of the logic circuit 12. When the transistor 19 is on, however, it connects ground to the switching input 11 of the switching component 9 via its collector-emitter junction. Of course, another switching element could be used instead of the transistor 19.

[0045] In the initial state of the circuit, where circuit input 8 is connected to a constant voltage below the reference value, the switch 9 is off. No voltage is present at circuit output 10, so the microcontroller 16, which is connected to circuit output 10 via a voltage regulator 33, is not supplied with a voltage and therefore outputs a voltage of 0 volts. Consequently, transistor 19 is off, and the output signal of the start circuit 15—which at that point corresponds to the input voltage—is applied to the switch 9. The voltage difference between circuit input 8 and switch input 11 (i.e., the gate-source voltage of the MOSFET) is thus 0 volts, which keeps the switch 9 off.

[0046] If the voltage at circuit input 8 increases from this initial state, the start circuit delays the voltage increase before passing it to control input 11. This causes the voltage difference (gate-source voltage) to rise, and the switch 9 then conducts. This temporarily supplies the microcontroller with power (until the voltage at switch input 11 rises too high or the gate-source voltage becomes too low), and the microcontroller begins to compare the voltage at the circuit output (which, due to the conducting switch 9, is equal to the voltage at the circuit input) with the reference value. In addition to or as an alternative to comparing the voltage at the circuit output with the reference value, the microcontroller 16 can also, as indicated by arrows 35 and 36, directly check the voltage at power sources 4 and 5 and compare it with the reference value.The gradual activation of the microcontroller 16 by the start circuit 15 is also called bootstrapping.

[0047] If the microcontroller detects a voltage above the reference value, the transistor 19 is controlled by the microcontroller 16 via its base or control electrode such that it is either continuously open or pulsed (depending on the microcontroller's configuration), i.e., it opens and closes pulse by pulse. Whenever the transistor 19 opens, the capacitor 22 is discharged. In pulsed operation, this preferably occurs at regular intervals, which are chosen such that the voltage at the switching input 11 does not rise sufficiently between discharges for the voltage difference or gate-source voltage to fall below the corresponding switching threshold of the switch 9. The switch 9 remains on in both continuous and pulsed operation of the transistor 19 until the voltage at the circuit input falls below the reference value.

[0048] If the microcontroller 16 detects that the voltage at circuit output 10 is below the specified limit, transistor 19 is continuously switched off. The voltage at the switching input therefore rises until the voltage difference between circuit input 8 and switching input 11 is too small to keep the switch 9 in the on state. Since this preferably takes at least a few milliseconds (ideally between one millisecond and one second), even brief fluctuations at the circuit input do not directly cause the switch to switch off.

[0049] Not in the Fig. 1 One can recognize a Fig. 2The illustrated protection against excessive inrush current is implemented by a capacitor 20. The capacitor 20 transmits a voltage rise on its side facing the circuit output 10 to the switching input 11 of the switch component 9, thus acting as a differentiator. If the current during switch-on is so high that it would be dangerous for either the microcontroller 16 or the load 6, the voltage present on the side of the capacitor 20 facing the switching input 11 rises quickly enough immediately after the switch component 9 is switched on to reduce the conductivity of the switch component 9 before damage to the microcontroller 16 or the load 6 can occur. After the switch-on process, however, the effect of the capacitor 20 disappears, since the side of the capacitor 20 facing the switching input 11 is connected to ground via the transistor 19. Furthermore, in addition to the above, Figure 1 The parts shown are in Fig. 2a diode 34, which serves as overvoltage protection for the gate-source voltage of the switch component 9.

[0050] In Figure 3 This is a section of the circuit arrangement from Fig. 2 shown. Identical components are marked with the same reference symbols. In addition to those already shown. Fig. 2 known components are in Fig. 3 Points 23, 24, 25 and 26 are marked. In the following Figures 4 to 6 The voltage waveforms simulated for the circuit described above are shown at the marked points. Fig. 4 This refers to embodiments in which the microcontroller outputs a continuous signal, while Fig. 5 refers to embodiments with a pulsed microcontroller. Figure 6This simply shows a power-on process, which occurs regardless of whether the microcontroller operates in pulsed or continuous mode. Each graph is labeled with the reference symbol corresponding to the respective marked point. Fig. 3 This corresponds to the point at which the voltage plotted by the respective graph is applied. Graph 23 thus represents a voltage waveform at input 8, graph 24 a voltage waveform at output 10, graph 25 a voltage waveform at the gate or switching input 11 of the switch component 9, and graph 26 a signal output by the microcontroller 16. Graph 27, on the other hand, shows the voltage difference between the voltage at input 8 and the voltage at switching input 11.

