A multi-cell lithium battery voltage detection circuit

Abstract

The present invention relates to a multi-cell lithium battery voltage detection circuit, the detection circuit comprises a high-precision comparator, two groups of split capacitors, a control switch and a lithium battery pack, the lithium battery pack is formed by connecting m (m≥2) lithium batteries in series, wherein the lithium battery pack is connected to the positive input end of the high-precision comparator through a group of split capacitors, and the high-precision basic voltage of the circuit content is connected to the negative input end of the high-precision comparator through another group of split capacitors.

Description

Technical Field

[0001] The invention relates to a detection circuit, in particular to a multi-cell lithium battery voltage detection circuit, belonging to the technical field of voltage detection. Background Art

[0002] At present, more and more devices are powered by lithium batteries. Compared with plug-in devices, lithium battery-powered devices greatly improve the portability of devices. However, lithium batteries need to be charged and discharged within a certain voltage range. If the charging voltage is too high or the discharging voltage is too low, it will cause danger. Therefore, it is very important to accurately detect and protect the charging and discharging voltage of lithium batteries. For a single lithium battery, we can directly sample the battery voltage and compare it with a certain reference voltage. If the battery voltage is greater than or equal to a certain reference voltage, we think that the lithium battery is in an overcharged state, and we need to turn off the charging loop of the lithium battery to protect the lithium battery. Similarly, if the lithium battery voltage is less than or equal to another reference voltage, we think that the lithium battery is in an over-discharged state, and we need to turn off the discharge loop of the lithium battery to protect the lithium battery. For the use of multiple lithium batteries in series, we need to detect the voltage of each lithium battery separately and protect them. At this time, how to accurately detect the voltage of each lithium battery in series becomes a difficult problem we need to face. Figure 1 101-104 are respectively lithium battery 1, lithium battery 2, lithium battery 3 and lithium battery 4 connected in series; V1-V4 are the voltages of each series node, wherein V1 is equal to the voltage (Vb1) of lithium battery 1, V2 is equal to the sum of the voltage (Vb1) of lithium battery 1 and the voltage (Vb2) of lithium battery 2, V3 is equal to the sum of the voltage (Vb1) of battery 1, the voltage (Vb2) of lithium battery 2 and the voltage (Vb3) of lithium battery 3, and V4 is equal to the sum of the voltage (Vb1) of battery 1, the voltage (Vb2) of lithium battery 2, the voltage (Vb3) of lithium battery 3 and the voltage (Vb4) of lithium battery 4;

[0003] For the usual lithium battery protection circuit, it is necessary to use complex circuit units to calculate the voltage of each lithium battery, namely:

[0004] Voltage of lithium battery 1: Vb1;

[0005] Voltage of lithium battery 2: Vb2 = V2 - V1;

[0006] Voltage of lithium battery 3: Vb3 = V3 - V2;

[0007] Voltage of lithium battery 4: Vb4 = V4 - V3;

[0008] Then Vb1~Vb4 are respectively sent to the overcharge and over-discharge comparators to be compared with the reference voltage to determine whether the battery is in an unsafe state of overcharge or over-discharge.

[0009] The conventional lithium battery voltage detection method mentioned above has a large circuit scale, high cost, and complex calculation. In the process of voltage processing, voltage errors are introduced, resulting in poor accuracy.

[0010] Based on the above reasons, this patented circuit was invented to simplify the method of lithium battery voltage detection, with low cost and high voltage detection accuracy. Summary of the invention

[0011] The present invention aims at the problems existing in the prior art and provides a multi-cell lithium battery voltage detection circuit. The circuit of the technical solution is extremely simple, requiring only one comparator and two sets of voltage-dividing capacitors, and cooperating with various control switches, the chip area of ​​the circuit is reduced to 20%.

[0012] In order to achieve the above-mentioned purpose, the technical solution of the present invention is as follows: a multi-cell lithium battery voltage detection circuit, the detection circuit includes a high-precision comparator, two sets of splitting capacitors, a control switch and a lithium battery pack, the lithium battery pack is composed of m (m≥2) lithium batteries connected in series, wherein the lithium battery pack is connected to the positive input terminal of the high-precision comparator through a set of splitting capacitors, and the high-precision basic voltage of the circuit content is connected to the negative input terminal of the high-precision comparator through another set of splitting capacitors.

[0013] As an improvement of the present invention, in a lithium battery pack connected in series, each lithium battery is connected in series with a control switch.

