CN217010899U

CN217010899U - POE switch with UPS emergency power supply

Info

Publication number: CN217010899U
Application number: CN202121018387.5U
Authority: CN
Inventors: 王镇; 郭敏; 蒋汉柏
Original assignee: Hunan Fullriver High Technology Co ltd
Current assignee: Hunan Fullriver High Technology Co ltd
Priority date: 2021-05-12
Filing date: 2021-05-12
Publication date: 2022-07-19
Anticipated expiration: 2031-05-12

Abstract

The utility model discloses a POE (Power over Ethernet) switch with a UPS (uninterrupted Power supply), which comprises a switch module, a PSE (Power supply equipment) power supply module, a power supply module and a UPS (uninterrupted Power supply) power supply module, wherein the switch module realizes data interaction; the input end of the PSE power supply module is connected with the switch module, and the output end of the PSE power supply module is externally connected with POE equipment; the input end of the power supply module 300 is connected with the mains supply, and the output end of the power supply module is connected with the power supply end of the switch module; the UPS power supply module comprises a charging circuit, a pulse width modulation integrated circuit and a battery, wherein the input end of the charging circuit is connected with a mains supply, the output end of the charging circuit is connected with the charging end of the battery, and the pulse width modulation integrated circuit is connected with the charging circuit. The monitoring system can be prevented from stopping working in a power failure state, the voltage and the current can be regulated in the charging process, overshoot is avoided, and the service life of the battery is prolonged.

Description

POE switch with UPS emergency power supply

Technical Field

The utility model relates to the field of switches, in particular to a POE switch with a UPS emergency power supply.

Background

Poe (power Over ethernet) refers to a technology that can transmit data signals to IP-based terminals (such as IP phones, wireless lan access points AP, webcams, etc.) and simultaneously provide direct current for such devices, without any change to the existing ethernet cat.5 wiring infrastructure, and is an exchange that supports power Over ethernet.

At present, a conventional PoE switch is not provided with a UPS emergency battery, the PoE switch stops working under the condition of mains supply power failure, power cannot be supplied to an external camera, and a whole video monitoring system cannot work, so that monitoring blank appears in a period of time, and certain potential safety hazards exist. In order to solve the problem, rechargeable spare batteries are added to part of POE switches, but the POE switches cannot adjust charging current and charging voltage, so that overshoot is caused, the service life of the batteries is influenced, and the practical value is low.

SUMMERY OF THE UTILITY MODEL

The present invention is directed to solving at least one of the problems of the prior art. Therefore, the POE switch with the UPS emergency power supply can maintain the operation of the video monitoring system in a power failure state and can adjust the charging current and the charging voltage.

The POE switch with the UPS emergency power supply comprises: the switch module is used for realizing data interaction; the PSE power supply module is connected with the switch module and used for supplying power to external POE equipment;

the input end of the power supply module is used for connecting commercial power, and the output end of the power supply module is connected with the power supply end of the switch module; UPS power module, UPS power module includes charging circuit, pulse width modulation integrated circuit, feedback circuit and battery, charging circuit's input is used for connecting the commercial power, the charging end of battery is connected to charging circuit's output, feedback circuit's input is connected the charging end of battery, feedback circuit's output is connected pulse width modulation integrated circuit's feedback end, pulse width modulation integrated circuit with charging circuit links to each other in order to be used for adjusting charging current and charging voltage through feedback circuit's signal. The video monitoring system can be maintained to operate in a power failure state, and the charging current and the charging voltage can be adjusted.

The POE switch with the UPS emergency power supply provided by the embodiment of the utility model at least has the following technical effects: according to the embodiment of the utility model, the UPS power module is added at the power supply end of the switch module and is connected with the power module in parallel, the power module supplies power to the switch module in a normal state of mains supply, the charging circuit charges the battery at the same time, the charging time pulse width modulation integrated circuit adjusts the charging current and the charging voltage in real time according to the feedback signal of the feedback circuit, overshoot is avoided, the pulse width modulation integrated circuit judges whether the charging is saturated, if the charging is saturated, the charging to the battery is stopped, and the electric energy only ensures the work requirement of the switch. And when the mains supply is in a power failure state, the power supply module stops supplying power, the switch automatically switches to supply power by the battery in the UPS power module, and the whole switch is guaranteed to normally work.

