CN112737067B

CN112737067B - Protection method, device and system of battery charging circuit

Info

Publication number: CN112737067B
Application number: CN202110337609.8A
Authority: CN
Inventors: 陈鑫
Original assignee: Shenzhen Injoinic Technology Co Ltd
Current assignee: Shenzhen Injoinic Technology Co Ltd
Priority date: 2021-03-30
Filing date: 2021-03-30
Publication date: 2021-08-20
Anticipated expiration: 2041-03-30
Also published as: CN112737067A

Abstract

The invention discloses a protection method, a device and a system of a battery charging circuit, wherein the battery charging circuit at least comprises a discharge transistor and a body diode connected between a source electrode and a drain electrode of the discharge transistor, and the protection method comprises the following steps: detecting the level of the charging current; when receiving the high level of the charging current, setting the grid electrode of the discharging transistor to be the high level, conducting the discharging transistor, and enabling the current flowing through the body diode to be shunted through the discharging transistor. The invention can protect the body diode and ensure that the high-power MOS transistor is not burnt.

Description

Protection method, device and system of battery charging circuit

Technical Field

The invention relates to a charging protection technology of a low battery of a lithium battery, in particular to a protection method, a device and a system of a battery charging circuit.

Background

The mainstream technology for manufacturing transistors at present is a technology called Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) or MOS Transistor. The MOS transistor has three external connections: source (Source), Drain (Drain) and Gate (Gate). MOS transistors are largely divided into two types, one being nMOS transistors and one being pMOS transistors. The drain of the high-power MOS tube is led out from the bottom of the silicon chip, and a parasitic diode, or a body diode, is formed. The body diode has the function that when a large instantaneous reverse current is generated in the circuit, the current can be led out through the diode, so that the MOS transistor is not broken down. Thereby playing a role of protecting the MOS transistor.

Fig. 1 shows a schematic diagram of a conventional lithium battery protection, which is composed of a lithium battery/low battery BAT, resistors R1 and R2, a capacitor C, high-power MOS transistors CO and DO, and a lithium battery protection control chip, wherein EB + and EB-are connected to an external charging device or a load. The resistor R1 and the capacitor C play a role in filtering, and the resistor R1 also plays a role in voltage resistance protection. The CO and DO ends of the lithium battery protection control chip respectively drive the CO and DO of the high-power MOS transistors, the VM end is an external load or a ground electrode of charging equipment, and the resistor R2 is connected with the ground electrode of the load or the charging device. In most chip applications, after a lithium battery is over-discharged and under the condition of low voltage, at the moment, a load is connected between EB + and EB-, a high-power MOS transistor at a CO end is switched on, a high-power MOS transistor at a DO end is switched off, current passes through the high-power MOS transistors at the EB +, EB-, and CO ends from a BAT positive electrode in sequence, the lithium battery protects a control chip, and finally returns to the BAT negative electrode; when the BAT battery is charged and the voltage of the BAT battery is lower than the reference voltage VREF, the high-power MOS crystal at the DO end is not conducted, and the BAT battery is charged by current through the body diode. When the voltage of the BAT battery is charged to be higher than the reference voltage VREF, the high-power MOS transistor at the DO end is conducted to charge the battery. When the high-power MOS transistor at the DO terminal is not turned on, if the battery impedance is too small under a low voltage condition, a large current will appear, and at this time, the body diode is not enough to flow and bear such a large current, and the body diode will be burned out, that is, the MOS transistor at the DO terminal is broken down.

Disclosure of Invention

Accordingly, it is desirable to provide a method, an apparatus and a system for protecting a battery charging circuit, which can protect a body diode and prevent a high power MOS transistor from being burned.

A protection method of a battery charging circuit, wherein the battery charging circuit includes at least one discharge transistor, and a body diode connected between a source and a drain of the discharge transistor, the protection method comprising:

detecting the level of the charging current;

judging the voltage of the battery and the preset reference voltage;

when the battery voltage is lower than the preset reference voltage and the high level of the charging current is received, setting the grid electrode of the discharging transistor to be the high level, and conducting the discharging transistor to enable the current flowing through the body diode to be shunted through the discharging transistor.

In one embodiment, after the step of determining the battery voltage and the preset reference voltage, the method further includes:

and when the battery voltage is higher than the preset reference voltage, setting the grid electrode of the discharge transistor to be at a low level.

