CN107482722B - Constant current charger circuit - Google Patents
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- CN107482722B CN107482722B CN201710739758.0A CN201710739758A CN107482722B CN 107482722 B CN107482722 B CN 107482722B CN 201710739758 A CN201710739758 A CN 201710739758A CN 107482722 B CN107482722 B CN 107482722B
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- 238000007600 charging Methods 0.000 claims abstract description 90
- 238000005070 sampling Methods 0.000 claims abstract description 68
- 239000003990 capacitor Substances 0.000 claims abstract description 66
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 30
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 30
- 238000006243 chemical reaction Methods 0.000 claims abstract description 29
- 238000010277 constant-current charging Methods 0.000 claims abstract description 23
- 230000001105 regulatory effect Effects 0.000 claims description 15
- 238000000034 method Methods 0.000 abstract description 7
- 238000010586 diagram Methods 0.000 description 11
- 230000001276 controlling effect Effects 0.000 description 4
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000003071 parasitic effect Effects 0.000 description 2
- 230000003321 amplification Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000003199 nucleic acid amplification method Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
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Abstract
The invention discloses a constant current charger circuit, which mainly solves the problems of charging current precision and circuit stability caused by offset voltage in the lithium battery charging process.The invention comprises the following steps: the sampling unit (2) samples the charging unit (1) to obtain a sampling current signal IBFETH(ii) a The switched capacitor circuit unit (3), the voltage compensation unit (4) and the signal conversion unit (5) form negative feedback and are used for ensuring sampling precision. Sampling current signal IBFETHThe sampling voltage is converted by a signal conversion unit (5) and output to a charging current regulation unit (6). The charging current adjusting unit (6) obtains a charging current adjusting signal according to the sampling voltage and feeds the charging current adjusting signal back to the charging unit (1) for controlling and adjusting the magnitude of the constant current charging current. The digital control unit (7) is used for switching the working state of the switched capacitor circuit unit (3) so as to eliminate the influence of offset voltage of the operational amplifier. The invention can keep the charging current accurate and stable under different offset voltages, and can be used for a lithium battery charger.
Description
Technical Field
The invention belongs to the technical field of electronic circuits, and particularly relates to a high-precision high-stability constant-current charging circuit which can be used in a single lithium battery charger.
Background
With the popularity of cell phones, tablets, wearable electronic devices, power management for these mobile electronic devices is becoming increasingly important. Lithium batteries are widely used in mobile electronic devices due to their advantages of high operating voltage, long life, and the like. However, according to the chemical characteristics of lithium batteries, the most popular charging method at present is a three-stage charging method: trickle charge, constant current charge, constant voltage charge. Wherein constant current charging occupies the main process of charging lithium batteries.
Fig. 1 is a schematic diagram of a conventional constant current charging circuit for a lithium battery. Wherein SYS is the stable output of a DC-DC (direct current-direct current) voltage regulatorIn the constant current charging phase, the SYS voltage is always higher than the battery voltage by △ V1(△ V1)>0V), the N1 pipe is the power tube of lithium battery charger, and the S1 pipe is the sampling pipe. BAT is the lithium cell that needs to charge, and R1 is the zero temperature high accuracy resistance of external connection, and REF is the reference level, and PUMPC is the output of charge pump. The constant-current charging principle is that the gate, drain and substrate voltages of the sampling tube S1 and the power tube N1 are respectively equal, and the source end voltages of S1 and N1 are also equal through the deep negative feedback of the operational amplifier. In the case of equal voltages at four terminals, the sampling ratio is only related to the width-to-length ratio of the MOS transistor. Sampling the current IBFETHThe sampled voltage is generated by flowing through the resistor R1, and compared with the reference voltage to adjust the gate voltage PUMP of the power tube, thereby controlling the charging current at a constant value.
Due to design and process reasons, offset voltage (offset) exists in the operational amplifier a1, which may cause an error in the sampling current and further cause a deviation in the constant current charging current. The offset current is:
from this equation, it can be seen that the offset voltage (offset) error is amplified by (V)PUMP-VBAT-VTH) Multiple (V)PUMP-VBAT-VTH) Is the overdrive voltage of the power transistor N1, which means that the current deviation is larger when the preset charging current is larger. At this time, the current is easy to exceed the regulation range of the constant current charging loop, and the constant current charging function is invalid. Nowadays, with the increasing of battery capacity and the strict requirement of users for charging time, the constant current charging current will increase continuously, which means that the problem of circuit stability caused by offset voltage will be amplified continuously.