According to some embodiments of the present invention, the charging circuit includes a first rectifying and filtering circuit, a MOS transistor Q1, and a transformer T1, an input end of the first rectifying and filtering circuit is used for connecting to a mains supply, an output end of the first rectifying and filtering circuit is respectively connected to one end of a primary winding of the transformer T1 and a start end of the pwm ic, another end of the primary winding of the transformer T1 is connected to a drain of the MOS transistor Q1, a source of the MOS transistor Q1 is grounded through a resistor R25, a gate of the MOS transistor Q1 is connected to a pulse output end of the pwm ic, a primary secondary winding of the transformer T1 is connected to a power supply end of the pwm ic, and a secondary output winding of the transformer T1 is connected to a charging positive electrode of the battery.

According to some embodiments of the present invention, the first rectifying and filtering circuit includes a bidirectional filter T0, a bridge rectifier D1, and a filter capacitor C11, an input terminal of the bidirectional filter T0 is used for connecting a commercial power, an output terminal of the bidirectional filter T0 is connected to an input terminal of the bridge rectifier D1, and an output terminal of the bridge rectifier D1 is connected to one end of the primary winding of the transformer T1 and the power supply terminal of the pwm integrated circuit through the filter capacitor C11, respectively.

According to some embodiments of the utility model, the transformer T1 is a high frequency pulse transformer.

According to some embodiments of the present invention, the pwm integrated circuit includes a pwm integrated chip U1, a resistor R5, a capacitor C8, a capacitor C3, a reference voltage source U3, and an optical coupler U2, a power supply anode of the pwm integrated chip U1 is connected to a cathode of a filter capacitor C11 through a capacitor C8 and a capacitor C3 which are connected in parallel, a power supply anode of the pwm integrated chip U1 is connected to one end of the resistor R5, the other end of the resistor R5 is connected to an anode of the filter capacitor C11, a pulse output terminal of the pwm integrated chip U1 is connected to a gate of the MOS transistor Q1, a power supply cathode of the pwm integrated chip U1 is grounded, a voltage feedback pin of the pwm integrated chip U1 is connected to one output pin of the optical coupler U2 through a resistor R21, another output pin of the optical coupler U2 is connected to a power supply anode of the pwm integrated chip U1, one input pin of the optocoupler U2 is connected with the reference voltage source U3, and the other input pin of the optocoupler U2 is connected with the feedback circuit.

According to some embodiments of the utility model, the model number of the pwm integrated chip U1 is TL 3842.

According to some embodiments of the present invention, a second rectifying and smoothing circuit and a diode D7 are disposed between the output terminal of the charging circuit and the charging terminal of the battery, the output terminal of the charging circuit is connected to the input terminal of the second rectifying and smoothing circuit, the output terminal of the second rectifying and smoothing circuit is connected to the anode of the diode D7, and the cathode of the diode D7 is connected to the charging anode of the battery.

According to some embodiments of the present invention, the feedback circuit includes a dual operational amplifier, a diode D9 and a current sampling resistor R27, the output terminal of the charging circuit is connected to the positive power supply of the dual operational amplifier through a second rectifying and filtering circuit, the negative power supply of the dual operational amplifier is grounded, one end of the current sampling resistor R27 is connected to the charging negative electrode of the battery, the other end of the current sampling resistor R27 is grounded, the positive electrode of the diode D9 is connected to the 12V power supply through a resistor R16, the negative electrode of the diode D9 is grounded, two ends of the diode D9 are connected in parallel to a voltage dividing resistor R26 and a voltage dividing resistor R4, the common terminal of the voltage dividing resistors R26 and R4 is connected to the first non-phase input terminal and the second non-phase input terminal of the dual operational amplifier, the second non-phase input terminal of the dual operational amplifier is connected to the charging negative electrode of the battery through a resistor R17, the first inverting input end of the double operational amplifier is connected with the second output end of the double operational amplifier, and the first output end of the double operational amplifier is connected with the feedback end of the pulse width modulation integrated circuit through a diode D8 and a potentiometer W1.

According to some embodiments of the present invention, the charging indication unit further comprises a transistor Q2, a transistor Q3, a power indicator D10 and a charging indicator D6, wherein a first output terminal of the dual operational amplifier is connected to a base of the transistor Q3 through a resistor R22, an emitter of the transistor Q3 is grounded through the power indicator D10, a collector of the transistor Q3 is connected to a 12V power supply, a second output terminal of the dual operational amplifier is connected to a base of the transistor Q2 through a resistor R18, an emitter of the transistor Q2 is grounded through a charging indicator D6, and a collector of the transistor Q2 is connected to an output terminal of the second rectifying and filtering circuit.

