Xenon lamp driving monostable circuit based on NE555

Abstract

The utility model provides a xenon lamp driving monostable circuit based on NE555, comprising a xenon lamp driving control module, the xenon lamp driving control module comprises a power supply for supplying power to a xenon lamp and a primary side PWM chip U401 for controlling the power supply to supply power to the xenon lamp; the NE555 control module is used for receiving an external square wave pulse signal and outputting a high-low level signal according to the square wave pulse signal; and the optocoupler switch module receives the high and low level signals output by the NE555 control module and controls a primary side PWM chip U401 in the xenon lamp driving control module according to the high and low level signals so as to realize power supply control of the xenon lamp. The xenon lamp driving monostable circuit based on NE555 can be suitable for driving a xenon lamp, and is beneficial to improving the stability and reliability of the operation of the xenon lamp.

Description

Technical Field

[0001] The utility model belongs to the field of power supply circuits, in particular to a xenon lamp driving monostable circuit based on NE555. Background Art

[0002] Xenon lamp light source (XenonLight) is an electric light source that emits light by discharging high-pressure or ultra-high-pressure xenon gas. Because its spectrum is similar to sunlight, it is also called a primary sunlight simulator. Different series of xenon lamp light sources have different applications, and the intensity and spot size of the output light are different. Xenon lamp light sources are widely used in various photocatalytic experiments, such as photolysis of water to produce hydrogen, photodegradation of pollutants; simulated sunlight visible light acceleration experiments; various simulated sunlight ultraviolet band acceleration experiments and other studies. Therefore, in order to ensure the progress of the experiment, the xenon lamp needs a stable, reliable and reliable driving circuit, but the existing xenon lamp monostable driving circuit cannot provide reliable delayed output, and lacks voltage closed loop and triode constant current protection functions, which is not conducive to improving the stability and reliability of xenon lamps in actual use. Utility Model Content

[0003] In view of this, the utility model aims to propose a xenon lamp driving monostable circuit based on NE555 to solve the problem that the existing xenon lamp monostable driving circuit lacks protection function and affects the operating stability of the xenon lamp.

[0004] In order to achieve the above object, the technical solution of the utility model is implemented as follows:

[0005] A xenon lamp driving monostable circuit based on NE555, comprising:

[0006] A xenon lamp drive control module, the xenon lamp drive control module includes a power supply for supplying power to the xenon lamp, and a primary side PWM chip U401 for controlling the power supply to supply power to the xenon lamp;

[0007] NE555 control module, the NE555 control module receives an external square wave pulse signal and outputs high and low level signals according to the square wave pulse signal;

[0008] An optocoupler switch module receives high and low level signals output by the NE555 control module, and controls the primary PWM chip U401 in the xenon lamp drive control module according to the high and low level signals to realize power supply control of the xenon lamp;

[0009] The NE555 control module includes a NE555 chip unit, a charge and discharge unit, and an output control unit; the NE555 chip unit receives an external square wave pulse signal through the charge and discharge unit; the control end of the output control unit is connected to the output end of the NE555 chip unit;

[0010] The optocoupler switch module includes a comparator U403B, an optocoupler unit, a xenon lamp output voltage sampling unit, and a constant current source protection unit; the in-phase input end of the comparator U403B is connected to the voltage regulator through the output control unit; the inverting input end of the comparator U403B is connected to the output end of the xenon lamp through the xenon lamp output voltage sampling unit; one end of the optocoupler unit is connected to the output end of the comparator U403B through the constant current source protection unit, and the other end is connected to the primary side PWM chip U401, and the control end of the constant current source protection unit is connected to the output end of the power supply.

[0011] Furthermore, the charge and discharge unit includes a resistor R420, a resistor R421, and a capacitor C409; one end of the resistor R420 is connected to the power supply VCC, and the other end is connected to the TRIG end of the NE555 chip unit; one end of the resistor R421 is connected to the power supply VCC, and the other end of the capacitor C409 is connected to the TRIG end of the NE555 chip unit; the input end of the square wave pulse signal is set corresponding to the connection between the resistor R421 and the capacitor C409.

