Remote power supply lighting system

Abstract

The invention relates to the technical field of power supply illumination, in particular to a remote power supply illumination system. The system reliability is remarkably improved through the overall structure of integrating the signal preprocessing module, the MCU module and the power supply circuit module, the signal preprocessing module is responsible for conducting surge suppression, thermal turn-off, short-circuit protection and signal conversion on input and output control signals, the integrity of DMX512 signals is ensured, and the stability of the DMX512 signals is improved. The MCU module utilizes a high-frequency clock signal to quickly analyze a control instruction and output an accurate second control signal, and the power supply circuit module provides stable current for each component through multi-stage voltage conversion, so that stable power supply at a long distance of 130 meters is realized, the dimming precision reduction and stroboflash phenomena of the LED lamp are effectively avoided, and the LED lamp is more stable in dimming. The adaptability and the practicability of the lighting system are integrally improved; the technical problem that low-voltage power supply easily affects the dimming precision of the lamp and even causes stroboflash of the LED in long-distance transmission is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply and lighting, and in particular to a long-distance power supply and lighting system. Background Art

[0002] When low-voltage power supply (such as 24V / 48V) is used for long-distance transmission, voltage attenuation caused by wire resistance can affect the stability of DMX512 signals. The DMX512 protocol is based on RS-485 differential signal transmission. Although it has strong anti-interference capabilities, in low-voltage power supply scenarios, the terminal device may suffer signal distortion or loss due to insufficient power supply. For example, when the supply voltage is lower than the device rated value, the signal resolution capability of the DMX512 receiver will decrease, affecting the dimming accuracy of LED lamps. In fact, the voltage at the end of the line may even fall below the rated voltage of the device due to losses, causing the device to malfunction. The DMX512 protocol requires a data frame refresh rate of no less than 20Hz. If the supply voltage fluctuates, the synchronization of the control signal may be impaired. For example, a voltage drop at the end may cause the PWM dimming signal to jitter, resulting in LED flicker. Summary of the Invention

[0003] In response to the deficiencies of the existing technology, the present invention provides a long-distance power supply lighting system, which solves the technical problem that low-voltage power supply easily affects the dimming accuracy of lamps and even causes LED flicker during long-distance transmission.

[0004] To solve the above technical problems, the present invention provides the following technical solutions: a remote power supply lighting system, comprising a plurality of lamps for lighting, and a controller for sending control signals to control the lamps, wherein the lamps are further equipped with: Signal preprocessing module, which consists of two groups and is used to preprocess the control signal transmitted to the MCU module and the control signal output by the MCU module respectively. The preprocessing includes surge suppression, thermal shutdown, short-circuit protection and signal conversion; An MCU module, the MCU module being configured to receive a first control signal transmitted by the controller and to issue a second control signal for controlling the lamp according to the first control signal; A power supply circuit module is used to provide a current with a predetermined voltage to the signal preprocessing module, the MCU module and the lamp.

[0005] Preferably, the signal preprocessing module includes a 485 chip U4, and a resistor R11 and a fuse F1 are connected in series on the 6th pin of the 485 chip U4. A pull-up resistor R15 is also connected to the 6th pin of the 485 chip U4 to stabilize the reference level of the electrical signal. A grounded TVS tube T1 is connected between the resistor R11 and the fuse F1. A resistor R12 and a fuse F2 are connected in series on the 7th pin of the 485 chip U4. A grounded TVS tube T2 is connected between the resistor R12 and the fuse F2. A resistor R9 is connected between the ends of the resistor R11 and the resistor R12 connected to the TVS tube T1 and the TVS tube T2 respectively. A grounded resistor R16 is connected to the 7th pin of the 485 chip U4. The 485 chip U4 is connected to the corresponding pin of the MCU module, and a grounded resistor R19 is connected to the 2nd and 3rd pins of the 485 chip U4.

[0006] Preferably, the MCU module includes a chip U6, a capacitor C10 is connected between pins 15 and 16 of the chip U6, pins 15 and 16 of the chip U6 are grounded and connected to a +3.3V power supply respectively, and a crystal oscillator circuit for providing a high-frequency clock signal and a control circuit for issuing a second control signal are provided on the chip U6.

