Circuit arrangement

Abstract

Circuit arrangement for implementing a capacitor, with at least three partial capacitors (120, 122, 124) which are connected in series with one another in the alternating current equivalent circuit diagram, and a rectifier (118) with components which are assigned to the partial capacitors (120, 122, 124) in such a way that, in the case of a reversed polarity of the operating voltage applied to the circuit arrangement (100), an applied negative voltage is limited at at least two of the partial capacitors (120, 122, 124).

Description

[0001] The invention relates to a circuit arrangement, wherein this circuit arrangement is designed to implement a capacitor, and to an on-board electrical system with such a circuit arrangement. State of the art

[0002] The circuit arrangement presented here serves to provide a capacitance, in particular a capacitance in an on-board electrical system of a motor vehicle.

[0003] In supply voltage networks, such as 12V / 24V vehicle electrical systems, where polarity reversal may occur in rare cases, especially for a short time, e.g., due to incorrectly polarized jump starting, only capacitors that are suitable or approved for negative operating voltages, at least for a short time, can be used for voltage stabilization or filtering. Capacitors suitable for negative operating voltages include ceramic capacitors or film capacitors. However, these typically have lower capacitance values.

[0004] There are also applications where larger capacitance values ​​are required for filtering or voltage stabilization. Higher capacitance values ​​can be provided, for example, by electrolytic capacitors, such as aluminum electrolytic capacitors or polymer (hybrid) electrolytic capacitors. However, these capacitors are polarized, so they cannot normally be operated at negative operating voltages, or only to a very limited extent.

[0005] A known circuit arrangement comprises a series circuit of two anti-serially connected polarized capacitors, in which the negative voltage at each of the capacitors is limited to the diode forward voltage via diodes connected in parallel. This can, in principle, be operated at a negative voltage, but the positive and negative operating voltage components must or should be balanced, i.e. the circuit arrangement should be operated with a pure alternating voltage. If a predominantly negative voltage is applied to one of the capacitors, which is the case when operated predominantly at a positive operating voltage, this capacitor will be destroyed in the long term. It should be noted that capacitors with reversed polarity can be subjected to a slightly negative voltage of, for example, less than 1V for a short time. For this purpose, Fig. 1.

[0006] Another well-known circuit arrangement uses bipolar electrolytic capacitors, such as those used in audio applications. These are typically pure AC capacitors, meaning that both positive and negative voltages must occur in equal proportions. However, these capacitors are not suitable for negative voltages, which only rarely occur. It should be noted that bipolar capacitors, as described above, are essentially two polarized capacitors connected in reverse series, but without clamping diodes.

[0007] In some cases, it is possible to obtain manufacturer approval for capacitor reversal with restrictions regarding duration, voltage level, and frequency of polarity reversals. However, this approval is usually only granted in a few cases, as it ultimately does not represent a sound technical solution, as reversed polarity will destroy the dielectric in the medium to long term. Approval for higher or longer-lasting reversed polarity voltages is typically not granted. It should be noted that this procedure is currently used for 12V systems. However, it is likely no longer applicable for 24V systems.

[0008] The requirements for passive reverse polarity protection for polarized capacitors are as follows: If a polarized capacitor is to be operated at an operating voltage that may be temporarily negative or reversed, the following aspects should be observed and the following requirements should be met: The negative voltage across the capacitor is significantly reduced in the event of a potentially high negative (reverse polarity) operating voltage, e.g., less than 1V. The voltage across the capacitor is positive during normal operation, i.e., most of the time. This means that no negative voltage should be present across the capacitor when the operating voltage is positive. The capacitor, including the protection circuit, must have an alternating current path; otherwise, the capacitor would no longer function as a capacitor. Thus, although the capacitor is intended to be protected from negative voltages, both positive and negative currents must be able to flow. At positive operating voltage, no direct current may flow. The standby current / quiescent current must be 0A. This is especially important when operating directly from a vehicle's electrical system to prevent the vehicle battery from discharging. Disclosure of the invention

[0009] Against this background, a circuit arrangement according to claim 1 and an on-board electrical system with the features of claim 8 are presented. Embodiments emerge from the dependent claims and from the description.

[0010] The presented circuit arrangement for implementing a capacitor, with at least three partial capacitors that are connected in series with one another in the alternating current equivalent circuit, and a rectifier with components that are assigned to the partial capacitors in such a way that, in the event of a reversed polarity of the operating voltage applied to the circuit arrangement, a negative voltage applied to at least two of the partial capacitors is limited.

[0011] In a specific application, a polarized capacitor is used as part of a filter connected directly to the vehicle's electrical system. The filter is intended to protect sensitive components, such as MOSFETs, a downstream active reverse polarity protection device and / or an on / off switch, from high voltage pulses or similar events that may occur in the vehicle's electrical system.

[0012] The presented electrical system is used, for example, in a motor vehicle and has a circuit arrangement of the type described herein.