[0014] Compared with the prior art, the present invention has the following advantages: 1) The circuit of this technical solution is extremely simple, requiring only one comparator and two sets of voltage-dividing capacitors, and in conjunction with various control switches, the chip area of ​​the circuit is reduced to 20%; 2) The battery voltage sampling of this technical solution is simple and accurate, with the highest accuracy reaching 0.1mV; 3) The battery detection adopts a cyclic scanning working mode, and the overall power consumption current of the circuit can be lower than 5uA. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of a voltage detection circuit in the prior art;

[0016] Figure 2 This is a schematic diagram of a voltage detection circuit of the present invention;

[0017] Figure 3 Schematic diagram of control timing according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to deepen the understanding of the present invention, the present embodiment is described in detail below with reference to the accompanying drawings.

[0019] Example 1: See Figure 1 A multi-cell lithium battery voltage detection circuit, the detection circuit includes a high-precision comparator, two groups of split capacitors, a control switch and a lithium battery pack, the lithium battery pack is composed of m (m≥2) lithium batteries connected in series, wherein the lithium battery pack is connected to the positive input terminal of the high-precision comparator through a group of split capacitors, and the high-precision basic voltage of the circuit content is connected to the negative input terminal of the high-precision comparator through another group of split capacitors. In the series-connected lithium battery pack, each lithium battery is connected in series with a control switch.

[0020] The circuit diagram of the present invention is as follows: Figure 2 As shown, this article takes 4 lithium batteries in series as an example, and it can also be expanded to other numbers of lithium batteries in series. In the figure, V1~V4 are the voltages of each series node, where V1 is equal to the voltage of lithium battery 1 (Vb1), V2 is equal to the sum of the voltage of lithium battery 1 (Vb1) and the voltage of lithium battery 2 (Vb2), V3 is equal to the sum of the voltage of battery 1 (Vb1), the voltage of lithium battery 2 (Vb2) and the voltage of lithium battery 3 (Vb3); V4 is equal to the sum of the voltage of battery 1 (Vb1), the voltage of lithium battery 2 (Vb2), the voltage of battery 3 (Vb3) and the voltage of lithium battery 4 (Vb4); K1~K10 are switch control circuits, and the switch is turned on when the control level is high; C1~C4 are capacitors, and their capacitance values ​​C1=C2=C3=C4; COMP is a high-precision comparator, INP is the positive input terminal of the comparator, INN is the negative input terminal of the comparator, and VOUT is the output of the comparator. Vref1 and Vref2 are high-precision reference voltages inside the circuit, Vref1>Vref2, which serve as comparison thresholds for battery overcharge and overdischarge voltages, respectively.

[0021] The control timing of the control switches K1 to K10 in the circuit is as follows: Figure 3 shown.

[0022] At time t1, the control switches K5, K6, K7, and K8 are all at high level, and the voltages of the nodes VIN, INP, VR, and INN in the circuit are reset to 0 level. After the control switches K5, K6, K7, and K8 are released to low level, the voltages of the nodes in the circuit remain unchanged.

[0023] At time t2, the control switch K1 is set to high level, and the voltage of the VIN node suddenly changes from 0 to V1. The change amount is equal to the voltage of the first lithium battery (Vb1). Since capacitors C1 and C2 are in series for voltage division, the voltage of the INP node is Vb1 / 2. At the same time, the control switch K9 is set to high level, and the voltage of the VR node suddenly changes from 0 to Vref1. Since capacitors C3 and C4 are in series for voltage division, the voltage of the INN node is Vref1 / 2. At this time, the comparator COMP starts to compare the voltages at both ends of INP and INN: Vb1 / 2 and Vref1 / 2. That is, it compares the voltage of the first lithium battery Vb1 with the reference voltage Vref1. If Vb1 > Vref1, the output VOUT of the comparator COMP is high level, indicating that the first lithium battery is in an overcharged state; if Vb1 < Vref1, the output VOUT of the comparator COMP is low level, indicating that the first lithium battery has not reached the overcharged state.

[0024] At time t3, the control switches K7 and K8 are set to high level, and the voltages of the nodes VR and INN in the circuit are both reset to 0 level. After the control switches K7 and K8 are released to low level, the voltages of the nodes VR and INN in the circuit remain unchanged. At time t4, the control switch K10 is set to high level, and the voltage of the VR node suddenly changes from 0 to Vref2. Since capacitors C3 and C4 are in series for voltage division, the voltage of the INN node is Vref2 / 2. At this time, the comparator COMP starts to compare the voltages at both ends of INP and INN: Vb1 / 2 and Vref2 / 2. That is, it compares the voltage of the first lithium battery Vb1 with the reference voltage Vref2. If Vb1 < Vref2, the output VOUT of the comparator COMP is low level, indicating that the first lithium battery is in an overdischarged state; if Vb1 > Vref1, the output VOUT of the comparator COMP is high level, indicating that the first lithium battery has not reached the overdischarged state.