Accordingly, a protection device for a battery charging circuit, wherein said battery charging circuit comprises at least a discharge transistor, and a body diode connected between the source and drain of said discharge transistor,

the protection device includes: the power supply circuit comprises a first current source I1, wherein the first current source I1 is connected with a power supply voltage VDD and a drain terminal of a first NMOS transistor N1, a source electrode of the first NMOS transistor N1 is grounded, a grid electrode of the first NMOS transistor N1 is connected with an output terminal of a comparator, a positive input terminal of the comparator is connected with VM, a negative input terminal of the comparator is connected with GND, the power supply circuit further comprises a PMOS transistor, a source electrode of the PMOS transistor is connected with VDD, a grid electrode of the PMOS transistor is connected with an OR output terminal, a second current source I2 is connected with a drain electrode of the PMOS transistor, an output terminal of the second current source I2 is connected with a drain terminal of a second NMOS transistor N2, a grid electrode of the second NMOS transistor N2 is connected with a drain electrode of a first NMOS transistor N1, a source electrode of the second NMOS transistor is connected with a DO terminal, OR an OR input terminal is respectively connected with ENB and PUN _ VM.

Accordingly, a protection system for a battery charging circuit, comprising:

a protection device for a battery charging circuit as described above;

a battery charging circuit comprising at least one discharge transistor, and a body diode connected between the source and drain of the discharge transistor.

Accordingly, in one embodiment, the method comprises the following steps:

a lithium battery connected between the protection device of the battery charging circuit and the battery charging circuit.

Accordingly, in one embodiment, the method further comprises:

and the charging transistor is connected between the protection device of the battery charging circuit and is used for disconnecting the charging current when the battery is fully charged.

The invention has the following beneficial effects:

a method for protecting a battery charging circuit, wherein the battery charging circuit comprises at least one discharge transistor and a body diode connected between the source and the drain of the discharge transistor. The body diode is a permanent protective device in the transistor and plays a key role in the service life of the battery charging circuit. The protection method comprises the following steps: detecting the level of the charging current; when the battery charging circuit is connected with the charging current, suddenly increased current impact exists, and at the moment, great risk exists on the circuit. When receiving the high level of the charging current, setting the grid electrode of the discharging transistor to be the high level, conducting the discharging transistor, and enabling the current flowing through the body diode to be shunted through the discharging transistor. Therefore, when the battery voltage is too low, when the charger is detected to be connected, the current flows through the high-power MOS transistor at the DO end, the problem that the current only flows through the body diode at low voltage can be solved, and the high-power MOS transistor is prevented from being burnt due to the excessive current.

Drawings

FIG. 1 is a schematic diagram of a conventional lithium battery circuit protection;

FIG. 2 is a schematic diagram of the level of circuit protection of a lithium battery in the prior art;

FIG. 3 is a schematic diagram of a protection device of a battery charging circuit according to the present invention;

fig. 4 is a schematic level diagram of the lithium battery circuit protection of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings.

Fig. 1 is a schematic diagram of a conventional lithium battery circuit protection. A protection method of a battery charging circuit is provided, wherein the battery charging circuit at least comprises a DO terminal discharging transistor and a DO terminal body diode connected between the source electrode and the drain electrode of the DO terminal discharging transistor.

Fig. 2 is a schematic level diagram of a lithium battery circuit protection in the prior art. The method is a common lithium battery protection working schematic diagram, when the battery voltage is higher than a reference voltage VREF, the battery voltage is in a normal discharge state, at the moment, the PUN _ VM is at a high level, the CO end and the DO end are at high levels, and the high-power MOS at the CO end and the high-power MOS at the DO end are conducted and discharged to the outside; when the voltage of the battery is gradually reduced and is smaller than VREF, the PUN _ VM is changed into a low level, the CO end is kept at a high level, the DO end is at a low level, the high-power MOS transistor at the CO end is switched on, and the high-power MOS transistor at the DO end is switched off; at a certain moment, a CHARGER is inserted, the CHARGER is at a high level, the battery is charged, because the voltage of the battery is less than VREF, the high-power MOS transistor at the DO end keeps closed, the body diode of the high-power MOS transistor at the DO end charges the battery, and when the voltage of the battery is more than VREF, the high-power MOS transistor at the DO end is conducted to charge the battery. Under low voltage conditions, when the battery impedance is too low, a large current will appear, and at this time, the body diode is not enough to flow to bear such a large current, and the body diode will be burnt out, i.e., the MOS transistor at the DO terminal will be broken down.

A protection method of a battery charging circuit is provided, wherein the battery charging circuit at least comprises a DO terminal discharging transistor and a DO terminal body diode connected between the source electrode and the drain electrode of the DO terminal discharging transistor. The DO terminal body diode is a permanent protective device in the transistor that plays a critical role in the useful life of the battery charging circuit. The protection method comprises the following steps: detecting the level of the charging current; when the battery charging circuit is connected with the charging current, suddenly increased current impact exists, and at the moment, great risk exists on the circuit. When receiving the high level of the charging current, setting the grid electrode of the discharging transistor to be the high level, conducting the discharging transistor, and enabling the current flowing through the body diode to be shunted through the discharging transistor. Therefore, when the battery voltage is too low, when the charger is detected to be connected, the current flows through the high-power MOS transistor at the DO end, the problem that the current only flows through the body diode at low voltage can be solved, and the high-power MOS transistor is prevented from being burnt due to the excessive current.

