INRUSH CURRENT LIMITING CIRCUIT IN A SWITCHING POWER SUPPLY, ASSOCIATED INPUT STAGE, SWITCHING POWER SUPPLY AND LIGHT SIGNALING DEVICE

Abstract

The invention relates to a circuit (12a) for limiting the inrush current in a switching power supply comprising:– a diode bridge (11); and– a filter capacitor (Cf) connected between, on the one hand, a high power supply (V+) and a high point (Ph) of the diode bridge (11) and, on the other hand, a low power supply (V-) and to a low point (Pb) of the diode bridge (11);the limiting circuit (12a) comprising:– a voltage divider bridge made by a high resistor (Rh) connected to the high power supply and a low resistor (Rb) connected to the low point;– a field effect transistor (T) whose source and drain are connected between the low point and the low power supply, the gate being connected to a midpoint (Pm) of the voltage divider bridge; and– a limiting capacitor (Cl) connected between the low point and the midpoint. Figure for the abstract: Fig 3

Description

Title of the invention: CIRCUIT FOR LIMITING THE INRUSH CURRENT IN A SWITCHING POWER SUPPLY, INPUT STAGE, SWITCHING POWER SUPPLY AND ASSOCIATED LIGHT SIGNALING DEVICE Technical field

[0001] The invention relates to the field of electronics, and more particularly to switching power supplies, for example for a light signaling device.

[0002] The invention finds a particularly advantageous application for limiting the inrush current in a switching power supply and thus finds an application in numerous fields implementing such a power supply. Background of the invention

[0003] In a power supply, particularly a switching power supply, a large number of problems can be caused by the inrush current, also called "inrush current" in the English literature. This inrush current refers to the excessive current peak that occurs when the power supply is initially switched on. This peak can cause damage to electronic components, lead to premature wear of the power supply, cause unexpected voltage drops on the network and unnecessarily trigger protective devices, such as circuit breakers.

[0004] More specifically, as illustrated in [Fig.l], the input stage 100 of a switching power supply typically includes a diode bridge 11 and a filter capacitor Cf. The diode bridge 11 is responsible for converting the alternating current into direct current, while the filter capacitor Cf has the role of smoothing the voltage from the diode bridge. To do this, the diode bridge typically includes four diodes D1-D4. The input alternating voltage Vin is applied between the diodes D1-D3 and D2-D4.

[0005] Furthermore, diodes D1-D2 are connected to the high point Ph of the diode bridge 11 while diodes D3-D4 are connected to the low point Pb of the diode bridge 11.

[0006] The filter capacitor Cf is connected between the high point Ph and the low point Pb, also connected respectively to a high supply V+ and a low supply V-.

[0007] This configuration is essential to provide a stable power supply to the switching device, located downstream.

[0008] The inrush current is formed mainly due to the initial charge of the filter capacitor Cf. At the time of switching on, the filter capacitor The filter capacitor Cf, which is initially discharged, behaves like a short circuit, causing a very high current draw from the network. This current peak is all the more significant as the capacity of the filter capacitor Cf is large. It persists until the filter capacitor Cf reaches its maximum charge, corresponding to the peak voltage of the AC input voltage Vin. This situation is critical because it can induce excessive thermal and electrical stresses on the diode bridge 11 and the filter capacitor Cf, as well as on the electrical network itself.

[0009] To limit this inrush current, it is known to use at least one precharge resistor Ra connected between the low point Pb of the diode bridge 11 and the filtering capacitor Cf, as illustrated in [Fig.2].

[0010] The use of this precharge resistor Ra can be controlled by an activation circuit, often made using relays, as well as a circuit for measuring the voltage across the filter capacitor.

[0011] The activation circuit is designed to control the application of the precharge resistor Ra to the circuit. This activation is typically managed by relays, which can connect or disconnect the precharge resistor depending on certain operating parameters of the circuit, such as the voltage across the filter capacitor Cf. This process is supervised by the voltage measurement circuit, which continuously monitors the voltage across the filter capacitor Cf and sends signals to the activation circuit.

[0012] However, this approach has several drawbacks. First, closing the relay imposes an all-or-nothing behavior of the precharge resistor Ra.

