TWI536695B - Undervoltage protecting load latch circuit applied to variety of lithium battery protection solutions - Google Patents

Description

Undervoltage protection load latch circuit suitable for various lithium battery protection schemes

The present invention relates to the field of lithium battery protection technology, and in particular to an undervoltage protection load latch circuit suitable for various lithium battery protection schemes.

Lithium batteries are widely used in power tools, electric bicycles, Uninterruptible Power Supply (UPS) and mobile power supplies. The characteristics of the lithium battery itself determine the necessity of the undervoltage protection circuit: In order to prevent the discharge circuit from oscillating near the undervoltage point, the undervoltage hysteresis point is generally set. However, under severe conditions, for example, lithium batteries have poor performance after long-term use, resulting in an increase in internal resistance and a large load current, especially in the vicinity of the undervoltage point. If a large current is discharged under heavy load, it may still cause oscillation near the undervoltage point, causing the voltage to rise sufficiently after the discharge loop is closed in response to the undervoltage (more than the preset undervoltage hysteresis voltage). Therefore, the discharge circuit is turned on again, and a large current is discharged again. Repeatedly, the discharge end (DSG) is frequently switched and oscillated, which may cause damage to the load, lithium battery, lithium battery protection board, and even cause safety. problem.

FIG. 1 is a schematic diagram of various parameters of a conventional undervoltage protection circuit embodying an oscillation problem under severe conditions. As shown in Figure 1, LOAD represents whether the load is connected (LOAD = 1 for connection, otherwise it is not connected), Vcell for lithium battery voltage, Vdrv for protection circuit undervoltage hysteresis (pre-set), Vdv To protect the undervoltage turn-over point of the circuit (also preset), Odischarge represents whether the lithium battery enters an undervoltage condition (Odischarge=0 represents normal discharge, otherwise it represents entering undervoltage condition), and DSG is a switch for output discharge loop (DSG= 1 means open and normal discharge, and vice versa means closed and enters undervoltage condition).

Therefore, the problem of the discharge loop oscillation encountered in the above-mentioned lithium battery application field is a difficult problem to be solved in the field. .

The technical problem to be solved by the present invention is to provide an undervoltage protection load latch circuit suitable for a plurality of lithium battery protection schemes to prevent the discharge loop from oscillating near an undervoltage point under severe conditions.

In order to solve the above technical problem, the present invention provides an undervoltage protection load latch circuit suitable for a plurality of lithium battery protection schemes, including an undervoltage detection circuit and a load/charger detection circuit; wherein the input of the undervoltage detection circuit The side has a voltage input end of the plurality of lithium batteries and an undervoltage release end, the output side of which has an undervoltage state end and a non-undervoltage state end; the load/charger detection circuit includes: a first comparator, a comparator, a third comparator, a three-input or gate, a filter circuit, a D flip-flop, a high voltage NMOS transistor, a high voltage PMOS transistor, a first resistor and a second resistor; a positive input terminal of the first comparator a load detection reference voltage, the negative input end of which is connected to a load detection end, and the output end thereof generates a load removal signal; the positive input end of the second comparator is connected to a first charger detection reference voltage, and the negative input end thereof is connected a charger detecting end, the output end of which generates a first charger connection signal; the positive input end of the third comparator is connected to the charger detecting end, and the negative input end thereof a second charger detects a reference voltage, and an output terminal generates a second charger connection signal; the input of the three input or gate respectively receives the load extraction signal, the first charger connection signal, and the a second charger connection signal, the output end of which generates an OR operation output signal; the input end of the filter circuit receives the OR operation output signal; the D flip-flop has a D end, a Q end, a terminal, a clock terminal and a reset terminal, wherein the clock terminal is connected to an output end of the filter circuit, the reset terminal is connected to the non-undervoltage state end, and the Q terminal is connected to the undervoltage release terminal. The D end is connected to a power end, The gate of the high voltage NMOS transistor is connected to the undervoltage state end, the source thereof is grounded, and the drain is connected to the load detecting end via the first resistor; the high voltage PMOS transistor is The gate is connected to the non-undervoltage state end, the source thereof is connected to the power terminal, and the drain is connected to the charger detecting end via the second resistor.

Optionally, the lithium battery protection scheme includes: a same port, a half port, a full port, and a P charge.

Optionally, the undervoltage protection load latch circuit can be applied to a power tool, an electric bicycle, an uninterruptible power supply system, or a mobile power source in a lithium battery application field.

Optionally, in the lithium battery protection scheme of the same port, the positive and negative terminals connected to the load and the positive and negative connections of the connected charger in a lithium battery application circuit including the undervoltage protection load latch circuit The terminals are respectively identical; the lithium battery application circuit further comprises: an overvoltage protection circuit; an overcurrent protection circuit; and other protection circuits; a control logic circuit, wherein the input ends are respectively associated with the undervoltage protection load latch circuit, An overvoltage protection circuit, the overcurrent protection circuit and the other protection circuit are connected, and an output end thereof is connected to a charging end and a discharging end for receiving, including undervoltage protection, overvoltage protection, overcurrent protection and other protection And controlling a switch of the charging end and/or the discharging end; the charging circuit controls the switching transistor, the gate thereof is connected to the charging end, and the source, the load detecting end and the charger detecting end are both Connected to a negative connection terminal connected to the load/charger; a charging loop resistor connected between the gate and the source of the charging circuit control switch transistor; and a discharge loop control switch Transistor having a gate electrode connected to said discharge end, the drain and its charging circuit control switch drain of the transistor and a cathode connected to the source thereof by a plurality of the lithium battery composed of a lithium battery.

Optionally, in the lithium battery protection scheme of the half-port, the positive connection end of the connection load of the lithium battery application circuit including the undervoltage protection load latch circuit is the same as the positive connection end of the connection charger The negative connection end of the connection load is separated from the negative connection end of the connection charger; the lithium battery application circuit further includes: an overvoltage protection circuit; an overcurrent protection circuit; other protection circuits; a control logic circuit, and an input thereof The terminals are respectively connected to the undervoltage protection load latch circuit, the overvoltage protection circuit, the overcurrent protection circuit and the other protection circuit, and the output end thereof is connected to a charging end and a discharging end for receiving Including undervoltage protection, overvoltage protection, overcurrent protection, and other protection signals and controlling the opening of the charging terminal and/or the discharging terminal a charging circuit control switch transistor having a gate connected to the charging terminal, a source and a charger detecting end connected to a negative connection terminal connected to the charger; a charging loop resistor connected to the The charging circuit controls the gate and the source of the switching transistor; and the discharging circuit controls the switching transistor, the gate of which is connected to the discharging end, and the drain thereof is connected to the drain of the charging circuit control switch transistor, And together with the load detecting end, the negative connection end connected to the load is connected, and the source thereof is connected to the negative electrode of the lithium battery pack composed of a plurality of the lithium batteries.

