UPS automatic switching circuit

Abstract

The utility model provides a UPS automatic switching circuit which comprises an AC-DC conversion circuit, an AC detection circuit, an automatic switching circuit, a battery over-discharge detection circuit, a lead-acid battery, a charging circuit and a load power supply circuit, the input end of the AC detection circuit is connected with commercial power, and the output end of the AC detection circuit generates an ACOK signal. The battery over-discharge detection circuit is connected in series between the charging circuit and the lead-acid battery, the battery over-discharge detection circuit outputs ODP signals, the output end of the automatic switching circuit is connected with the load power supply circuit, and the automatic switching circuit comprises a relay driving unit and a logic control unit. The automatic switching circuit controls contact switching of the relay driving unit based on ACOK and ODP signals received by the logic control unit, an automatic switching circuit structure controlled by pure hardware replaces an existing circuit structure controlled by a single-chip microcomputer, a single-chip microcomputer circuit does not need to be arranged, pure hardware control is high in operation safety and reliability, the structure is simple, the production cost is low, and the automatic switching circuit is suitable for popularization and application. And an anti-backflow circuit is not additionally arranged, so that the production cost is further reduced.

Description

TECHNICAL FIELD

[0001] The utility model relates to the technical field of electricity, more particularly to a kind of UPS automatic switching circuit. BACKGROUND

[0002] UPS (Uninterruptible Power Supply), uninterruptible power supply provides temporary power for equipment through battery / generator when power grid fails, and UPS switching system is responsible for the control module of automatic or manual switching between main power (mains) and backup power (battery / generator), and the core goal is to realize zero interruption or minimum power-off time.

[0003] The closest prior art is an authorized announcement number: CN114243892B, an automatic power switching device and method, comprising first switching circuit, second switching circuit and sampling judgment circuit; sampling judgment circuit is connected with battery, first switching circuit and second switching circuit respectively, for collecting the output voltage of battery to obtain sampling voltage signal, and judging whether sampling voltage signal is lower than voltage setting lower limit value, and when sampling voltage signal is lower than voltage setting lower limit value, control signal is output to first switching circuit, control signal and sampling voltage signal are output to second switching circuit; when control signal is high level signal, first switching circuit works; when control signal is low level signal, second switching circuit works; first switching circuit is used to charge battery using mains power supply; second switching circuit is used to charge battery using generator according to sampling voltage signal.

[0004] The existing switching circuit, structure depends on single-chip microcomputer to control, single-chip microcomputer is easy to bring software failure risk, for example program dead machine, logic error, possibly leading to system failure, affect the continuous power supply of equipment, and the structure is complex.

[0005] Therefore, the utility model provides a kind of pure hardware logic control, simple structure, a kind of UPS automatic switching circuit. INVENTION CONTENTS

[0006] The utility model discloses a kind of pure hardware logic control, simple structure, a kind of UPS automatic switching circuit.

[0007] A kind of UPS automatic switching circuit, including AC-DC conversion circuit, alternating current detection circuit, automatic switching circuit, battery overdischarge detection circuit, lead-acid battery, charging circuit, load power supply circuit, it is characterized in that:

[0008] Mains input is connected to AC-DC conversion circuit, and the output end of AC-DC conversion circuit is connected charging circuit and automatic switching circuit respectively;

[0009] The AC detection circuit input end is connected with the commercial power, and the AC detection circuit output end generates an AC_OK signal, wherein AC_OK=0 indicates that the commercial power is normal, and AC_OK=1 indicates that the commercial power is missing.

[0010] The charging circuit is connected with the lead-acid battery in series with a battery over-discharge detection circuit, and the battery over-discharge detection circuit outputs an ODP signal, wherein ODP=0 indicates that the battery is over-discharged, and ODP=1 indicates that the battery is normal.

[0011] The automatic switching circuit output end is connected with the load power supply circuit, the automatic switching circuit includes a relay driving unit and a logic control unit, the automatic switching circuit controls the contact switching of the relay driving unit based on the AC_OK and ODP signals accepted by the logic control unit, when AC_OK=0, the relay driving unit of the automatic switching circuit keeps the NC normally closed contact conductive, and the commercial power is preferentially output, when AC_OK=1 and ODP=1, the relay driving unit of the automatic switching circuit is attracted, the NO normally open contact is conductive, and the lead-acid battery is switched to supply power, and when ODP=0, no matter the state of AC_OK, the relay driving unit of the automatic switching circuit keeps the NC normally closed contact conductive or cuts off the lead-acid battery power supply.