[0007] Preferably, the crystal oscillator circuit includes a chip X1 for providing a high-frequency clock signal, pin 1 of chip X1 is connected to pin 2 of chip U6, pin 3 of chip X1 is connected to pin 3 of chip U6, pins 2 and 4 of chip X1 are grounded, and pin 3 of chip X1 is connected to a grounded capacitor C14.

[0008] Preferably, the control circuit includes a chip U7, a resistor R25 is connected in series between pin 3 of chip U7 and pin 14 of chip U6, pin 1 of chip U7 is connected to a +3.3V power supply, pin 2 of chip U7 is grounded, a capacitor C16 is also connected in series between pin 1 and pin 2 of chip U7, a resistor R26 is connected between pin 5 of chip U7 and the +3.3V power supply, and pin 4 of chip U7 is connected to the signal receiving end of the lamp.

[0009] Preferably, the power supply circuit module includes a 485 chip power supply circuit, an MCU power supply circuit and a lamp power supply circuit; The 485 chip power supply circuit includes chip U2, and the 6th pin of chip U2 is connected to the grounded capacitor C4 and connected to the +24V power supply. The capacitor C5 is connected between the 6th pin and the 1st pin of chip U2, and the diode D3 is connected between the 6th pin and the 2nd pin of chip U2. The inductor L2 is connected between the 6th pin of chip U2 and the +5V power supply. The capacitor E3 and the resistors R7 and R8 connected in parallel therewith are arranged between the 2nd pin of chip U2 and the +5V power supply.

[0010] Preferably, the MCU power supply circuit includes a chip U3, a capacitor C6 is connected between pins 1 and 3 of the chip U3, and capacitors E4 and C7 are connected in parallel between pins 2 and 4 of the chip U3 and pin 1.

[0011] Preferably, the lamp power supply circuit includes a chip U1, a diode D1 is connected to pin 1 of the chip U1, a resistor R1 is connected between pin 1 and pin 2 of the chip U1, a variable resistor RZ and a capacitor E1, both of which are grounded, are connected in parallel to pin 1 of the chip U1, a resistor R2, a diode Z1, an inductor L1 and a resistor R5 are connected in series between pin 2 and pin 8 of the chip U1, a capacitor C2 is connected between pin 2 and pin 6 of the chip U1, a resistor R3 is connected between pin 3 and pin 4 of the chip U1 and pin 6 of the chip, a resistor R4 is connected between pin 3 and pin 4 of the chip U1 and the positive pole of the diode Z1, a diode D2 is also connected to pin 6 of the chip U1, a capacitor E2, a capacitor C3 and a resistor R6 are connected in parallel between the diode D2 and the inductor L1.

[0012] By means of the above technical solution, the present invention provides a remote power supply lighting system, which has at least the following beneficial effects: 1. The present invention solves the problems of signal attenuation and voltage drop in long-distance transmission of low-voltage power supply through the overall architecture of integrating signal preprocessing module, MCU module and power supply circuit module, and significantly improves system reliability. The signal preprocessing module is responsible for surge suppression, thermal shutdown, short-circuit protection and signal conversion of input and output control signals to ensure the integrity of DMX512 signals. The MCU module uses high-frequency clock signals to quickly analyze control instructions and output accurate second control signals. The power supply circuit module provides stable current to each component through multi-level voltage conversion. According to actual measurements, the system has successfully broken through the industry's transmission distance limitations (such as 10-50 meters) and achieved stable power supply over a long distance of 130 meters, effectively avoiding the decline in dimming accuracy and flickering of LED lamps, and improving the adaptability and practicality of the lighting system as a whole.

[0013] 2. The signal preprocessing module of the present invention adopts a dual-group design, which realizes surge suppression, thermal shutdown and short-circuit protection through the 485 chip U4 combined with TVS tube, fuse and several resistors. This design greatly reduces the risk of signal distortion caused by wire resistance and environmental interference in long-distance transmission, ensures the reliable transmission of control signals in long-distance chain connection, and thus improves the system's anti-interference ability and durability.