[0051] In Fig. 4 and 5 The voltage curves for a simulated switching-on and switching-off process are shown, as described above in principle based on... Figure 2As already described, the circuit is initially in the state described above. The voltage 23 at circuit input 8 and the voltage 25 at switch input 11 are both 3 volts. The gate-source voltage 27 is therefore 0 volts. Since the switch component 9 is off, the circuit output 10 is 0 volts.

[0052] At time t1, the voltage at input 8 suddenly rises from 3 volts to approximately 4.5 volts (see graph 23). This can result, for example, from the switching of the supply path switch 3 from the first energy source 4 to the second energy source 5.

[0053] As can be seen from graph 25, the voltage at the switching input 11 of the switch component 9 rises only slowly. Accordingly, the gate-source voltage 27 briefly rises to 1.5 volts, which causes the switch component 9 to switch and thus the voltage at the circuit output to rise from 0 volts to 4.5 volts. Immediately after the switching of the switch component 9 and the resulting increase in voltage 24 at the circuit output 10, a voltage spike 28 can be observed.

[0054] This voltage spike is due to the fact that capacitor 20 is charged by the voltage applied to output 10. The charging of the side of capacitor 20 facing output 10 causes the opposite side of capacitor 20, facing the switching input 11 of switching element 9, to accumulate a charge with the opposite polarity. This induces a current flow through resistor 37, resulting in a voltage drop across resistor 37 and thus changing the potential at switching input 11, as can be seen from the voltage spike 28. The capacitor therefore acts as a differentiator. This feedback of the voltage at input 10 to switching input 11 limits the maximum inrush current, as already mentioned, thereby protecting downstream components, in particular the load 6 and the microcontroller 16, as described above.

[0055] After the voltage spike 28, the voltage at gate 25 shows a continuous increase, which is due to the fact that the capacitor 22 of the start circuit 15 is being charged.

[0056] Graph 26 shows that the voltage at output 10, which corresponds to the voltage at circuit input 8 due to the closed switch component 9, is considered sufficiently high by the microcontroller 16. However, as mentioned earlier, the microcontroller can also, as indicated by arrows 35 and 36, directly determine the voltage at power sources 4 and 5 and compare it to the reference value. Because the voltage is higher than the reference value, the microcontroller 16 outputs a continuous signal (shown in Figure 4 ) or rectangular pulses 29 and 30 (shown in Figure 5, of course other pulse shapes are also possible) which indicate that the voltage at output 10 is sufficiently large and that therefore there is no risk of deep discharge of the energy storage device 4 or 5 connected to the circuit.

[0057] The continuous signal, or the square wave pulses 29 and 30, are passed through an unmarked low-pass filter to the base of transistor 19. This voltage causes transistor 19 to switch on briefly or continuously (depending on whether the microcontroller outputs a pulsed or continuous signal). This connects the collector-emitter junction of capacitor 22 to ground, discharging it completely. Consequently, the voltage at switch input 11 drops to zero (ground potential) or close to zero.

[0058] In variants with a pulsed microcontroller (see below). Fig. 5 After the first rectangular pulse 29, the voltage at the switching input 11 slowly rises again, whereby the transistor 19 is switched on again by the second rectangular pulse 30, well before the voltage at the switching input 11 exceeds the voltage required to switch the switch component 9, so that the capacitor 22 is completely discharged again. In variants with a continuously operating microcontroller, however, the voltage at the switching input remains constant throughout the entire time period in which the microcontroller detects a voltage above the reference value.

[0059] At time t2, the voltage at the input drops again to 3 V. This voltage is lower than the reference value. With a continuously operating microcontroller, the voltage output by the microcontroller drops to 0 V. In variants with a pulsed microcontroller 16, no further square wave pulses are output by the microcontroller 16. In both continuously and pulsed operation, the voltage at the switching input 11 approaches the voltage at input 8. Since, in this case, the switching component 9 is implemented as a MOSFET, this causes the resistance of the switching component 9 to increase rapidly, which in turn causes the voltage at output 10 to drop quickly.

[0060] In Fig. 6 The switching-on process is significantly more detailed in terms of timing than in the Fig. 4 and 5 depicted. During the Fig. 4The depicted time period is approximately 1.4 seconds long in total, is in Fig. 5 Only a time interval of approximately 3.5 milliseconds, during which the switch-on process takes place, is shown. Naturally, the exact times depend on the circuit design and can be longer or shorter depending on the specific implementation. As can be seen, the voltage applied to the switching input 11 (see Graph 25) increases abruptly due to the feedback via capacitor 20 when the input voltage (see Graph 23) is increased. Subsequently, the voltage shown in Graph 25 drops almost back to its initial value, before undergoing a change that is not visible in this time interval but is already apparent from the graph. Fig. 4 to complete the described slow, continuous increase. The brief increase in voltage at input 11 slightly delays the increase in voltage at output 10 (see graph 24).