[0012] Further, the charging circuit and the lead-acid battery are provided with a battery reverse connection prevention circuit, which is used to ensure that the relay in the automatic switching circuit does not malfunction when the battery is reversely connected.

[0013] In some embodiments, the automatic switching circuit output end is connected with the load power supply circuit, the automatic switching circuit outputs an RLY signal, when ODP=0 and AC_OK=0, RLY=0, that is, the commercial power is output, when ODP=0 and AC_OK=1, RLY=0, that is, the commercial power is output, when ODP=10 and AC_OK=0, RLY=0, that is, the commercial power is output, and when ODP=1 and AC_OK=1, RLY=1, that is, the lead-acid battery is output.

[0014] In some embodiments, the AC detection circuit includes capacitor C5, capacitor C6, optocoupler U3, diode D2, resistor R12, R13, resistor R14, resistor R15, resistor R16, resistor R17, resistor R18, resistor R19, the optocoupler U3 functions to convert AC state into a logic signal AC_OK, the mains is connected to the 2 pin of the optocoupler U3 through the AC_L pin, the resistor R13, R14, R15, R16, R17, R18, R19 are connected in series between the AC_L pin and the 2 pin of the optocoupler U3, the resistor R13, R14, R15, R16, R17, R18, R19 are used to divide the mains voltage to protect the optocoupler U3, the 4 pin of the optocoupler U3 is connected to the AC_N pin through the diode D2, the diode D2 functions to prevent negative voltage from affecting the subsequent circuit and protecting the optocoupler U3, the 1 pin of the optocoupler U3 is connected to 5V through the resistor R12, the resistor R12 functions to limit current, the 3 pin of the optocoupler U3 is connected to the AC_OK pin through the parallel capacitor C5, C6, the capacitor C5, C6 functions to filter.

[0015] In some embodiments, the battery over-discharge detection circuit uses a hysteresis comparator circuit, the low threshold voltage is 10.5V±5%, and the high threshold voltage is 12.20V±5%.

[0016] In some embodiments, the battery over-discharge detection circuit includes comparator U2A, resistor R2, R6, R8, R9, R1, R7, R3, the 3 pin of the comparator U2A is connected to the VBAT pin, the 3 pin of the comparator U2A is used to monitor the VBAT pin, the resistor R2, R6, R8, R9 are connected between the 3 pin of the comparator U2A and the VBAT pin, the resistor R2, R6, R8, R9 functions to divide the voltage of the lead-acid battery VBAT, the 2 pin of the comparator U2A is connected to the voltage dividing point between the resistor R1, R7, the 2 pin of the comparator U2A is used to provide a reference voltage, the resistor R1, R7 functions to provide a fixed reference voltage as a comparison reference, the 1 pin of the comparator U2A is connected to 5V through the resistor R3, the 1 pin of the comparator U2A is used for ODP signal output, the resistor R3 is a pull-up resistor used to pull up the ODP signal, when the voltage of the 3 pin of the comparator U2A is greater than the voltage of the 2 pin of the comparator U2A, ODP=1, i.e. normal discharge, when the voltage of the 3 pin of the comparator U2A is lower than the voltage of the 2 pin of the comparator U2A, ODP=0, i.e. battery over-discharge.