In one embodiment, after the step of detecting the level of the charging current, and before receiving the high level of the charging current, the method further includes:

judging the voltage of the battery and the preset reference voltage;

and when the battery voltage is lower than the preset reference voltage, setting the grid electrode of the discharge transistor to be a high level, and conducting the discharge transistor to enable the current flowing through the body diode to be shunted through the discharge transistor.

and when the battery voltage is higher than the preset reference voltage, setting the grid electrode of the discharge transistor to be at a high level.

Fig. 3 is a circuit structure implementation diagram of a protection device of a battery charging circuit according to the present invention, in which a first current source I1 is connected to a power voltage VDD and a drain terminal of an NMOS first transistor N1, a drain terminal of the NMOS first transistor N1 is connected to a current source I1, a source terminal is grounded, a gate terminal is connected to an output terminal of a comparator, a positive input terminal of the comparator is connected to VM, a negative input terminal is connected to GND, a source terminal of a PMOS transistor (i.e., a P transistor) is connected to VDD, a gate terminal is connected to an OR gate output terminal, a second current source I2 is connected to a drain terminal of the PMOS transistor and a drain terminal of an NMOS second transistor N2, a gate terminal of an NMOS second transistor N2 is connected to a drain terminal of the NMOS first transistor N1, a drain terminal is connected to I2, a source terminal is connected to a DO terminal, OR an input terminal is connected to ENB, PUN _ VM, and a gate terminal of the PMOS transistor.

When the ENB =0 and the battery is in an overdischarge condition, the discharging DO-end high-power transistor is closed, DO is 0, PUN _ VM is equal to 0, and the CO-end high-power MOS transistor is in a conducting state. When the charger is inserted, the VM is a negative value relative to the GND, at the moment, the grid electrode of the NMOS second transistor N2 is high, the NMOS second transistor N2 is conducted, the NMOS second transistor N2 charges the DO end of the control signal to a high level through the current with the size of I2, the high-power MOS transistor of the DO end is driven to be conducted, the current passes through the high-power MOS transistor of the DO end to charge the battery, and the problem that the battery voltage is charged to a certain fixed level only through the body diode by the current is solved.

FIG. 4 is a schematic diagram of the lithium battery protection operation of the present invention, wherein when the battery voltage is higher than the reference voltage VREF, the battery voltage is in a normal discharge state, at this time, the PUN _ VM is at a high level, the CO terminal and the DO terminal are at a high level, and the high-power MOS at the CO terminal and the high-power MOS at the DO terminal are turned on to discharge to the outside; when the voltage of the battery is gradually reduced and is smaller than VREF, the PUN _ VM is changed into a low level, the CO end is kept at a high level, the DO end is at a low level, the high-power MOS transistor at the CO end is switched on, and the high-power MOS transistor at the DO end is switched off; at a certain moment, a CHARGER is inserted, a CHARGER is at a high level, the battery is charged, the battery voltage is less than VREF, but in the invention, a DO-end high-power MOS transistor is opened, and the DO-end high-power MOS transistor charges the battery.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A protection device for a battery charging circuit, wherein the battery charging circuit includes at least a discharge transistor and a body diode connected between a source and a drain of the discharge transistor, the protection device comprising: the power supply circuit comprises a first current source I1, wherein the first current source I1 is connected with a power supply voltage VDD and a drain terminal of a first NMOS transistor N1, a source terminal of the first NMOS transistor N1 is grounded, a gate terminal of the first NMOS transistor N1 is connected with an output terminal of a comparator, a positive input terminal of the comparator is connected with VM, a negative input terminal of the comparator is connected with GND, the power supply circuit further comprises a PMOS transistor, a source terminal of the PMOS transistor is connected with VDD, a gate terminal of the PMOS transistor is connected with an OR output terminal, an input terminal of a second current source I2 is connected with a drain terminal of the PMOS transistor, an output terminal of the second current source I2 is connected with a drain terminal of a second NMOS transistor N2, a gate terminal of the second NMOS transistor N2 is connected with a drain terminal of a first NMOS transistor N1, a source terminal of the second NMOS transistor is connected with a DO, and an OR input terminal is respectively connected with ENB and PUN _ VM.

2. A protection system for a battery charging circuit, comprising:

a protection device of a battery charging circuit according to claim 1;

the battery charging circuit comprises at least one discharge transistor and a body diode connected between the source and the drain of the discharge transistor.

3. The battery charging circuit protection system of claim 2, comprising:

4. The battery charging circuit protection system of claim 2, further comprising: