Protection device for switching power supply, switching power supply and protection method for switching power supply thereof

Abstract

The application discloses a kind of switch power supply protection device, switch power supply and its switch power supply protection method, the device includes: in the front end of the protection device of switching unit, switch tube unit is provided;Sampling unit is configured to sample the harmonic current of the power grid;Control unit is configured to generate control signal according to the harmonic current of the power grid;The control signal is the signal for controlling switch tube unit conduction or turn-off;Switch tube unit is configured to, under the condition of receiving the control signal, according to the control signal make switch tube unit itself conduction or turn-off, to realize the protection of the protection device in the case where switch tube unit itself conduction, further realize the protection of the switch power supply.The scheme, by the size of harmonic current in power grid to the protection mode of protection device such as NTC resistance of switch power supply, such as, guarantee that switch power supply can normally output.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of switching power supply, and particularly relates to a protection device of a switching power supply, the switching power supply and a protection method of the switching power supply. BACKGROUND

[0002] The large current harmonics often appearing in the power grid cause great impact on the power supply (such as the switching power supply) of the product, although there are protection circuits and protection devices in the switching power supply, when the current is long-term at the maximum limit value of the protection device or exceeds the protection rated value, the protection device will be damaged, so when the harmonic is too large, the protection circuit and the protection device, and the switching power supply will be inevitably harmed. For example, the excessive harmonic current causes the burnout of the protection devices such as NTC resistance, causes the bus voltage of the switching power supply to be too high, and makes the switching power supply frequently protect, thereby causing the switching power supply to be unable to normally output.

[0003] The above content is only used to assist in understanding the technical solutions of the present application, and does not represent the acknowledgement of the above content as prior art. SUMMARY

[0004] The present application aims to provide a protection device of a switching power supply, the switching power supply and a protection method of the switching power supply, to solve the problem that the excessive harmonic current in the power grid causes the burnout of the protection devices such as NTC resistance of the switching power supply, causes the bus voltage of the switching power supply to be too high, and makes the switching power supply frequently protect, thereby causing the switching power supply to be unable to normally output, to achieve the effect that the protection mode of the protection devices such as NTC resistance of the switching power supply is adjusted according to the size of the harmonic current in the power grid, the real-time protection of the switching power supply is realized, and the normal output of the switching power supply is ensured.

[0005] The application provides a protection device for a switching power supply, wherein the switching power supply has a rectifying unit and a bus capacitor unit; a protection device is arranged between a power grid and an input side of the rectifying unit; the bus capacitor unit is arranged at an output side of the rectifying unit; the protection device for the switching power supply comprises a sampling unit, a switching tube unit and a control unit; the switching tube unit is connected to a common end of the power grid and the protection device; the sampling unit is configured to sample a harmonic current of the power grid; the control unit is configured to generate a control signal according to the harmonic current of the power grid; the control signal is a signal for controlling the switching tube unit to be turned on or turned off; the switching tube unit is configured to turn on or turn off itself according to the control signal when the control signal is received, so as to realize protection of the protection device and further realize protection of the switching power supply when the switching tube unit is turned on.

[0006] In some embodiments, the protection device comprises an NTC resistor; the switching tube unit comprises a MOS tube; the power grid is connected to a first end of the rectifying unit through the NTC resistor; a common end of the power grid and the NTC resistor is connected to a drain of the MOS tube; a source of the MOS tube is grounded; and a control signal output by the control unit can be input to a gate of the MOS tube.

[0007] In some embodiments, the control signal comprises any one of the following PWM signals: a first PWM signal with a duty cycle of 0, a second PWM signal with a duty cycle of a, and a third PWM signal with a duty cycle of 100%; a is greater than 0 and less than 100%; the control unit generates the control signal according to the harmonic current of the power grid, which comprises: determining whether the harmonic current of the power grid is greater than 0 and less than a set first current threshold, or determining whether the harmonic current of the power grid is greater than or equal to the set first current threshold and less than a set second current threshold, or determining whether the harmonic current of the power grid is greater than or equal to the set second current threshold; if it is determined that the harmonic current of the power grid is greater than 0 and less than the set first current threshold, the first PWM signal with the duty cycle of 0 is generated; if it is determined that the harmonic current of the power grid is greater than or equal to the set first current threshold and less than the set second current threshold, the second PWM signal with the duty cycle of a is generated; and if it is determined that the harmonic current of the power grid is greater than or equal to the set second current threshold, the third PWM signal with the duty cycle of 100% is generated.

