CN102412611B - Constant-current charging circuit applied to linear charger - Google Patents

Abstract

The invention discloses a constant-current charging circuit applied to a linear charger, mainly solving the problem of overlong charging time caused by the adoption of thermal shutdown in charging in the prior art. The circuit comprises a constant-current modulation circuit, a temperature sampling circuit, a second operational amplifier OP2 and a PMOS (p-channel metal oxide semiconductor) transistor M2; the source electrode of the PMOS transistor M2 is connected with the power supply voltage; the grid is connected with the output of the constant-current modulation circuit, and the drain electrode of the PMOS transistor M2 is the output of the charger; the constant-current modulation circuit is provided with two input ends; the first input end A is connected with the reference voltage Va so as to generate constant output current IO in constant current charging at the normal temperature; the second input end B is connected with the temperature sampling circuit through the second operational amplifier OP2 so as to form a temperature feedback control loop. By using the constant-current charging circuit provided by the invention, output current can be reduced when the temperature of a chip is high, so that the temperature of the chip can be stabilized to be within the range of refining temperature T1, and charging is continued, and thus the problem of too long charging time resulting from the adoption of thermal shutdown is avoided. The constant-current charging circuit can be used in linear chargers.

Description

Be applied to the constant-current charging circuit of linear charger

Technical field

The invention belongs to the electronic circuit technology field, relate to analog integrated circuit, particularly a kind of constant-current charging circuit that is applied to linear charger.

Background technology

Linear charger is mainly the system that utilizes the linear stabilized power supply technology to charge the battery, and charging modes is generally typical constant current/constant voltage mode.During charging be mainly by constant current to battery fast repairing charge volume, when battery approaches when being full of, switch to constant voltage mode, charging current begins to reduce, until be full of.

Fig. 1 has provided the constant-current charging circuit of existing linear charger, comprises that mainly operational amplifier OP, resistance R, PMOS manage M ₁And M ₂The positive input of operational amplifier OP is connected to an end of resistance R, and is connected to simultaneously PMOS pipe M ₁Drain electrode, the other end ground connection of resistance R 1, the reverse input end of operational amplifier OP connects reference voltage V _A, the output of operational amplifier OP1 is connected to PMOS pipe M ₁And M ₂Grid, PMOS manages M ₁And M ₂Source electrode connect supply voltage so that PMOS pipe M ₁And M ₂Consist of current mirror.The advantage of linear charger is simple in structure, and shortcoming is that energy efficiency is low, in charging process, due to the power tube consumed power, the junction temperature of power tube is raise, and too high junction temperature will make semiconductor device work unreliable, even burn semiconductor device.The temperature of linear-charging managing chip can be calculated by following formula:

T _J＝T _A+(V _CC-V _BAT)×I _O×K _A (1)

Wherein: T _JIt is the temperature of chip; T _AIt is the ambient temperature of chip; V _CCIt is input voltage; V _BATIt is cell voltage; I _OIt is charging current; K _AIt is the thermal resistance of chip.

Can be found out by top formula, when the ambient temperature of chip is higher, when perhaps large the or charging current of the voltage difference of input voltage and cell voltage was larger, the temperature of chip had obvious rising.In the pond application of typical single-lithium-battery, the lithium battery voltage that a joint is full of electricity is 4.2V, it has been generally acknowledged that the voltage when not having is 3.3V, and the lithium battery voltage of some overdischarge even can be less than 2V.When the 5V power supply is given the battery charging of a cell voltage that does not have electricity fully as 2V take the electric current of 1A, the power of electrical source consumption is 5W, and the power of battery storage is 2W, namely adjusts and manages to such an extent that consume the power of 3W, will make chip overheating like this, can cause chip to burn in serious situation.

Traditional solution is to adopt heat to turn-off to control, and when namely chip temperature surpasses the maximum temperature threshold value that arranges, stops charging.Chip just can restart charging after after a while naturally cooling, to turn-off temperature be 160 ℃ to heat usually.Because cell voltage can fast rise, so after excess temperature recovered, the power tube consumed power did not reduce, and therefore, circuit excess temperature can occur again turn-offs, and enters among a circulation of turn-offing and recovering.Due to the existence of cooling time, this will extend the time of battery charging greatly.In addition, excess temperature also can affect the reliability of circuit frequently.

