Single live wire switch system and control method thereof

Abstract

The invention provides a single-live-wire switch system and a control method thereof, the single-live-wire switch system comprises a switch panel and a load module, the switch panel is connected between a live-wire input end and a live-wire output end, and the load module is connected between a zero line and the live-wire output end; the system further comprises a flash elimination module, the flash elimination module is connected between the zero line and the live wire output end, the flash elimination module rectifies voltage between the zero line and the live wire output end to obtain rectified voltage, and the flash elimination module judges whether a load in the load module is switched on or not according to the rectified voltage. If it is judged that the load is switched on, the flash elimination module is switched off; and if the load is judged to be switched off, the flash elimination module is kept switched on within a preset time period of each work period and is kept switched off beyond the preset time period. The efficiency of the whole lamp can be improved, and the service life of a system switching device is prolonged.

Description

Technical Field

[0001] This invention relates to the field of power electronics, and in particular to a single-wire switching system and its control method. Background Technology

[0002] When a single-wire smart switch panel draws power from a lamp while it is off, the current flows through the lamp's bus capacitor, causing the bus capacitor voltage to rise. When this voltage rises to a certain level, it can cause the lamp to suddenly flicker. To solve this problem, there are two main solutions: Solution 1, see... Figure 1 Option 1: Connect capacitor C2 (CBB) in parallel across the two ends of the lamp to bypass the current draw; Option 2: Connect a semiconductor switch in parallel across the two ends of the lamp and control the switch to remain on within a specific voltage window range to bypass the current draw.

[0003] The disadvantage of Scheme 1 in the existing scheme is that the bypass current of the CBB capacitor is limited by the capacitance value, making its application inflexible, and the lifespan of the CBB capacitor is relatively short. The disadvantage of Scheme 2 in the existing scheme is that the switching device is always on within a certain window range, which will reduce the efficiency, THD and PF value of the entire lamp, and will also shorten the lifespan of the semiconductor switch. Summary of the Invention

[0004] The purpose of this invention is to provide a low-power single-wire switching system and its control method. This invention can improve the lifespan of semiconductor switches without reducing the efficiency, THD, and PF of the entire lamp load.

[0005] The present invention also provides a single live wire switch system, including a switch panel and a load module. The switch panel is connected between the live wire input terminal and the live wire output terminal, and the load module is connected between the neutral wire and the live wire output terminal. The system is characterized in that it further includes a flashover suppression module, which is connected between the neutral wire and the live wire output terminal. The flashover suppression module rectifies the voltage between the neutral wire and the live wire output terminal to obtain a rectified voltage.

[0006] The flashover suppression module determines whether the load in the load module is turned on based on the rectified voltage. If the load is turned on, the flashover suppression module is turned off. If the load is turned off, the flashover suppression module remains on for a preset period of each working cycle to establish a current flow path between the neutral wire and the live wire output terminal. Outside of the preset period, the flashover suppression module is turned off. The preset period is less than one working cycle, and one working cycle is equal to half a power frequency cycle.

[0007] Optionally, the flash suppression module includes:

[0008] The rectifier unit is used to rectify the voltage between the neutral wire and the output terminal of the live wire to obtain a rectified voltage;

[0009] The first switch is connected between the two output terminals of the rectifier unit;

[0010] The flashover control unit receives the rectified voltage, determines whether the load in the load module is turned on based on the rectified voltage, and generates a flashover control signal to control the on / off state of the first switch.

[0011] If the load is turned on, the flashover control signal is invalid to control the first switch to turn off; if the load is turned off, the flashover control signal is valid to control the first switch to turn on within the preset time period; outside the preset time period, the flashover control signal is invalid to control the first switch to turn off.

[0012] Optionally, the time when the rectified voltage reaches its valley value is within the preset time period, and the time when the rectified voltage reaches its peak value is outside the preset time period.

[0013] Optionally, the period during which the rectified voltage is less than the first preset voltage is the preset period.

[0014] Optionally, outside the preset time period, if the flashover suppression control unit detects that the rectified voltage is greater than the second preset voltage, it determines that the load is turned on; if the flashover suppression control unit does not detect that the rectified voltage is greater than the second preset voltage, it determines that the load is turned off.