[0017] In some embodiments, the logic control unit includes a logic controller U4, a resistor R11, a resistor R20, a resistor R21, the relay drive unit includes a transistor Q1, a resistor R10, a relay JK1A, a relay JK1B, a diode D1, the 1 pin of the logic controller U4 is connected with the ODP pin, the 1 pin of the logic controller U4 is used for monitoring whether the battery is over-discharged, the 2 pin of the logic controller U4 is connected with the AC_OK pin, the 2 pin of the logic controller U4 is used for monitoring whether the alternating current exists, the 4 pin of the 1 pin of the logic controller U4 is connected with the base of the transistor Q1 of the relay drive unit through the resistor R11, the resistor R11 provides the drive current of the transistor Q1, the 4 pin of the logic controller U4 is used for controlling the relay JK1A to determine whether to switch to the lead-acid battery power supply, the 3 pin of the logic controller U4 is grounded, the 3 pin of the logic controller U4 is used for the logic low level reference, the 5 pin of the logic controller U4 is connected with 5V, the 5 pin of the logic controller U4 is used for supplying power to the logic controller U4, the transistor Q1 is connected with the resistor R20 and the resistor R20, the resistor R20 plays a current limiting role to prevent the transistor Q1 from being misdirected, the resistor R21 plays a pull-down role to ensure that the transistor Q1 is completely cut off when it is turned off, the collector of the transistor Q1 is connected with one end of the relay JK1A coil through the resistor R10, the resistor R10 plays a role of limiting the instantaneous current protection circuit when the transistor Q1 is turned on, the other end of the relay JK1A coil is connected with 12V, the normally open contact NO of the relay JK1A is connected with the VBAT pin, the COM common end of the relay JK1A is connected with the input end of the relay JK1B, the relay JK1B is connected with the VOUT pin, the diode D1 is arranged between the resistor R10 and the relay JK1B, and the diode D1 plays a role of providing a freewheeling path to prevent the transistor Q1 from being damaged.

[0018] In some embodiments, the automatic switching circuit further includes a power filter and stabilizing unit, the power filter and stabilizing unit includes a capacitor C1, a capacitor C3, a resistor R4, a resistor R5, the capacitor C1 is connected with the VBAT in parallel, the capacitor C1 is used for smoothing the VBAT voltage, the capacitor C3 is connected with the 12V in parallel, the capacitor C3 is used for smoothing the 12V voltage, the capacitor C3 and the 12V are connected in series with the resistor R4, the capacitor C1 and the VBAT are connected in series with the resistor R5, and the resistor R4 and the resistor R5 play a current limiting protection role.

[0019] In some embodiments, the logic control unit of the automatic switching circuit is an SN74AHC1608DBVR chip, and the relay JK1A and the relay JK1B are SLA-12VDC-SL-C.

[0020] The utility model discloses a beneficial effect: the utility model provides a kind of UPS automatic switching circuit, including AC-DC conversion circuit, AC detection circuit, automatic switching circuit, battery overdischarge detection circuit, lead-acid battery, charging circuit, load power supply circuit, AC detection circuit input end connects commercial power, and AC detection circuit output end generates AC_OK signal, battery overdischarge detection circuit is connected between charging circuit and lead-acid battery, the battery overdischarge detection circuit output ODP signal, automatic switching circuit output end connects load power supply circuit, and automatic switching circuit includes relay drive unit, logic control unit, and automatic switching circuit is based on the AC_OK and ODP signal control relay drive unit contact switching that logic control unit accepts, cooperate by above-mentioned circuit, for pure hardware control automatic switching circuit structure replaces the circuit structure of existing single-chip microcontroller control, need not set single-chip microcomputer circuit, pure hardware control operation safety and reliability are high, structure is simple, and production cost is low, and no additional setting anti backfill circuit, further reduce production cost. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is whole structure schematic diagram of the UPS automatic switching circuit of the application.

[0022] Figure 2 It is the logic truth table of the automatic switching circuit of the application.

[0023] Figure 3 It is structure schematic diagram of the automatic switching circuit of the application.

[0024] Figure 4 It is structure schematic diagram of the battery overdischarge detection circuit of the application.

[0025] Figure 5 It is structure schematic diagram of the AC detection circuit of the application.

[0026] The following specific embodiments will further illustrate the utility model in conjunction with the above drawings. DETAILED DESCRIPTION

[0027] The following embodiments are described to assist in the understanding of the application, the embodiments are not and should not be interpreted as limiting the protection scope of the application in any way.

[0028] In the following description, those skilled in the art will recognize that throughout the present discussion, components can be described as single functional units (which can include sub-units), but those skilled in the art will recognize that the various components, or portions thereof, can be divided into separate components, or can be integrated together (including integrated within a single system or component).

