CN201215817Y - Protective circuit for lithium battery - Google Patents

Abstract

The utility model relates to a lithium battery protection circuit, the purpose of which is to provide a lithium battery protection circuit manufactured by a low-voltage process and applicable to various charging voltage values. Control tube, over-discharge control tube and protection IC. The over-charge control tube and over-discharge control tube are monitored and controlled by the protection IC. The protection IC is a CMOS integrated circuit block, including an over-charge protection circuit and an over-discharge protection circuit. And overcurrent protection circuit, in the protection IC, there is a clamping circuit between the output negative pole V- and the gate of the MOS transistor connected to the output negative pole V-, when the voltage of the output negative pole V- changes in a wide range , the clamping circuit bears most of the negative voltage, so that the gate withstand voltage of the MOS transistor is limited within -2.5V, and does not affect the functions of the overcharge protection circuit, overdischarge protection circuit and overcurrent protection circuit.

Description

A lithium battery protection circuit

technical field

The utility model relates to a semiconductor integrated circuit, in particular to a protection circuit of a lithium ion battery.

Background technique

Generally speaking, a lithium-ion battery consists of three parts: 1. Lithium-ion battery cell 2. Protection circuit (PCM) 3. Shell. The negative electrode of the lithium-ion cell is graphite crystal, and the positive electrode is usually lithium dioxide. When charging, lithium ions move from the positive electrode to the negative electrode and are embedded in the graphite layer. During discharge, lithium ions detach from the surface of the negative electrode in the graphite crystal and move to the positive electrode. Therefore, during the charging and discharging process of the battery, lithium always appears in the form of lithium ions, not in the form of metallic lithium. Therefore, this battery is called a lithium-ion battery, or lithium battery for short. Lithium batteries have the advantages of small size, large capacity, light weight, no pollution, high single-cell voltage, low self-discharge rate, and many battery cycles. There are certain requirements for charging and discharging lithium batteries. According to the structural characteristics of lithium batteries, The maximum charging termination voltage should be 4.2V, and it should not be overcharged, otherwise the battery will be scrapped due to the removal of too much lithium ions from the positive electrode. Due to the internal structure of the lithium battery, the lithium ions cannot all move to the positive electrode during discharge, and a part of the lithium ions must be kept at the negative electrode to ensure that the lithium ions can be inserted into the channel smoothly during the next charge. Otherwise, battery life is shortened accordingly. In order to ensure that some lithium ions remain in the graphite layer after discharge, it is necessary to strictly limit the minimum discharge termination voltage, that is to say, the lithium battery cannot be over-discharged. In order to meet the charging and discharging requirements of lithium-ion batteries, lithium batteries are equipped with protection circuits to control the external charging and discharging current.

As shown in Figure 1, the existing lithium battery protection circuit is generally composed of two FETs and a protection integrated block. The overcharge control tube M1 and the over-discharge control tube M2 are connected in series in the circuit, and the battery voltage is monitored and controlled by the protection IC. , The protection integrated block includes an overcharge protection circuit, an overdischarge protection circuit and an overcurrent protection circuit. The protection IC detects the battery voltage. When the battery voltage rises to the battery overcharge point (assumed to be 4.2V), the overcharge protection is activated, and the overcharge protection tube M1 is cut off to stop charging. When the battery is in the discharge state, the protection IC detects the battery voltage, and when the battery voltage drops to its over-discharge voltage detection point (assumed to be 2.55V), the over-discharge protection is activated, the over-discharge control tube M2 is cut off, and the power supply to the load is stopped. The over-discharge protection function can only be released when the battery is connected to the charger and the lithium battery voltage is higher than the over-discharge voltage. Overcurrent protection is to control M2 to cut off when a large current flows through the load, and stop discharging to the load. The purpose is to protect the battery and FET. Overcurrent detection uses the conduction resistance of the FET as a detection resistor to monitor its voltage drop, and stops discharging when the voltage drop exceeds the set value.

When chargers with different voltage specifications are used to charge the lithium battery, the protection IC will be loaded to different voltage ranges at the VDD-V- terminal. If a high-voltage charger is used to charge the battery, the V- pin of the protection IC will have a relatively high negative voltage after the battery is fully charged. If the MOSFET transistor inside the protection IC is designed according to the low-voltage (5V and below) The withstand voltage value is not enough. The usual design is to use a high-voltage tube for the MOS connected to the V-pin inside the protection IC. In this way, the ordinary 5V and below 5V CMOS process cannot be used to produce the protection IC, but a higher withstand voltage process must be used to increase the voltage. Big cost. That is, the withstand voltage value of the protection IC at the VDD-V- terminal limits the use range of lithium batteries in chargers of different specifications. If the protection IC designed according to the low-voltage process can withstand a voltage higher than 12V or above at the VDD-V- terminal, Its application range will expand, making the cost of lithium batteries lower.