[0008] In some embodiments, the switch tube unit, upon receiving the control signal, turns on or turns off itself according to the control signal, including: in the case that the received control signal is a first PWM signal with a duty cycle of 0, then turning off itself in the case that the switch tube unit turns on itself, and keeping turning off itself in the case that the switch tube unit turns off itself; in the case that the received control signal is a second PWM signal with a duty cycle of a, then turning on itself for a fixed time period; the fixed time period is a corresponding on period of the second PWM signal with a duty cycle of a; in the case that the received control signal is a third PWM signal with a duty cycle of 100%, then turning on itself.

[0009] In another aspect, the present application provides a switching power supply, which is matched with the above-mentioned device.

[0010] In another aspect, the present application provides a protection method for a switching power supply, which has a rectifier unit and a bus capacitor unit; a protection device is arranged between a power grid and an input side of the rectifier unit; the bus capacitor unit is arranged at an output side of the rectifier unit; a switch tube unit is arranged at a front end of the protection device; the switch tube unit is connected to a common end of the power grid and the protection device; the protection method for the switching power supply includes: sampling a harmonic current of the power grid; generating a control signal according to the harmonic current of the power grid; the control signal is a signal for controlling the switch tube unit to turn on or turn off; and controlling the switch tube unit to turn on or turn off itself according to the control signal upon receiving the control signal, so as to realize protection of the protection device in the case that the switch tube unit turns on itself, and further realize protection of the switching power supply.

[0011] In some embodiments, the control signal comprises any one of the following PWM signals: a first PWM signal with a duty cycle of 0, a second PWM signal with a duty cycle of a, a third PWM signal with a duty cycle of 100%; a is greater than 0 and less than 100%; the control signal is generated according to the harmonic current of the power grid, comprising: determining whether the harmonic current of the power grid is greater than 0 and less than a set first current threshold, or determining whether the harmonic current of the power grid is greater than or equal to the set first current threshold and less than a set second current threshold, or determining whether the harmonic current of the power grid is greater than or equal to the set second current threshold; if it is determined that the harmonic current of the power grid is greater than 0 and less than the set first current threshold, the first PWM signal with a duty cycle of 0 is generated; if it is determined that the harmonic current of the power grid is greater than or equal to the set first current threshold and less than the set second current threshold, the second PWM signal with a duty cycle of a is generated; if it is determined that the harmonic current of the power grid is greater than or equal to the set second current threshold, the third PWM signal with a duty cycle of 100% is generated.

[0012] In some embodiments, the control of the switch tube unit comprises: in the case that the received control signal is the first PWM signal with a duty cycle of 0, the switch tube unit is turned off in the case that the switch tube unit is turned on, and the switch tube unit is still turned off in the case that the switch tube unit is turned off; in the case that the received control signal is the second PWM signal with a duty cycle of a, the switch tube unit is turned on for a fixed time period; the fixed time period is the turn-on period corresponding to the second PWM signal with a duty cycle of a; in the case that the received control signal is the third PWM signal with a duty cycle of 100%, the switch tube unit is turned on.

[0013] Therefore, the scheme of the present application can detect the harmonic current in the power grid by adding a MOS tube and its control circuit in front of the protection device such as NTC resistor of the switching power supply, control the turn-on or turn-off of the MOS tube through the control circuit of the MOS tube according to the size of the harmonic current in the power grid, control the MOS tube to turn on to release the harmonic current if the harmonic current in the power grid is too large, and control the MOS tube to turn off if the harmonic current in the power grid is not enough to make the protection device such as NTC resistor continuously heat up and burn out, so as to adjust the protection mode of the protection device such as NTC resistor of the switching power supply according to the size of the harmonic current in the power grid, realize real-time protection of the switching power supply, and ensure that the switching power supply can normally output.

[0014] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the present application.

[0015] The technical solutions of the present application will be further described in detail below with the aid of the accompanying drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 Structure diagram of an embodiment of the protection device for the switching power supply of the present application;

[0017] Figure 2 Structure diagram of an embodiment of the protection circuit for the switching power supply of the present application;

[0018] Figure 3 Flow diagram of an embodiment of the protection method for the switching power supply of the present application;

[0019] Figure 4 Flow diagram of an embodiment of the protection method for the switching power supply of the present application, in which a control signal is generated according to the harmonic current of the power grid;

[0020] Figure 5 Flow diagram of an embodiment of the control method for the protection circuit of the switching power supply of the present application. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and advantages of the present application clearer, the technical solutions of the present application will be described in detail below with the aid of specific embodiments of the present application and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0022] According to an embodiment of the present application, a protection device for a switching power supply is provided. Referring to Figure 1 Structure diagram of an embodiment of the device of the present application is shown. The switching power supply has a rectification unit, such as a rectification bridge DB1, and a bus capacitor unit, such as a bus capacitor CO. A protection device, such as an NTC resistor, is arranged between the power grid and the input side of the rectification unit. The bus capacitor unit is arranged at the output side of the rectification unit. The protection device for the switching power supply comprises a sampling unit, such as an external power grid monitoring system, a switching tube unit, such as a MOS tube, and a control unit, such as a PWM control module. The switching tube unit is connected to the common end of the power grid and the protection device.