[0029] Furthermore, the connection between components or systems is not intended to be limited to a direct connection; on the contrary, data between these components may be modified, reformatted, or otherwise altered by intermediate components. Additionally, other or fewer connections may be used. It should also be noted that the terms "connection," "link," or "input" should be understood to include direct connections, indirect connections via one or more intermediate devices, and wireless connections. Example 1:

[0030] like Figure 1 The diagram shown is an overall structural schematic of the UPS automatic switching circuit of this application. The UPS automatic switching circuit includes an AC-DC conversion circuit, an AC detection circuit, an automatic switching circuit, a battery over-discharge detection circuit, a lead-acid battery, a charging circuit, and a load power supply circuit. Its features are as follows:

[0031] The AC power input is connected to the AC-DC conversion circuit, and the output of the AC-DC conversion circuit is connected to the charging circuit and the automatic switching circuit respectively.

[0032] The input terminal of the AC detection circuit is connected to the mains power, and the output terminal of the AC detection circuit generates an AC_OK signal, where AC_OK=0 indicates that the mains power is normal, and AC_OK=1 indicates that the mains power is missing.

[0033] A battery over-discharge detection circuit is connected in series between the charging circuit and the lead-acid battery. The battery over-discharge detection circuit outputs an ODP signal, where ODP=0 indicates that the battery is over-discharged and ODP=1 indicates that it is normal.

[0034] The output of the automatic switching circuit is connected to the load power supply circuit, such as... Figure 3 The diagram shown is a structural schematic of the automatic switching circuit of this application. The automatic switching circuit includes a relay drive unit and a logic control unit. The automatic switching circuit controls the switching of the relay drive unit contacts based on the AC_OK and ODP signals received by the logic control unit. When AC_OK=0, the relay drive unit of the automatic switching circuit keeps the NC normally closed contact open and prioritizes the output of mains power. When AC_OK=1 and ODP=1, the relay drive unit of the automatic switching circuit is energized, the NO normally open contact is open, and the circuit switches to lead-acid battery power supply. When ODP=0, regardless of the AC_OK state, the relay drive unit of the automatic switching circuit keeps the NC normally closed contact open or cuts off the lead-acid battery power supply.

[0035] A reverse connection protection circuit is provided between the charging circuit and the lead-acid battery. The reverse connection protection circuit is used to ensure that the relay in the automatic switching circuit will not malfunction when the battery is reversed.

[0036] like Figure 2The figure shows the logic truth table of the automatic switching circuit of this application. The output terminal of the automatic switching circuit is connected to the load power supply circuit. The automatic switching circuit outputs the RLY signal. When ODP=0 and AC_OK=0, RLY=0, that is, AC power output; when ODP=0 and AC_OK=1, RLY=0, that is, AC power output; when ODP=10 and AC_OK=0, RLY=0, that is, AC power output; when ODP=1 and AC_OK=1, RLY=1, that is, lead-acid battery output.

[0037] like Figure 5 The diagram shown is a schematic of the AC detection circuit of this application. The AC detection circuit includes capacitor C5, capacitor C6, optocoupler U3, diode D2, resistors R12, R13, R14, R15, R16, R17, R18, and R19. Optocoupler U3 converts the AC power state into the logic signal AC_OK. The AC mains power is connected to pin 2 of optocoupler U3 via pin AC_L. Resistors R13, R14, R15, R16, R17, R18, and R19 are connected in series between pin AC_L and pin 2 of optocoupler U3. Resistors R19, R13, R14, R15, R16, R17, R18, and R19 are used to divide the mains voltage to protect optocoupler U3. Pin 4 of optocoupler U3 is connected to the AC_N pin through diode D2. Diode D2 prevents negative voltage from affecting subsequent circuits and protects optocoupler U3. Pin 1 of optocoupler U3 is connected to 5V through resistor R12, which limits current. Pin 3 of optocoupler U3 is connected to the AC_OK pin through parallel capacitors C5 and C6, which filter the voltage.

[0038] The battery over-discharge detection circuit uses a hysteresis comparator circuit with a low threshold voltage of 10.5V±5% and a high threshold voltage of 12.20V±5%.

