An LED driving circuit for suppressing common-mode leakage current

Abstract

The utility model provides a kind of LED drive circuit of common-mode leakage current inhibition, comprising: rectifier circuit, rectification to produce input voltage to alternating current;First switching unit, it is connected between the high potential end of input voltage and the anode of LED load, the cathode of LED load is connected the low potential end of input voltage;Wherein, when first switching unit is disconnected, the common-mode leakage current that flows through first flow path is inhibited, and first flow path includes: the high potential end of input voltage-LED load-parasitic common-mode capacitor-ground.The utility model proposes to set first switching unit between the high potential of input voltage and the anode of LED load, and the scheme that first switching unit is in off state when input single-way switch is turned off, can completely block or substantially reduce the common-mode leakage current that directly flows into LED load from the high potential end of input voltage, so as to solve the problem that LED load cannot be extinguished due to common-mode leakage current when input single-way switch is turned off.

Description

Technical Field

[0001] This utility model belongs to the field of lighting, and specifically relates to an LED driving circuit that suppresses common-mode leakage current. Background Technology

[0002] like Figure 1 As shown, in LED driving applications, taking the linear driving of a single-segment LED lamp group as an example, the input single-channel switch K1 is mistakenly connected between the neutral line N and the output terminal of the rectifier bridge. Simultaneously, because the LED lamp board grounding wire (the aluminum substrate of the lamp board is short-circuited to the metal casing, and the metal casing is connected to ground) creates a parasitic common-mode capacitance Cs between the LED load and ground. Under this condition, when the entire system is shut down or the input single-channel switch K1 is opened, a continuous common-mode leakage current path will form between the power grid, the LED load, the parasitic common-mode capacitance Cs, and the ground. When the voltage drop generated by the common-mode leakage current flowing through the LED exceeds the LED's conduction voltage drop, the LED load will become dimly lit and unable to be completely extinguished.

[0003] To put it another way, such as Figure 2 As shown, even if the input switch K1 is accurately connected between the live wire L and the output terminal of the rectifier bridge, the actual potential of the neutral wire N is higher than zero because one end of the power grid is grounded at a distant point through the transmission line. Therefore, when the system is powered off or the input switch K1 is opened, a continuous common-mode leakage current path will still be generated between the power grid, the LED load, the parasitic common-mode capacitance Cs, and the ground. When the voltage drop generated by the common-mode leakage current flowing through the LED is greater than the LED's conduction voltage drop, the LED load will not be completely extinguished.

[0004] Therefore, in LED driving applications, a solution must be proposed to address the problem that the common-mode leakage current flowing through the LED load when the input single-channel switch is turned off cannot completely extinguish the LED. Utility Model Content

[0005] To address the technical problem of common-mode leakage current flowing through the LED load and preventing complete extinguishing when the input single-channel switch is turned off, this invention proposes an LED driver circuit for suppressing common-mode leakage current, comprising:

[0006] A rectifier circuit rectifies alternating current to generate input voltage;

[0007] The first switching unit is connected between the high potential end of the input voltage and the positive terminal of the LED load, and the negative terminal of the LED load is connected to the low potential end of the input voltage.

[0008] Specifically, when the first switching unit is disconnected, the common-mode leakage current flowing through the first flow path is suppressed.

[0009] The first flow path includes: high potential end of input voltage - LED load - parasitic common mode capacitance - ground.

[0010] Furthermore, the LED driving circuit also includes a switching power supply disposed between the first switching unit and the LED load, or the LED driving circuit also includes a current source disposed on a branch of the LED load.

[0011] Furthermore, the LED driving circuit includes a single-segment LED group, a dimming tube, and a filter capacitor.

[0012] The LED light group is connected in series with the dimming tube, and the first switching unit is connected in series with the LED light group and then in parallel with the filter capacitor. When the first switching unit is open, it suppresses the common-mode leakage current flowing through the first flow path and the second flow path.

[0013] The second flow path includes: high potential end of input voltage - dimming tube - filter capacitor - LED load - parasitic common mode capacitor - ground.

[0014] Furthermore, the LED driving circuit includes a single-segment LED group, a dimming tube, and a filter capacitor. The LED group is connected in series with the dimming tube, and the LED group is connected in parallel with the filter capacitor.

