A circuit for reducing leakage current when an LED is turned off

Abstract

The present invention relates to the field of electronic circuits and provides a circuit for reducing the leakage current when an LED is turned off. The circuit includes a non-isolated power supply module, a first diode, and a switch isolation circuit. An auxiliary winding is provided on the energy storage inductor within the non-isolated power supply module. When the non-isolated power supply module is powered on, a voltage is generated in the auxiliary winding. Two output terminals of the non-isolated power supply module are respectively connected to the input terminal of the first diode and the input terminal of the switch isolation circuit. The output terminal of the first diode and the output terminal of the switch isolation circuit are respectively connected to both ends of the LED lamp. The switch isolation circuit includes a switching MOS transistor and an enabling circuit. The power supply terminal of the enabling circuit is connected to the auxiliary winding, and the output terminal is connected to the gate of the switching MOS transistor to turn on the switching MOS transistor when a voltage output is generated in the auxiliary winding. The drain of the switching MOS transistor is connected to the non-isolated power supply module, and the source is connected to the LED lamp. The present invention reduces the leakage current when the LED is turned off and has a lower cost.

Description

Technical Field

[0001] The present invention relates to the field of electronic circuits, and more particularly to a circuit for reducing leakage current when an LED is turned off. Background Art

[0002] Compared with traditional lighting, LED lighting has the characteristics of energy saving, high efficiency, high safety and excellent light quality. Therefore, more and more places begin to use LED lamps for lighting; a non-isolated power supply is a power supply in which there is a direct electrical connection between the input terminal and the load terminal without physical isolation. In recent years, non-isolated power supplies have been widely used in LED lamps due to their high cost performance and high efficiency. Traditional LED non-isolated drive power supplies are all grounded. In this case, if the grounding of the lamp is not processed, there will be a leakage current from the stray capacitance to the ground when the lamp is turned off. At this time, the lamp beads will glow slightly. Currently, most LED drive power supplies do not deal with the phenomenon that the lamp still glows slightly after being turned off. If the lamp is grounded, the lamp beads will glow slightly, and the customer experience is not very good. If the lamp is not grounded, the safety factor of use is reduced. Summary of the Invention

[0003] The problem solved by the present invention is how to provide a low-cost circuit for reducing the leakage current of an LED lamp using a non-isolated power supply in the standby state.

[0004] To solve the above problems, the present invention provides a circuit for reducing leakage current when an LED is turned off, including: a non-isolated power supply module, a first diode and a switch isolation circuit. The energy storage inductor in the non-isolated power supply module has an auxiliary winding. When the non-isolated power supply module is powered on, a voltage will be generated in the auxiliary winding. Two output terminals of the non-isolated power supply module are respectively connected to the input terminal of the first diode and the input terminal of the switch isolation circuit. The output terminal of the first diode and the output terminal of the switch isolation circuit are respectively connected to both ends of the LED lamp. The switch isolation circuit includes a switch MOS transistor and an enabling circuit. The power supply terminal of the enabling circuit is connected to the auxiliary winding, and the output terminal is connected to the gate of the switch MOS transistor, so that when a voltage output is generated in the auxiliary winding, the switch MOS transistor is turned on. The drain of the switch MOS transistor is connected to the non-isolated power supply module, and the source is connected to the LED lamp. When the lamp is turned on, the non-isolated power supply module supplies power to the LED lamp through the switch MOS transistor. When the lamp is turned off, the switch MOS transistor is turned off to prevent leakage current from flowing through the LED lamp to form a loop.

[0005] Further, the drain of the switch MOS transistor is connected to the positive output terminal of the non-isolated power supply module, the source is connected to the positive power input terminal of the LED lamp, the cathode of the first diode is connected to the drive ground terminal of the non-isolated power supply module, and the anode is connected to the negative power input terminal of the LED lamp.

[0006] Further, the turn-on circuit includes a charging circuit and a first capacitor. The input end of the charging circuit is connected to the first end of the auxiliary winding, and the output end is connected to the first end of the first capacitor. The first end of the first capacitor is connected to the gate of the switching MOS transistor, and the second end is connected to the second end of the auxiliary winding. When the auxiliary winding generates a voltage, the auxiliary winding charges the first capacitor through the charging circuit, so that the terminal voltage of the first capacitor reaches the turn-on voltage of the switching MOS transistor.

[0007] Further, the charging circuit includes a second capacitor, a first resistor, and a second diode. The first end of the auxiliary winding is sequentially connected to the anode of the second diode through the second capacitor and the first resistor, and the cathode of the second diode is connected to the first capacitor.

[0008] Further, the turn-on circuit further includes a second resistor, and the second resistor is connected in parallel across the two ends of the first capacitor.

[0009] Further, the turn-on circuit further includes a first voltage regulator diode, and the first voltage regulator diode is connected in parallel across the two ends of the first capacitor, so that the terminal voltage of the first capacitor can stably turn on the switching MOS transistor in the light-on state.

[0010] Further, the non-isolated power supply module includes an AC input protection and filtering circuit, a rectifying circuit, and a non-isolated power supply regulation circuit. The input end of the AC input protection and filtering circuit is connected to an external AC mains supply, and the output end is connected to the input end of the rectifying circuit. The output end of the rectifying circuit is connected to the input end of the non-isolated power supply regulation circuit. The rectifying circuit is used to convert the input AC power into a DC power supply and provide it to the non-isolated power supply regulation circuit. The two output ends of the non-isolated power supply regulation circuit are respectively connected to the input end of the first diode and the input end of the switch-off circuit.

[0011] Further, the non-isolated power supply regulation circuit includes a first power driver chip, a first switching transistor, a third diode, a third capacitor, and the main winding of a storage inductor. The input end of the first switching transistor is connected to the positive output end of the rectifying circuit, the controlled end is connected to the output end of the first power driver chip, and the output end is connected to the first end of the main winding. The cathode of the third diode is connected to the first end of the main winding, and the anode is connected to the negative output end of the rectifying circuit. The first end of the third capacitor is connected to the second end of the main winding, and the second end is connected to the negative output end of the rectifying circuit.

[0012] Compared with the prior art, the beneficial effects of the present invention are:

[0013] By adopting a energy storage inductor with an auxiliary winding in a non-isolated power supply module, the main winding of the energy storage inductor plays an energy storage role in the non-isolated power supply module. The auxiliary winding is connected to the turn-on circuit in the switch isolation circuit, and a voltage will be generated when the main winding works, enabling the turn-on circuit to charge and work to control the on-off of the switching MOS transistor. In this way, when the light is turned on, the auxiliary winding turns on the switching MOS transistor through the turn-on circuit, the switching MOS transistor conducts, and the output of the non-isolated power supply module normally supplies power to the LED lamp. When the light is turned off, the switching MOS transistor is in the off state, and combined with the single-phase conduction characteristic of the diode, the leakage current generated by the front-stage AC power supply in the non-isolated power supply module cannot form a loop through the LED lamp, effectively reducing the impact of the leakage current on the LED lamp. At the same time, only an auxiliary winding needs to be provided on the energy storage inductor in the non-isolated power supply module. By using the same voltage change of the auxiliary winding when the main winding is powered on or powered off, the control of the switching MOS transistor by the auxiliary winding through the turn-on circuit can be realized. While reducing the leakage current, the integration degree is high, greatly reducing the required electrical components, with a smaller overall volume and lower cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a schematic diagram of the overall principle structure of an embodiment of the present invention;

[0015] Figure 2 is a schematic diagram of the leakage current principle structure of an existing non-isolated power supply LED lamp in an embodiment of the present invention;

[0016] Figure 3 is a schematic diagram of the principle structure of a non-isolated power supply regulation circuit in an embodiment of the present invention;

[0017] Figure 4 is a schematic diagram of the overall circuit principle of the first implementation manner in an embodiment of the present invention;

[0018] Figure 5 is a schematic diagram of the overall circuit principle of the second implementation manner in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be given with reference to the accompanying drawings.

[0020] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "set", "install", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0021] In the description of this specification, the descriptions referring to terms such as "embodiment", "one embodiment", and "one implementation manner" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or implementation manner are included in at least one embodiment or implementation manner of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or implementation manner. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or implementation manners.