[0023] Among them, the sampling unit is configured to sample the harmonic current of the power grid, such as the harmonic current I0.

[0024] The control unit is configured to generate a control signal according to the harmonic current of the power grid. The control signal is a signal for controlling the switch tube unit to turn on or turn off.

[0025] The switch tube unit is configured to, in the case of receiving the control signal, turn on or turn off itself according to the control signal, so as to realize protection of the protection device and the switching power supply in the case of turning on itself.

[0026] The scheme of the present application provides a device for preventing excessive harmonic from causing power protection. A switch tube such as a MOS tube and its control circuit (i.e. a MOSFET tube and its control circuit) are added in front of a protection device such as an NTC resistor. The conduction or turn-off of the MOS tube is controlled according to the size of the harmonic current in the power grid. When the harmonic current in the power grid is large, the MOS tube is turned on, and the harmonic current in the power grid flows through the MOSFT instead of the NTC resistor. When the harmonic current in the power grid is insufficient to cause protection of the switching power supply, the MOS tube is turned off, thereby avoiding the NTC resistor from being burned due to continuous heating and avoiding the switching power supply from being frequently protected, and ensuring that the switching power supply can normally output.

[0027] In some embodiments, the protection device includes an NTC resistor. The switch tube unit includes a MOS tube. The power grid is connected to the first end of the rectifying unit through the NTC resistor. The common end of the power grid and the NTC resistor is connected to the drain of the MOS tube. The source of the MOS tube is grounded. The control signal output by the control unit can be input to the gate of the MOS tube.

[0028] Specifically, Figure 2 The structure diagram of an embodiment of the protection circuit of the switching power supply of the present application is shown in FIG. 1. Figure 2 As shown in FIG. 1, between the input end and the output end of the switching power supply, a protection device, a rectifying bridge DB1 and a bus capacitor C0 are arranged. The protection device is an NTC resistor RNTC. The first input line of the input end of the power grid is connected to the first end of the rectifying bridge DB1 through the NTC resistor RNTC. The second end of the rectifying bridge DB1 is connected to the output end through the bus capacitor C0 and is grounded. The second end of the rectifying bridge DB1 is connected to the output end. The second input line of the input end of the power grid is connected to the third end of the rectifying bridge DB1. The fourth end of the rectifying bridge DB1 is grounded. The drain of the MOS tube is connected to the common end of the first input line of the input end of the power grid and the NTC resistor RNTC. The source of the MOS tube is grounded. The control circuit of the MOS tube can output a PWM control signal to the gate of the MOS tube based on a pulse signal Signal.

[0029] In Figure 2In the shown example, I0 is the harmonic current input from the power grid, RNTC is the access current-limiting NTC resistor, DB1 is the rectifier bridge, C0 is the energy storage large electrolytic capacitor, and UL is the bus voltage. The input harmonic current I0 is connected to the D terminal (i.e., the drain terminal) of the MOS at the front end of RNTC, the S terminal (i.e., the source terminal) of the MOS is grounded, the G terminal (i.e., the gate terminal) of the MOS is connected to the PWM control module, the CONTROL terminal of the PWM control module is the control terminal of the PWM control signal, and Signal is the harmonic feedback signal of the online monitoring of the power grid. The external power grid monitoring system can monitor the size of the harmonic current of the power grid in real time, and the MOS control circuit can also receive the harmonic current signal sent by the external power grid monitoring system. The MOS control circuit generates a pulse signal based on the harmonic current signal, and then outputs a PWM control signal to the gate terminal of the MOS based on the pulse signal, to control the conduction or turn-off of the MOS.

[0030] In some embodiments, the control signal includes any one of the following PWM signals: a first PWM signal with a duty cycle of 0, a second PWM signal with a duty cycle of a, and a third PWM signal with a duty cycle of 100%. a is greater than 0 and less than 100%.

