CN101282036B - Overcurrent protection circuit for discharging electricity - Google Patents

Abstract

The invention provides a discharge overflow protection circuit which is characterized in that the invention comprises a discharge overflow comparator and a press control oscillating circuit, wherein, the two inputs of the discharge overflow comparator are a discharge overflow voltage threshold value and a discharge overflow voltage, the output terminals are connected to the enable control terminals of the press control oscillating circuit for judging whether appearing overcurrent state and starting the press control oscillating circuit when appearing the overcurrent state; the press control oscillating circuit comprises an input terminal for receiving the discharge overflow voltage, the enable control terminal receiving the discharge overflow comparator output and an output terminal for outputting the oscillating signal, for generating an oscillating period and an oscillating signal proportionable to the discharge overflow voltage, the discharge overflow protection is performed based on the oscillating signal. The discharge current delay time of the discharge overflow protection circuit is in the inverse ratio of the discharge current, namely realizing the discharge overflow protection time continuous return, thereby improving the security of cells for performing multiple charging and discharging in the discharging state.

Description

Discharge overcurrent protection circuit

Technical Field

The invention relates to a lithium battery protection circuit, in particular to a discharge overcurrent protection circuit in the lithium battery protection circuit.

Background

Currently, lithium ion batteries have no memory effect, and thus gradually replace conventional nickel-metal hydride batteries in more and more electronic systems, and become a main power source in portable electronic devices. However, lithium batteries have many safety problems and are prone to explosion. Therefore, complex protection circuits are present in lithium battery systems to ensure that unsafe conditions are prevented from causing damage to the battery in various accidental situations. Protection circuits in lithium batteries generally include charging overvoltage protection, discharging overvoltage protection, charging overcurrent protection, discharging overcurrent protection, and short-circuit protection.

Discharge overcurrent protection means that when the battery is discharged through a load, the discharge current exceeds a certain related voltage threshold value V_EDIAnd this state continues for more than a certain delay time T_EDIThe battery protection circuit can turn off the discharge path to prohibit discharge and enter a discharge overcurrent protection state. When the discharge current further increases to exceed the associated short-circuit protection voltage threshold V_SCAnd this state continues for more than a certain delay time T_SCWhen the battery protection circuit is in a short-circuit protection state, the discharge path is closed to prohibit discharge. The short-circuit protection state and the discharge overcurrent protection state are the same state for the control circuit, and the circuit performance is that the discharge is forbidden. The two protection states are the same when exiting, and the voltage difference between the voltage of the VM end and the voltage of the G end is detected to be less than V_EDIAnd the exit is continuously carried out after a certain delay time. The main difference is the short-circuit protection threshold V_SCGreater than V_EDIAnd T is_SCLess than T_EDIThat is, when the discharge current is too large, the delay time is shorter as the current value is larger.

In the prior art, several discharge overcurrent thresholds and short-circuit thresholds can be set to perform discharge overcurrent protection. However, between the several protection thresholds, there are other discharge overcurrent conditions that are true. Therefore, the prior art does not realize a discharge current protection time that continuously turns back with the discharge current, resulting in insufficient discharge overcurrent protection for the above-described intermediate state.

Disclosure of Invention

An object of the present invention is to provide a discharge overcurrent protection circuit in which the delay time of a discharge current is inversely proportional to the discharge current, which can solve the above problems.

The invention provides a discharge overcurrent protection circuit, which is characterized by comprising a discharge overcurrent comparator and a voltage-controlled oscillating circuit, wherein: the two inputs of the discharging overcurrent comparator are a discharging overcurrent voltage and a discharging overcurrent voltage threshold value (V)_EDI) The output end of the voltage-controlled oscillation circuit is connected to the enabling control end of the voltage-controlled oscillation circuit and is used for judging whether an overcurrent state occurs or not and starting the voltage-controlled oscillation circuit when the overcurrent state occurs; the voltage-controlled oscillating circuit comprises an input end for receiving the discharging overcurrent voltage, an enable control end for receiving the output of the discharging overcurrent comparator and an output end for outputting an oscillating signal, and is used for generating an oscillating signal with an oscillating period in inverse proportion to the discharging overcurrent voltage and performing discharging overcurrent protection according to the oscillating signal.

