Ternary lithium battery segmented voltage switching utilization circuit

Abstract

The invention discloses a segmented voltage switching utilization circuit for a ternary lithium battery, which is characterized in that two segments of voltage are distinguished for automatic switching use by detecting the voltage of the battery, and when the voltage of the battery is higher than a certain value (such as 3.6 V), the voltage is automatically switched to 3.3 V through LDO (Low Dropout Regulator) conversion to be used for supplying power to an Internet of Things module; and on the contrary, when the battery voltage is lower than the value, the battery voltage is automatically switched to be directly used for supplying power to the Internet of Things module, two PMOS transistors which are connected in series in a back-to-back manner are used after the two sections of voltage are automatically switched, and the two butted PMOS transistors have an anti-backflow function, so that the sectional voltages of the battery voltage can be mutually isolated and do not influence each other, the working time of the battery is prolonged, and the maintenance cost of equipment is reduced. Three different two-section voltage automatic switching implementation modes are given according to the situation that the difference between the input voltage and the output voltage is small and different LDO module models are adopted, and a three-end voltage detector can adopt a low-power-consumption voltage detector chip and can also adopt discrete components to form a Schmidt trigger circuit to distinguish the two sections of voltage.

Description

Technical Field

[0001] The invention relates to the field of battery voltage detection switching, and in particular to a ternary lithium battery segmented voltage switching utilizing circuit. Background Art

[0002] At present, the application of IoT communication terminals is very extensive, and various terminals have emerged. The IoT terminals currently on the market that integrate wireless data communication (such as NB-IOT) generally continuously and automatically collect sensor information and automatically report it to the information management center at a preset time interval. This means that the device is always in working condition. Although the device controller is in sleep mode for some time, the power consumption is slightly lower. However, for places where it is difficult to obtain city electricity or solar power (road manhole monitoring equipment), the use of ternary lithium batteries for power supply will shorten the battery working time if the battery cannot be fully utilized due to the limited battery power. In order to ensure working stability, timely charging is required, which means increasing the charging frequency and increasing maintenance costs. In addition, for some long-term working occasions, it is particularly important to make full use of the battery. For example, many IoT devices have begun to use single-string batteries. For example, sensors that require high voltage (12V) are DC-DC boosted, and other modules are still powered by single-string batteries to meet low power requirements.

[0003] Ternary lithium battery is a rechargeable battery, with a single string voltage range of 2.75V ~ 4.2V, a typical value of about 3.6V, and a relatively steep voltage discharge curve of ternary lithium battery; lithium iron phosphate battery is a rechargeable battery, with a single string voltage range of 2.5V ~ 3.65V, a typical value of about 3.2V, and a relatively flat voltage discharge curve of lithium iron phosphate battery; lithium thionyl chloride battery (referred to as lithium thionyl chloride battery) is a disposable battery, with a single string voltage range of 3.0V ~ 3.65V, a typical value of about 3.6V, and a very flat voltage discharge curve of lithium iron phosphate battery, and the voltage remains basically unchanged when 90% of the power is released.

[0004] The ternary lithium discharge curve is the relationship curve between the battery voltage and discharge capacity, which refers to the curve of the remaining capacity SOC. It can be seen from the discharge curve that the capacity of the ternary lithium battery is mainly concentrated around 3.35V~3.95V, and 80% of the capacity is concentrated in this voltage range; different discharge rates correspond to different discharge curves: the larger the discharge rate, the lower the discharge curve voltage, and the smaller the discharge rate, the higher the discharge curve voltage; in addition to being closely related to the discharge rate, the discharge curve of the ternary lithium battery is also related to temperature, and there are certain differences in the discharge curves at different temperatures.

[0005] The voltage curve of the ternary lithium battery during the entire discharge process can be divided into three stages:

[0006] 1) Initial stage: The voltage of the battery drops rapidly in the initial stage. The greater the discharge rate, the faster the voltage drops.

[0007] 2) Platform area: The battery voltage enters a stage of slow change. This period of time is called the platform area of ​​the battery. The smaller the discharge rate, the longer the platform area lasts, the higher the platform voltage, and the slower the voltage drops.

[0008] 3) Sharp drop zone: When the battery is nearly discharged, the battery load voltage begins to drop sharply until it reaches the discharge cut-off voltage (protection voltage) of the protection board, and then stops discharging. The protection voltage is generally 3.0V to 2.75V.