Disclosure of Invention
The invention aims to provide a constant current charger circuit with high precision and high stability aiming at the defects of the prior art, and the constant current charger circuit can eliminate offset voltage (offset) of operational amplifier and reduce current sampling error by using a switched capacitor technology, so that a lithium battery charger can still keep accurate charging current during large-current constant current charging, and a charging loop is stable.
In order to achieve the above object, a constant current charger circuit according to the present invention includes: charging unit 1, sampling unit 2, signal conversion unit 5, charging current regulating unit 6, digital control unit 7, its characterized in that includes: a switched capacitor circuit unit 3, a voltage compensation unit 4;
the charging unit 1 is used for carrying out constant current charging on the lithium battery; the charging current regulation circuit is provided with two paths of inputs, wherein a first input end is connected to the output voltage SYS of a preceding-stage DC-DC (direct current-direct current) converter, and a second input end is connected to the output of the charging current regulation unit 6; the output end is connected to the anode voltage BAT of the lithium battery to be charged;
the sampling unit 2 is provided with two paths of inputs and is used for sampling the charging current in proportion; a first input terminal connected to a DC-DC (direct current-direct current) converter output voltage SYS, a second input terminal connected to an input terminal of the charging unit 1; the output end BFETH outputs a sampling current signal IBFETH；
The switched capacitor circuit unit 3 is provided with four inputs, a first input end is connected to an anode voltage BAT of a lithium battery to be charged, a second input end is connected to an output end BFETH of the sampling unit 2, a third input end is connected to a logic control signal P1 output by the digital control unit 7, and a fourth input end is connected to a logic control signal P1X output by the digital control unit 7; the output end of the voltage compensation unit is connected to the input end of the voltage compensation unit 4;
the output end of the voltage compensation unit 4 is connected to the first input end of the signal conversion unit 5, and the voltage compensation unit is used for compensating the output voltage of the switched capacitor circuit unit 3 and reducing the sampling precision error;
the signal conversion unit 5 is provided with two paths of inputs, and the second input end of the signal conversion unit is connected with the sampling current signal IBFETH(ii) a The switched capacitor circuit unit 3, the voltage compensation unit 4 and the signal conversion unit 5 form a feedback loop for ensuring that the sampling unit 2 can accurately sample the charging current in proportion; the output end is connected to the first input end of the charging current regulating unit 6;
the charging current adjusting unit 6 is provided with two paths of inputs, the second input end of the charging current adjusting unit is connected with the reference voltage REF, and the output end of the charging current adjusting unit is connected with the input end of the signal sampling unit 2 and the input end of the charging unit 1, so that the charging current is adjusted and is ensured to be constant;
the digital control unit 7 is configured to generate two logic control signals P1 and P1X, where a first logic control signal P1 controls ganged switches S1 to S6 in the switched capacitor circuit unit 3, and a second logic control signal P1X controls ganged switches S7 to S12 in the switched capacitor circuit unit 3.
The charging unit 1 is composed of a first transistor MN1, the first transistor MN1 has a gate connected to the output terminal of the charging current regulating unit 6, a source connected to the anode voltage BAT of the lithium battery, and a drain connected to the output voltage SYS of the preceding DC-DC converter, where SYS is VBAT + △ V1(△ V1> 0V).