Optionally, in the lithium battery protection scheme of the full-port, the positive connection end of the connection load of the lithium battery application circuit including the under-voltage protection load latch circuit is the same as the positive connection end of the connection charger The negative connection end of the connection load is separated from the negative connection end of the connection charger; the lithium battery application circuit further includes: an overvoltage protection circuit; an overcurrent protection circuit; other protection circuits; and a control logic circuit. The input end is respectively connected to the undervoltage protection load latch circuit, the overvoltage protection circuit, the overcurrent protection circuit and the other protection circuit, and the output end thereof is connected to a charging end and a discharging end, and is used for Receiving a switch including undervoltage protection, overvoltage protection, overcurrent protection and other protection signals and controlling the charging terminal and/or the discharging terminal; the charging circuit controls the switching transistor, the gate of which is connected to the charging terminal, The source and the charger detecting end are both connected to a negative connection end connected to the charger, the drain is connected to a negative pole of a third diode, and the positive pole of the third diode is composed of a plurality of a negative electrode connection of a lithium battery pack composed of a lithium battery; a charge loop resistor connected between the gate and the source of the charge circuit control switch transistor; and a discharge loop control switch transistor, the gate and the discharge The end connection has a drain and a load detecting end connected to a negative connection end connected to the load, and a source thereof is also connected to a negative electrode of the lithium battery pack.

Optionally, in the lithium battery protection scheme of P charging, the negative connection end connecting the load and the negative connection end connecting the charger in a lithium battery application circuit including the undervoltage protection load latch circuit are The same, the positive connection end of the connection load is separated from the positive connection end of the connection charger; the lithium battery application circuit further includes: an overvoltage protection circuit; an overcurrent protection circuit; other protection circuits; a control logic circuit, The input end is respectively connected to the undervoltage protection load latch circuit, the overvoltage protection circuit, the overcurrent protection circuit and the other protection circuit, and the output end thereof is connected to a charging end and a discharging end, Receiving a switch including undervoltage protection, overvoltage protection, overcurrent protection, and other protection signals and controlling the charging terminal and/or the discharging end; the charging circuit controls the switching transistor, and the gate thereof is connected to the charging terminal, The source and the charger detecting end are both connected to a positive connection terminal connected to the charger, and the drain electrode and the positive connection end connecting the load are respectively connected with a lithium battery composed of a plurality of the lithium batteries. a positive pole connection; a charge loop resistor connected between the gate and the source of the charge circuit control switch transistor; and a discharge loop control switch transistor having a gate connected to the discharge end and a drain and a drain The load detecting end is connected to a negative connection terminal connected to the charger/load, and a source thereof is connected to a negative electrode of the lithium battery pack.

Optionally, the load detection reference voltage is reasonably selected according to an actual load and the first resistor divider and the second resistor and the first resistor divider point.

Optionally, the first charger detection reference voltage and the second charger detection reference voltage are both selected according to the characteristics of the charger.

Optionally, the other protection circuit comprises a temperature protection circuit, a wire break protection circuit and an extremely high voltage protection circuit.

Optionally, the undervoltage protection load latch circuit, the overvoltage protection power The circuit, the overcurrent protection circuit, the other protection circuit and the control logic circuit form a lithium battery protection wafer; the lithium battery protection chip edge has a plurality of voltage inputs of the lithium battery and one of the power sources end.

Compared with the prior art, the present invention has the following advantages: the present invention introduces an undervoltage protection load latch function: after the undervoltage shutdown of the discharge loop, if the load is still followed, even if the lithium battery voltage rises, it is still latched in an undervoltage state. Until the load is removed or the charger is connected, the undervoltage condition is judged according to the actual lithium battery voltage, thereby avoiding the discharge circuit oscillating near the undervoltage point under severe conditions.

The present invention can be applied to different lithium battery protection schemes including the same port, half-port, full-port and P-charge N in different application environments, load conditions, and cost considerations, and protects the chip for a cascade system or a single lithium battery. Also applicable.

The invention can be widely applied to lithium battery application fields such as electric tools, electric bicycles, uninterruptible power supply systems and mobile power sources.

200‧‧‧Undervoltage protection load latch circuit

202‧‧‧Load/charger detection circuit

400, 500, 600, 700‧‧‧ lithium battery application circuit

401, 501, 601, 701‧‧ ‧ overvoltage protection circuit

402, 502, 602, 702‧‧‧ overcurrent protection circuit

403, 503, 603, 703‧‧‧ other protection circuits

404, 504, 604, 704‧‧‧ control logic

410, 510, 610, 710‧‧‧ lithium battery protection chip

CDET‧‧‧Charger detection terminal

CELL1, CELL2, CELL3, CELLn‧‧‧Lithium battery

Cgron1‧‧‧First charger connection signal

Cgron2‧‧‧Second charger connection signal

CHG‧‧‧Charging end

Clk‧‧‧clock end

Cmp1‧‧‧ first comparator

Cmp2‧‧‧second comparator

Cmp3‧‧‧ third comparator

The positive connection of the C+‧‧‧ charger

C-‧‧‧ negative connection of the charger

D1‧‧‧First Diode

D2‧‧‧ second diode

D3‧‧‧ third diode

DF1‧‧D trigger

DSG‧‧‧ discharge end

LDET‧‧‧ load detection terminal

LOAD‧‧‧ load

Loadoff‧‧‧load removal signal

MCHG‧‧‧Charging circuit control switch transistor

MDSG‧‧‧Discharge loop control switch transistor

MN1‧‧‧High voltage NMOS transistor

MP1‧‧‧High Voltage PMOS Crystal

Odischarge‧‧‧Undervoltage/Undervoltage state

‧‧‧Non-undervoltage state

OD_RELS‧‧‧Undervoltage release end

OR3‧‧‧ three inputs or gates

Positive connection of P+‧‧‧ load

P-‧‧‧ negative connection of the load

R1‧‧‧first resistance

R2‧‧‧second resistance

RCHG‧‧‧Charging loop resistance

Reset‧‧‧Reset

SCH1‧‧‧Filter circuit

SCH2‧‧‧ undervoltage detection circuit

VA‧‧‧ or computing output signal

VC1, VC2, VC3, VCn‧‧‧ voltage input

Vcell‧‧‧Lithium battery voltage

VDD‧‧‧Power/Power Side

Vdv‧‧‧ undervoltage rollover point

Vdrv‧‧‧Undervoltage hysteresis flip point

Vtr_cgr1‧‧‧First charger detection reference voltage

Vtr_cgr2‧‧‧Second charger detection reference voltage

Vtr_Load‧‧‧Load detection reference voltage

The above and other features, aspects and advantages of the present invention will become more apparent from the description of the appended claims.

