LU101883B1 - Circuit arrangement for limiting an inrush current - Google Patents

Abstract

A circuit arrangement 10 for limiting an inrush current is proposed, among other things, which has a single inductance (20), a single capacitor (24), a first diode (23), a first electronic switch (30), an auxiliary voltage source (40) for providing a DC voltage and a control device (50) which is designed in particular for driving the first electronic switch (30) in such a way that an inrush current flowing into the single capacitor (24) when it is switched on can be limited to a predeterminable current value. The auxiliary voltage source (40), the first electronic switch (30) and the control device (50) are interconnected in such a way that they have a common reference potential.

Description

Circuit arrangement for limiting an inrush current description

The invention relates to a circuit arrangement for limiting an inrush current.

It is known that an electrical load with a capacitive input impedance draws high inrush currents when it is switched on.

One reason for this is that the internal capacitors of the electrical consumer are initially discharged and therefore behave like a short circuit when the device is switched on, resulting in a high

Inrush current builds up, but decreases as the internal capacitors charge.

A high inrush current must be limited, in particular to prevent the components of the electrical load and, for example, accidental triggering of protective elements in the

to avoid a load circuit.

At low power levels, a resistor can be connected in series with the capacitors of a capacitive load as a thermistor to limit the inrush current.

which is bypassed by a switch, in particular a relay, when the capacitors are charged.

However, the resistance must be matched to the capacitance of the capacitors in order to be able to withstand the corresponding amount of energy.

In addition, high electrical losses can occur.

Furthermore, relays are less suitable for bridging the resistance at high voltages and large currents.

It is also known to use a step-down converter as clocked inrush current limitation, the switching element of which can be controlled in such a way that the charging current of the internal capacitors of an electrical load can be limited in a targeted manner.

Such a buck converter is known, for example, from DE 10 2005 002 360 A1. | However, the known step-down converters have the circuit-related disadvantage that their switches and the control electronics provided for driving the switch do not have a common reference potential.

Consequently, the switch has to be driven in an isolated manner, for example by means of an isolated gate driver.

In addition, the switch and the control electronics require different voltage sources.

The invention is therefore based on the object of creating a circuit arrangement for limiting an inrush current, which can be operated with a low power loss during switch-on, which enables simple control of the switches and also requires fewer components.

A further aspect can be seen in the fact that the circuit arrangement can be operated properly even with high input voltages, which are 800V, for example.

The above technical problem is solved by the features of claim 1.

Advantageous developments are the subject of the subclaims.

The invention is explained in more detail below using a few exemplary embodiments in conjunction with the accompanying drawings. 1 shows an exemplary embodiment of a circuit arrangement according to the invention, which can perform a buck converter functionality, and | 2 shows an exemplary embodiment of a | 10 circuit arrangement according to the invention, which compared to the circuit arrangement shown in FIG. 1 has been extended by a step-up converter functionality.

FIG. 1 shows an exemplary circuit arrangement 10 which is preferably designed to limit the current flowing into a capacitor 24 in a targeted manner at the moment when it is switched on, i.e. when a voltage is applied to a first input connection 21 and to a second input connection 22. A mains plug can be connected to the input connections 21 and 22 for this purpose. If the input connections 21 and 22 are hardwired, for example, they can be switched on by means of an upstream main/protective circuit breaker. The circuit arrangement 10 shown as an example in FIG. 1 can, for example, be part of a switched-mode power supply.

The exemplary circuit arrangement 10 has an input with the first input connection 21 and the second input connection 22, to which a DC voltage can be applied, for example, at the moment of switching on. Furthermore, the circuit arrangement 10 has an output with a first output connection 25 and a second

Output terminal 26 to which a DC voltage can be provided. Furthermore, the circuit arrangement 10 has a single inductance 20 which can function as a storage inductor. A single capacitor 24, a first diode 23 and a first electronic switch 30 are also provided. With regard to the single inductor 20, the first diode 23 functions in a known manner as a freewheeling diode. Furthermore, a control device 50 is provided, which can contain a microcontroller, for example. The control device 50 is designed in particular to switch the first electronic switch 30 on and off and advantageously has the effect that an inrush current flowing into the capacitor 24 when it is switched on can be limited to a predeterminable current value. The single inductance 20 is electrically connected directly or indirectly to the first input connection 21 and the first output connection 25 .

In other words: the single inductance 20 is connected in a current path 29 which is electrically connected to the first input connection 21 and the first output connection 25 .