In another embodiment of the present invention, the discharge overcurrent protection circuit further includes a timer for receiving an oscillation signal of the oscillator and performing timing according to the oscillation signal.

In another embodiment of the present invention, there is also provided a discharge overcurrent protection circuit, including: discharge overcurrent comparator, operational amplifier, first P-type field effect transistor, second P-type field effect transistor, third P-type field effect transistor, resistor, inverter, first N-type field effect transistor, second N-type field effect transistor, and resistorA capacitor, an oscillator comparator, a terminal (VCC); the discharging overcurrent comparator comprises a positive phase input end for inputting discharging overcurrent voltage and a threshold value (V) for inputting discharging overcurrent voltage_EDI) The output end of the inverting input end of the second P-type field effect transistor is respectively connected to the input end of the inverter and the grid electrode of the third P-type field effect transistor; the inverting input end of the operational amplifier inputs the discharging overcurrent voltage, the non-inverting input end of the operational amplifier is connected with the drain electrode of the first P-type field effect transistor and one end of the resistor, and the output end of the operational amplifier is connected with the drain electrode of the third P-type field effect transistor and the grid electrodes of the first P-type field effect transistor and the second P-type field effect transistor; the sources of the first P-type field effect transistor, the second P-type field effect transistor and the third P-type field effect transistor are connected to the terminal (VCC), the drain of the first P-type field effect transistor is connected to one end of the resistor, and the drain of the second P-type field effect transistor is respectively connected to the drains of the first N-type field effect transistor and the second N-type field effect transistor, one end of the capacitor and the non-inverting input end of the oscillator comparator; the inverting input of the oscillator comparator is a reference voltage V set by the system_REF(ii) a The other end of the resistor is grounded; the source electrode of the first N-type field effect transistor is grounded, and the grid electrode of the first N-type field effect transistor is connected with the output end of the oscillator comparator; and the grid electrode of the second N-type field effect transistor is connected to the other end of the inverter, and the source electrode of the second N-type field effect transistor is connected with the other end of the capacitor and grounded.

In a further embodiment of the present invention, the current generated by the voltage-controlled current source is proportional to the discharge overcurrent voltage, and the oscillation period is inversely proportional to the current generated by the voltage-controlled current source.

The invention provides a lithium battery protection circuit with discharge current delay time inversely proportional to discharge current, so as to realize continuous turn-back of discharge overcurrent protection time, thereby improving the safety of a battery capable of being charged and discharged for many times in a discharge state.

Drawings

Specific embodiments of the present invention will be described in more detail below with reference to the attached drawing figures, wherein:

FIG. 1 is a battery protection circuit employing two-stage discharge over-current protection;

FIG. 2 is a graph of discharge overcurrent delay time as a function of over-discharge current in the circuit of FIG. 1;

FIG. 3 is a battery protection circuit employing three levels of discharge over-current protection;

FIG. 4 is a graph of discharge overcurrent delay time as a function of over-discharge current in the circuit of FIG. 3;

FIG. 5 is a battery protection circuit according to the present invention;

FIG. 6 is a graph of discharge delay time versus over-discharge current in the circuit of FIG. 5;

FIG. 7 shows a discharge overcurrent protection circuit according to the present invention in which the discharge delay time is inversely proportional to the discharge current, an

FIG. 8 is a structured circuit diagram of the circuit shown in FIG. 7;

FIG. 9 is a structured circuit diagram of the circuit shown in FIG. 8; and

fig. 10 is a structured circuit diagram of the circuit shown in fig. 9.

Detailed Description

Fig. 1 is a battery protection circuit employing two-stage discharge overcurrent protection.

As shown in fig. 1, the circuit includes an overcharge detection circuit, an overdischarge detection circuit, a charge overcurrent detection circuit, a discharge overcurrent detection circuit, a short-circuit protection detection circuit, a control circuit, and switches MD, MC. The discharge overcurrent detection circuit and the short-circuit protection detection circuit carry out voltage detection aiming at secondary discharge overcurrent protection, namely, the voltage difference between the voltage of the VM end and the voltage of the G end is detected to be larger than a certain voltage threshold value V_EDITo determine whether the discharge has occurredAnd (4) streaming. The voltage difference between the VM terminal and the G terminal is the conduction voltage drop of the switches MD and MC. If the on-resistances of MD and MC are R_{ON_MD}And R_{ON_MC}Then the detected discharge current threshold is:

$I_{\mathrm{EDI}}=\frac{V_{\mathrm{EDI}}}{R_{\mathrm{ON}\_\mathrm{MD}}+R_{\mathrm{ON}\_\mathrm{MC}}}$

when the discharge current increases beyond the discharge overcurrent protection threshold V_EDIAnd this state continues for more than a certain delay time T_EDIAnd when the battery protection circuit is in a discharging overcurrent protection state, the discharging circuit is switched off, discharging is forbidden, and the battery protection circuit enters the discharging overcurrent protection state.