FIG. 1 is a schematic diagram of various parameters of a conventional undervoltage protection circuit embodying an oscillation problem under severe conditions.

2 is a schematic diagram of an undervoltage protection load latch circuit according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of curves of various parameters of an undervoltage protection load latch circuit under severe conditions according to an embodiment of the present invention.

4 is a schematic diagram of a peripheral circuit of a "same port" lithium battery protection scheme of an undervoltage protection load latch circuit according to an embodiment of the present invention.

FIG. 5 is a schematic diagram of a peripheral circuit in a "half-port" lithium battery protection scheme of an undervoltage protection load latch circuit according to an embodiment of the present invention.

6 is a schematic diagram of a peripheral circuit in a "full-port" lithium battery protection scheme of an undervoltage protection load latch circuit according to an embodiment of the present invention.

FIG. 7 is a schematic diagram of a peripheral circuit in a “P-charged N-discharge” lithium battery protection scheme of an undervoltage protection load latch circuit according to an embodiment of the present invention.

The present invention will be further described in detail in the following description of the embodiments of the invention, A person skilled in the art can make similar promotion and deduction according to the actual application without departing from the connotation of the present invention. Therefore, the scope of the present invention should not be limited by the content of the specific embodiment.

2 is a schematic diagram of an undervoltage protection load latch circuit according to an embodiment of the present invention. As shown in FIG. 2, the undervoltage protection load latch circuit 200 is applicable to various lithium battery protection schemes, such as port, half-port, full-port and P-charge N, etc., which mainly includes an undervoltage detection circuit SCH2 and a load/ Charger detection circuit 202. The input side of the undervoltage detection circuit SCH2 has a plurality of lithium battery (not shown) voltage input terminals VC1, VC2, VC3, ..., VCn and an undervoltage release terminal OD_RELS, and the output side has an owu Pressure state end Odischarge and a non-undervoltage state end .

The load/charger detection circuit 202 mainly includes: a first comparator cmp1, a second comparator cmp2, a third comparator cmp3, a three-input or gate OR3, Filter circuit SCH1, D flip-flop DF1, high voltage NMOS transistor MN1, high voltage PMOS transistor MP1, first resistor R1 and second resistor R2.

The positive input terminal of the first comparator cmp1 is connected to a load detection reference voltage Vtr_Load, the negative input terminal is connected to a load detection terminal LDET, and the output terminal thereof generates a load extraction signal loadoff. The positive input terminal of the second comparator cmp2 is connected to a first charger detection reference voltage Vtr_cgr1, the negative input terminal thereof is connected to a charger detection terminal CDET, and the output terminal thereof generates a first charger connection signal cgron1. The positive input end of the third comparator cmp3 is connected to the charger detection terminal CDET, the negative input terminal is connected to a second charger detection reference voltage Vtr_cgr2, and the output terminal thereof generates a second charger connection signal cgron2.

In this embodiment, the load detection reference voltage Vtr_Load may be appropriately selected according to the actual load and the first resistor R1 divided voltage and the second resistor R2 and the first resistor R1 voltage dividing point; and the first charger detects the reference voltage Vtr_cgr1 and The second charger detection reference voltage Vtr_cgr2 may also be appropriately selected according to the characteristics of the charger. The second charger detection reference voltage Vtr_cgr2 is slightly larger than the highest power supply VDD of the chip, and the charger is detected in the P charge and discharge application.

In addition, the input terminals of the three-input or gate OR3 receive the load extraction signal loadoff, the first charger connection signal cgron1 and the second charger connection signal cgron2, respectively, and the output terminal thereof generates an OR operation output signal VA. The input terminal of the filter circuit SCH1 receives the OR operation output signal VA to generate a filtered signal. The filter circuit SCH1 can be debounced by counting using an RC counter. D flip-flop DF1 has D terminal, Q terminal, The terminal, the clock terminal Clk and the reset terminal Reset, the clock terminal Clk is connected to the output end of the filter circuit SCH1, the reset terminal Reset and the non-undervoltage state end of the undervoltage detection circuit SCH2 Connected, the Q terminal is connected to the undervoltage release terminal OD_RELS of the undervoltage detection circuit SCH2, and the D terminal is connected to a power supply terminal VDD. The terminal is vacant. The D flip-flop DF1 resets the undervoltage release terminal OD_RELS to 0 in a non-undervoltage state, and detects a load unloading signal loadoff or a first charger connection signal cgron1 or a second charger connection signal in an undervoltage state. Cgron2=1 and output OD_RELS=1 above the continuous debounce time.

The gate of the high voltage NMOS transistor MN1 is connected to the undervoltage state terminal Odischarge of the undervoltage detecting circuit SCH2, the source thereof is grounded, and the drain thereof is connected to the load detecting terminal LDET via the first resistor R1. The non-undervoltage state end of the gate of the high voltage PMOS transistor MP1 and the undervoltage detection circuit SCH2 The connection is connected to the power supply terminal VDD, and the drain is connected to the charger detection terminal CDET via the second resistor R2. The high voltage NMOS transistor MN1 and the high voltage PMOS transistor MP1 are turned on in an undervoltage state, and the load detection terminal LDET pull-down and the charger detection terminal CDET are pulled up, and the second resistor R2>>the first resistor R1.

When the undervoltage release terminal OD_RELS is 0, the undervoltage detection circuit SCH2 detects that the lithium battery voltage (ie, VC1-VC2, VC2-VC3, ...) is lower than the undervoltage value and continues to be greater than the preset time, and enters an undervoltage state. That is, Odischarge=1. After the undervoltage is detected, the undervoltage release terminal OD_RELS=0 will lock the undervoltage state. Otherwise, it will judge whether to exit the undervoltage state according to the lithium battery voltage and not lock the undervoltage.

FIG. 3 is a schematic diagram of curves of various parameters of an undervoltage protection load latch circuit under severe conditions according to an embodiment of the present invention. As shown in Figure 3, LOAD represents whether the load is connected (LOAD = 1 for connection, otherwise it is not connected), Vcell for lithium battery voltage, Vdrv for protection circuit undervoltage hysteresis (pre-set), Vdv To protect the undervoltage turn-over point of the circuit (also preset), Odischarge represents whether the lithium battery enters an undervoltage condition (Odischarge=0 represents normal discharge, otherwise The representative enters the undervoltage state), DSG is the switch of the output discharge loop (DSG=1 means open and normally discharge, otherwise it means off and enters undervoltage state).

After entering the undervoltage, if the load is still followed, even if the lithium battery voltage Vcell recovers, it is still latched in the undervoltage state. After the load is unplugged, the undervoltage is judged according to the actual lithium battery voltage Vcell, thereby avoiding DSG oscillation.

