CN113702688B - Off-current detection circuit, off-current detection method, and switch charging circuit - Google Patents

Off-current detection circuit, off-current detection method, and switch charging circuit Download PDF

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CN113702688B
CN113702688B CN202111262551.1A CN202111262551A CN113702688B CN 113702688 B CN113702688 B CN 113702688B CN 202111262551 A CN202111262551 A CN 202111262551A CN 113702688 B CN113702688 B CN 113702688B
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current
signal
charging
switch
output
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CN113702688A (en
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赖哲人
周晓智
丛锋
戴兴科
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Shenzhen Weiyuan Semiconductor Co ltd
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Shenzhen Weiyuan Semiconductor Co ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
    • 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
    • H02J7/0031—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with safety or protection devices or circuits using battery or load disconnect circuits
    • 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
    • H02J7/0047—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with monitoring or indicating devices or circuits
    • 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
    • H02J7/007—Regulation of charging or discharging current or voltage
    • H02J7/00712—Regulation of charging or discharging current or voltage the cycle being controlled or terminated in response to electric parameters
    • H02J7/00714—Regulation of charging or discharging current or voltage the cycle being controlled or terminated in response to electric parameters in response to battery charging or discharging current

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  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
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Abstract

The application belongs to the technical field of charging, and provides an off-current detection circuit, an off-current detection method and a switch charging circuit, a first current sampling signal is obtained by sampling the current output by the second switch tube, and the second switch tube is switched off when the first current sampling signal rises to a preset current value, sampling the current output by the third switch tube to obtain a second current sampling signal, turning off the third switch tube when the second current sampling signal reaches a preset zero-crossing threshold value, generating an error amplification signal based on a difference between the output voltage and a target voltage to determine an idle time period, and the cut-off current judging module generates a cut-off current judging signal when the ratio of the charging time length to the idle time length reaches a preset ratio, therefore, whether the cut-off current reaches the preset value can be judged according to the ratio of the charging time length to the idle time length, and the problem that the cut-off current detection precision is low in the traditional cut-off current detection scheme is solved.

Description

Off-current detection circuit, off-current detection method, and switch charging circuit
Technical Field
The application belongs to the technical field of charging, and particularly relates to a cut-off current detection circuit, a cut-off current detection method and a switch charging circuit.
Background
Switched charging circuits have higher energy efficiency than linear charging circuits and are therefore often used in high power or high current charging applications. The charge cutoff current is the current near the end of charging, and the current value is lower and is also an important parameter in the charging circuit. Since the current value of the off-state current is low, it needs a high-precision detection circuit to detect the off-state current, and if the detection error is too large, adverse effects may be caused, such as: if the cut-off current is too high, the charging is ended too early and the battery cannot be fully charged, if the cut-off current is too small, the charging time is too long, or the detection circuit cannot detect, and the charging circuit is charged continuously.
Since the detection accuracy of the cut-off current is low, how to increase the detection accuracy of the cut-off current becomes a problem to be solved urgently at present.
Disclosure of Invention
An object of the present application is to provide an off-current detection circuit, an off-current detection method, and a switch charging circuit, which aim to increase the detection accuracy of an off-current.
The embodiment of the application provides an off-current detection circuit, is applied to switch charging circuit, switch charging circuit includes: the first end of the second switch tube is connected with the power supply, the second end of the second switch tube and the first end of the third switch tube are connected with the first end of the output inductor in a common mode, the second end of the third switch tube is grounded, and the cut-off current detection circuit comprises:
the first current comparison module is used for sampling the current output by the second switch tube to obtain a first current sampling signal and generating a first current comparison signal when the first current sampling signal rises to a preset current value so as to switch off the second switch tube and switch on the third switch tube;
the second current comparison module is used for sampling the current output by the third switching tube to obtain a second current sampling signal, and generating a second current zero-crossing signal when the second current sampling signal reaches a preset zero-crossing threshold value so as to turn off the third switching tube;
the error amplifier module is used for sampling the voltage of the second end of the output inductor to obtain an output sampling voltage and generating an error amplification signal according to the difference value between the output sampling voltage and a target voltage;
the idle time control module is used for generating an idle time control signal according to the error amplification signal and the second current zero-crossing signal to determine the idle time, and controlling the second switching tube to be conducted when the idle time is over;
the cutoff current judging module is used for generating a cutoff current judging signal when the ratio of the charging time length to the idle time length reaches a preset ratio; wherein a charging cycle of the switched charging circuit includes the charging duration and the idle duration.
In one embodiment, the off-current determining module includes:
a latch unit, configured to generate a first control signal and a second control signal according to the second current zero-crossing signal and the idle time duration control signal, where the first control signal and the second control signal have opposite levels;
and the timing unit is used for detecting the ratio of the charging time length to the idle time length according to the first control signal and the second control signal and generating a cut-off current judgment signal when the ratio of the charging time length to the idle time length reaches the preset ratio.
In one embodiment, the timing unit includes:
a timing capacitor;
a discharge subunit for discharging the timing capacitor with a current I;
the charging subunit is used for charging the timing capacitor by using current N x I, wherein N is the preset ratio;
a reset subunit, configured to reset the timing capacitor when a rising edge of the idle duration control signal occurs before a rising edge of the second current zero-crossing signal;
the voltage comparison subunit is used for detecting voltages at two ends of the timing capacitor to obtain a timing capacitor voltage signal, and comparing the voltage value of the timing capacitor voltage signal with a preset monitoring threshold value to generate a zero-crossing comparison signal;
and the first edge comparison subunit is used for judging that the ratio of the charging time length to the idle time length reaches the preset ratio when the rising edge of the idle time length control signal and the edge of the zero-crossing comparison signal are at the same moment, and outputting a cut-off judgment signal.