[0012] Furthermore, the output control unit includes a transistor Q409 and a resistor R422, the base of the transistor Q409 is connected to the output end of the NE555 chip unit through the resistor R422, the emitter is grounded, and the collector is connected to the in-phase input end of the comparator U403B.

[0013] Furthermore, the xenon lamp output voltage sampling unit includes a resistor R432, a resistor R431, a resistor R430, and a resistor R329; the resistor R430 and the resistor R329 are connected in series, and one end is connected to the inverting input end of the comparator U403B, and the other end is grounded; the resistor R432, the resistor R431, and the resistor R430 are connected in series, and one end is connected to the inverting input end of the comparator U403B, and the other end is connected to the output end of the xenon lamp.

[0014] Furthermore, the xenon lamp output voltage sampling unit further includes a capacitor C416, one end of the capacitor C416 is connected to the inverting input end of the comparator U403B, and the other end is grounded.

[0015] Furthermore, the constant current source protection unit includes a constant current source transistor Q406, a constant current source transistor Q407, a capacitor C417, a resistor R414, and a resistor R415; the base of the constant current source transistor Q406 is connected to the voltage stabilizing source, and the collector is connected to the collector of the constant current source transistor Q407; the base of the constant current source transistor Q407 is grounded, and the emitter is connected to the output end of the power supply through the resistor R415; one end of the capacitor C417 is connected to the emitter of the constant current source transistor Q407, and the other end is grounded; one end of the resistor R414 is connected to the emitter of the constant current source transistor Q407 through the resistor R415, and the other end is grounded.

[0016] Furthermore, the optocoupler switch module also includes a resistor R426, a resistor R427, a resistor R428, a capacitor C414, a capacitor C415, a capacitor C418, and a voltage regulator ZD403; after the resistor R426 and the resistor R427 are connected in series, one end is connected to the voltage regulator source, and the other end is connected to the non-inverting input terminal of the comparator U403B; after the capacitor C418 and the resistor R428 are connected in series, one end is connected to the non-inverting input terminal of the comparator U403B, and the other end is grounded; the cathode of the voltage regulator ZD403 is connected to the non-inverting input terminal of the comparator U403B through the resistor R428, and the anode is grounded; one end of the capacitor C414 is connected to the voltage regulator source through the resistor R426, and the other end is connected to the non-inverting input terminal of the comparator U403B; one end of the capacitor C415 is connected to the emitter of the transistor Q409, and the other end is connected to the non-inverting input terminal of the comparator U403B.

[0017] Furthermore, the optical coupling unit includes an optical coupler U404, a resistor R433, a MOS tube Q408, a transistor Q402, and a transistor Q403; the anode of the optical coupler U404 is connected to the power supply VCC, the cathode is connected to the D pole of the MOS tube Q408 through the resistor R433, the emitter is grounded, and the collector is connected to the base of the transistor Q402; the G pole of the MOS tube Q408 is connected to the base of the constant current source transistor Q406 and the output end of the comparator U403B, and the S pole is grounded; the collector of the transistor Q402 is connected to the VREF end of the primary PWM chip, and the emitter is grounded; the base of the transistor Q403 is connected to the OUTPUT end of the primary PWM chip, the collector is connected to the VREF end of the primary PWM chip, and the emitter is grounded.

[0018] Furthermore, the optical coupling unit further includes a capacitor C401, one end of the capacitor C401 is connected to the VREF end of the primary PWM chip, and the other end is grounded.

