Improved reverse polarity protection circuit

Abstract

An electrical load (1) is to be supplied with an electrical DC voltage (U) via two connections (2, 3). The two connections (2, 3) are connected to one another via a diode assembly (6) which permits a current flow across the diode assembly (6) in a forward direction of the diode assembly (6) while preventing a current flow across the diode assembly (6) in a reverse direction of the diode assembly (6). A protection circuit (11) has a harvester circuit (8) and a switch assembly (9), the switch assembly (9) being connected in parallel with the diode assembly (6). The harvester circuit (8) is coupled to the diode assembly (6) and absorbs energy whenever a current flow occurs across the diode assembly (6) and stores same as electrical energy. Whenever the stored electrical energy reaches an upper storage level (N1), the harvester circuit (8) actuates the switch assembly (9) such that the switch assembly (9) bridges the diode assembly (6) with low resistance, and whenever the stored electrical energy drops to a lower storage level (N2) below the upper storage level (N1), the harvester circuit (8) actuates the switch assembly (9) such that the switch assembly (9) no longer bridges the diode assembly (6) with low resistance.

Description

[0001] Description

[0002] Improved reverse polarity protection circuit

[0003] The present invention relates to a protective circuit for an electrical load that is to be supplied with a DC voltage via two terminals, wherein the two terminals are connected to each other via a diode arrangement that allows current flow through the diode arrangement in a forward direction while preventing current flow through the diode arrangement in a reverse direction. The reverse direction is, of course, opposite to the forward direction.

[0004] The diode arrangement can be a standalone diode or diode assembly specifically designed for this purpose. Alternatively, it can be a diode arrangement that is part of another device and arises incidentally, so to speak. For example, the diode arrangement can be implemented as part of a half-bridge circuit containing series-connected switching elements, each with a diode connected in parallel. This applies equally to the prior art and to the present invention.

[0005] Such a reverse polarity protection circuit is generally known. For example, reference can be made to the entry "Reverse polarity protection" in the German Wikipedia, accessed on June 24, 2024.

[0006] The protection circuit of the state of the art functions perfectly in principle. However, it can happen that if the DC voltage is connected incorrectly to the terminals, the current is limited by the DC voltage source supplying the terminals. This can result in the current being limited to a value at which a fuse does not trip. In this case, a high current flows through the diode arrangement for an extended period, causing a corresponding power loss with all its associated negative consequences. This power loss can amount to several watts. For example, if the forward voltage is 1 V and the current from the voltage source is limited to 50 A, the resulting power loss is 50 W.The object of the present invention is to create possibilities by which the power loss can be reduced even in the case where a fuse which would completely interrupt the current flow has not yet tripped.

[0007] The problem is solved by a protective circuit with the features of claim 1. Advantageous embodiments of the protective circuit are the subject of dependent claims 2 to 9.

[0008] According to the invention, a protective circuit of the type mentioned above is designed by:

[0009] - that the protection circuit includes a harvester circuit and a switch arrangement,

[0010] - that the switch arrangement is connected in parallel with the diode arrangement,

[0011] - that the harvester circuit is coupled to the diode arrangement and absorbs energy and stores it as electrical energy whenever a current flows through the diode arrangement,

[0012] - that the harvester circuit always activates the switch arrangement whenever the stored electrical energy reaches an upper storage level, so that the switch arrangement bridges the diode arrangement with low resistance, and

[0013] - that whenever the stored electrical energy falls to a lower storage level below the upper storage level, the harvester circuit activates the switch arrangement, so that the switch arrangement no longer bridges the diode arrangement with low resistance.

[0014] As a result, the high current continues to flow during the period in which the switch arrangement bypasses the diode arrangement. However, the voltage drop across the switch arrangement is no longer the forward voltage of the diode arrangement, but a significantly lower value, for example, only 10% of the forward voltage. Due to the considerably lower voltage, the resulting power loss is also reduced accordingly. Furthermore, with a suitable choice of harvester circuit and switch arrangement, it is readily possible to ensure that the period during which the switch arrangement bypasses the diode arrangement with low resistance is considerably longer than the period during which the switch arrangement does not bypass the diode arrangement with low resistance.