In one embodiment, the timing unit includes:
the counter subunit is used for performing addition counting at the clock frequency of N & ltx & gt f in the charging duration according to the first control signal, performing subtraction counting at the clock frequency of f in the idle duration according to the second control signal, and generating a counting signal;
and the second edge comparison subunit is used for judging that the ratio of the charging time length to the idle time length reaches the preset ratio when the rising edge of the idle time length control signal and the edge of the counting signal are at the same moment, and outputting a stop judgment signal.
In one embodiment, the off-current detection circuit further includes:
the second switch control module is used for receiving the first current comparison signal and the idle time control signal and controlling the on and off of the second switch tube according to the first current comparison signal and the idle time control signal;
and the third switch control module is used for receiving the second current zero-crossing signal and the first current comparison signal and controlling the on and off of the third switch tube according to the second current zero-crossing signal and the first current comparison signal.
In one embodiment, the idle period is inversely related to the error amplified signal.
In one embodiment, the cutoff current determining module is configured to obtain a charging duration according to the input voltage of the second switching tube, the output sampling voltage, the preset current value, and the output inductor, where a calculation formula of the charging duration is as follows: t1 = IPK*L/（VOUT/ VIN/（VIN-VOUT））；
Wherein, IPKFor the preset current value, VINIs the input voltage of the second switch tube, VOUTThe voltage is sampled for the output.
The embodiment of the present application further provides a method for detecting an off-current, which is applied to a switch charging circuit, where the switch charging circuit includes: the off-current detection method comprises the following steps that a first end of a second switching tube is connected with a power supply, a second end of the second switching tube and a first end of a third switching tube are connected with a first end of an output inductor in a shared mode, a second end of the third switching tube is grounded, and the off-current detection method comprises the following steps:
sampling the current output by the second switch tube to obtain a first current sampling signal, and generating a first current comparison signal when the first current sampling signal rises to a preset current value so as to turn off the second switch tube and turn on the third switch tube;
sampling the current output by the third switching tube to obtain a second current sampling signal, and generating a second current zero-crossing signal when the second current sampling signal reaches a preset zero-crossing threshold value so as to turn off the third switching tube;
sampling the voltage of the second end of the output inductor to obtain an output sampling voltage, and generating an error amplification signal according to the difference value between the output sampling voltage and a target voltage;
generating an idle time control signal according to the error amplification signal and the second current zero-crossing signal to determine an idle time, and controlling the second switching tube to be conducted when the idle time is over;
generating a cut-off current judgment signal when the ratio of the charging time length to the idle time length reaches a preset ratio; wherein a charging cycle of the switched charging circuit includes the charging duration and the idle duration.
The embodiment of the present application further provides a switch charging circuit, including: the first end of the second switching tube is connected with a power supply, the second end of the second switching tube and the first end of the third switching tube are connected to the first end of the output inductor in a shared mode, and the second end of the third switching tube is grounded; and
an off-current detection circuit as claimed in any one of the preceding claims.
In one embodiment, the switch charging circuit further comprises: the circuit comprises a first switch tube, an input capacitor and an output capacitor;
the first switch tube is arranged between the power supply and the second switch tube, the first end of the input capacitor is connected with the first end of the second switch tube, the second end of the input capacitor is grounded, the first end of the output capacitor is connected with the second end of the output inductor in a common mode to the battery, and the second end of the output capacitor is grounded.
The application provides an off-current detection circuit, an off-current detection method and a switch charging circuit, a first current sampling signal is obtained by sampling the current output by the second switch tube, and the second switch tube is switched off when the first current sampling signal rises to a preset current value, sampling the current output by the third switch tube to obtain a second current sampling signal, turning off the third switch tube when the second current sampling signal reaches a preset zero-crossing threshold value, generating an error amplification signal according to a difference between the voltage of the output inductor and a target voltage to determine an idle period, and the cut-off current judging module generates a cut-off current judging signal when the ratio of the charging time length to the idle time length reaches a preset ratio, therefore, whether the cut-off current reaches the preset value can be judged according to the ratio of the charging time length to the idle time length, and the problem that the cut-off current detection precision is low in the traditional cut-off current detection scheme is solved.
Drawings
Fig. 1 is a schematic diagram illustrating a relationship between an average charging current and a battery voltage of a switched charging circuit according to an embodiment of the present application.
Fig. 2 is a schematic structural diagram of a Buck circuit according to an embodiment of the present application.
Fig. 3 is a schematic waveform diagram of a switching charging circuit in a constant current phase according to an embodiment of the present application.
Fig. 4 is a waveform diagram of a switching charging circuit in a constant voltage phase according to an embodiment of the present application.
Fig. 5 is a schematic structural diagram of an off-current detection circuit according to an embodiment of the present application.
Fig. 6 is a schematic structural diagram of an off-current determining module according to an embodiment of the present application.
Fig. 7 is a schematic structural diagram of an off-current determining module according to another embodiment of the present application.
Fig. 8 is a schematic diagram of waveforms of a control signal of the second switching transistor Q2, a control signal of the third switching transistor Q3, a inductor current at the output inductor L1, and a voltage signal at the first end of the timing capacitor CT according to an embodiment of the present application.