[0009] The operating voltage range of MCU, memory chip, Bluetooth and other modules in IoT devices is generally 3.0V to 3.6V. If a single-string battery is used for power supply, the voltage range of a single-string lithium iron phosphate battery and lithium-ion battery can be directly used to power IoT devices without voltage conversion. The voltage range of ternary lithium batteries is 2.7V to 4.2V, which means that voltages exceeding 3.6V require LDO (low-dropout linear regulator) or DC-DC (switching power supply) voltage conversion to power IoT devices, otherwise it may cause device damage. LDO has outstanding advantages such as low cost, low noise, low quiescent current, and few external components. It can achieve high efficiency when used in situations where the difference between input voltage and output voltage is small. LDO is a new generation of integrated circuit regulator. The biggest difference from the three-terminal regulator is that LDO is a micro system on chip (SoC) with very low power consumption. It can be used for current main channel control. The chip integrates MOS tubes with extremely low on-resistance, Schottky diodes, sampling resistors, voltage divider resistors and other hardware circuits, and has over-current protection, over-temperature protection, precision reference source, differential amplifier, delayer and other functions. For example, LDO regulators are mostly used in ternary lithium battery applications to convert ternary lithium voltage into 3.3V output voltage.

[0010] DC-DC converters include boost, buck, boost / buck and inverting circuits, which have the advantages of high efficiency, large current, and small quiescent current. They are suitable for situations where the difference between input voltage and output voltage is large. However, they require external inductors, freewheeling diodes, capacitors and other devices, and the output ripple voltage and switching noise are large, and the cost is relatively high.

[0011] When the output current of TI's LDO chip TPS79633 is 1A, the typical voltage difference is 220mV and the maximum is 325mV. If the output current increases, the input-output voltage difference will also increase. It is advisable to take the voltage difference as 300mV. Since the working voltage range of the module is generally 3.0V~3.6V, plus the voltage difference of the LDO chip is 0.3V, it means that the battery capacity below 3.3V (3.0V+0.3V) cannot be released, which accounts for about 10% of the battery capacity. For battery-powered occasions, it is particularly important to make full use of the remaining 10% of the power of the ternary lithium battery: the traditional method uses LDO in hardware, so the remaining 10% of the power cannot be fully utilized; using DC-DC to step down (if the battery voltage is greater than 3.6V) or boost to 3.3V (if the battery voltage is lower than 3.0V), the efficiency can reach more than 90%, but for voltages around 3.3V, the difference between the input voltage and the output voltage is small when converted to 3.3V through DC-DC, so the use of DC-DC is not appropriate.

[0012] In the design and application of electronic products, the interface protection circuit is still very important. If the interface circuit is not designed properly, it will cause abnormal operation at the least, or burn the microprocessor or chip IO port at the worst. Sometimes it cannot be found during design and debugging, and the chip will be burned during mass production or when the user is using it. If the backflow protection can be considered during the design, the problem can be reduced and the reliability of the product can be improved.

[0013] Just like water flows to lower places, current always flows from high voltage to low voltage. If two power supplies with different voltages are connected together, the current will flow from the higher voltage side to the lower voltage side, which is called backflow. For chips, backflow means that the current flows into the chip in the opposite direction.

[0014] At present, the efficient (full) utilization of ternary lithium in Internet of Things electronic products mainly adopts recycling, step-by-step utilization, battery management system and other aspects.

[0015] (1) Cyclic use: Currently, battery manufacturers promise that the ternary battery cells they process can be used for more than 500 times (charged and discharged under standard conditions) in their specifications. However, after the cells are assembled into battery packs, due to consistency issues, mainly the voltage and internal resistance cannot be exactly the same, and the cycle life is about 400 times. In addition, if lithium-ion batteries are often discharged at high rates and high temperatures, the battery life will drop significantly to less than 200 times. At present, the market price of ternary lithium-ion batteries is higher than that of liquid lithium-ion batteries. Due to the long life and good safety performance of liquid lithium-ion batteries, it is believed that there will be a lot of room for growth in the near future. Based on the actual use, if the battery can only be charged and discharged 1,000 times, the ternary lithium-ion battery has decayed by 50% after 1,000 times, that is, the capacity has decayed by half. The nominal capacity at the end of the battery life is currently considered to be 70%; since battery decay is irreversible, the battery can only be replaced.