Under different application environments, load conditions and cost considerations, lithium battery protection wafers may adopt different lithium battery protection schemes such as the same port, half-port, full-port, P-charge and N-discharge. The peripheral circuits are respectively described as follows: Figure 4 is the present invention. A schematic diagram of a peripheral circuit of an undervoltage protection load latch circuit of one embodiment in a "same port" lithium battery protection scheme. As shown in FIG. 4, in the "same port" lithium battery protection scheme, the positive and negative terminals P+, P- and the connection charge connected to the load in a lithium battery application circuit 400 including the undervoltage protection load latch circuit 200 are shown. The positive and negative terminals C+ and C- of the device are identical. The lithium battery application circuit 400 further includes: an overvoltage protection circuit 401, an overcurrent protection circuit 402, other protection circuits 403, a control logic circuit 404, a charging loop control switch transistor MCHG, a charging loop resistor RCHG, and a discharge loop control switch transistor. MDSG. Among them, the other protection circuit 403 includes a temperature protection circuit, a wire break protection circuit and an extremely high voltage protection circuit, which are common protection circuits in a common lithium battery protection chip. The input terminals of the control logic circuit 404 are respectively connected to the undervoltage protection load latch circuit 200, the overvoltage protection circuit 401, the overcurrent protection circuit 402 and other protection circuits 403, and the output terminals thereof are connected to a charging terminal CHG and a discharging terminal DSG. And for receiving a switch including undervoltage protection, overvoltage protection, overcurrent protection and other protection signals and controlling the charging terminal CHG and/or the discharging terminal DSG.

In this embodiment, the undervoltage protection load latch circuit 200 and the overvoltage protection circuit The circuit 401, the overcurrent protection circuit 402, the other protection circuit 403, and the control logic circuit 404 may constitute a lithium battery protection wafer 410. The lithium battery protection wafer 410 has a plurality of lithium batteries CELL1, CELL2, CELL3, ..., CELLn voltage input terminals VC1, VC2, VC3, ..., VCn and a power supply terminal VDD.

In addition, the gate of the charging circuit control switch transistor MCHG is connected to the charging terminal CHG, and the source, the load detecting terminal LDET and the charger detecting terminal CDET are both connected to the negative connection terminal P-/C- connected to the load/charger. The charging loop resistor RCHG is connected between the gate and the source of the charging loop control switch transistor MCHG. The gate of the discharge loop control switch transistor MDSG is connected to the discharge terminal DSG, and the drain is connected to the drain of the charging circuit control switch transistor MCHG, and the source thereof is composed of a plurality of lithium batteries CELL1, CELL2, CELL3, ..., CELLn The negative electrode of the assembled lithium battery pack is connected.

The discharge loop control switch transistor MDSG and the charge loop control switch transistor MCHG are external power NMOS tubes, respectively controlling the switches of the discharge loop and the charge loop, and the charge loop resistor RCHG is used to turn off the charge loop control switch transistor MCHG. The first diode D1 and the second diode D2 are a parasitic body diode of the discharge loop control switch transistor MDSG and the charge loop control switch transistor MCHG, respectively.

In the “same port” application environment, the pin of the charger detection terminal CDET/load detection terminal LDET is connected to the negative connection terminal P-/C- of the load/charger, and the discharge circuit control switch transistor MDSG is turned off after undervoltage. Stop discharging, and simultaneously turn on the load detection terminal LDET pull-down and charger detection terminal CDET pull-up: 1) If the load is followed, the load detection terminal LDET=charger detection terminal CDET=power terminal is detected due to the load <<first resistance R1 VDD, or OR operation The output signal VA=0, after the filter circuit SCH1 is filtered, the undervoltage release terminal OD_RELS=0. At this time, the undervoltage detection circuit SCH2 locks the undervoltage state when the undervoltage release terminal OD_RELS is 0, even if the switch transistor is controlled by the discharge loop MDSG Closing the discharge circuit causes the lithium battery voltage to rise greatly and does not exit the undervoltage, thereby avoiding oscillation. 2) If the load is unplugged, the second detection resistor R2>>the first resistor R1, the load detection terminal LDET and the charger The detection terminal CDET will be pulled to the ground (GND) potential by the first resistor R1, or the output signal VA will be changed from 0 to 1. After filtering by the filter circuit SCH1, the output undervoltage release terminal OD_RELS=1, once the lithium battery voltage rises When the undervoltage hysteresis is above, the undervoltage is no longer latched; 3) If the charger is connected, the load detection terminal LDET and the charger detection terminal CDET will be pulled down to the GND by the charger, and the output signal VA is also detected or calculated. 0 becomes 1, after filtering by the filter circuit SCH1, the output undervoltage release terminal OD_RELS=1, once the lithium battery voltage rises above the undervoltage hysteresis, the exit undervoltage is no longer latched.

The lithium battery protection wafer 410 in this embodiment compares the common lithium battery protection wafer with the load detection terminal LDET and the charger detection terminal CDET pin for load and charger detection respectively, and the load is applied after the wafer enters undervoltage. The detection terminal LDET pull-down, the charger detection terminal CDET pull-up and the two are detected, the load detection terminal LDET detection level is the load detection reference voltage Vtr_Load, and the charger detection terminal CDET detection level is the first charger detection reference voltage Vtr_cgr1 And the second charger detects the reference voltage Vtr_cgr2, after filtering the comparator result, as long as the load unloading signal loadoff or the first charger connection signal cgron1 or the second charger connection signal cgron2=1 is detected, it means that the load is unplugged. Or charger On, the undervoltage lockout is exited, otherwise the undervoltage is locked by the undervoltage detection circuit.

FIG. 5 is a schematic diagram of a peripheral circuit in a "half-port" lithium battery protection scheme of an undervoltage protection load latch circuit according to an embodiment of the present invention. As shown in FIG. 5, in the "half-port" lithium battery protection scheme, a positive connection terminal P+ that connects the load and a positive connection terminal that connects the charger are included in a lithium battery application circuit 500 of the undervoltage protection load latch circuit 200. C+ is the same, and the negative connection P- of the connection load is separated from the negative connection C- of the connection charger. The lithium battery application circuit 500 further includes: an overvoltage protection circuit 501, an overcurrent protection circuit 502, other protection circuits 503, a control logic circuit 504, a charging loop control switch transistor MCHG, a charging loop resistor RCHG, and a discharge loop control switch transistor. MDSG. Among them, the other protection circuit 503 includes a temperature protection circuit, a wire break protection circuit and an extremely high voltage protection circuit, which are common protection circuits in a common lithium battery protection chip. The input ends of the control logic circuit 504 are respectively connected to the undervoltage protection load latch circuit 200, the overvoltage protection circuit 501, the overcurrent protection circuit 502 and other protection circuits 503, and the output ends thereof are connected to a charging terminal CHG and a discharging terminal DSG. And for receiving a switch including undervoltage protection, overvoltage protection, overcurrent protection and other protection signals and controlling the charging terminal CHG and/or the discharging terminal DSG.

