CN204103460U - The undervoltage protection device of Switching Power Supply and there is its Switching Power Supply - Google Patents

Abstract

The utility model discloses an undervoltage protection device for a switching power supply and a switching power supply having the same, which discloses an undervoltage protection device for a switching power supply, comprising: a voltage detection circuit for detecting the voltage input to the switching power supply; a controllable device , the control terminal of the controllable device is connected to the output terminal of the voltage detection circuit, wherein, when the voltage detection circuit detects that the voltage of the switching power supply is lower than the first preset protection voltage, the controllable device is cut off, and when the voltage detection circuit detects that the voltage of the switching power supply The controllable device is turned on when the voltage is greater than or equal to the second preset protection voltage, and the second preset protection voltage is greater than the first preset protection voltage; an undervoltage protection circuit, and the undervoltage protection circuit outputs an undervoltage protection signal when the controllable device is cut off To the power chip of the switching power supply for undervoltage protection. The undervoltage protection device is not easy to cause false action to the fluctuation of voltage in a small range, and can perform undervoltage protection on different voltage systems, so the application range is wider. The utility model also discloses a switching power supply.

Description

Undervoltage protection device for switching power supply and switching power supply having it

technical field

The utility model relates to the technical field of power electronics, in particular to an undervoltage protection device for a switching power supply and a switching power supply with the undervoltage protection device for the switching power supply.

Background technique

When the car is running, the battery is usually used to provide voltage for the car's controller, etc. When the voltage provided by the battery is too low, the controller may not work normally, and at the same time, overcurrent may damage the components. Therefore, when the voltage provided by the battery is too low, the safety of the entire vehicle cannot be guaranteed. In addition, the input voltage of the circuit is getting higher and higher, and the range of operating voltage is required to be larger and larger, which poses new problems for circuit design and device selection.

In related technologies, a control chip with an undervoltage protection function is usually used to perform undervoltage protection on the controller and components. However, the related technologies mainly have the following disadvantages: first, the voltage range is relatively narrow, and most of the related chips can only be used in 12V or 24V voltage systems, and cannot be used in 48V voltage systems or systems compatible with three voltages. The voltage for powering the chip can only be 12V or 24V, not 48V; secondly, it is easy to cause malfunction due to voltage fluctuations, thus making the working state of the circuit unstable.

Utility model content

The utility model aims to solve one of the technical problems in the related art at least to a certain extent.

For this reason, an object of the present utility model is to propose an undervoltage protection device for a switching power supply, which can perform undervoltage protection for different voltage systems, and will not easily cause malfunctions for small-scale fluctuations in voltage .

Another purpose of the utility model is to provide a switching power supply.

According to the utility model, an undervoltage protection device for a switching power supply includes: a voltage detection circuit for detecting the voltage input to the switching power supply; a controllable device, the control terminal of the controllable device is connected to the The output terminal of the voltage detection circuit is connected, wherein, when the voltage detection circuit detects that the voltage of the switching power supply is lower than the first preset protection voltage, the controllable device is cut off, and when the voltage detection circuit detects that the The controllable device is turned on when the voltage of the switching power supply is greater than or equal to a second preset protection voltage, and the second preset protection voltage is greater than the first preset protection voltage; an undervoltage protection circuit, the undervoltage protection circuit When the controllable device is cut off, an undervoltage protection signal is output to the power chip of the switching power supply to realize undervoltage protection.

According to the undervoltage protection device of the switching power supply proposed by the utility model, the voltage input to the switching power supply is detected by the voltage detection circuit, and the controllable device is cut off when the voltage detection circuit detects that the voltage of the switching power supply is lower than the first preset protection voltage , when the voltage detection circuit detects that the voltage of the switching power supply is greater than or equal to the second preset protection voltage, the controllable device is turned on, and at the same time, the undervoltage protection circuit outputs an undervoltage protection signal to the power chip of the switching power supply when the controllable device is turned off. undervoltage protection. Thus, the undervoltage protection device can perform undervoltage protection on the power supply chip of the switching power supply when the voltage of the switching power supply is lower than the first preset protection voltage, and until the voltage of the switching power supply is greater than the second preset protection voltage, the switching power supply The power supply chip works normally, so it is not easy to cause misoperation for small-scale fluctuations in voltage, and, compared with related technologies, the voltage detection circuit can detect different voltages without being affected by the chip design, so the undervoltage protection device can Undervoltage protection for different voltage systems has a wider range of applications.