Fig. 9 is a schematic diagram of waveforms of a control signal of the second switching transistor Q2, a control signal of the third switching transistor Q3, an inductor current at the output inductor L1, and a voltage signal at the first end of the timing capacitor CT according to another embodiment of the present application.
Fig. 10 is a schematic structural diagram of a timing unit according to an embodiment of the present application.
Fig. 11 is a schematic diagram of waveforms of a control signal of the second switching transistor Q2, a control signal of the third switching transistor Q3, an inductor current at the output inductor L1, and a voltage signal at the first end of the timing capacitor CT according to another embodiment of the present application.
Fig. 12 is a schematic structural diagram of an off-current detection circuit according to another embodiment of the present application.
Fig. 13 is a flowchart illustrating an off-current detection method according to an embodiment of the present application.
Fig. 14 is a schematic structural diagram of a switch charging circuit according to an embodiment of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
Fig. 1 is a diagram of a lithium battery charging process, in which the input voltage of a charging circuit is kept constant, the charging process includes a constant current stage (CC stage) and a constant voltage stage (CV stage), in the CC stage, the average charging current of a switching charging circuit is kept constant (for example, the input voltage of 5V in fig. 1 is kept constant), the battery voltage of a lithium battery is gradually increased (for example, gradually increased from 2.8V), in the CV stage, the average charging current of the switching charging circuit is decreased, the battery voltage of the lithium battery is kept constant, and the cutoff current is the current near the end of charging, at this time, since the average charging current of the switching charging circuit is lower, the requirement on the detection accuracy is higher.
The switch charging circuit may adopt a switching circuit with a Buck topology, and taking the Buck topology as an example, as shown in fig. 2, the switch charging circuit includes: the power supply comprises a second switching tube Q2, a third switching tube Q3 and an output inductor L1, specifically, a first end of the second switching tube Q2 is connected with the power supply 10, a second end of the second switching tube Q2 and a first end of the third switching tube Q3 are commonly connected with a first end of the output inductor L1, and a second end of the third switching tube Q3 is grounded.
When the switch charging circuit operates at a larger inductor current value, the inductor current operates in a Continuous Conduction Mode (CCM for short), and the current waveform thereof is shown as CL in fig. 3, where a square wave QG is a control signal of the gates of the second switching tube Q2 and the third switching tube Q3, and a triangular wave is a current waveform in the output inductor L1. When the square wave signal is "high", the second switching tube Q2 is turned on, the third switching tube Q3 is turned off, and the inductor current in the output inductor L1 rises, and when the square wave signal is "low", the second switching tube Q2 is turned off, the third switching tube Q3 is turned on, and the inductor current in the output inductor L1 falls.
When the Buck switching circuit operates at a smaller value of the inductor current, the inductor current tends to operate in a Discontinuous Conduction Mode (DCM), and current waveforms thereof are as shown in fig. 4, where Q2G and Q3G are control signals of control ends of the second switching tube Q2 and the third switching tube Q3, respectively, and the triangular wave is a current waveform CL in the output inductor L1.
When the Q2G signal is "high", the second transistor Q2 is turned on, and the third transistor Q3 is turned off, so that the inductor current in the output inductor L1 rises. When the inductor current in the output inductor L1 rises to a predetermined current value IPKWhen the signal Q3G goes high, the second transistor Q2 is turned off, the third transistor Q3 is turned on, and the inductor current in the output inductor L1 decreases.When the inductor current drops to 0, the second switching tube Q2 and the third switching tube Q3 are turned off simultaneously. The above control occurs periodically, and the feedback control circuit adjusts the length of the idle time period T2 in fig. 4 to control the average output current, i.e., the average charging current, of the Buck switching circuit. When the charging is in the CV stage, the charging current gradually decreases, and the time of the idle time period T2 gradually increases.
Because the Buck switching circuit works in the discontinuous conduction mode, the closer to the end of charging, the smaller the inductance current value on the output inductance L1, and the higher the requirement on the detection accuracy of the current, in order to improve the detection accuracy of the off-current, the embodiment of the present application provides an off-current detection circuit, which is applied to a switching charging circuit, and as shown in fig. 5, the off-current detection circuit in the embodiment includes: the circuit comprises a first current comparison module 21, a second current comparison module 22, an error amplifier module 23, an idle time control module 24 and a cut-off current judgment module 25.
Specifically, the first current comparing module 21 is connected to the second end of the second switch tube Q2, the first end of the second switch tube Q2 is connected to the input power source 10, when the second switch tube Q2 is turned on and the third switch tube Q3 is turned off, the switch charging circuit is in a charging time period, and the inductor current at the output inductor L1 gradually rises, in a specific application, the first current comparing module 21 samples the current output by the second switch tube Q2, for example, a sampling resistor is arranged at the output end of the second switch tube Q2, so as to convert the current at the output end thereof into a corresponding voltage signal, that is, the first current sampling signal is obtained by sampling the current output by the second switch tube Q2 through the first current comparing module 21, and when the first current sampling signal rises to a preset current value, a first current comparing signal is generated to turn off the second switch tube Q2 and turn on the third switch tube Q3, at this time, when the current flowing through the second switch tube Q2 reaches the preset current value, the second switch Q2 is turned off, and the third switch Q3 is turned on, so that the predetermined current value is the peak current of the inductor current in the output inductor L1.
In a specific application, the second current comparing module 22 samples the current output by the third switching tube Q3, for example, a sampling resistor is disposed at the output end of the third switching tube Q3, so as to convert the current at the output end thereof into a corresponding voltage signal, that is, the second current comparing module 22 samples the current output by the third switching tube Q3 to obtain a second current sampling signal, and when the second current sampling signal reaches a preset zero-crossing threshold, a second current zero-crossing signal is generated to turn off the third switching tube Q3. When the second switching tube Q2 is turned off, the third switching tube Q3 is turned on, and the switch charging circuit is in a discharging time period at this time, the inductor current on the output inductor L1 gradually decreases, the second current comparing module 22 is configured to monitor the current flowing through the second switching tube Q2, and when the current flowing through the second switching tube Q2 reaches a preset zero-crossing threshold, the current indicates that discharging is completed, and the preset zero-crossing value may be "0".
The error amplifier module 23 is connected to the second end of the output inductor L1 and is connected to the positive terminal of the battery 12, and the error amplifier module 23 is configured to sample the voltage at the second end of the output inductor L1 to obtain an output sampling voltage, and generate an error amplification signal according to a difference between the output sampling voltage and a target voltage.
The idle duration control module 24 is connected to the error amplifier module 23 and the second current comparison module 22, the idle duration control module 24 generates an idle duration control signal according to the error amplification signal and the second current zero-crossing signal to determine an idle duration, and controls the second switch tube Q2 to be turned on when the idle duration is finished, after the second switch tube Q2 is turned on, the inductor current in the output inductor L1 starts to rise, and when the inductor current reaches a preset current value, the second switch tube Q2 is turned off, and the third switch tube Q3 is turned on, so that a new period starts.
The cut-off current judging module 25 is connected with the idle time length control module 24 and the second current comparing module 22, the cut-off current judging module 25 is used for judging the ratio of the charging time length to the idle time length, and generating a cut-off current judging signal when the ratio of the charging time length to the idle time length reaches a preset ratio, so that the charging current of the switch charging circuit reaches the cut-off current is determined according to the ratio of the charging time length to the idle time length, when the charging current of the switch charging circuit reaches the cut-off current, the second switch tube Q2 and the third switch tube Q3 are controlled to be turned off, and the switch charging circuit stops charging; wherein one charging cycle of the switched charging circuit comprises a charging duration and an idle duration.
In the CV charging stage of the switching charging circuit, the voltage of the battery also gradually rises, the difference between the output sampling voltage and the target voltage gradually decreases, the idle time duration gradually increases, and the charging current of the switching charging circuit is gradually lowered, wherein the idle time duration T2 is a time period from when the current in the third switching tube Q3 reaches a preset zero crossing value to when the second switching tube Q2 is turned on in a new period, and the charging time duration is the sum of the charging time and the discharging time of the output inductor L1.
Referring to FIG. 4, during the CV charging phase of the switched charging circuit, the average charging current I of the switched charging circuitAVThe calculation formula is as follows:
IAV=0.5IPK*T1/(T1+T2) = 0.5IPK/(1+T2/T1) (1)；
wherein, T1For the duration of the charge in the charging cycle, T2For the idle duration in the charging cycle, IPKIn order to output the peak value of the inductor current on the inductor L1, based on the principle of formula (1), in the specific application, a higher I is adoptedPKThe value is used to improve the measurement accuracy, and the cut-off current is taken as IAVThe value of (1) can determine the off-current monitoring ratio of T2/T1, and when T2/T1 reaches the set off-current monitoring ratio, the average charging current I can be judgedAVWhen the cut-off current is reached, the Buck switch circuit is cut off and charged, and the T2/T1 is a relative value, the relative value is easier to monitor, and therefore the detection accuracy of the cut-off current is easier to improve.
Referring to fig. 5, the first current comparing module 21 compares the sampled current in the second switching transistor Q2 with the set IPKValue, when the sampled current reaches IPKWhen the voltage is high, the output signal turns off the second transistor Q2, and controls the third transistor Q3 to turn on, so that the inductive current will decrease. The second current comparison module 22 comparesThe sampled current of the third switching tube Q3 and a preset zero-crossing threshold, which may be 0, are sent out to turn off the third switching tube Q3 when the current crosses zero, and at the same time, the idle duration control module 24 is started. The idle period control signal is controlled by the error amplifier output to determine the idle period T2, and as the CV stage charging progresses, the charging current will decrease and the idle period T2 will increase. When the time T2 expires, the idle period control module 24 outputs a signal to turn on the second switch Q2, which is the beginning of the rise of the inductor current when the inductor current reaches IPKAt this time, the second transistor Q2 is turned off, the third transistor Q3 is turned on, and a new cycle is started.
In the present embodiment, the cutoff current determining module 25 monitors the ratio of the idle time period T2 and the charging time period T1, generates a cutoff current determining signal when the ratio reaches a preset ratio, and the charging management unit determines that the average current of the output inductor L1 (i.e., the average current of charging) has reached the charging cutoff current according to the cutoff current determining signal. For example, if the value of T2/T1 is set to 8, when the value of T2 reaches 8 times the value of T1, the average charging current drops to the set cutoff current, I, according to equation (1)PKIs IAV18 times of that ofPKIs much higher than IAVTherefore I isAVThe accuracy of (c) can be relatively high.
In one embodiment, referring to fig. 6, the off-current determining module 25 includes: latch unit 251 and timing unit 252.
The latch unit 251 is connected to the second current comparing module 22 and the idle time period controlling module 24, and the latch unit 251 performs a logic operation according to the second current zero-crossing signal and the idle time period controlling signal to generate a first controlling signal and a second controlling signal, wherein the levels of the first controlling signal and the second controlling signal are opposite.