[0015] The second preset voltage is greater than the first preset voltage.

[0016] Optionally, if the flashover control unit detects that the rectified voltage is greater than the second preset voltage in each of N consecutive working cycles, then the load is turned on.

[0017] If the flashover suppression control unit does not detect that the rectified voltage is greater than the second preset voltage in each working cycle, then it is determined that the load is turned off.

[0018] The second preset voltage is greater than the first preset voltage, and N is an integer greater than or equal to 2.

[0019] Optionally, the flashover suppression control unit includes a first comparator, a second comparator, and a logic control unit.

[0020] The first comparator compares the rectified voltage with the first preset voltage to generate a first comparison signal;

[0021] The second comparator compares the rectified voltage with the second preset voltage to generate a second comparison signal;

[0022] The logic control unit receives the first comparison signal and the second comparison signal to generate the flashover control signal.

[0023] Optionally, when the rectified voltage is greater than the first preset voltage, the first comparison signal is valid; when the rectified voltage is greater than the second preset voltage, the second comparison signal is valid.

[0024] When the first comparison signal is valid, if the second comparison signal is detected to be valid, it is determined that the load is turned on, and the logic control unit generates an invalid flashover control signal.

[0025] If the second comparison signal is not detected when the first comparison signal is valid, the load is determined to be turned off. The logic control unit generates a valid anti-flicker control signal when the first comparison signal is invalid.

[0026] Optionally, the flashover suppression module further includes a first resistor, which is connected in series with the first switch.

[0027] Optionally, the load module includes a second rectifier unit, a first capacitor, a load drive unit, and the load.

[0028] The input terminal of the second rectifier unit is connected to the neutral wire and the output terminal of the live wire. The output terminal of the second rectifier unit is connected to the first capacitor. The load driving unit is connected in parallel across the two ends of the first capacitor. The load driving unit is used to drive the load, which is an LED string.

[0029] Optionally, the switch panel includes a light-off power supply module, a switch module, a light-on power supply module, a main control module, and a power supply capacitor, with the switch module connected between the light-on power supply module and the light-off power supply module;

[0030] When the main control module receives a light-on command, it sends an on signal to control the switch module to turn on and instructs the light-on control module to control the voltage of the power supply capacitor.

[0031] When the main control module receives a light-off command, it sends a shutdown signal to control the switch module to shut off and instructs the light-off control module to control the voltage of the power supply capacitor.

[0032] The power supply capacitor is used to provide power supply voltage to the main control module.

[0033] The present invention also provides a control method for a single live wire switch system, the single live wire switch system including a switch panel and a load module, the switch panel being connected between the live wire input terminal and the live wire output terminal, the load module being connected between the neutral wire and the live wire output terminal, the voltage between the neutral wire and the live wire output terminal being rectified to obtain a rectified voltage, and the load in the load module being determined as to whether it is turned on based on the rectified voltage;

[0034] If it is determined that the load is turned on, a current flow path is established between the neutral and live wire output terminals within a preset time period of each working cycle. The preset time period is less than one working cycle, and one working cycle is equal to half a power frequency cycle.

[0035] Optionally, the time when the rectified voltage reaches its valley value is within the preset time period, and the time when the rectified voltage reaches its peak value is outside the preset time period;

[0036] The period during which the rectified voltage is less than the first preset voltage is the preset period.

[0037] Optionally, outside the preset time period, if the rectified voltage is detected to be greater than the second preset voltage, the load is determined to be turned on; if the rectified voltage is not detected to be greater than the second preset voltage, the load is determined to be turned off.

[0038] The second preset voltage is greater than the first preset voltage.

[0039] Optionally, if the rectified voltage is detected to be greater than the second preset voltage in each of N consecutive working cycles, then the load is determined to be turned on.

[0040] If the rectified voltage is not detected to be greater than the second preset voltage in each working cycle, then the load is determined to be turned off.

[0041] The second preset voltage is greater than the first preset voltage, and N is an integer greater than or equal to 2.

[0042] Compared with the prior art, the present invention has the following advantages: When the lamp is detected to be off, the switching device of the anti-flicker module is always turned on to bypass the power supply current within a specific window voltage range. When the lamp is normally on, the switching device will not be turned on after the lamp is detected to be on, so as not to reduce the efficiency, THD and PF value of the whole lamp, and at the same time improve the service life of the semiconductor switch. Attached Figure Description

[0043] Figure 1 The schematic diagram of an existing single-wire switch system;

[0044] Figure 2 This is a schematic diagram of the single live wire switch system of the present invention;

[0045] Figure 3 for Figure 2 Schematic diagram of the flashover suppression control unit;

[0046] Figure 4 This is a waveform diagram of the flashover suppression control unit of the present invention.

[0047] Figure 5 for Figure 2 Schematic diagram of the switch panel;

[0048] Figure 6 This is a flowchart illustrating the operation of the flashover elimination module of the present invention. Detailed Implementation

[0049] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the present invention.

[0050] To provide the public with a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the invention, but those skilled in the art can fully understand the invention without these details.

[0051] The invention is described in more detail below by way of example with reference to the accompanying drawings. It should be noted that the drawings are simplified and use non-precise proportions to facilitate and clearly illustrate the embodiments of the invention.

[0052] See Figure 2 The diagram illustrates the schematic of the single-wire switch system of the present invention, including a load module, a switch panel, and a flashover suppression module. The switch panel is connected between the live wire input terminal L1 and the live wire output terminal L2. The load module and the flashover suppression module are connected between the live wire output terminal L2 and the neutral wire N. An AC voltage is input between the neutral wire and the live wire input terminal. The input voltage of the load module is rectified by a first rectifier circuit and filtered by a bus capacitor C1 to obtain the bus voltage V. BUS The load drive unit controls the LED (load) to turn on and off based on the bus voltage. Under the "light on" command, the load module's input voltage is high enough to drive the LED to turn on via the load drive unit. Under the "light off" command, the load module's input voltage is low, and the LED turns off. When the LED is off and the switch panel draws power, to prevent the current from flowing through the load module and causing a drop in bus voltage V... BUS To address the issue of sudden LED flashing caused by rising bus voltage, this invention incorporates an anti-flicker module. This module shuts off when the LED is on / lit and turns on within a specific window voltage range when the LED is off / extinguished, and shuts off outside the window voltage range. This intermittent bypass current draw prevents LED flashing caused by rising bus voltage.

[0053] Furthermore, the flashover suppression module includes a second rectifier circuit, a first switching transistor Q1, and a flashover suppression control unit. The second rectifier circuit is connected between the live wire output terminal L2 and the neutral wire N, used to rectify its input voltage to obtain a rectified voltage. The first switching transistor Q1 is connected between the two output terminals of the second rectifier circuit. The flashover suppression control unit determines the LED on / off state by detecting the rectified voltage and generates a corresponding flashover suppression control signal PWM1 to control the switching state of switch Q1 based on the LED on / off state. When the LED is on, the PWM1 signal controls the first switching transistor to turn off. When the LED is off, the PWM1 signal controls the first switching transistor to turn on within a specific time period (within the window voltage range) of each working cycle and turn off outside the specific time period (outside the window voltage range). One working cycle is half a power frequency cycle. Optionally, the flashover suppression module also includes a first resistor R1 connected in series with the first switching transistor Q1 to limit the magnitude of the bypass current flowing through the first switching transistor when the first switching transistor is on, thereby limiting the magnitude of the current flowing into the bus of the load module. Since the load module is typically integrated into the lighting fixture, the second rectifier circuit in the flashback suppression module usually does not reuse the first rectifier circuit in the load module. See the schematic diagram of the flashback suppression control unit. Figure 3 .

[0054] like Figure 3 The diagram illustrates the schematic of the flashover suppression control unit, which includes a first comparator 101, a second comparator 102, and a logic control unit 103. The first comparator compares the rectified voltage Vab output from the output terminals of the second rectifier circuit (points a and b in the diagram) with a first preset voltage VinTH to obtain a first comparison signal VC1. The second comparator compares the rectified voltage Vab with a second preset voltage VINP (the second preset voltage is greater than the first preset voltage) to obtain a second comparison signal VC2. The logic control unit 103 receives the first and second comparison signals and generates a flashover suppression control signal PWM1. When the rectified voltage Vab is greater than the first preset voltage VinTH, the first comparison signal VC1 is valid; when the rectified voltage Vab is greater than the second preset voltage VINP, the second comparison signal VC2 is valid. The signal processing by the logic control unit 103 is explained below:

[0055] Optionally, if the second comparison signal VC2 is valid during the validity period of the first comparison signal VC1, the LED is determined to be on, and an invalid PWM1 signal is subsequently generated to control the first switch transistor Q1 to remain off. If the second comparison signal VC2 remains invalid during the validity period of the first comparison signal VC1, the LED is determined to be off. Subsequently, when the first comparison signal is invalid, the anti-flicker control signal PWM1 is valid to control the first switch transistor Q1 to turn on; when the first comparison signal is valid, the anti-flicker control signal PWM1 is invalid to control the first switch transistor Q1 to turn off. Optionally, to improve the accuracy of LED on / off (on / off) determination, when the first comparison signal is valid, if the second comparison signal is detected for the first time, the LED is not immediately determined to be on; only when the second comparison signal is detected multiple times consecutively is the LED determined to be on. Similarly, when the first comparison signal is valid, the LED is determined to be off only when the second comparison signal is not detected multiple times consecutively is the LED determined to be off. Figure 4 To further explain.

[0056] See Figure 4The diagram illustrates the working waveform of the flashback suppression control unit. Timing begins when the rectified voltage Vab is less than the first preset voltage VINTH. Timing ends when the rectified voltage Vab is greater than VINTH and then again less than VINTH. The timing period is t1 in the diagram, which is the time during which Vab is greater than VINTH (the period when the first comparison signal is valid). When the LED is off, Vab remains less than VINP during the timing period t1 (the second comparison signal remains invalid). When the LED is on, there will be a phase where Vab is greater than VINP during the timing period t1. If Vab is detected to be greater than VINP for the first time during the timing period, to avoid inaccurate detection, the LED will not be immediately determined to be on. A high-level valid PWM1 signal is still generated when Vab is less than VINTH. If Vab is detected to be greater than VIN for the second time during the timing period, the LED is determined to be on, and thereafter the PWM1 signal remains low and invalid. During the timing period, if Vab is consistently less than VINP for the first time, to avoid inaccurate detection, the LED will not be immediately determined to be off. While Vab is less than VinTH, PWM1 remains low and inactive. If Vab is consistently greater than VINP for the second time during the timing period, the LED is determined to be off. Afterward, when Vab is less than VinTH, PWM1 becomes high and active. This improves the accuracy of determining whether the LED is off. After determining that the LED load is off, this invention turns on the first switching transistor within a window voltage range (Vab less than VinTH) and turns it off outside the window voltage range. Specifically, it turns on the first switching transistor near the rectified voltage valley to bypass the current flowing through the load module and turns it off near the rectified voltage peak. When the first switching transistor is turned on, the voltage across it is relatively small, resulting in lower instantaneous turn-on losses.

[0057] See Figure 5The diagram illustrates the principle of a switch panel embodiment of the present invention, which includes a power supply module for light off, a switch module, a power supply module for light on, a power supply capacitor C3, and an MCU. The MCU receives an external input signal Inx, and its output terminals are connected to the power supply modules for light off, light on, and the switch module, respectively. The power supply capacitor is connected to the output terminal of the switch panel. When the MCU inputs a light-off command, it sends a turn-off signal to the relay driver unit of the switch module to turn off the relay, thereby controlling the LED to turn off. The input terminal of the light-off power supply module is connected to the live wire output terminal. The input voltage of the light-off power supply module is current-limited by resistor R2 and half-wave rectified by diode D1 before being input to capacitor C2. The light-off power supply control unit receives the light-off control signal from the MCU and converts the voltage of capacitor C2 to the power supply capacitor C3. The voltage of power supply capacitor C3 is used to power the MCU, etc. If the power supply capacitor C3 is undervoltage and needs to draw power, the current on the input wire will flow through the bus capacitor C1 of the load module, diode D1, and capacitor C2 into the power supply capacitor C3 and then back to the input wire. This process may cause the voltage of the bus capacitor C1 to rise to the flashing voltage threshold, causing the LED to flash. At this time, the switch Q1 of the anti-flash module needs to be turned on so that the current flows through the anti-flash module and no longer flows into the bus capacitor C1, thus preventing the LED from flashing. When the MCU inputs a light-on command, it sends an on signal to the relay driver unit of the switch module. The relay driver unit is powered by the output voltage Vo to drive the relay to close, thereby controlling the LED to light up. The light-on power supply module draws power from the live wire input terminal. The input voltage of the light-on power supply module is half-wave rectified by the switch transistor QP and diode D2 and then input to the light-on power supply control unit. The light-on power supply control unit receives the light-on control signal from the MCU and converts the voltage after rectification by diode D2 to the power supply capacitor C3. The voltage of the power supply capacitor C3 is used to power the MCU, etc. If the power supply capacitor C3 is undervoltage and needs to draw power, the switch transistor QP is not turned on, and the current on the input wire will flow into capacitor C3 through diode D2 and then return to the input wire.

