Charging mode switching circuit suitable for boost lithium battery charging chip

Abstract

The invention is suitable for the technical field of lithium battery charging management, and provides a charging mode switching circuit suitable for a boost lithium battery charging chip. The PWM boost type lithium battery charging chip is connected in the boost lithium battery charging circuit with the mode switching function, the charging current is controlled through the first inductive current detection input end, the battery voltage is monitored through the battery voltage detection input end, and when it is detected that the battery voltage reaches the final cut-off voltage for the first time, the final cut-off voltage is cut off through de-jitter time delay. When the battery voltage reaches the final cut-off voltage for the second time, the charging current is controlled through a second inductive current detection input end, at the moment, a normal charging mode is switched into a low-current charging mode, and when it is detected that the battery voltage reaches the final cut-off voltage for the second time, de-jitter time delay is conducted, the low-current charging mode ends, and charging ends. Therefore, the battery voltage is prevented from being greatly reduced when the charging current is closed after the charging is finished, so that the charging saturation of the PWM boost type lithium battery charging chip circuit is effectively increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery charging management, and in particular relates to a charging mode switching circuit suitable for a boost lithium battery charging chip. Background Art

[0002] With the development of technology, the electronic products we use are becoming more and more portable, such as flashlights, small fans, etc., which usually use lithium batteries. In order to charge lithium batteries, we need to use lithium battery charging chips. When the input voltage of the charging power supply is lower than the voltage when the lithium battery is fully charged, a boost type lithium battery charging chip is required.

[0003] In a boost-type lithium battery charging chip, when it is detected that the lithium battery voltage reaches the full voltage (such as the full voltage of a dual-cell lithium battery is 8.4V), the charging current will be turned off. However, at this time, the battery voltage will drop, resulting in insufficient battery charging saturation. Therefore, a charging mode switching circuit suitable for a boost-type lithium battery charging chip is proposed. Summary of the invention

[0004] The object of the present invention is to provide a charging mode switching circuit suitable for a boost lithium battery charging chip, aiming to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A charging mode switching circuit suitable for a boost lithium battery charging chip, comprising:

[0007] A PWM boost type lithium battery charging chip, the PWM boost type lithium battery charging chip comprising a battery voltage detection input terminal, a gate drive terminal, an input voltage terminal, a chip ground, a full indicator light, a first inductor current detection input terminal, a second inductor current detection input terminal and a charging indicator light;

[0008] Electronic components, including a power supply, a first capacitor, a second capacitor, a third resistor, a fourth resistor, a first resistor, a second resistor, a first LED indicator, a second LED indicator, an inductor, a diode, an N-channel power field effect transistor, and a battery;

[0009] The power supply is connected to the chip input voltage terminal and is grounded through the first capacitor; one end of the first resistor is connected to the power supply, and the other end is connected in series with the second resistor, the other end of the second resistor is connected to the positive electrode of the diode through the inductor, and the negative electrode of the diode is grounded through the second capacitor; the positive electrode of the battery is connected to the negative electrode of the diode, and the negative electrode of the battery is grounded; the first inductor current detection input terminal is connected between the first resistor and the second resistor, and the second inductor current detection input terminal is connected between the second resistor and the inductor; the drain terminal of the N-channel power field effect transistor is connected between the inductor and the positive electrode of the diode, the gate terminal of the N-channel power field effect transistor is connected to the gate driving terminal, and the source terminal of the N-channel power field effect transistor is grounded; the battery voltage detection input terminal is connected between the positive electrode of the battery and the negative electrode of the diode.

[0010] Furthermore, the voltage of the power supply is not less than one quarter of the final cut-off voltage of the lithium battery.

[0011] Furthermore, the first capacitor is an input filter capacitor, and the second capacitor is an output filter capacitor.

[0012] Furthermore, the first resistor and the second resistor are both inductor current detection resistors, and the first inductor current detection input terminal and the second inductor current detection input terminal detect voltage through the inductor current detection resistors.

[0013] Furthermore, the first resistor is smaller than the second resistor.

[0014] Furthermore, the charging indicator light is connected to the cathode of the first LED indicator light, and the anode of the first LED indicator light is connected to the power supply via a third resistor.

[0015] Furthermore, the full charge indicator light is connected to the cathode of the second LED indicator light, and the anode of the second LED indicator light is connected to the power supply via a fourth resistor.

[0016] Furthermore, when in the charging state, the first LED indicator light is on; when charging is completed, the second LED indicator light is on.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The charging mode switching circuit suitable for the boost lithium battery charging chip can avoid a large drop in battery voltage when the charging current is turned off after charging is completed, thereby effectively increasing the charging saturation of the PWM boost lithium battery charging chip circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the present invention.