The timing unit 252 is configured to detect a ratio of the charging duration to the idle duration according to the first control signal and the second control signal, and generate an off-current determination signal when the ratio of the charging duration to the idle duration reaches a preset ratio.
In this embodiment, during the charging period T1, the second current comparing module 22 compares the sampled current of the third switching tube Q3 with a preset zero-crossing threshold, and generates a second current zero-crossing signal to the R terminal of the latch unit 251 when the current crosses zero, at which time the third switching tube Q3 is turned off, the charging period T1 in the timing unit 252 is timed out, and the idle period T2 is started. The idle duration control module 24 generates an idle duration control signal to determine an idle duration T2, and sends the idle duration T2 to the S terminal of the latch unit 251, at this time, the idle duration T2 in the timing unit 252 is timed to end, the timing unit 252 determines the ratio of the charging duration to the idle duration, and generates a cutoff current determination signal when the ratio of the charging duration to the idle duration reaches a preset ratio.
In one embodiment, the latch unit 251 can be an RS latch, which is a two-input and two-output circuit, and the RS latch is composed of two nand gates connected with each other in a cross feedback manner, and the two output signals of the two nand gates have opposite levels.
In one embodiment, referring to fig. 7, the timing unit 252 includes: a timing capacitor CT, a charging subunit 2522, a discharging subunit 2521, a resetting subunit 2523, a voltage comparator subunit 2524, and a first edge comparator subunit 2525.
The charging unit 2522 charges the timing capacitor CT with a current N × I, where N is a preset ratio; the discharge subunit 2521 is configured to discharge the timing capacitor CT with the current I; the reset subunit 2523 is configured to reset the timing capacitor CT when a rising edge of the idle-time long control signal occurs before a rising edge of the second current zero-crossing signal; the voltage comparison subunit 2524 is configured to detect voltages at two ends of the timing capacitor CT to obtain a timing capacitor CT voltage signal, and compare a voltage value of the timing capacitor CT voltage signal with a preset monitoring threshold value to generate a zero-crossing comparison signal; the first edge comparison subunit 2525 is configured to determine that the ratio of the charging time duration to the idle time duration reaches a preset ratio when a rising edge of the idle time duration control signal and an edge of the zero-crossing comparison signal are at the same time, and output a cut-off determination signal.
In the present embodiment, the timing unit 252 performs ratio monitoring of the charging time period and the idle time period through the timing capacitor CT, during T1, the capacitor CT is charged by N times of the current I (for example, 8 times), and during T2, the capacitor CT is discharged by 1 time of the current I. The voltage comparison subunit 2524 compares the voltage value of the voltage signal of the timing capacitor CT with a preset monitoring threshold (e.g., 0) to generate a zero-crossing comparison signal, and the first edge comparison subunit 2525 determines that the ratio of the charging time period T1 to the idle time period T2 reaches a preset ratio when the rising edge of the idle time period control signal and the edge of the zero-crossing comparison signal are at the same time, and outputs a cut-off determination signal.
The rising edge of the idle period control signal output by the idle period control module 24 represents the start of T1, and the second current zero crossing signal output by the second current comparison module 22 represents the start of T2. If the next rising edge of the output of the idle period control module 24 (i.e. the rising edge of the signal at the S terminal of the latch unit 251) occurs before the zero crossing of the current of the third switch Q3 (i.e. the rising edge of the signal at the R terminal of the latch unit 251), the first control signal output by the latch unit 251 will enable the reset subunit 2523 to reset the timing capacitor CT, and start a new period, at this time, the first edge comparator subunit 2525 will not output the off determination signal, the waveform of the control signal Q2G of the second switch Q2, the waveform of the control signal Q3G of the third switch Q3, and the waveform I of the inductor current at the output inductor L1AVAnd a voltage signal V at a first terminal of the timing capacitor CTCTIs shown in FIG. 8, wherein VCTPKAs a voltage signal VCTThe peak voltage of (c).
If the rising edge of the output of the next idle time period control module 24 occurs when the current of the third switching tube Q3 passes through zero, the rising edge of the idle time period control signal and the edge of the zero-crossing comparison signal are at the same time, at this time, the timing capacitor CT is completely discharged, the voltage value of the voltage signal of the timing capacitor CT reaches the preset monitoring threshold (for example, 0), the voltage comparison subunit 2524 generates the zero-crossing comparison signal, the first edge comparison subunit 2525 judges that the rising edge of the idle time period control signal and the edge of the zero-crossing comparison signal are at the same time, judges that the ratio of the charging time period T1 to the idle time period T2 reaches the preset ratio, and outputs a cut-off judgment signal, the waveform of the control signal Q2G of the second switching tube Q2,the waveform of the control signal Q3G of the third switching tube Q3 outputs the waveform I of the inductor current on the inductor L1AVAnd a voltage signal V at a first terminal of the timing capacitor CTCTIs shown in FIG. 9, where VCTPKAs a voltage signal VCTThe peak voltage of (c).
In one embodiment, the reset subunit 2523 may include a single pulse reset circuit and a reset switch, the first end of the reset switch is connected to the first end of the timing capacitor CT, the second end of the reset switch is grounded, the control end of the reset switch is connected to the single pulse reset circuit, when the single pulse reset circuit receives the first control signal from the output Q of the latch unit 251, the single pulse reset circuit is activated to send a reset control signal, and the reset switch is turned on according to the reset control signal, so as to reset the timing capacitor CT, and start a new cycle.