According to another aspect of the utility model, a switching power supply is proposed, comprising: a power chip; and the undervoltage protection device of the switching power supply.

According to the switching power supply proposed by the utility model, the undervoltage protection device can perform undervoltage protection on the power supply chip when the voltage of the switching power supply is lower than the first preset protection voltage, and restart the power chip until the voltage of the switching power supply is greater than the second preset protection voltage. The power supply chip works normally, so that it is not easy to cause misoperation for small-scale voltage fluctuations, and it can perform under-voltage protection for different voltage systems, and the application range is wider.

Description of drawings

Fig. 1 is a schematic block diagram of an undervoltage protection device for a switching power supply according to an embodiment of the present invention;

Fig. 2 is a schematic circuit diagram of an undervoltage protection device for a switching power supply according to an embodiment of the present invention; and

Fig. 3 is a schematic block diagram of a switching power supply according to an embodiment of the present invention.

Detailed ways

Embodiments of the present invention are described in detail below, examples of which are shown in the drawings, wherein the same or similar reference numerals represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the figures are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

The undervoltage protection device and the switching power supply proposed according to the embodiments of the utility model are described below with reference to the accompanying drawings.

FIG. 1 is a schematic block diagram of an undervoltage protection device for a switching power supply according to an embodiment of the present invention. As shown in FIG. 1 , the undervoltage protection device of the switching power supply includes: a voltage detection circuit 1 , a controllable device 2 and an undervoltage protection circuit 3 .

Among them, the voltage detection circuit 1 is used to detect the voltage VCC input to the switching power supply; the control terminal of the controllable device 2 is connected to the output terminal of the voltage detection circuit 1, wherein the voltage VCC of the switching power supply is detected in the voltage detection circuit 1 When the voltage detection circuit 1 detects that the voltage VCC of the switching power supply is greater than or equal to the second preset protection voltage V _TH+ , the controllable device ₂ is turned on, and the second preset The protection voltage V _TH+ is set to be greater than the first preset protection voltage V _TH- ; the undervoltage protection circuit 3 outputs an undervoltage protection signal to the power chip of the switching power supply to realize the undervoltage protection when the controllable device 2 is turned off.

That is to say, when the voltage VCC of the switching power supply is less than the first preset protection voltage V _TH- , the detection voltage output by the voltage detection circuit 1 will cause the controllable device 2 to be turned off, and when the controllable device 2 is turned off, the undervoltage protection circuit 3 Output under-voltage protection signal such as high-level signal to the power chip of the switching power supply, so as to perform under-voltage protection on the circuit connected to the switching power supply, for example, the power chip stops supplying power to the circuit connected to the switching power supply; under-voltage protection During the process, the voltage detection circuit 1 continues to detect the voltage VCC of the switching power supply until the voltage VCC of the switching power supply is greater than or equal to the second preset protection voltage V _TH+ , and the detection voltage output by the voltage detection circuit 1 will turn on the controllable device 2 again. , when the controllable device 2 is turned on, the undervoltage protection circuit 3 outputs a normal working signal such as a low-level signal to the power chip of the switching power supply, and the power chip works normally, for example, the power chip continues to supply power to the circuit connected to the switching power supply.

According to a specific example of the utility model, the controllable device 2 can be a three-terminal controllable device, and when the voltage of the control terminal of the controllable device 2 is greater than or equal to its internal reference voltage VREF, the controllable device 2 is in a conduction state; When the voltage at the control terminal of the device 2 is lower than its internal reference voltage VREF, the controllable device 2 is in a cut-off state. Specifically, the controllable device 2 may be TL431.