The sampling unit 2 is composed of a second transistor MN2, the size of the sampling unit is completely the same as that of an NMOS transistor composing a first transistor MN1, and the number ratio is 1: N; the drain terminal of the second transistor MN2 is connected with the drain terminal of the first transistor MN1, the gate terminal of the second transistor MN2 is connected with the gate terminal of the first transistor MN1, the source terminal of the second transistor MN2 is used as the output terminal BFETH of the sampling unit 2, and a sampling current signal I is outputBFETH。
The switched capacitor circuit unit 3 includes a first operational amplifier a1, a second operational amplifier a2, a first capacitor C1, a second capacitor C2, and 12 ganged switches S1 to S12:
the first linkage switch S1 is connected with the output end BFETH of the sampling unit 2 and the upper pole plate of the first capacitor C1, and the lower pole plate of the first capacitor C1 is connected with the reverse input end of the first operational amplifier A1;
the second linkage switch S2 is connected with the anode voltage BAT of the lithium battery and the positive input end of the first operational amplifier A1;
the third linkage switch S3 connects the output end of the first operational amplifier a1 and the input end a of the voltage compensation unit 4;
the fourth ganged switch S4 is connected across the inverting input and the output of the second operational amplifier A2;
the fifth linkage switch S5 is connected with the upper plate of the second capacitor C2 and the positive input end of the second operational amplifier A2;
the sixth ganged switch S6 is connected with the positive input end of the second operational amplifier A2 and the input end A of the voltage compensation unit 4;
the seventh ganged switch S7 is connected across the inverting input and output of the first operational amplifier A1;
the eighth ganged switch S8 is connected with the upper plate of the first capacitor C1 and the positive input end of the first operational amplifier A1;
the ninth ganged switch S9 is connected with the positive input end of the first operational amplifier A1 and the input end A of the voltage compensation unit 4;
the tenth gang switch S10 is connected to the output end BFETH of the sampling unit 2 and the upper plate of the second capacitor C2, and the lower plate of the second capacitor C2 is connected to the inverting input end of the second operational amplifier a 2;
the eleventh gang switch S11 is connected with the anode voltage BAT of the lithium battery and the positive input end of the second operational amplifier A2;
the twelfth ganged switch S12 connects the output terminal of the second operational amplifier a2 and the input terminal a of the voltage compensation unit 4.
The voltage compensation unit 4 includes a third transistor MN3 and a constant current source I1;
a gate terminal of the third transistor MN3 is used as an input terminal of the voltage compensation unit 4, a drain terminal is connected to the power supply voltage VCC, and a source terminal is used as an output terminal of the voltage compensation unit 4;
the current source I1 is connected across the source terminal of the third transistor MN3 and ground.
The signal conversion unit 5 includes a fourth transistor MP1 and a first resistor R1;
a gate terminal of the fourth transistor MP1 is used as an input terminal of the signal conversion unit 5, a source terminal is connected to an output terminal BFETH of the sampling unit 2, and a drain terminal is used as an output terminal of the signal conversion unit 5;
the first resistor R1 is connected across the drain terminal of the fourth transistor MP1 and ground.
The above-mentioned charging current regulating unit 6 includes a third operational amplifier a3, a fifth transistor MN4 and a second resistor R2;
the inverting input terminal of the third operational amplifier a3 is used as the first input terminal of the charging current adjusting unit 6, the positive input terminal is used as the second input terminal of the charging current adjusting unit 6, and the third operational amplifier a3 is connected with the reference voltage REF; an output terminal thereof is connected to a gate terminal of the fifth transistor MN 4;
the source end of the fifth transistor MN4 is connected to ground, and the drain end thereof is connected to the external charge pump output voltage pucpc through a second resistor R2; the common terminal PUMP of the fifth transistor MN4 and the second resistor R2 serves as an output terminal of the charging current adjusting unit 6.
Compared with the prior art, the invention has the following advantages:
1. according to the invention, the offset voltage of the amplifier is recorded and stored in the capacitor by introducing the switched capacitor circuit, and is released to offset the original offset voltage in the sampling process, so that the sampling precision of the charging current is ensured, the problem that a constant current charging loop is unstable and easy to lose efficacy during heavy current charging due to sampling errors is solved, and the current precision of constant current charging and the stability of a circuit system are greatly improved.
2. The invention corrects the direct current working point of the operational amplifier at the offset voltage storage stage by introducing the voltage compensation circuit, and reduces the influence of the parasitic capacitance at the input end of the operational amplifier on the circuit precision when the state of the switched capacitor circuit is switched.