[0039] like Figure 4As shown, it is the structural schematic diagram of the battery over-discharge detection circuit of the application, the battery over-discharge detection circuit includes comparator U2A, resistance R2, resistance R6, resistance R8, resistance R9, resistance R1, resistance R7, resistance R3, the 3 pin of comparator U2A is connected with VBAT pin, the 3 pin of comparator U2A is used to monitor VBAT pin, resistance R2, resistance R6, resistance R8, resistance R9 are connected between the 3 pin of comparator U2A and VBAT pin, resistance R2, resistance R6, resistance R8, resistance R9 play the role of voltage division to lead acid battery VBAT, the 2 pin of comparator U2A is connected with the voltage division point between resistance R1 and resistance R7, the 2 pin of comparator U2A is used to provide reference voltage, resistance R1 and resistance R7 play the role of providing fixed reference voltage as comparison reference, the 1 pin of comparator U2A is connected with 5V through resistance R3, the 1 pin of comparator U2A is used for ODP signal output, resistance R3 is pull-up resistance for pulling up ODP signal, when the voltage of the 3 pin of comparator U2A is greater than the 2 pin of comparator U2A, ODP=1, that is, normal discharge, when the voltage of the 3 pin of comparator U2A is lower than the 2 pin of comparator U2A, ODP=0, that is, battery over-discharge.

[0040] As Figure 3As shown, the logic control unit includes logic controller U4, resistor R11, resistor R20, resistor R21, the relay drive unit includes triode Q1, resistor R10, relay JK1A, relay JK1B, diode D1, the 1 pin of logic controller U4 is connected with ODP pin, the 1 pin of logic controller U4 is used for monitoring whether the battery is over-discharged, the 2 pin of logic controller U4 is connected with AC_OK pin, the 2 pin of logic controller U4 is used for monitoring whether the AC power exists, the 4 pin of the 1 pin of logic controller U4 is connected with the base of triode Q1 of the relay drive unit through resistor R11, resistor R11 provides the drive current of triode Q1, the 4 pin of logic controller U4 is used for controlling relay JK1A to determine whether to switch to lead-acid battery power supply, the 3 pin of logic controller U4 is grounded, the 3 pin of logic controller U4 is used for logic low level reference, the 5 pin of logic controller U4 is connected with 5V, the 5 pin of logic controller U4 is used for supplying power to logic controller U4, triode Q1 is connected with resistor R20, resistor R20, resistor R20 plays a current limiting role to prevent triode Q1 from being misdirected, resistor R21 plays a pull-down role to ensure that triode Q1 is completely cut off when it is turned off, the collector of triode Q1 is connected with one end of relay JK1A coil through resistor R10, resistor R10 plays a role of limiting the instantaneous current protection circuit when triode Q1 is turned on, the other end of relay JK1A coil is connected with 12V, the normally open contact NO of relay JK1A is connected with VBAT pin, the COM common end of relay JK1A is connected with the input end of relay JK1B, relay JK1B is connected with VOUT pin, diode D1 is arranged between resistor R10 and relay JK1B, diode D1 plays a role of providing a freewheeling path to prevent triode Q1 from being damaged.

[0041] The automatic switching circuit further includes a power filtering and stabilizing unit, the power filtering and stabilizing unit includes capacitor C1, capacitor C3, resistor R4, resistor R5, capacitor C1 is connected in parallel with VBAT, capacitor C1 is used for smoothing VBAT voltage, capacitor C3 is connected in parallel with 12V, capacitor C3 is used for smoothing 12V voltage, resistor R4 is connected in series between capacitor C3 and 12V, resistor R5 is connected in series between capacitor C1 and VBAT, resistor R4 and resistor R5 play a current limiting protection role.

[0042] The logic control unit of the automatic switching circuit is an SN74AHC1608DBVR chip, and the relay JK1A and the relay JK1B are SLA-12VDC-SL-C models.