Specifically, the voltage at the control terminal of the controllable device 2 is the detection voltage output by the output terminal of the voltage detection circuit 1. When the power chip of the switching power supply is working normally, if the voltage VCC of the switching power supply is undervoltage, that is, if the If the voltage VCC is less than the first preset protection voltage V _TH- , the detection voltage output by the output terminal of the voltage detection circuit 1 will be less than the threshold voltage inside the controllable device 2, the controllable device 2 is cut off, and the undervoltage protection circuit 3 is in the controllable When the device 2 is turned off, it outputs an undervoltage protection signal to the power chip of the switching power supply to realize undervoltage protection; after that, if the voltage VCC of the switching power supply returns to normal and the voltage VCC is greater than or equal to the second preset protection voltage V _TH+ , the voltage detection circuit Only when the detection voltage output by the output terminal of 1 is greater than or equal to the threshold voltage inside the controllable device 2, the controllable device 2 is turned on again, and the undervoltage protection circuit 3 can re-output the normal working signal to the power chip of the switching power supply, and the power chip is normal Work.

Thus, the undervoltage protection device can perform undervoltage protection on the power supply chip of the switching power supply when the voltage of the switching power supply is lower than the first preset protection voltage, and until the voltage of the switching power supply is greater than the second preset protection voltage, the switching power supply The power chip works normally, so it is not easy to cause false action for small fluctuations in voltage.

Specifically, according to an embodiment of the present invention, as shown in FIG. 2 , the voltage detection circuit 1 includes: a first resistor R1 and a second resistor R2.

Wherein, one end of the first resistor R1 is connected to the preset power supply 4 that provides the voltage VCC of the switching power supply; one end of the second resistor R2 is connected to the other end of the first resistor R1, and the other end of the second resistor R2 is grounded. There is a first node a between R1 and the second resistor R2 , the first node a is connected to the control terminal 20 of the controllable device 2 , and the first node a is the output terminal of the voltage detection circuit 1 .

Specifically, when the voltage Va of the first node a between the first resistor R1 and the second resistor R2, that is, the voltage of the control terminal 20 of the controllable device 2 is greater than or equal to the internal reference voltage VREF of the controllable device 2, it can be The control device 2 is turned on; when the voltage Va of the first node a between the first resistor R1 and the second resistor R2, that is, the voltage of the control terminal 20 of the control device 2 is less than the internal reference voltage VREF of the control device 2, the controllable Device 2 is off.

Specifically, according to an embodiment of the present utility model, as shown in FIG. 2 , the undervoltage protection circuit 3 further includes: a third resistor R3, a first switching tube Q1, a second switching tube Q2, a third switching tube Q3, a Four switching tubes Q4.

Wherein, one end of the third resistor R3 is connected to one end of the second resistor; the first end 101 of the first switching tube Q1 is connected to the other end of the third resistor R3, the second end 102 of the first switching tube Q1 is grounded, and the first The third terminal 103 of the switching tube Q3 is connected to the preset power supply 4; the first terminal 201 of the second switching tube Q2 is connected to the third terminal 103 of the first switching tube Q1, and the second terminal 202 of the second switching tube Q2 is grounded; The first terminal 301 of the third switching tube Q3 is connected to the third terminal 203 of the second switching tube Q2, the second terminal 302 of the third switching tube Q3 is connected to the preset power supply 4, and the third terminal 303 of the third switching tube Q3 It is connected with the first terminal 21 of the controllable device 2, wherein the second terminal 22 of the controllable device 2 is grounded; the first terminal 401 of the fourth switching tube Q4 is connected with the preset power supply 4, and the second terminal of the fourth switching tube Q4 The terminal 402 is grounded, the third terminal 403 of the fourth switching tube Q4 is connected to the first terminal 301 of the third switching tube Q3, and the first terminal 401 of the fourth switching tube Q4 outputs an undervoltage protection signal when the controllable device 2 is turned off.

According to a specific embodiment of the present invention, the first switching tube Q1 , the second switching tube Q2 and the fourth switching tube Q4 are NPN transistors, and the third switching tube Q3 is a PNP transistor.