Drawings
FIG. 1 is a schematic diagram of a conventional constant current charging circuit for a lithium battery;
FIG. 2 is a block diagram of a lithium battery constant current charging system of the present invention;
FIG. 3 is a circuit diagram of a switched capacitor circuit unit of the present invention;
FIG. 4 is a circuit diagram of a voltage compensation unit according to the present invention;
FIG. 5 is a circuit diagram of a signal conversion unit of the present invention;
FIG. 6 is a circuit diagram of a charging current regulating unit according to the present invention;
FIG. 7 is a schematic diagram of logic control signals generated by the digital control unit of the present invention;
FIG. 8 is a schematic diagram of the overall operation of the constant current charging circuit of the present invention;
fig. 9 is an equivalent circuit diagram of the constant current charging circuit of the present invention in different operating states;
Detailed Description
The following further describes embodiments of the present invention with reference to the drawings attached in the specification.
Referring to fig. 2, the present invention provides a constant current charger circuit, which includes a charging unit 1, a sampling unit 2, a switched capacitor circuit unit 3, a voltage compensation unit 4, a signal conversion unit 5, a charging current adjustment unit 6, and a digital control unit 7, wherein:
the charging unit 1 is used for carrying out constant current charging on the lithium battery; the charging current regulation circuit is provided with two paths of inputs, wherein a first input end is connected to the output voltage SYS of a preceding-stage DC-DC (direct current-direct current) converter, and a second input end is connected to the output of the charging current regulation unit 6; the output end is connected to the anode voltage BAT of the lithium battery to be charged;
the sampling unit 2 is provided with two paths of inputs and is used for sampling the charging current in proportion; a first input terminal connected to a DC-DC (direct current-direct current) converter output voltage SYS, a second input terminal connected to an input terminal of the charging unit 1; the output end BFETH outputs a sampling current signal IBFETH；
The switched capacitor circuit unit 3 is provided with four inputs, a first input end is connected to an anode voltage BAT of a lithium battery to be charged, and a second input end is connected with a sampling current signal IBFETHA third input terminal is connected to the logic control signal P1 of the output of the digital control unit 7, and a fourth input terminal is connected to the logic control signal P1X of the output of the digital control unit 7; the output end of the voltage compensation unit is connected to the input end of the voltage compensation unit 4;
the output end of the voltage compensation unit 4 is connected to the first input end of the signal conversion unit 5, and the voltage compensation unit is used for compensating the output voltage of the switched capacitor circuit unit 3 and reducing the sampling precision error;
the above-mentionedA signal conversion unit 5 having two inputs, a second input connected to the sampled current signal IBFETH(ii) a The output terminal is connected to a first input terminal of the charging current adjusting unit 6. The switched capacitor circuit unit 3, the voltage compensation unit 4 and the signal conversion unit 5 form a feedback loop to ensure that the sampling unit 2 can accurately sample the charging current in proportion.
The charging current adjusting unit 6 is provided with two paths of inputs, the second input end of the charging current adjusting unit is connected with the reference voltage REF, and the output end of the charging current adjusting unit is connected with the input end of the signal sampling unit 2 and the input end of the charging unit 1, so that the charging current is adjusted and is ensured to be constant;
the digital control unit 7 is configured to generate two logic control signals P1 and P1X, where a first logic control signal P1 controls ganged switches S1 to S6 in the switched capacitor circuit unit 3, and a second logic control signal P1X controls ganged switches S7 to S12 in the switched capacitor circuit unit 3.
Further, referring to fig. 2, the charging unit 1, is formed of a first transistor MN1, which is formed of N (N)>1) The NMOS tubes which are completely the same are connected in parallel; the sampling unit 2 is composed of a second transistor MN2, and the size of the sampling unit is identical to that of an NMOS transistor constituting a first transistor MN1, and the number ratio is 1: N. The drain terminal of the second transistor MN2 is connected with the drain terminal of the first transistor MN1, the gate terminal of the second transistor MN2 is connected with the gate terminal of the first transistor MN1, and the source terminal of the second transistor MN2 outputs a sampling current signal IBFETH(ii) a A feedback loop is formed by the switched capacitor circuit unit 3, the voltage compensation unit 4 and the signal conversion unit 5, so that the source end voltage of the second transistor MN2 is equal to the source end voltage of the first transistor MN1 in the charging unit 1, the current flowing through the second transistor MN2 is 1/N of the current flowing through the first transistor MN1, and the purpose of current sampling is achieved. Simultaneous sampling of current signals IBFETHConverted into a sampling voltage by the signal conversion unit 5 and output to the charging current adjustment unit 6. The charging current regulating unit 6 compares the sampling voltage with a reference voltage REF to obtain a charging current regulating signal, and the charging current regulating signal is fed back to the gate terminal of the first transistor MN1 for controlling and regulatingMagnitude of the constant current charging current.
