CN108306348B - Lithium battery control circuit and lithium battery charger - Google Patents
Lithium battery control circuit and lithium battery charger Download PDFInfo
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- CN108306348B CN108306348B CN201710025572.9A CN201710025572A CN108306348B CN 108306348 B CN108306348 B CN 108306348B CN 201710025572 A CN201710025572 A CN 201710025572A CN 108306348 B CN108306348 B CN 108306348B
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 82
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 82
- 238000006243 chemical reaction Methods 0.000 claims abstract description 17
- 230000007246 mechanism Effects 0.000 claims abstract description 9
- 238000007600 charging Methods 0.000 claims description 69
- 239000003990 capacitor Substances 0.000 claims description 17
- 230000007704 transition Effects 0.000 claims description 13
- 238000009877 rendering Methods 0.000 claims 1
- 230000010355 oscillation Effects 0.000 abstract description 9
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- 238000010586 diagram Methods 0.000 description 16
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- 230000008569 process Effects 0.000 description 6
- 230000000694 effects Effects 0.000 description 5
- 238000007599 discharging Methods 0.000 description 4
- 230000008878 coupling Effects 0.000 description 3
- 238000010168 coupling process Methods 0.000 description 3
- 238000005859 coupling reaction Methods 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 2
- 238000013459 approach Methods 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 229910044991 metal oxide Inorganic materials 0.000 description 2
- 150000004706 metal oxides Chemical class 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 230000008901 benefit Effects 0.000 description 1
- 238000010280 constant potential charging Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000009795 derivation Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/0029—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with safety or protection devices or circuits
- H02J7/0036—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with safety or protection devices or circuits using connection detecting circuits
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Abstract
The invention relates to a lithium battery control circuit and a lithium battery charger. The lithium battery charger includes a lithium battery control circuit. The lithium battery control circuit comprises a smooth conversion circuit and a closing time control circuit. The smoothing conversion circuit generates a first voltage according to the sensing current signal and the feedback signal, and generates a second voltage according to the mode signal. The smooth conversion circuit compares the first voltage with the second voltage to generate a reset signal. The closing time control circuit converts the feedback signal through a voltage conversion current mechanism to generate a first current, and generates a setting signal by using the first current and the duty ratio signal. The invention can prevent surge current and oscillation phenomenon through the smooth conversion circuit. The switching frequency and the ripple magnitude of the output current are controlled by the closing time control circuit. The technical scheme does not need to be provided with a complex compensation circuit, has simple structure and can reduce the manufacturing cost.
Description
Technical Field
The present invention relates to a lithium battery charging technology, and more particularly, to a lithium battery control circuit and a lithium battery charger capable of improving the efficiency of the entire charger.
Background
Fig. 1A is an equivalent circuit diagram of a conventional lithium battery charging. In the actual lithium battery 100, the internal resistance Rbir is not constant but has a variable value. The reason is that the internal resistance Rbir varies depending on the temperature, the charging current Ich, the number of uses, and the like.
Fig. 1B is a diagram illustrating the correlation between the internal resistance and the current of a lithium battery. In either the charging or discharging condition, the internal resistance Rbir of the lithium battery will have a larger resistance value for a larger charging or discharging current.
Fig. 1C is a diagram illustrating a correlation between the internal resistance and the battery capacity of a lithium battery. The internal resistance Rbir of a lithium battery, whether in a charging or discharging condition, will also have a larger resistance value when the lithium battery is at a lower percentage capacity or a higher percentage capacity.
Generally, a lithium battery may be subjected to various types of charging modes when being charged. For example, a small current (TC) mode, a Constant Current (CC) mode, and a Constant Voltage (CV) mode. Fig. 2A is a schematic diagram of a charging process from a low current mode to a constant current mode. Fig. 2B is a schematic diagram of a charging process from a constant current mode to a constant voltage mode. When a charging mode of one type is switched (or entered) to a charging mode of another type, a surge current is generated on the circuit and oscillates, as shown by the dashed circle 210 in fig. 2A or the dashed circle 220 in fig. 2B.