[0013] This means that the precharge resistor Ra is either fully engaged or fully disconnected, which may not be ideal for precise inrush current regulation. Too abrupt a transition can result in unwanted current spikes or other harmful electrical phenomena.

[0014] In addition, the use of relays and a voltage measuring circuit requires a large number of additional components. These components not only increase the overall complexity of the circuit, but also its cost and size. In addition, the reliability of the system may be compromised, since the addition of additional components, especially mechanical relays, increases the risk of failure.

[0015] In summary, although the use of a pre-charge resistor Ra combined with a relay-based activation circuit and a voltage measurement circuit offers a solution for controlling the inrush current in switching power supplies, it has limitations in terms of control accuracy, complexity, cost and reliability.

[0016] Another approach to forming the precharge resistor Ra uses a resistor technology whose resistivity varies with temperature. These components, known as "surge guard" or "inrush current limiter" in the English literature, exploit the properties of thermistor materials to control the inrush current.

[0017] When the equipment is off and the component is cold, the precharge resistor Ra has a high resistivity. This high initial resistance effectively limits the inrush current by reducing the current flow to the filter capacitor Cf at the time of power-up. As current flows through the precharge resistor Ra, it begins to heat up, which decreases its resistivity. Thus, the resistance gradually decreases, allowing a higher current to pass and ensuring a gradual rise in voltage of the filter capacitor Cf, which protects other components in the circuit from current spikes.

[0018] However, this solution presents a significant problem in the event of a sudden loss of power.

[0019] Indeed, if the power supply is cut off and restored quickly (for example, in the event of a micro-cut), the precharge resistor Ra remains hot from the previous cycle and therefore does not have the large initial resistance necessary to limit the inrush current during restart. As a result, the filter capacitor Cf may be exposed to a high inrush current peak, similar to that which it would have without any precharge resistor. This can cause thermal and electrical stress on the circuit components, in particular the diode bridge 11 and the filter capacitor Cf, and potentially reduce their lifetime or cause failures.

[0020] This limitation of the precharge resistance Ra highlights the need for a more robust and reliable solution to manage the inrush current in switching power supplies, especially in scenarios where power outages are frequent or unpredictable. Statement of the invention

[0021] To solve this technical problem, the invention proposes using a precharge resistor associated with a switching circuit integrating a field effect transistor whose gate gradually charges when powered up so as to gradually inhibit the precharge resistor.

[0022] To do this, the switching circuit comprises a voltage divider bridge made of two resistors: a high resistor connected to the high power supply and a low resistor connected to the low point of the diode bridge. The source and drain of the field effect transistor are connected respectively between the low point of the diode bridge and the low power supply, while the gate is connected to a midpoint of the voltage divider bridge. In addition, a limiting capacitor is also connected between the low point of the diode bridge and the midpoint of the voltage divider bridge.

[0023] This switching circuit allows for progressive switching of the precharge resistor, with reliable and inexpensive components, while allowing rapid discharge of the limiting capacitor between two power-ups.

[0024] According to a first aspect, the invention relates to a circuit for limiting the inrush current in a switching power supply comprising: - a diode bridge; and - a filter capacitor connected between, on the one hand, a high supply and a high point of the diode bridge and, on the other hand, a low supply and, via at least one pre-charge resistor, a low point of the diode bridge.

[0025] The invention is characterized in that the limiting circuit comprises: - a voltage divider bridge made of at least two resistors: a high resistor connected to the high power supply and a low resistor connected to the low point of the diode bridge; - a field effect transistor whose source and drain are connected between the low point of the diode bridge and the low power supply, the gate being connected to a midpoint of the voltage divider bridge; and - a limiting capacitor connected between the low point of the diode bridge and the midpoint of the voltage divider bridge.

[0026] Thus, the limiting circuit integrates at least one voltage divider bridge composed of two resistors, in conjunction with a field effect transistor. This configuration ensures progressive regulation of the precharge resistance, thus effectively minimizing the inrush current peak.

[0027] Preferably, the limiting circuit also comprises a zener diode connected between the low point of the diode bridge and the midpoint of the voltage divider bridge, which makes it possible to precisely limit the gate voltage of the field effect transistor to a safe value, typically less than 20 volts.