The drain terminal of the first transistor MN1 is connected to the output voltage SYS of the preceding DC-DC converter, and SYS + △ V1(△ V1>0V), the gate terminal is connected to the output terminal of the charging current adjusting unit 6, the source terminal is connected to the anode voltage BAT of the lithium battery to be charged, since the SYS voltage is higher than the BAT voltage by △ V, this means that the source-drain voltage of the power tube is constant, and the magnitude of the current passed by the power tube is uniquely determined by the gate terminal voltage.
Referring to fig. 3, the switched capacitor circuit unit 3 includes a first operational amplifier a1, a second operational amplifier a2, a first capacitor C1, a second capacitor C2, and 12 ganged switches S1 to S12:
the first ganged switch S1 is connected with the output end BFETH of the sampling unit (2) and the upper polar plate of the first capacitor C1, and the lower polar plate of the first capacitor C1 is connected with the reverse input end of the first operational amplifier A1;
the second linkage switch S2 is connected with the anode voltage BAT of the lithium battery and the positive input end of the first operational amplifier A1;
the third linkage switch S3 is connected with the output end of the first operational amplifier A1 and the input end A of the voltage compensation unit (4);
the fourth ganged switch S4 is connected across the inverting input and the output of the second operational amplifier A2;
the fifth linkage switch S5 is connected with the upper plate of the second capacitor C2 and the positive input end of the second operational amplifier A2;
the sixth ganged switch S6 is connected with the positive input end of the second operational amplifier A2 and the input end A of the voltage compensation unit (4);
the seventh ganged switch S7 is connected across the inverting input and output of the first operational amplifier A1;
the eighth ganged switch S8 is connected with the upper plate of the first capacitor C1 and the positive input end of the first operational amplifier A1;
the ninth ganged switch S9 is connected with the positive input end of the first operational amplifier A1 and the input end A of the voltage compensation unit (4);
the tenth gang switch S10 is connected with the output end BFETH of the sampling unit (2) and the upper polar plate of the second capacitor C2, and the lower polar plate of the second capacitor C2 is connected with the reverse input end of the second operational amplifier A2;
the eleventh gang switch S11 is connected with the anode voltage BAT of the lithium battery and the positive input end of the second operational amplifier A2;
the twelfth ganged switch S12 connects the output terminal of the second operational amplifier a2 and the input terminal a of the voltage compensation unit (4).
Referring to fig. 4, the voltage compensation unit 4 includes a third transistor MN3 and a constant current source I1; a gate terminal of the third transistor MN3 is used as an input terminal a of the voltage compensation unit 4, a drain terminal is connected to the power supply voltage VCC, and a source terminal is used as an output terminal B of the voltage compensation unit 4; the current source I1 is connected between the source terminal of the third transistor MN3 and the ground; the MN3 is connected in the form of a source follower, and is used for performing voltage compensation on the output voltage of the switched capacitor circuit unit 3, and reducing the influence of the parasitic capacitance of the positive and negative input ends of the first operational amplifier a1 and the second operational amplifier a2 in the switched capacitor circuit unit 3 on the precision.
Referring to fig. 5, the signal conversion unit 5 includes a fourth transistor MP1 and a first resistor R1; a gate terminal of the fourth transistor MP1 serves as an input terminal of the signal conversion unit 5, a source terminal is connected to an output terminal BFETH of the sampling unit 2, and a drain terminal serves as an output terminal of the signal conversion unit 5; the first resistor R1 is connected across the drain terminal of the fourth transistor MP1 and ground.