The reason why the inrush current occurs during the charging may be analyzed as follows. In fig. 1A, when the charger 120 detects that the battery voltage VB is high enough and before entering the constant voltage mode from the constant current mode, the lithium battery 100 corresponds to a larger charging current and a higher battery capacity, as shown in fig. 1B and fig. 1C, respectively. The internal resistance Rbir in this case will be large relative to the case at lower charging currents and lower battery capacities. Based on the large current and the large resistance value, there will be a significant voltage drop across the inner resistor Rbir. When the charger 120 enters the constant voltage mode, the charging current Ich becomes small, the internal resistance Rbir of the lithium battery 100 also relatively decreases, so that the voltage drop becomes small instantaneously, and the charger 120 makes a misjudgment that the battery voltage VB is insufficient, so that the constant voltage mode is converted into the constant current mode to operate. However, the voltage drop will rise again, and the charger 120 enters the constant voltage mode again, and the oscillation will not be stopped until the voltage of the lithium battery 100 reaches the preset value.
In a general lithium battery buck charger, when the charging operation is in the second half (e.g., constant voltage mode), the buck converter in the circuit architecture is a voltage mode buck converter, so that two overlapping poles are present at the output terminal of the buck charger. In order to prevent oscillation of the system, the prior art adopts a compensation circuit with a complex design to solve the stability problem, thereby increasing the research and development time and cost.
Since the compensation circuit for the charger is rather complicated and occupies a considerable circuit area. Considering the overall circuit of the charger and the safety of the battery, a circuit or mechanism for preventing the generation of surge current should be provided.
Disclosure of Invention
The invention provides a lithium battery control circuit and a lithium battery charger, which are used for solving the problems in the prior art.
The invention provides a lithium battery control circuit. The lithium battery control circuit comprises a smooth conversion circuit and a closing time control circuit. The smoothing conversion circuit generates a first voltage according to the sensing current signal and the feedback signal, generates a second voltage according to the mode signal, and compares the first voltage and the second voltage to generate a reset signal. The sensed current signal is related to the output current. The feedback signal is related to the output voltage. The mode signal is used for indicating whether the charging device is in the first charging mode, and the second voltage in the first charging mode is smaller than the second voltage in the non-first charging mode. The closing time control circuit converts the feedback signal through a voltage conversion current mechanism to generate a first current, and generates a setting signal by using the first current and the duty ratio signal.
The invention provides a lithium battery charger. The lithium battery charger comprises a lithium battery control circuit, a current sensing circuit and a feedback circuit. Lithium battery control circuit includes: a smooth conversion circuit for generating a first voltage according to a sensing current signal and a feedback signal, generating a second voltage according to a mode signal, and comparing the first voltage and the second voltage to generate a reset signal, wherein the feedback signal is related to the output voltage, the mode signal is used for indicating whether the charging mode is the first charging mode, and the second voltage in the first charging mode is smaller than the second voltage in the non-first charging mode; the closing time control circuit converts the feedback signal through a voltage conversion current mechanism to generate a first current, and generates a setting signal by using the first current and the duty ratio signal; a current sensing circuit for generating a sensing current signal according to the output current; and a feedback circuit for generating a feedback signal according to the output voltage.
Based on the above, the lithium battery control circuit and the lithium battery charger of the invention adopt the smooth switching circuit in combination with the closing time control circuit. The surge current and the oscillation phenomenon are prevented by the smooth switching circuit when each charging mode is switched, and the switching frequency and the ripple magnitude of the output current can be controlled by closing the time control circuit, so that the efficiency of the whole charger is improved. The lithium battery control circuit and the lithium battery charger do not need to be provided with a complex compensation circuit on the path of the feedback circuit, and are simple in structure. On the other hand, compared with the existing charger, the invention can reduce the complexity of the charger and the manufacturing cost, and conforms to the development trend of the current flexible consumer electronic products.
Drawings
Fig. 1A is an equivalent circuit diagram of a conventional lithium battery charging.
Fig. 1B is a diagram illustrating the correlation between the internal resistance and the current of a lithium battery.
Fig. 1C is a diagram illustrating a correlation between the internal resistance and the battery capacity of a lithium battery.
Fig. 2A is a schematic diagram of a charging process from a low current mode to a constant current mode.
Fig. 2B is a schematic diagram of a charging process from a constant current mode to a constant voltage mode.
Fig. 3 is a schematic diagram of a lithium battery charger according to an embodiment of the invention.
Fig. 4 is a circuit diagram of a smooth transition circuit according to an embodiment of the present invention.
Fig. 5 is a waveform diagram of a constant current mode to a constant voltage mode according to an embodiment of the invention.
FIG. 6 is another waveform diagram of constant current mode to constant voltage mode according to an embodiment of the invention.
