Main and standby power switching circuit with under-voltage protection and fire alarm system

Abstract

The invention discloses a main and standby power switching circuit with undervoltage protection and a fire alarm system. The main and standby power switching circuit comprises a power input interface module, a main power monitoring module, a standby power monitoring module, a first switch control module, a second switch control module, a third switch control module and a load output interface module, the power input interface module is connected with the main power supply, the standby power supply, the first switch control module, the main power monitoring module and the standby power monitoring module. The first switch control module is connected with the main power monitoring module, the standby power monitoring module, the second switch control module and the load output interface module; the second switch control module is connected with the main power monitoring module and the standby power monitoring module, and the main power monitoring module is connected with the standby power monitoring module; and the third switch control module is connected with the main power monitoring module, the standby power monitoring module and the first switch control module. According to the invention, the working stability of the system is ensured when the main power supply of the system is powered off, and the working safety and reliability of the standby power supply are also ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of fire alarm technology, and in particular to a main-standby power switching circuit with undervoltage protection and a fire alarm system. Background Art

[0002] In the fire alarm control system, it is required to have a main power supply and a backup power supply, and the backup power supply is generally set to a battery. When the main power supply is cut off, the backup power supply can automatically switch to the backup power supply. In fact, in the process of automatically switching to the backup power supply when the main power supply is cut off, due to the slow response speed of components and untimely switching, the voltage of the power supply to the system will drop within a few milliseconds or tens of milliseconds before switching to the backup power supply. The voltage drops during the switching process, causing the detectors at the end of the bus in the fire protection system to drop more seriously due to the long bus distance, and even causing the terminal to reset due to unstable power supply, resulting in the detectors being unable to detect fire in time.

[0003] In addition, the main and standby power switching systems of the above-mentioned fire alarm control systems all use the power-off process of the main power supply as a switching signal by detecting it. This detection method cannot set the voltage point of power-off. It can only wait for the voltage of the main power supply to drop to a certain point as a switch signal for the standby power supply to turn on the standby power supply to continue powering the system. This switching method of the main power supply and the standby power supply is not flexible enough and has low controllability. Therefore, inventing a reliable main and standby power switching circuit with undervoltage protection and a fire alarm system is an urgent problem to be solved by technicians in this field. Summary of the invention

[0004] The purpose of the present application is to provide a main-backup power switching circuit and a fire alarm system with undervoltage protection. In this solution, not only the problem of the terminal resetting caused by the drop in power supply voltage when the main power supply and the backup power supply of the fire alarm control system are switched is solved, but also the precise adjustment of the power-off voltage in the main power supply is realized; after switching to the backup power supply, the present application can also realize over-discharge protection of the backup power supply and extend the service life of the backup battery; in addition, when the backup power supply turns on the over-discharge protection, the system automatically powers off and needs to be powered on after the main power supply is restored to charge the backup power supply. When the charging voltage of the backup battery is greater than the undervoltage recovery point, the power supply switch of the backup battery will automatically turn on. Therefore, the present application ensures the stability of the system operation when the main power supply of the system is cut off, and ensures the safety and reliability of the backup power supply.

[0005] In order to solve the above technical problems, the present application provides a main-backup power switching circuit with undervoltage protection, including a power input interface module, a main power monitoring module, a backup power monitoring module, a first switch control module, a second switch control module, a third switch control module and a load output interface module;

[0006] The power input interface module is electrically connected to the main power supply, the backup power supply, the first switch control module, the main power monitoring module and the backup power monitoring module respectively; the first switch control module is electrically connected to the main power monitoring module, the backup power monitoring module, the second switch control module and the load output interface module respectively; the second switch control module is electrically connected to the main power monitoring module and the backup power monitoring module respectively, and the main power monitoring module is electrically connected to the backup power monitoring module; the third switch control module is electrically connected to the main power monitoring module, the backup power monitoring module and the first switch control module respectively.

[0007] Preferably, the main power monitoring module comprises a first operational amplifier, a first resistor and a second resistor;

[0008] The non-inverting input terminal of the first operational amplifier is electrically connected to the first end of the first resistor and the first end of the second resistor respectively, the second end of the first resistor is grounded, the second end of the second resistor is electrically connected to the main electrical connection pin of the power input interface module, the inverting input terminal of the first operational amplifier is electrically connected to the backup power monitoring module, the first switch control module, the second switch control module and the backup power connection pin of the power input interface module respectively, and the output terminal of the first operational amplifier is electrically connected to the third switch control module.