[0031] The control unit generates a control signal based on the harmonic current of the power grid, including:

[0032] The control unit is specifically further configured to determine whether the harmonic current of the power grid is greater than 0 and less than a set first current threshold, or determine whether the harmonic current of the power grid is greater than or equal to the set first current threshold and less than a set second current threshold, or determine whether the harmonic current of the power grid is greater than or equal to the set second current threshold.

[0033] The control unit is specifically further configured to generate a first PWM signal with a duty cycle of 0 if it is determined that the harmonic current of the power grid is greater than 0 and less than the set first current threshold.

[0034] The control unit is specifically further configured to generate a second PWM signal with a duty cycle of a if it is determined that the harmonic current of the power grid is greater than or equal to the set first current threshold and less than the set second current threshold.

[0035] The control unit is specifically further configured to generate a third PWM signal with a duty cycle of 100% if it is determined that the harmonic current of the power grid is greater than or equal to the set second current threshold.

[0036] Specifically, refer to Figure 2The example shows that when the harmonic current I0 of the power grid input is too large, the power consumption of the NTC resistor RNTC increases, and the heat generation increases. The harmonic current I0 charges the capacitor C0 after passing through the rectifier bridge DB1. The large harmonic current I0 continuously charges the capacitor C0 in a short time, so that the bus voltage UL at both ends of the capacitor rises, and the bus voltage UL is too high to exceed the bus voltage tolerance range of the switching power supply, thereby causing the switching power supply to be overvoltage protected and the output to be abnormal. To solve this problem, the scheme of the application sends an instruction to the PWM control module through the feedback signal Signal of the size of the harmonic current of the power grid. The feedback signal Signal of the size of the harmonic current of the power grid is a signal sent after the power grid monitors the harmonic online. The PWM control module outputs a PWM control signal with a certain duty cycle after receiving the instruction, controls the conduction or turn-off of the MOS tube, and the harmonic current I0 is consumed through the MOS tube without passing through the power supply circuit when the MOS tube is turned on. In this way, the NTC resistor will not be burned out due to continuous heating, and the bus voltage will not be too high due to continuous charging of the electrolytic capacitor C0.

[0037] In some embodiments, the switch tube unit, upon receiving the control signal, turns on or turns off itself according to the control signal, including any one of the following control situations:

[0038] The first control situation: the switch tube unit, specifically in the case where the received control signal is a first PWM signal with a duty cycle of 0, turns off itself in the case where the switch tube unit is turned on, and keeps off itself in the case where the switch tube unit is turned off.

[0039] The second control situation: the switch tube unit, specifically in the case where the received control signal is a second PWM signal with a duty cycle of a, turns on itself in a fixed time period. The fixed time period is the conduction period corresponding to the second PWM signal with a duty cycle of a.

[0040] The third control situation: the switch tube unit, specifically in the case where the received control signal is a third PWM signal with a duty cycle of 100%, turns on itself.

[0041] Specifically, Figure 5 The flowchart of an embodiment of the control method of the protection circuit of the switching power supply is shown in the figure. Figure 5 As shown in the figure, the control method of the protection circuit of the switching power supply includes:

[0042] Step 1: The power grid online monitors the size of the harmonic current value and feeds back the corresponding signal to obtain the harmonic current I0.

[0043] Step 2, specifically, the size of the harmonic current I0 is judged, and the PWM control signal is adjusted according to the size of the harmonic current I0.

[0044] Specifically, when 0 < harmonic current I0 < set first current threshold I1, the PWM control signal is not output. Wherein, when harmonic current I0 = set first current threshold I1, NTC resistance power Pntc is normal, and bus voltage UL is normal.

[0045] When the set first current threshold I1 ≤ harmonic current I0 < set second current threshold I2, NTC resistance power Pntc is increased, bus voltage UL is normal, the output duty cycle DPWM is a control signal, and the MOS tube is turned on in a fixed time period. Wherein, I1 takes the maximum allowed current of the NTC resistance, and I2 takes the capacitor charging current value under the bus overvoltage UMAX. 0 < a < 100%, the value of a is determined by the size of the harmonic current I0, for example, I0 = I1 + 0.5I1, then a takes 50%, I0 increases, then the duty cycle a increases, and decreases, the MOS tube is turned on when the PWM control signal is high.

[0046] When the harmonic current I0 ≥ set second current threshold I2, NTC resistance power Pntc is increased, bus voltage UL reaches the switching power bus overvoltage value UMAX, the output duty cycle DPWM is 100% control signal, and the harmonic current does not pass through the NTC resistance RNTC.

