CN205231203U - Current detecting circuit - Google Patents

Abstract

The utility model discloses a current detecting circuit, it includes: operational amplifier, it is including first input end, second input and output, connect the first switch between reference voltage and operational amplifier's first input end, connect the second switch between current detection end and operational amplifier's first input end, connect in operational amplifier's output and the third switch between the second input, establish ties in proper order fourth switch, second resistance and first resistance between mains voltage end and earthing terminal, establish ties electric capacity between the intermediate node of first resistance and second resistance and operational amplifier's second input. Compared with the prior art, the utility model provides an overcurrent protection's electric current threshold value can not change along with mains voltage's change to the precision of electric current protection has been improved.

Description

current detection circuit

【Technical field】

The utility model relates to the field of circuit design, in particular to a current detection circuit in a battery protection chip.

【Background technique】

FIG. 1 is a structural diagram of an existing battery protection system. The battery protection system 100 includes a battery battery, a battery protection chip and a protection switch combination 110 . The battery protection chip protects the charging and discharging of the battery. BP+ is the positive output terminal of the battery, and BP- is the negative output terminal of the battery. The battery protection chip includes a power supply terminal VCC, a ground terminal VSS, a discharge protection control terminal DOUT, a charge protection control terminal COUT, and a current detection terminal VM. The protection switch assembly 110 includes a discharge tube 111 and a charge tube 112 .

The battery protection chip needs to detect the charging current and the discharging current, so as to avoid charging overcurrent or discharging overcurrent. Whether the charging overcurrent or the discharging overcurrent is determined by detecting the voltage of the current detection terminal VM. Taking the discharge overcurrent detection as an example, the battery protection chip needs to detect whether the voltage difference between the voltage ground terminal VSS of the current detection terminal VM is higher than the predetermined overcurrent protection voltage threshold VEDI, if yes, it indicates discharge overcurrent, If not, it means no discharge overcurrent.

There is a current detection circuit in the battery protection chip (or battery protection circuit) for overcurrent detection, and the voltage threshold VEDI of the discharge overcurrent protection remains unchanged under different cell voltages. Discharge overcurrent detection means that when the current detection terminal VM is higher than the voltage threshold VEDI of the ground terminal VSS overcurrent protection, the discharge protection control terminal DOUT changes from high level (VDD) to low level (VSS), that is, the shutdown is controlled by DOUT discharge tube, stop discharging. When the chip is in normal charging and discharging, both COUT and DOUT are high level (VDD), and the voltage of the current detection terminal VM is determined by the discharge current flowing through the charge and discharge tube resistance Ron controlled by COUT and DOUT, where

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; x</span>}}\frac{\mathrm{<span\; class="notranslate">\; W</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; )</span>}$

Among them, V _GS is the gate-source voltage of the charge-discharge tube, and V _TH is the threshold voltage of the charge-discharge tube. As the power supply voltage rises, V _GS increases, and R _ON decreases. If the value of VEDI remains unchanged, the corresponding discharge overcurrent protection current threshold will also increase with the rise of the power supply voltage, resulting in The reduction of current protection accuracy.

Therefore, it is necessary to propose a new technical solution to solve the above problems.

【Content of utility model】

One of the purposes of the present invention is to provide a current detection circuit, the current threshold of the over-current protection will not change with the change of the power supply voltage, thereby improving the accuracy of the current protection.

In order to achieve the above object, according to one aspect of the present invention, the present invention provides a current detection circuit, which includes: an operational amplifier, which includes a first input terminal, a second input terminal and an output terminal; connected to the reference voltage and A first switch between the first input terminals of the operational amplifier; a second switch connected between the current detection terminal and the first input terminal of the operational amplifier; a second switch connected between the output terminal of the operational amplifier and the second input terminal Three switches; the fourth switch, the second resistor and the first resistor connected in series between the power supply voltage terminal and the ground terminal; capacitance.

Further, during the first period, the first switch, the third switch, and the fourth switch are turned on, and the second switch is turned off; during the second period, the first switch, the third switch, and the fourth switch are turned off, and the second switch conduction, the first period and the second period alternate continuously.

Further, the overcurrent protection threshold VEDI is:

$\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; D.</span>}\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; ,</span>$

Where VREFF is the reference voltage, R1 is the resistance of the first resistor, R2 is the resistance of the second resistor, VCC is the voltage of the power supply voltage terminal, VM is the voltage of the current detection terminal, and Vc is the voltage drop of the capacitor.

Compared with the prior art, in the current detection circuit of the utility model, the current threshold of the overcurrent protection will not change with the change of the power supply voltage, thereby improving the precision of the current protection.

【Description of drawings】

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings that need to be used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention , for those skilled in the art, other drawings can also be obtained according to these drawings on the premise of not paying creative labor. in:

FIG. 1 is a structural diagram of an existing battery protection system;

FIG. 2 is a circuit schematic diagram of an embodiment of the current detection circuit in the present invention.

【detailed description】

The detailed description of the utility model directly or indirectly simulates the operation of the technical solution of the utility model mainly through programs, steps, logic blocks, processes or other symbolic descriptions. In the ensuing description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The invention may still be practiced without these specific details. These descriptions and representations herein are used by those skilled in the art to effectively convey the substance of their work to others skilled in the art. In other words, for the purpose of avoiding obscuring the present invention, well-known methods and procedures have not been described in detail since they are already easily understood.

Reference herein to "one embodiment" or "an embodiment" refers to a specific feature, structure or characteristic that may be included in at least one implementation of the present invention. "In one embodiment" appearing in different places in this specification does not all refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

FIG. 2 is a circuit schematic diagram of an embodiment of the current detection circuit 200 in the present invention. The current detection circuit 200 includes an operational amplifier X0, a first switch S1, a second switch S2, a third switch S3, a fourth switch S4, a first resistor R1, a second resistor R2, and a capacitor C0.

The operational amplifier X0 includes a first input terminal 1 , a second input terminal 2 and an output terminal RSLT. The first switch S1 is connected between the reference voltage VREF and the first input terminal 1 of the operational amplifier X0 . The second switch S2 is connected between the current detection terminal VM and the first input terminal 1 of the operational amplifier X0 . The third switch S3 is connected between the output terminal of the operational amplifier X0 and the second input terminal 2 . The fourth switch S4, the second resistor R2 and the first resistor R1 are serially connected in series between the power supply voltage terminal VCC and the ground terminal VSS. A capacitor C0 is connected in series between the middle node 3 of the first resistor R1 and the second resistor R2 and the second input terminal 2 of the operational amplifier X0.

The control signal Phi of each switch is

exist , the first switch S1, the third switch S3, and the fourth switch S4 are turned on, and the second switch S2 is turned off. At this time, the operational amplifier OP works in an operational amplification state. exist , the first switch S1, the third switch S3, and the fourth switch S4 are turned off, and the second switch S2 is turned on. At this time, the operational amplifier OP works in a comparison state, which compares the voltages of the two input terminals, so as to realize the comparison between the difference between the detection voltage VM and the voltage of the ground terminal VSS and the predetermined overcurrent protection threshold VEDI. The period of can be referred to as the first period, The period of time can be referred to as the second period, and the first period and the second period are constantly alternating.

As shown in Figure 2, in Time sample storage and in time comparison and

exist hour,

exist hour,

when and when equal,

Have $V\mathrm{E.}\mathrm{D.}I=Vm=V_C=VR\mathrm{E.}f-\frac{R1}{R1+R2}VCC,$

Wherein, VREFF is the reference voltage, R1 is the resistance value of the first resistor, R2 is the resistance value of the second resistor, VCC is the voltage at the power supply voltage terminal, VM is the voltage at the current detection terminal, Vc is the voltage drop of the capacitor C0, V1 is the voltage of the first input terminal 1, and V2 is the voltage of the second input terminal 2.

To sum up, it can be seen that the voltage threshold VEDI of overcurrent protection and the change requirements with the power supply voltage can be guaranteed by selecting an appropriate VREF and adjusting R1 and R2. For example, as the power supply voltage increases, the voltage threshold VEDI of overcurrent protection decreases gradually, thereby The current threshold of the corresponding overcurrent protection is slowed down with the change trend of the power supply voltage, and kept flat or unchanged, thereby improving the accuracy of the current protection.

Words such as "connected", "connected" or "phase-connected" in the present utility model that indicate electrical connection all indicate indirect or direct electrical connection. The above description has fully disclosed the specific implementation manners of the present utility model. It should be pointed out that any changes made by those skilled in the art to the specific embodiments of the utility model will not depart from the scope of the claims of the utility model. Correspondingly, the scope of the claims of the present utility model is not limited only to the foregoing specific embodiments.

Claims (3)

1. A current detection circuit, characterized in that it comprises: An operational amplifier comprising a first input terminal, a second input terminal and an output terminal; a first switch connected between the reference voltage and the first input terminal of the operational amplifier; a second switch connected between the current detection terminal and the first input terminal of the operational amplifier; a third switch connected between the output terminal of the operational amplifier and the second input terminal; A fourth switch, a second resistor and a first resistor connected in series between the power supply voltage terminal and the ground terminal in sequence; A capacitor connected in series between the intermediate node of the first resistor and the second resistor and the second input terminal of the operational amplifier. 2. The current detection circuit according to claim 1, characterized in that: During the first period, the first switch, the third switch, and the fourth switch are turned on, and the second switch is turned off, During the second period, the first switch, the third switch, and the fourth switch are turned off, and the second switch is turned on, The first period and the second period alternate continuously. 3. The current detection circuit according to claim 2, characterized in that: The overcurrent protection threshold VEDI is: $\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; D.</span>}\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; ,</span>$ Where VREFF is the reference voltage, R1 is the resistance of the first resistor, R2 is the resistance of the second resistor, VCC is the voltage of the power supply voltage terminal, VM is the voltage of the current detection terminal, and Vc is the voltage drop of the capacitor.