Fig. 7 is a circuit diagram of a turn-off time control circuit according to an embodiment of the invention.
Fig. 8 is a waveform diagram of a conventional fixed off time.
Description of reference numerals:
100: a lithium battery;
120: a charger;
210: a dashed circle;
220: a dashed circle;
300: a lithium battery charger;
310: a lithium battery control circuit;
320: a smooth switching circuit;
330: a turn-off time control circuit;
340: a logic control circuit;
350: a current sensing circuit;
360: a feedback circuit;
370: a drive circuit;
380: an output stage;
390: a lithium battery;
400: a mode selection circuit;
410: a current source;
412: a PMOS transistor;
414: a PMOS transistor;
416: a PMOS transistor;
418: a comparator;
420: a resistor;
422: a PMOS transistor;
424: a resistor;
426: a PMOS transistor;
428: a current source;
430: a switch;
432: a resistor;
434: a comparator;
510: a dashed circle;
520: a dashed rectangle;
610: a dashed circle;
710: a PMOS transistor;
712: a PMOS transistor;
714: an NMOS transistor;
716: a resistor;
718: a comparator;
720: a capacitor;
722: an NMOS transistor;
724: a comparator;
810: a waveform;
a1: a comparator;
CCF: a mode signal;
FB: a feedback signal;
GND: a ground terminal;
ich: a charging current;
IL: outputting current;
irefi: current flow;
isen: sensing a current signal;
ivmix: a current signal;
l: an inductor;
and (3) Rbir: an internal resistance;
REF: a reference voltage;
rf 1: a resistor;
rf 2: a resistor;
rsen: a resistor;
sres: resetting the signal;
sset: setting a signal;
sduty: a duty ratio signal;
VB: a battery voltage;
vmix: a first voltage;
vout: outputting the voltage;
vrefv: a reference voltage;
vrefi: a second voltage;
vsignal: a voltage signal.
Detailed Description
In the embodiments described below, when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. The term "circuit" may refer to at least one element or a plurality of elements, or elements actively and/or passively coupled together to provide suitable functionality. It should be understood that the physical characteristics of the signals referred to throughout this specification and the accompanying drawings may be voltages or currents.
Please refer to fig. 3. The lithium battery charger 300 may be used to charge the lithium battery 390. The lithium battery charger 300 may include a lithium battery control circuit 310, a current sensing circuit 350, a feedback circuit 360, a driving circuit 370, and an output stage 380. Hereinafter, the entire circuit composed of the lithium battery charger 300 and the lithium battery 390 will be referred to as a "charging system" or a "system".
The lithium battery control circuit 310 may include a smooth transition circuit 320, a shutdown time control circuit 330, and a logic control circuit 340. The current sensing circuit 350 may include an inductor L, a resistor Rsen, and a comparator a 1. The current sensing circuit 350 may sense the output current IL flowing through the inductor L and generate a sensing current signal Isen according to the output current IL. It is sufficient that the current sensing circuit 350 can generate the sensing current signal Isen according to the output current IL. The feedback circuit 360 may include a resistor Rf1 and a resistor Rf2, and may include a resistor network or a resistor-capacitor network. As long as the feedback circuit 360 can generate the feedback signal FB according to the output voltage Vout.
The following describes the prevention of the surge current and the oscillation phenomenon by the smooth switching circuit 320, and the control of the switching frequency and the ripple magnitude of the output current IL by the off-time control circuit 330.
Please refer to fig. 3 and 4. The smooth transition circuit 320 may include a current source 410, a P-type metal oxide semiconductor (PMOS) transistor 412, a PMOS transistor 414, a PMOS transistor 416, a comparator 418, and a resistor 420.
The detailed element coupling relationship is as follows. The current source 410 is related to the sensing current signal Isen, and the two are linearly proportional. A first terminal (e.g., a source) of the PMOS transistor 412 is coupled to a first terminal of the current source 410, and a second terminal (e.g., a drain) and a control terminal (e.g., a gate) of the PMOS transistor 412 are coupled to a second terminal of the current source 410. The first terminal of the PMOS transistor 414 is coupled to the first terminals of the current source 410 and the PMOS transistor 412, and the control terminal of the PMOS transistor 414 is coupled to the control terminal of the PMOS transistor 412. A first input (e.g., a positive input) of the comparator 418 receives the reference voltage Vrefv, and a second input (e.g., a negative input) of the comparator 418 receives the feedback signal FB.