Further, with reference to fig. 3, 4, 5; the output end voltage BFETH of the sampling unit 2 passes through the switched capacitor circuit unit 3, the voltage compensation unit 4 obtains an output voltage B and is connected to the gate end of the fourth transistor MP1, and the fourth transistor MP1 feeds back the output voltage B to the input end of the switched capacitor circuit unit 3 to form a negative feedback loop. The voltages of the two input ends BFETH and BAT of the switched capacitor circuit unit 3 are ensured to be equal, that is, the voltage of the drain end of MN2 in the sampling unit 2 is ensured to be equal to the voltage of the drain end of MN1 in the charging unit 1, and at this time, the voltages of the source end, the gate end and the drain end of MN2 and MN1 are all equal, so that the sampling unit 2 is ensured to accurately sample the charging current in proportion.
Referring to fig. 6, the charging current adjusting unit 6 includes a third operational amplifier a3, a fifth transistor MN4, and a resistor R2; the inverting input terminal of the third operational amplifier a3 is used as the first input terminal of the charging current adjusting unit 6, the positive input terminal is used as the second input terminal of the charging current adjusting unit 6, and the third operational amplifier a3 is connected with the reference voltage REF; an output terminal thereof is connected to a gate terminal of the fifth transistor MN 4; the source end of the fifth transistor MN4 is grounded, and the drain end of the fifth transistor MN4 is connected to the external charge pump output voltage pucpc through a second resistor R2; the common terminal PUMP of the fifth transistor MN4 and the resistor R2 serves as an output terminal of the charging current adjusting unit 6; the drain terminal of the fifth transistor MN4 is connected to the gate terminal of the charging unit 1 as the output of the unit, and is used for regulating the constant current charging current of the charging unit 1.
The digital control unit 7 of the present invention is used for generating a logic control signal for controlling the on and off of the ganged switch in the switched capacitor circuit unit 3, thereby changing the operating state of the circuit. The operation control timing for controlling the switched capacitor circuit unit 3 is shown in fig. 7, in which a high level represents that the switch is closed and a low level represents that the switch is open.
FIG. 8 is a schematic diagram of the overall operation of the constant current charging circuit with high precision and high stability according to the present invention, assuming that the offset voltages of the first operational amplifier A1 and the second operational amplifier A2 are V respectivelyOS1And VOS2。
With reference to fig. 7 and 8, the specific working process of the present invention is described as follows:
when the ganged switches S1 to S6 are defined to be closed and the ganged switches S7 to S12 are defined to be open, the whole circuit is in the stage T1, and the equivalent structure is shown in fig. 9 a. At this time, the second operational amplifier A2 is connected into a deep negative feedback mode, the voltages of the positive and negative input terminals are equal, and then the voltage V at the two ends of the second capacitor C2 is providedC2＝VOS2This means that the offset voltage V of the second operational amplifier A2OS2Is stored in the second capacitance C2;
when the ganged switches S7 to S12 are defined to be closed and the ganged switches S1 to S6 are defined to be open, the whole circuit is in the stage T2, and the equivalent structure is shown in fig. 9 b. At this time, the second operational amplifier A2, the second capacitor C2, the voltage compensation unit 4 and the signal conversion unit 5 constituteVoltage signal loop, the positive and negative input voltages of the second operational amplifier A2 are equal, i.e. BFETH-VC2＝BAT-VOS2Since the voltage V across the second capacitor C2 is in the T1 phaseC2Equal to offset voltage VOS2And the capacitor voltage can not be suddenly changed, BFETH is equal to BAT, and the offset voltage V is eliminatedOS2Influence on Circuit precision (BAT-V in conventional circuits)OSBFETH, and BAT ═ BFETH + VOS)。
Similarly, the offset voltage V of the first operational amplifier A1OS1Can also be eliminated, the first capacitor C1 records the offset voltage V of the first operational amplifier A1 during the T2 stageOS1In the T1 state, the offset voltage VOS1And the voltage V between the two ends of the first capacitor C1C1To cancel out, BFETH is still equal to BAT.
Because the stages T1 and T2 represent a complete signal acquisition and amplification processing period, BFETH is constantly equal to BAT during the whole period, and the offset voltage of the operational amplifier does not affect the current sampling precision.