[0047] In this way, the PWM control module is given instructions by the power grid feedback signal, and the PWM control module controls the conduction or turn-off of the MOS through the output of the corresponding PWM control signal, so as to realize the normal and stable output of the switching power supply under the harmonic.

[0048] The scheme of the application can solve the phenomenon that the commercial air conditioning product works abnormally due to the interference in the power grid, and is also applicable to other products that use this method to solve power supply problems.

[0049] The scheme of the present application adds a MOS control circuit in front of a protection device such as an NTC resistor of a switching power supply to share power consumption, specifically, according to harmonic current in a power grid, the MOS tube in front of the NTC resistor is turned on through a PWM signal control, which avoids continuous power consumption and heat burning of the NTC resistor due to continuous excessive current, achieves the protection effect of the NTC device, avoids frequent protection of the switching power supply, solves the problems of heat of the NTC resistor and overvoltage of the bus voltage of the switching power supply, and ensures normal output of the switching power supply. In this way, when the harmonic current in the power grid is found to be too large, a signal is sent to the control circuit (i.e. the MOS control circuit), and then the control circuit controls the MOS tube in front of the NTC resistor to be turned on, which avoids excessive current passing through the NTC for a long time, and overall solves the problem that the protection device such as the NTC resistor of the switching power supply cannot self-regulate according to the size of external interference current, and achieves the effect of real-time protection of the switching power supply.

[0050] The technical scheme of the present application adds a MOS tube and its control circuit in front of a protection device such as an NTC resistor of a switching power supply, detects harmonic current in a power grid, controls the conduction or turn-off of the MOS tube through the control circuit of the MOS tube according to the size of the harmonic current in the power grid, controls the MOS tube to be turned on to release the harmonic current if the harmonic current in the power grid is too large, and controls the MOS tube to be turned off if the harmonic current in the power grid is not enough to cause the protection device such as the NTC resistor to continuously heat and burn out, thereby adjusting the protection mode of the protection device such as the NTC resistor of the switching power supply according to the size of the harmonic current in the power grid, realizing real-time protection of the switching power supply, and ensuring normal output of the switching power supply.

[0051] According to the embodiment of the present application, a switching power supply corresponding to the protection device of the switching power supply is also provided. The switching power supply can include the protection device of the switching power supply described above.

[0052] Since the processing and functions realized by the switching power supply of the present embodiment are basically corresponding to the embodiments, principles and examples of the device, the description of the present embodiment will not be elaborated, and the related description in the foregoing embodiments can be referred to, which will not be repeated here.

[0053] The technical scheme of the present application adds a MOS tube and its control circuit in front of a protection device such as an NTC resistor of a switching power supply, detects harmonic current in a power grid, controls the conduction or turn-off of the MOS tube through the control circuit of the MOS tube according to the size of the harmonic current in the power grid, controls the MOS tube to be turned on to release the harmonic current if the harmonic current in the power grid is too large, and controls the MOS tube to be turned off if the harmonic current in the power grid is not enough to cause the protection device such as the NTC resistor to continuously heat and burn out, thereby adjusting the protection mode of the protection device such as the NTC resistor of the switching power supply according to the size of the harmonic current in the power grid, realizing real-time protection of the switching power supply, and ensuring normal output of the switching power supply.

[0054] According to the embodiments of the present application, a protection method for a switching power supply is also provided, as shown in the following. Figure 3 The switching power supply has a rectifier unit, such as a rectifier bridge DB1, and a bus capacitor unit, such as a bus capacitor CO. A protection device, such as an NTC resistor, is arranged between the power grid and the input side of the rectifier unit. The bus capacitor unit is arranged at the output side of the rectifier unit. A switch tube unit is arranged at the front end of the protection device. The switch tube unit is connected to the common end of the power grid and the protection device. The protection method for the switching power supply comprises steps S110-S130.

[0055] At step S110, the harmonic current of the power grid, such as a harmonic current I0, is sampled.

[0056] At step S120, a control signal is generated according to the harmonic current of the power grid. The control signal is a signal for controlling the switch tube unit to be turned on or turned off.

[0057] At step S130, the switch tube unit is controlled to be turned on or turned off according to the control signal in the case of receiving the control signal, so as to achieve protection of the protection device and the switching power supply in the case of the switch tube unit being turned on.