That is to say, the collector of the first switching tube Q1 is connected to the other end of the third resistor R3, the emitter of the first switching tube Q1 is grounded, and the base of the first switching tube Q3 is connected to the preset power supply 4; the second switch The collector of the tube Q2 is connected to the base of the first switching tube Q1, and the emitter of the second switching tube Q2 is grounded; the collector of the third switching tube Q3 is connected to the base of the second switching tube Q2, and the third switching tube Q3 The emitter of the switch tube Q3 is connected to the preset power supply 4, the base of the third switch tube Q3 is connected to the cathode of the controllable device 2, wherein the anode of the controllable device 2 is grounded; the collector of the fourth switch tube Q4 is connected to the preset power supply 4 connected, the emitter of the fourth switching tube Q4 is grounded, the base of the fourth switching tube Q4 is connected to the collector of the third switching tube Q3, and the collector of the fourth switching tube Q4 outputs undervoltage protection when the controllable device 2 is cut off. Signal.

Specifically, according to an embodiment of the present invention, as shown in FIG. 2 , the undervoltage protection circuit 3 further includes: a fourth resistor R4 and a fifth resistor R5.

Wherein, the fourth resistor R4 is connected between the third terminal 103 of the first switching transistor Q1 and the preset power supply 4 ; the fifth resistor R5 is connected between the preset power supply 4 and the first terminal 401 of the fourth switching transistor Q4 . That is to say, one end of the fourth resistor R4 is connected to the base of the first switch tube Q1, the other end of the fourth resistor R4 is connected to the preset power supply 4; one end of the fifth resistor R5 is connected to the preset power supply 4, and the fifth resistor The other end of R5 is connected to the collector of the fourth switching tube Q4, and there is a second node b between the fifth resistor R5 and the fourth switching tube Q4, wherein the second node b outputs undervoltage protection when the controllable device 2 is turned off Signal.

Specifically, according to an embodiment of the present invention, as shown in FIG. 2 , the undervoltage protection circuit 3 further includes: a sixth resistor R6 , a seventh resistor R7 and an eighth resistor R8 .

Wherein, the sixth resistor R6 is connected between the first terminal 21 of the controllable device 2 and the third terminal 303 of the third switching tube Q3; the seventh resistor R7 is connected between the first terminal 301 of the third switching tube Q3 and the fourth terminal 303 of the third switching tube Q3. Between the third end 403 of the switch tube Q4; one end of the eighth resistor R8 is connected to the third end 403 of the fourth switch tube Q4, and the other end of the eighth resistor R8 is grounded.

That is to say, one end of the sixth resistor R6 is connected to the cathode of the controllable device 2, the other end of the sixth resistor R6 is connected to the base of the third switching tube Q3; one end of the seventh resistor R7 is connected to the collector of the third switching tube Q3 The electrodes are connected, the other end of the seventh resistor R7 is connected to the base of the fourth switching tube Q4; one end of the eighth resistor R8 is connected to the base of the fourth switching tube Q4, and the other end of the eighth resistor R8 is grounded.

Specifically, according to an embodiment of the present invention, as shown in FIG. 2 , the undervoltage protection device of the switching power supply further includes: a ninth resistor R9. The ninth resistor R9 is connected between the preset power source 4 and the first terminal 21 of the controllable device 2 . In other words, one end of the ninth resistor R9 is connected to the preset power supply 4 , and the other end of the ninth resistor R9 is connected to the cathode of the controllable device 2 .