[0022] As Figure 1 shown, the present invention provides a circuit for reducing the leakage current when an LED is turned off, including: a non-isolated power supply module, a first diode, and a switch isolation circuit. The energy storage inductor in the non-isolated power supply module has an auxiliary winding. When the non-isolated power supply module is powered on, a voltage will be generated in the auxiliary winding. The two output terminals of the non-isolated power supply module are respectively connected to the input terminal of the first diode and the input terminal of the switch isolation circuit. The output terminal of the first diode and the output terminal of the switch isolation circuit are respectively connected to both ends of the LED lamp. The switch isolation circuit includes a switch MOS transistor and an enabling circuit. The power supply terminal of the enabling circuit is connected to the auxiliary winding, and the output terminal is connected to the gate of the switch MOS transistor, so that when a voltage is output from the auxiliary winding, the switch MOS transistor is turned on. The drain of the switch MOS transistor is connected to the non-isolated power supply module, and the source is connected to the LED lamp. When the lamp is turned on, the non-isolated power supply module supplies power to the LED lamp through the switch MOS transistor. When the lamp is turned off, the switch MOS transistor is turned off to prevent the leakage current from flowing through the LED lamp to form a loop.

[0023] It should be noted that the main reason for the generation of leakage current is that in order to enable the power input and the lamp housing to play corresponding protection roles, grounding needs to be provided at both the power input terminal and the lamp housing. In an LED lamp, there is a parasitic capacitance between the LED lamp and the lamp housing. The AC input of the non-isolated power supply will form a leakage current path through the parasitic capacitance in the non-isolated power supply and the lamp. The leakage current flows through the LED lamp beads. Specifically, reference can be made to Figure 2 , the leakage current generated by the front stage will flow through the non-isolated power supply module through the lamp beads and form a loop with the power input of the front stage through the parasitic capacitance. Therefore, when the lamp is turned off, it is necessary to cut off the leakage current path between the non-isolated power supply module and the LED lamp.

[0024] There are various configurations of non-isolated power supplies. Taking Figure 2 as an example, the non-isolated power supply module includes an AC input protection and filtering circuit, a rectification circuit, and a non-isolated power supply regulation circuit.

[0025] The input end of the AC input protection and filtering circuit is connected to the external AC mains, and the output end is connected to the input end of the rectification circuit. Its main function is to protect and filter the input AC power supply. There are various forms of its circuit structure. For example, a common-mode inductor is connected to both ends of the AC incoming line to form an EMI filtering circuit to reduce the influence of external electromagnetic interference, or a filtering capacitor is set between the power incoming line and the ground for input filtering, or a fuse tube is connected in series in the live wire to achieve overcurrent protection, or a varistor is set between the two incoming lines for overvoltage protection, etc. It can also adopt a combination of the above multiple forms to achieve filtering protection of the incoming line;

[0026] The output end of the rectification circuit is connected to the input end of the non-isolated power supply regulation circuit. The rectification circuit is used to convert the input AC power supply into a DC power supply and provide it to the non-isolated power supply regulation circuit. The rectification circuit can adopt a rectifier bridge to convert the AC power at the input end into a DC voltage;

[0027] The two output ends of the non-isolated power supply regulation circuit are respectively connected to the input end of the first diode and the input end of the switch isolation circuit. Among them, the non-isolated power supply regulation circuit can adopt various circuit forms such as BUCK, BOOST and their combinations. In this embodiment, taking the simplest step-down voltage regulation for non-isolated power supply regulation as an example: as Figure 3 shown, the non-isolated power supply regulation circuit includes a first power driver chip, a first switch tube Q2, a third diode D3, a third capacitor C3 and the main winding L1A of the energy storage inductor. The input end of the first switch tube Q2 is connected to the positive output end of the rectification circuit, the controlled end is connected to the output end of the first power driver chip, and the output end is connected to the first end of the main winding L1A. The cathode of the third diode D3 is connected to the first end of the main winding L1A, and the anode is connected to the negative output end of the rectification circuit. The first end of the third capacitor C3 is connected to the second end of the main winding L1A, and the second end is connected to the negative output end of the rectification circuit. Among them, the first switch tube Q2 can be a triode, a MOS tube, etc. When in use, the first switch tube Q2 is sent a PWM signal by the power driver chip to control the conduction or disconnection of the first switch tube Q2, realizing the control of the charge and discharge switching state of the main winding L1A, and then forming a corresponding supply voltage on the third capacitor C3 to achieve the control of voltage regulation and voltage stabilization.