[0015] Energy harvesting is a well-known phenomenon. Specifically, it refers to the extraction of small amounts of electrical energy from readily available sources such as ambient temperature, vibrations, or air currents for low-power mobile devices. The structures used for this purpose are sometimes called nanogenerators. See the relevant entries for "energy harvesting". 1 references can be found in the German and English Wikipedia, accessed on 01.07.2024.

[0016] Preferably, the switch arrangement comprises voltage-controlled switching elements. Voltage-controlled switching elements have the advantage that they require hardly any electrical power apart from the switching itself.

[0017] It is possible that the voltage-controlled switching elements are designed as IGBTs or the like. Preferably, however, the voltage-controlled switching elements are designed as field-effect transistors.

[0018] The type of field-effect transistor can be chosen according to requirements. Preferably, the field-effect transistors are MOSFETs.

[0019] It is possible for the harvester circuit to be thermally coupled to the diode array, absorbing energy as thermal energy and converting it into electrical energy. For example, such a thermal coupling of the harvester circuit can be achieved using a Peltier element. A purely thermal coupling to the diode array has the advantage that any current flow through the harvester circuit, which might occur if the DC voltage were properly connected to the terminals, does not need to be considered.

[0020] Alternatively, the harvester circuit can be electrically coupled to the diode array and absorb the energy directly as electrical energy. In this case, the harvester circuit is electrically connected in parallel with the diode array. This design offers advantages in terms of energy efficiency.

[0021] In the case of electrical coupling of the harvester circuit to the diode arrangement, the harvester circuit is preferably equipped with a protective device that connects the harvester circuit to at least one of its two terminals with high resistance when the diode arrangement prevents current flow in the reverse direction, and to both terminals with low resistance when the diode arrangement allows current flow in the forward direction. This design protects the harvester circuit when the DC voltage is correctly connected to the terminals. Preferably, the protective device comprises a diode and a switch connected in parallel to the diode, the switch being controlled by the harvester circuit. This maximizes the amount of energy that can be "harvested" by the harvester circuit in the event of an incorrect connection of the DC voltage to the terminals.

[0022] Preferably, the harvester circuit either directly absorbs the energy as electrical energy at a lower voltage level or converts the absorbed energy to electrical energy at the lower voltage level. Furthermore, the harvester circuit preferably includes an actuator that converts the electrical energy from the lower voltage level to an upper voltage level that is higher than the lower voltage level. Finally, the harvester circuit preferably stores the stored electrical energy at the upper voltage level. This configuration is particularly efficient.

[0023] The properties, features, and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more readily understandable in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings. These show, in schematic representation:

[0024] FIG 1 a block diagram,

[0025] FIGS. 2 and 3 Switch arrangements,

[0026] FIGS. 4 and 5 Time diagrams,

[0027] FIGS. 6 and 7 Block diagrams,

[0028] FIG 8 a protective device and

[0029] FIGS. 9 and 10 Block diagrams.

[0030] According to FIG. 1, an electrical load 1 is to be supplied with a DC voltage U via two terminals 2 and 3. Terminal 2 is to have the higher potential and is therefore marked with “+”. Consequently, terminal 3 is to have the lower potential and is therefore marked with marked. A fuse 5 is usually installed in the lines 4 from terminals 2, 3 to the load 1.

[0031] It can happen that the potentials are accidentally connected to the wrong terminals 2 and 3, i.e., that terminal 2 is connected to the lower potential and terminal 3 to the higher potential. This is indicated in FIG. 1 by the fact that, in addition to the "+" in parentheses, terminal 2 is also shown, and similarly, terminal 3 is also shown in addition to the "+" in parentheses. To protect the load 1 from the incorrectly polarized DC voltage U in such a case, the two terminals 2 and 3 are connected to each other via a diode arrangement 6. In the simplest case, the diode arrangement 6 is designed as a single diode.