[0058] See Figure 6The following is a flowchart of the flashback elimination module of the present invention. The process steps are as follows: S01-S02: After the system starts up, the MCU is reset and Vab is detected, and then proceeds to step S03; S03: The size of Vab and VINTH is determined. If Vab is less than VINTH, proceed to step S04; otherwise, continue with step S03; S04: The timer is refreshed and restarted, and then proceeds to step S05; S05: Within the timer period, it is determined whether Vab is first greater than VINTH and then less than VINTH. If so, proceed to step S05. 06. If not, return to step S04; S06. End timing and refresh timing cycle and proceed to step S07; S07. Determine if there is a Vab greater than VINP within the timing cycle. If yes, proceed to step seven S08; otherwise, proceed to step S10; Steps seven S08-S09. Detect the light on state and set the PWM1 signal low; S10. Detect the light off state and proceed to step seven S11. Determine if Vab is less than VINTH. If yes, proceed to step S12; otherwise, proceed to step seven S09; S12. Set the PWM1 signal high.

[0059] This invention can accurately detect whether a light is on or off, and turn off the switching transistor of the anti-flicker module when the light is on. The switching transistor of the anti-flicker module will only be turned on within the window voltage VINTH when the light is off. The anti-flicker module added by this invention will not affect the efficiency of the LED, and at the same time can improve the service life of the anti-flicker module.

[0060] 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.

[0061] 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. A single hot line switch system comprising a switch panel connected between a hot line input and a hot line output, and a load module connected between a neutral line and the hot line output, characterized in that: It also includes a flashover suppression module, which is connected between the neutral wire and the live wire output terminal. The flashover suppression module rectifies the voltage between the neutral wire and the live wire output terminal to obtain a rectified voltage. The flashover suppression module determines whether the load in the load module is turned on based on the rectified voltage. If the load is turned on, the flashover suppression module turns off. If the load is determined to be off, the flashover suppression module remains on for a preset period of each working cycle to establish a current flow path between the neutral wire and the live wire output terminal. Outside the preset period, the flashover suppression module is turned off. The preset period is less than one working cycle, and one working cycle is equal to half a power frequency cycle.

2. The single hot switch system of claim 1, wherein: The flashover suppression module includes: The rectifier unit is used to rectify the voltage between the neutral wire and the output terminal of the live wire to obtain a rectified voltage; The first switch is connected between the two output terminals of the rectifier unit; The flashover control unit receives the rectified voltage, determines whether the load in the load module is turned on based on the rectified voltage, and generates a flashover control signal to control the on / off state of the first switch. If the load is turned on, the flashover control signal is invalid to control the first switch to turn off; if the load is turned off, the flashover control signal is valid to control the first switch to turn on within the preset time period; outside the preset time period, the flashover control signal is invalid to control the first switch to turn off.

3. The single-wire switching system according to claim 2, characterized in that: The time when the rectified voltage reaches its valley value is within the preset time period, and the time when the rectified voltage reaches its peak value is outside the preset time period.

4. The single-wire switching system according to claim 3, characterized in that: The period during which the rectified voltage is less than the first preset voltage is the preset period.

5. The single-wire switching system according to claim 4, characterized in that: Outside of the preset time period, if the flashover suppression control unit detects that the rectified voltage is greater than the second preset voltage, it determines that the load is turned on; if the flashover suppression control unit does not detect that the rectified voltage is greater than the second preset voltage, it determines that the load is turned off. The second preset voltage is greater than the first preset voltage.

6. The single-wire switching system according to claim 4, characterized in that: If the flashover control unit detects that the rectified voltage is greater than the second preset voltage in each of N consecutive working cycles, then it is determined that the load is turned on. If the flashover suppression control unit does not detect that the rectified voltage is greater than the second preset voltage in each working cycle, then it is determined that the load is turned off. The second preset voltage is greater than the first preset voltage, and N is an integer greater than or equal to 2.

7. The single-wire switching system according to claim 5, characterized in that: The flashover suppression control unit includes a first comparator, a second comparator, and a logic control unit. The first comparator compares the rectified voltage with the first preset voltage to generate a first comparison signal; The second comparator compares the rectified voltage with the second preset voltage to generate a second comparison signal; The logic control unit receives the first comparison signal and the second comparison signal to generate the flashover control signal.

8. The single-wire switching system according to claim 7, characterized in that: When the rectified voltage is greater than the first preset voltage, the first comparison signal is valid; when the rectified voltage is greater than the second preset voltage, the second comparison signal is valid. When the first comparison signal is valid, if the second comparison signal is detected to be valid, it is determined that the load is turned on, and the logic control unit generates an invalid flashover control signal. If the second comparison signal is not detected when the first comparison signal is valid, the load is determined to be turned off. The logic control unit generates a valid anti-flicker control signal when the first comparison signal is invalid.

9. The single-wire switching system according to claim 1, characterized in that: The flashover suppression module also includes a first resistor, which is connected in series with the first switch.

10. The single-wire switching system according to claim 1, characterized in that: The load module includes a second rectifier unit, a first capacitor, a load drive unit, and the load. The input terminal of the second rectifier unit is connected to the neutral wire and the output terminal of the live wire. The output terminal of the second rectifier unit is connected to the first capacitor. The load driving unit is connected in parallel across the two ends of the first capacitor. The load driving unit is used to drive the load, which is an LED string.

11. The single-wire switching system according to claim 1, characterized in that: The switch panel includes a light-off power supply module, a switch module, a light-on power supply module, a main control module, and a power supply capacitor. The switch module is connected between the light-on power supply module and the light-off power supply module. When the main control module receives a light-on command, it sends an on signal to control the switch module to turn on and instructs the light-on control module to control the voltage of the power supply capacitor. When the main control module receives a light-off command, it sends a shutdown signal to control the switch module to shut off and instructs the light-off control module to control the voltage of the power supply capacitor. The power supply capacitor is used to provide power supply voltage to the main control module.

12. A control method for a single-live-wire switch system, the single-live-wire switch system comprising a switch panel and a load module, the switch panel being connected between a live wire input terminal and a live wire output terminal, and the load module being connected between a neutral wire and the live wire output terminal, characterized in that: The voltage between the neutral wire and the output terminal of the live wire is rectified to obtain a rectified voltage, and the load in the load module is turned on based on the rectified voltage. If it is determined that the load is turned on, a current flow path is established between the neutral and live wire output terminals within a preset time period of each working cycle. The preset time period is less than one working cycle, and one working cycle is equal to half a power frequency cycle.

13. The control method according to claim 12, characterized in that: The time when the rectified voltage reaches its valley value is within the preset time period, and the time when the rectified voltage reaches its peak value is outside the preset time period; The period during which the rectified voltage is less than the first preset voltage is the preset period.

14. The control method according to claim 12, characterized in that: Outside of the preset time period, if the rectified voltage is detected to be greater than the second preset voltage, the load is determined to be turned on; if the rectified voltage is not detected to be greater than the second preset voltage, the load is determined to be turned off. The second preset voltage is greater than the first preset voltage.

15. The control method according to claim 12, characterized in that: If the rectified voltage is detected to be greater than the second preset voltage in each of N consecutive working cycles, then the load is determined to be turned on. If the rectified voltage is not detected to be greater than the second preset voltage in each working cycle, then the load is determined to be turned off. The second preset voltage is greater than the first preset voltage, and N is an integer greater than or equal to 2.

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