In the present embodiment, the undervoltage protection load latch circuit 200, the overvoltage protection circuit 501, the overcurrent protection circuit 502, the other protection circuit 503, and the control logic circuit 504 may constitute a lithium battery protection wafer 510. The lithium battery protection wafer 510 has a plurality of lithium batteries CELL1, CELL2, CELL3, ..., CELLn voltage input terminals VC1, VC2, VC3, ..., VCn and a power supply terminal VDD.

In addition, the gate of the charging circuit control switch transistor MCHG is connected to the charging terminal CHG, and the source and the charger detecting end CDET are both connected to the negative connection of the charger. The terminal is C-connected. The charging loop resistor RCHG is connected between the gate and the source of the charging loop control switch transistor MCHG. The gate of the discharge circuit control switch transistor MDSG is connected to the discharge terminal DSG, and the drain is connected to the drain of the charging circuit control switch transistor MCHG, and is connected to the negative connection terminal P- of the connection load together with the load detection terminal LDET. The source is connected to a negative electrode of a lithium battery pack composed of a plurality of lithium batteries CELL1, CELL2, CELL3, ..., CELLn.

The discharge loop control switch transistor MDSG and the charge loop control switch transistor MCHG are external power NMOS tubes, respectively controlling the switches of the discharge loop and the charge loop, and the charge loop resistor RCHG is used to turn off the charge loop control switch transistor MCHG. The first diode D1 and the second diode D2 are a parasitic body diode of the discharge loop control switch transistor MDSG and the charge loop control switch transistor MCHG, respectively.

In the "half-port" application environment, the pin of the charger detection terminal CDET is connected to the negative terminal C- of the charger for detecting the charger; the pin of the load detection terminal LDET is connected to the negative connection terminal of the load P- It is used to detect the load. After the undervoltage, the load detection terminal LDET pull-down and the charger detection terminal CDET pull-up are simultaneously turned on: 1) If the load is followed, the load detection terminal LDET=power terminal is detected due to the load <<first resistance R1 VDD, the charger detection terminal CDET is pulled up to the power supply terminal VDD by the second resistor R2, or the output signal VA=0 is calculated, and the undervoltage release terminal OD_RELS=0 after filtering by the filter circuit SCH1, at which time the undervoltage detection circuit SCH2 is When the undervoltage release terminal OD_RELS is 0, the undervoltage state is locked. Even if the discharge circuit is closed due to the discharge loop control switch transistor MDSG, the lithium battery voltage will rise greatly and will not exit the undervoltage, thereby avoiding oscillation; 2) if the load is pulled Off, because the second resistor R2>> the first resistor R1, then The load detection terminal LDET and the charger detection terminal CDET (through the second resistor D2) are respectively pulled down to the ground GND and GND+VD2 (<0.6V) potential by the first resistor R1, or the operation output signal VA is changed from 0 to 1, After filtering by the filter circuit SCH1, the output undervoltage release terminal OD_RELS=1, once the lithium battery voltage rises above the undervoltage hysteresis, the exit undervoltage is no longer latched; 3) if the charger is connected and the load is followed, the load detection terminal LDET The load is pulled to the power supply terminal VDD, but the charger detection terminal CDET is pulled down to the ground GND by the charger, or the operation output signal VA is changed from 0 to 1, after filtering by the filter circuit SCH1, the output undervoltage release terminal OD_RELS= 1. Once the lithium battery voltage rises above the undervoltage hysteresis, the exit undervoltage is no longer latched. By withdrawing the undervoltage lockout by connecting the charger, it is possible to prevent the charger and the load from being present. Even if the charge returns the normal voltage to the lithium battery, it is still latched under undervoltage.

The lithium battery protection wafer 510 in this embodiment compares the common lithium battery protection wafer with the load detection terminal LDET and the charger detection terminal CDET pin for load and charger detection respectively, and the load is applied after the wafer enters undervoltage. The detection terminal LDET pull-down, the charger detection terminal CDET pull-up and the two are detected, the load detection terminal LDET detection level is the load detection reference voltage Vtr_Load, and the charger detection terminal CDET detection level is the first charger detection reference voltage Vtr_cgr1 And the second charger detects the reference voltage Vtr_cgr2, after filtering the comparator result, as long as the load unloading signal loadoff or the first charger connection signal cgron1 or the second charger connection signal cgron2=1 is detected, it means that the load is unplugged. Or the charger is connected, the undervoltage lockout is exited, otherwise the undervoltage is locked by the undervoltage detection circuit.

6 is a schematic diagram of a peripheral circuit in a "full-port" lithium battery protection scheme of an undervoltage protection load latch circuit according to an embodiment of the present invention. As shown in Figure 6 It is shown that in the "full-port" lithium battery protection scheme, the positive connection terminal P+ connecting the load in a lithium battery application circuit 600 including the undervoltage protection load latch circuit 200 is the same as the positive connection terminal C+ of the connection charger. The negative connection terminal P- of the connection load is separated from the negative connection terminal C- of the connection charger. The lithium battery application circuit 600 further includes: an overvoltage protection circuit 601, an overcurrent protection circuit 602, other protection circuits 603, a control logic circuit 604, a charge loop control switch transistor MCHG, a charge loop resistor RCHG, and a discharge loop control switch transistor. MDSG. Among them, the other protection circuit 603 includes a temperature protection circuit, a wire break protection circuit and an extremely high voltage protection circuit, which are common protection circuits in a common lithium battery protection chip. The input end of the control logic circuit 604 is respectively connected to the undervoltage protection load latch circuit 200, the overvoltage protection circuit 601, the overcurrent protection circuit 602 and other protection circuits 603, and the output end thereof is connected to a charging terminal CHG and a discharging terminal DSG. And for receiving a switch including undervoltage protection, overvoltage protection, overcurrent protection and other protection signals and controlling the charging terminal CHG and/or the discharging terminal DSG.

In the present embodiment, the undervoltage protection load latch circuit 200, the overvoltage protection circuit 601, the overcurrent protection circuit 602, the other protection circuit 603, and the control logic circuit 604 may constitute a lithium battery protection wafer 610. The lithium battery protection chip 610 has a plurality of lithium batteries CELL1, CELL2, CELL3, ..., CELLn voltage input terminals VC1, VC2, VC3, ..., VCn and a power supply terminal VDD.