[0028] It is recommended that the limiting capacitor within the circuit have a capacitance chosen between 0.5 and 2 pF, thus perfectly balancing the limitation of the inrush current and the responsiveness of the circuit.

[0029] The circuit should ideally include a high resistor with a resistivity between 0.5 and 2 mega-ohms and a low resistor with a resistivity between 0.1 and 0.8 mega-ohms, thus allowing precise adjustment of the voltage divider bridge for optimal inrush current control.

[0030] The limiting circuit, according to the first aspect of the invention, is advantageously integrated into the input stage of a switching power supply, with a specified pre-charge resistor to provide a complete and efficient solution for power supplies cutting.

[0031] The circuit, in accordance with the configurations described, is particularly suitable for use in switching power supplies and light signaling devices, thus ensuring increased performance and longevity of the equipment concerned. Summary description of the figures

[0032] The manner of carrying out the invention, as well as the advantages which result therefrom, will emerge clearly from the description of the embodiments which follow, with the support of the appended figures in which:

[0033] [Fig.l] illustrates a simplified electrical diagram of an input stage of a switching power supply according to the state of the art;

[0034] [Fig.2] illustrates a simplified electrical diagram of an input stage of a switching power supply with a pre-charge resistor according to the state of the art;

[0035] [Fig. 3] illustrates a simplified electrical diagram of an input stage of a switching power supply according to a first embodiment of the invention; and

[0036] [Fig.4] illustrates a simplified electrical diagram of an input stage of a switching power supply according to a second embodiment of the invention. Detailed description

[0037] [Fig.3] illustrates the input stage 10a of a switching power supply, integrating a diode bridge 11, a filter capacitor Cf, a pre-charge resistor Ra, and an inrush current limiting circuit 12a.

[0038] The diode bridge 11 converts the alternating current into direct current, while the filter capacitor Cf has the role of smoothing the voltage from the diode bridge. To do this, the diode bridge conventionally comprises four diodes D1-D4. The alternating input voltage Vin is applied between the diodes D1-D3 and D2-D4.

[0039] Furthermore, diodes D1-D2 are connected to the high point Ph of the diode bridge 11 while diodes D3-D4 are connected to the low point Pb of the diode bridge 11.

[0040] The filter capacitor Cf is connected between the high point Ph and the low point Pb, also connected respectively to a high supply V+ and a low supply V-.

[0041] The connection of the filter capacitor Cf to the low point Pb of the diode bridge 11 is made via the precharge resistor Ra. For example, this precharge resistor Ra may have a resistivity of between 1 and 1000 ohms. Preferably, this precharge resistor Ra may be implemented by two 100 ohm SMD resistor components placed in series.

[0042] The low point Pb of the diode bridge 11 is also connected to the inrush current limiting circuit 12a. This circuit integrates a voltage divider bridge formed by a re high resistance Rh and a low resistance Rb, a limiting capacitor Cl positioned in parallel with the low resistance Rb and a field effect transistor T. The limiting capacitor Cl preferably has a capacity between 0.5 and 2 pF, for example a capacity of 1 pF.

[0043] The high resistance Rh preferably has a resistivity of between 0.5 and 2 mega-ohms, for example 1 mega-ohm, while the low resistance Rb preferably has a resistivity of between 0.1 and 0.8 mega-ohms, for example 0.47 mega-ohms.

[0044] The source S and the drain D are connected between the low point Pb of the diode bridge 11 and the low supply V-.

[0045] The field effect transistor T is preferably an N-type MOSFET transistor.

[0046] The gate G of the field effect transistor T is connected to a midpoint Pm of the voltage divider bridge.

[0047] When a voltage is applied to the input Vin of the input stage 10a, the current flows through the diode bridge 11 and charges the filter capacitor Cf by passing through the high point Ph. The current then flows through the pre-charge resistor Ra to return to the diode bridge 11 via the low point Pb. As the filter capacitor Cf charges, the voltage in the high supply V+ increases.