[0058] The present application proposes a method for preventing excessive harmonic current from causing power supply protection. A switch tube, such as a MOS tube, and its control circuit (i.e. a MOSFET tube and its control circuit) are added at the front end of a protection device, such as an NTC resistor. The MOS tube is controlled to be turned on or turned off according to the harmonic current in the power grid. When the harmonic current in the power grid is large, the MOS tube is turned on, and the harmonic current in the power grid flows through the MOSFT instead of the NTC resistor. When the harmonic current in the power grid is insufficient to cause protection of the switching power supply, the MOS tube is turned off, thereby avoiding the NTC resistor from being burned due to continuous heating, avoiding frequent protection of the switching power supply, and ensuring normal output of the switching power supply.

[0059] In some embodiments, the control signal comprises any one of the following PWM signals: a first PWM signal with a duty cycle of 0, a second PWM signal with a duty cycle of a, and a third PWM signal with a duty cycle of 100%. a is greater than 0 and less than 100%.

[0060] In some embodiments, the specific process of generating the control signal according to the harmonic current of the power grid in step S120 is described in the following exemplary description.

[0061] The following will be described in combination with the accompanying drawings. Figure 4An embodiment flowchart of a method of the application shown in the figure further illustrates the specific process of generating the control signal according to the harmonic current of the power grid in step S120, which comprises steps S210 to S240.

[0062] In step S210, it is determined whether the harmonic current of the power grid is greater than 0 and less than a set first current threshold, or whether the harmonic current of the power grid is greater than or equal to the set first current threshold and less than a set second current threshold, or whether the harmonic current of the power grid is greater than or equal to the set second current threshold.

[0063] In step S220, if it is determined that the harmonic current of the power grid is greater than 0 and less than the set first current threshold, a first PWM signal with a duty cycle of 0 is generated.

[0064] In step S230, if it is determined that the harmonic current of the power grid is greater than or equal to the set first current threshold and less than the set second current threshold, a second PWM signal with a duty cycle of a is generated.

[0065] In step S240, if it is determined that the harmonic current of the power grid is greater than or equal to the set second current threshold, a third PWM signal with a duty cycle of 100% is generated.

[0066] Specifically, referring to Figure 2 In the example shown, when the harmonic current I0 input by the power grid is too large, the power consumption of the NTC resistor RNTC increases, and the heat generation increases. After the harmonic current I0 passes through the rectifier bridge DB1, the capacitor C0 is charged, and the large harmonic current I0 causes the capacitor C0 to be continuously charged in a short time, causing the bus voltage UL across the capacitor to rise, and the bus voltage UL being too high exceeds the bus voltage tolerance range of the switching power supply, thereby causing the switching power supply to be overvoltage protected and the output to be abnormal. To solve this problem, the scheme of the application uses the feedback signal Signal of the size of the harmonic current of the power grid, which is a signal sent by the power grid after online monitoring of the harmonic, to send an instruction to the PWM control module. After receiving the instruction, the PWM control module outputs a PWM control signal with a certain duty cycle to control the conduction or turn-off of the MOS tube. When the harmonic current I0 is conducted through the MOS tube, it is consumed without passing through the power supply circuit. In this way, the NTC resistor will not be burned out due to continuous heating, and the electrolytic capacitor C0 will not cause the bus voltage to be too high due to continuous charging.

[0067] In some embodiments, in step S130, the switching tube unit is controlled to conduct or turn off itself according to the control signal in the case of receiving the control signal, including any one of the following control situations:

[0068] The first control case: control the switch tube unit, specifically, in the case that the received control signal is the first PWM signal with a duty cycle of 0, the switch tube unit is turned off when it is turned on, and the switch tube unit is still turned off when it is turned off.

[0069] The second control case: control the switch tube unit, specifically, in the case that the received control signal is the second PWM signal with a duty cycle of a, the switch tube unit is turned on for a fixed time period. The fixed time period is the corresponding on period of the second PWM signal with a duty cycle of a.

[0070] The third control case: control the switch tube unit, specifically, in the case that the received control signal is the third PWM signal with a duty cycle of 100%, the switch tube unit is turned on.

[0071] Specifically, Figure 5 The flowchart of an embodiment of the control method of the protection circuit of the switching power supply. As shown in the figure, the control method of the protection circuit of the switching power supply comprises: Figure 5 The control method of the protection circuit of the switching power supply comprises:

[0072] Step 1, the grid online monitors the harmonic current value and feeds back the corresponding signal to obtain the harmonic current I0.

[0073] Step 2, specifically, the size of the harmonic current I0 is judged, and the PWM control signal is adjusted according to the size of the harmonic current I0.