[0013] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0014] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention. Short description of the drawings Fig. 1 shows a circuit arrangement with a series connection of two anti-serially connected polarized capacitors according to the prior art. Fig. 2 shows an embodiment of the presented circuit arrangement with a bridge rectifier. Fig. 3 shows another embodiment of the circuit arrangement with discrete diodes. Fig. 4 shows the circuit arrangement of Fig. 3 in an equivalent circuit diagram with positive operating voltage. Fig. 5 shows the embodiment of Fig. 3 in the equivalent circuit diagram at negative operating voltage. Fig. 6 shows the embodiment of Fig. 3 in the small-signal alternating current equivalent circuit. Fig. 7 shows a large-signal alternating current equivalent circuit of the circuit arrangement from Fig. 3. Fig. Figure 8 shows alternative diode arrangements. Embodiments of the invention

[0015] The invention is illustrated schematically in the drawings using embodiments and is described in detail below with reference to the drawings.

[0016] Fig. Figure 1 shows a prior art circuit arrangement, designated overall by reference numeral 10. This circuit arrangement 10 comprises a series circuit of two anti-serially connected polarized capacitors 12, 14 with two additional diodes 16, 18 connected in parallel, which limit the negative voltage at one of the capacitors 12 and 14, respectively.

[0017] Fig. Figure 2 shows, on the left, a capacitor 50 connected between terminals U+ 52 and U- 54. This capacitor 50 is transferred into a circuit arrangement 60 with a bridge rectifier 62, which is implemented by a diode network 64 with diodes D1 70, D2 72, D3 74, and D4 76. Furthermore, the illustration shows a first partial capacitor C1 80, a second partial capacitor C2 82, a third partial capacitor C3 84, a first resistor R1 90, and a second resistor 92.

[0018] It should be noted that resistors 90, 92 are not required if only one capacitor 50 is provided. Resistors 90, 92 are only necessary when the three partial capacitors 80, 82, 84 are connected in series to enable voltage equalization. Otherwise, the two terminals of the middle partial capacitor 84 would have no DC voltage reference.

[0019] In the illustrated circuit arrangement 60, the capacitor 50 to be protected from a negative operating voltage is divided into three sub-capacitors C1 80, C2 82, and C3 84, essentially connected in series. The diode network 64 prevents the occurrence of high negative voltages at two of the sub-capacitors, namely C1 80 and C2 82, particularly in the case of reversed operating voltage, and ensures that the voltage remains positive at one of the sub-capacitors C3 84. The two high-ohm resistors R1 90 and R2 92 ensure that the sub-capacitors 80, 82, and 84 are maintained at the operating voltage level or discharged over a longer period.

[0020] Fig. Figure 3 shows a further embodiment of the circuit arrangement, designated overall by reference numeral 100, which operates with discrete diodes. This circuit arrangement 100 is connected to terminals U+ 102 and U- 104. The illustration shows the discrete diodes D1 110, D2 112, D3 114, and D4 116, which also form a rectifier 118. The illustration also shows partial capacitors C1 120, C2 122, and C3 124, as well as resistors R1 130 and R2 132.

[0021] Fig. 4 shows an equivalent circuit diagram 150 of the circuit arrangement 100 from Fig. 3 at positive operating voltage (U+ > U-). The diagram shows the diodes D1 110 and D2 112, the capacitors or partial capacitors C1 120, C2 122, and C3 124, and the resistors R1 130 and R2 132.

[0022] It should be noted that the voltages across all three capacitor sections are positive. No direct current flows, meaning no standby current. The voltages across C1 120, C2 122, and C3 124 may eventually equalize to the voltage between U+ and U- over a longer period of time.

[0023] Fig. 5 shows an equivalent circuit diagram 200 of the circuit arrangement 100 from Fig. 3 with negative polarity reversal of the operating voltage (U+ < U-). Note that in this circuit diagram, the positive potential is at the bottom (reference number 104) and the negative potential is at the top (reference number 102). The diagram shows diodes D3 114 and D4 116, capacitors or partial capacitors C1 120, C2 122, and C3 124, and resistors R1 130 and R2 132.

[0024] The voltages across partial capacitors C1 120 and C2 122 are negative, but clamped to the diode forward voltages of diodes D3 114 and D4 116, i.e., less than 1V. The voltage across partial capacitor C3 124 is positive (approximately U- - U+). A small reverse polarity current flows through paths R1 / D3 and D4 / R2. The current level can be regulated or limited via the high-resistance resistors R1 130 and R2 132. It should be noted that a particularly small quiescent current is permissible or acceptable in a vehicle control unit due to reverse polarity.

[0025] Fig. 6 shows a small-signal alternating current equivalent circuit 250 of the circuit arrangement 100. The illustration shows the partial capacitors C1 120, C2 122 and C3 124 as well as the resistors R1 130 and R2 132.