When the discharge current is larger, the short-circuit protection threshold V is exceeded_SCAnd this state continues for more than a certain delay time T_SCWhen the battery protection circuit is in a short-circuit protection state, the battery protection circuit can turn off the discharge path, forbid discharging and enter the short-circuit protection state. The short circuit protection state and the discharge overcurrent protection state are the same state for the control circuit, and the short circuit protection state and the discharge overcurrent protection state are both represented by discharge inhibition. When the two protection states exit, the voltage difference between the voltage of the VM end and the voltage of the G end is detected to be less than V_EDIAnd exits the protection state continuously after a certain delay time. The main difference between the two is the short-circuit protection threshold V_SCGreater than V_EDIAnd T is_SCLess than T_EDIThat is, the delay time is shortened when the discharge current increases. The short-circuit current threshold is determined by:

$I_{\mathrm{SC}}=\frac{V_{\mathrm{SC}}}{R_{\mathrm{ON}\_\mathrm{MD}}+R_{\mathrm{ON}\_\mathrm{MC}}}$

this is because the larger the discharge current is, the larger the power consumption generated in the same time becomes for a certain battery voltage, and the larger the amount of heat generated becomes. Many electronic systems are damaged by overheating. Usually, a specific heat value of a specific system is provided, and the temperature rise caused by a certain amount of heat can be calculated. When the temperature rises to a certain value, the system is damaged. A delay time is required to fold back with the discharge current. If the battery voltage is V_BCurrent is I_BThe heat P generated at a certain time T is:

P＝V_B.I_B.T

fig. 2 is a graph of discharge overcurrent delay time as a function of over-discharge current in the circuit of fig. 1.

When the over-discharge current is at I, as shown in FIG. 2_EDI1And I_SCIn between, the discharge overcurrent delay time is T_EDI1When the over-discharge current exceeds the short-circuit protection current threshold I_SCTime, discharge overcurrent delay time becomes T_SC. Obviously, I_SC、I_EDI1The value of (A) varies from large to small, T_SC、T_EDIThe value of (d) is changed from small to large, i.e., the larger the overdischarge current value, the shorter the discharge overcurrent delay time.

Fig. 3 is a battery protection circuit employing three-stage discharge overcurrent protection.

Since the boundary I can also appear in real systems_EDIAnd I_SCIn order to achieve more sufficient protection, the S8261 of the fine work electronics adopts three-level current protection (discharge overcurrent protection 1, discharge overcurrent protection 2 and short-circuit protection), as shown in fig. 3. The circuit comprises an overcharge detection circuit, an overdischarge detection circuit, a charge overcurrent detection circuit, a discharge overcurrent detection circuit 1, a discharge overcurrent detection circuit 2, a short-circuit protection detection circuit, a control circuit and switches MD and MC. The discharge overcurrent protection principle of the circuit is the same as that of the circuit shown in FIG. 1. It is different in that it addsThe discharge overcurrent detection circuit 2. Wherein, the threshold value I of the discharge overcurrent protection 2_EDI2Threshold I of specific discharge overcurrent protection 1_EDI1Delay time T of high, discharge overcurrent protection 2_EDI2Delay time T of specific discharge overcurrent protection 1_EDI1Short. Thus realizing the pair I_EDIAnd I_SCAnd protecting the discharge overcurrent state.

Fig. 4 is a graph of discharge overcurrent delay time as a function of over-discharge current in the circuit shown in fig. 3.

As shown in FIG. 4, when the over-discharge current is at I_EDI1And I_EDI2In between, the discharge overcurrent delay time is T_EDI1. When over-discharge current is in I_EDI1And I_SCIn between, the discharge overcurrent delay time is T_EDI2. When the over-discharge current exceeds the short-circuit protection current threshold I_SCTime, discharge overcurrent delay time becomes T_SC. Obviously, I_SC、I_EDI2、I_EDI1The value of (A) varies from large to small, T_SC、T_EDI2、T_EDI1The value of (d) is changed from small to large, i.e., the larger the overdischarge current value, the shorter the discharge overcurrent delay time.