[0016] (2) Step Utilization

[0017] Sequential utilization refers to the process of continuing to use a product that has reached its original design life and then fully or partially restores its functions through other methods, and this process is basically the same level or downgraded application. "Sequential utilization" is basically the same as "gradient utilization, step utilization, and downgraded use" in concept.

[0018] After a certain number of times of use, if the ternary lithium battery is directly discarded, it will not only waste resources, but also be a burden on the environment; due to its usage characteristics, the ternary lithium battery can be recycled after retirement. For example, if a 100AH ​​battery has been used for a period of time, its capacity will decay to 80AH. At this time, the 80AH battery needs to be replaced. If the 80AH battery is used for other purposes, it can continue to be used. Therefore, to maximize the recycling of ternary lithium batteries, they must first be used in cascades. If a failure occurs after cascade use, the lithium battery can be recycled.

[0019] Battery consistency has always been an important challenge in the operation of ternary lithium battery cascade utilization projects. The inconsistency of lithium battery capacity, internal resistance and voltage is closely related to the charge and discharge reaction mechanism of the battery itself. Even with tens of thousands of retired batteries, it is impossible to completely avoid the consistency of discrete batteries in the operation of the system when building a cascade utilization energy storage system. According to current technology and processes, the cost advantage of realizing the cascade utilization of power lithium batteries is not high. At the same time, with the decline of power lithium batteries, the service life of power lithium batteries will be greatly shortened. From recycling and transportation to evaluation and testing, the hidden costs of waste power lithium batteries are high.

[0020] Secondary utilization is a form of mild scrapping, mainly for batteries whose capacity has dropped below 80% and cannot be used in new energy vehicles. However, the batteries themselves are not scrapped, and retired batteries can be recycled, screened, and reused in other fields. Typical applications include energy storage, such as wind and solar energy storage, peak shaving and valley filling, backup power supply, and household power regulation.

[0021] Recycling is considered heavy scrapping. Generally, the battery capacity has been severely depleted and cannot be used anymore. The only way to achieve the purpose of recycling is to chemically extract precious metals such as nickel, cobalt, and lithium from the battery.

[0022] Cascade utilization can ease recycling pressure, reduce environmental pollution, improve economic benefits, and help the development of renewable energy.

[0023] (3) Battery Management System

[0024] The battery management system (BMS), commonly known as the battery nanny or battery butler, is mainly used to intelligently manage and maintain battery cells, prevent overcharging and over-discharging of the battery, extend the battery life, and monitor the battery status.

[0025] For example, the battery management system is closely integrated with the power battery of the electric vehicle. The battery voltage, current and temperature are monitored in real time through sensors. It also performs leakage detection, thermal management, battery balancing management, alarm reminders, calculates the remaining capacity (SOC), discharge power, reports the battery degradation degree (SOH) and remaining capacity (SOC) status, and uses algorithms to control the maximum output power according to the battery voltage, current and temperature to obtain the maximum mileage, and uses algorithms to control the charger for the optimal charging current. It communicates in real time with the on-board master controller, motor controller, energy control system, on-board display system, etc. through the CAN bus interface.

[0026] The above-mentioned recycling and step-utilization technologies are mainly about how to fully utilize the battery and make full use of the entire life cycle of the battery, that is, make the best use of it; the battery management system is mainly based on protecting, managing and maintaining the battery, mainly preventing the battery from overcharging and discharging, and extending the battery life as much as possible, which belongs to the maintenance aspect.

[0027] In order to make full use of the battery, IoT products use new technologies to fully use it during a discharge cycle, releasing the power in the battery as much as possible without damaging the battery (i.e. over-discharge). Therefore, they are compatible with the advantages of the above-mentioned recycling and step-by-step utilization technologies, making full use of the battery during the discharge cycle to protect the battery. For places where it is difficult to obtain city electricity or solar power (road manhole monitoring equipment), ternary lithium batteries are used for power supply. Due to the limited battery power, if the battery cannot be fully utilized, the battery working time will be shortened. In order to ensure working stability, it is necessary to charge in time, which means increasing the charging frequency and increasing maintenance costs. In addition, for some long-term working applications, it is particularly important to make full use of the battery.