[0025] At time t5, the control switches K6, K7, and K8 are set to high level, and the voltages of the nodes INP, VR, and INN in the circuit are all reset to 0 level. After the control switches K6, K7, and K8 are released to low level, the voltages of the nodes INP, VR, and INN in the circuit remain unchanged.

[0026] At time t6, the control switch K1 has been set to low level, the control switch K2 is set to high level, the voltage of the VIN node changes suddenly from V1 to V2, and the change amount is equal to the voltage of the second lithium battery (Vb2). Since the capacitors C1 and C2 are in series for voltage division, the voltage of the INP node is Vb2 / 2. At the same time, the control switch K9 is set to high level, the voltage of the VR node changes suddenly from 0 to Vref1. Since the capacitors C3 and C4 are in series for voltage division, the voltage of the INN node is Vref1 / 2. At this time, the comparator COMP starts to compare the voltages at both ends of INP and INN: Vb2 / 2 and Vref1 / 2. That is, it compares the voltage Vb2 of the second lithium battery with the reference voltage Vref1. If Vb2 > Vref1, the output VOUT of the comparator COMP is high level, indicating that the second lithium battery is in an overcharged state; if Vb2 < Vref1, the output VOUT of the comparator COMP is low level, indicating that the second lithium battery has not reached the overcharged state.

[0027] At time t7, the control switches K7 and K8 are set to high level, and the voltages of the nodes VR and INN in the circuit are reset to 0 level. After the control switches K7 and K8 are released to low level, the voltages of the nodes VR and INN in the circuit remain unchanged. At time t8, the control switch K10 is set to high level, the voltage of the VR node changes suddenly from 0 to Vref2. Since the capacitors C3 and C4 are in series for voltage division, the voltage of the INN node is Vref2 / 2. At this time, the comparator COMP starts to compare the voltages at both ends of INP and INN: Vb2 / 2 and Vref2 / 2. That is, it compares the voltage Vb2 of the second lithium battery with the reference voltage Vref2. If Vb2 < Vref2, the output VOUT of the comparator COMP is low level, indicating that the second lithium battery is in an overdischarged state; if Vb2 > Vref1, the output VOUT of the comparator COMP is high level, indicating that the second lithium battery has not reached the overdischarged state.

[0028] Using the same method, it is possible to detect whether the third and fourth lithium batteries are in an overcharged state or an overdischarged state. After detecting the last lithium battery, the circuit will return to the state at time t1 and start to detect the safety state of the first lithium battery. In this way, it scans cyclically and monitors the safety state of each lithium battery in the series battery pack at all times.

[0029] It should be noted that the above embodiments are not used to limit the protection scope of the present invention. Equivalent transformations or substitutions made on the basis of the above technical solutions all fall within the protection scope of the claims of the present invention.