[0074] Specifically, when 0 < harmonic current I0 < the set first current threshold I1, no PWM control signal is output. When the harmonic current I0 = the set first current threshold I1, the NTC resistance power Pntc is normal, and the bus voltage UL is normal.

[0075] When the set first current threshold I1 ≤ harmonic current I0 < the set second current threshold I2, the NTC resistance power Pntc increases, the bus voltage UL is normal, the control signal with a duty cycle DPWM of a is output, and the MOS tube is turned on for a fixed time period.

[0076] When the harmonic current I0 ≥ the set second current threshold I2, the NTC resistance power Pntc increases, the bus voltage UL reaches the switching power supply bus overvoltage value UMAX, the control signal with a duty cycle DPWM of 100% is output, and the harmonic current does not pass through the NTC resistance RNTC.

[0077] In this way, the PWM control module is instructed by the grid feedback signal, and the PWM control module outputs corresponding PWM control signals to control the conduction or turn-off of the MOS, thereby realizing the normal and stable output of the switching power supply under the harmonic.

[0078] The scheme of the present application can solve the abnormal working phenomenon of the commercial air conditioner product in the power grid, and is also applicable to other products using the present method to solve the power supply problem.

[0079] In the scheme of the present application, the MOS control circuit is added in front of the protection device such as NTC resistor of the switching power supply to share the power consumption, specifically, the MOS tube in front of the NTC resistor is turned on by the PWM signal according to the harmonic current in the power grid, thereby avoiding the continuous power consumption and heating and burning of the NTC resistor due to the continuous excessive current, achieving the protection effect of the NTC device, avoiding the frequent protection of the switching power supply, solving the problems of heating of the NTC resistor and overvoltage of the bus voltage of the switching power supply, and ensuring the normal output of the switching power supply. In this way, the harmonic current in the power grid is monitored, and when the harmonic current in the power grid is found to be too large, a signal is sent to the control circuit (i.e., the MOS control circuit), and then the control circuit controls the MOS tube in front of the NTC resistor to be turned on, thereby avoiding the excessive current passing through the NTC for a long time, and overall solving the problem that the protection device such as NTC resistor of the switching power supply cannot self-regulate according to the external interference current, and achieving the effect of real-time protection of the switching power supply.

[0080] Since the processing and functions realized by the method of the present embodiment are basically corresponding to the foregoing embodiments, principles and examples of the switching power supply, the description of the present embodiment will not be described in detail, and the related description in the foregoing embodiments can be referred to, which will not be described herein.

[0081] By adopting the technical scheme of the present embodiment, the MOS tube and its control circuit are added in front of the protection device such as NTC resistor of the switching power supply to detect the harmonic current in the power grid, the MOS tube is controlled to be turned on or turned off by the control circuit of the MOS tube according to the size of the harmonic current in the power grid, the MOS tube is turned on to release the harmonic current if the harmonic current in the power grid is too large, and the MOS tube is turned off if the harmonic current in the power grid is not enough to cause the protection device such as NTC resistor to continuously heat and burn, thereby avoiding the burning of the NTC resistor due to continuous heating, avoiding the frequent protection of the switching power supply, and ensuring the normal output of the switching power supply.

[0082] In summary, those skilled in the art can easily understand that the above advantageous modes can be freely combined and superimposed without conflict.

[0083] The above merely illustrates the embodiments of the present application but should not be taken as limitations. Various changes and modifications can be made by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of claims of the present application.

Claims

1. A protection device for a switching power supply, characterized by comprising: The switching power supply has a rectifier unit and a bus capacitor unit; a protection device is arranged between the power grid and the input side of the rectifier unit; the bus capacitor unit is arranged at the output side of the rectifier unit; The protection device of the switching power supply comprises a sampling unit, a switch tube unit and a control unit; the switch tube unit is connected to the common end of the power grid and the protection device; wherein, The sampling unit is configured to sample the harmonic current of the power grid; The control unit is configured to generate a control signal according to the harmonic current of the power grid; the control signal is a signal for controlling the switch tube unit to be turned on or turned off; The switch tube unit is configured to turn on or turn off itself according to the control signal when the control signal is received, so as to realize the protection of the protection device and the switching power supply when the switch tube unit is turned on itself; The control signal comprises any one of the following PWM signals: a first PWM signal with a duty cycle of 0, a second PWM signal with a duty cycle of a, and a third PWM signal with a duty cycle of 100%; a is greater than 0 and less than 100%; The control unit generates a control signal according to the harmonic current of the power grid, comprising: determining whether the harmonic current of the power grid is greater than 0 and less than a set first current threshold, or determining whether the harmonic current of the power grid is greater than or equal to a set first current threshold and less than a set second current threshold, or determining whether the harmonic current of the power grid is greater than or equal to a set second current threshold; if it is determined that the harmonic current of the power grid is greater than 0 and less than a set first current threshold, a first PWM signal with a duty cycle of 0 is generated; if it is determined that the harmonic current of the power grid is greater than or equal to a set first current threshold and less than a set second current threshold, a second PWM signal with a duty cycle of a is generated; if it is determined that the harmonic current of the power grid is greater than or equal to a set second current threshold, a third PWM signal with a duty cycle of 100% is generated.