[0028] After searching for relevant literature, no relevant materials such as papers and patents on segmented use according to the voltage of the battery have been found. The technology of fully using the battery according to the voltage of the battery and increasing the release of the battery is worth further study. Based on this, a battery automatic switching circuit based on voltage detection is designed, which does not require other circuits to assist in segmented voltage use, and fully discharges the battery as much as possible without damaging the battery, prolongs the battery working time, reduces the number of battery charging times, and saves expenses. Summary of the invention

[0029] The technical problem to be solved by the present invention is to provide a battery automatic switching circuit based on voltage detection, which does not require the assistance of other circuits to use segmented voltage, discharges the battery as fully as possible without damaging the battery, and prolongs the battery working time, thereby solving the problems existing in the prior art.

[0030] In order to solve the above technical problems, the technical solution provided by the present invention is: a ternary lithium battery segmented voltage switching circuit, characterized in that: the circuit includes a three-terminal voltage detector D2, a low voltage difference linear regulator D1, an NMOS tube V3 and two groups of PMOS tube pairs V1 and V2, V4 and V5, the three-terminal voltage detector is used to detect the battery voltage, and is divided into two voltage segments for automatic switching.

[0031] When the battery voltage is higher than the threshold, it automatically switches to the low-dropout linear regulator to generate the specified voltage, and the PMOS pair of tubes V1 and V2 are turned on to power the IoT module, while the PMOS pair of tubes V4 and V5 are turned off.

[0032] When the battery voltage is lower than the threshold, the power supply channel is automatically switched: the low voltage difference linear regulator is turned off, the NMOS tube V3 is cut off, the PMOS tube pair V1 and V2 are cut off, and the PMOS tube pair V4 and V5 are directly turned on to power the IoT module.

[0033] Preferably, the two groups of PMOS pairs are connected in series back to back, their sources or drains are connected, and their gates are connected in parallel for composite use.

[0034] Preferably, the three-terminal voltage detector comprises any one of a low-power voltage detector chip and a Schmitt trigger circuit composed of discrete components.

[0035] Preferably, the low power consumption voltage detector chip comprises a standard voltage source, a comparator, a hysteresis circuit and an output driver.

[0036] Preferably, the conduction threshold voltage V TP ≥-3V.

[0037] Preferably, the NMOS tube conduction threshold voltage V TN ≤3V.

[0038] Preferably, an inverter is further connected between the low-power voltage detector chip and the low-voltage dropout linear regulator, and the inverter includes an additionally arranged NMOS tube V6 and three resistors;

[0039] When the battery voltage is higher than the threshold, the low-power voltage detector chip outputs EN at a high level, the NMOS tube V6 is turned on, and the output EN_N is low after the inverter, turning on the low-voltage dropout linear regulator to generate the specified voltage VCCH, the NMOS tube V3 is turned on, the PMOS pair of tubes V1 and V2 are turned on to power the IoT module, and the PMOS pair of tubes V4 and V5 are turned off;

[0040] When the battery voltage is lower than the threshold, the low-power voltage detector chip outputs EN as a low level, the NMOS tube V6 is cut off, and EN outputs EN_N as a high level through the inverter, and automatically switches the power supply channel for the Internet of Things module: turns off the low-voltage difference linear regulator, the NMOS tube V3 is cut off, the PMOS pair of tubes V1 and V2 are cut off, and the PMOS pair of tubes V4 and V5 are turned on.

[0041] Preferably, the three-terminal voltage detector is a low-power voltage detector chip, and a load switch is further connected between the low-power voltage detector chip and the low-voltage dropout linear regulator, and the load switch includes an additionally arranged NMOS tube V6, a PMOS tube V7 and four resistors;

[0042] When the battery voltage is higher than the threshold, the low-power voltage detector chip outputs EN at a high level, the load switch is turned on, the NMOS tube V6 and the PMOS tube V7 are turned on, the low-voltage difference linear regulator is turned on to generate a specified voltage for powering the IoT module, the NMOS tube V3, the PMOS pair of tubes V1 and V2 are turned on, and the PMOS pair of tubes V4 and V5 are turned off;

[0043] When the battery voltage is less than the threshold, the low-power voltage detector chip outputs EN at a low level, the battery voltage output powers the IoT module, the output EN is low, the load switch is cut off, the NMOS tube V6 and PMOS tube V7 are cut off, the NMOS tube V3 is cut off, the PMOS pair of tubes V1 and V2 are cut off, and the PMOS pair of tubes V4 and V5 are turned on.

[0044] Preferably, the threshold is 3.6V.