[0009] Preferably, the backup power monitoring module includes a second operational amplifier, a third resistor and a fourth resistor;

[0010] The non-inverting input terminal of the second operational amplifier is electrically connected to the first end of the third resistor and the first end of the fourth resistor respectively, the second end of the third resistor is electrically connected to the inverting input terminal of the second operational amplifier, the main power monitoring module, the first switch control module, the second switch control module and the spare connection pin of the power input interface module respectively, the power supply terminal of the second operational amplifier is electrically connected to the second switch control module, and the second end of the fourth resistor is electrically connected to the output terminal of the second operational amplifier and the third switch control module respectively.

[0011] Preferably, the main power monitoring module further includes a first voltage regulator tube, a fifth resistor and a first capacitor;

[0012] The cathode of the first voltage regulator is electrically connected to the inverting input terminal of the first operational amplifier, the first end of the first capacitor and the first end of the fifth resistor, respectively; the second end of the fifth resistor is electrically connected to the backup power connection pins of the backup power monitoring module, the first switch control module, the second switch control module and the power input interface module, respectively; the anode of the first voltage regulator is grounded, and the second end of the first capacitor is grounded.

[0013] Preferably, the backup power monitoring module further includes a second voltage regulator tube, a sixth resistor and a second capacitor;

[0014] The anode of the second voltage regulator is electrically connected to the first end of the second capacitor, the first end of the sixth resistor and the inverting input end of the second operational amplifier, respectively; the second end of the sixth resistor is electrically connected to the non-inverting input end of the second operational amplifier, the main power monitoring module, the first switch control module, the second switch control module and the spare connection pin of the power input interface module, respectively; the anode of the second voltage regulator is grounded, and the second end of the second capacitor is grounded.

[0015] Preferably, the first switch control module includes a first switch tube and a first diode;

[0016] The first end of the first switch tube is electrically connected to the main power monitoring module, the backup power monitoring module and the second switch control module respectively, the second end of the second switch tube is electrically connected to the second switch control module, the third end of the second switch tube is electrically connected to the anode of the first diode, and the cathode of the first diode is electrically connected to the load output interface.

[0017] Preferably, the first switch control module further includes a seventh resistor;

[0018] A first end of the seventh resistor is electrically connected to a first end of the first switch tube, and a second end of the seventh resistor is electrically connected to a second end of the first switch tube.

[0019] Preferably, the second switch control module includes a second switch tube and a third voltage regulator tube;

[0020] The first end of the second switch tube is electrically connected to the first switch control module, the second end of the second switch tube is electrically connected to the cathode of the third voltage regulator tube, the anode of the third voltage regulator tube is grounded, and the third end of the second switch tube is electrically connected to the backup monitoring module.

[0021] Preferably, the third switch control module includes a third switch tube and a second diode;

[0022] The cathode of the second diode is electrically connected to the main power monitoring module, the anode of the second diode is electrically connected to the first end of the third switch tube, the second end of the third switch tube is electrically connected to the backup power monitoring module, and the third end of the third switch tube is electrically connected to the third switch control module.

[0023] In order to solve the above technical problems, the present application provides a fire alarm system, including the main-standby power switching circuit with undervoltage protection.

[0024] A main-standby power switching circuit with undervoltage protection and a fire alarm system of the present invention have the following beneficial effects. A main-standby power switching circuit with undervoltage protection disclosed in the present invention comprises: a power input interface module, a main power monitoring module, a backup power monitoring module, a first switch control module, a second switch control module, a third switch control module and a load output interface module. In the present application, the power input interface module is connected to the main power supply and the backup power supply respectively; the main power monitoring module is used to realize the monitoring of the power-off voltage of the main power supply; the backup power monitoring module is used to realize the monitoring of the power consumption voltage of the backup power supply; if the main power monitoring module monitors that the power-off voltage of the main power supply is greater than the first preset threshold, the main power monitoring module controls the first switch control module to be turned on, so that the backup power supply supplies power to the system through the load output interface module; after the backup power supply is supplied, if the backup power monitoring module monitors that the power consumption voltage of the backup power supply is greater than the second preset threshold, the backup monitoring module controls the third switch control module to turn off to control the first switch control module to turn off, and disconnect the power supply of the system; if the main power supply does not charge the backup power supply for a long time, resulting in too low voltage of the backup power supply, the backup power monitoring module controls the second switch control module to turn off, and disconnects the external power supply path of the backup power supply. Therefore, the present invention not only ensures the stability of the system operation when the main power supply of the system is cut off, but also ensures the safety and reliability of the backup power supply operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. The drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work:

[0026] Figure 1 It is a schematic diagram of the principle of a main-standby power switching circuit with undervoltage protection according to a preferred embodiment of the present invention;

[0027] Figure 2 The present invention is a schematic circuit diagram of a main-standby power switching circuit with undervoltage protection according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0028] The core of the present application is to provide a main-backup power switching circuit and a fire alarm system with undervoltage protection. In this solution, not only the problem of the terminal resetting caused by the drop in power supply voltage when the main power supply and the backup power supply of the fire alarm control system are switched is solved, but also the precise adjustment of the power-off voltage in the main power supply is realized; after switching to the backup power supply, the present application can also realize over-discharge protection of the backup power supply and extend the service life of the backup battery; in addition, when the backup power supply turns on the over-discharge protection, the system automatically powers off and needs to be powered on after the main power supply is restored to charge the backup power supply. When the charging voltage of the backup battery is greater than the undervoltage recovery point, the power supply switch of the backup battery will automatically turn on. Therefore, the present application ensures the stability of the system operation when the main power supply of the system is cut off, and ensures the safety and reliability of the backup power supply.

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0030] See also Figure 1 , Figure 1 A schematic diagram of the structure of a main-backup power switching circuit with undervoltage protection provided in the present application, comprising a power input interface module 1, a main power monitoring module 2, a backup power monitoring module 3, a first switch control module 4, a second switch control module 5, a third switch control module 6 and a load output interface module 7;

[0031] The power input interface module 1 is electrically connected to the main power supply, the backup power supply, the first switch control module 4, the main power monitoring module 2 and the backup power monitoring module 3 respectively; the first switch control module 4 is electrically connected to the main power monitoring module 2, the backup power monitoring module 3, the second switch control module 5 and the load output interface module 7 respectively; the second switch control module 5 is electrically connected to the main power monitoring module 2 and the backup power monitoring module 3 respectively, and the main power monitoring module 2 is electrically connected to the backup power monitoring module 3; the third switch control module 6 is electrically connected to the main power monitoring module 2, the backup power monitoring module 3 and the first switch control module 4 respectively.

[0032] In the prior art, the voltage of the main and backup power supplies of the fire alarm control system drops during the switching process, and the unstable power supply causes the terminal to reset, resulting in the detector being unable to detect the fire in time. This detection method uses the power-off process of the main power supply as a switching signal. This detection method cannot set the power-off voltage point. It can only wait until the voltage of the main power supply drops to a certain point as a backup power switch switching signal to turn on the backup power supply to continue powering the system. This switching method of the main power supply and the backup power supply is not flexible enough and has low controllability.

[0033] In response to the above-mentioned shortcomings, in this application, seamless switching of the main and backup power supplies is achieved through the cooperation of the power input interface module 1, the main power monitoring module 2, the backup power monitoring module 3, the first switch control module 4, the second switch control module 5, the third switch control module 6 and the load output interface module 7, thereby improving the power supply response speed of the backup power supply.

[0034] Specifically, in the present application, the power input interface module 1 is connected to the main power supply and the backup power supply respectively; the main power monitoring module 2 is used to realize the monitoring of the power-off voltage of the main power supply; the backup power monitoring module 3 is used to realize the monitoring of the power consumption voltage of the backup power supply; if the main power monitoring module monitors that the power-off voltage of the main power supply is greater than the first preset threshold, the main power monitoring module 2 controls the first switch control module to be turned on, so that the backup power supply supplies power to the system through the load output interface module 7; after the backup power supply is supplied, if the backup power monitoring module 3 monitors that the power consumption voltage of the backup power supply is greater than the second preset threshold, the backup monitoring module 3 controls the third switch control module 6 to be turned off to control the first switch control module 6 to be turned off, and the system power supply is disconnected; if the main power supply does not charge the backup power supply for a long time, resulting in too low a voltage of the backup power supply, the backup power monitoring module 3 controls the second switch control module 5 to be turned off, and the external power supply path of the backup power supply is disconnected. Therefore, the present invention not only ensures the stability of the system operation when the main power supply of the system is powered off, but also ensures the safety and reliability of the backup power supply operation.