The single capacitor 24 is connected in series with the first electronic switch 30, with a first terminal of the single capacitor 24 connected to the first output terminal 25 and a first terminal 32 of the first electronic switch 30 connected to both the second input terminal 22 and the second output terminal 26 is connected. The second input connection 22 and the second output connection 26 are at a common reference potential, which can be ground (GND), for example. Furthermore, the cathode terminal of the first diode 23 is connected to the first input terminal 21 while the anode terminal of the first diode 23 is connected to a common connection point 5 27 of the single capacitor 24 and the first electronic switch 30 . A first connection 42 of an auxiliary voltage source 40 is connected to the second input connection 22 and the second output connection 26 , while a second connection 41 of the auxiliary voltage source 40 is connected to the control device 50 and a further connection 33 of the control device 50 . In particular, the first connection 42 of the auxiliary voltage source 40 is connected to the common reference potential of the control device 50 and the first electronic switch 30 , while an operating potential VCC is present at the connection 41 of the auxiliary voltage source 40 . The auxiliary voltage source 40 preferably provides a DC voltage.

The first electronic switch 30 can be a field effect transistor, for example an n-channel MOSFET. In this case, the first connection 32 of the first electronic switch 30 forms a source connection, the further connection 33 a gate connection, a third connection 31 a drain connection and a fourth connection 34 a bulk connection. The gate connection 33 functioning as a control input is connected to an output Gl of the control device 50 via which the control device 50 sends out corresponding control signals for driving the electronic switch 30 . The clocked control of the switch 30 by the control device 50 is shown symbolically in Figure 1 by a positive pulse between the

Gate terminal 33 and the voltage terminal 41 of the auxiliary voltage source 40 is located.

The drain connection 31 of the control device 50 is connected to a second connection of the single capacitor 24,

while the source terminal 32 is connected to the second input terminal 22 and the second output terminal 26 .

The control device 50 is connected via a connection GND to the second input connection 22, the second output connection 26 and the ground connection 42 of the

Auxiliary voltage source 40 connected.

As a result, they lie

Auxiliary voltage source 40, the electronic switch 30 and the control device 50 at a common reference potential.

Accordingly, the electronic switch 30 and the controller 50 by a single

Auxiliary voltage source, namely the auxiliary voltage source 40 are supplied with energy.

In addition, the control device 50 can control the switch 30 directly.

As already noted, the circuit arrangement 10 has the further advantage that a current which is lower than the input current of the circuit arrangement 10 flows in the capacitor path has a lower power loss than conventional step-down converters.

For example, a resonant converter, for example an LLC converter, can be connected to the output connections 25 and 26 , the switching elements of which can also be supplied with energy from the auxiliary voltage source 40 .

This shows a further advantage of the circuit arrangement 10, whose auxiliary voltage source 40 can supply energy not only to the control device 50 and the first electronic switch 30, but also to the components of a downstream circuit. In order to obtain at the output terminals 25 and 26 an increased | To make voltage available, the circuit arrangement 10 can be expanded, for example, by a step-up converter functionality. A correspondingly expanded exemplary circuit arrangement 70 is shown in FIG. 2, the components which are also implemented in the circuit arrangement 10 being provided with the same reference symbols in FIG. The circuit arrangement 70 has a second diode 28 and a second electronic switch 80 in addition to the components of the circuit arrangement 10 . It should be noted that circuit arrangement 70, which has a buck converter and a boost converter functionality, requires only a single inductor, namely inductor 20, a single capacitor, namely capacitor 24, and a single auxiliary voltage source, namely auxiliary voltage source 40. One can also say that the circuit arrangement 70 is a boost inrush buck circuit.

With regard to the circuit arrangement 70, only the supplements or circuit-related changes compared to the circuit arrangement 10 are explained below.

The second diode 28 is connected in series with the single inductor 20 in the current path 29 , the cathode connection of the second diode 28 being connected to the first output connection 25 . A first connection 81 of the second electronic switch 80 is connected to the anode connection of the second diode 28 which in turn is connected to a connection of the inductor 20 . A second connection 82 of the second electronic switch 80 is connected to the second input connection 22 and the second output connection 26 .

The circuit arrangement 70 has a control device 50' | on, in which the functionality of the control device 50 is implemented. In addition to a control output G1, a ground connection GND and a supply connection VCC, the control device 50' also has a further control output G2, via which the control device 50" can control the second electronic switch 80, in particular switching it on and off. The control output Gl is connected to the first electronic switch 30, as previously described in connection with FIG.

As FIG. 2 also shows, the connection 41 of the auxiliary voltage source 40 is connected to the supply connection VCC of the control device 50 ′ and a control connection 83 of the electronic switch 80 .