[0020] In the figure: battery voltage detection input terminal BAT1, gate drive terminal DRV, input voltage terminal VDD, chip ground GND, full charge indicator STDBY, first inductor current detection input terminal CS1, second inductor current detection input terminal CS2, charging indicator CHRG, power supply VIN, first capacitor C1, second capacitor C2, third resistor R1, fourth resistor R2, first resistor RCS1, second resistor RCS2, first LED indicator LED1, second LED indicator LED2, inductor L1, diode D1, N-channel power field effect transistor N1, battery BAT2. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0023] like Figure 1 As shown, a charging mode switching circuit suitable for a boost lithium battery charging chip provided by an embodiment of the present invention includes:

[0024] A PWM boost type lithium battery charging chip, the PWM boost type lithium battery charging chip comprises a battery voltage detection input terminal BAT1, a gate drive terminal DRV, an input voltage terminal VDD, a chip ground GND, a full indicator light STDBY, a first inductor current detection input terminal CS1, a second inductor current detection input terminal CS2 and a charging indicator light CHRG;

[0025] The electronic components include a power supply VIN, a first capacitor C1, a second capacitor C2, a third resistor R1, a fourth resistor R2, a first resistor RCS1, a second resistor RCS2, a first LED indicator LED1, a second LED indicator LED2, an inductor L1, a diode D1, an N-channel power field effect transistor N1 and a battery BAT2.

[0026] The power supply VIN is connected to the chip input voltage terminal VDD and is grounded through the first capacitor C1. One end of the first resistor RCS1 is connected to the power supply VIN, and the other end is connected in series with the second resistor RCS2. The other end of the second resistor RCS2 is connected to the positive electrode of the diode D1 through the inductor L1, and the negative electrode of the diode D1 is grounded through the second capacitor C2. The positive electrode of the battery BAT2 is connected to the negative electrode of the diode D1, and the negative electrode of the battery BAT2 is grounded. The first inductor current detection input terminal CS1 is connected between the first resistor RCS1 and the second resistor RCS2, and the second inductor current detection input terminal CS2 is connected between the second resistor RCS2 and the inductor L1. The drain end of the N-channel power field effect transistor N1 is connected between the inductor L1 and the positive electrode of the diode D1, the gate end of the N-channel power field effect transistor N1 is connected to the gate drive end DRV, and the source end of the N-channel power field effect transistor N1 is grounded. The positive electrode of the battery BAT2 and the negative electrode of the diode D1 are connected to the battery voltage detection input terminal BAT1. The charging indicator light CHRG is connected to the cathode of the first LED indicator light LED1, and the anode of the first LED indicator light LED1 is connected to the power source VIN through the third resistor R1. The full charge indicator light STDBY is connected to the cathode of the second LED indicator light LED2, and the anode of the second LED indicator light LED2 is connected to the power source VIN through the fourth resistor R2.

[0027] In the embodiment of the present invention, when in the charging state, the charging indicator light CHRG is pulled to a low level, and the first LED indicator light LED1 is on. When charging is completed, the charging indicator light STDBY is pulled to a low level, and the second LED indicator light LED2 is on.

[0028] The PWM boost type lithium battery charging chip is connected to the boost lithium battery charging circuit with mode switching. The PWM boost type lithium battery charging chip controls the charging current through the first inductor current detection input terminal CS1, and the battery voltage detection input terminal BAT1 monitors the battery BAT2 voltage. When the battery BAT2 voltage reaches the final cut-off voltage for the first time, the charging will not be stopped immediately. The system enters a de-jitter delay stage. After the de-jitter delay, if the battery voltage still remains near the final cut-off voltage, the charging current is controlled through the second inductor current detection input terminal CS2. At this time, the charging mode is switched from the normal charging mode to the low current charging mode. When it is detected that the battery BAT2 voltage reaches the final cut-off voltage for the second time, the de-jitter delay is used again to confirm this state. If the battery BAT2 voltage remains unchanged during the de-jitter delay period, the low current charging mode ends and the charging is terminated. This avoids a large drop in the battery voltage when the charging current is turned off after the charging is completed, thereby effectively increasing the charging saturation of the PWM boost type lithium battery charging chip circuit.

[0029] like Figure 1As shown, as a preferred embodiment of the present invention, the power supply VIN supplies power to the charging circuit. Because it is a boost charging circuit, the power supply VIN does not need an excessively high voltage, and generally does not need to be lower than one-fourth of the final cut-off voltage of the lithium battery.

[0030] like Figure 1 As shown in FIG. 1 , as a preferred embodiment of the present invention, the first capacitor C1 is an input filter capacitor, and the second capacitor C2 is an output filter capacitor. The first capacitor C1 is used to filter out high-frequency noise on VIN, and the second capacitor C2 is used to smooth the output voltage after the diode D1. The value of the capacitor is related to the charging current, etc.

[0031] like Figure 1 As shown in FIG. 1 , as a preferred embodiment of the present invention, the first resistor RCS1 and the second resistor RCS2 are both inductor current detection resistors, and the first inductor current detection input terminal CS1 and the second inductor current detection input terminal CS2 detect voltages through the inductor current detection resistors.