A first terminal of the PMOS transistor 416 is coupled to the first terminal of the PMOS transistor 414, a second terminal of the PMOS transistor 416 is coupled to the second terminal of the PMOS transistor 414, and a control terminal of the PMOS transistor 416 is coupled to the output terminal of the comparator 418. The first terminal of the resistor 420 is coupled to the second terminal of the PMOS transistor 414 and the second terminal of the PMOS transistor 416, and the second terminal of the resistor 420 is coupled to the ground GND. A first voltage Vmix is generated at a first end of the resistor 420.
The detailed element coupling relationship is as follows. A first terminal of the resistor 424 is coupled to the second terminal of the PMOS transistor 422, and a second terminal of the resistor 424 is coupled to the ground GND. A first terminal of PMOS transistor 426 is coupled to a first terminal of PMOS transistor 422, and a control terminal of PMOS transistor 426 is coupled to a control terminal of PMOS transistor 422. The first terminal of the current source 428 is coupled to the second terminal of the PMOS transistor 426, and the second terminal of the current source 428 is coupled to the ground GND. A control terminal of the switch 430 receives the mode signal CCF, and a first terminal of the switch 430 is coupled to a first terminal of the resistor 424. A first terminal of the resistor 432 is coupled to the second terminal of the switch 430, and a second terminal of the resistor 432 is coupled to the ground GND. A second voltage Vrefi is generated at a first end of resistor 424.
As shown in fig. 3, the mode selection circuit 400 may generate the mode signal CCF according to the output voltage Vout. For example, when the mode selection circuit 400 determines that the output voltage Vout is smaller than the predetermined voltage, the mode signal CCF indicates the first charging mode.
In the present embodiment, the smooth converting circuit 320 can generate the first voltage Vmix according to the sensing current signal Isen and the feedback signal FB, generate the second voltage Vrefi according to the mode signal CCF, and compare the first voltage Vmix and the second voltage Vrefi by the comparator 434 to generate the reset signal Sres.
The current source 428 is used to make the PMOS transistor 422 generate a current Irefi. When the mode signal CCF indicates the first charging mode (e.g., the output voltage Vout is less than 2.65V, but not limited thereto), the switch 430 connects the resistor 424 and the resistor 432 in parallel, and the equivalent resistance value is smaller than the resistance value of the resistor 424 or the resistor 432, so that the equivalent resistance value and the current Irefi can be used to generate the second voltage Vrefi, thereby controlling the reset signal Sres and achieving the purpose of small current.
In addition, various types of charging modes may be adopted for the charging operation of the lithium battery.
When the mode signal CCF indicates a non-first charging mode, then the switch 430 renders the resistor 432 non-conductive so that the equivalent resistance value will be equal to the resistor 424. Thus, the equivalent resistance and the current Irefi generate a second voltage Vrefi higher than that of the parallel connection, and the ground charging mode also has a larger charging current. More specifically, the first charging mode may be a small current mode, and the non-first charging mode may be a constant current mode or a constant voltage mode.
In the last charging process (i.e., in the latter half of the charging operation), the constant current mode enters the constant voltage mode. Please refer to fig. 3 to 5 together. In the constant current mode, since the output voltage Vout does not reach a predetermined value (for example, the predetermined value may be 4.2V, but not limited thereto), the feedback signal FB has a smaller voltage value and the voltage loop gain is not large enough. The current signal Ivmix flowing at the first voltage Vmix has only information from the sense current signal Isen. When the output voltage Vout approaches the predetermined value, the voltage loop gain of the feedback circuit 360 is large enough, and the feedback signal FB causes the voltage signal Vsignal to slowly flow into the first voltage Vmix to be mixed with the current signal Ivmix, so that the mixed signal shown by the dashed circle 510 can be used to control the variation of the output current IL. Furthermore, the effect shown by the dashed rectangle 520 is a smooth output current IL. Therefore, the smooth conversion circuit 320 can be used to achieve the purpose of constant voltage charging and the purpose of mixing both voltage and current signals.
Please refer to fig. 3, fig. 4 and fig. 6. In fig. 6, when the charging operation is in the constant current mode, the voltage signal Vsignal is zero due to insufficient loop gain because the output voltage Vout from the output terminal is not large enough, and there is no influence on the control of the charging system. The lithium battery charger 300 only performs current locking with respect to the sensing current signal Isen from the current sensing circuit 350, and the current signal Ivmix flowing out at the first voltage Vmix only has information from the sensing current signal Isen. The comparator 434 compares the current signal Ivmix with the second voltage Vrefi to perform peak current control (peak current control) locking, so as to lock the output terminal to be a constant current.