Summary of the invention

The object of the invention is to the deficiency for above-mentioned prior art, propose a kind of constant-current charging circuit that is applied to linear charger, adopt heat to turn-off the long problem of charging interval that is caused to solve when prior art is charged.

For achieving the above object, constant-current charging circuit of the present invention comprises constant current modulation circuit and PMOS pipe M ₂, PMOS manages M ₂Source electrode connect supply voltage, grid connects the output of constant current modulation circuit, PMOS manages M ₂Drain electrode be charger output; It is characterized in that: the constant current modulation circuit is provided with two inputs, and first input end A connects reference voltage V _A, produce constant output current I when being used for carrying out constant current charge under normal temperature _OThe second input B is connected with the second operational amplifier OP2, and the positive input of this operational amplifier OP2 is connected with temperature sampling circuit, and reverse input end connects reference voltage V ₁, consist of the temperature feedback control loop, be used for surpassing at chip temperature the refining temperature T that sets ₁The time, reduce output current, make chip temperature be stabilized in refining temperature T ₁

Described refining temperature T ₁, less than the temperature threshold that heat is turn-offed, T ₁Be 120 ℃～125 ℃, it is 160 ℃ that heat is turn-offed temperature.

Described temperature sampling circuit comprises a PNP pipe Q1, the 2nd PNP pipe Q2, the first current source I ₂, the second current source I ₃And resistance R ₂, collector electrode and the equal ground connection of base stage of a PNP pipe Q1, emitter meets the first current source I ₂, and be connected to the base stage that the 2nd PNP manages Q2, the grounded collector of the 2nd PNP pipe Q2, emitter connecting resistance R ₂An end, resistance R ₂Another termination the second current source I ₃, and as the output of temperature sampling circuit, for generation of temperature voltage V _TThis temperature voltage V _THave negative temperature coefficient, when in chip, temperature reaches 120 ℃, temperature voltage V _TEqual reference voltage V ₁

Described constant current modulation circuit comprises that the first operational amplifier OP1, PMOS manage M ₁And resistance R ₁The positive input of the first operational amplifier OP1 is connected to an end of resistance R 1, and is connected to simultaneously PMOS pipe M ₁Drain electrode, the other end ground connection of resistance R 1, PMOS manages M ₁Source electrode connect supply voltage, the first operational amplifier OP1 has 2 reverse input ends, two input A and B as the constant current modulation circuit connect respectively reference voltage V _AOutput V with the second operational amplifier OP2 _B, the output of the first operational amplifier OP1 is connected to PMOS pipe M ₁Grid, and as the output of constant current modulation circuit.

The present invention compared with prior art has following advantage:

The present invention has consisted of the temperature feedback control loop owing to connecting temperature sampling circuit at the input of constant current modulation circuit by the second operational amplifier OP2, makes that temperature surpasses refining temperature T in chip ₁The time, can reduce output current, with temperature stabilization in chip at refining temperature T ₁, can continue charging, not only avoided circuit to enter the long problem of charging interval that heat is turn-offed and the circulation that recovers causes, can not affect because of excess temperature frequently the reliability of circuit simultaneously yet.

Description of drawings

Fig. 1 is existing constant-current charging circuit;

Fig. 2 is constant-current charging circuit of the present invention.

Embodiment

Be described in further detail referring to 2 pairs of specific implementations of the present invention of accompanying drawing.

Constant-current charging circuit in the present invention is mainly by constant current modulation circuit, temperature sampling circuit, the second operational amplifier OP2 and PMOS pipe M ₂Form.The output of temperature sampling circuit connects the positive input of the second operational amplifier OP2, and the reverse input end of the second operational amplifier OP2 connects reference voltage V ₁, its output is connected to the second input B of constant-current source circuit, and the output of constant current modulation circuit is connected to the grid of PMOS pipe M2, and the drain electrode of PMOS pipe M2 is the output of charging circuit.