[0032] In the embodiment of the present invention, the N-channel power field effect transistor N1 controls the switch through the gate drive terminal DRV. When the N-channel power field effect transistor N1 is turned on, the power supply VIN charges the inductor L1, the current of the inductor L1 increases, and the voltage difference across the inductor current detection resistor increases. When the voltage detection high threshold is reached, the gate drive terminal DRV changes from a high level to a low level, the N-channel power field effect transistor N1 is turned off, and the energy in the inductor L1 is transferred to the second capacitor C2 and the battery BAT2. The inductor current decreases, and the voltage difference across the inductor current detection resistor decreases. When the low threshold is reached, the gate drive terminal DRV changes from a low level to a high level, and the N-channel power field effect transistor N1 is turned on again, and a new cycle begins.

[0033] like Figure 1 As shown, as a preferred embodiment of the present invention, the normal charging mode sets the inductor current through the first resistor RCS1; the low current charging mode sets the inductor current through the first resistor RCS1 plus the second resistor RCS2. Generally, the first resistor RCS1 is smaller than the second resistor RCS2. In this way, the charging current of the low current charging mode can be much smaller than that of the normal mode, further improving the saturation of the battery after charging is completed.

[0034] The working principle of the present invention is:

[0035] The PWM boost lithium battery charging chip controls the charging current through the first inductor current detection input terminal CS1, and monitors the battery BAT2 voltage through the battery voltage detection input terminal BAT1. When it is detected that the battery BAT2 voltage reaches the final cut-off voltage for the first time, charging will not be stopped immediately, and the system will enter a de-jitter delay stage. After the de-jitter delay, if the battery voltage remains near the final cut-off voltage, the charging current is controlled through the second inductor current detection input terminal CS2. At this time, the charging mode is switched from the normal charging mode to the low-current charging mode. When it is detected that the battery BAT2 voltage reaches the final cut-off voltage for the second time, this state is confirmed again after the de-jitter delay. If the battery BAT2 voltage remains unchanged during the de-jitter delay period, the low-current charging mode ends and charging is terminated.

[0036] The above are only preferred embodiments of the present invention. It should be pointed out that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention. These should also be regarded as the protection scope of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. A charging mode switching circuit suitable for a boost lithium battery charging chip, characterized in that: include: A PWM boost type lithium battery charging chip, the PWM boost type lithium battery charging chip comprising a battery voltage detection input terminal, a gate drive terminal, an input voltage terminal, a chip ground, a full indicator light, a first inductor current detection input terminal, a second inductor current detection input terminal and a charging indicator light; Electronic components, including a power supply, a first capacitor, a second capacitor, a third resistor, a fourth resistor, a first resistor, a second resistor, a first LED indicator, a second LED indicator, an inductor, a diode, an N-channel power field effect transistor, and a battery; The power supply is connected to the chip input voltage terminal and is grounded through the first capacitor; one end of the first resistor is connected to the power supply, and the other end is connected in series with the second resistor, the other end of the second resistor is connected to the positive electrode of the diode through the inductor, and the negative electrode of the diode is grounded through the second capacitor; the positive electrode of the battery is connected to the negative electrode of the diode, and the negative electrode of the battery is grounded; the first inductor current detection input terminal is connected between the first resistor and the second resistor, and the second inductor current detection input terminal is connected between the second resistor and the inductor; the drain terminal of the N-channel power field effect transistor is connected between the inductor and the positive electrode of the diode, the gate terminal of the N-channel power field effect transistor is connected to the gate driving terminal, and the source terminal of the N-channel power field effect transistor is grounded; the battery voltage detection input terminal is connected between the positive electrode of the battery and the negative electrode of the diode.

2. The charging mode switching circuit suitable for a boosted lithium battery charging chip according to claim 1, characterized in that: The voltage of the power supply is not less than one quarter of the final cut-off voltage of the lithium battery.

3. The charging mode switching circuit suitable for a boosted lithium battery charging chip according to claim 1, characterized in that: The first capacitor is an input filter capacitor, and the second capacitor is an output filter capacitor.

4. The charging mode switching circuit suitable for a boosted lithium battery charging chip according to claim 1, characterized in that: The first resistor and the second resistor are both inductor current detection resistors, and the first inductor current detection input terminal and the second inductor current detection input terminal detect voltage through the inductor current detection resistors.

5. The charging mode switching circuit suitable for a boosted lithium battery charging chip according to claim 1, characterized in that: The first resistor is smaller than the second resistor.

6. The charging mode switching circuit suitable for a boosted lithium battery charging chip according to claim 1, characterized in that: The charging indicator light is connected to the cathode of the first LED indicator light, and the anode of the first LED indicator light is connected to the power supply through the third resistor.

7. The charging mode switching circuit for a boosted lithium battery charging chip according to claim 1, characterized in that: The full indicator light is connected to the cathode of the second LED indicator light, and the anode of the second LED indicator light is connected to the power supply through a fourth resistor.

8. The charging mode switching circuit suitable for a boosted lithium battery charging chip according to claim 1, characterized in that: When in charging state, the first LED indicator light is on; when charging is completed, the second LED indicator light is on.

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