2. The protection device for a switching power supply according to claim 1, wherein The protection device comprises an NTC resistor; the switch tube unit comprises a MOS tube; wherein, The power grid is connected to the first end of the rectifier unit through the NTC resistor; the common end of the power grid and the NTC resistor is connected to the drain of the MOS tube; the source of the MOS tube is grounded; the control signal output by the control unit can be input to the gate of the MOS tube.

3. The protection device for a switching power supply according to claim 1, wherein The switch tube unit turns on or turns off itself according to the control signal when the control signal is received, comprising: if the received control signal is a first PWM signal with a duty cycle of 0, the switch tube unit turns off itself when the switch tube unit is turned on itself, and the switch tube unit still turns off itself when the switch tube unit is turned off itself; In the case that the received control signal is a second PWM signal with a duty cycle of a, the switch tube unit is made to conduct itself in a fixed time period; the fixed time period is a conduction period corresponding to the second PWM signal with a duty cycle of a; In the case that the received control signal is a third PWM signal with a duty cycle of 100%, the switch tube unit is made to conduct itself.

4. A switching power supply, characterized by comprising: The protection device of the switching power supply comprises: The protection device of the switching power supply according to any one of claims 1 to 3.

5. A protection method for a switching power supply, which implements protection for a switching power supply using a protection device for a switching power supply according to any one of claims 1 to 3, characterized by The switching power supply has a rectifier unit and a bus capacitor unit; a protection device is arranged between a power grid and an input side of the rectifier unit; the bus capacitor unit is arranged at an output side of the rectifier unit; A switch tube unit is arranged at a front end of the protection device; The switch tube unit is connected to a common end of the power grid and the protection device; The protection method of the switching power supply comprises: Sampling a harmonic current of the power grid; Generating a control signal according to the harmonic current of the power grid; the control signal is a signal for controlling the switch tube unit to conduct or turn off; Controlling the switch tube unit to conduct or turn off itself according to the control signal in the case that the control signal is received, so as to realize protection of the protection device and the switching power supply in the case that the switch tube unit conducts itself.

6. The protection method of a switching power supply according to claim 5, wherein The control signal comprises any one of the following PWM signals: a first PWM signal with a duty cycle of 0, a second PWM signal with a duty cycle of a, and a third PWM signal with a duty cycle of 100%; a is greater than 0 and less than 100%; Generating a control signal according to the harmonic current of the power grid comprises: Determining whether the harmonic current of the power grid is greater than 0 and less than a set first current threshold, or determining whether the harmonic current of the power grid is greater than or equal to the set first current threshold and less than a set second current threshold, or determining whether the harmonic current of the power grid is greater than or equal to the set second current threshold; If it is determined that the harmonic current of the power grid is greater than 0 and less than the set first current threshold, a first PWM signal with a duty cycle of 0 is generated; If it is determined that the harmonic current of the power grid is greater than or equal to the set first current threshold and less than the set second current threshold, a second PWM signal with a duty cycle of a is generated; If it is determined that the harmonic current of the power grid is greater than or equal to the set second current threshold, a third PWM signal with a duty cycle of 100% is generated.

7. The protection method of a switching power supply according to claim 5 or 6, characterized in that, Controlling the switch tube unit to conduct or turn off itself according to the control signal in the case that the control signal is received comprises: In the case that the received control signal is a first PWM signal with a duty cycle of 0, the switch tube unit is made to turn off itself in the case that the switch tube unit conducts itself, and the switch tube unit is still made to turn off itself in the case that the switch tube unit turns off itself. In the case that the received control signal is a second PWM signal with a duty cycle of a, the switch tube unit is made to conduct itself in a fixed time period; the fixed time period is a conduction period corresponding to the second PWM signal with a duty cycle of a; In the case that the received control signal is a third PWM signal with a duty cycle of 100%, the switch tube unit is made to conduct itself.

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