Like the first electronic switch 30, the second electronic switch 80 can be a field effect transistor, for example an n-channel MOSFET. In this case, the second electronic switch 80 has a

TTS

Gate connection 83 which is connected to the control output G2 of the control device 50'. Furthermore, the second electronic switch 80 designed as a field effect transistor has a drain connection 81 which is connected to the anode connection of the second diode 28 . The source connection 82 of the second electronic switch is connected to the second input connection 22 and the second output connection 26 . A Kelvin connection 84 is also connected to the second input connection 22 and the second output connection 26 . The ground connection 42 of the auxiliary voltage source 40 is connected to the ground connection GND of the control device 50', while the operating voltage connection 41 is connected to the supply connection VCC of the control device 50'.

As already mentioned in connection with FIG. 1, the clocked operation of the switches 30 and 80 is represented by a switching block 100 or 101 representing a pulse. The switching block 100 is connected to the gate connection 83 and the switching block 101 to the gate connection 33 . The switching blocks 100 and 101 can each be implemented by a controllable gate driver, for example. In this case, both switching blocks 100 and 101 are each connected to the connection 41 of the auxiliary voltage source 40, the switching block 100 also being connected to the control output G2 and the switching block 101 to the control output Gl of the control device 50'.

The functioning of the circuit arrangement 70 shown in FIG. 2 is explained in more detail below.

It is assumed that the circuit arrangement 10 has been switched on, i.e. a DC voltage is present at the input terminals 21 and 22, for example.

The control device 50' is designed to keep the second electronic switch 80 open during the switch-on phase, while the first electronic switch 30 is used to limit the current in the capacitor 24 | is switched on and off so that the output current can be limited to a predeterminable current value. For this purpose, the control device 50' can apply a pulse or activation pattern to the electronic switch 30, as a result of which a current can be set with which the single capacitor 24 is charged. As soon as the capacitor 24 is charged and the voltage across the capacitor 24 thus corresponds to the input voltage, the electronic switch 30 is permanently switched on by means of the control device 50'. The control device 50' can then ensure that the second electronic switch 80 is clocked and can thus fulfill the function of a power factor compensation. At least some of the aspects explained above are summarized below in connection with the figures.

An exemplary circuit arrangement 10, shown in FIG. 1, for limiting an inrush current and an exemplary circuit arrangement 70, shown in FIG. PT &

~ a first diode 23, ~ a first electronic switch 30, - an auxiliary voltage source 40 for providing a DC voltage, - an input with a first input terminal 21 and a second input terminal 22, - an output with a first output terminal 25 and | a second output connection 26, and - a control device 50 or 50', which is used for switching on and off

Switching off the first electronic switch 30 is designed in such a way that an inrush current flowing into the single capacitor 24 when the circuit arrangement 10 is switched on can be limited to a predeterminable current value,

wherein the single inductor 20 is connected in a current path 29 which is connected to the first input terminal 21 and the first output terminal 25, wherein the single capacitor 24 is connected in series with the first electronic switch 30, wherein a first

Connection of the single capacitor 24 is connected to the first output connection 25 and a first connection 32 of the first electronic switch 30 is connected to the second input connection 22 and to the second output connection 26, the second input connection 22 and the second output connection 26 being at a common reference potential, the cathode terminal of the first diode 23 being connected to the first input terminal 21 and the anode terminal of the first diode 23 being connected to a common connection point

27 of the single capacitor 24 and the first electronic switch 30 is connected, and wherein a first terminal 42 of the auxiliary voltage source 40 to the second input terminal 22, with the second

EEE.

Output connection 26 and is connected to the control device 50 or 50', and wherein the control device 50 or 50' is connected to a second connection 41 of the auxiliary voltage source 40. | 5 It should be noted once again that switching on the circuit arrangement 10 means that a voltage is applied to the input terminals 21 and 22 . Advantageously, the first electronic switch 30 can be a field effect transistor, the gate terminal 33 of which is connected to the control device 50, the drain terminal 31 of which is connected to a second terminal of the single capacitor 24, and the first terminal of which is a source terminal 32 which is connected to the second input terminal 22 and the second output terminal 26 is connected.

The circuit arrangement 10 or 70 is advantageously characterized, among other things, by the fact that the first electronic switch 30 and the control device 50 or 50' have a common electrical reference point, so that the first electronic switch 30 can be operated directly by the control device 50 or 50. ' can be controlled.

In this respect, the mode of operation of the circuit arrangement 10 or 70 preferably corresponds to that of a conventional step-down converter.