[0032] The diode arrangement 6 allows current to flow through it in a forward bias, while it prevents current flow in a reverse bias. In this case, the forward bias is from terminal 3 to terminal 2, and the reverse bias is from terminal 2 to terminal 3. Therefore, if the potentials are correctly connected to terminals 2 and 3, the diode arrangement 6 prevents current flow, resulting in a DC voltage drop across the diode arrangement 6 and supplying the load with this DC voltage. However, if the potentials are incorrectly connected to terminals 2 and 3, the diode arrangement 6 allows current flow, resulting in only the forward voltage drop across the diode arrangement 6. The forward voltage is typically around 1 V. Consequently, a high current flows through the diode arrangement 6.

[0033] In many cases, the current will be so high that fuse 5 trips, thus completely interrupting the current flow. In other cases, the current is limited by a voltage source (not shown) that provides the DC voltage U. In such cases, it can happen that the current is high, but not high enough to trip fuse 5, or at least not immediately. In this case, a relatively high power dissipation occurs continuously, or at least for an extended period, at the diode arrangement 6.

[0034] To reduce this power loss, a protective circuit 7 is also provided. The protective circuit 7 comprises a harvester circuit 8 and a switch arrangement 9. The switch arrangement 9 is connected in parallel to the diode arrangement 6. According to FIGS. 2 and 3, the switch arrangement 9 has voltage-controlled switching elements 10. FIGS. 2 and 3 show the particularly preferred embodiment in which the voltage-controlled switching elements 10 are field-effect transistors, specifically MOSFETs. The number of switching elements 10 can be determined as required. In the minimal case, as shown in FIGS. 2 and 3, only a single switching element 10 is present. If several switching elements 10 are present, they are generally connected in parallel. The harvester circuit 8 is coupled to the diode arrangement 6. The harvester circuit 8 absorbs energy whenever a current flows through the diode arrangement 6 and stores it as electrical energy.FIG. 4 shows the course of a level N of stored electrical energy as a function of time t. In FIG. 4 and also in FIG. 5, it is always assumed that the potentials are "incorrectly" connected to terminals 2 and 3.

[0035] The incorrect application of the DC voltage U begins at time t1, as shown in FIG. 4. From this time, the energy level N rises until it reaches an upper energy level N1 at time t2. Reaching this upper energy level causes the harvester circuit 8 to activate the switch assembly 9, which then bypasses the diode assembly 6 with a low-impedance connection. Therefore, as shown in FIG. 5, the switch assembly 9 changes from the off state to the on state at time t2. The change from the off state to the on state is depicted in FIG. 5 as requiring a certain time interval. However, in practice, this time interval is very short and practically negligible. The transient state of the switch assembly 9, during which power is lost, is therefore very brief.Rapid attainment of the fully switched-on state can be achieved, for example, by selecting a suitable switching signal for controlling the switch assembly 9, such as +10 V. However, controlling the switch assembly 9 requires a certain amount of energy. Therefore, the level N drops slightly immediately after time t2.

[0036] By bridging the diode arrangement 6, the voltage drop is now determined by the switch arrangement 9. The voltage drop can be considerably lower than the forward voltage of the diode arrangement 6. For example, it can be 100 mV and in some cases even lower. Accordingly, the power dissipation decreases, since the current, although still high, does not increase compared to the previous state.

[0037] It is possible that keeping the switch assembly 9 in the on state requires very little energy (ideally no energy at all). Therefore, after the switch assembly 9 is switched, the level N continues to decrease only very, very slowly. It may even be possible that the remaining amount of energy that the harvester circuit 8 can harvest when the switch assembly 9 is switched on can continuously compensate for the energy loss.