[0045] Compared with the prior art, the present invention has the following advantages: the circuit adopts low-power discrete components, and when working, both the NMOS tube and the PMOS tube are turned on and the current consumption is in the micro-ampere level; when not working, the NMOS tube and the PMOS tube are turned off, the current consumption is small, and the average power consumption is in the micro-ampere level, which greatly reduces the power consumption of the equipment, uses the segmented voltage as much as possible to fully utilize the battery, prolongs the working time of the battery, and reduces the maintenance cost of the equipment BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 To implement method 1: the battery switching principle block diagram with the LDO enable terminal at a high level;

[0047] Figure 2 To implement method 2: the battery switching principle block diagram with the LDO enable terminal at a low level;

[0048] Figure 3 To implement method 3: the principle block diagram of battery switching without LDO enable end;

[0049] Figure 4 This is a block diagram of the voltage detector composed of discrete components;

[0050] Figure 5 for Figure 4 Voltage detector simulation diagram (I);

[0051] Figure 6 for Figure 4 Voltage detector simulation diagram (II). DETAILED DESCRIPTION

[0052] The present invention is further described in detail below in conjunction with the accompanying drawings. These drawings are all simplified schematic diagrams, which only illustrate the basic circuit structure of the present invention in a schematic manner. There are three implementation methods and the composition of the three-terminal voltage detector, which are specifically as follows.

[0053] Implementation method 1:

[0054] The LDO enable terminal is high level effective battery switching principle block diagram: Figure 1As shown: Component D2 is a three-terminal low-loss voltage detector chip, which consists of a high-precision, low-power standard voltage source, a comparator, a hysteresis circuit, and an output driver. It is manufactured using CMOS technology, thus ensuring low power consumption. The detection voltage range is from 2.2V to 5.0V, and it can be used with external components to detect the specified threshold voltage.

[0055] When the voltage VCC of the ternary lithium battery is greater than 3.6V, the voltage detector output EN is high (the level is VCC), and the LDO module D1 is turned on to output the power supply VCCH = 3.3V.

[0056] The NMOS tube V3 is turned on, and the PMOS pair of tubes V1 and V2 are also turned on, that is, Vout = 3.3V; because EN is at a high level (VCC), the PMOS pair of tubes V4 and V5 are cut off, that is, Vout cannot pass through the drain-source channels of the PMOS pair of tubes V5 and V4 to VCC, which plays a role in preventing backflow.

[0057] As the ternary lithium battery is gradually consumed, when the voltage VCC is less than 3.6V, the voltage detector output EN is low (0V), and the PMOS pair of tubes V4 and V5 are turned on, that is, the VCC voltage is output through the drain-source channel of the PMOS pair of tubes V4 and V5, that is, Vout = VCC; because EN is low, the LDO module is turned off, D1 cannot output the power supply VCCH, the NMOS tube V3 is cut off, and the PMOS pair of tubes V1 and V2 are also cut off, that is, the Vout voltage cannot pass through the drain-source channel of the PMOS tubes V2 and V1 to VCC, which plays a role in preventing backflow.

[0058] With the further consumption of the ternary lithium battery, when the ternary lithium battery is discharged to the cut-off voltage of the protection board (protection voltage), the protection voltage is generally 3.0V~2.75V, the protection board of the ternary lithium battery begins to protect the battery, and the ternary lithium battery no longer releases power further. The remaining power can no longer be discharged and is used for later charging backup. At this time, the ternary lithium battery has been fully utilized.

[0059] PMOS tubes are selected to be power-type, low turn-on voltage (turn-on threshold voltage |VTP|≤3V), and low on-resistance models to meet the requirements of large current and low voltage drop. PMOS pairs packaged together are preferred. PMOS pairs are two transistors of the same type (NPN tube, PNP tube, NMOS tube or PMOS tube) with extremely similar parameters made on the same substrate and packaged in a single chip. The temperatures of the two transistors will affect each other, and the ambient temperature will have the same effect on the two transistors. The noise coefficient, characteristic curve, and amplification factor of the two transistors are required to be as consistent as possible, and the consistency can be within 10%, or even 1%. In this case, by forming a circuit through a specific wiring method, the noise of the transistor itself, the zero drift caused by temperature, and the influence of the common-mode signal on the differential-mode signal can be offset to a considerable extent.

[0060] PMOS pair tubes: Dual PMOS tubes can be connected in series back to back (Back To Back), the sources or drains of the two PMOS tubes are connected, and the gates are connected in parallel for composite use. This can achieve both load switching and backflow prevention functions to achieve physical isolation.