[0019] Compared with the prior art, the xenon lamp driving monostable circuit based on NE555 described in the utility model has the following advantages:

[0020] The utility model discloses a xenon lamp driving monostable circuit based on NE555, which is applicable to driving xenon lamps and is beneficial to improving the stability and reliability of xenon lamp operation. The NE555 monostable circuit provides a reliable delayed output and cooperates with a comparator to complete the voltage closed loop and triode constant current protection functions on the driving pole side of the xenon lamp. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation on the present invention. In the accompanying drawings:

[0022] Figure 1 This is a schematic diagram of a circuit structure in which a NE555 control module and an optical coupler switch module are connected according to an embodiment of the utility model;

[0023] Figure 2 This is a schematic diagram of the circuit structure in which the optocoupler switch module described in an embodiment of the utility model is connected to the xenon lamp drive control module. DETAILED DESCRIPTION

[0024] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0025] In the description of the present utility model, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present utility model and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present utility model. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present utility model, unless otherwise specified, "multiple" means two or more.

[0026] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" 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 or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0027] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0028] A xenon lamp driving monostable circuit based on NE555, such as Figure 1 and Figure 2 As shown, including:

[0029] The xenon lamp driving control module includes a power supply for supplying power to the xenon lamp, and a primary PWM chip U401 for controlling the power supply to supply power to the xenon lamp. Specifically, the power supply can adopt an existing xenon lamp power supply circuit, and the primary PWM chip U401 can adopt a Uc3843bvd chip. The use of the primary PWM chip and the power supply to supply power to the xenon lamp is a common technical means for those skilled in the art. The present utility model does not involve improvements to the power supply and the primary PWM chip U401, so it will not be described here.

[0030] The NE555 control module receives an external square wave pulse signal and outputs high and low level signals according to the square wave pulse signal.

[0031] The optocoupler switch module receives the high and low level signals output by the NE555 control module, and controls the primary PWM chip U401 in the xenon lamp drive control module according to the high and low level signals to realize power supply control of the xenon lamp.

[0032] The NE555 control module comprises a NE555 chip unit, a charge-discharge unit, and an output control unit; the NE555 chip unit receives an external square wave pulse signal through the charge-discharge unit; and the control end of the output control unit is connected to the output end of the NE555 chip unit.

[0033] Exemplarily, the NE555 chip unit can adopt the NE555DR chip, and the internal structure of the NE555 DR chip includes three main functional modules: a comparator, an RS trigger, and an output stage, and the external pins provide an interface for connecting with other circuit elements. This embodiment uses the NE555 monostable circuit to provide a reliable delayed output, and cooperates with the comparator to complete the voltage closed loop and triode constant current protection function of the xenon lamp driving pole side. In addition, the power supply and interface connection of the NE555 chip unit can adopt the existing technology, so it will not be repeated here.

[0034] Optionally, the charge and discharge unit includes a resistor R420, a resistor R421, and a capacitor C409; one end of the resistor R420 is connected to the power supply VCC, and the other end is connected to the TRIG end of the NE555 chip unit; one end of the resistor R421 is connected to the power supply VCC, and the other end of the capacitor C409 is connected to the TRIG end of the NE555 chip unit; the input end of the square wave pulse signal is set corresponding to the connection between the resistor R421 and the capacitor C409.

[0035] In actual application, the RC time composed of resistor R425, capacitor C413 and capacitor C411 realizes the high level output time of the OUT pin of the NE555DR chip. At the same time, the external signal sends a square wave pulse signal, and the high and low level changes of the OUT pin are realized by charging and discharging the capacitor C409.

[0036] The above-mentioned optocoupler switch module includes a comparator U403B, an optocoupler unit, a xenon lamp output voltage sampling unit, and a constant current source protection unit; the in-phase input terminal of the comparator U403B is connected to the voltage regulator through the output control unit; the inverting input terminal of the comparator U403B is connected to the output terminal of the xenon lamp through the xenon lamp output voltage sampling unit; one end of the optocoupler unit is connected to the output terminal of the comparator U403B through the constant current source protection unit, and the other end is connected to the primary side PWM chip U401, and the control end of the constant current source protection unit is connected to the output terminal of the power supply.

[0037] Optionally, the output control unit includes a transistor Q409 and a resistor R422, wherein the base of the transistor Q409 is connected to the output end of the NE555 chip unit through the resistor R422, the emitter is grounded, and the collector is connected to the in-phase input end of the comparator U403B.