[0061] Up in Fig. 5 The current flowing through the switch 9 is plotted. As can be seen, the current rises more slowly than the voltage at the circuit input. This delayed rise is due to the coupling signal of capacitor 20 (i.e., the voltage spike 28), which reduces the conductivity of the switch, as the voltage spike 28 reduces the gate-source voltage 27 to a value close to the switching threshold of the switch 9.

Claims

1. An electrical device (7), comprising: - a circuit (2) for connecting to a first energy source (4) or to a second energy source (5) and for controlling a connection between a circuit input (8) and a circuit output (10) depending on a voltage (23) applied to the circuit input (8), comprising: - a switch component (9) that is connected to the circuit input (8) and the circuit output (10) and has a switching input (11), and that is designed to switch to pass-through or interruption depending on a control signal (25) applied to the switching input (11), and - a control circuit (32) that is designed to feed a control signal (25) for switching the switch component (9) to pass-through to the switching input (11) of the switch component (9) if the voltage applied to the circuit output (10) is above a reference value, and then to supply a control signal for switching the switch component (9) to interruption if the voltage applied to the circuit output (10) is below the reference value, wherein the control circuit (32) is connected to the circuit output (10) such that the voltage supply of the control circuit (32) is implemented depending on the voltage at the circuit output (10), and wherein a starting circuit (15) is connected to the circuit input (8) and is designed to switch the switch component (9) to pass-through depending on a voltage rise at the circuit input (8) even if the control circuit (32) is not supplied with voltage via the circuit output (10), wherein the circuit (2) further comprises limiting means (20) for limiting a switch-on current, which are designed to at least temporarily reduce a conductivity of the switch component (9) depending on a voltage (24) at the circuit output (10) and / or the circuit input (8), specifically in such a way that the limiting means (20) comprise coupling means which are connected to output a coupling signal to the switching input (11) between the circuit input (8) and the switching input (11) or are connected between the circuit output (10) and the switching input (11), and wherein the control circuit (32) comprises a comparison circuit for comparing a voltage, dependent on the voltage applied to the circuit input, namely the voltage at the circuit output (10), with the reference value, wherein the comparison circuit is designed as a microcontroller (16), and wherein the control circuit (32) comprises a linking circuit (12) which is connected to the starting circuit (15) and is designed, - when the control circuit (32) detects a voltage above the reference value at the circuit input (8), to connect the switching input (11) of the switch component (9) to a potential which at least temporarily forms the control signal, for switching the switch component (9) to a pass-through, and - when the control circuit (32) detects a voltage below the reference value or when the control circuit (32) does not compare the voltage with the reference value in the absence of a voltage supply, to feed an output signal of the starting circuit (15) as a control signal to the switching input (11) of the switch component (9), and wherein the linking circuit (12) comprises a switching element, specifically a transistor (19), which comprises an input, an output, and a control input for controlling a connection between the input and the output, wherein - the input is connected to the potential of ground, - the output is connected both to the starting circuit (15) and to the switching input (11) of the switch component, and - the control input is connected to the comparison circuit (16), - at least one internal battery (4) and at least one terminal for a vehicle battery (5), wherein the internal battery is the first energy source (4) and the vehicle battery is the second energy source (5), - a supply path changeover switch (3), which is designed to connect the internal battery (4) or the terminal for the vehicle battery (5) to the circuit input (8) of the circuit (2) depending on a voltage at the terminal of the vehicle battery (5), a voltage of the internal battery (4), and / or depending on a signal that is fed.

2. The electrical device (7) as claimed in claim 1, characterized in that the starting circuit is designed as a delay circuit (15) for delayed and / or smoothed output of a voltage (23) applied to the circuit input (8), wherein the delay circuit (15) is preferably designed as a low-pass filter.

3. The electrical device (7) as claimed in claim 2, characterized in that the delay circuit and the control circuit are designed such that the delayed and / or smoothed voltage is at least temporarily forwarded as a control signal to the switching input (11) of the switch component, and in that the switch component (9) is configured to switch depending on a voltage difference (27) between the voltage at the circuit input (8) and the voltage at the switching input (11).

4. The electrical device (7) as claimed in any one of the preceding claims, characterized in that the starting circuit (15) comprises a memory element (22) and is designed in such a way that, the control signal, when the connection between the input and output of the switching element is switched to pass-through, corresponds to the potential of ground and, when the switching element is switched to interrupt, it corresponds to a voltage of the memory element (22), wherein the memory element (22), when it is connected to the potential, is discharged and, when the switching element is switched to interrupt, it is charged via the voltage at the circuit input (8).

5. The electrical device (7) as claimed in any one of the preceding claims, characterized in that the coupling means are designed as capacitors, differentiators, and / or operational amplifiers.

6. The electrical device (7) as claimed in any one of the preceding claims, characterized in that the switch component (9) is designed as a transistor, preferably as a MOSFET.

7. The electrical device (7) as claimed in any one of the preceding claims, designed as a toll device or tachograph.