Since the boundary I can also appear in real systems_EDI1And I_EDI2Between or bounded by I_EDI2And I_SCAny other overcurrent conditions in between, so these intermediate discharge overcurrent conditions need to be protected. In short, the discharge overcurrent protection time of continuous turn-back is realized, and the turn-back relation is that the discharge overcurrent delay time is inversely proportional to the discharge overcurrent value.

Fig. 5 is a battery protection circuit according to an embodiment of the present invention.

As shown in fig. 5, the circuit includes an overcharge detection circuit, an overdischarge detection circuit, a charge overcurrent detection circuit, a discharge overcurrent detection circuit whose delay time is inversely proportional to the current, a control circuit, and switches MD and MC. In the figure, a discharge overcurrent detection circuit with time delay inversely proportional to current is used for detecting voltage aiming at discharge overcurrent protection. The relationship between the overdischarge current and the discharge overcurrent delay time follows:

$T_{\mathrm{EDI}}=\frac{Q}{I_{\mathrm{EDI}}}$

wherein T is_EDIDelay time for discharge over-current, I_EDIFor over-discharge current, Q is a design constant.

Fig. 6 is a graph of discharge delay time versus over-discharge current in the circuit shown in fig. 5.

As shown in fig. 6, the discharge overcurrent delay time T_EDIInversely proportional to the over-discharge current I_EDIThereby realizing the continuous variation of the discharge overcurrent delay time along with the over-discharge current.

Fig. 7 shows a discharge overcurrent protection circuit according to the present invention in which the discharge delay time is inversely proportional to the discharge current value.

As shown in fig. 7, the circuit diagram includes an operational amplifier, an EDI (discharge overcurrent) comparator, MP1 (P-type field effect transistor), MP2, MP3, an inverter U1, a resistor R1, MN1 (N-type field effect transistor), MN2, a capacitor C1, an oscillator comparator, and a timer.

The positive phase input end of the EDI comparator is VM, and the negative phase input end is a discharge overcurrent voltage threshold value V set by the system_EDIThe output ends of the two-way inverter are respectively connected to the input end of the inverter U1 and the gate of the MP 3;

the inverting input end of the operational amplifier is connected to the VM end, the non-inverting input end of the operational amplifier is connected with the drain electrode of the MP1 and is connected to one end of the resistor R1, and the output end of the operational amplifier is connected to the drain electrode of the MP3 and the grid electrodes of the MP1 and MP 2;

the sources of MP1, MP2 and MP3 are all connected to VCC end, the drain of MP1 is connected to resistor R1, the drain of MP2 is connected to the drains of MN1 and MN2, one end of capacitor C1 and the non-inverting input end of the oscillator comparator respectively;

the inverting input of the oscillator comparator is the reference voltage V set by the system_REF；

The other end of the resistor R1 is grounded;

the source of MN1 is grounded, and the grid is respectively connected to the output end of the oscillator comparator and the input end of the timer;

MN2 has its gate connected to the output of the inverter and its source connected to the other end of capacitor C1 and to ground.

When VM is larger than V_EDIAt this time, MP3 is turned off, MN2 is also turned off, and the op-amp and oscillator are both turned on. The operational amplifier adjusts the voltage at its non-inverting input to be equal to the voltage at its inverting input, so that the current flowing through R1 is equal to VM/R1. This current flows out from the drain of MP2 via the mirror of the current mirror circuit constituted by MP1 and MP2, and charges capacitor C1. When the voltage at C1 rises to V_REFWhen the voltage of the oscillator comparator is low, MN1 is turned off, and the voltage of C1 is continuously charged and increased by the drain of MP2, and the oscillation is formed. And after the timer counts N periods, the EDI of the protection signal becomes high, and overcurrent protection control is carried out. Here, the timer is not necessary, but its adoption can make the capacitance of C1 reduced, thereby saving chip area.