[0015] The LED driving circuit further includes a first diode disposed between the negative terminal of the LED load and the low potential end of the input voltage, the first diode being used to block the common-mode leakage current flowing through the second flow path.

[0016] The second flow path includes: high potential end of input voltage - dimming tube - filter capacitor - LED load - parasitic common mode capacitor - ground.

[0017] Preferably, the first switching unit includes a single MOSFET or multiple MOSFETs connected in series, wherein the equivalent parasitic capacitance of the multiple MOSFETs connected in series is smaller than the parasitic capacitance of the single MOSFET.

[0018] Furthermore, when the first switching unit is turned off, it completely blocks the common-mode leakage current.

[0019] Alternatively, when the first switching unit is turned off, the common-mode leakage current is reduced so that the voltage drop generated by the common-mode leakage current flowing through the LED load is less than the on-state voltage drop of the LED load.

[0020] In one embodiment, the first input terminal of the rectifier bridge is connected to the live wire via an input single-channel switch, and the second input terminal of the rectifier bridge is connected to the neutral wire.

[0021] During the period when the input single-channel switch is turned off, the actual voltage of the neutral line is greater than zero, and the first switch unit is controlled to turn off.

[0022] In another embodiment, the first input terminal of the rectifier bridge is connected to the live wire, and the second input terminal of the rectifier bridge is connected to the neutral wire via an input switch.

[0023] The first switching unit is controlled to turn off during the period when the input single-channel switch is turned off.

[0024] Furthermore, the LED driving circuit also includes a control unit, which controls the switching of the first switching unit according to the input voltage and a preset threshold, and controls the first switching unit to turn off when the input voltage is less than the preset threshold.

[0025] Furthermore, it also includes a bus capacitor connected in parallel with the output terminal of the rectifier circuit. The bus capacitor filters the input voltage. The first switching unit is disposed between the rectifier circuit and the bus capacitor, or between the bus capacitor and the LED load.

[0026] Furthermore, it also includes a second switching unit, which is disposed between the low potential end of the input voltage and the negative terminal of the LED load. When the second switching unit is turned off, it suppresses the common-mode leakage current flowing from the ground to the LED load.

[0027] Furthermore, it also includes a second diode disposed between the high potential end of the input voltage and the positive terminal of the LED load, the negative terminal of the second diode being connected to the positive terminal of the LED load.

[0028] This invention proposes a scheme in which a first switching unit is placed between the high-potential end of the input voltage and the positive terminal of the LED load, and the first switching unit is controlled to be in the off state when the input single-channel switch is turned off. This can completely block or significantly reduce the common-mode leakage current flowing directly into the LED load from the high-potential end of the input voltage, thereby solving the problem that the LED load cannot be turned off when the input single-channel switch is turned off. Furthermore, a second switching unit is placed between the low-potential end of the input voltage and the negative terminal of the LED load to further suppress the common-mode leakage current flowing from ground to the LED load, thereby further reducing the common-mode leakage current flowing through the LED load. Attached Figure Description

[0029] Figure 1 and Figure 2 This is a schematic diagram of the common-mode leakage current path in existing technologies;

[0030] Figure 3 The first switching unit is used in single-segment LED linear dimming applications;

[0031] Figure 4 Other paths for common-mode leakage current in single-segment LED linear dimming applications;

[0032] Figure 5 This is an LED driver circuit that can simultaneously suppress common-mode leakage current from different paths in one embodiment;

[0033] Figure 6 In another embodiment, an LED driver circuit can simultaneously suppress common-mode leakage current in different paths;

[0034] Figure 7 This is the preferred structure for the first switching unit;

[0035] Figure 8 Other paths for common-mode leakage current when the neutral line voltage is greater than the live line voltage;

[0036] Figure 9 and Figure 10 for Figure 8 The LED driver circuit under the shown operating conditions. Detailed Implementation

[0037] To facilitate understanding of this utility model, a more comprehensive description will be given below with reference to the accompanying drawings. The drawings illustrate preferred embodiments of this utility model. However, this utility model can be implemented in various forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this utility model.