In addition, when the output voltage Vout approaches the rated value, the voltage signal Vsignal will start to be added to the system, and what is equivalent to the signal analysis is to raise the sensing current signal Isen to synthesize the current signal Ivmix. Peak current control can be performed through both the current signal Ivmix and the second voltage Vrefi to lock the voltage of the output terminal. Thus, the lithium battery control circuit 310 has an advantage of preventing a large surge current from occurring.
Furthermore, the effect shown by the dashed circle 610 is smooth. The control of the lithium battery control circuit 310 uses both voltage and current signals simultaneously, so the system operates as a current mode buck converter. The whole system can be simplified into a single-pole system in terms of stability analysis, so that the effect of simplifying the compensation circuit of the charger is achieved.
In addition, the smooth transition circuit 320 may operate in cooperation with the turn-off time control circuit 330 described below, and may also have an effect of simplifying a compensation circuit of the charger in the configuration of the system.
Please refer to fig. 3 and fig. 7. Off-time control circuit 330 may include a PMOS transistor 710, a PMOS transistor 712, an N-type metal oxide semiconductor (NMOS) transistor 714, a resistor 716, a comparator 718, a capacitor 720, an NMOS transistor 722, and a comparator 724.
The detailed element coupling relationship is as follows. A first terminal of the PMOS transistor 712 is coupled to the first terminal of the PMOS transistor 710, and a control terminal of the PMOS transistor 712 is coupled to the second terminal and the control terminal of the PMOS transistor 710. A first terminal (e.g., a drain) of the NMOS transistor 714 is coupled to the second terminal and the control terminal of the PMOS transistor 710. A first terminal of the resistor 716 is coupled to a second terminal (e.g., a source) of the NMOS transistor 714, and a second terminal of the resistor 716 is coupled to the ground GND. A first input (e.g., a positive input) of the comparator 718 receives the feedback signal FB, a second input (e.g., a negative input) of the comparator 718 is coupled to the first terminal of the resistor 716 and the second terminal of the NMOS transistor 714, and an output of the comparator 718 is coupled to a control terminal (e.g., a gate) of the NMOS transistor 714.
The first terminal of the capacitor 720 is coupled to the second terminal of the PMOS transistor 712, and the second terminal of the capacitor 720 is coupled to the ground GND. A first terminal of the NMOS transistor 722 is coupled to the first terminal of the capacitor 720, a second terminal of the NMOS transistor 722 is coupled to the ground GND, and a control terminal of the NMOS transistor 722 receives the duty ratio signal Sduty. A first input (e.g., a positive input) of the comparator 724 is coupled to the second terminal of the PMOS transistor 712 and the first terminal of the capacitor 720, a second input (e.g., a negative input) of the comparator 724 receives the reference voltage REF, and an output of the comparator 724 outputs the set signal Sset.
Note that the current ratio through PMOS transistor 710 and PMOS transistor 712 is N: 1, where the current through PMOS transistor 712 is defined as the first current 726, and N is a positive number.
Further, the configuration of the comparator 718, the PMOS transistor 710, the PMOS transistor 712, and the NMOS transistor 714 may be used as a mechanism for voltage converting current. The off-time control circuit 330 converts the feedback signal FB by the voltage-to-current mechanism to generate a first current 726. The off-time control circuit 330 may further use the first current 726 and the duty signal Sduty to generate the setting signal Sset.
In addition, the logic control circuit 340 in fig. 3 may be an SR flip-flop, but the present invention is not limited thereto. For example, the S terminal of the logic control circuit 340 is coupled to the output terminal of the off-time control circuit 330, and the R terminal of the logic control circuit 340 is coupled to the output terminal of the smooth transition circuit 320. The Q terminal of the logic control circuit 340 may generate a duty ratio signal Sduty for pulse frequency modulation according to the received reset signal Sres and the setting signal Sset, and output the duty ratio signal Sduty to the driving circuit 370. The driving circuit 370 may operate the output stage 380 according to the duty ratio signal Sduty. The lithium battery charger 300 performs a frequency conversion operation by using the duty ratio signal Sduty, so that the system is prevented from subharmonic oscillation.