In addition, the gate of the charging circuit control switch transistor MCHG is connected to the charging terminal CHG, and the source and the charger detecting end CDET are connected to the negative connecting terminal C- of the connection charger, and the drain and the third diode are connected. The negative electrode of D3 is connected, and the positive electrode of the third diode D3 is connected to the negative electrode of the lithium battery pack composed of a plurality of lithium batteries CELL1, CELL2, CELL3, ..., CELLn. Charging loop resistor RCHG is connected to charge back The circuit controls the gate and source of the switch transistor MCHG. The gate of the discharge loop control switch transistor MDSG is connected to the discharge terminal DSG, and both the drain and the load detection terminal LDET are connected to the negative connection terminal P- connected to the load, and the source thereof is also connected to the negative electrode of the lithium battery pack.

The discharge loop control switch transistor MDSG and the charge loop control switch transistor MCHG are external power NMOS tubes, respectively controlling the switches of the discharge loop and the charge loop, and the charge loop resistor RCHG is used to turn off the charge loop control switch transistor MCHG. The first diode D1 and the second diode D2 are a parasitic body diode of the discharge loop control switch transistor MDSG and the charge loop control switch transistor MCHG, respectively.

In the "full-port" application environment, the charger detection terminal CDET is connected to the negative connection terminal C- of the charger for detecting the charger, and the load detection terminal LDET is connected to the negative connection terminal P- of the connection load for detecting the load. After the undervoltage, the load detection terminal LDET pull-down and the charger detection terminal CDET pull-up are simultaneously turned on: 1) If the load is followed, the load detection terminal LDET=power supply terminal VDD is detected due to the load <<first resistance R1, and the charger detects The CDET is pulled up to the power supply terminal VDD by the second resistor R2, or the output signal VA=0 is calculated, and the undervoltage release terminal OD_RELS=0 after filtering by the filter circuit SCH1, and the undervoltage detection circuit SCH2 is at the undervoltage release terminal OD_RELS. When it is 0, the undervoltage state is locked. Even if the discharge circuit is turned off due to the discharge circuit control switch transistor MDSG, the lithium battery voltage will rise greatly and will not exit the undervoltage, thus avoiding the oscillation; 2) If the load is unplugged, the load detection The terminal LDET is pulled down to the ground GND by the first resistor R1, and the charger detection terminal CDET is pulled up to the power terminal VDD by the second resistor R2, or the operation output signal VA is changed from 0 to 1, and filtered by the filter circuit SCH1. After the wave, the output undervoltage release terminal OD_RELS=1, once the lithium battery voltage rises above the undervoltage hysteresis, the exit undervoltage is no longer latched; 3) If the charger is connected and the load is followed, the load detection terminal LDET is pulled by the load The power supply terminal VDD, but the charger detection terminal CDET will be pulled down to the ground GND by the charger, or the operation output signal VA will change from 0 to 1. After filtering by the filter circuit SCH1, the output undervoltage release terminal OD_RELS=1, once the lithium battery When the cell voltage rises above the undervoltage hysteresis, the exit undervoltage is no longer latched.

The lithium battery protection chip 610 in this embodiment compares the common lithium battery protection wafer with the load detection terminal LDET and the charger detection terminal CDET pin for load and charger detection respectively, and the load is applied after the wafer enters undervoltage. The detection terminal LDET pull-down, the charger detection terminal CDET pull-up and the two are detected, the load detection terminal LDET detection level is the load detection reference voltage Vtr_Load, and the charger detection terminal CDET detection level is the first charger detection reference voltage Vtr_cgr1 And the second charger detects the reference voltage Vtr_cgr2, after filtering the comparator result, as long as the load unloading signal loadoff or the first charger connection signal cgron1 or the second charger connection signal cgron2=1 is detected, it means that the load is unplugged. Or the charger is connected, the undervoltage lockout is exited, otherwise the undervoltage is locked by the undervoltage detection circuit.

FIG. 7 is a schematic diagram of a peripheral circuit in a "P-charged-discharge" lithium battery protection scheme of an undervoltage protection load latch circuit according to an embodiment of the present invention. As shown in FIG. 7, in the "P-charged-discharge" lithium battery protection scheme, the negative connection terminal P- and the connection charger connected to the load in a lithium battery application circuit 700 including the undervoltage protection load latch circuit 200 are shown. The negative connection C- is the same, and the positive connection P+ connecting the load is separate from the positive connection C+ of the connection charger. The lithium battery application circuit 700 further includes: an overvoltage protection circuit 701, an overcurrent protection circuit 702, and other protection circuits. 703. Control logic circuit 704, charge loop control switch transistor MCHG, charge loop resistor RCHG, and discharge loop control switch transistor MDSG. Among them, the other protection circuit 703 includes a temperature protection circuit, a wire break protection circuit and an extremely high voltage protection circuit, which are common protection circuits in a common lithium battery protection chip. The input ends of the control logic circuit 704 are respectively connected to the undervoltage protection load latch circuit 200, the overvoltage protection circuit 701, the overcurrent protection circuit 702 and other protection circuits 703, and the output terminals thereof are connected to a charging terminal CHG and a discharging terminal DSG. And for receiving a switch including undervoltage protection, overvoltage protection, overcurrent protection and other protection signals and controlling the charging terminal CHG and/or the discharging terminal DSG.

In the present embodiment, the undervoltage protection load latch circuit 200, the overvoltage protection circuit 701, the overcurrent protection circuit 702, the other protection circuit 703, and the control logic circuit 704 may constitute a lithium battery protection wafer 710. The lithium battery protection wafer 710 has a plurality of lithium batteries CELL1, CELL2, CELL3, ..., CELLn voltage input terminals VC1, VC2, VC3, ..., VCn and a power supply terminal VDD.

In addition, the gate of the charging circuit control switch transistor MCHG is connected to the charging terminal CHG, and the source and the charger detecting end CDET are connected to the positive connecting terminal C+ of the connection charger, and the drain terminal and the positive connecting end of the connected load P+ Both are connected to the positive electrode of a lithium battery pack composed of a plurality of lithium batteries CELL1, CELL2, CELL3, ..., CELLn. The charging loop resistor RCHG is connected between the gate and the source of the charging loop control switch transistor MCHG. The gate of the discharge loop control switch transistor MDSG is connected to the discharge terminal DSG, and both the drain and the load detection terminal LDET are connected to the negative connection terminal C-/P- connected to the charger/load, and the source thereof and the lithium battery pack are The negative electrode is connected.

The discharge loop control switch transistor MDSG is an external power NMOS tube, and the charge loop control switch transistor MCHG is an external power PMOS tube, respectively controlled The switch of the discharge circuit and the charging circuit, the charging circuit resistance RCHG is used to turn off the charging circuit control switch transistor MCHG. The first diode D1 and the second diode D2 are a parasitic body diode of the discharge loop control switch transistor MDSG and the charge loop control switch transistor MCHG, respectively.