Specifically, when the voltage VCC of the switching power supply is normal, the voltage Va of the first node a between the first resistor R1 and the second resistor R2 is greater than or equal to the internal reference voltage VREF of the controllable device 2, and the controllable device 2 is turned on. , the cathode of the controllable device 2 is at a low level; thus, the voltage between the emitter and the base of the third switching tube Q3 is greater than the conduction voltage of the third switching tube Q3, the third switching tube Q3 is turned on, and the third switching tube Q3 is turned on. The collector of the switching tube Q3 is at a high level; furthermore, the voltage between the base and the emitter of the second switching tube Q2 is greater than the conduction voltage of the second switching tube Q2, the second switching tube Q2 is turned on, and the second switching tube Q2 is turned on. The collector of the tube Q2 is at a low level; thus, the voltage between the base and the emitter of the first switching tube Q1 is 0, and the first switching tube Q1 is cut off; at the same time, the base and emitter of the fourth switching tube Q4 The voltage between them is greater than the turn-on voltage of the fourth switching tube Q4, the fourth switching tube Q4 is turned on, the collector of the fourth switching tube Q4 is at a low level, and the second node b is at a low level, that is, the undervoltage protection circuit 3 Output a low-level signal to the power chip of the switching power supply, and the power chip works normally. At this time, the voltage Va of the first node a is the voltage obtained by dividing the voltage VCC of the switching power supply by the first resistor R1 and the second resistor R2, that is, Afterwards, if the voltage VCC of the switching power supply drops, when the voltage VCC drops to the first preset protection voltage _VTH- , the voltage Va of the first node a can be lower than the internal reference voltage VREF of the controllable device 2, and the controllable device 2 cut off, the undervoltage protection circuit 3 will output the undervoltage protection signal to the power supply chip of the switching power supply to realize the undervoltage protection, that is, the first preset protection voltage $V_{\mathrm{TH}-}=\frac{R1+R2}{R2}\×\mathrm{VREF}.$

That is to say, when the voltage VCC of the switching power supply is less than the first preset protection voltage , the controllable device 2 is cut off, and the cathode of the controllable device 2 is at a high level; thus, the voltage between the emitter and the base of the third switching tube Q3 is 0, the third switching tube Q3 is off, and the third switching tube The collector of Q3 is at low level, and the voltage between the base and emitter of the second switching tube Q2 is also 0, the second switching tube Q2 is cut off, and the collector of the second switching tube Q2 is at high level; Therefore, the voltage between the base and the emitter of the first switching tube Q1 is greater than the conduction voltage of the first switching tube Q1, and the first switching tube Q1 is turned on; at the same time, the voltage between the base and the emitter of the fourth switching tube Q4 The voltage between them is 0, the fourth switching tube Q4 is cut off, the collector of the fourth switching tube Q4 is at a high level, and the second node b is at a high level, that is, the undervoltage protection circuit 3 outputs a high level signal to the switching power supply The power chip realizes undervoltage protection. At this time, the voltage Va of the first node a is the voltage obtained by dividing the voltage VCC of the switching power supply by the first resistor R1 and the parallel connection of the second resistor R2 and the third resistor R3, namely Afterwards, if the voltage VCC of the switching power supply rises, when the voltage VCC rises to the second preset protection voltage VTH ₊ , the voltage Va of the first node a can be made greater than or equal to the internal reference voltage VREF of the controllable device 2, and the controllable device 2 is turned on, the second node b is at low level, the undervoltage protection circuit 3 will output a normal working signal to the power chip of the switching power supply, and the power chip works normally, that is, the second preset protection voltage

That is, when the voltage VCC of the switching power supply is greater than or equal to the second preset protection voltage , the controllable device 2 is turned on, the second switch tube Q2, the third switch tube Q3, and the fourth switch tube Q4 are turned on, the first switch tube Q1 is turned off, and the second node b is at a low level, that is, the undervoltage protection circuit 3 The low-level signal will be output to the power chip of the switching power supply, and the power chip will work normally again.

In general, when the power chip of the switching power supply is working normally, the voltage of the first node a The first preset protection voltage Afterwards, if the voltage VCC of the switching power supply drops, undervoltage protection is required, that is, when the voltage Va of the first node a is lower than the internal reference voltage VREF of the controllable device 2, that is, the voltage VCC of the switching power supply is lower than the first preset protection voltage V _{TH -} , the controllable device 2 is turned off, the third switch tube Q3, the fourth switch tube Q4, and the second switch tube Q2 are turned off, the first switch tube Q1 is turned on, and the second node b outputs a high-level signal to the power chip of the switching power supply , to realize undervoltage protection; at this time, during the process of undervoltage protection, the voltage Va of the first node a becomes $\mathrm{Va}=\frac{R2//R3}{R1+R2//R3}\×\mathrm{VCC},$ The second preset protection voltage $V_{\mathrm{TH}+}=\frac{R1+R2//R3}{R2//R3}\×\mathrm{VREF},$ Afterwards, when the voltage VCC of the switching power supply returns to normal, the divided voltage value Va of R2//R3 and R1 needs to be greater than the internal reference voltage VREF of the controllable device 2, and the controllable device 2 is turned on, and the third switching tube Q3 and the fourth switching tube Q4, the second switching tube Q2 is turned on, the first switching tube Q1 is turned off, the second node b outputs a low-level signal to the power chip of the switching power supply, and the power chip works normally again.