Further, the off-time control circuit 330 is the core of the entire charger. The off-time control circuit 330 is responsible for adjusting the length of the off-time (off-time) and suppressing the output ripple from becoming large. The off-time control circuit 330 uses a feedback signal FB related to the output voltage Vout to control the length of the off-time. In this way, the lithium battery control circuit 310 can control the switching frequency and the ripple magnitude of the output current IL.
In addition, off-time control circuit 330 may use a single periodicity of "off-time control" to cancel the subharmonic oscillation effect of the current in the current-mode step-down transformer.
On the other hand, since the output voltage Vout of the charger will rise continuously during the charging process, if the fixed off-time mechanism in the prior art is adopted, the problem that the output current ripple becomes continuously large will certainly occur. For example, fig. 8 shows waveform 810 as being related to the output current IL, and each sine wave in waveform 810 exhibits a fixed off time. In the architectural characteristics of the buck converter, the discharge slope of the "off-time" is proportional to the output voltage, as shown in equation 1 below.
Off-time slope-Vout/L, where Vout represents the output voltage value and L represents the inductance value
(formula 1).
If the off-time is a fixed constant and based on the architectural characteristics of the buck converter, the relative slope is larger when the output voltage is higher, and will result in an increasingly larger output current ripple. Therefore, the present invention needs to linearly control and adjust the length of the turn-off time by the feedback signal, and suppress the output current, so as to make the charging efficiency of the system better.
As shown in fig. 7, the feedback signal FB and a voltage (V) to current (I) circuit are used to generate a voltage-dependent current in the present embodiment. The voltage dependent current is scaled by a suitable linear scale (e.g., N: 1) to current 726 to charge capacitor 720, and the length of this charging time is defined as the off time.
The off-time control circuit 330 may operate in conjunction with the smooth transition circuit 320 described above. In the present embodiment, the NMOS transistor 722 controls the path to discharge using the duty signal Sduty. Comparator 724 uses reference voltage REF as the upper bound of the charging voltage. The invention can define the closing time by charging and discharging the capacitor 720, thereby controlling the switching frequency of the system.
The way the current is converted due to the voltage is a linear conversion/scaling. When the characteristics of the capacitor current are used, a turn-off time linearly related to the output voltage can be obtained as shown in the following equations 2 and 3.
(formula 2).
Closing time
If FB equals k × Vout and Vc equals REF, where k is a coefficient or constant parameter and REF represents the value of the reference voltage (equation 5).
Closing time
(formula 8).
The feedback signal FB is related to the magnitude of the output voltage Vout. As the output voltage Vout is higher, and consequently the properly scaled current 726 is larger, the relative charging time is reduced, which is equivalent to reducing the off-time of the circuit.
As can be seen from the derivation of equations 4 to 8, the value of the parameter proportional to the output voltage Vout in the output ripple equation can be cancelled by the feedback signal FB related to the output voltage. Therefore, when the equation has only constant parameters and no function of the output voltage, the output current ripple will not become larger with the rise of the output voltage, and the output current ripple can be improved or reduced.
In consideration of the system performance, the present invention can be applied to a chip, and the current sensing and peak current control methods are used to replace the conventional methods of sensing the resistance and average current, so as to improve the efficiency of the prior art and further improve the efficiency of the entire charger.
In addition, the peak current control method can be applied to the ripple problem encountered in the switching charging circuit, and can also be applied to the off-time control circuit of the ripple control, so as to solve the ripple problem.
The use of a smooth switching circuit in combination with smooth switching and peak current control can successfully prevent charging mode oscillations during the switching and non-ideal inrush currents on the charger operation, while taking into account system stability and safety. The charging operation of the charger of the invention also comprises a current mode, and can simplify the complex compensating circuit of the common switching type charger.
Based on the disclosure of the above embodiments, the lithium battery charger of the present invention has a circuit architecture with smooth transition in the current mode. The present invention improves upon the design of lithium battery chargers for high performance, high stability, low cost, and low complexity, and operates with peak current control, and with both off-time control and current mode.
The invention not only solves the problem of ripple and surge current, but also can effectively protect the battery and prolong the service life of the battery.
The system of the invention integrates three characteristics of simplified compensation, protection circuit and system architecture into the smooth conversion circuit. The invention indirectly reduces the complexity of the switching charger and the manufacturing cost, and conforms to the development trend of the current flexible consumer electronics (3C) products.