According to some embodiments of the utility model, the dual operational amplifier is model LM 358.

Additional aspects and advantages of the utility model will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the utility model.

Drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

fig. 1 is a schematic block diagram of a POE switch with an UPS emergency power supply according to an embodiment of the present invention;

fig. 2 is a schematic circuit diagram of a UPS power module according to an embodiment of the utility model.

Reference numerals

Switch module 100, PSE power supply module 200, power supply module 300, UPS power supply module 400.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention and are not to be construed as limiting the present invention.

In the description of the present invention, a plurality of means are one or more, a plurality of means are two or more, and the terms greater than, less than, exceeding, etc. are understood as not including the number, and the terms greater than, less than, within, etc. are understood as including the number. If there is a description of first and second for the purpose of distinguishing technical features only, this is not to be understood as indicating or implying a relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of technical features indicated.

In the description of the present invention, unless otherwise explicitly limited, terms such as arrangement, installation, connection and the like should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present invention in combination with the specific contents of the technical solutions.

Referring to fig. 1, a POE switch with UPS emergency power supply includes: the switch module 100, the PSE power supply module 200, the power supply module 300 and the UPS power supply module 400, wherein the switch module 100 realizes data interaction; the input end of the PSE power supply module 200 is connected to the switch module 100, and the output end of the PSE power supply module 200 is externally connected to POE equipment; the input end of the power module 300 is connected with the mains supply, and the output end of the power module 300 is connected with the power supply end of the switch module 100; the UPS power module 400 comprises a charging circuit, a pulse width modulation integrated circuit and a battery, wherein the input end of the charging circuit is connected with 220V mains supply, the output end of the charging circuit is connected with the charging end of the battery, and the pulse width modulation integrated circuit is connected with the charging circuit.

The switch module 100, the PSE power supply module 200, and the power supply module 300 are components of a commercially available POE switch.

In practical application, the PSE power supply module 200 is connected to a plurality of monitoring cameras, the switch module 100 is connected to the video monitoring terminal, the power module 300 is inserted into a 220V socket, and the UPS power module 400 obtains power through the power module 300.

Referring to fig. 2, the charging circuit includes a bi-directional filter T0, a bridge rectifier D1, a filter capacitor C11, the input end of the bidirectional filter T0 is connected with 220 mains supply, the output end of the bidirectional filter T0 is connected with the input end of the bridge rectifier D1, the bidirectional filter T0 is used for achieving bidirectional filtering interference suppression, the output end of the bridge rectifier D1 is connected with a primary main coil of the transformer T1 through a filter capacitor C11, the bridge rectifier D1 rectifies 220V alternating current into pulsating direct current, the pulsating direct current is filtered through a filter capacitor C11 to form stable direct current of about 300V, the filter capacitor C11 is connected with the power supply end of the pulse width modulation integrated circuit, one end of the primary main coil of the transformer T1 is connected with the positive electrode of the filter capacitor C11, the other end of the primary main coil of the transformer T1 is connected with the drain electrode of the MOS tube 737Q 6, and the source electrode of the MOS tube Q1 is grounded through a resistor R25.

The pulse width modulation integrated circuit comprises a pulse width modulation integrated chip U1, a resistor R5, a capacitor C8, a capacitor C3, a reference voltage source U3 and an optical coupler U2, wherein a pin 5 of the pulse width modulation integrated chip U1 is a power supply cathode, a pin 7 is a power supply anode, a pin 6 is a pulse output pin, a pin 3 is a maximum current limiting end, and a pin 2 is a voltage feedback end. The positive electrode of a power supply of a pulse width modulation integrated chip U1 is connected with the negative electrode of a filter capacitor C11 through a capacitor C8 and a capacitor C3 which are connected in parallel, a pin 7 of the pulse width modulation integrated chip U1 is connected with one end of a resistor R5, the capacitor C8 and one end of a capacitor C3, the other end of the resistor R5 is connected with the positive electrode of the filter capacitor C11, a pin 6 of the pulse width modulation integrated chip U1 is connected with the grid of a MOS tube Q1, a pin 5 of the pulse width modulation integrated chip U1 is grounded, a pin 2 of the pulse width modulation integrated chip U1 is connected with one output pin of an optical coupler U2 through a resistor R21, the other output pin of the optical coupler U2 is connected with a pin 7 of the pulse width modulation integrated chip U1, one input pin of the optical coupler U2 is connected with a reference voltage source U3, the other input pin of the optical coupler U2 is connected with a feedback circuit, a reference voltage source U3 is connected with a potentiometer w2, and the potentiometer w2 can finely adjust the voltage of the charger, the precision reference voltage source U3 cooperates with the optocoupler U2 to function as an automatic adjustment for the charger voltage. Pin 4 of the pwm ic U1 is externally connected to the oscillating resistor R1 and the oscillating capacitor C1.