Thus, the under-voltage protection device of the switching power supply realizes the hysteresis function, that is, when the voltage VCC of the switching power supply drops below V _TH- , the second node b outputs a high-level under-voltage protection signal, and when VCC rises to be greater than or equal to When V _TH+ (V _TH+ >V _TH- ), the second node b outputs a low-level normal working signal, and the switching power supply returns to a normal working state. In this way, after the voltage VCC of the switching power supply increases the hysteresis △V, the switching power supply can recover from the undervoltage protection state to the normal working state. The hysteresis △V is the second preset protection voltage V _TH+ and the first preset protection voltage V _TH- difference, hysteresis $\mathrm{\ΔV}=V_{\mathrm{TH}+}-V_{\mathrm{TH}-}$ $=\frac{R1+R2//R3}{R2//R3}\×\mathrm{VREF}-\frac{R1+R2}{R2}\×\mathrm{VREF}=\frac{R1}{R3}\×\mathrm{VREF}>0,$ In this way, the undervoltage protection device of the switching power supply is less prone to misoperation for small fluctuations in voltage. It should be noted that the first preset protection voltage V _TH- , the second preset protection voltage V _TH+ and the hysteresis ΔV can be designed according to requirements, so that the undervoltage protection device can be flexibly used according to requirements.

In addition, according to an embodiment of the present invention, the voltage VCC input to the switching power supply may be 12V, 24V or 48V.

That is to say, the undervoltage protection device can be applied to voltage systems of different voltage levels, for example, it can be applied to voltage systems of 12V, 24V, and 48V, and there is no need to change the circuit structure of the undervoltage protection device, only need to select according to specific requirements The device model, that is, it can withstand different voltages only by replacing resistors with different resistance values.

Taking the 24V voltage system as an example, the undervoltage protection device of the switching power supply according to the embodiment of the present invention will be described in detail below. For example, the first resistor R1 can be 20kΩ, the second resistor R2 can be 5.5kΩ, the third resistor R3 can be 36kΩ, the fourth resistor R4 can be 20kΩ, the fifth resistor R5 can be 10kΩ, and the sixth resistor R6 can be 10kΩ , the seventh resistor R7 can be 10kΩ, the eighth resistor R8 can be 10kΩ, the ninth resistor R9 can be 1kΩ, the first switch tube Q1, the fourth switch tube Q4, the second switch tube Q2 can be BC847B, the third switch tube Q3 can be BC857B, controllable device 2 can be TL431, and its internal reference voltage VREF is 2.5V.

According to the description of the above embodiment, the first preset protection voltage The second preset protection voltage In this way, when the voltage VCC of the switching power supply is normal, that is, when the power chip is working normally, TL431 is turned on, the cathode of TL431 outputs low level, the third switching tube Q3, the fourth switching tube Q4, and the second switching tube Q2 are turned on, and the first switching tube Q1 is turned off, the second node b outputs a low-level signal to the power chip of the switching power supply, and the power chip works normally. At this time, the undervoltage protection point is the first preset protection voltage V _TH- =11.6V. When the voltage VCC of the switching power supply drops to less than 11.6V, TL431 is turned off, the cathode of TL431 outputs a high level, the third switching tube Q3, the fourth switching tube Q4, and the second switching tube Q2 are turned off, and the first switching tube Q1 is turned on. The second node b outputs a high level to realize undervoltage protection. At this time, the undervoltage protection point is the second preset protection voltage V _TH+ =13V. When the voltage VCC of the switching power supply needs to rise to greater than or equal to 13V, the power chip of the switching power supply resumes normal operation.