The oscillator comparator needs to be designed with a certain delay time, which is generally less than 100nS and greater than 10 nS. Specifically, when the oscillator outputs a high level, the gate of MN1 is at a higher voltage, typically the supply voltage. In particular, the discharging current after MN1 turns on is much larger than the current of MP2 (i.e., the charging current of capacitor C1). Generally, the discharge time of the capacitor C1 is less than 5% of the oscillation period, negligible with respect to its charge time. It is also desirable that the voltage at C1 be discharged to zero during this discharge time. The oscillating signal generated by charging and discharging the capacitor C1 is a sawtooth wave. The width-to-length ratio of MN2 in the discharge circuit is generally greater than 5: 1 to meet the design requirement.

When VM is less than V_EDIAt this time, MP3 is on, MN2 is also on, and both the op-amp and the oscillator are off.

The currents of the MP1 and the MP2 are in a mirror relationship, and can be equal or M times. In an actual circuit design, the MP1 and MP2 can be designed according to specific requirements of discharge overcurrent delay time and cost, thereby determining the multiple relation of the current flowing between MP1 and MP 2. In one embodiment of the present invention, the ratio of the current flowing through MP1 to the current flowing through MP2 is 1, i.e., equal. In operation, the current through MP1 and MP2 is equal to VM/R1, where VM is the voltage at the VM node. Voltage of VM is equal to I_EDI·(R_{ON_MD}+R_{ON_MC}). MP2 outputs a current whose value is proportional to voltage VM to start the oscillator. Period T of the oscillator_OSCComprises the following steps:

$T_{\mathrm{OSC}}=\frac{V_{\mathrm{REF}}.C1}{I_{\mathrm{MP}2}}=\frac{V_{\mathrm{REF}}.R1.C1}{\mathrm{VM}}=\frac{V_{\mathrm{REF}}.R1.C1}{I_{\mathrm{EDI}}.(R_{\mathrm{ON}\_\mathrm{MD}}+R_{\mathrm{ON}\_\mathrm{MC}})}$

timing delay T over N cycles_DEqual to N.T_D。

$T_D=\frac{N.V_{\mathrm{REF}}.R1.C1}{I_{\mathrm{EDI}}.(R_{\mathrm{ON}\_\mathrm{MD}}+R_{\mathrm{ON}\_\mathrm{MC}})}=\frac{Q}{I_{\mathrm{EDI}}}$

Wherein,

$Q=\frac{N.V_{\mathrm{REF}}.R1.C1}{(R_{\mathrm{ON}\_\mathrm{MD}}+R_{\mathrm{ON}\_\mathrm{MC}})}$

from the above, it can be seen that the delay time TD and the over-discharge current I_EDIIn inverse proportion.

According to the functional principle division, the operational amplifier, MP1, MP2 and resistor R1 in fig. 7 can be regarded as a voltage-controlled current source, and MP3 can be regarded as an enable control circuit. In addition, the capacitor C1, the oscillator comparator, and the MN1 in fig. 7 can be regarded as an oscillation unit, and the inverters U1 and MN2 can be regarded as an enable control circuit. The circuit generalizations described herein should not be considered limiting, but rather illustrative. In other words, the voltage-controlled current source, the oscillation unit and the two respective enable control circuits may be replaced by other devices/circuits having different components but achieving the same function.

Fig. 8 is a structured circuit diagram of the circuit shown in fig. 7.

According to the circuit generalization/structuring described in fig. 7, the circuit shown in fig. 8 preferably includes a discharge overcurrent (EDI) comparator, a voltage-controlled current source, an enable control circuit 1, an oscillation unit, an enable control circuit 2, and a timer.

The input end of the enabling control circuit 1 is connected to the output end of the discharging overcurrent comparator, and the output end of the enabling control circuit is connected to the enabling control end of the voltage-controlled current source and used for starting the voltage-controlled current source according to the judgment result of the discharging overcurrent comparator; the input end of the voltage-controlled current source receives the discharging overcurrent voltage, and the output end of the voltage-controlled current source is the output end of the voltage-controlled current source circuit and is used for generating a current with the value proportional to the discharging overcurrent voltage value. In the embodiment illustrated in fig. 7, the current generated by the voltage controlled current source circuit is inversely proportional to the discharge overcurrent voltage. The reason for this is that the current generated by the voltage-controlled current source is proportional to the discharge overcurrent voltage, and the oscillation period of the oscillator is inversely proportional to the current generated by the voltage-controlled current source.