Contents of the invention

The purpose of this utility model is to overcome the defect of prior art, provide a kind of lithium battery protection circuit, this circuit adopts the CMOS integrated circuit block that low voltage (5V and below 5V) process manufactures, and its VDD-V- terminal has more than 18V Withstand voltage, the circuit can be used in both 5V withstand voltage and high voltage, which reduces the manufacturing cost of the lithium battery.

The technical solution for realizing the above-mentioned invention is: a lithium battery protection circuit, which is composed of an overcharge control tube, an over-discharge control tube and a protection IC (that is, a protection integrated block), and the over-charge control tube and the over-discharge control tube are composed of The protection IC monitors the battery voltage and controls it. The protection IC is a CMOS integrated circuit block, which includes an overcharge protection circuit, an overdischarge protection circuit and an overcurrent protection circuit. In the protection IC, the output negative pole and the output negative pole are connected There is a clamping circuit between the gates of the MOS transistors. When the voltage of the output negative electrode changes in a large range, the clamping circuit bears most of the negative voltage, so that the gate voltage of the MOS transistor is limited within -3V , and does not affect the functions of the overcharge protection circuit, overdischarge protection circuit and overcurrent protection circuit.

The functions of the above clamping circuit can be realized in various structural forms.

As a specific implementation of the clamp circuit, the circuit is composed of a control circuit and a voltage divider circuit, the control circuit and the voltage divider circuit are connected in series; the control circuit controls the opening of the clamp circuit according to the voltage of the output negative pole, and the voltage divider circuit is used to bear pressure.

The utility model adds a clamping circuit between the output negative electrode of the protection IC and the gate of the internal MOS transistor, the gate of the MOS transistor is connected to the voltage control point of the clamping circuit, and the clamping circuit controls the voltage of the voltage control point Within -2.5V, the gate of the MOS transistor does not need to withstand high voltage, which solves the problem of insufficient withstand voltage of the gate of the MOSFET transistor that protects the IC output negative V-, so that it is produced by ordinary 5V and CMOS processes below 5V The resulting protection IC can be used for protection when lithium batteries are charged with chargers of different voltage specifications.

Description of drawings

Fig. 1 is the utility model background technology circuit diagram

Fig. 2 is the circuit diagram of the utility model

Fig. 3 is the circuit structure diagram of the utility model embodiment 1

Fig. 4 is the clamping circuit diagram of the utility model embodiment 2

Fig. 5 is the computer simulation figure of the utility model embodiment 1

Detailed ways

Further description will be made below in conjunction with the accompanying drawings.

Example 1

A lithium battery protection circuit 1, consisting of an overcharge control tube M1, an over-discharge control tube M2 and a protection IC1, the over-charge control tube M1 and the over-discharge control tube M2 are connected in series in the circuit, the over-charge control tube M1 and the over-discharge control tube M2 monitors the battery voltage and controls it by the protection IC1. The protection IC1 is a CMOS integrated circuit block, including an overcharge control circuit 2 , an overdischarge control circuit 3 , an overcurrent protection circuit 4 and a logic control circuit 5 . A clamping circuit 6 is provided between the output negative pole V- and the gate of the MOS transistor connected to the output negative pole V-. When the voltage of the output negative pole V- changes within a wide range, the clamping circuit bears most of the Negative pressure, so that the gate withstand voltage of the MOS transistor in the overcurrent protection circuit 4 is limited within -3V, and does not affect the overcharge protection circuit, overdischarge protection circuit, overcurrent protection circuit and logic control circuit in the protection IC function.

As shown in Figure 3, a clamping circuit 6 is provided between the gates of the MOS transistors P3 and N2 in the overcurrent protection circuit 4 and the output negative pole V-, and the gates of the MOS transistors P3 and N2 in the overcurrent protection circuit 4 are connected to The voltage control point B of the clamping circuit 6 is connected.