In one embodiment, the voltage comparator subunit 2524 may be a comparator.
In one embodiment, referring to fig. 10, the timing unit 252 includes: a counter subunit 2526 and a second edge comparator subunit 2527.
The counter subunit 2526 is configured to perform an addition count at a clock frequency of N × f during the charging duration according to the first control signal, perform a subtraction count at a clock frequency of f during the idle duration according to the second control signal, and generate a count signal.
The second edge comparing subunit 2527 is configured to determine that the ratio of the charging duration to the idle duration reaches a preset ratio when the rising edge of the idle duration control signal and the edge of the count signal are at the same time, and output a stop determination signal.
In this embodiment, the clock of the counter subunit 2526 has two frequencies, one is the basic output frequency N × f of the clock, and the other is the clock frequency f that is N times (e.g., 8 times) smaller. At the beginning of the charging period T1, the counter subunit 2526 is cleared and then counted up at the basic clock frequency N × f. When the idle period T2 is entered, the counter counts down at a clock frequency f that is N times smaller. The second edge comparing subunit 2527 compares the edge of the count signal output by the counter subunit 2526 with the rising edge of the idle time period control signal, determines that the average charging current of the switched charging circuit reaches the off-current if the counter reaches zero before the rising edge of the output of the idle time period control module 24, otherwise the average charging current of the switched charging circuit does not reach the off-current, and the waveforms of the control signal of the second switching transistor Q2, the control signal of the third switching transistor Q3, the inductor current at the output inductor L1, and the voltage signal at the first terminal of the timing capacitor CT are as shown in fig. 11.
In one embodiment, referring to fig. 12, the off-current detection circuit further includes: a second switch control module 26, and a third switch control module 27.
The second switch control module 26 is configured to receive the first current comparison signal and the idle duration control signal, and control the on and off of the second switch Q2 according to the first current comparison signal and the idle duration control signal.
The third switching control module 27 is configured to receive the second current zero-crossing signal and the first current comparison signal, and control the on/off of the third switching tube Q3 according to the second current zero-crossing signal and the first current comparison signal.
In this embodiment, the second switch control module 26 and the third switch control module 27 are used as signal relay processing circuits, and are configured to respectively control the switching states of the second switch tube Q2 and the third switch tube Q3 according to an input signal, when a current flowing through the second switch tube Q2 reaches a preset current value, a first current comparison signal is generated and sent to the second switch control module 26 and the third switch control module 27, the second switch control module 26 controls the second switch tube Q2 to be turned off, the third switch control module 27 controls the third switch tube Q3 to be turned on, and the second switch control module 26 controls the second switch tube Q2 to be turned on according to an idle duration control signal, so as to control the size of the idle duration T2. When the second current sampling signal reaches the preset zero-crossing threshold, the second current comparing module 22 generates a second current zero-crossing signal, and the third switching control module 27 turns off the third switching tube Q3 according to the second current zero-crossing signal.
In one embodiment, the idle duration is inversely related to the error amplified signal.
In this embodiment, the idle period control signal is controlled by the error amplifier output to determine the idle period T2, and as the CV stage charging progresses, the charging current decreases and the idle period T2 increases. When the time T2 expires, the idle period control module 24 outputs a signal to turn on the second switch Q2, which is the beginning of the rise of the inductor current when the inductor current reaches IPKAt this time, the second transistor Q2 is turned off, the third transistor Q3 is turned on, and a new cycle is started.
In an embodiment, the off-current determining module 25 is configured to obtain a charging duration according to the input voltage, the output sampling voltage, the preset current value and the output inductor L1 of the second switch transistor Q2, where the charging duration is calculated by:
T1 =IPK*L/（VOUT/ VIN/（VIN-VOUT））（2）；
wherein, IPKTo a predetermined current value, VINIs the input voltage, V, of the second switching tube Q2OUTTo output a sampled voltage.
In this embodiment, IPKThe value is a fixed preset value, L is the inductance value of the output inductor L1, the charging time period T1 can be calculated by formula (2), the cutoff current judgment module 25 generates a cutoff current judgment signal when the ratio of the charging time period T1 to the idle time period T2 reaches a preset ratio, and the average charging current I of the switching charging circuit at this time isAVAnd when the preset cut-off current is reached, the charging is finished.
The embodiment of the present application further provides a method for detecting an off-current, which is applied to a switch charging circuit, where the switch charging circuit includes: the second switch tube Q2, the third switch tube Q3 and the output inductor L1, the first end of the second switch tube Q2 is connected to the power supply 10, the second end of the second switch tube Q2 and the first end of the third switch tube Q3 are connected to the first end of the output inductor L1 in common, and the second end of the third switch tube Q3 is connected to the ground.
Referring to fig. 13, the off-current detection method in the present embodiment includes steps S10 to S60.
In step S10, the current output from the second switch Q2 is sampled to obtain a first current sampling signal, and when the first current sampling signal rises to a preset current value, a first current comparison signal is generated to turn off the second switch Q2 and turn on the third switch Q3.
Specifically, in this embodiment, when the second switch Q2 is turned on and the third switch Q3 is turned off, the switch charging circuit is in a charging time period, the inductor current in the output inductor L1 gradually rises, the first current comparison module 21 samples the current output by the second switch Q2 to obtain a first current sampling signal, and generates a first current comparison signal when the first current sampling signal rises to a preset current value, so as to turn off the second switch Q2 and turn on the third switch Q3, at this time, since the current flowing through the second switch Q2 reaches the preset current value, the second switch Q2 is turned off, and the third switch Q3 is turned on, so that the preset current value is the peak current of the inductor current in the output inductor L1.