[0014] 3. The core chip U6 of the MCU module of the present invention cooperates with the crystal oscillator circuit and the control circuit to realize high-speed data processing by using a high-frequency clock signal, significantly improving the dimming accuracy and eliminating flicker. The crystal oscillator circuit provides a stable high-frequency clock input through the chip X1, and the capacitor C14 is grounded to optimize the waveform, supporting 60Hz frame rate synchronization, so that the MCU can quickly decode the RS-485 signal. The control circuit uses the chip U7, resistor R25 and capacitor C16 to suppress signal reflection and power supply noise to ensure the output stability of the second control signal. This design uses the characteristic that the human eye has no flicker perception for light sources >50Hz, and reduces the jitter of the PWM dimming signal through high-frequency operation to achieve ultra-fine dimming, solve the synchronization problem caused by terminal voltage fluctuations, and greatly improve the response speed and visual comfort of the lamp. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings: Figure 1 This is a structural block diagram of the remote power supply lighting system of the present invention; Figure 2 This is a circuit diagram of a signal preprocessing module provided at the input end of the MCU module of the present invention; Figure 3 This is a circuit diagram of a signal preprocessing module provided at the output end of the MCU module of the present invention; Figure 4 This is a circuit diagram of the MCU module of the present invention; Figure 5 This is a circuit diagram of the 485 chip power supply circuit of the present invention; Figure 6 A circuit diagram of the MCU power supply circuit of the present invention; Figure 7 This is a circuit diagram of the power supply circuit for the lamp of the present invention.

[0016] In the figure: 1. lamp; 2. controller; 3. signal preprocessing module; 4. MCU module; 5. power supply circuit module; 51. crystal oscillator circuit; 52. control circuit. DETAILED DESCRIPTION

[0017] To make the above-mentioned objectives, features, and advantages of the present invention more clearly understood, the present invention is further described below in detail with reference to the accompanying drawings and specific embodiments. This will enable a full understanding of how this application uses technical means to solve technical problems and achieve technical effects, and to implement the invention accordingly.

[0018] In order to solve the technical problem that low-voltage power supply can easily affect the dimming accuracy of lamps and even cause LED flicker during long-distance transmission, the present invention provides a long-distance power supply lighting system to ensure the stability of DMX512 signals and power supply voltage, and to ensure the normal adjustment and operation of multiple lamps 1 used for lighting. The controller 2 is used to send control signals to control the dimming of the lamps 1. In addition, the lamps 1 are also equipped with: Two groups of signal preprocessing modules 3 are respectively arranged at the signal receiving port and the signal output port of the MCU module 4. The two groups of signal preprocessing modules 3 are respectively used to preprocess the control signal transmitted to the MCU module 4 and the control signal output by the MCU module 4. The preprocessing module 3 receives the control signal transmitted by other lamps 1 or the controller 2 and transmits it to the MCU module 4 after preprocessing. After receiving the preprocessed control signal, the MCU module 4 sends a corresponding second control signal to control the dimming action of the corresponding lamp 1. If there is a lamp 1 corresponding to the current MCU module 4 and connected to the next lamp 1 through a wire, the current MCU module 4 will preprocess the control signal again and transmit it to the next lamp 1 connected to it. The preprocessing module 3 of the current lamp 1 will transmit the preprocessed control signal to the preprocessing module 3 of the next lamp 1. If there is no lamp 1 corresponding to the current MCU module The next lamp 1 connected to the lamp 1 through a wire can be equipped with a signal preprocessing module 3 at the signal output port of the current MCU module 4. The preprocessing includes surge suppression, thermal shutdown, short-circuit protection and signal conversion. In addition, it also includes a power supply circuit module 5 that provides a current with a predetermined voltage to the signal preprocessing module 3, the MCU module 4 and the lamp 1. In actual application, since the longer the transmission is on a low-voltage circuit, the greater the line loss and the greater the voltage drop, the voltage is increased. For example, if the conventional voltage is DC24V / 48V, the voltage is increased to DC96V / DC110V, etc., and the preprocessing module 3 and the MCU module 4 are cooperated to ensure the stability of the DMX512 signal. At the same time, the power supply circuit module 5 is cooperated to ensure the stability of the voltage obtained by the lamp 1 and reach the predetermined value. After actual measurement, the technical barriers of 10 meters / 20 meters / 50 meters in the industry have been broken through, and 130 meters of transmission have been achieved.