The source of the MOS transistor Q1 and the common terminal of the resistor R25 are connected to the pin 3 of the pwm integrated chip U1 through the resistors R3 and R23 which are connected in series in sequence, and the maximum charging current can be adjusted by adjusting the resistance of the resistor R25, where the resistor R25 is 2.5 ohms in this embodiment.

In the present embodiment, the transformer T1 is a high-frequency pulse transformer, and has three functions. The first is to impress the high voltage pulse into a low voltage pulse. The second is to isolate the high voltage to prevent electric shock, and the third is to provide the working power supply for the pulse width modulation integrated chip U1. The model number of the pulse width modulation integrated chip U1 in the embodiment is TL 3842.

A second rectifying and filtering circuit and a diode D7 are arranged between a secondary output coil of the transformer T1 and a charging positive electrode of the battery, the second rectifying and filtering circuit comprises a half-bridge rectifier D4 and a filter capacitor C10, the D4 is a high-frequency rectifier tube, the C10 is a low-voltage filter capacitor, an output end of the secondary output coil of the transformer T1 is connected with an input end of the half-bridge rectifier D4, an output end of the half-bridge rectifier D4 is connected with a positive electrode of the filter capacitor C10, a positive electrode of the filter capacitor C10 is connected with a positive electrode of the diode D7, a negative electrode of the diode D7 is connected with the charging positive electrode of the battery, and a positive electrode of the filter capacitor C10 is connected with a collector of the triode Q2 through a capacitor C9 and a resistor R15.

The feedback circuit comprises a double operational amplifier, a diode D9 and a current sampling resistor R27, wherein the model of the double operational amplifier is LM358 in the embodiment, the cathode of a filter capacitor C10 is connected with the anode of the power supply of the double operational amplifier through a diode D5, a diode D5 is a 12V voltage stabilizing diode, the cathode of the power supply of the double operational amplifier is grounded, one end of a current sampling resistor R27 is connected with the charged cathode of a battery, the other end of the current sampling resistor R27 is grounded, the anode of a diode D9 is connected with the 12V power supply through a resistor R16, the cathode of a diode D9 is grounded, two ends of a diode D9 are connected in parallel with voltage dividing resistors R26 and R4, the common end of the voltage dividing resistors R26 and R4 is connected with the first non-phase input end and the second anti-phase input end of the double operational amplifier, the second non-phase input end of the double operational amplifier is connected with the charged cathode of the battery through a resistor R17, the first anti-phase input end of the double operational amplifier is connected with the second output end of the double operational amplifier, the first output end of the double operational amplifier is connected with one input pin of the optocoupler U2 through a diode D8 and a potentiometer W1, and the charged high constant voltage value can be adjusted by changing the resistance value of W1.

In order to visually display the charging state, the charging indicating unit is further included, the charging indicating unit comprises a triode Q2, a triode Q3, a power indicator lamp D10 and a charging indicator lamp D6, a first output end of the dual operational amplifier is connected with a base electrode of a triode Q3 through a resistor R22, an emitter electrode of the triode Q3 is grounded through the power indicator lamp D10, a collector electrode of the triode Q3 is connected with a 12V power supply, a second output end of the dual operational amplifier is connected with a base electrode of the triode Q2 through a resistor R18, an emitter electrode of a triode Q2 is grounded through a charging indicator lamp D6, and a collector electrode of the triode Q2 is connected with a negative electrode of a filter capacitor C10.