In summary, according to the undervoltage protection device of the switching power supply proposed by the utility model, the voltage input to the switching power supply is detected by the voltage detection circuit, and when the voltage detection circuit detects that the voltage of the switching power supply is lower than the first preset protection voltage, it can When the voltage detection circuit detects that the voltage of the switching power supply is greater than or equal to the second preset protection voltage, the controllable device is turned on. At the same time, the undervoltage protection circuit outputs an undervoltage protection signal to the power supply of the switching power supply when the controllable device is cut off. chip for undervoltage protection. Thus, the undervoltage protection device can perform undervoltage protection on the power supply chip of the switching power supply when the voltage of the switching power supply is lower than the first preset protection voltage, and until the voltage of the switching power supply is greater than the second preset protection voltage, the switching power supply The power supply chip works normally, so it is not easy to cause misoperation for small-scale fluctuations in voltage, and, compared with related technologies, the voltage detection circuit can detect different voltages without being affected by the chip design, so the undervoltage protection device can Applied to different voltage systems to realize undervoltage protection, the application range is wider, and when applied to different voltage systems, there is no need to change the circuit structure of the undervoltage protection device, only the device model needs to be selected according to specific requirements. In addition, the undervoltage protection device has simple design, complete functions and low cost.

Fig. 3 is a schematic block diagram of a switching power supply according to an embodiment of the present invention. As shown in FIG. 3 , the switching power supply includes: a power chip 100 and the above-mentioned undervoltage protection device 200 of the switching power supply.

Wherein, the undervoltage protection device 200 of the switching power supply is used to output an undervoltage protection signal such as a high level to the power supply chip 100 to realize undervoltage protection when the voltage VCC of the switching power supply is less than the first preset protection voltage; and, the switching power supply The undervoltage protection device 200 is used for outputting a normal operation signal, such as a low level, to the power chip 100 to make the power chip 100 work normally when the voltage VCC of the switching power supply is greater than or equal to the second preset protection voltage.

In summary, according to the switching power supply proposed by the utility model, the undervoltage protection device can perform undervoltage protection on the power supply chip when the voltage of the switching power supply is lower than the first preset protection voltage, and until the voltage of the switching power supply is greater than the second preset protection voltage The voltage restores the normal operation of the power chip, so that it is not easy to cause misoperation for small-scale fluctuations in the voltage, and it can perform undervoltage protection for different voltage systems, and the application range is wider.

In describing the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "Back", "Left", "Right", "Vertical", "Horizontal", "Top", "Bottom", "Inner", "Outer", "Clockwise", "Counterclockwise", "Axial" The orientation or positional relationship indicated by , "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the utility model and simplifying the description, rather than indicating or implying the referred device Or elements must have a specific orientation, be constructed and operate in a specific orientation, and thus should not be construed as limiting the invention.

In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be interpreted as indicating or implying relative importance or implicitly specifying the quantity of indicated technical features. Thus, the features defined as "first" and "second" may explicitly or implicitly include at least one of these features. In the description of the present utility model, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

In this utility model, unless otherwise specified and limited, terms such as "installation", "connection", "connection" and "fixation" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection. Connected, or integrated; may be mechanically or electrically connected; may be directly connected or indirectly connected through an intermediary, and may be an internal communication between two elements or an interactive relationship between two elements, unless otherwise stated Clearly defined. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present utility model according to specific situations.

In the present invention, unless otherwise clearly specified and limited, the first feature may be in direct contact with the first feature or the first feature and the second feature through an intermediary indirect contact. Moreover, "above", "above" and "above" the first feature on the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. "Below", "beneath" and "beneath" the first feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is less horizontally than the second feature.

In the description of this specification, descriptions referring to the terms "one embodiment", "some embodiments", "example", "specific examples", or "some examples" mean that specific features described in connection with the embodiment or example , structures, materials or features are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the described specific features, structures, materials or characteristics may be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples and features of different embodiments or examples described in this specification without conflicting with each other.