[0038] As mentioned in the background art, the design of LED drivers needs to address the problem of common-mode leakage current preventing the LED load from completely extinguishing. To address this problem, this invention proposes an LED driver circuit that suppresses common-mode leakage current, such as... Figure 3 As shown, it includes:

[0039] A rectifier circuit rectifies alternating current to generate input voltage;

[0040] The first switching unit is connected between the high potential terminal of the input voltage and the positive terminal of the LED load, and the negative terminal of the LED load is connected to the low potential terminal of the input voltage.

[0041] When the input single-channel switch K1 is opened, the first switching unit is opened, thereby suppressing the common-mode leakage current flowing through the first flow path.

[0042] The first flow path includes: high potential end of input voltage - LED load - parasitic common mode capacitance - ground.

[0043] Comparing the prior art with the present invention, we can conclude that:

[0044] Figure 1 and Figure 2The prior art shown does not have a first switching unit. When the input single-channel switch K1 (connected to the neutral or live wire) is open, the voltage of the live wire and the neutral wire of the power grid is greater than zero potential. A path is formed between the high potential end of the input voltage, the LED load, the parasitic common-mode capacitance, and the ground, and the common-mode leakage current flows continuously.

[0045] Figure 3 The present invention, as shown, sets a first switching unit between the high-potential end of the input voltage and the positive terminal of the LED load. When the input single-channel switch K1 is turned off, the first switching unit switches to the off state. At this time, the high-potential end of the input voltage and the LED load are in an open circuit state, and no common-mode leakage current can be formed, thus preventing the LED load from failing to turn off. Conversely, even if a current path still exists between the high-potential end of the input voltage and the positive terminal of the LED load due to the parasitic effect of the first switching unit when it is turned off, the common-mode leakage current flowing through the LED load through the parasitic element is greatly reduced. At this time, the voltage drop generated by the common-mode leakage current flowing through the LED load is less than the conduction voltage drop of the LED load, and the LED load will not exhibit the phenomenon of dim lighting and failure to turn off.

[0046] Therefore, this utility model proposes a scheme to set a first switching unit between the high potential of the input voltage and the positive terminal of the LED load, and to control the first switching unit to be in the off state when the input single-channel switch is turned off. This can completely block or significantly reduce the common-mode leakage current flowing directly into the LED load from the high potential terminal of the input voltage, thereby solving the problem that the LED load cannot be turned off when the input single-channel switch is turned off.

[0047] In addition, it should be noted that, Figure 3 The diagram shows the linear drive of a single-segment LED light group. The single-segment LED light group comprises multiple LEDs connected in series. Each LED forms a parasitic common-mode capacitance with ground. The last LED, LEDn, is reverse-biased, and each of the remaining LEDs forms a corresponding first current path. Meanwhile, Figure 3 The content shown does not limit the scheme of adding a first switching unit to linear drive scenarios for single-segment LED light groups. In PWM dimming scenarios, a switching power supply is provided between the high potential terminal of the input voltage and the LED load. The switching power supply converts the input voltage into an output voltage to drive the LED load. Under this condition, a first switching unit can still be added to suppress common-mode leakage current when the input single-channel switch is turned off. The first switching unit is located between the high potential terminal of the input voltage and the input terminal of the first switching unit.

[0048] Furthermore, such as Figure 4As shown, in a linear driving scenario for a single-segment LED light group, a filter capacitor C2 is typically installed at both ends of the LED light group. Under these conditions, when the input single-channel switch K1 is turned off, a path is formed between the high-potential end of the input voltage, the bus capacitor C1, the dimming tube or its body diode, the filter capacitor C2, the LED light group, the parasitic common-mode capacitor CS, and ground. This continuously generates common-mode leakage current, creating a second path for the common-mode leakage current, preventing the LED load from turning off. To suppress the common-mode leakage current flowing through this second path, this invention further proposes:

[0049] In one embodiment, such as Figure 5 As shown, the connection position of the first switching unit is adjusted so that the first switching unit and the LED load are connected in series and then in parallel with the filter capacitor C2. Therefore, when the input single-channel switch K1 is turned off, the first switching unit in the off state suppresses the common-mode leakage current flowing directly from the high-potential end of the input voltage to the LED load, and also suppresses the common-mode leakage current flowing indirectly from the high-potential end of the input voltage to the LED load through the dimming tube and the filter capacitor. That is, when the input single-channel switch is turned off, the first switching unit in the off state can simultaneously suppress the common-mode leakage current flowing through the first flow path and the second flow path.