The clamp circuit 6 is composed of a control circuit 61 and a voltage divider circuit 62, and the control circuit 61 and the voltage divider circuit 62 are connected in series, wherein the control circuit 61 is composed of a constant current source I1, a first NMOS transistor N1, a second NMOS transistor N3, and a PNP transistor Q1 is composed of the first PMOS transistor P1 and the second PMOS transistor P2, and the voltage dividing circuit 62 is a resistor R1. The gate-drain of the first NMOS transistor N1, the first PMOS transistor P1, and the second PMOS transistor P2 are short-circuited, the collector-base of the PNP transistor Q1 is short-circuited, one end of the constant current source I1 is connected to the power supply, and the other end A is connected to N3 The gate is connected to the gate-drain of the first NMOS transistor, the source of the first NMOS transistor is connected to the emitter of the PNP transistor Q1, the base collector of the PNP transistor Q1 is grounded, and the drain of the second NMOS transistor N3 is connected to the power supply. The source of the second NMOS transistor N3 is connected to the source of the first PMOS transistor P1, the drain of the first PMOS transistor P1 is connected to the source of P2, the drain of P2 is connected to one end B of the resistor R1, and the other end of the resistor R1 Connect to output negative pole V- terminal.

The principle of the clamping circuit 6 is: the first NMOS transistor is a diode-connected NMOS, and the PNP transistor Q1 is a diode-connected PNP transistor. A constant current source I1 is connected from the power supply to point A, because the current is constant, and point A The fixed voltage is a reference voltage, approximately equal to 1.4V.

VA=Vbe_Q1+Vgs_N1, VA is the voltage value at point A, Vbe_Q1 is the BE junction voltage of Q1, and Vgs_N1 is the Vgs voltage of the first NMOS transistor.

When there is no negative voltage at the V- terminal, it is generally greater than 0V. Assuming V->0V, from the power supply VDD, N3, P1, P2, R1 to the V- terminal, there is no current flowing at this time, no path is formed, and the work of the original circuit is not affected.

Since V->0V, then

VA—V-<1.4V<|VthP1|+|VthP2|+|VthN3|,

Here, VthP1, VthP2, and VthN3 are the turn-on voltages of P1, P2, and N3, respectively.

When a negative voltage appears at the V- terminal, and VA—V->|VthP5|+|VthP6|+|VthN3|,

The branch from the power supply VDD, N3, P1, P2, R1 to the V- terminal will be turned on, the voltage drop across R1 VR1=I×R1, due to the large resistance of R1, the current flowing through the branch

I=[VA—(Vgs_N3+Vgs_P1+Vgs_P2)—V-]/R1

(Vgs_N3+Vgs_P1+Vgs_P2) Compared with the voltage drop across the resistor R1, VR1 is a weak function of the current. In other words, once the branch is turned on, the condition VA—V->|VthP1|+|VthP2 is satisfied |+|VthN3|, most of the V- voltage change will fall on both ends of R1, then the voltage at point B will not change greatly due to the V- voltage change, and it will be limited within a certain negative voltage range, which solves the problem The Vgs of N2 and P3 in the current protection circuit cannot withstand negative high voltage.

Moreover, with this circuit structure, when the power supply VDD and the output negative V- terminal are connected to the charger, there will be no current from VDD→lithium battery→GND→V-, which can ensure that there will be no charging after the overcharge voltage protection Current flows through the battery.

Referring to the computer simulation results in Fig. 5, the X-axis is the V-terminal voltage, and the Y-axis is the voltage at point B in Fig. 3, and point B is connected to the gate of the internal circuit MOSFET. It can be seen that when the V- voltage changes between -25----0V, the voltage at point B only changes between about 2.5V----0V. So the gate of the internal MOSFET is not subjected to negative high voltage. This solves the technical problem that the gate of the MOSFET in the 5V CMOS process cannot withstand the negative 18V high voltage at the V- terminal.

Example 2

This embodiment is another structure of the clamping circuit.

As shown in FIG. 4 , there is a clamping circuit 7 between the gates of the transistors N2 and P3 in the overcurrent protection circuit 4 and the output negative pole V-. The clamping circuit 7 is composed of a control circuit 71 and a voltage dividing circuit 72, and the control circuit 71 and the voltage dividing circuit 72 are connected in series. The control circuit 71 is composed of the first to tenth PNP transistors Q0, Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, and the voltage divider circuit 72 is a resistor R1. The collectors and bases of the first PNP transistor to the tenth PNP transistor Q0-Q9 are respectively short-circuited to form a diode, and then connected in series, the emitter of the first PNP transistor Q0 is connected to the power supply, and the emitter of the tenth PNP transistor Q9 The collector is connected to one end B of the resistor R1, and B is connected to the gates of the transistors N2 and P3 in the overcurrent protection circuit 4, and the other end of the resistor is connected to the output negative pole V-.