Claims

1. A detection method using a multi - section lithium - battery voltage detection circuit, characterized in that, The detection circuit includes: One ends of control switches K1 - K4 are respectively and correspondingly connected to the output ends of the first - section lithium battery, the second - section lithium battery, the third - section lithium battery, and the fourth - section lithium battery. The other ends of control switches K1 - K4 are short - circuited and then commonly connected to the VIN terminal of capacitor C1 together with one end of control switch K5; The INP terminal of capacitor C1 is connected to one end of capacitor C2, one end of control switch K6, and the positive input terminal of comparator COMP; The other ends of control switches K5, capacitor C2, and control switch K6 are all grounded; One end of control switch K9 is connected to reference voltage Vref1, One end of control switch K10 is connected to reference voltage Vref2. The other ends of K9 and K10 are short - circuited and then commonly connected to the VR terminal of capacitor C3 together with one end of control switch K7. The INN terminal of capacitor C3 is connected to one end of capacitor C4, one end of control switch K8, and the negative input terminal of comparator COMP; The other ends of control switches K7, capacitor C4, and control switch K8 are all grounded; The output of comparator COMP is VOUT; The capacitance values of capacitors C1 - C4 are equal, The specific detection method includes: At time t1, control switches K5, K6, K7, and K8 are all at high level, and the voltages of nodes VIN, INP, VR, and INN in the circuit are all reset to 0 level. After control switches K5, K6, K7, and K8 are released to low level, the voltages of each node in the circuit remain unchanged; At time t2, control switch K1 is set to high level, and the voltage of node VIN suddenly changes from 0 to V1, and the change amount is equal to the voltage Vb1 of the first - section lithium battery. Because capacitors C1 and C2 are in series for voltage division, the voltage of node INP is Vb1 / 2; At the same time, control switch K9 is set to high level, and the voltage of node VR suddenly changes from 0 to Vref1. Because capacitors C3 and C4 are in series for voltage division, the voltage of node INN is Vref1 / 2. At this time, comparator COMP starts to compare the voltages of the positive input terminal and the negative input terminal: Vb1 / 2, Vref1 / 2; That is, compare the voltage Vb1 of the first - section lithium battery with reference voltage Vref1. If Vb1 > Vref1, the output VOUT of comparator COMP is at high level, indicating that the first - section lithium battery is in an over - charged state; If Vb1 < Vref1, the output VOUT of comparator COMP is at low level, indicating that the first - section lithium battery has not reached the over - charged state; At time t3, the control switch K9 has been set to low level, the control switches K7 and K8 are set to high level, and the voltages of the nodes VR and INN in the circuit are both reset to 0 level. After the control switches K7 and K8 are released to low level, the voltages of the nodes VR and INN in the circuit remain unchanged; At time t4, the control switches K7 and K8 have been set to low level, the control switch K10 is set to high level, and the voltage of the VR node suddenly changes from 0 to Vref2. Because the capacitors C3 and C4 are in series for voltage division, the voltage of the INN node is Vref2 / 2; At this time, the comparator COMP starts to compare the voltages of the positive input terminal and the negative input terminal: Vb1 / 2, Vref2 / 2; That is, it compares the voltage Vb1 of the first lithium battery with the reference voltage Vref2. If Vb1 < Vref2, the output VOUT of the comparator COMP is low level, indicating that the first lithium battery is in an over-discharged state; If Vb1 > Vref2, the output VOUT of the comparator COMP is high level, indicating that the first lithium battery has not reached the over-discharged state; At time t5, the control switches K1 and K10 have been set to low level, the control switches K6, K7 and K8 are set to high level, and the voltages of the nodes INP, VR and INN in the circuit are all reset to 0 level. After the control switches K6, K7 and K8 are released to low level, the voltages of the nodes INP, VR and INN in the circuit remain unchanged; At time t6, the control switch K1 has been set to low level, the control switch K2 is set to high level, and the voltage of the VIN node suddenly changes from V1 to V2, and the change amount is equal to the voltage Vb2 of the second lithium battery. Because the capacitors C1 and C2 are in series for voltage division, the voltage of the INP node is Vb2 / 2; At the same time, the control switch K9 is set to high level, the voltage of the VR node suddenly changes from 0 to Vref1, and because the capacitors C3 and C4 are in series for voltage division, the voltage of the INN node is Vref1 / 2. At this time, the comparator COMP starts to compare the voltages of the positive input terminal and the negative input terminal: Vb2 / 2, Vref1 / 2; That is, it compares the voltage Vb2 of the second lithium battery with the reference voltage Vref1. If Vb2 > Vref1, the output VOUT of the comparator COMP is high level, indicating that the second lithium battery is in an over-charged state; If Vb2 < Vref1, the output VOUT of the comparator COMP is low level, indicating that the second lithium battery has not reached the over-charged state; At time t7, the control switch K9 has been set to low level, the control switches K7 and K8 are set to high level, and the voltages of the nodes VR and INN in the circuit are reset to 0 level. After the control switches K7 and K8 are released to low level, the voltages of the nodes VR and INN in the circuit remain unchanged. At time t8, the control switches K7 and K8 have been set to low level, the control switch K10 is set to high level, and the voltage of the VR node suddenly changes from 0 to Vref2. Due to the series voltage division of capacitors C3 and C4, the voltage of the INN node is Vref2 / 2. At this time, the comparator COMP starts to compare the voltages of the positive input terminal and the negative input terminal: Vb2 / 2 and Vref2 / 2; that is, it compares the voltage of the second lithium battery Vb2 with the reference voltage Vref2. If Vb2 < Vref2, the output VOUT of the comparator COMP is low level, indicating that the second lithium battery is in an over-discharged state; if Vb2 > Vref2, the output VOUT of the comparator COMP is high level, indicating that the second lithium battery has not reached the over-discharged state.

Images