In the "P charging and discharging" application environment, the charger detection terminal CDET is connected to the positive connection terminal C+ of the charger for detecting the charger, and the load detection terminal LDET is connected to the negative connection terminal P- of the connection load for detecting the load. After the undervoltage, the load detection terminal LDET pull-down and the charger detection terminal CDET pull-up are simultaneously turned on: 1) If the load is followed, the load detection terminal LDET=power supply terminal VDD is detected due to the load <<first resistance R1, and the charger detects The CDET is pulled up to the power supply terminal VDD by the second resistor R2, or the output signal VA=0 is calculated, and the undervoltage release terminal OD_RELS=0 after filtering by the filter circuit SCH1, and the undervoltage detection circuit SCH2 is at the undervoltage release terminal OD_RELS. When it is 0, the undervoltage state is locked. Even if the discharge circuit is closed due to the discharge circuit control switch transistor MDSG, the lithium battery voltage will rise greatly and will not exit the undervoltage and avoid oscillation. 2) If the load is unplugged, the load detection terminal The LDET is pulled down to the ground GND by the first resistor R1, and the charger detection terminal CDET is pulled up to the power supply terminal VDD by the second resistor R2, or the operation output signal VA is changed from 0 to 1, and the output is undervoltage after being filtered by the filter circuit SCH1. Release end OD_RELS=1 Once the lithium battery voltage rises above the undervoltage hysteresis, the undervoltage is no longer latched; 3) If the charger is connected, the load detection terminal LDET will be pulled down to the ground GND by the charger, and the charger detection terminal CDET will be charged. Pull up to > power supply VDD, generally the charger voltage near the undervoltage is much higher than the power supply VDD, that is, the charger detection terminal CDET> the second charger detection reference voltage Vtr_cgr2, or the operation output The signal VA changes from 0 to 1. After filtering by the filter circuit SCH1, the output undervoltage release terminal OD_RELS=1, and once the lithium battery voltage rises above the undervoltage hysteresis, the exit undervoltage is no longer latched.

The lithium battery protection wafer 710 in this embodiment compares the common lithium battery protection wafer with the load detection terminal LDET and the charger detection terminal CDET pin for load and charger detection respectively, and the load is applied after the wafer enters undervoltage. The detection terminal LDET pull-down, the charger detection terminal CDET pull-up and the two are detected, the load detection terminal LDET detection level is the load detection reference voltage Vtr_Load, and the charger detection terminal CDET detection level is the first charger detection reference voltage Vtr_cgr1 And the second charger detects the reference voltage Vtr_cgr2, after filtering the comparator result, as long as the load unloading signal loadoff or the first charger connection signal cgron1 or the second charger connection signal cgron2=1 is detected, it means that the load is unplugged. Or the charger is connected, the undervoltage lockout is exited, otherwise the undervoltage is locked by the undervoltage detection circuit.

In summary, the present invention introduces an undervoltage protection load latch function: after the undervoltage shutdown of the discharge loop, if the load is still followed, even if the lithium battery voltage rises, it is still latched in an undervoltage state until the load is removed or the charger is connected. After that, the undervoltage state is exited according to the actual lithium battery voltage, thereby avoiding the discharge circuit oscillating near the undervoltage point under severe conditions.

The present invention can be applied to different lithium battery protection schemes including the same port, half-port, full-port and P-charge N in different application environments, load conditions, and cost considerations, and protects the chip for a cascade system or a single lithium battery. Also applicable.

The invention can be widely applied to lithium battery application fields such as electric tools, electric bicycles, uninterruptible power supply systems and mobile power sources.

Although the present invention is disclosed above in the preferred embodiment, it is not intended to be limiting. In the present invention, any changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, any modifications, equivalent changes, and modifications of the above embodiments may be made without departing from the spirit and scope of the invention.

200‧‧‧Undervoltage protection load latch circuit

202‧‧‧Load/charger detection circuit

CDET‧‧‧Charger detection terminal

Cgron1‧‧‧First charger connection signal

Cgron2‧‧‧Second charger connection signal

Clk‧‧‧clock end

Cmp1‧‧‧ first comparator

Cmp2‧‧‧second comparator

Cmp3‧‧‧ third comparator

DF1‧‧D trigger

LDET‧‧‧ load detection terminal

Loadoff‧‧‧load removal signal

MN1‧‧‧High voltage NMOS transistor

MP1‧‧‧High Voltage PMOS Crystal

Odischarge‧‧‧Undervoltage state

‧‧‧Non-undervoltage state

OD_RELS‧‧‧Undervoltage release end

OR3‧‧‧ three inputs or gates

R1‧‧‧first resistance

R2‧‧‧second resistance

Reset‧‧‧Reset

SCH1‧‧‧Filter circuit

SCH2‧‧‧ undervoltage detection circuit

VA‧‧‧ or computing output signal

VC1, VC2, VC3, VCn‧‧‧ voltage input

VDD‧‧‧Power/Power Side

Vtr_cgr1‧‧‧First charger detection reference voltage

Vtr_cgr2‧‧‧Second charger detection reference voltage

Vtr_Load‧‧‧Load detection reference voltage

Claims (10)