The input end of the enable control circuit 2 is connected to the output end of the discharging overcurrent comparator, and the output end of the enable control circuit is connected to the enable control end of the oscillation unit, so that the oscillation unit is started according to the judgment result of the discharging overcurrent comparator. It should be noted that the enable control circuit described herein may be any circuit that can implement enable control and may be constructed of different components to achieve this purpose. The input end of the oscillation unit receives the current generated by the voltage-controlled current source circuit, and the output end of the oscillation unit is the output end of the oscillator and is used for generating an oscillation signal with an oscillation period proportional to the current and performing discharge overcurrent protection according to the oscillation signal.

As shown in fig. 8, the EDI comparator is used to determine whether an overcurrent condition occurs, and its two input terminals are VM and V, respectively_EDI，V_EDIA reference voltage set for the system. When the voltage at the VM terminal is higher than V_EDIWhen the voltage-controlled current source is in operation, the circuit with the delay time inversely proportional to the overdischarge current starts to work, namely, the enable control circuits 1 and 2 are respectively sent out enable signals, and then the voltage-controlled current source and the oscillating unit are started by the enable control circuits. Otherwise, the circuit in which the delay time is inversely proportional to the overdischarge current is inhibited from operating. In operation, the voltage controlled current source generates a current source. Preferably, the current value of the current source is proportional to VM according to specific circuit designA voltage. The current source outputs to the oscillation unit, and the oscillation period of the oscillation unit is inversely proportional to the current value. The timer is used for timing according to the oscillation signal of the oscillation unit, and the discharge overcurrent delay time is N times of the period of the oscillation signal. From the description of fig. 7, it can be seen that N is also theoretically a design constant related to Q.

Fig. 9 is a structured circuit diagram of the circuit shown in fig. 8.

Similar to the transition from fig. 7 to fig. 8, fig. 8 can be further generalized/structured functionally into the circuit diagram shown in fig. 9. Preferably, the enable control circuit 1 and the voltage-controlled current source shown in fig. 8 may constitute one voltage-controlled current source circuit, and the enable control circuit 2 and the oscillation unit may constitute one oscillator.

As shown in fig. 9, the voltage-controlled current source circuit includes an input terminal for receiving the discharging overcurrent voltage, an enable control terminal for receiving the output of the discharging overcurrent comparator, and an output terminal for outputting to the oscillator, and is configured to generate a current having a current value proportional to the discharging overcurrent voltage value and output to the oscillator; the oscillator comprises an input end for receiving the current generated by the voltage-controlled current source circuit, an enable control end for receiving the output of the discharging overcurrent comparator and an output end, and is used for generating an oscillation signal with an oscillation period proportional to the current and outputting the oscillation signal to the timer, and the timer performs timing according to the oscillation signal so as to perform discharging overcurrent protection.

Fig. 10 is a structured circuit diagram of the circuit shown in fig. 9.

Again, fig. 9 can be further generalized/structured in functional principle into the circuit diagram shown in fig. 10. Preferably, the voltage-controlled current source circuit and the oscillator shown in fig. 9 may constitute one voltage-controlled oscillation circuit.

As shown in fig. 10, the circuit includes a discharge overcurrent comparator and a voltage-controlled oscillation circuit, wherein: the two inputs of the discharging overcurrent comparator are discharging overcurrent voltage and a discharging overcurrent voltage threshold (VEDI), the output end of the discharging overcurrent comparator is connected to the enabling control end of the voltage-controlled oscillation circuit, and the discharging overcurrent comparator is used for judging whether an overcurrent state occurs or not and starting the voltage-controlled oscillation circuit when the overcurrent state occurs; the voltage-controlled oscillating circuit comprises an input end for receiving the discharging overcurrent voltage, an enable control end for receiving the output of the discharging overcurrent comparator and an output end for outputting an oscillating signal, the oscillating signal is used for generating an oscillating signal with an oscillating period proportional to the discharging overcurrent voltage and outputting the oscillating signal to the timer, and the timer performs timing according to the oscillating signal so as to perform discharging overcurrent protection.

It will be obvious that many variations of the invention described herein are possible without departing from the true spirit and scope of the invention. Accordingly, all changes which are obvious to one skilled in the art are intended to be included within the scope of the appended claims. The scope of the invention is only limited by the appended claims.