The working principle in this embodiment is as follows:

at the start of energization, the filter capacitor C11 has a voltage of about 300 v. This voltage is applied to the MOS transistor Q1 through the transformer T1. The second path is through R5, C8, C3 to pin 7 of the pwm integrated chip U1 forcing the pwm integrated chip U1 to start. The pin 6 of the pulse width modulation integrated chip U1 outputs square wave pulse, the MOS tube Q1 works, and the current is connected to the ground through the resistor R25. Meanwhile, the primary and secondary windings of the transformer T1 generate induced voltage, which is supplied to the PWM IC U1 via the diode D3 and the resistor R12. The voltage of the output coil of the transformer T1 is rectified and filtered by a diode D4 and a filter capacitor C10 to obtain stable voltage. The voltage is charged to the battery through the diode D7, and the diode D7 prevents the current of the battery from flowing backwards. The second path provides 12V working power supply for LM358 and its peripheral circuits through resistor R14, diode D5 and capacitor C9. Diode D9 provides the reference voltage for LM358, which is divided by resistors R26 and R4 to pin 2 and pin 5 of LM 358. During normal charging, the voltage of about 0.15-0.18V is applied to the upper end of the resistor R27, and the voltage is applied to the pin 3 of the LM358 through the resistor R17, and high voltage is sent from the pin 1. One path of the voltage passes through the resistor R18 and reaches the grid of the Q2 to enable the Q2 to be conducted, at the moment, the charging indicator lamp D6 (red lamp) is turned on, the second path of the voltage is injected into the pin 6 of the LM358, the pin 7 of the LM358 outputs low voltage, the triode Q3 is forced to be turned off, at the moment, the power indicator lamp D10 (green lamp) is turned off, and the UPS power supply module 400 enters a constant-current charging stage. When the battery voltage rises to about 48V, the UPS power module 400 enters a constant voltage charging stage, the output voltage is maintained at about 48V, and the current gradually decreases. When the charging current is reduced to 250 mA-400 mA, the voltage at the upper end of the resistor R27 drops, the voltage of the pin 3 of the LM358 is lower than the voltage of the pin 2, the pin 1 of the LM358 outputs low voltage, at the moment, the triode Q2 is turned off, and the charging indicator lamp D6 is turned off. Meanwhile, pin 7 of LM358 outputs a high voltage, which makes transistor Q3 conductive all the way, and at this time, power indicator D10 lights up. The other path of the voltage reaches the feedback end of the pulse width modulation integrated circuit through a diode D8 and a potentiometer W1 to reduce the voltage. At this time, the UPS power module 400 enters the trickle charge phase and the battery charge ends after 1-2 hours. When the mains supply is powered off, the UPS module 400 is automatically switched to supply power to the PoE switch, and the normal operation of the monitoring system is guaranteed. Of course, the technical solution of the present invention can be applied to other network device fields requiring POE power supply besides the monitoring field.

In summary, the embodiment of the present invention enables the PoE switch to automatically switch to the UPS power module 400 in the power failure state of the utility power, so that the entire monitoring system can still operate for a period of time, and no monitoring gap is caused. The design structure is simple, the existing switch can be directly modified, and the cost is reduced. And voltage and current can be regulated in the charging process, overshoot is avoided, and the service life of the battery is prolonged.

The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention.

Claims

1. The utility model provides a take UPS emergency power source's POE switch which characterized in that includes:

a switch module (100), the switch module (100) for enabling data interaction;

the PSE power supply module (200), the PSE power supply module (200) is connected with the switch module (100), and the PSE power supply module (200) is used for supplying power to an external POE device;

the input end of the power supply module (300) is used for connecting commercial power, and the output end of the power supply module (300) is connected with the power supply end of the switch module (100);

UPS power module (400), UPS power module (400) includes charging circuit, pulse width modulation integrated circuit, feedback circuit and battery, charging circuit's input is used for connecting the commercial power, charging circuit's output is connected the charging end of battery, feedback circuit's input is connected the charging end of battery, feedback circuit's output is connected pulse width modulation integrated circuit's feedback end, pulse width modulation integrated circuit with charging circuit links to each other in order to be used for adjusting charging current and charging voltage through the feedback signal that feedback circuit sent.

2. The POE switch with UPS emergency power supply of claim 1, wherein: the charging circuit comprises a first rectifying and filtering circuit, a MOS tube Q1 and a transformer T1, wherein the input end of the first rectifying and filtering circuit is used for being connected with commercial power, the output end of the first rectifying and filtering circuit is respectively connected with one end of a primary main coil of the transformer T1 and the starting end of the pulse width modulation integrated circuit, the other end of the primary main coil of the transformer T1 is connected with the drain electrode of the MOS tube Q1, the source electrode of the MOS tube Q1 is grounded through a resistor R25, the grid electrode of the MOS tube Q1 is connected with the pulse output end of the pulse width modulation integrated circuit, a primary auxiliary coil of the transformer T1 is connected with the power supply end of the pulse width modulation integrated circuit, and a secondary output coil of the transformer T1 is connected with the charging positive electrode of the battery.