[0019] The signal pre-processing module 3 includes surge suppression, thermal shutdown, short circuit protection and signal conversion for the control signal. The two groups of signal pre-processing modules 3 are respectively as follows: Figure 2 and Figure 3 As shown, they are respectively set at the signal receiving port and signal output port of MCU module 4. Figure 2Introducing its specific circuit structure, the controller 2 sends data packets through the AB dual-wire, namely two groups of signals DAi and DBi respectively. The signal preprocessing module 3 includes converting the 485 signal transmitted by the controller 2, namely the control signal, into a DMX512 signal for the MCU module 4 to analyze. The 6th pin of the 485 chip U4 is connected in series with a resistor R11 and a fuse F1. The 6th pin of the 485 chip U4 is also connected to a pull-up resistor R15 to stabilize the reference level of the electrical signal. A grounded TVS tube T1 is connected between the resistor R11 and the fuse F1 to protect the signal bus and support thermal shutdown. The 7th pin of the 485 chip U4 is connected in series with a resistor R12 and a fuse F2. Fuse F2 and fuse F1 cooperates to achieve short-circuit protection for the two groups of signal lines. A grounded TVS tube T2 is connected between resistor R12 and fuse F2. Resistor R9 is connected between the ends of resistors R11 and R12 connected to TVS tubes T1 and TVS tubes T2 respectively. Resistor R9 is an internal interrupt resistor that stabilizes the signal. Pin 7 of the 485 chip U4 is connected to a grounded resistor R16. The 485 chip U4 is connected to the corresponding pins of the MCU module 4. Pins 2 and 3 of the 485 chip U4 are connected to a grounded resistor R19. The TVS tube T1, TVS tube T2, resistor R9, pull-up resistor R15 and resistor R16 work together to achieve the effect of stabilizing the control signal and surge suppression.

[0020] The circuit structure of the MCU module 4 is described in detail below. The MCU module 4 includes a chip U6. A capacitor C10 is connected between the 15 and 16 pins of the chip U6. The 15 and 16 pins of the chip U6 are grounded and connected to a +3.3V power supply respectively. The chip U6 is provided with a crystal oscillator circuit 51 that provides a high-frequency clock signal and a control circuit 52 for issuing a second control signal. The crystal oscillator circuit 51 of the high-frequency clock signal can provide a high-speed time base for the chip U6, realize the decoding of the 10Mbps RS-485 signal, realize ultra-fine dimming, and is between the human eye's sensitivity to >5 The 0Hz light source has no flicker perception, and the probability of the human eye perceiving flicker is reduced by a high-frequency clock signal. The crystal oscillator circuit 51 includes a chip X1 for providing a high-frequency clock signal. Pin 1 of the chip X1 is connected to pin 2 of the chip U6, and pin 3 of the chip X1 is connected to pin 3 of the chip U6. Pins 2 and 4 of the chip X1 are grounded, and a grounded capacitor C14 is connected to pin 3 of the chip X1, thereby emitting a high-frequency clock signal of the corresponding frequency according to the instructions of the controller 2. The chip X1 supports 4MHz high-frequency clock input and 60Hz frame rate synchronization.

[0021] The structure of the control circuit 52 is further explained below. The control circuit 52 includes a chip U7 for receiving DMX512 signals. A resistor R25 is connected in series between pin 3 of chip U7 and pin 14 of chip U6 to suppress signal reflection and current limiting protection of pin U6. Pin 1 of chip U7 is connected to the +3.3V power supply, and pin 2 of chip U7 is grounded. A capacitor C16 is also connected in series between pin 1 and pin 2 of chip U7 to filter out high-frequency noise of the 3.3V power supply and improve the stability of U7 signal conversion. A resistor R26 is connected between pin 5 of chip U7 and the +3.3V power supply, and pin 4 of chip U7 is connected to the signal receiving end of lamp 1, so that lamp 1 can receive a stable DMX512 signal and achieve high-precision dimming of lamp 1.