[0035] In summary, the present invention provides a main-backup power switching circuit with undervoltage protection. In this solution, it includes a power input interface module 1, a main power monitoring module 2, a backup power monitoring module 3, a first switch control module 4, a second switch control module 5, a third switch control module 6 and a load output interface module 7; the power input interface module 1 is electrically connected to the main power supply, the backup power supply, the first switch control module 4, the main power monitoring module 2 and the backup power monitoring module 3 respectively; the first switch control module 4 is electrically connected to the main power monitoring module 2, the backup power monitoring module 3, the second switch control module 5 and the load output interface module 7 respectively; the second switch control module 5 is electrically connected to the main power monitoring module 2 and the backup power monitoring module 3 respectively, and the main power monitoring module 2 is electrically connected to the backup power monitoring module 3; the third switch control module 6 is electrically connected to the main power monitoring module 2, the backup power monitoring module 3 and the first switch control module 4 respectively. Therefore, the present invention not only ensures the stability of the system operation when the main power supply of the system is powered off, but also ensures the safety and reliability of the backup power supply operation.

[0036] Based on the above embodiments:

[0037] Please refer to Figure 2 , Figure 2 A circuit schematic diagram of a main-standby power switching circuit with undervoltage protection provided in this application.

[0038] As a preferred embodiment, the main power monitoring module 2 includes a first operational amplifier U1 B, a first resistor R9 and a second resistor R8;

[0039] The non-inverting input terminal of the first operational amplifier U1 B is electrically connected to the first end of the first resistor R9 and the first end of the second resistor R8 respectively, the second end of the first resistor R9 is grounded, the second end of the second resistor R8 is electrically connected to the main electrical connection pin of the power input interface module 1, the inverting input terminal of the first operational amplifier U1 B is electrically connected to the backup power monitoring module 3, the first switch control module 4, the second switch control module 5 and the backup power connection pin of the power input interface module 1 respectively, and the output terminal of the first operational amplifier U1 B is electrically connected to the third switch control module 6.

[0040] As a preferred embodiment, the main power monitoring module 2 further includes a first voltage regulator tube ZD2, a fifth resistor R7 and a first capacitor C3;

[0041] The cathode of the first voltage regulator tube ZD2 is electrically connected to the inverting input terminal of the first operational amplifier U1 B, the first end of the first capacitor C3 and the first end of the fifth resistor R7 respectively, the second end of the fifth resistor R7 is electrically connected to the backup power connection pins of the backup power monitoring module 3, the first switch control module 4, the second switch control module 5 and the power input interface module 1 respectively, the anode of the first voltage regulator tube ZD2 is grounded, and the second end of the first capacitor C3 is grounded.

[0042] Specifically, in this embodiment, the power input interface module 1J1 is the input interface of the main power supply and the backup power supply, wherein the 1st pin of J1 is the interface for the backup power supply to supply power to the system, and the backup power supply is connected to the system power supply of the load output interface module 7 through the on-off pair of the first switch control module 4. Among them, the 4th pin of J1 is connected to the main power supply, and is divided by the first resistor R9 and the second resistor R8 to the positive input terminal of the first operational amplifier U1B, and the inverting input terminal of the first operational amplifier U1B is connected to the first voltage regulator ZD2, and the first voltage regulator ZD2 is used to stabilize the voltage at 9.1V, and the voltage of the backup power supply is input to the inverting input terminal of the first operational amplifier U1B, and the first operational amplifier U1B is used to monitor the power-off voltage of the main power supply, that is, the switching voltage point of the main power supply and the backup power supply.

[0043] Specifically, in this embodiment, if the main power supply is powered off, the voltage at the non-inverting input terminal 5 of the first operational amplifier U1B is VU1B-5, and the main power supply voltage is Vmain, then VU1B-5=V 主 *R9 / (R8+R9), when VU1B-5<9.1V, the pin 7 of the first operational amplifier U1B outputs a low level, so that a voltage difference is formed across the two ends of the diode D3 in the third switch control module 6, and the third switch control module 6 is turned on, thereby turning on the first switch control module 4, and the backup power supply supplies power to the system through the load output interface module 7.