[0061] For NMOS tubes, ordinary switch tubes with low turn-on threshold voltage (such as VTN≤3V) can be used as much as possible.

[0062] For other voltages, the voltage can be detected after being divided by the voltage divider circuit composed of R11 and R13. In the automatic switching circuit of a single-string ternary lithium battery, NC means no welding assembly.

[0063] Implementation method 2:

[0064] The LDO enable terminal is low level effective battery switching principle block diagram: Component D2 is a three-terminal low power voltage detector. It is necessary to insert an inverter (composed of NMOS tube V6, resistors R14, R15, R16) between the voltage detector D2 and the LDO power chip D1. Figure 2 As shown. When the voltage VCC of the ternary lithium battery is greater than 3.6V, the voltage detector outputs EN at a high level (the level is VCC), and the output EN_N is low through an inverter, turning on the LDO module D1 to output the power supply VCCH = 3.3V, the NMOS tube V3 is turned on, and the PMOS pair of tubes V1 and V2 are also turned on, that is, Vout = 3.3V; because EN is at a high level (VCC), the PMOS pair of tubes V4 and V5 are cut off, that is, Vout cannot pass through the drain-source channels of the PMOS pair of tubes V5 and V4 to VCC, which plays a role in preventing backflow.

[0065] As the ternary lithium battery is gradually consumed, when the voltage VCC is less than 3.6V, the voltage detector output EN is low (0V), and the PMOS pair of tubes V4 and V5 are turned on, that is, the VCC voltage is output through the drain-source channel of the PMOS pair of tubes V4 and V5, that is, Vout = VCC; because EN is low, the output EN_N is high after an inverter, the LDO module is turned off, D1 cannot output the power supply VCCH, the NMOS tube V3 is turned off, and the PMOS pair of tubes V1 and V2 are also turned off, that is, the Vout voltage cannot pass through the drain-source channel of the PMOS tubes V2 and V1 to VCCH and VCC, which plays a role in preventing backflow.

[0066] As the ternary lithium battery is further consumed, when the ternary lithium battery is discharged to the protection board cut-off voltage (protection voltage 3.0V ~ 2.75V), the protection board of the ternary lithium battery begins to protect the battery, and the ternary lithium battery no longer releases further power.

[0067] Implementation method three:

[0068] The battery switching principle block diagram of LDO without enable terminal is as follows Figure 3 As shown: Component D2 is a three-terminal low-power voltage detector. A load switch (composed of NMOS tube V6, PMOS tube V7, resistors R14, R15, R16, and R17) needs to be inserted between the voltage detector D2 and the LDO power chip D1. The load switch controls the power supply of VCC>3.6V. Figure 3 As shown. When the voltage VCC of the ternary lithium battery is greater than 3.6V, the voltage detector output EN is high level (level is VCC), the load switch is turned on (NMOS tube V6 and PMOS tube V7 are both turned on), the LDO module D1 output power VCCH = 3.3V, NMOS tube V3 is turned on, and PMOS pair tubes V1 and V2 are also turned on, that is, Vout = 3.3V; because EN is high level (VCC), PMOS pair tubes V4 and V5 are cut off, that is, Vout cannot pass through the drain-source channel of PMOS pair tubes V5 and V4 to VCC, which plays a role in preventing backflow.

[0069] As the ternary lithium battery is gradually consumed, when the voltage VCC is less than 3.6V, the voltage detector output EN is low (0V), and the PMOS pair of tubes V4 and V5 are turned on, that is, the VCC voltage is output through the drain-source channel of the PMOS pair of tubes V4 and V5, that is, Vout = VCC; because EN is low, the load switch is turned off (NMOS tube V6 and PMOS tube V7 are both turned off), the LDO module is turned off, D1 cannot output the power supply VCCH, the NMOS tube V3 is turned off, and the PMOS pair of tubes V1 and V2 are also turned off, that is, the Vout voltage cannot pass through the drain-source channel of the PMOS tubes V2 and V1 to VCCH and VCC, which plays a role in preventing backflow.

[0070] As the ternary lithium battery is further consumed, when the ternary lithium battery is discharged to the protection board cut-off voltage (protection voltage 3.0V ~ 2.75V), the protection board of the ternary lithium battery begins to protect the battery, and the ternary lithium battery no longer releases further power.