[0048] Now, this high supply V+ is also connected to the high resistance Rh of the voltage divider bridge of the inrush current limiting circuit 12a. Thus, the increase in voltage in the high supply V+ charges the limiting capacitor Cl and the gate G of the field effect transistor T. It follows that the gate G of the field effect transistor T gradually charges until it becomes conductive. When the field effect transistor T is conductive, the low supply V- is connected to the low point Pb of the diode bridge 11 and the precharge resistor Ra is short-circuited.

[0049] When the voltage is no longer applied to the input of the switching power supply, the filter capacitor Cf discharges quickly into the low resistor Rb, typically in less than one second. Thus, it is possible to quickly reconnect the power supply in a very short time while benefiting from the protection offered by the precharge resistor Ra and the inrush current limiting circuit 12a.

[0050] In the embodiment of [Fig.4], the inrush current limiting circuit 12b also comprises a zener diode DI connected in parallel with the low resistance Rb and the filter capacitor Cf. This zener diode DI is typically configured to limit the gate voltage G of the field effect transistor T to a voltage below 20 volts.

[0051] With the association of the precharge resistor Ra and the limiting circuit of the inrush current 12a-12b, the invention makes it possible to provide a progressive closure of a switching power supply with inexpensive components.

[0052] This invention can be applied in a large number of fields, in particular for powering one or more light sources of a light signaling device.

Claims

Claims

1. A circuit (12a-12b) for limiting the inrush current in a switching power supply comprising: - a diode bridge (11); and - a filter capacitor (Cf) connected between, on the one hand, a high power supply (V+) and a high point (Ph) of the diode bridge (11) and, on the other hand, a low power supply (V-) and, via at least one precharge resistor (Ra), to a low point (Pb) of the diode bridge (11); characterized in that the limiting circuit (12a-12b) comprises: - a voltage divider bridge made of at least two resistors: a high resistor (Rh) connected to the high power supply (V+) and a low resistor (Rb) connected to the low point (Pb) of the diode bridge (11); - a field effect transistor (T) whose source (S) and drain (D) are connected between the low point (Pb) of the diode bridge (11) and the low power supply (V-), the gate (G) being connected to a midpoint (Pm) of the voltage divider bridge;and - a limiting capacitor (Cl) connected between the low point (Pb) of the diode bridge (11) and the midpoint (Pm) of the voltage divider bridge.;

2. An inrush current limiting circuit according to claim 1, wherein the limiting circuit (12b) also comprises a zener diode (Dl) connected between the low point (Pb) of the diode bridge (11) and the midpoint (Pm) of the voltage divider bridge so as to limit the gate voltage (G) of the field effect transistor (T).

3. An inrush current limiting circuit according to claim 2, wherein the zener diode (Dl) is configured to limit the gate voltage (G) of the field effect transistor (T) to a voltage less than 20 volts.

4. Inrush current limiting circuit according to one of claims 1 to 3, in which the limiting capacitor (Cl) has a capacitance of between 0.5 and 2 pF.

5. An inrush current limiting circuit according to one of claims 1 to 4, wherein the high resistance (Rh) has a resistivity of between 0.5 and 2 mega-ohms.

6. An inrush current limiting circuit according to one of claims 1 to 5, wherein the low resistor (Rb) has a resistivity of between 0.1 and 0.8 megaohms.

7. Input stage (10a-10b) of a switching power supply comprising: a diode bridge (11) for converting an AC input voltage (Vin) into a DC voltage; a filter capacitor (Cf) connected between, on the one hand, a high supply (V+) and a high point (Ph) of the diode bridge (11) and, on the other hand, a low supply (V-) and a low point (Pb) of the diode bridge (11); and at least one precharge resistor (Ra) connected between the low point (Pb) of the diode bridge (11) and the filter capacitor (Cf); characterized in that the input stage (10a-10b) also comprises a circuit for limiting the inrush current according to one of claims 1 to 6.

8. Input stage of a switching power supply according to claim 7, in which the precharge resistor (Ra) has a resistivity of between 1 and 1000 ohms.

9. A switching power supply comprising an input stage according to one of claims 7 or 8 and a switching device connected to the input stage.

10. A light signaling device comprising at least one light source and a switching power supply according to claim 9.

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