[0038] It is subsequently assumed that the level N at time t3 is at a lower level

[0039] The energy level N2 has dropped below the upper energy level N1. This drop to the lower energy level N2 causes the harvester circuit 8 to re-energize the switch assembly 9, but this time in such a way that the switch assembly 9 no longer bridges the diode assembly 6 with a low impedance, as shown in FIG. 5. Therefore, as shown in FIG. 5, the switch assembly 9 changes from the on state to the off state at time t3. The change from the on state to the off state is depicted in FIG. 5 as requiring a certain time interval. In practice, however, this time interval is very short and practically negligible. The transient state of the switch assembly 9, during which power is lost in the switch assembly 9, is therefore again very brief.The rapid achievement of the fully locked state can be achieved, for example, by selecting a suitable switching signal for controlling the switch arrangement 9, for example, at 0 V.

[0040] However, controlling the switch arrangement 9 still requires a certain amount of energy. Therefore, the energy level N drops slightly immediately after time t3. The lower energy level N2 must therefore be determined such that the harvester circuit 8 can still provide this switching energy.

[0041] From time t3 onwards, the cycle described above begins again. This is because the forward voltage across the diode arrangement 6 drops again. As a result, the harvester circuit 8 can "harvest" energy again until level N reaches the upper energy level N1 again.

[0042] As shown in FIG. 6, the harvester circuit 8 can be thermally coupled to the diode arrangement 6. In this case, the harvester circuit 8 absorbs the energy as thermal energy and converts it into electrical energy. For example, the harvester circuit 8 can have a Peltier element for absorbing the thermal energy, which is thermally coupled to the diode arrangement 6. A connection between the harvester circuit 8 and one of the lines 4 is still possible to set the harvester circuit 8 to a defined potential. Alternatively, the switch arrangement 9 could be controlled, for example, via an optocoupler.

[0043] As shown in FIG. 7, as an alternative to the configuration in FIG. 6, the harvester circuit 8 can be electrically coupled to the diode arrangement 6. In this case, the harvester circuit 8 is electrically connected in parallel to the diode arrangement 6 and absorbs the energy directly as electrical energy. In the case of electrical coupling to the diode arrangement 6, a protective device 11 is preferably associated with the harvester circuit 8. The protective device 11 connects the harvester circuit 8 to at least one of the two terminals 2, 3 with a high resistance when the diode arrangement 6 prevents current flow in the reverse direction, i.e., when the DC voltage U is correctly applied to the terminals 2, 3. Conversely, the protective device 11 connects the harvester circuit 8 to both terminals 2, 3 with a low resistance when the diode arrangement 6 allows current flow in the forward direction, i.e., when the DC voltage U is incorrectly applied to the terminals 2, 3.The protective device can, for example, comprise a diode 12 and a switch 13 connected in parallel to the diode 12, as shown in FIG. 8. In this case, the switch 13 is controlled by the harvester circuit 8. The switch 13 is preferably designed analogously to the switching elements 10.

[0044] According to FIG. 9, the harvester circuit 8 includes an actuator 14. The actuator 14 converts electrical energy from a lower voltage level U1 to an upper voltage level U2, which is higher than the lower voltage level U1. The actuator 14 thus acts as a boost converter. The upper voltage level U2 is the voltage level at which the harvester circuit 8 stores the stored electrical energy. The lower voltage level U1 is the voltage level at which the harvester circuit 8 directly absorbs the energy in the configuration shown in FIG. 7. In the configuration shown in FIG. 6, the lower voltage level U1 is the voltage level generated by the harvester circuit 8 when converting the absorbed energy into electrical energy. The same applies to other situations in which the harvester circuit 8 converts absorbed energy into electrical energy.