The foregoing description is only an example of the present invention and should not be construed as limiting the invention, as it will be apparent to those skilled in the art that various modifications and variations in form and detail can be made without departing from the principle and structure of the invention after understanding the present disclosure and the principles, but such modifications and variations are considered to be within the scope of the appended claims.
Claims (6)
1. A constant current charger circuit, comprising: charging unit (1), sampling unit (2), signal conversion unit (5), charging current regulating unit (6), digital control unit (7), its characterized in that includes: a switched capacitor circuit unit (3) and a voltage compensation unit (4);
the charging unit (1) is used for carrying out constant current charging on the lithium battery; the charging current regulation circuit is provided with two paths of inputs, wherein a first input end is connected to the output voltage SYS of a preceding-stage DC-DC (direct current-direct current) converter, and a second input end is connected to the output of the charging current regulation unit (6); the output end is connected to an anode BAT of the lithium battery to be charged;
the sampling unit (2) is provided with two paths of inputs and is used for sampling the charging current in proportion; a first input terminal is connected to a DC-DC converter output voltage SYS, a second input terminal is connected to an input terminal of the charging unit (1); the output end BFETH outputs a sampling current signal IBFETH；
The switched capacitor circuit unit (3) is provided with four inputs, a first input end is connected to an anode BAT of a lithium battery to be charged, a second input end is connected with an output end BFETH of the sampling unit (2), a third input end is connected to a control signal P1 output by the digital control unit (7), and a fourth input end is connected to a control signal P1X output by the digital control unit (7); the output end of the voltage compensation unit is connected to the input end of the voltage compensation unit (4); the switched capacitor circuit unit (3) comprises a first operational amplifier A1, a second operational amplifier A2, a first capacitor C1, a second capacitor C2 and 12 ganged switches S1-S12; the first ganged switch S1 is connected with the output end BFETH of the sampling unit (2) and the upper polar plate of the first capacitor C1, and the lower polar plate of the first capacitor C1 is connected with the reverse input end of the first operational amplifier A1; the second linkage switch S2 is connected with the anode BAT of the lithium battery and the positive input end of the first operational amplifier A1; the third linkage switch S3 is connected with the output end of the first operational amplifier A1 and the input end A of the voltage compensation unit (4); the fourth ganged switch S4 is connected across the inverting input and output of the second operational amplifier a 2; the fifth ganged switch S5 is connected with the upper plate of the second capacitor C2 and the positive input end of the second operational amplifier A2; the sixth ganged switch S6 is connected with the positive input end of the second operational amplifier A2 and the input end A of the voltage compensation unit (4); the seventh ganged switch S7 is connected across the inverting input and output of the first operational amplifier a 1; the eighth ganged switch S8 is connected with the upper plate of the first capacitor C1 and the positive input end of the first operational amplifier A1; the ninth ganged switch S9 is connected with the positive input end of the first operational amplifier A1 and the input end A of the voltage compensation unit (4); the tenth gang switch S10 is connected with the output end BFETH of the sampling unit (2) and the upper polar plate of the second capacitor C2, and the lower polar plate of the second capacitor C2 is connected with the reverse input end of the second operational amplifier A2; the eleventh gang switch S11 is connected with the anode BAT of the lithium battery and the positive input end of the second operational amplifier A2; the twelfth ganged switch S12 is connected with the output end of the second operational amplifier A2 and the input end A of the voltage compensation unit (4);
the output end of the voltage compensation unit (4) is connected to the first input end of the signal conversion unit (5) and is used for compensating the output voltage of the switched capacitor circuit unit (3) and reducing the sampling precision error;
the signal conversion unit (5) is provided with two paths of inputs, and the second input end of the signal conversion unit is connected with a sampling current signal IBFETH(ii) a The switched capacitor circuit unit (3), the voltage compensation unit (4) and the signal conversion unit (5) form a feedback loop to ensure that the sampling unit (2) can accurately sample the charging current in proportion; the output end is connected to the first input end of the charging current regulating unit (6);
the charging current adjusting unit (6) is provided with two paths of inputs, the second input end of the charging current adjusting unit is connected with the reference voltage REF, and the output end of the charging current adjusting unit is connected with the input end of the signal sampling unit (2) and the input end of the charging unit (1) and used for adjusting the charging current and ensuring the charging current to be constant;
the digital control unit (7) is used for generating two logic control signals P1 and P1X, wherein a first logic control signal P1 controls ganged switches S1-S6 in the switched capacitor circuit unit (3), and a second logic control signal P1X controls ganged switches S7-S12 in the switched capacitor circuit unit (3).