[0044] Specifically, if the switching voltage between the main power supply and the backup power supply in the main power supply, i.e., the first preset threshold value, needs to be adjusted, according to the principle, VU1B-5 can be adjusted, i.e., the resistance values ​​of R8 and R9 are adjusted, so as to adjust the switching voltage between the main power supply and the backup power supply. Therefore, the present invention can realize the accurate adjustment of the power-off voltage in the main power supply, and realize the seamless switching of the main and backup power supplies.

[0045] As a preferred embodiment, the backup power monitoring module 3 includes a second operational amplifier U1A, a third resistor R5 and a fourth resistor R6;

[0046] The non-inverting input terminal of the second operational amplifier U1A is electrically connected to the first end of the third resistor R5 and the first end of the fourth resistor R6, respectively; the second end of the third resistor R5 is electrically connected to the inverting input terminal of the second operational amplifier U1A, the main power monitoring module 2, the first switch control module 4, the second switch control module 5 and the spare connection pin of the power input interface module 1, respectively; the power supply terminal of the second operational amplifier U1A is electrically connected to the second switch control module 5, and the second end of the fourth resistor R6 is electrically connected to the output terminal of the second operational amplifier U1A and the third switch control module 6, respectively.

[0047] As a preferred embodiment, the backup power monitoring module 3 further includes a second voltage regulator tube ZD1, a sixth resistor R3 and a second capacitor C2;

[0048] The anode of the second voltage-stabilizing tube ZD1 is electrically connected to the first end of the second capacitor C2, the first end of the sixth resistor R3 and the inverting input end of the second operational amplifier U1A, respectively; the second end of the sixth resistor R3 is electrically connected to the non-inverting input end of the second operational amplifier U1A, the main power monitoring module 2, the first switch control module 4, the second switch control module 5 and the spare connection pin of the power input interface module 1, respectively; the anode of the second voltage-stabilizing tube ZD1 is grounded, and the second end of the second capacitor C2 is grounded.

[0049] Specifically, in this embodiment, the second voltage regulator ZD1 stabilizes the voltage of the inverting input terminal of the second operational amplifier U1A at 20V. When the non-inverting input terminal of the second operational amplifier U1A is lower than 20V, the second operational amplifier U1A outputs a low level to control the third switch control module 6 to turn off to control the first switch control module 4 to turn off, thereby realizing the cutting off of the backup power supply to the system.

[0050] Specifically, after the main power supply is powered off and switched to the backup power supply, the voltage of the non-inverting input terminal of the second operational amplifier U1A is VU1A-3, and the voltage of the non-inverting input terminal 2 of the second operational amplifier U1A is stabilized at 20V by the second voltage regulator ZD1; the second operational amplifier U1A acts as a hysteresis comparator. Under normal circumstances, the pin 1 of the second operational amplifier U1A outputs a high level. When VU1A-3<20*(1+R5 / R6)-R5 / R6*V 备 When the output state of the pin 1 of the second operational amplifier U1A changes from a high level to a low level, the third switch control module 6 is turned off, so that the G pole voltage of the MOS tube in the first switch control module 4 is equal to the backup power supply voltage, and the first switch control module 4 is turned off, cutting off the backup power supply to the system.

[0051] As a preferred embodiment, the first switch control module 4 includes a first switch tube Q1 and a first diode D1;

[0052] The first end of the first switch tube Q1 is electrically connected to the main power monitoring module 2, the backup power monitoring module 3 and the second switch control module 5 respectively, the second end of the second switch tube Q4 is electrically connected to the second switch control module 5, the third end of the second switch tube Q4 is electrically connected to the anode of the first diode, and the cathode of the first diode is electrically connected to the load output interface.

[0053] As a preferred embodiment, the first switch control module 4 further includes a seventh resistor R1;

[0054] A first end of the seventh resistor R1 is electrically connected to a first end of the first switch tube Q1 , and a second end of the seventh resistor R1 is electrically connected to a second end of the first switch tube Q1 .

[0055] As a preferred embodiment, the second switch control module 5 includes a second switch tube Q4 and a third voltage regulator tube ZD3;

[0056] The first end of the second switch tube Q4 is electrically connected to the first switch control module 4, the second end of the second switch tube Q4 is electrically connected to the cathode of the third voltage regulator tube ZD3, the anode of the third voltage regulator tube ZD3 is grounded, and the third end of the second switch tube Q4 is electrically connected to the standby monitoring module.