[0038] Optionally, the xenon lamp output voltage sampling unit includes a resistor R432, a resistor R431, a resistor R430, and a resistor R329; one end of the resistor R430 and the resistor R329 connected in series is connected to the inverting input end of the comparator U403B, and the other end is grounded; one end of the resistor R432, the resistor R431, and the resistor R430 connected in series is connected to the inverting input end of the comparator U403B, and the other end is connected to the output end of the xenon lamp. The xenon lamp output voltage sampling unit also includes a capacitor C416, one end of the capacitor C416 is connected to the inverting input end of the comparator U403B, and the other end is grounded.

[0039] In actual application, resistors R432, R431, R429, and R430 form a sample of the output voltage of the xenon lamp at pin 6 (inverting input terminal) of comparator U403B. After voltage division, the samples are connected to the external reference (6-10V) at pin 2 (inverting input terminal) and pin 5 of the non-inverting input terminal of U403B. Specifically, when the voltage at the inverting input terminal of comparator U403B is higher than the voltage at the non-inverting input terminal (that is, when the output voltage of the xenon lamp increases), the output terminal outputs a low level. At this time, the optical coupler U404 is not turned on, and the optical coupler unit will not participate in the drive control of the primary PWM chip. Similarly, when the voltage at the inverting input terminal is lower than the voltage at the non-inverting input terminal, the optical coupler U404 is turned on, and the drive of the primary PWM chip is pulled down. This process realizes the closed-loop regulation of the power supply, thereby realizing the adjustable and stable output voltage of the power supply.

[0040] Optionally, the constant current source protection unit includes a constant current source transistor Q406, a constant current source transistor Q407, a capacitor C417, a resistor R414, and a resistor R415; the base of the constant current source transistor Q406 is connected to the voltage stabilizing source, and the collector is connected to the collector of the constant current source transistor Q407; the base of the constant current source transistor Q407 is grounded, and the emitter is connected to the output end of the power supply through the resistor R415; one end of the capacitor C417 is connected to the emitter of the constant current source transistor Q407, and the other end is grounded; one end of the resistor R414 is connected to the emitter of the constant current source transistor Q407 through the resistor R415, and the other end is grounded.

[0041] Specifically, when the power supply is working normally, a high-voltage xenon lamp is connected between HV and GND. The current loop is emitted from HV, passes through the xenon lamp and returns to GND, and then passes through the transformer. This is the entire flow loop of the current loop. When current flows, a potential difference will be formed between resistors R414 and R415. The potential of point K is lower than GND, that is, a voltage lower than 0V is formed at pin 8 in the figure. When the current flowing through is large enough to make the potential of point K exceed 0.7V, the constant current source transistor Q407 is turned on, the constant current source transistor Q406 is forward biased, and the B pole of the constant current source transistor Q406 is clamped at 1.4V. At this time, the MOS tube Q408 is not turned on, and the primary PWM chip drive is pulled down, thereby realizing the constant current function. In actual use, resistor R414, resistor R415, and transistor Q407 form a simple constant current source circuit. Once the overcurrent threshold is triggered, the primary PWM chip will be driven through the optical coupler U404 to achieve protection.

[0042] In actual application, the optocoupler switch module also includes a resistor R426, a resistor R427, a resistor R428, a capacitor C414, a capacitor C415, a capacitor C418, and a voltage regulator ZD403; after the resistor R426 and the resistor R427 are connected in series, one end is connected to the voltage regulator source, and the other end is connected to the non-inverting input terminal of the comparator U403B; after the capacitor C418 and the resistor R428 are connected in series, one end is connected to the non-inverting input terminal of the comparator U403B, and the other end is grounded; the cathode of the voltage regulator ZD403 is connected to the non-inverting input terminal of the comparator U403B through the resistor R428, and the anode is grounded; one end of the capacitor C414 is connected to the voltage regulator source through the resistor R426, and the other end is connected to the non-inverting input terminal of the comparator U403B; one end of the capacitor C415 is connected to the emitter of the transistor Q409, and the other end is connected to the non-inverting input terminal of the comparator U403B.