[0026] It should be noted that the AC voltage amplitude is smaller than the forward voltage of the diodes D1 110 and D2 112. For alternating currents, the path via C1 120, C2 122 and C3 124 is available. Neglecting the resistances (R→∞) results in a total capacitance of Ctotal=1 / (1 / C1+1 / C2+1 / C3), at C1=C2=C3=C→Ctotal=C / 3.

[0027] Fig. Figure 7 shows a large-signal alternating current equivalent circuit 300 of the circuit arrangement 100. The illustration shows the diodes D1 110 and D2 112, the capacitors C1 120, C2 122 and C3 124 as well as the resistors R1 130 and R2 132.

[0028] At high AC voltage amplitudes on the operating voltage, the diodes D1 110 and D2 112 become temporarily conductive and can thus cause distortions in the total current, leading to non-ideal capacitor behavior. This is exemplified by C1=C2=C3 at>3 / 2 the forward voltage of diodes D1 110 and D2 112. One remedy, in the event that this is disruptive, e.g., with regard to electromagnetic compatibility (EMC), is to increase the forward voltages of diodes D1 110 and D2 112. This can be achieved, for example, by connecting several diodes in series or by diode / Zener diode combinations. However, the AC current path via the three capacitors C1 120, C2 122, and C3 124 is still available.

[0029] As an alternative to the diodes D1 110 and D2 112, in order to increase the threshold for switching through and to avoid distortions of the total current at high AC voltage amplitudes, two or more diodes can be connected in series or a diode / Z-diode combination can be used.

[0030] Discrete diodes or a bridge rectifier, i.e. four diodes in one package, could be used as the diode network. Fig. 8 possible realizations of a diode 400 by an arrangement 410 of two series-connected diodes 412 and 414, an arrangement 420 with three series-connected diodes 422, 424, 426 and an arrangement 430 of a diode 432 and a series-connected Zener diode 434.

[0031] The circuit arrangement presented has, at least in some of the versions, a number of advantages: In contrast to a single capacitor, in the circuit arrangement presented, none of the partial capacitors has a high negative voltage at negative reversed polarity operating voltage. Compared to the Fig. In the circuit arrangement 10 presented in Figure 1, no negative voltage is applied to any of the partial capacitors during normal operation, ie at a positive operating voltage. In contrast to the use of a bipolar electrolytic capacitor explained at the beginning, the applied voltage does not have to be a pure alternating voltage without DC components. In contrast to the proposal, which requires approval from the manufacturer, there is no need to obtain approval from the manufacturer for reversed polarity operation of the capacitor, if such approval were to be granted at all.

[0032] It should be noted that at operating voltages with high AC amplitudes, distortions in the total current may occur because diodes D1 and D2 become conductive. This means that the circuit no longer has pure capacitor behavior. To compensate for this, according to the suggestion from Fig. 8 should be followed.

Claims

[1] Circuit arrangement for implementing a capacitor (50), with at least three partial capacitors (80, 82, 84, 120, 122, 124) connected in series in the alternating current equivalent circuit, and a rectifier (118) with components which are assigned to the partial capacitors (80, 82, 84, 120, 122, 124) in such a way that, in the case of a reversed polarity of the operating voltage applied to the circuit arrangement (60, 100), a negative voltage applied to at least two of the partial capacitors (80, 82, 84, 120, 122, 124) is limited. [2] Circuit arrangement according to claim 1, wherein the rectifier (118) is implemented by a bridge rectifier (62). [3] Circuit arrangement according to claim 1, in which diodes (70, 72, 74, 76, 110, 112, 114, 116, 400, 412, 414, 422, 424, 426, 432) are used as components of the rectifier (118). [4] Circuit arrangement according to claim 3, in which at least one of the diodes (70, 72, 74, 76, 110, 112, 114, 116, 400, 412, 414, 422, 424, 426, 432) is realized by a series connection of several diodes (70, 72, 74, 76, 110, 112, 114, 116, 400, 412, 414, 422, 424, 426, 432). [5] Circuit arrangement according to claim 3, in which at least one of the diodes (70, 72, 74, 76, 110, 112, 114, 116, 400, 412, 414, 422, 424, 426, 432) is realized by a series circuit of at least one diode (70, 72, 74, 76, 110, 112, 114, 116, 400, 412, 414, 422, 424, 426, 432) and at least one Zener diode (434). [6] Circuit arrangement according to one of claims 1 to 5, in which the capacitor (50) is designed to be operated as part of a filter directly on an on-board network voltage. [7] Circuit arrangement according to one of claims 1 to 6, in which additional resistors (90, 92, 130, 132) are provided in order to set a current level in the circuit arrangement (60, 100). [8] On-board network with a circuit arrangement (60, 100) according to one of claims 1 to 7. [9] On-board network according to claim 8, wherein the capacitor (50) implemented by the circuit arrangement (60, 100) is to be operated as part of a filter directly on an on-board network voltage.

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