[0043] The utility model discloses a UPS automatic switching circuit, including AC-DC conversion circuit, alternating current detection circuit, automatic switching circuit, battery overdischarge detection circuit, lead acid battery, charging circuit, load power supply circuit, alternating current detection circuit input connects commercial power, and alternating current detection circuit output generates AC_OK signal, and the battery overdischarge detection circuit is connected in series between charging circuit and lead acid battery, the battery overdischarge detection circuit output ODP signal, and automatic switching circuit output connects load power supply circuit, and automatic switching circuit includes relay drive unit, logic control unit, and automatic switching circuit is based on the AC_OK and ODP signal control relay drive unit contact switching of logic control unit acceptance, through above-mentioned circuit cooperation, for pure hardware control automatic switching circuit structure replaces the circuit structure of existing singlechip control, need not set up singlechip circuit, pure hardware control operation safety and reliability are high, simple structure, low in production cost, and no additional setting anti -backfill circuit, further reduce production cost.

[0044] Although the present application has disclosed a plurality of aspects and embodiments, other aspects and embodiments will be apparent to those skilled in the art, and several modifications and improvements can be made without departing from the concept of the present application, which all belong to the protection scope of the present application. The aspects and embodiments disclosed in the present application are only used for illustration, and are not intended to limit the present application, and the actual protection scope of the present application is subject to the claims.

Claims

1. A UPS automatic switching circuit, comprising an AC-DC conversion circuit, an AC detection circuit, an automatic switching circuit, a battery over-discharge detection circuit, a lead-acid battery, a charging circuit, and a load power supply circuit, characterized in that: The AC power input is connected to the AC-DC conversion circuit, and the output of the AC-DC conversion circuit is connected to the charging circuit and the automatic switching circuit respectively. The input terminal of the AC detection circuit is connected to the mains power, and the output terminal of the AC detection circuit generates an AC_OK signal, where AC_OK=0 indicates that the mains power is normal, and AC_OK=1 indicates that the mains power is missing. A battery over-discharge detection circuit is connected in series between the charging circuit and the lead-acid battery. The battery over-discharge detection circuit outputs an ODP signal, where ODP=0 indicates that the battery is over-discharged and ODP=1 indicates that it is normal. The output of the automatic switching circuit is connected to the load power supply circuit. The automatic switching circuit includes a relay drive unit and a logic control unit. The automatic switching circuit controls the switching of the relay drive unit contacts based on the AC_OK and ODP signals received by the logic control unit. When AC_OK=0, the relay drive unit of the automatic switching circuit keeps the NC normally closed contact open and prioritizes the output of mains power. When AC_OK=1 and ODP=1, the relay drive unit of the automatic switching circuit is energized and the NO normally open contact is open, switching to lead-acid battery power supply. When ODP=0, regardless of the AC_OK state, the relay drive unit of the automatic switching circuit keeps the NC normally closed contact open or cuts off the lead-acid battery power supply.

2. The UPS automatic switching circuit as described in claim 1, characterized in that: A reverse connection protection circuit is provided between the charging circuit and the lead-acid battery. The reverse connection protection circuit is used to ensure that the relay in the automatic switching circuit will not malfunction when the battery is reversed.

3. The UPS automatic switching circuit as described in claim 1, characterized in that: The output of the automatic switching circuit is connected to the load power supply circuit. The automatic switching circuit outputs the RLY signal. When ODP=0 and AC_OK=0, RLY=0 means AC power output; when ODP=0 and AC_OK=1, RLY=0 means AC power output; when ODP=10 and AC_OK=0, RLY=0 means AC power output; when ODP=1 and AC_OK=1, RLY=1 means lead-acid battery output.

4. The UPS automatic switching circuit as described in claim 1, characterized in that: The AC detection circuit includes capacitors C5 and C6, optocoupler U3, diode D2, and resistors R12, R13, R14, R15, R16, R17, R18, and R19. Optocoupler U3 converts the AC power state into the logic signal AC_OK. The AC power is connected to pin 2 of optocoupler U3 via pin AC_L. Resistors R13, R14, R15, R16, R17, R18, and R19 are connected in series between pin AC_L and pin 2 of optocoupler U3. Resistors R14, R15, R16, R17, R18, and R19 are used to divide the mains voltage to protect optocoupler U3. Pin 4 of optocoupler U3 is connected to pin AC_N via diode D2. Diode D2 prevents negative voltage from affecting subsequent circuits and protects optocoupler U3. Pin 1 of optocoupler U3 is connected to 5V via resistor R12, which limits current. Pin 3 of optocoupler U3 is connected to pin AC_OK via parallel capacitors C5 and C6, which filter the voltage.