In step S20, the current output by the third switching tube Q3 is sampled to obtain a second current sampling signal, and when the second current sampling signal reaches a preset zero-crossing threshold, a second current zero-crossing signal is generated to turn off the third switching tube Q3.
In this embodiment, the second current sampling signal may be obtained by sampling the current output by the third switching tube Q3 through the second current comparing module 22, and when the second current sampling signal reaches the preset zero-crossing threshold, the second current zero-crossing signal is generated to turn off the third switching tube Q3. When the second switching tube Q2 is turned off, the third switching tube Q3 is turned on, and the switch charging circuit is in a discharging time period at this time, the inductor current on the output inductor L1 gradually decreases, the second current comparing module 22 is configured to monitor the current flowing through the second switching tube Q2, and when the current flowing through the second switching tube Q2 reaches a preset zero-crossing threshold, the current indicates that discharging is completed, and the preset zero-crossing value may be "0".
In step S30, the voltage at the second terminal of the output inductor L1 is sampled to obtain an output sampled voltage, and an error amplified signal is generated according to a difference between the output sampled voltage and a target voltage.
In this embodiment, the idle period control signal is controlled by the error amplifier output to determine the idle period T2, and as the CV stage charging progresses, the charging current decreases and the idle period T2 increases.
In step S40, an idle duration control signal is generated according to the error amplification signal and the second current zero crossing signal to determine an idle duration, and the second switch Q2 is controlled to be turned on when the idle duration ends.
In this embodiment, the idle duration control module 24 may generate an idle duration control signal according to the error amplification signal and the second current zero-crossing signal to determine the idle duration, and control the second switch Q2 to be turned on when the idle duration T2 ends, after the second switch Q2 is turned on, the inductor current in the output inductor L1 starts to rise, and when the inductor current reaches a preset current value, the second switch Q2 is turned off, and the third switch Q3 is turned on, so as to start a new period.
In step S50, a cutoff current determination signal is generated when the ratio of the charging period to the idle period reaches a preset ratio; wherein one charging cycle of the switched charging circuit comprises a charging duration and an idle duration.
In the embodiment, when the charging current of the switch charging circuit reaches the cut-off current, the second switching tube Q2 and the third switching tube Q3 are controlled to be turned off, and the switch charging circuit stops charging.
In the CV charging stage of the switching charging circuit, the voltage of the battery also gradually rises, the difference between the output sampling voltage and the target voltage gradually decreases, the idle time duration gradually increases, and the charging current of the switching charging circuit is gradually lowered, wherein the idle time duration T2 is a time period from when the current in the third switching tube Q3 reaches a preset zero crossing value to when the second switching tube Q2 is turned on in a new period, and the charging time duration is the sum of the charging time and the discharging time of the output inductor L1.
The embodiment of the present application further provides a switch charging circuit, including: the second switch tube Q2, the third switch tube Q3 and the output inductor L1, the first end of the second switch tube Q2 is connected to the power supply 10, the second end of the second switch tube Q2 and the first end of the third switch tube Q3 are connected to the first end of the output inductor L1 in common, and the second end of the third switch tube Q3 is connected to the ground; and an off-current detection circuit as in any one of the above embodiments.
In one embodiment, referring to fig. 14, the switch charging circuit further comprises: input capacitance CINAn output capacitor COUTAnd a first switching tube Q1.
A first switch Q1 between the power supply 10 and the second switch Q2, and an input capacitor CINIs connected to a first terminal of a second switching tube Q2, an input capacitor CINIs grounded, and an output capacitor COUTAnd the second end of the output inductor L1 are connected to the battery 11 in common, and the output capacitor COUTThe second terminal of (a) is grounded.
In this embodiment, the first switch Q1 in fig. 14 functions to block reverse current and may not be part of the basic Buck switch circuit.
In a specific application, the input capacitor C in the charging circuit is switchedINA second switch tube Q2, a third switch tube Q3, an output inductor L1 and an output capacitor COUTA Buck switching circuit is formed.
The application provides an off-current detection circuit, an off-current detection method and a switch charging circuit, a first current sampling signal is obtained by sampling the current output by the second switch tube, and the second switch tube is switched off when the first current sampling signal rises to a preset current value, sampling the current output by the third switch tube to obtain a second current sampling signal, turning off the third switch tube when the second current sampling signal reaches a preset zero-crossing threshold value, generating an error amplification signal according to a difference between the voltage of the output inductor and a target voltage to determine an idle period, and the cut-off current judging module generates a cut-off current judging signal when the ratio of the charging time length to the idle time length reaches a preset ratio, therefore, whether the cut-off current reaches the preset value can be judged according to the ratio of the charging time length to the idle time length, and the problem that the cut-off current detection precision is low in the traditional cut-off current detection scheme is solved.