The circuit arrangement 70 can advantageously have a second diode 28 and a second electronic switch 80, the second diode 28 being connected in series with the single inductor 20, the cathode connection of the second diode 28 being connected to the first

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Output terminal 25 is connected, wherein a first terminal 81 of the second electronic switch 80 is connected to the anode terminal of the second diode 28 and a second terminal 82 of the second electronic switch 80 is connected to the second input terminal 22 and the second output terminal 26 | is connected, and wherein the control device 50' can be designed to switch the second electronic switch 80 on and off.

In this way, a circuit arrangement 70 is created which is based on a step-down converter-step-up converter topology, also known as boost and buck technology. It should also be noted at this point that the circuit arrangement has the further advantage over a conventional step-down converter that the current in the capacitor path is lower than the total input current. The extension of the circuit arrangement 10 or 70 by a step-up converter advantageously serves to ensure that in normal operation, i. H. after the end of the switch-on process, the circuit arrangement can carry out a power factor compensation, also referred to as power forward compensation (PFC), with regard to the switched-on load.

Expediently, the second electronic switch 80 can also be a field effect transistor whose gate connection 83 is connected to the control device 50 ′, whose first connection is the drain connection 81 and whose second connection is the source connection 82 . Advantageously, a circuit 60,

EEE, in particular, a resonant converter can be connected, it being possible for at least some electronic components of the circuit 60 to be supplied by means of the single auxiliary voltage source 40 .

Alternatively, an electrical load 90 can also be connected to the output 25, 26. The load 90, if present, can also be connected to the output of the circuit 60 | will.

It should also be noted that the single capacitor 24 can preferably have a capacitance between 50pF and 750uF and advantageously between 300pF and 750pF. The circuit arrangement 10 or 70 can be operated properly even with high input voltages of, for example, 800 V.

Claims (6)

patent claims First circuit arrangement (10; 70) for limiting an inrush current, comprising: - a single inductor (20), - a single capacitor (24), - a first diode (23), - a first electronic switch (30), - a Auxiliary voltage source (40) for providing a DC voltage, | - an input with a first input terminal (21) and a second input terminal (22), - an output with a first output terminal (25) and a second output terminal (26), and - a control device (50; 50 '), the one - and switching off the first electronic switch (30) is designed in such a way that an inrush current flowing into the single capacitor (24) when it is switched on can be limited to a predeterminable current value, the single inductor (20) being connected into a current path (29). , which is connected to the first input terminal (21) and the first output terminal 25), the single capacitor (24) being connected in series with the first electronic switch (30), a first terminal of the single capacitor (24) being connected to the first output connection (25) and a first connection (32) of the first electronic switch (30) both with the second input connection (22) and with the second output connection (2 6) is connected, wherein the second input port (22) and the second output port (26) on a common TTS N reference potential, the cathode connection of the first diode (23) being connected to the first input connection (21) and the anode connection of the first diode (23) being connected to a common connection point (27) of the single capacitor (24) and the first electronic switch (30 ) is connected, and wherein a first connection (42) of the auxiliary voltage source (40) is connected to the second input connection (22), to the second output connection (26) and to the control device (50; 50°), and wherein the control device ( 50; 50') is connected to a second connection (41) of the auxiliary voltage source (40). 2. Circuit arrangement according to Claim 1, characterized in that the first electronic switch (30) is a field effect transistor, the gate connection (33) of which is connected to the control device (50), the drain connection (31) of which is connected to a second connection of the single capacitor (24 ) and whose first terminal is a source terminal (32) which is connected to the second input terminal (22) and the second output terminal (26). 3. Circuit arrangement (70) according to Claim 1 or 2, characterized by - a second diode (28), - a second electronic switch (80), the second diode (28) being connected in series with the single inductance (20), the cathode connection of the second diode (28) being connected to the ETE. first output terminal (25), wherein a first terminal (81) of the second electronic switch (80) is connected to the anode terminal of the second diode (28) and a second terminal (82) of the second electronic switch (80) is connected to the second Input terminal (22) and the second output terminal (26) is connected, and wherein the control device (50 ') for switching on and off the second electronic switch (80) is formed. ; 4. Circuit arrangement (70) according to claim 3, characterized in that the second electronic switch (80) is a field effect transistor whose gate connection (83) is connected to the control device (50'), whose first connection is the drain connection (81) and whose second terminal is the source terminal (82). 5. Circuit arrangement (10) according to one of the preceding claims, characterized in that a circuit (60), in particular a resonant converter, is connected to the output (25, 26), at least some electronic components of the circuit (60) being fed by means of the Auxiliary voltage source (40) takes place. 6. Circuit arrangement (10, 70) according to any one of the preceding claims, characterized in that the single capacitor (24) can have a capacitance between 50uF and 750pF. EE