[0071] Three-terminal voltage detector:

[0072] In addition to using low-power voltage detector chips, the three-terminal voltage detector can also use discrete components to form a Schmitt trigger circuit. The specific circuit is as follows Figure 4 As shown in the figure, the Schmitt trigger circuit is a circuit often used in level conversion. It is a two-stage positive feedback amplifier circuit coupled by a common emitter resistor. It has two characteristics in performance:

[0073] The input level VT+ (positive threshold voltage, upward threshold) corresponding to the circuit output state transition when the input signal gradually rises from a low level is different from the input level VT- (negative threshold voltage, downward threshold) corresponding to the circuit output state transition when the input signal gradually drops from a high level, that is, VT+≠VT-.

[0074] During the state transition of the circuit, the edge of the output voltage waveform becomes very steep through the internal positive feedback process.

[0075] By utilizing the above two characteristics, the signal waveform with slowly changing edges can be shaped into a rectangular wave with very steep edges, and noise can be effectively eliminated.

[0076] Schmitt trigger circuit Figure 4 As shown, the emitters of two NPN transistors are connected together. The two stable states of the circuit: V1 is saturated and turned on, V2 is cut off, or V1 is cut off, V2 is saturated and turned on. The conversion depends on the size of the input signal (potential trigger). When the input signal level reaches the upward threshold (on-level) and remains greater than the upward threshold VT+, the circuit remains in a certain stable state; if the input signal level drops to the downward threshold (cut-off level) and remains less than the downward threshold VT-, the circuit quickly flips and remains in another state. There is a fixed voltage difference between the downward threshold and the upward threshold, |VT+-VT-|=ΔVT, which is called the hysteresis voltage, that is, hysteresis. Hysteresis can eliminate the detection output disorder caused by the noise of the detected signal or the unstable battery voltage caused by the sudden change of the load. When the NPN tube V2 is saturated and turned on, the low level of the EN output is approximately VCC×R6 / (R6+R4)+VCE(sat)×R4 / (R6+R4), which is not a logic low level close to 0V. General chips also need to add a level conversion circuit at the output end to convert the output low level into a standard logic low level.

[0077] The main function of the Schmitt trigger circuit is to shape the slowly changing input signal into a rectangular pulse with steep edges, so that small interference will not affect the inverter, thus avoiding the occurrence of false operation. The Schmitt trigger uses its hysteresis voltage to improve the anti-interference ability of the circuit. If the conduction level is 5V, then when the input signal fluctuates slightly around 5V, the inverter circuit will continue to operate. By adding a Schmitt trigger, a voltage operation range can be set: for example, the voltage drops to 4.7V to cut off, and it can only be turned on when it rises back to 5V. The hysteresis voltage range is 4.7V~5V.

[0078] Analysis of normal working process: The voltage of Zener diode D1 is 3.0V. Assuming that the threshold voltage of NPN diode VBE(TH)=0.7V, when voltage V1B is low level (0V), V1B-V1E<V1BE(TH)=VF=0.7V, V1 is cut off and V2 is turned on. If V1B gradually increases and reaches V1BE>0.7V, V1 diode is turned on, and through the positive feedback of emitter coupling resistor R1, V1 diode is quickly turned on to saturation, V2 diode is cut off, and EN output is high level VCC. When V1B gradually decreases and reaches V1BE≈0.7V, through the positive feedback of emitter coupling resistor, V1 diode is quickly turned off, V2 diode is saturated, EN output is low level, V1 diode is turned on, V2 diode is cut off. The hysteresis voltage range is difficult to calculate, and generally engineering test data or simplified processing is used.

[0079] Use Multisim14 software to simulate Figure 5 As shown: the voltage regulator D1 model is BZT52H-B3V0, the voltage regulator voltage is 3.0V, VCC (red line, triangle wave signal) starts to step down from 4.2V, when VCC (=4.197V)>3.6V, D1 is turned on, transistor V1 is turned on, transistor V2 is turned off, and EN is high level (4.187V, green line); when VCC (=3.598V)<3.6V, D1 is turned on, V1 is gradually turned off, V2 starts to turn on, EN is low level (0.433V), from Figure 5 It can be seen that when the VCC voltage is slowly decreasing, the Schmitt trigger circuit can shape the VCC voltage signal waveform with slow edge changes into a rectangular wave with very steep edges, and can effectively remove noise. Figure 6 When VCC is around 3.773V, the output signal EN drops very quickly and has a very steep edge.