[0028] In order to eliminate the generation of leakage current, in this embodiment, a storage inductor with an auxiliary winding is adopted in the non-isolated power supply module, that is, a dual coil is wound around the magnetic core of the storage inductor, one of which forms the main winding and the other forms the auxiliary winding. The main winding of the storage inductor plays a role in energy storage in the non-isolated power supply module. The auxiliary winding is connected to the turn-on circuit in the switch isolation circuit and generates a voltage when the main winding works, so that the turn-on circuit is charged and works to control the on-off of the switch MOS transistor. In this way, when the light is turned on, the auxiliary winding turns on the switch MOS transistor through the turn-on circuit, the switch MOS transistor conducts, and the output of the non-isolated power supply module normally supplies power to the LED lamp. When the light is turned off, the switch MOS transistor is in the off state, and combined with the single-phase conduction characteristic of the diode, the leakage current generated by the front-stage AC power supply in the non-isolated power supply module cannot form a loop through the LED lamp, effectively reducing the influence of the leakage current on the LED lamp. For reference, Figure 3 、 4 As shown, the main winding and the auxiliary winding of the storage inductor L1 are L1A and L1B respectively.

[0029] In an embodiment of the present invention, as Figure 4 shown, LED+ and LED- are the positive and negative power input terminals of the LED lamp. The first diode D2 is arranged at the negative power input terminal of the LED lamp, and the switch isolation circuit is arranged at the positive power input terminal of the LED lamp. The drain of the switch MOS transistor Q1 is connected to the positive output terminal of the non-isolated power supply module, and the source is connected to the positive power input terminal of the LED

[0030] lamp. The cathode of the first diode is connected to the drive ground terminal of the non-isolated power supply module, and the anode is connected to the negative power input terminal of the LED lamp.

[0031] Among them, the turn-on circuit includes a charging circuit and a first capacitor C2. The input terminal of the charging circuit is connected to the first end of the auxiliary winding L1B, and the output terminal is connected to the first end of the first capacitor C2. The first end of the first capacitor C2 is connected to the gate of the switch MOS transistor Q1, and the second end is connected to the second end of the auxiliary winding L1B. When the auxiliary winding L1B generates a voltage, the auxiliary winding L1B charges the first capacitor C2 through the charging circuit, so that the terminal voltage of the first capacitor C2 reaches the turn-on voltage of the switch MOS transistor. The charging circuit includes a second capacitor C1, a first resistor R1 and a second diode D1. The first end of the auxiliary winding L1B is sequentially connected through the second capacitor C1, the first resistor R1 and the anode of the second diode D1, and the cathode of the second diode D1 is connected to the first capacitor C2. A second resistor is connected in parallel across the first capacitor. When in use, its working principle is as follows:

[0032] When the light is turned on and the main winding L1A in the non-isolated power supply module starts to work, the auxiliary winding L1B charges the first capacitor C2 through the second capacitor C1, the first resistor R1, and the second diode D1. When the terminal voltage of the first capacitor C2 reaches the turn-on voltage of Vgs (switching MOS transistor Q1), the switching MOS transistor Q1 conducts, and the circuit operates normally.

[0033] When the light is turned off, the energy in the main winding L1A of the non-isolated power supply module starts to decrease to 0, the auxiliary winding L1B loses power and stops charging the first capacitor C2. The terminal voltage of the first capacitor C2 starts to drop. When the voltage drops to a level insufficient to turn on Vgs (switching MOS transistor Q1), the second resistor R2 determines the Vgs voltage of the switching MOS transistor Q1 at turn-off to be 0V, the switching MOS transistor Q1 turns off, and the first diode D2 isolates the drive ground from the earth and disconnects the leakage current working circuit.

[0034] In this embodiment, the turn-on circuit further includes a first voltage regulator diode ZD1. The first voltage regulator diode ZD1 is connected in parallel across the two ends of the first capacitor C2 to stably turn on the switching MOS transistor Q1 with the terminal voltage of the first capacitor C2 in the light-on state. An output circuit may also be provided between the switch-off circuit and the lamp to filter the power supply output to the lamp when the light is turned on. Figure 4 In this way, by adopting a combination of an inductor, a resistor, and a capacitor, the stability of the DC power supply output to the LED lamp is ensured.