The working principle of the clamping circuit 7 is: when there is no negative voltage at the V- terminal, it is generally greater than 0V. Assuming the power supply voltage = 4.2V, V->0V, from the power supply Q0-Q9, R1 to the V-terminal, there is no current flowing at this time, no path is formed, and the work of the original circuit is not affected.

When a negative voltage appears at the V-terminal, and VDD—V->10×Vbe_Q0, where Vbe_Q0 is the forward conduction voltage of the diode, the branch from the power supply Q0—Q9, R1 to the V-terminal is turned on, and current flows the slip. Thus the voltage at point B is clamped at:

VDD—10×Vbe_Q0=4.2-10×0.7=-2.8V, assuming Vbe_Q0=0.7V

Therefore, the gates of the transistors N2 and P3 in the overcurrent protection circuit 4 bear a negative voltage of -2.8V at most, and the excess voltage is borne by the resistor. This method can also solve the withstand voltage problem of the transistors N2 and P3 in the overcurrent protection circuit 4 .

Claims (5)

1. A lithium battery protection circuit, consisting of an overcharge control tube, an over-discharge control tube and a protection IC. The over-charge control tube and the over-discharge control tube are monitored and controlled by a protection IC. The protection IC is A CMOS integrated circuit block, which includes an overcharge protection circuit, an overdischarge protection circuit and an overcurrent protection circuit, is characterized in that, in the protection IC, the output negative pole (V-) and the MOS connected to the output negative pole (V-) There is a clamping circuit between the gates of the transistors. When the voltage of the output negative electrode (V-) changes in a large range, the clamping circuit bears most of the negative voltage, so that the voltage borne by the gate of the MOS transistor is limited to -3V, and does not affect the functions of the overcharge protection circuit, overdischarge protection circuit and overcurrent protection circuit. 2. The lithium battery protection circuit according to claim 1, wherein the clamping circuit is arranged between the output negative pole (V-) and the gate of the MOS transistor of the overcurrent protection circuit. 3. The lithium battery protection circuit according to claim 1, wherein the clamping circuit is composed of a control circuit and a voltage divider circuit in series; the control circuit controls the opening of the clamping circuit according to the voltage of the output negative pole (V-) , The voltage divider circuit is used to withstand negative pressure. 4. The lithium battery protection circuit according to claim 3, characterized in that the control circuit (61) consists of a constant current source (I1), a first NMOS transistor (N1), a second NMOS transistor (N3), a PNP Transistor (Q1), the first PMOS transistor (P1), the second PMOS transistor (P2), the voltage divider circuit (62) is a resistor (R1); the first NMOS transistor (N1), the first PMOS transistor (P1), The gate-drain of the second PMOS transistor (P2) is short-circuited, the collector-base of the PNP transistor (Q1) is short-circuited, one end of the constant current source (I1) is connected to the power supply, and the other end (A) is connected to the second NMOS transistor (N3) ) is connected to the gate-drain of the first NMOS transistor (N1), the source of the first NMOS transistor (N1) is connected to the emitter of the PNP transistor (Q1), and the base collector of the PNP transistor (Q1) is grounded , the drain of the second NMOS transistor (N3) is connected to the power supply, the source of the second NMOS transistor (N3) is connected to the source of the first PMOS transistor (P1), and the drain of the first PMOS transistor (P1) is connected to the second The source of the PMOS transistor (P2) is connected, the drain of the second PMOS transistor (P2) is connected to one end (B) of the resistor (R1), and the other end of the resistor (R1) is connected to the output negative electrode (V-). 5. The lithium battery protection circuit according to claim 3, characterized in that the control circuit (71) consists of the first PNP transistor to the tenth PNP transistor (Q0, Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9), the voltage divider circuit (72) is a resistor (R1); the first PNP transistor to the tenth PNP transistor (Q0, Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9) Short-circuit the respective collectors and bases, connect them in the form of diodes, and then connect them in series. The emitter of the first PNP transistor (Q0) is connected to the power supply, and the collector of the tenth PNP transistor (Q9) is connected to the resistor (R1). One end (B), the other end of the resistor (R1) is connected to the output negative pole (V-).

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