[0045] FIG 10 shows an embodiment of the circuit arrangement of FIG 1, in which the harvester circuit 8, as shown in FIG 7, is electrically coupled to the diode arrangement 6 and includes the protective device 11 of FIG 8 and the actuator 14 of FIG 9. According to FIG 10, in addition to the capacitors 15 of the actuator 14, a further storage capacitor 16 is present. Furthermore, a pulse generator 17 is present, which generates the switching signals for the switch arrangement 9 and the switch 13. The harvester circuit 8 also generates an auxiliary voltage II' if such an auxiliary voltage LT is required for controlling the switch 13. Finally, the harvester circuit 8 generates a so-called "power good" signal, which is supplied to the pulse generator 17 so that the pulse generator 17 can generate the corresponding switching signals at the correct times t2 and t3.The further construction of the harvester circuit 8 can be of a conventional nature. In particular, integrated circuits are known which include suitable harvester circuits 8. The present invention has many advantages. In particular, the power loss in the event of an incorrect connection of the DC voltage U can be significantly reduced. This prevents damage even in the case of reverse polarity with currents that would not trip a fuse. Although the invention has been illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples, and other variations can be derived from them by those skilled in the art without departing from the scope of protection of the invention.

Claims

Patent claims 1. Protection circuit for an electrical load (1) which is to be supplied with an electrical DC voltage (II) via two terminals (2, 3), wherein the two terminals (2, 3) are connected to each other via a diode arrangement (6) which allows a current flow through the diode arrangement (6) in a forward direction of the diode arrangement (6) while preventing a current flow through the diode arrangement (6) in a reverse direction of the diode arrangement (6), - wherein the protection circuit comprises a harvester circuit (8) and a switch arrangement (9), - wherein the switch arrangement (9) is connected in parallel to the diode arrangement (6), - wherein the harvester circuit (8) is coupled to the diode arrangement (6) and absorbs energy and stores it as electrical energy whenever a current flow occurs through the diode arrangement (6), - wherein the harvester circuit (8) always activates the switch arrangement (9) when the stored electrical energy reaches an upper storage level (N1), so that the switch arrangement (9) bridges the diode arrangement (6) with low resistance, and - wherein whenever the stored electrical energy falls to a lower storage level (N2) below the upper storage level (N1), the harvester circuit (8) controls the switch arrangement (9), so that the switch arrangement (9) no longer bridges the diode arrangement (6) with low resistance.

2. Protective circuit according to claim 1, characterized in that the switch arrangement (9) has voltage-controlled switching elements (10).

3. Protection circuit according to claim 2, characterized in that the voltage-controlled switching elements (10) are field-effect transistors.

4. Protection circuit according to claim 3, characterized in that the field-effect transistors are MOSFETs.

5. Protective circuit according to one of claims 1 to 4, characterized by , that the harvester circuit (8) is exclusively thermally coupled to the diode arrangement (6), absorbs the energy as thermal energy and converts the thermal energy into electrical energy.

6. Protection circuit according to one of claims 1 to 4, characterized in that the harvester circuit (8) is electrically coupled to the diode arrangement (6) and directly absorbs the energy as electrical energy.

7. Protection circuit according to claim 6, characterized in that a protection device (11) is assigned to the harvester circuit (8), which connects the harvester circuit (8) to at least one of the two terminals (2, 3) with high resistance when the diode arrangement (6) prevents current flow in the reverse direction, and connects it to both terminals (2, 3) with low resistance when the diode arrangement (6) allows current flow in the forward direction.

8. Protection circuit according to claim 7, characterized in that the protection device (11) comprises a diode (12) and a switch (13) connected in parallel to the diode (12) and that the switch (13) is controlled by the harvester circuit (8).

9. Protection circuit according to one of the above claims, characterized in that the harvester circuit (8) directly receives the absorbed energy as electrical energy at a lower voltage level (U1) or converts the absorbed energy to electrical energy at the lower voltage level (U1), that the harvester circuit (8) comprises an actuating device (14) which converts the electrical energy from the lower voltage level (U1) to an upper voltage level (U2) which is higher than the lower voltage level (U1), and that the harvester circuit (8) stores the stored electrical energy at the upper voltage level (U2).

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