Although the embodiments of the present invention have been shown and described above, it can be understood that the above-mentioned embodiments are exemplary and should not be construed as limitations of the present invention, and those skilled in the art are within the scope of the present invention. Variations, modifications, substitutions and variations can be made to the above-described embodiments.

Claims (9)

1. An undervoltage protection device for a switching power supply, characterized in that, comprising: A voltage detection circuit for detecting the voltage input to the switching power supply; A controllable device, the control end of the controllable device is connected to the output end of the voltage detection circuit, wherein, when the voltage detection circuit detects that the voltage of the switching power supply is lower than the first preset protection voltage, the controllable The control device is turned off, and the control device is turned on when the voltage detection circuit detects that the voltage of the switching power supply is greater than or equal to a second preset protection voltage, and the second preset protection voltage is greater than the first preset protection voltage; An undervoltage protection circuit, the undervoltage protection circuit outputs an undervoltage protection signal to the power chip of the switching power supply when the controllable device is turned off, so as to realize undervoltage protection. 2. The undervoltage protection device of the switching power supply as claimed in claim 1, wherein the voltage detection circuit comprises: a first resistor, one end of the first resistor is connected to a preset power supply that provides the voltage of the switching power supply; a second resistor, one end of the second resistor is connected to the other end of the first resistor, the other end of the second resistor is grounded, and there is a first node between the first resistor and the second resistor, The first node is connected to the control terminal of the controllable device. 3. The undervoltage protection device of the switching power supply as claimed in claim 2, wherein the undervoltage protection circuit further comprises: a third resistor, one end of the third resistor is connected to one end of the second resistor; A first switch tube, the first end of the first switch tube is connected to the other end of the third resistor, the second end of the first switch tube is grounded, and the third end of the first switch tube is connected to the other end of the third resistor. connected to the preset power supply; a second switch tube, the first end of the second switch tube is connected to the third end of the first switch tube, and the second end of the second switch tube is grounded; The third switch tube, the first end of the third switch tube is connected to the third end of the second switch tube, the second end of the third switch tube is connected to the preset power supply, and the third switch tube is connected to the preset power supply. The third end of the switch tube is connected to the first end of the controllable device, wherein the second end of the controllable device is grounded; A fourth switch tube, the first end of the fourth switch tube is connected to the preset power supply, the second end of the fourth switch tube is grounded, the third end of the fourth switch tube is connected to the third The first ends of the switch tubes are connected, and the first end of the fourth switch tube outputs an undervoltage protection signal when the controllable device is turned off. 4. The undervoltage protection device of the switching power supply as claimed in claim 3, wherein the undervoltage protection circuit further comprises: a fourth resistor, the fourth resistor is connected between the third terminal of the first switch tube and the preset power supply; A fifth resistor, the fifth resistor is connected between the preset power supply and the first end of the fourth switch tube, and there is a second node between the fifth resistor and the fourth switch tube, wherein , the second node outputs an undervoltage protection signal when the controllable device is turned off. 5. The undervoltage protection device of the switching power supply as claimed in claim 4, wherein the undervoltage protection circuit further comprises: a sixth resistor, the sixth resistor is connected between the first terminal of the controllable device and the third terminal of the third switch tube; a seventh resistor, the seventh resistor is connected between the first end of the third switch tube and the third end of the fourth switch tube; An eighth resistor, one end of the eighth resistor is connected to the third end of the fourth switch tube, and the other end of the eighth resistor is grounded. 6. The undervoltage protection device of switching power supply as claimed in claim 3, is characterized in that, also comprises: A ninth resistor, the ninth resistor is connected between the preset power supply and the first terminal of the controllable device. 7. The undervoltage protection device of a switching power supply according to claim 3, wherein, the first switch tube, the second switch tube, and the fourth switch tube are NPN transistors, and the The third switch tube is a PNP transistor. 8. The undervoltage protection device for a switching power supply according to claim 1, wherein the voltage input to the switching power supply is 12V, 24V or 48V. 9. A switching power supply, characterized in that it comprises: power chips; and The undervoltage protection device of a switching power supply according to any one of claims 1-8.