[0043] Optionally, the optical coupling unit includes an optical coupler U404, a resistor R433, a MOS tube Q408, a transistor Q402, and a transistor Q403; the anode of the optical coupler U404 is connected to the power supply VCC, the cathode is connected to the D pole of the MOS tube Q408 through the resistor R433, the emitter is grounded, and the collector is connected to the base of the transistor Q402; the G pole of the MOS tube Q408 is connected to the base of the constant current source transistor Q406 and the output end of the comparator U403B, and the S pole is grounded; the collector of the transistor Q402 is connected to the VREF end of the primary PWM chip, and the emitter is grounded; the base of the transistor Q403 is connected to the OUTPUT end of the primary PWM chip, the collector is connected to the VREF end of the primary PWM chip, and the emitter is grounded. The optical coupling unit also includes a capacitor C401, one end of which is connected to the VREF end of the primary PWM chip, and the other end is grounded.

[0044] The working process of this circuit is as follows:

[0045] When the OUT output pin of the NE555 chip unit (i.e., U402) outputs a low level, the MOS tube Q408 is turned on, the optocoupler unit is turned on, and the primary PWM chip U401 works normally. At this time, the xenon lamp outputs normally. When the OUT output pin of the NE555 chip unit (i.e., U402) outputs a high level, the MOS tube Q408 is not turned on, the optocoupler unit is no longer turned on, the primary PWM chip U401 is pulled down, and the xenon lamp is no longer output to the outside, and slowly decreases to 0V. Specifically, when the MOS tube Q408 is not turned on, the primary diode of the optocoupler U404 in the optocoupler unit does not generate photoelectric conduction. At this time, the secondary side of the optocoupler U404 is at a high level, turning on the triode, and then pulling down the primary PWM chip U401.

[0046] The utility model discloses a xenon lamp driving monostable circuit based on NE555, which is applicable to driving xenon lamps and is beneficial to improving the stability and reliability of xenon lamp operation. The NE555 monostable circuit provides a reliable delayed output and cooperates with a comparator to complete the voltage closed loop and triode constant current protection functions on the driving pole side of the xenon lamp.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A xenon lamp driving monostable circuit based on NE555, characterized in that: include: A xenon lamp drive control module, the xenon lamp drive control module includes a power supply for supplying power to the xenon lamp, and a primary side PWM chip U401 for controlling the power supply to supply power to the xenon lamp; NE555 control module, the NE555 control module receives an external square wave pulse signal and outputs high and low level signals according to the square wave pulse signal; An optocoupler switch module, which receives high and low level signals output by the NE555 control module, and controls the primary PWM chip U401 in the xenon lamp drive control module according to the high and low level signals, so as to realize power supply control of the xenon lamp; The NE555 control module includes a NE555 chip unit, a charge and discharge unit, and an output control unit; the NE555 chip unit receives an external square wave pulse signal through the charge and discharge unit; the control end of the output control unit is connected to the output end of the NE555 chip unit; The optocoupler switch module includes a comparator U403B, an optocoupler unit, a xenon lamp output voltage sampling unit, and a constant current source protection unit; the in-phase input end of the comparator U403B is connected to the voltage regulator through the output control unit; the inverting input end of the comparator U403B is connected to the output end of the xenon lamp through the xenon lamp output voltage sampling unit; one end of the optocoupler unit is connected to the output end of the comparator U403B through the constant current source protection unit, and the other end is connected to the primary side PWM chip U401, and the control end of the constant current source protection unit is connected to the output end of the power supply.

2. According to claim 1, a xenon lamp driving monostable circuit based on NE555 is characterized in that: The charge and discharge unit includes a resistor R420, a resistor R421, and a capacitor C409; one end of the resistor R420 is connected to the power supply VCC, and the other end is connected to the TRIG end of the NE555 chip unit; one end of the resistor R421 is connected to the power supply VCC, and the other end of the capacitor C409 is connected to the TRIG end of the NE555 chip unit; the input end of the square wave pulse signal is set corresponding to the connection between the resistor R421 and the capacitor C409.