5. The UPS automatic switching circuit as described in claim 1, characterized in that: The battery over-discharge detection circuit uses a hysteresis comparator circuit with a low threshold voltage of 10.5V±5% and a high threshold voltage of 12.20V±5%.

6. The UPS automatic switching circuit as described in claim 5, characterized in that: The battery over-discharge detection circuit includes a comparator U2A, resistors R2, R6, R8, R9, R1, R7, and R3. Pin 3 of comparator U2A is connected to the VBAT pin and is used to monitor the VBAT pin. Resistors R2, R6, R8, and R9 are connected between pin 3 of comparator U2A and the VBAT pin, and these resistors divide the VBAT voltage of the lead-acid battery. Pin 2 of comparator U2A is connected to resistors R1, R7, and R3. The voltage divider is connected between pins 7 and 8. Pin 2 of comparator U2A is used to provide a reference voltage. Resistors R1 and R7 provide a fixed reference voltage as a comparison base. Pin 1 of comparator U2A is connected to 5V through resistor R3. Pin 1 of comparator U2A is used for ODP signal output. Resistor R3 is a pull-up resistor used to pull up the ODP signal. When the voltage at pin 3 of comparator U2A is greater than that at pin 2 of comparator U2A, ODP=1, indicating normal discharge. When the voltage at pin 3 of comparator U2A is lower than that at pin 2 of comparator U2A, ODP=0, indicating over-discharge of the battery.

7. The UPS automatic switching circuit as described in claim 1, characterized in that: The logic control unit includes a logic controller U4, resistors R11, R20, and R21. The relay drive unit includes a transistor Q1, resistor R10, relays JK1A and JK1B, and diode D1. Pin 1 of the logic controller U4 is connected to the ODP pin and is used to monitor whether the battery is over-discharged. Pin 2 of the logic controller U4 is connected to the AC_OK pin and is used to monitor the presence of AC power. Pin 4 of the logic controller U4 is connected to the base of the transistor Q1 in the relay drive unit through resistor R11, which provides the drive current for transistor Q1. Pin 4 of the logic controller U4 is used to control relay JK1A to determine whether to switch to lead-acid battery power. Pin 3 of the logic controller U4 is grounded and serves as a logic low-level reference. Pin 5 of U4 is connected to 5V. Pin 5 of logic controller U4 is used to power logic controller U4. Transistor Q1 is connected to resistors R20 and R21. Resistor R20 limits current to prevent transistor Q1 from being mis-conducted. Resistor R21 acts as a pull-down resistor to ensure that transistor Q1 is completely cut off when it is off. The collector of transistor Q1 is connected to one end of the coil of relay JK1A through resistor R10. Resistor R10 limits the instantaneous current when transistor Q1 is conducting, providing protection. The other end of the coil of relay JK1A is connected to 12V. The normally open contact NO of relay JK1A is connected to the VBAT pin. The COM common terminal of relay JK1A is connected to the input terminal of relay JK1B. Relay JK1B is connected to the VOUT pin. A diode D1 is placed between resistor R10 and relay JK1B. Diode D1 provides a freewheeling path to prevent damage to transistor Q1.

8. The UPS automatic switching circuit as described in claim 7, characterized in that: The automatic switching circuit also includes a power supply filtering and stabilization unit, which includes capacitor C1, capacitor C3, resistor R4, and resistor R5. Capacitor C1 is connected in parallel with VBAT and is used to smooth the VBAT voltage. Capacitor C3 is connected in parallel with 12V and is used to smooth the 12V voltage. Resistor R4 is connected in series between capacitor C3 and 12V, and resistor R5 is connected in series between capacitor C1 and VBAT. Resistors R4 and R5 serve as current limiting protection.

9. The UPS automatic switching circuit as described in claim 7, characterized in that: The logic control unit of the automatic switching circuit is an SN74AHC1608DBVR chip, and the relays JK1A and JK1B are model SLA-12VDC-SL-C.

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