In summary, the lithium battery control circuit and the lithium battery charger of the present invention can prevent the surge current and the oscillation phenomenon through the smooth switching circuit. The lithium battery control circuit and the lithium battery charger can control the switching frequency and the ripple magnitude of the output current by closing the time control circuit.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (12)
1. A lithium battery control circuit is suitable for control in a lithium battery charger, receives a sensing current signal from a current sensing circuit, a feedback signal from a feedback circuit and a duty ratio signal from a logic control circuit, and comprises:
a smooth transition circuit for generating a first voltage according to the sensing current signal and the feedback signal, generating a second voltage according to a mode signal, and comparing the first voltage and the second voltage to generate a reset signal, wherein the sensing current signal is related to an output current, the feedback signal is related to an output voltage, the mode signal is used for indicating whether in a first charging mode, and the second voltage in the first charging mode is smaller than the second voltage in a non-first charging mode, wherein the charging current generated by the lithium battery charger when the mode signal indicates in the first charging mode is smaller than the charging current generated by the lithium battery charger when the mode signal indicates in the non-first charging mode; and
a turn-off time control circuit, converting the feedback signal by a voltage-to-current conversion mechanism to generate a first current, and generating a setting signal by using the first current and the duty ratio signal,
wherein the logic control circuit generates the duty ratio signal according to the reset signal and the set signal.
2. The lithium battery control circuit as claimed in claim 1, wherein the smooth transition circuit comprises:
a first current source associated with the sense current signal;
a first PMOS transistor, a first terminal of the first PMOS transistor being coupled to a first terminal of the first current source, a second terminal and a control terminal of the first PMOS transistor being coupled to a second terminal of the first current source;
a second PMOS transistor, a first terminal of the second PMOS transistor being coupled to the first terminal of the first current source and a first terminal of the first PMOS transistor, a control terminal of the second PMOS transistor being coupled to the control terminal of the first PMOS transistor;
a first comparator, a first input terminal of which receives a first reference voltage, and a second input terminal of which receives the feedback signal;
a third PMOS transistor, a first terminal of the third PMOS transistor being coupled to the first terminal of the second PMOS transistor, a second terminal of the third PMOS transistor being coupled to a second terminal of the second PMOS transistor, and a control terminal of the third PMOS transistor being coupled to an output terminal of the first comparator; and
a first resistor having a first end coupled to the second end of the second PMOS transistor and the second end of the third PMOS transistor and a second end coupled to a ground, wherein the first voltage is generated at the first end of the first resistor.
3. The lithium battery control circuit as claimed in claim 1, wherein the smooth transition circuit comprises:
a fourth PMOS transistor;
a second resistor, a first end of the second resistor being coupled to a second end of the fourth PMOS transistor, a second end of the second resistor being coupled to a ground terminal;
a fifth PMOS transistor, a first terminal of the fifth PMOS transistor being coupled to a first terminal of the fourth PMOS transistor, a control terminal of the fifth PMOS transistor being coupled to a control terminal of the fourth PMOS transistor;
a second current source, a first terminal of the second current source being coupled to a second terminal of the fifth PMOS transistor, a second terminal of the second current source being coupled to the ground terminal;
a switch, a control terminal of the switch receiving the mode signal, a first terminal of the switch being coupled to the first terminal of the second resistor; and
a third resistor, a first end of the third resistor being coupled to a second end of the switch, a second end of the third resistor being coupled to the ground terminal;
wherein the second voltage is generated at the first end of the second resistor.
4. The lithium battery control circuit as recited in claim 3, wherein the switch connects the second resistor in parallel with the third resistor when the mode signal indicates the first charging mode, the switch rendering the third resistor non-conductive when the mode signal indicates a non-first charging mode.
5. The lithium battery control circuit as claimed in claim 1, wherein the smooth transition circuit comprises:
a second comparator, a first input terminal of the second comparator receives the first voltage, a second input terminal of the second comparator receives the second voltage, and an output terminal of the second comparator outputs the reset signal.