2. The constant current charger circuit of claim 1, wherein the charging unit (1) is composed of a first transistor MN1, the first transistor is composed of N (N >1) identical NMOS transistors connected in parallel, a gate terminal of the first transistor MN1 is connected to an output terminal of the charging current regulating unit (6), a source terminal is connected to an anode BAT of a lithium battery, the anode BAT has a voltage VBAT, a drain terminal is connected to an output voltage SYS of a preceding DC-DC converter, and SYS is VBAT + △ V1, △ V1> 0V.
3. A constant current charger circuit according to claim 2, wherein: the sampling unit (2) is composed of a second transistor MN2The size of the NMOS transistor is completely the same as that of the NMOS transistor forming the first transistor MN1, and the number ratio is 1: N; the drain terminal of the second transistor MN2 is connected with the drain terminal of the first transistor MN1, the gate terminal of the second transistor MN2 is connected with the gate terminal of the first transistor MN1, the source terminal of the second transistor MN2 is used as the output terminal BFETH of the sampling unit (2) to output a sampling current signal IBFETH。
4. A constant current charger circuit according to claim 1, wherein: the voltage compensation unit (4) comprises a third transistor MN3 and a constant current source I1;
the gate terminal of the third transistor MN3 is used as the input terminal of the voltage compensation unit (4), the drain terminal is connected to the power supply voltage VCC, and the source terminal is used as the output terminal of the voltage compensation unit (4);
the current source I1 is connected across the source terminal of the third transistor MN3 and ground.
5. A constant current charger circuit according to claim 1, wherein: the signal conversion unit (5) includes a fourth transistor MP1 and a first resistor R1;
a gate terminal of the fourth transistor MP1 is used as an input terminal of the signal conversion unit (5), a source terminal is connected to an output terminal BFETH of the sampling unit (2), and a drain terminal is used as an output terminal of the signal conversion unit (5);
the first resistor R1 is connected across the drain terminal of the fourth transistor MP1 and ground.
6. A constant current charger circuit according to claim 1, wherein: the charging current regulating unit (6) includes a third operational amplifier A3, a fifth transistor MN4 and a second resistor R2;
the inverting input end of the third operational amplifier A3 is used as the first input end of the charging current regulating unit (6), the positive input end is used as the second input end of the charging current regulating unit (6), and the third operational amplifier A3 is connected with the reference voltage REF; an output terminal thereof is connected to a gate terminal of the fifth transistor MN 4;
the source end of the fifth transistor MN4 is connected to ground, and the drain end thereof is connected to the external charge pump output voltage pucpc through a second resistor R2; the common terminal PUMP of the fifth transistor MN4 and the second resistor R2 serves as an output terminal of the charging current adjusting unit (6).
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| CN109038741B (en) * | 2018-08-16 | 2023-11-28 | 上海艾为电子技术股份有限公司 | Charging circuit, switch charging chip and charging current sampling circuit thereof |
| KR20210054331A (en) * | 2019-11-05 | 2021-05-13 | 주식회사 엘지화학 | Apparatus for battery diagnosis, nergy storage system including same, and method thereof |
| TWI739363B (en) * | 2020-03-27 | 2021-09-11 | 矽統科技股份有限公司 | Constant current charging device |
| CN113448371B (en) * | 2020-03-27 | 2023-02-17 | 矽统科技股份有限公司 | Constant current charging device |
| CN113970664B (en) * | 2020-07-24 | 2024-04-12 | 圣邦微电子（北京）股份有限公司 | High-precision current sampling circuit, constant-current control circuit and sampling method |
| CN115037024B (en) * | 2022-08-09 | 2022-11-08 | 成都信息工程大学 | High-efficiency milliwatt-level photovoltaic energy collection and energy storage management circuit |
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