[0050] In another embodiment, such as Figure 6 As shown, the first switching unit is positioned between the high-potential end of the input voltage and the positive terminal of the LED load. The filter capacitor C2 is directly connected in parallel across the LED load. A first diode D1 is positioned between the LED load and the low-potential end of the input voltage, with the anode of the first diode D1 connected to the cathode of the LED load. Due to the unidirectional conduction characteristic of the first diode D1, the common-mode leakage current cannot flow indirectly to the LED load through the dimming tube and the filter capacitor C2, thus blocking the common-mode leakage current flowing through the second flow path.

[0051] Preferred, Figure 3 , Figure 5 and Figure 6 The first switching unit shown is a MOSFET. Because MOSFETs exhibit parasitic effects, they cannot completely block common-mode leakage current. Therefore, to further reduce common-mode leakage current, multiple MOSFETs can be connected in series, such as... Figure 7As shown, the total equivalent parasitic capacitance of multiple MOSFETs connected in series is less than that of a single MOSFET, thus further reducing the common-mode leakage current flowing through the parasitic capacitance. The switching of MOSFET Q1 is controlled based on the relationship between the input voltage and the threshold voltage. When the input voltage is less than the threshold voltage, the input single-channel switch is turned off, and the control unit controls Q1 to turn off. When the input voltage is greater than the threshold voltage, the control unit controls Q1 to turn on. How the control unit specifically drives the switching of MOSFET Q1 is conventional technology in this field and will not be elaborated further. Furthermore, it should be noted that when a fully controllable device is used for the first switching unit, complete blocking of the common-mode leakage current can be achieved. For example, gate-turn-off thyristors, optocouplers, relays, etc. Generally, to reduce the current stress on the first switching unit, it is placed after the bus capacitor C1 (between the bus capacitor and the LED load). However, in some cases, the first switching unit may also be placed before the bus capacitor C1 (between the rectifier circuit and the bus capacitor).

[0052] Furthermore, considering that when the neutral wire (N) voltage is greater than the live wire (L) voltage, during the off-state of the input single-channel switch K1, common-mode leakage current will flow from ground into the LED load, thus preventing the LED load from turning off. Specifically, as follows... Figure 8 As shown, when the potential of the neutral wire N is greater than that of the live wire L, since both the neutral wire N and the parasitic common-mode capacitor CS are connected to ground, taking the LED chip LEDn in the LED load as an example, the common-mode leakage current can flow from ground to the LED chip LEDn, then through the dimming tube or through the filter capacitor C2 to the low potential end of the rectifier bridge, and then into the live wire L. In this case, the LED chip LEDn will not be able to turn off. Therefore, in order to suppress the common-mode leakage current on this path, such as... Figure 9 As shown, this utility model also proposes to set a second switching unit between the low potential end of the rectifier bridge (the low potential end of the input voltage) and the negative terminal of the LED load, thereby blocking the common mode leakage current flowing from the ground through the LED load and the dimming tube and finally into the live wire L.

[0053] Furthermore, such as Figure 10 As shown, when a MOSFET is selected as the first switching unit, due to the presence of the MOSFET's body diode, the common-mode leakage current flowing from ground can flow into the live wire L through the filter capacitor C2 and the MOSFET's body diode. Therefore, a second diode D2 is further placed between the high-potential end of the input voltage and the LED load to block the common-mode leakage current along this path. If other switches are selected for the first switching unit that can completely block the current when turned off, then... Figure 9 As shown, there is no need to install a second diode D2.

[0054] It should be noted that in the above-described operating conditions, the bus capacitor C1 is just an example. In reality, the bus capacitor C1 can be any current path between the two ends of the input voltage. The common-mode leakage current flowing out of the ground can flow into the live wire L through the filter capacitor C2 and the current path.

[0055] It should be noted that the specific implementation and corresponding illustrations provided are merely one way of describing the implementation method of this utility model, and are not intended to limit the specific structure of the implementation scheme of this utility model. Various changes or modifications can be made to these implementation methods without departing from the principles and essence of this utility model, but all such changes and modifications fall within the protection scope of this utility model.

[0056] Although the embodiments are described and illustrated separately above, some common technologies are involved. Those skilled in the art can replace and integrate them between the embodiments. If there is any content not explicitly described in one embodiment, then another embodiment that is described can be referred to.