An undervoltage protection load latch circuit suitable for a plurality of lithium battery protection schemes, comprising an undervoltage detection circuit and a load/charger detection circuit; wherein an input side of the undervoltage detection circuit has a voltage input of a plurality of lithium batteries And an undervoltage release terminal having an undervoltage state terminal and a non-undervoltage state terminal on the output side; the load/charger detection circuit includes: a first comparator, a second comparator, a third comparator, a three-input gate, a filter circuit, a D flip-flop, a high voltage NMOS transistor, a high voltage PMOS transistor, a first resistor and a second resistor; a positive input terminal of the first comparator is coupled to a load detection reference voltage, and a negative input The end is connected to a load detecting end, and the output end thereof generates a load removing signal; the positive input end of the second comparator is connected to a first charger detecting reference voltage, and the negative input end is connected to a charger detecting end, and the output end thereof is connected Generating a first charger connection signal; a positive input terminal of the third comparator is connected to the charger detection terminal, and a negative input terminal is connected to a second charger to detect a reference voltage, The output end generates a second charger connection signal; the input terminals of the three input or gate respectively receive the load removal signal, the first charger connection signal and the second charger connection signal, and the output end thereof is generated An OR operation output signal; the input end of the filter circuit receives the OR operation output signal; the D flip-flop has a D end, a Q end, a terminal, a clock terminal and a reset terminal, wherein the clock terminal is connected to an output end of the filter circuit, the reset terminal is connected to the non-undervoltage state end, and the Q terminal is connected to the undervoltage release terminal. The D end is connected to a power end, The gate of the high voltage NMOS transistor is connected to the undervoltage state end, the source thereof is grounded, and the drain is connected to the load detecting terminal through the first resistor; the high voltage PMOS transistor is The gate is connected to the non-undervoltage state end, the source thereof is connected to the power terminal, and the drain is connected to the charger detecting end via the second resistor. The undervoltage protection load latch circuit of claim 1, wherein the lithium battery protection scheme comprises: a same port, a half port, a full port, and a P charge. The undervoltage protection load latch circuit of claim 2, wherein the undervoltage protection load latch circuit can be applied to a power tool, an electric bicycle, an uninterruptible power supply system, or a mobile in a lithium battery application field. Inside the power supply. The undervoltage protection load latch circuit of claim 3, wherein in the lithium battery protection scheme of the same port, a lithium battery application circuit including the undervoltage protection load latch circuit is connected to the load The positive and negative terminals are the same as the positive and negative terminals of the connection charger; the lithium battery application circuit further includes: an overvoltage protection circuit; an overcurrent protection circuit; other protection circuits; a control logic circuit, and an input thereof. The terminals are respectively connected to the undervoltage protection load latch circuit, the overvoltage protection circuit, the overcurrent protection circuit and the other protection circuit, and the output end thereof is connected to a charging end and a discharging end for receiving a switch including undervoltage protection, overvoltage protection, overcurrent protection, and other protection signals and controlling the charging terminal and/or the discharging terminal; the charging circuit controls the switching transistor, the gate of which is connected to the charging terminal, and the source thereof a pole, the load detecting end and the charger detecting end are both connected to a negative connection end connected to the load/charger; a charging loop resistor is connected to the charging circuit control switch And a gate electrode body Between the sources; the discharge circuit controls the switching transistor, the gate of which is connected to the discharge end, the drain of which is connected to the drain of the charging circuit control switch transistor, and the source thereof and the plurality of lithium batteries The negative electrode of the assembled lithium battery pack is connected. The undervoltage protection load latch circuit of claim 3, wherein in the lithium battery protection scheme of the half-port, the lithium-ion battery application circuit including the undervoltage protection load latch circuit is connected to the load The positive connection end is the same as the positive connection end of the connection charger, and the negative connection end connecting the load is separated from the negative connection end connected to the charger; the lithium battery application circuit further includes: a voltage protection circuit; an overcurrent protection circuit; another protection circuit; a control logic circuit having an input terminal and the undervoltage protection load latch circuit, the overvoltage protection circuit, the overcurrent protection circuit, and the other protection a circuit connection having an output connected to a charging terminal and a discharging terminal for receiving a switch including undervoltage protection, overvoltage protection, overcurrent protection, and other protection signals and controlling the charging terminal and/or the discharging terminal; a charging circuit controls a switching transistor, a gate thereof is connected to the charging end, and a source thereof and the charger detecting end are connected to a negative connection end connected to the charger; Connected between the gate and the source of the charging circuit control switch transistor; the discharge circuit controls the switching transistor, the gate is connected to the discharging end, and the drain thereof and the charging circuit control switch transistor a drain connection, and together with the load detecting end, a negative connection end connected to the load, the source and the plurality of The negative electrode of the lithium battery pack composed of a lithium battery is connected. The undervoltage protection load latch circuit of claim 3, wherein in the lithium battery protection scheme of the full-portion, a lithium battery application circuit including the undervoltage protection load latch circuit is connected The positive connection end of the load is the same as the positive connection end of the connection charger, and the negative connection end connecting the load is separated from the negative connection end connected to the charger; the lithium battery application circuit further includes: Overvoltage protection circuit; overcurrent protection circuit; other protection circuit; control logic circuit, the input end thereof and the undervoltage protection load latch circuit, the overvoltage protection circuit, the overcurrent protection circuit and the other a protection circuit connection, the output end of which is connected to a charging end and a discharging end for receiving a switch including undervoltage protection, overvoltage protection, overcurrent protection and other protection signals and controlling the charging terminal and/or the discharging end a charging circuit control switch transistor having a gate connected to the charging end, a source and a charger detecting end connected to a negative connection end connected to the charger, and a drain and a a cathode of the triode body is connected, a cathode of the third diode is connected to a cathode of a lithium battery pack composed of a plurality of the lithium batteries; a charging loop resistor is connected to the gate of the charging circuit control switch transistor Between the pole and the source; the discharge circuit controls the switching transistor, the gate of which is connected to the discharge end, and the drain and the load detecting end are connected to the negative connection end connected to the load, and the source thereof is also The negative electrode of the lithium battery pack is connected. An undervoltage protection load latch circuit as described in claim 3, In the lithium battery protection scheme in which P is charged, the negative connection terminal connected to the load in the lithium battery application circuit including the undervoltage protection load latch circuit is the same as the negative connection terminal connected to the charger. The positive connection end connecting the load is separated from the positive connection end connected to the charger; the lithium battery application circuit further comprises: an overvoltage protection circuit; an overcurrent protection circuit; other protection circuits; and a control logic circuit The input end is respectively connected to the undervoltage protection load latch circuit, the overvoltage protection circuit, the overcurrent protection circuit and the other protection circuit, and the output end thereof is connected to a charging end and a discharging end. And a switch for receiving the undervoltage protection, overvoltage protection, overcurrent protection and other protection signals and controlling the charging terminal and/or the discharging end; the charging circuit controls the switching transistor, and the gate thereof is connected to the charging end a source and a charger detecting end are connected to a positive connection terminal connected to the charger, and a drain electrode and a positive connection end connecting the load are connected to a lithium battery composed of a plurality of the lithium batteries a positive connection of the group; a charging loop resistor connected between the gate and the source of the charging circuit control switch transistor; the discharging circuit controls the switching transistor, the gate is connected to the discharging end, and the drain is The load detecting end is connected to a negative connection terminal connected to the charger/load, and a source thereof is connected to a negative electrode of the lithium battery pack. The undervoltage protection load latch circuit according to any one of claims 4 to 7, wherein: the load detection reference voltage is based on an actual load and the first resistor divider And the second resistor and the first resistor divider point are reasonably selected; the first charger detection reference voltage and the second charger detection reference voltage are both reasonably selected according to charger characteristics. The undervoltage protection load latch circuit according to any one of claims 4 to 7, wherein the other protection circuit comprises a temperature protection circuit, a wire breakage protection circuit and an extremely high voltage protection circuit. The undervoltage protection load latch circuit of claim 9, wherein the undervoltage protection load latch circuit, the overvoltage protection circuit, the overcurrent protection circuit, the other protection circuit, and the The control logic circuit constitutes a lithium battery protection wafer; the lithium battery protection wafer edge has a plurality of voltage input terminals of the lithium battery and one of the power terminals.