6. The lithium battery control circuit as claimed in claim 1, wherein the off-time control circuit comprises:
a sixth PMOS transistor;
a seventh PMOS transistor, a first terminal of the seventh PMOS transistor being coupled to a first terminal of the sixth PMOS transistor, a control terminal of the seventh PMOS transistor being coupled to a second terminal and a control terminal of the sixth PMOS transistor;
a first NMOS transistor having a first terminal coupled to the second terminal and the control terminal of the sixth PMOS transistor;
a fourth resistor, a first end of the fourth resistor being coupled to a second end of the first NMOS transistor, a second end of the fourth resistor being coupled to a ground terminal;
a third comparator, a first input terminal of the third comparator receiving the feedback signal, a second input terminal of the third comparator being coupled to the first terminal of the fourth resistor and the second terminal of the first NMOS transistor, an output terminal of the third comparator being coupled to a control terminal of the first NMOS transistor;
a first capacitor, a first terminal of which is coupled to a second terminal of the seventh PMOS transistor, and a second terminal of which is coupled to the ground terminal;
a second NMOS transistor, a first terminal of the second NMOS transistor being coupled to the first terminal of the first capacitor, a second terminal of the second NMOS transistor being coupled to the ground terminal, and a control terminal of the second NMOS transistor receiving the duty ratio signal; and
a fourth comparator, a first input terminal of the fourth comparator is coupled to the second terminal of the seventh PMOS transistor and the first terminal of the first capacitor, a second input terminal of the fourth comparator receives a second reference voltage, and an output terminal of the fourth comparator outputs the setting signal.
7. The lithium battery control circuit as claimed in claim 6, wherein a current ratio through the sixth PMOS transistor to the seventh PMOS transistor is N: 1, wherein a current through the seventh PMOS transistor is defined as the first current, and N is a positive number.
8. The lithium battery control circuit as recited in claim 7, wherein the off-time control circuit charges the first capacitor with the first current according to the duty ratio signal to obtain an off-time that is linearly related to the output voltage.
9. The lithium battery control circuit of claim 1, wherein
The logic control circuit is coupled with the smooth conversion circuit and the closing time control circuit, and the logic control circuit generates the duty ratio signal for pulse frequency modulation according to the reset signal and the set signal.
10. The lithium battery control circuit as claimed in claim 1, wherein the first charging mode is a low current mode.
11. A lithium battery charger comprising:
a lithium battery control circuit, comprising:
a smooth transition circuit, generating a first voltage according to a sensing current signal and a feedback signal, generating a second voltage according to a mode signal, and comparing the first voltage with the second voltage to generate a reset signal, wherein the feedback signal is related to an output voltage, the mode signal is used for indicating whether in a first charging mode, and the second voltage in the first charging mode is smaller than the second voltage in a non-first charging mode, wherein the charging current generated by the lithium battery charger when the mode signal indicates in the first charging mode is smaller than the charging current generated by the lithium battery charger when the mode signal indicates in the non-first charging mode; and
a turn-off time control circuit, converting the feedback signal by a voltage-to-current conversion mechanism to generate a first current, and generating a setting signal by using the first current and a duty ratio signal;
a current sensing circuit for generating the sensing current signal according to an output current; and
a feedback circuit for generating the feedback signal according to an output voltage,
the lithium battery control circuit further comprises a logic control circuit, and the logic control circuit generates the duty ratio signal according to the reset signal and the setting signal.
12. The lithium battery charger of claim 11, further comprising a driver circuit, wherein the logic control circuit generates the duty cycle signal to the driver circuit and feeds back to the off-time control circuit based on the reset signal and the set signal.
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| CN201710025572.9A CN108306348B (en) | 2017-01-13 | 2017-01-13 | Lithium battery control circuit and lithium battery charger |
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| CN201710025572.9A CN108306348B (en) | 2017-01-13 | 2017-01-13 | Lithium battery control circuit and lithium battery charger |
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| CN108306348B true CN108306348B (en) | 2021-07-27 |
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| US7405539B2 (en) * | 2004-11-29 | 2008-07-29 | Mediatek Incorporation | Battery charger for preventing charging currents from overshooting during mode transition and method thereof |
| CN102280908B (en) * | 2010-06-10 | 2013-09-11 | 力林科技股份有限公司 | Heterodyne slope frequency generation mode for light and heavy load switching of power supply |
| CN105337497B (en) * | 2014-05-29 | 2019-07-05 | 展讯通信（上海）有限公司 | Improve the system of DC voltage booster circuit transient response |
| KR102452492B1 (en) * | 2015-05-06 | 2022-10-07 | 삼성전자주식회사 | Voltage converter and power management device including the same |
| CN105939040A (en) * | 2016-06-20 | 2016-09-14 | 深圳天珑无线科技有限公司 | Battery charging circuit, battery charging method and electronic equipment |
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