[0057] The embodiments described above do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the above embodiments should be included within the scope of protection of this technical solution.

Claims

1. An LED driving circuit for suppressing common-mode leakage current, characterized in that, include: A rectifier circuit rectifies alternating current to generate input voltage; The first switching unit is connected between the high potential end of the input voltage and the positive terminal of the LED load, and the negative terminal of the LED load is connected to the low potential end of the input voltage. Specifically, when the first switching unit is disconnected, the common-mode leakage current flowing through the first flow path is suppressed. The first flow path includes: high potential end of input voltage - LED load - parasitic common mode capacitance - ground.

2. The LED driving circuit as described in claim 1, characterized in that, The LED driving circuit further includes a switching power supply disposed between the first switching unit and the LED load, or the LED driving circuit further includes a current source disposed on a branch of the LED load.

3. The LED driving circuit as described in claim 1, characterized in that, The LED driving circuit includes a single-segment LED lamp group, a dimming tube, and a filter capacitor. The LED light group is connected in series with the dimming tube, and the first switching unit is connected in series with the LED light group and then in parallel with the filter capacitor. When the first switching unit is open, it suppresses the common-mode leakage current flowing through the first flow path and the second flow path. The second flow path includes: high potential end of input voltage - dimming tube - filter capacitor - LED load - parasitic common mode capacitor - ground.

4. The LED driving circuit as described in claim 1, characterized in that, The LED driving circuit includes a single-segment LED group, a dimming tube, and a filter capacitor. The LED group is connected in series with the dimming tube, and the LED group is connected in parallel with the filter capacitor. The LED driving circuit further includes a first diode disposed between the negative terminal of the LED load and the low potential end of the input voltage, the first diode being used to block the common-mode leakage current flowing through the second flow path. The second flow path includes: high potential end of input voltage - dimming tube - filter capacitor - LED load - parasitic common mode capacitor - ground.

5. The LED driving circuit as described in claim 1, 3, or 4, characterized in that, The first switching unit includes a single MOSFET or multiple MOSFETs connected in series, wherein the equivalent parasitic capacitance of the multiple MOSFETs connected in series is smaller than the parasitic capacitance of the single MOSFET.

6. The LED driving circuit as described in claim 1, 3, or 4, characterized in that, When the first switching unit is turned off, it completely blocks the common-mode leakage current. Alternatively, when the first switching unit is turned off, the common-mode leakage current is reduced so that the voltage drop generated by the common-mode leakage current flowing through the LED load is less than the on-state voltage drop of the LED load.

7. The LED driving circuit as described in claim 1, 3, or 4, characterized in that, The first input terminal of the rectifier circuit is connected to the live wire via an input single-channel switch, and the second input terminal of the rectifier circuit is connected to the neutral wire. During the period when the input single-channel switch is turned off, the actual voltage of the neutral line is greater than zero, and the first switch unit is controlled to turn off.

8. The LED driving circuit as described in claim 1, 3, or 4, characterized in that, The first input terminal of the rectifier circuit is connected to the live wire, and the second input terminal of the rectifier circuit is connected to the neutral wire via an input switch. The first switching unit is controlled to turn off during the period when the input single-channel switch is turned off.

9. The LED driving circuit as described in claim 1, 3, or 4, characterized in that, The LED driving circuit also includes a control unit, which controls the switching of the first switching unit according to the input voltage and a preset threshold, and controls the first switching unit to turn off when the input voltage is less than the preset threshold.

10. The LED driving circuit as described in claim 1, characterized in that, It also includes a bus capacitor connected in parallel with the output terminal of the rectifier circuit, the bus capacitor filtering the input voltage, and the first switching unit being disposed between the rectifier circuit and the bus capacitor, or between the bus capacitor and the LED load.

11. The LED driving circuit as described in claim 1, characterized in that, It also includes a second switching unit, which is located between the low potential end of the input voltage and the negative terminal of the LED load. When the second switching unit is turned off, it suppresses the common-mode leakage current flowing from the ground to the LED load.

12. The LED driving circuit as described in claim 11, characterized in that, It also includes a second diode disposed between the high potential end of the input voltage and the positive terminal of the LED load, wherein the negative terminal of the second diode is connected to the positive terminal of the LED load.

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