[0080] The above is only a preferred embodiment of the present invention, and the present invention is not limited to the above embodiment. There may be local minor structural changes during the implementation process. If the various changes or modifications of the present invention do not depart from the spirit and scope of the present invention and fall within the claims of the present invention and the equivalent technical scope, the present invention is also intended to include these changes and modifications.

Claims

1. A ternary lithium battery segmented voltage switching circuit, characterized in that: The circuit includes a three-terminal voltage detector D2, a low voltage drop linear regulator D1, an NMOS tube V3 and two sets of PMOS tube pairs V1 and V2, V4 and V5. The three-terminal voltage detector is used to detect the high and low voltage of the battery, and is divided into two voltage sections for automatic switching. When the battery voltage is higher than the threshold, it automatically switches to the low-dropout linear regulator to generate the specified voltage, and the PMOS pair of tubes V1 and V2 are turned on to power the IoT module, while the PMOS pair of tubes V4 and V5 are turned off. When the battery voltage is lower than the threshold, the power supply channel is automatically switched: the low voltage difference linear regulator is turned off, the NMOS tube V3 is cut off, the PMOS tube pair V1 and V2 are cut off, and the PMOS tube pair V4 and V5 are directly turned on to power the IoT module.

2. The ternary lithium battery segmented voltage switching circuit according to claim 1, characterized in that: The two groups of PMOS tube pairs are connected in series back to back, with their sources or drains connected, and their gates connected in parallel for composite use.

3. The ternary lithium battery segmented voltage switching circuit according to claim 2, characterized in that: The three-terminal voltage detector includes any one of a low-power voltage detector chip and a Schmitt trigger circuit composed of discrete components.

4. The ternary lithium battery segmented voltage switching circuit according to claim 3, characterized in that: The low power consumption voltage detector chip comprises a standard voltage source, a comparator, a hysteresis circuit and an output driver.

5. The ternary lithium battery segmented voltage switching circuit according to claim 1, characterized in that: The PMOS tube conduction threshold voltage V TP ≥-3V.

6. The ternary lithium battery segmented voltage switching circuit according to claim 1, characterized in that: The NMOS tube conduction threshold voltage V TN ≤3V.

7. The ternary lithium battery segmented voltage switching circuit according to claim 3, characterized in that: An inverter is also connected between the low-power voltage detector chip and the low-voltage dropout linear regulator, and the inverter includes an additionally arranged NMOS tube V6 and three resistors; When the battery voltage is higher than the threshold, the low-power voltage detector chip outputs EN at a high level, the NMOS tube V6 is turned on, and the output EN_N is low after the inverter, turning on the low-voltage dropout linear regulator to generate the specified voltage VCCH, the NMOS tube V3 is turned on, the PMOS pair of tubes V1 and V2 are turned on to power the IoT module, and the PMOS pair of tubes V4 and V5 are turned off; When the battery voltage is lower than the threshold, the low-power voltage detector chip outputs EN as a low level, the NMOS tube V6 is cut off, and EN outputs EN_N as a high level through the inverter, and automatically switches the power supply channel for the Internet of Things module: turns off the low-voltage difference linear regulator, the NMOS tube V3 is cut off, the PMOS pair of tubes V1 and V2 are cut off, and the PMOS pair of tubes V4 and V5 are turned on.

8. The ternary lithium battery segmented voltage switching circuit according to claim 3, characterized in that: The three-terminal voltage detector is a low-power voltage detector chip. A load switch is also connected between the low-power voltage detector chip and the low-voltage dropout linear regulator. The load switch includes an additionally arranged NMOS tube V6, a PMOS tube V7 and four resistors. When the battery voltage is higher than the threshold, the low-power voltage detector chip outputs EN at a high level, the load switch is turned on, the NMOS tube V6 and the PMOS tube V7 are turned on, the low-voltage difference linear regulator is turned on to generate a specified voltage for powering the IoT module, the NMOS tube V3, the PMOS pair of tubes V1 and V2 are turned on, and the PMOS pair of tubes V4 and V5 are turned off; When the battery voltage is less than the threshold, the low-power voltage detector chip outputs EN at a low level, the battery voltage output powers the IoT module, the output EN is low, the load switch is cut off, the NMOS tube V6 and PMOS tube V7 are cut off, the NMOS tube V3 is cut off, the PMOS pair of tubes V1 and V2 are cut off, and the PMOS pair of tubes V4 and V5 are turned on.

9. The ternary lithium battery segmented voltage switching circuit according to claims 1-8, characterized in that: The threshold value is 3.6V.

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