The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims (10)

1. An off-current detection circuit for a switched charging circuit, the switched charging circuit comprising: the utility model discloses a power supply, its characterized in that, cut-off current detection circuit includes:
the first current comparison module is used for sampling the current output by the second switch tube to obtain a first current sampling signal and generating a first current comparison signal when the first current sampling signal rises to a preset current value so as to switch off the second switch tube and switch on the third switch tube;
the second current comparison module is used for sampling the current output by the third switching tube to obtain a second current sampling signal, and generating a second current zero-crossing signal when the second current sampling signal reaches a preset zero-crossing threshold value so as to turn off the third switching tube;
the error amplifier module is used for sampling the voltage of the second end of the output inductor to obtain an output sampling voltage and generating an error amplification signal according to the difference value between the output sampling voltage and a target voltage;
the idle time control module is used for generating an idle time control signal according to the error amplification signal and the second current zero-crossing signal to determine the idle time, and controlling the second switching tube to be conducted when the idle time is over;
the cutoff current judging module is used for generating a cutoff current judging signal when the ratio of the charging time length to the idle time length reaches a preset ratio; wherein a charging cycle of the switched charging circuit includes the charging duration and the idle duration.
2. The off-current detection circuit according to claim 1, wherein the off-current determination module includes:
a latch unit, configured to generate a first control signal and a second control signal according to the second current zero-crossing signal and the idle time duration control signal, where the first control signal and the second control signal have opposite levels;
and the timing unit is used for detecting the ratio of the charging time length to the idle time length according to the first control signal and the second control signal and generating a cut-off current judgment signal when the ratio of the charging time length to the idle time length reaches the preset ratio.
3. The off-current detection circuit according to claim 2, wherein the timing unit includes:
a timing capacitor;
a discharge subunit for discharging the timing capacitor with a current I;
the charging subunit is used for charging the timing capacitor by using current N x I, wherein N is the preset ratio, and I is a discharging current;
a reset subunit, configured to reset the timing capacitor when a rising edge of the idle duration control signal occurs before a rising edge of the second current zero-crossing signal;
the voltage comparison subunit is used for detecting voltages at two ends of the timing capacitor to obtain a timing capacitor voltage signal, and comparing the voltage value of the timing capacitor voltage signal with a preset monitoring threshold value to generate a zero-crossing comparison signal;
and the first edge comparison subunit is used for judging that the ratio of the charging time length to the idle time length reaches the preset ratio when the rising edge of the idle time length control signal and the edge of the zero-crossing comparison signal are at the same moment, and outputting a cut-off judgment signal.
4. The off-current detection circuit according to claim 2, wherein the timing unit includes:
the counter subunit is used for performing addition counting at the clock frequency of N & ltx & gt f in the charging duration according to the first control signal, performing subtraction counting at the clock frequency of f in the idle duration according to the second control signal, and generating a counting signal; wherein N is the preset ratio;
and the second edge comparison subunit is used for judging that the ratio of the charging time length to the idle time length reaches the preset ratio when the rising edge of the idle time length control signal and the edge of the counting signal are at the same moment, and outputting a stop judgment signal.
5. The off-current detection circuit according to claim 1, further comprising:
the second switch control module is used for receiving the first current comparison signal and the idle time control signal and controlling the on and off of the second switch tube according to the first current comparison signal and the idle time control signal;
and the third switch control module is used for receiving the second current zero-crossing signal and the first current comparison signal and controlling the on and off of the third switch tube according to the second current zero-crossing signal and the first current comparison signal.
6. The off-current detection circuit of claim 1, wherein the idle period is inversely related to the error amplified signal.
7. The off-current detection circuit of claim 1, wherein the off-current determination module is configured to obtain a charging duration according to the input voltage of the second switching tube, the output sampling voltage, the preset current value, and the output inductor, and the charging duration is calculated by a formula: t1 = IPK*L/（VOUT/ VIN/（VIN-VOUT））；
Wherein, IPKFor the preset current value, VINIs the input voltage of the second switch tube, VOUTThe voltage is sampled for the output.
8. An off-current detection method is applied to a switch charging circuit, and the switch charging circuit comprises: the detection method comprises a second switching tube, a third switching tube and an output inductor, wherein the first end of the second switching tube is connected with a power supply, the second end of the second switching tube and the first end of the third switching tube are connected with the first end of the output inductor in a shared mode, and the second end of the third switching tube is grounded, and the detection method is characterized by comprising the following steps:
sampling the current output by the second switch tube to obtain a first current sampling signal, and generating a first current comparison signal when the first current sampling signal rises to a preset current value so as to turn off the second switch tube and turn on the third switch tube;
sampling the current output by the third switching tube to obtain a second current sampling signal, and generating a second current zero-crossing signal when the second current sampling signal reaches a preset zero-crossing threshold value so as to turn off the third switching tube;
sampling the voltage of the second end of the output inductor to obtain an output sampling voltage, and generating an error amplification signal according to the difference value between the output sampling voltage and a target voltage;
generating an idle time control signal according to the error amplification signal and the second current zero-crossing signal to determine an idle time, and controlling the second switching tube to be conducted when the idle time is over;
generating a cut-off current judgment signal when the ratio of the charging time length to the idle time length reaches a preset ratio; wherein a charging cycle of the switched charging circuit includes the charging duration and the idle duration.
9. A switched charging circuit, comprising: the first end of the second switching tube is connected with a power supply, the second end of the second switching tube and the first end of the third switching tube are connected to the first end of the output inductor in a shared mode, and the second end of the third switching tube is grounded; and
the off-current detection circuit as claimed in any one of claims 1 to 7.
10. The switched charging circuit of claim 9, further comprising: the circuit comprises a first switch tube, an input capacitor and an output capacitor;
the first switch tube is arranged between the power supply and the second switch tube, the first end of the input capacitor is connected with the first end of the second switch tube, the second end of the input capacitor is grounded, the first end of the output capacitor is connected with the second end of the output inductor in a common mode to the battery, and the second end of the output capacitor is grounded.
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