[0057] As a preferred embodiment, the third switch control module 6 includes a third switch tube Q2 and a second diode D3;

[0058] The cathode of the second diode D3 is electrically connected to the main power monitoring module 2, the anode of the second diode D3 is electrically connected to the first end of the third switch tube Q2, the second end of the third switch tube Q2 is electrically connected to the backup power monitoring module 3, and the third end of the third switch tube Q2 is electrically connected to the third switch control module 6.

[0059] Specifically, in this embodiment, after the backup power supply stops supplying power to the system, the backup power supply continues to supply power to the first operational amplifier U1B and the second operational amplifier U1A, and monitors the operation of the main power supply and the backup power supply. If the main power supply is not powered on for a long time to charge the backup power supply, resulting in the backup power supply voltage being too low, and lower than the voltage set by the third voltage regulator ZD3, the second switch tube Q4, i.e., the triode Q4, is turned off, completely disconnecting the backup power supply from all external circuits, thereby protecting the backup power supply.

[0060] Specifically, in the present embodiment, after the backup power supply cuts off the power supply to the system because it works to the protection point, the main power supply has not been powered on to charge the backup power supply. At this time, the backup power supply still supplies power to the operational amplifier and continuously monitors the status of the main power supply and the backup power supply, but the current is relatively small. When the main power supply is still not powered on for a long time, and the operational amplifier works for too long, and the current of the backup power supply is consumed to the voltage set by the third voltage regulator tube ZD3, the second switch tube Q4 is turned off, cutting off the power supply of the backup power supply to the operational amplifier, so that the backup power supply has no power-consuming equipment, avoiding damage caused by over-discharge of the backup power supply.

[0061] Specifically, after the main power supply is powered on, the backup power supply will be charged, and the backup power supply voltage will rise. When the backup power supply voltage V is greater than the voltage point set by the third voltage regulator tube ZD3, the second switch tube Q4 is turned on, and the backup power supply supplies power to the operational amplifier, thereby restoring the monitoring of the main power supply and the emergency power supply.

[0062] Specifically, in this embodiment, if the main power supply is powered off, the voltage at the non-inverting input terminal 5 of the first operational amplifier U1B is VU1B-5, and the main power supply voltage is Vmain, then VU1B-5=V 主 *R9 / (R8+R9), when VU1B-5<9.1V, the 7th pin of the first operational amplifier U1B outputs a low level, so that a voltage difference is formed at both ends of the diode D3 in the third switch control module 6, the diode D3 is turned on, the first switch tube Q1 is also turned on, the G pole voltage of the first switch tube, i.e., the PMOS tube, is VG, and the voltage of the backup power supply is V 备 At this time, VG=Vbackup*R2 / (R1+R2), the voltage drop of VG forms the condition for the first switch tube, namely the PMOS tube, to be turned on, so that the backup power supply supplies power to the system through the load output interface module 7.

[0063] Specifically, in this embodiment, when the main power supply is powered on to charge the backup power supply, the voltage of the backup power supply increases accordingly, and VU1A-3 also increases. When VU1A-3>20*(1+R5 / R6), the level of the 1st pin of the second operational amplifier U1A changes and outputs a high level, so that the first switch tube Q1 is turned on again, so that the power supply and the backup power supply are switched. If it is necessary to adjust the voltage at which the backup power supply cuts off the power supply to the system, that is, the second preset threshold, the parameters of the voltage stabilizing diode ZD1 can be adjusted.

[0064] The present application also provides a fire alarm system, including a main-standby power switching circuit with undervoltage protection.

[0065] For an introduction to a main-standby power switching circuit with undervoltage protection provided in the present application, please refer to the above-mentioned embodiment, and the present application will not go into details here.

[0066] It should be noted that, in this specification, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "includes a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0067] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A main power switching circuit with undervoltage protection, characterized in that: It includes a power input interface module, a main power monitoring module, a backup power monitoring module, a first switch control module, a second switch control module, a third switch control module and a load output interface module; The power input interface module is electrically connected to the main power supply, the backup power supply, the first switch control module, the main power monitoring module and the backup power monitoring module respectively; the first switch control module is electrically connected to the main power monitoring module, the backup power monitoring module, the second switch control module and the load output interface module respectively; the second switch control module is electrically connected to the main power monitoring module and the backup power monitoring module respectively, and the main power monitoring module is electrically connected to the backup power monitoring module; the third switch control module is electrically connected to the main power monitoring module, the backup power monitoring module and the first switch control module respectively.