3. The POE switch with UPS emergency power supply of claim 2, wherein: the first rectifying and filtering circuit comprises a bidirectional filter T0, a bridge rectifier D1 and a filter capacitor C11, wherein the input end of the bidirectional filter T0 is used for being connected with a mains supply, the output end of the bidirectional filter T0 is connected with the input end of the bridge rectifier D1, and the output end of the bridge rectifier D1 is respectively connected with one end of a primary main coil of the transformer T1 and the power supply end of the pulse width modulation integrated circuit through the filter capacitor C11.

4. The POE switch with UPS emergency power supply of claim 2, wherein: the transformer T1 is a high-frequency pulse transformer.

5. The POE switch with UPS emergency power supply of claim 3, wherein: the pulse width modulation integrated circuit comprises a pulse width modulation integrated chip U1, a resistor R5, a capacitor C8, a capacitor C3, a reference voltage source U3 and an optical coupler U2, wherein the positive power supply electrode of the pulse width modulation integrated chip U1 is connected with the negative electrode of a filter capacitor C11 through a capacitor C8 and a capacitor C3 which are connected in parallel, the positive power supply electrode of the pulse width modulation integrated chip U1 is connected with one end of the resistor R5, the other end of the resistor R5 is connected with the positive electrode of the filter capacitor C11, the pulse output end of the pulse width modulation integrated chip U1 is connected with the gate of the MOS tube Q1, the negative power supply electrode of the pulse width modulation integrated chip U1 is grounded, the voltage feedback pin of the pulse width modulation integrated chip U1 is connected with one output pin of the optical coupler U2 through a resistor R21, the other output pin of the optical coupler U2 is connected with the positive power supply electrode of the pulse width modulation integrated chip U1, one input pin of the optocoupler U2 is connected with the reference voltage source U3, and the other input pin of the optocoupler U2 is connected with the feedback circuit.

6. POE switch with UPS emergency power supply according to claim 5, characterized in that: the model number of the pulse width modulation integrated chip U1 is TL 3842.

7. The POE switch with UPS emergency power supply of claim 1, wherein: a second rectifying and filtering circuit and a diode D7 are arranged between the output end of the charging circuit and the charging end of the battery, the output end of the charging circuit is connected with the input end of the second rectifying and filtering circuit, the output end of the second rectifying and filtering circuit is connected with the anode of the diode D7, and the cathode of the diode D7 is connected with the charging anode of the battery.

8. The POE switch with UPS emergency power supply of claim 7, wherein: the feedback circuit comprises a double operational amplifier, a diode D9 and a current sampling resistor R27, the output end of the charging circuit is connected with the positive electrode of the power supply of the double operational amplifier through a second rectifying and filtering circuit, the negative electrode of the power supply of the double operational amplifier is grounded, one end of the current sampling resistor R27 is connected with the charging negative electrode of the battery, the other end of the current sampling resistor R27 is grounded, the positive electrode of the diode D9 is connected with the 12V power supply through a resistor R16, the negative electrode of the diode D9 is grounded, two ends of the diode D9 are connected with a voltage dividing resistor R26 and a voltage dividing resistor R4 in parallel, the common ends of the voltage dividing resistors R26 and R4 are connected with the first non-inverting input end and the second inverting input end of the double operational amplifier, the second non-inverting input end of the double operational amplifier is connected with the charging negative electrode of the battery through a resistor R17, the first inverting input end of the double operational amplifier is connected with the second output end of the double operational amplifier, the first output end of the double operational amplifier is connected with the feedback end of the pulse width modulation integrated circuit through a diode D8 and a potentiometer W1.

9. The POE switch with UPS emergency power supply of claim 8, wherein: still include the instruction unit that charges, the instruction unit that charges includes triode Q2, triode Q3, power indicator D10 and charge indicator D6, two operational amplifier's first output passes through resistance R22 and connects triode Q3's base, triode Q3's projecting pole passes through power indicator D10 ground connection, 12V power is connected to triode Q3's collecting electrode, two operational amplifier's second output passes through resistance R18 and connects triode Q2's base, triode Q2's projecting pole is through charge indicator D6 ground connection, triode Q2's collecting electrode is connected second rectification filter circuit's output.

10. The POE switch with UPS emergency power supply of claim 8 or 9, wherein: the model of the dual operational amplifier is LM 358.