Described constant current modulation circuit, the output current when controlling constant current charge, it comprises that the first operational amplifier OP1, PMOS manage M ₁And resistance R ₁Wherein the positive input of the first operational amplifier OP1 is connected to an end of resistance R 1, and is connected to simultaneously PMOS pipe M ₁Drain electrode, the other end ground connection of resistance R 1, PMOS manages M ₁Source electrode connect supply voltage; The first operational amplifier OP1 adopts compound calculation amplifier, is provided with two reverse input ends, and two input A and B as the constant current modulation circuit connect respectively reference voltage V _AOutput V with the second operational amplifier OP2 _B, the output of the first operational amplifier OP1 is connected to PMOS pipe M ₁Grid, and as the output of constant current modulation circuit.PMOS manages M ₂The grid output of also receiving the first operational amplifier OP1, PMOS manages M ₂Source electrode connect supply voltage and and PMOS manage M ₁Formed current mirror, PMOS manages M ₂Breadth length ratio and PMOS pipe M ₁Breadth length ratio be K ₁, to put big pmos M ₁In electric current I ₁The first operational amplifier OP1 in this constant current modulation circuit is provided with two reverse input end A and B, as the voltage V of first input end A _AVoltage V higher than the second input B _BThe time, the output of operational amplifier OP1 is by the voltage V of the second input B _BAnd the difference between positive input voltage determines; Voltage V as first input end A _AVoltage V lower than the second input B _BThe time, the output of operational amplifier OP1 is by the voltage V of first input end A _AAnd the difference between positive input voltage determines; Therefore, for the constant current modulation circuit, the electric current I of the resistance R of flowing through 1 ₁For:

$I_1=\frac{\min (V_A,V_B)}{R_1}---\left(2\right)$

Min (V wherein _A, V _B) the expression reference voltage V _AOutput V with the second operational amplifier OP2 _BMiddle magnitude of voltage is less one.

PMOS manages M ₂Breadth length ratio and PMOS pipe M ₁Breadth length ratio be K ₁Therefore, output current I _OFor:

$I_O=K_1{\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="HDA0000117250110000011.png"\; state="\{\{state\}\}">I</figure-callout>}}_1=\frac{{\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="HDA0000117250110000011.png"\; state="\{\{state\}\}">K</figure-callout>}}_1\&times;\min (V_A,V_B)}{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HDA0000117250110000011.png"\; state="\{\{state\}\}">R</figure-callout>}}_1}.---\left(3\right)$

Described temperature sampling circuit comprises a PNP pipe Q1, the 2nd PNP pipe Q2, the first current source I ₂, the second current source I ₃And resistance R ₂, collector electrode and the equal ground connection of base stage of a PNP pipe Q1, emitter meets the first current source I ₂, and be connected to the base stage that the 2nd PNP manages Q2, the grounded collector of the 2nd PNP pipe Q2, emitter connecting resistance R ₂An end, resistance R ₂Another termination the second current source I ₃With the positive input of the second operational amplifier OP2, and as the output of temperature sampling circuit, produce temperature voltage V _T:

V _T＝V _EB1+V _EB2+I ₃R ₂ (4)

V wherein _EB1The emitter base voltage of a PNP pipe Q1, V _EB2The emitter base voltage of the 2nd PNP pipe Q2, I ₃The current value of the second current source, R ₂Represent resistance R ₂Value.

Emitter base voltage due to a PNP pipe Q1 and the 2nd PNP pipe Q2 has negative temperature coefficient, at normal temperatures, when their emitter base voltage is 750mV, temperature coefficient is-1.5mV/ ℃, and their two emitter base voltages superpose simultaneously, therefore temperature voltage V _TTemperature coefficient be-3mV/ ℃.By selecting suitable resistance R ₂With power supply I ₃Value, can guarantee when chip temperature reaches 120 ℃ of refining temperatures temperature voltage V _TValue equal reference voltage V ₁

The present invention controls by introduce temperature feedback in constant current modulation loop, avoids occurring in the constant current charge process excess temperature and turn-offs phenomenon, and the operation principle of its whole constant-current charging circuit is as follows:

After charger output access battery, begin charging, under normal circumstances the initial temperature T in chip _ALower than refining temperature T ₁, the output temperature voltage V of temperature sampling circuit _THigher than reference voltage V ₁, the voltage V of the second input B _BReference voltage V higher than the first input end A of constant current modulation circuit _AAccording to formula (3), output current I _OBy reference voltage V _ADetermining, is also the maximum of output current simultaneously

Temperature sampling circuit and the first operational amplifier OP1 can't affect the normal operation of constant current modulation loop.At this moment, PMOS pipe M ₂The power of upper consumption is:

$P=(V_{\mathrm{CC}}-V_{\mathrm{BAT}})\frac{K_1{V}_A}{R_1}---\left(5\right)$

V wherein _CCBe supply voltage, V _BATBe cell voltage.

The thermal resistance of supposing chip is K _A℃/W, namely the power consumption of 1W makes temperature rising K in chip _A℃, the temperature T when chip charges _JFor:

$T_J=T_A+K_{A}P$

$=T_A+K_A\frac{K_1(V_{\mathrm{CC}}-V_{\mathrm{BAT}})V_A}{R_1}---\left(6\right)$

Wherein, T _AInitial temperature during for the charging beginning in chip.

If this moment supply voltage V _CCWith cell voltage V _BATThe large or initial temperature T of difference _AHigher, in chip, temperature will surpass hot refining temperature T ₁This moment temperature voltage V _TBe down to reference voltage V ₁Under, thereby make the output voltage V of the first operational amplifier OP1 _BDescend.As voltage V _BBe down to reference voltage V _AUnder the time, the temperature feedback loop is started working, and carries out heat modulation.According to formula (3), output current I _OBy reference voltage V _BDetermine, for

Due to voltage V this moment _BLess than reference voltage V _A, so the time output current corresponding I _OReduce, PMOS manages M ₂On power consumption also decrease, make that temperature begins to descend in chip.Through the adjusting of temperature feedback loop, final chip temperature can be stabilized in refining temperature T ₁, T ₁It is 120 ℃～125 ℃.

Along with continuing of charging process, cell voltage V _BATRising, in identical charging current situation, PMOS manages M ₂On power consumption can descend thereupon.But in the process of heat modulation, temperature stabilization is at refining temperature T ₁, PMOS manages M ₂On power consumption constant, and supply voltage V _CCWith cell voltage V _BATPressure reduction reduce gradually, so output current I _ORise, until reach maximum

Break away from hot modulated process, enter in normal constant current charge process.

Be only below a preferred example of the present invention, do not consist of any limitation of the invention, obviously under design of the present invention, can carry out different changes and improvement to its circuit, but these are all at the row of protection of the present invention.

Claims (3)

1. a constant-current charging circuit that is applied to linear charger, comprise constant current modulation circuit and PMOS pipe M ₂, PMOS manages M ₂Source electrode connect supply voltage, grid connects the output of constant current modulation circuit, PMOS manages M ₂Drain electrode be charger output; It is characterized in that: the constant current modulation circuit is provided with two inputs, and first input end A connects reference voltage V _A, produce constant output current I when being used for carrying out constant current charge under normal temperature _OThe second input B is connected with the second operational amplifier OP2, and the positive input of this operational amplifier OP2 is connected with temperature sampling circuit, and reverse input end connects reference voltage V ₁, to consist of the temperature feedback control loop, be used for surpassing at chip temperature the refining temperature T that sets ₁The time, reduce output current, make chip temperature be stabilized in refining temperature T ₁

Described temperature sampling circuit comprises a PNP pipe Q1, the 2nd PNP pipe Q2, the first current source I ₂, the second current source I ₃And resistance R ₂, collector electrode and the equal ground connection of base stage of a PNP pipe Q1, emitter meets the first current source I ₂, and be connected to the base stage that the 2nd PNP manages Q2, the grounded collector of the 2nd PNP pipe Q2, emitter connecting resistance R ₂An end, resistance R ₂Another termination the second current source I ₃, and as the output of temperature sampling circuit, for generation of temperature voltage V _T

Described constant current modulation circuit comprises that the first operational amplifier OP1, PMOS manage M ₁And resistance R ₁The positive input of the first operational amplifier OP1 is connected to an end of resistance R 1, and is connected to simultaneously PMOS pipe M ₁Drain electrode, the other end ground connection of resistance R 1, PMOS manages M ₁Source electrode connect supply voltage, the first operational amplifier OP1 has two reverse input ends, two input A and B as the constant current modulation circuit connect respectively reference voltage V _AWith the output of the second operational amplifier OP2, the output of the first operational amplifier OP1 is connected to PMOS pipe M ₁Grid, and as the output of constant current modulation circuit.

2. constant-current charging circuit described according to claims 1, is characterized in that described refining temperature T ₁, less than the temperature threshold that heat is turn-offed, T ₁Be 120 ℃～125 ℃, it is 160 ℃ that heat is turn-offed temperature.

3. constant-current charging circuit described according to claims 1, is characterized in that described temperature voltage V _T, have negative temperature coefficient, when in chip, temperature reaches 120 ℃, temperature voltage V _TEqual reference voltage V ₁

Images