Claims (16)

1. A discharge overcurrent protection circuit is characterized by comprising a discharge overcurrent comparator and a voltage-controlled oscillating circuit, wherein:

the two inputs of the discharging overcurrent comparator are a discharging overcurrent voltage and a discharging overcurrent voltage threshold value (V)_EDI) The output end of the voltage-controlled oscillation circuit is connected to the enabling control end of the voltage-controlled oscillation circuit and is used for judging whether an overcurrent state occurs or not and starting the voltage-controlled oscillation circuit when the overcurrent state occurs;

the voltage-controlled oscillating circuit comprises an input end for receiving the discharging overcurrent voltage, an enable control end for receiving the output of the discharging overcurrent comparator and an output end for outputting an oscillating signal, and is used for generating an oscillating signal with an oscillating period in inverse proportion to the discharging overcurrent voltage and performing discharging overcurrent protection according to the oscillating signal.

2. The discharge overcurrent protection circuit of claim 1, further comprising a timer for receiving an oscillating signal of the voltage-controlled oscillating circuit and for timing based on the oscillating signal.

3. The discharge overcurrent protection circuit of claim 1, wherein the voltage-controlled oscillation circuit comprises a voltage-controlled current source circuit and an oscillator:

the voltage-controlled current source circuit comprises an input end for receiving the discharging overcurrent voltage, an enable control end for receiving the output of the discharging overcurrent comparator and an output end for outputting to the oscillator, and is used for generating a current with a current value proportional to the value of the discharging overcurrent voltage and outputting the current to the oscillator;

the oscillator comprises an input end for receiving the current generated by the voltage-controlled current source circuit, an enable control end for receiving the output of the discharging overcurrent comparator and an output end, and is used for generating an oscillation signal with an oscillation period proportional to the current and performing discharging overcurrent protection according to the oscillation signal.

4. The discharge overcurrent protection circuit of claim 3, wherein the voltage-controlled current source circuit comprises a first enable control circuit and a voltage-controlled current source,

the input end of the first enabling control circuit is connected to the output end of the discharging overcurrent comparator, and the output end of the first enabling control circuit is connected to the enabling control end of the voltage-controlled current source and used for starting the voltage-controlled current source according to the judgment result of the discharging overcurrent comparator;

the input end of the voltage-controlled current source receives the discharge overcurrent voltage, and the output end of the voltage-controlled current source is the output end of the voltage-controlled current source circuit and is used for generating a current with a value proportional to the value of the discharge overcurrent voltage.

5. The discharge overcurrent protection circuit of claim 4, wherein the first enable control circuit comprises a third P-type field effect transistor and terminal (VCC):

and the source electrode of the third P-type field effect transistor is connected to the terminal (VCC), the grid electrode of the third P-type field effect transistor is connected to the output end of the discharging overcurrent comparator, and the drain electrode of the third P-type field effect transistor is the output end of the first enabling control circuit.

6. The discharge overcurrent protection circuit of claim 5, wherein the voltage-controlled current source comprises an operational amplifier, a first P-type field effect transistor, a second P-type field effect transistor, and a resistor;

the currents flowing through the first P-type field effect transistor and the second P-type field effect transistor are in mirror image relation with each other;

the inverting input end of the operational amplifier is the input end of the voltage-controlled current source, the non-inverting input end of the operational amplifier is connected with the drain electrode of the first P-type field effect transistor and the resistor, and the output end of the operational amplifier is connected with the grid electrodes of the first P-type field effect transistor and the second P-type field effect transistor and is connected with the output end of the first enabling control circuit;

the sources of the first P-type field effect transistor and the second P-type field effect transistor are connected to the terminal (VCC), and the drain of the second P-type field effect transistor is the output end of the voltage-controlled current source;

one end of the resistor is grounded.

7. The discharge overcurrent protection circuit of claim 3, wherein the oscillator comprises a second enable control circuit and an oscillation unit,

the input end of the second enabling control circuit is connected to the output end of the discharging overcurrent comparator, and the output end of the second enabling control circuit is connected to the enabling control end of the oscillating unit, so that the oscillating unit is started according to the judgment result of the discharging overcurrent comparator;

the input end of the oscillation unit receives the current generated by the voltage-controlled current source circuit, and the output end of the oscillation unit is the output end of the oscillator and is used for generating an oscillation signal with an oscillation period proportional to the current and performing discharge overcurrent protection according to the oscillation signal.