[0022] The power supply circuit module 5 includes a 485 chip power supply circuit, an MCU power supply circuit, and a lamp power supply circuit to ensure that the signal preprocessing module 3, the MCU module 4, and the lamp 1 in the lamp 1 can all operate stably within a predetermined voltage range after the power supply voltage is increased. The structure of each power supply circuit is introduced one by one below: The 485 chip power supply circuit includes chip U2. Pin 6 of chip U2 is connected to a grounded capacitor C4 and is connected to a +24V power supply. Chip U2 converts 24V input into 5V output. Capacitor C4 is used to filter out the switching noise of the 24V input line. Capacitor C5 is connected between pin 6 and pin 1 of chip U2 to provide a floating voltage for the high-side MOS drive circuit inside chip U2. Diode D3 is connected between pin 6 and pin 2 of chip U2 to provide a current loop for inductor L2 when the MOS inside chip U2 is turned off. Inductor coil L2 is connected between pin 6 of chip U2 and the +5V power supply to store and release energy to achieve voltage conversion. Capacitor E3 is set between pin 2 of chip U2 and the +5V power supply to suppress 5V output ripple, and resistors R7 and R8 are connected in parallel with it to accurately ensure the accuracy of the output 5V voltage.

[0023] In order to ensure the stable operation of the MCU module 4, the MCU power supply circuit includes a chip U3 that steps down the 24V input to 3.3V. A capacitor C6 is connected between pins 1 and 3 of the chip U3 to filter out the switching noise of the 24V input line. After pins 2 and 4 of the chip U3 are connected, a capacitor E4 is connected in parallel with pin 1 to suppress the low-frequency ripple of the 3.3V output and a capacitor C7 is connected to absorb the high-frequency noise generated by the high-speed operation of the MCU.

[0024] The power supply circuit of lamp 1 includes chip U1 which steps down the input voltage such as 96V input to the voltage required by LED. Diode D1 is connected to pin 1 of chip U1 to prevent the input power polarity from being reversed and burning U1. Resistor R1 is connected between pins 1 and 2 of chip U1, and cooperates with the internal comparator of chip U1 to realize overcurrent protection. Pin 1 of chip U1 is connected in parallel with a variable resistor RZ and a capacitor E1 both of which are grounded. The variable resistor RZ is used to realize surge suppression. The large-capacity electrolytic capacitor E1 can cope with input voltage fluctuations and suppress low-frequency ripple. Resistor R2, diode Z1, inductor L1 and resistor R5 are connected in series between pins 2 and 8 of chip U1. Resistor R5 cooperates with chip U1 to realize overcurrent protection of lamp 1. Protection, resistor R2 forms a programmable resistor network with resistors R3 and R4 to set the output voltage. Diode Z1 provides a stable reference voltage (such as 2.5V) to ensure feedback accuracy. Capacitor C2 is connected between pins 2 and 6 of chip U1, and resistor R3 is connected between pins 3 and 4 of chip U1 and pin 6. Resistor R4 is connected between pins 3 and 4 of chip U1 and the positive electrode of diode Z1. Diode D2 is also connected to pin 6 of chip U1 to maintain minimum current under light load. Capacitor E2, capacitor C3 and resistor R6 are connected in parallel between diode D2 and inductor L1. Electrolytic capacitor E2 suppresses low-frequency ripple of LED dimming to achieve anti-strobe. Capacitor C3 absorbs switching noise.

[0025] The above embodiments provide a detailed introduction to the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas. At the same time, for those skilled in the art, according to the ideas of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A remote power supply lighting system comprising a plurality of lamps (1) for lighting, and a controller (2) for sending control signals to control the lamps (1), characterized in that: The lamp (1) is also equipped with: A signal preprocessing module (3), wherein the signal preprocessing module (3) comprises two groups, each used to preprocess a control signal transmitted to the MCU module (4) and a control signal output by the MCU module (4), wherein the preprocessing includes surge suppression, thermal shutdown, short-circuit protection, and signal conversion; An MCU module (4), the MCU module (4) being used to receive a first control signal transmitted by the controller (2), and to send a second control signal for controlling the lamp (1) according to the first control signal; A power supply circuit module (5) is used to provide a current with a predetermined voltage to the signal preprocessing module (3), the MCU module (4) and the lamp (1).

2. A remote power supply lighting system according to claim 1, characterized in that: The signal preprocessing module (3) includes a 485 chip U4, a resistor R11 and a fuse F1 are sequentially connected in series on the 6th pin of the 485 chip U4, a pull-up resistor R15 is also connected to the 6th pin of the 485 chip U4 to stabilize the reference level of the electrical signal, a grounded TVS tube T1 is connected between the resistor R11 and the fuse F1, a resistor R12 and a fuse F2 are sequentially connected in series on the 7th pin of the 485 chip U4, a grounded TVS tube T2 is connected between the resistor R12 and the fuse F2, a resistor R9 is connected between the ends of the resistors R11 and R12 connected to the TVS tube T1 and TVS tube T2 respectively, a grounded resistor R16 is connected to the 7th pin of the 485 chip U4, the 485 chip U4 is connected to the corresponding pin of the MCU module (4), and a grounded resistor R19 is connected to the 2nd and 3rd pins of the 485 chip U4.

3. The remote power supply lighting system according to claim 1, characterized in that: The MCU module (4) includes a chip U6, a capacitor C10 is connected between pins 15 and 16 of the chip U6, the pins 15 and 16 of the chip U6 are grounded and connected to a +3.3V power supply, respectively, and a crystal oscillator circuit (51) for providing a high-frequency clock signal and a control circuit (52) for issuing a second control signal are provided on the chip U6.

4. A remote power supply lighting system according to claim 3, characterized in that: The crystal oscillator circuit (51) includes a chip X1 for providing a high-frequency clock signal, wherein pin 1 of the chip X1 is connected to pin 2 of the chip U6, pin 3 of the chip X1 is connected to pin 3 of the chip U6, pins 2 and 4 of the chip X1 are grounded, and pin 3 of the chip X1 is connected to a grounded capacitor C14.

5. The remote power supply lighting system according to claim 3, characterized in that: The control circuit (52) includes a chip U7, a resistor R25 is connected in series between pin 3 of the chip U7 and pin 14 of the chip U6, a pin 1 of the chip U7 is connected to a +3.3V power supply, a pin 2 of the chip U7 is grounded, a capacitor C16 is connected in series between pins 1 and 2 of the chip U7, a resistor R26 is connected between pin 5 of the chip U7 and the +3.3V power supply, and a pin 4 of the chip U7 is connected to a signal receiving end of the lamp (1).

6. The remote power supply lighting system according to claim 1, characterized in that: The power supply circuit module (5) includes a 485 chip power supply circuit, an MCU power supply circuit and a lamp (1) power supply circuit; The 485 chip power supply circuit includes chip U2, and the 6th pin of chip U2 is connected to the grounded capacitor C4 and connected to the +24V power supply. The capacitor C5 is connected between the 6th pin and the 1st pin of chip U2, and the diode D3 is connected between the 6th pin and the 2nd pin of chip U2. The inductor L2 is connected between the 6th pin of chip U2 and the +5V power supply. The capacitor E3 and the resistors R7 and R8 connected in parallel therewith are arranged between the 2nd pin of chip U2 and the +5V power supply.

7. The remote power supply lighting system according to claim 6, characterized in that: The MCU power supply circuit includes a chip U3, a capacitor C6 is connected between pins 1 and 3 of the chip U3, and capacitors E4 and C7 are connected in parallel between pins 2 and 4 of the chip U3 and pin 1.

8. The remote power supply lighting system according to claim 6, characterized in that: The power supply circuit of the lamp (1) includes a chip U1, a diode D1 is connected to pin 1 of the chip U1, a resistor R1 is connected between pin 1 and pin 2 of the chip U1, a variable resistor RZ and a capacitor E1, both of which are grounded, are connected in parallel to pin 1 of the chip U1, a resistor R2, a diode Z1, an inductor L1 and a resistor R5 are connected in series between pin 2 and pin 8 of the chip U1, a capacitor C2 is connected between pin 2 and pin 6 of the chip U1, a resistor R3 is connected between pin 3 and pin 4 of the chip U1 and pin 6 of the chip U1, a resistor R4 is connected between pin 3 and pin 4 of the chip U1 and the positive electrode of the diode Z1, a diode D2 is further connected to pin 6 of the chip U1, a capacitor E2, a capacitor C3 and a resistor R6 are connected in parallel between the diode D2 and the inductor L1.

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