[0035] In an embodiment of the present invention, as Figure 5 shown, different from the previous embodiment, the first diode D2 can also be arranged at the positive power input terminal of the LED lamp, and the switch-off circuit can be arranged at the negative power input terminal of the LED lamp for interchange. Its working principle is the same as that of the previous embodiment, and the switching of the leakage current loop when the light is turned off is also achieved.

[0036] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will all fall within the protection scope of the present invention.

Claims

1. A circuit for reducing leakage current when an LED is turned off, characterized in that: include: A non-isolated power supply module, a first diode and a switch isolation circuit, wherein the energy storage inductor in the non-isolated power supply module has an auxiliary winding, and when the non-isolated power supply module is powered on, the auxiliary winding generates a voltage, and two output ends of the non-isolated power supply module are respectively connected to the input end of the first diode and the input end of the switch isolation circuit, and the output end of the first diode and the output end of the switch isolation circuit are respectively connected to two ends of an LED lamp, and the switch isolation circuit comprises a switch MOS tube and an opening circuit, wherein the power end of the opening circuit is connected to the auxiliary winding, and the output end is connected to the gate of the switch MOS tube, so that when the auxiliary winding generates a voltage output, the switch MOS tube is turned on, the drain of the switch MOS tube is connected to the non-isolated power supply module, and the source is connected to the LED lamp, when the light is turned on, the non-isolated power supply module supplies power to the LED lamp through the switch MOS tube, and when the light is turned off, the switch MOS tube is disconnected to prevent leakage current from flowing through the LED lamp to form a loop; The drain of the switch MOS tube is connected to the positive output terminal of the non-isolated power module, the source is connected to the positive power input terminal of the LED lamp, the cathode of the first diode is connected to the driving ground terminal of the non-isolated power module, and the anode is connected to the negative power input terminal of the LED lamp; The start-up circuit includes a charging circuit and a first capacitor, wherein an input end of the charging circuit is connected to a first end of the auxiliary winding, and an output end is connected to a first end of the first capacitor, a first end of the first capacitor is connected to a gate of the switch MOS tube, and a second end is connected to a second end of the auxiliary winding. When the auxiliary winding generates a voltage, the auxiliary winding charges the first capacitor through the charging circuit, so that a terminal voltage of the first capacitor reaches a start-up voltage of the switch MOS tube.

2. The circuit for reducing leakage current when the LED is turned off according to claim 1, characterized in that: The charging circuit includes a second capacitor, a first resistor and a second diode. The first end of the auxiliary winding is connected to the anode of the second diode via the second capacitor and the first resistor in sequence, and the cathode of the second diode is connected to the first capacitor.

3. The circuit for reducing leakage current when the LED is turned off according to claim 2, characterized in that: The start-up circuit further includes a second resistor connected in parallel to both ends of the first capacitor.

4. The circuit for reducing leakage current when the LED is turned off according to claim 3, characterized in that: The start-up circuit further includes a first voltage regulator tube, which is connected in parallel to both ends of the first capacitor, so that the terminal voltage of the first capacitor can stably turn on the switch MOS tube in the light-on state.

5. The circuit for reducing leakage current when the LED is turned off according to claim 4, characterized in that: The non-isolated power supply module includes an AC input protection filter circuit, a rectifier circuit and a non-isolated power supply control circuit. The input end of the AC input protection filter circuit is connected to the external AC mains, and the output end is connected to the input end of the rectifier circuit. The output end of the rectifier circuit is connected to the input end of the non-isolated power supply control circuit. The rectifier circuit is used to convert the input AC power into a DC power supply and then provide it to the non-isolated power supply control circuit. The two output ends of the non-isolated power supply control circuit are respectively connected to the input end of the first diode and the input end of the switch isolation circuit.

6. The circuit for reducing leakage current when the LED is turned off according to claim 5, characterized in that: The non-isolated power supply control circuit includes a first power supply driver chip, a first switch tube, a third diode, a third capacitor and a main winding of an energy storage inductor, the input end of the first switch tube is connected to the positive output end of the rectifier circuit, the controlled end is connected to the output end of the first power supply driver chip, the output end is connected to the first end of the main winding, the cathode of the third diode is connected to the first end of the main winding, the anode is connected to the negative output end of the rectifier circuit, the first end of the third capacitor is connected to the second end of the main winding, and the second end is connected to the negative output end of the rectifier circuit.

Images