8. The discharge overcurrent protection circuit of claim 7, wherein the second enable control circuit comprises an inverter and a second N-type field effect transistor:

the input end of the inverter is connected to the output end of the discharge overcurrent comparator, and the output end of the inverter is connected to the grid electrode of the second N-type field effect transistor;

and the source electrode of the second N-type field effect transistor is grounded, and the drain electrode of the second N-type field effect transistor is the output end of the second enabling control circuit.

9. The discharge overcurrent protection circuit of claim 7, wherein the oscillating unit comprises a capacitor, an oscillator comparator, and a first N-type field effect transistor:

the inverting input of the oscillator comparator is a reference voltage (V)_REF) The output end of the oscillation unit is connected with the grid electrode of the first N-type field effect transistor and serves as the output end of the oscillation unit;

one end of the capacitor, the drain electrode of the first N-type field effect transistor and the positive phase input end of the oscillator comparator are connected and used as the input end of the oscillation unit;

the other end of the capacitor is grounded with the source electrode of the first N-type field effect transistor.

10. The discharge overcurrent protection circuit of any one of claims 3-9, wherein:

the current generated by the voltage-controlled current source is in direct proportion to the discharge overcurrent voltage, and the oscillation period is in inverse proportion to the current generated by the voltage-controlled current source.

11. A discharge overcurrent protection circuit, comprising:

the output switch is used for opening or closing the discharge path;

the control circuit is used for outputting a control signal to control the output switch to close the discharge passage after receiving the discharge overcurrent detection signal; and

discharge and overflow the detection circuitry for detect the electric current on the discharge path and provide the discharge and overflow the detection signal and give the control circuit, it includes:

a comparator circuit for outputting an enable signal when a current on a discharge path exceeds a predetermined threshold;

the current generation circuit is used for generating a current which is in direct proportion to the current on the discharge path after receiving the enabling signal;

an oscillator circuit for generating an oscillation signal having a period inversely proportional to a generated current of the current generation circuit after receiving the enable signal; and

and the counter is used for generating a discharge overcurrent detection signal after a preset number of oscillation signals are passed.

12. The discharge overcurrent protection circuit of claim 11, wherein the current generating circuit comprises an operational amplifier, a first transistor, a second transistor, and a resistor;

the grid electrode of the first transistor is connected with the grid electrode of the second transistor, the source electrodes of the first transistor and the second transistor are connected with a power supply, the drain electrode of the first transistor is also connected with one end of the resistor, the other end of the resistor is grounded,

one input terminal of the operational amplifier receives a voltage signal reflecting a current on the discharge path, the other input terminal of the operational amplifier is connected to the drain of the first transistor, the output terminal of the operational amplifier is connected to the gate of the first transistor,

and the drain electrode of the second transistor is used as the current output end of the current generation circuit.

13. The discharge overcurrent protection circuit of claim 12, wherein the current generation circuit further comprises an enable circuit configured to receive an enable signal from the comparator circuit and to enable the first transistor upon receiving the enable signal.

14. The discharge overcurrent protection circuit of claim 11 or 12, wherein the oscillator circuit comprises a capacitor, an oscillation comparator and a discharge circuit;

one end of the capacitor is connected with the output end of the current generation circuit, and the other end of the capacitor is grounded;

one input end of the oscillation comparator is connected with the output end of the current generation circuit, the other input end of the oscillation comparator is connected with a preset reference voltage, and the output end of the oscillation comparator is connected with the control end of the discharge circuit; wherein,

the generated current of the current generating circuit charges the capacitor;

when the voltage drop of the capacitor is higher than the preset reference voltage, the output of the oscillation comparator is inverted to control the discharge circuit to discharge the capacitor;

when the voltage drop of the capacitor is lower than the preset reference voltage, the output of the oscillation comparator is inverted to control the discharge circuit to stop charging the capacitor, and the output signal of the oscillation comparator is delayed for a preset time.

15. The discharge overcurrent protection circuit of claim 14, wherein the oscillator circuit further comprises an enable circuit configured to receive an enable signal from the comparator and to allow the capacitor to be charged upon receiving the enable signal.

16. A lithium battery protection circuit comprising the discharge overcurrent protection circuit according to claim 1.

Images