3. The xenon lamp driving monostable circuit based on NE555 according to claim 1, characterized in that: The output control unit includes a transistor Q409 and a resistor R422. The base of the transistor Q409 is connected to the output end of the NE555 chip unit through the resistor R422, the emitter is grounded, and the collector is connected to the in-phase input end of the comparator U403B.

4. The xenon lamp driving monostable circuit based on NE555 according to claim 3 is characterized in that: The xenon lamp output voltage sampling unit includes a resistor R432, a resistor R431, a resistor R430, and a resistor R329; one end of the resistor R430 and the resistor R329 connected in series is connected to the inverting input end of the comparator U403B, and the other end is grounded; one end of the resistor R432, the resistor R431, and the resistor R430 connected in series is connected to the inverting input end of the comparator U403B, and the other end is connected to the output end of the xenon lamp.

5. The xenon lamp driving monostable circuit based on NE555 according to claim 4 is characterized in that: The xenon lamp output voltage sampling unit further includes a capacitor C416, one end of which is connected to the inverting input end of the comparator U403B, and the other end of which is grounded.

6. A xenon lamp driving monostable circuit based on NE555 according to claim 4 or 5, characterized in that: The constant current source protection unit includes a constant current source transistor Q406, a constant current source transistor Q407, a capacitor C417, a resistor R414, and a resistor R415; the base of the constant current source transistor Q406 is connected to the voltage stabilizing source, and the collector is connected to the collector of the constant current source transistor Q407; the base of the constant current source transistor Q407 is grounded, and the emitter is connected to the output end of the power supply through the resistor R415; one end of the capacitor C417 is connected to the emitter of the constant current source transistor Q407, and the other end is grounded; one end of the resistor R414 is connected to the emitter of the constant current source transistor Q407 through the resistor R415, and the other end is grounded.

7. The xenon lamp driving monostable circuit based on NE555 according to claim 6, characterized in that: The optocoupler switch module also includes a resistor R426, a resistor R427, a resistor R428, a capacitor C414, a capacitor C415, a capacitor C418, and a voltage regulator ZD403; after the resistor R426 and the resistor R427 are connected in series, one end is connected to the voltage regulator source, and the other end is connected to the non-inverting input terminal of the comparator U403B; after the capacitor C418 and the resistor R428 are connected in series, one end is connected to the non-inverting input terminal of the comparator U403B, and the other end is grounded; the cathode of the voltage regulator ZD403 is connected to the non-inverting input terminal of the comparator U403B through the resistor R428, and the anode is grounded; one end of the capacitor C414 is connected to the voltage regulator source through the resistor R426, and the other end is connected to the non-inverting input terminal of the comparator U403B; one end of the capacitor C415 is connected to the emitter of the transistor Q409, and the other end is connected to the non-inverting input terminal of the comparator U403B.

8. The NE555-based xenon lamp driving monostable circuit according to claim 6, characterized in that: The optical coupling unit includes an optical coupler U404, a resistor R433, a MOS tube Q408, a transistor Q402, and a transistor Q403; the anode of the optical coupler U404 is connected to the power supply VCC, the cathode is connected to the D pole of the MOS tube Q408 through the resistor R433, the emitter is grounded, and the collector is connected to the base of the transistor Q402; the G pole of the MOS tube Q408 is connected to the base of the constant current source transistor Q406 and the output end of the comparator U403B, and the S pole is grounded; the collector of the transistor Q402 is connected to the VREF end of the primary PWM chip, and the emitter is grounded; the base of the transistor Q403 is connected to the OUTPUT end of the primary PWM chip, the collector is connected to the VREF end of the primary PWM chip, and the emitter is grounded.

9. The NE555-based xenon lamp driving monostable circuit according to claim 8, characterized in that: The optical coupling unit further includes a capacitor C401 , one end of which is connected to the VREF end of the primary PWM chip, and the other end of which is grounded.

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