2. A main-standby power switching circuit with undervoltage protection according to claim 1, characterized in that: The main power monitoring module includes a first operational amplifier, a first resistor and a second resistor; The non-inverting input terminal of the first operational amplifier is electrically connected to the first end of the first resistor and the first end of the second resistor respectively, the second end of the first resistor is grounded, the second end of the second resistor is electrically connected to the main electrical connection pin of the power input interface module, the inverting input terminal of the first operational amplifier is electrically connected to the backup power monitoring module, the first switch control module, the second switch control module and the backup power connection pin of the power input interface module respectively, and the output terminal of the first operational amplifier is electrically connected to the third switch control module.

3. The main power switching circuit with undervoltage protection according to claim 1, characterized in that: The backup power monitoring module includes a second operational amplifier, a third resistor and a fourth resistor; The non-inverting input terminal of the second operational amplifier is electrically connected to the first end of the third resistor and the first end of the fourth resistor respectively, the second end of the third resistor is electrically connected to the inverting input terminal of the second operational amplifier, the main power monitoring module, the first switch control module, the second switch control module and the spare connection pin of the power input interface module respectively, the power supply terminal of the second operational amplifier is electrically connected to the second switch control module, and the second end of the fourth resistor is electrically connected to the output terminal of the second operational amplifier and the third switch control module respectively.

4. The main-standby power switching circuit with undervoltage protection according to claim 2, characterized in that: The main power monitoring module also includes a first voltage regulator tube, a fifth resistor and a first capacitor; The cathode of the first voltage regulator is electrically connected to the inverting input terminal of the first operational amplifier, the first end of the first capacitor and the first end of the fifth resistor, respectively; the second end of the fifth resistor is electrically connected to the backup power connection pins of the backup power monitoring module, the first switch control module, the second switch control module and the power input interface module, respectively; the anode of the first voltage regulator is grounded, and the second end of the first capacitor is grounded.

5. The main power switching circuit with undervoltage protection according to claim 3, characterized in that: The backup power monitoring module also includes a second voltage regulator tube, a sixth resistor and a second capacitor; The anode of the second voltage regulator is electrically connected to the first end of the second capacitor, the first end of the sixth resistor and the inverting input end of the second operational amplifier, respectively; the second end of the sixth resistor is electrically connected to the non-inverting input end of the second operational amplifier, the main power monitoring module, the first switch control module, the second switch control module and the spare connection pin of the power input interface module, respectively; the anode of the second voltage regulator is grounded, and the second end of the second capacitor is grounded.

6. The main-standby power switching circuit with undervoltage protection according to claim 1, characterized in that: The first switch control module includes a first switch tube and a first diode; The first end of the first switch tube is electrically connected to the main power monitoring module, the backup power monitoring module and the second switch control module respectively, the second end of the second switch tube is electrically connected to the second switch control module, the third end of the second switch tube is electrically connected to the anode of the first diode, and the cathode of the first diode is electrically connected to the load output interface.

7. A main-standby power switching circuit with undervoltage protection according to claim 6, characterized in that: The first switch control module further includes a seventh resistor; A first end of the seventh resistor is electrically connected to a first end of the first switch tube, and a second end of the seventh resistor is electrically connected to a second end of the first switch tube.

8. The main-standby power switching circuit with undervoltage protection according to claim 1, characterized in that: The second switch control module includes a second switch tube and a third voltage regulator tube; The first end of the second switch tube is electrically connected to the first switch control module, the second end of the second switch tube is electrically connected to the cathode of the third voltage regulator tube, the anode of the third voltage regulator tube is grounded, and the third end of the second switch tube is electrically connected to the backup monitoring module.

9. The main-standby power switching circuit with undervoltage protection according to claim 1, characterized in that: The third switch control module includes a third switch tube and a second diode; The cathode of the second diode is electrically connected to the main power monitoring module, the anode of the second diode is electrically connected to the first end of the third switch tube, the second end of the third switch tube is electrically connected to the backup power monitoring module, and the third end of the third switch tube is electrically connected to the third switch control module.

10. A fire alarm system, characterized in that: A main-standby power switching circuit with undervoltage protection comprising the one described in any one of claims 1 to 9.

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