CN201159747Y - Inductor current sensing circuit for switch power source - Google Patents

Abstract

Disclosed is an inductance current detection circuit used for a switching power supply, comprising two switching tubes MS1 and MS2, a reference current source I <1>, a sampling current tube MR, three NMOS tubes M1, M2 and M3 which are in mirror connection; a current detection tube MP2 is in mirror connection with the MP3; two PMOS tubes M4 and M5 which are in mirror connection with each other; the three groups of mirror tubes are in serial connection sequentially; the reference current source I <1> is in serial connection with the NMOS tube M1 for providing current for the mirror tubes; the switching tube MS1 is in serial and common-gate connection with the power tube MP1, and in parallel connection with the switching tube MS2 with the reverse gate voltage; the output sampling current I <sen> is outputted from the drain electrode of the sampling current tube MR. the detection circuit has the advantages of simple structure, avoiding the temperature feature influence, low power consumption, effectively improving the efficiency of the switching power supply, high detection accuracy, good temperature feature and easy integration.

Description

A kind of inductive current detection circuit that is used for Switching Power Supply

Technical field

The utility model relates to a kind of mimic channel, particularly relates to a kind of analogue detection circuitry.

Background technology

Along with the continuous development of VLSI (very large scale integrated circuit) (VLSI), switching power source chip integrated swift and violent development, and be widely used in especially portable type electronic product of various device.Because current control type switching power supply has stability, the high-precision output voltage of automatic overcurrent protection, height; transient response and inherent control and current limiting capacity fast to the power switch electric current; therefore present Switching Power Supply adopts current control mode more; be illustrated in figure 1 as a kind of current mode DC/DC step-down controller, its principle of work is: output voltage V _OThe feedback voltage bV that obtains through electric resistance partial pressure _OAfter comparing with reference voltage Vref, error amplifier output Vea.The voltage that the detected inductive current of this Vea and current detection circuit is transformed into compares, the conducting of the pulse signal gauge tap pipe that obtains and ending, thus regulate output voltage.This shows that the performance of current detection circuit directly influences the performance of Switching Power Supply.

There is multiple different inductive current detection technique in the prior art, relatively commonly used just like Fig. 2 (a), Fig. 2 (b), three kinds of detection modes of Fig. 2 (c), all obtained in various degree realization and application, concrete is described below:

(1) resistance in series detection method

The circuit of resistance in series detection method realizes that shown in Fig. 2 (a) very little resistance R of series connection detects electric current by detecting ohmically pressure drop on inductance L.The advantage of described detection mode is the accuracy of detection height, but resistance can produce extra loss, and particularly during the super-high-current of power tube upper reaches, this loss is very big, have a strong impact on the conversion efficiency of power supply, and the resistance of accurate integrated tens milliohms is difficult in integrated circuit technology.

(2) detection power tube voltage drop method

The circuit of detection power tube voltage drop method realizes that shown in Fig. 2 (b) current amplifier in parallel at the power tube two ends when detecting amplifier generation upset, then obtains the power tube both end voltage.When the equivalent resistance of known power pipe, by the drain-source voltage V of detection power pipe at linear zone _DSThereby obtain the electric current on the power tube.

When power tube was operated in linear zone, its drain-source voltage was very little, and the computing formula of equivalent resistance can be similar to formula (1) expression.

$R_{\mathrm{DS}}=\frac{L}{{\mathrm{\&mu;C}}_{\mathrm{OX}}W(V_{\mathrm{GS}}-V_T)}---\left(1\right)$

Wherein μ is the mobility of channel electrons, C _OXBe unit area gate capacitance, V _TBe the threshold voltage of power tube, V _GSBe gate source voltage, W, L are respectively the width and the length of raceway groove.

Theoretically, described detection mode is very perfect, does not introduce excess loss, does not influence chip efficient, yet but has very big defective in the practical application, and most importantly the precision of Jian Ceing is very low, and reason has following 2 points:

The first, effect of nonlinear, owing to ignored the non-linear effects of drain-source voltage, the relation of current/voltage is seen linear, thereby the approximate formula (1) that obtains, but when sensed current was positioned near the peak value, the non-linear effects of described drain-source voltage can not be ignored.

The second, the influence of temperature characterisitic, from formula (1) as can be seen, resistance R _DSBe subjected to parameter μ, C _OX, V _TInfluence, and described parameter μ, C _OX, V _TAll with temperature correlation, so resistance R _DSTherefore temperature influence is bigger, though described method designs ingeniously, only is applied in the not high occasion of accuracy of detection usually.

(3) equal proportion electric current testing

The circuit of equal proportion electric current testing is realized shown in Fig. 2 (c), current sample pipe M1 is connected by amplifier OP parallel connection and mirror image with power tube M2, then current sample pipe M1 has identical grid leak source voltage with power tube M2, again because the electric current of MOS as shown in Equation (2):

$I_D=\frac{1}{2}\mathrm{\&mu;}{C}_{\mathrm{OX}}\frac{W}{L}[2(V_{\mathrm{GS}}-V_T)V_{\mathrm{DS}}-{V_{\mathrm{DS}}}^2]---\left(2\right)$

By formula (2) as can be known, after the breadth length ratio of current sample pipe M1 and power tube M2 was determined, then the electric current of current sample pipe M1 and power tube M2 just had certain proportionate relationship, and for example: the breadth length ratio of supposing two pipes is that N doubly concerns:

$N{\left(\frac{W}{L}\right)}_1={\left(\frac{W}{L}\right)}_2,$

Then: ${\mathrm{<figure-callout\; id="1"\; label="I\; d"\; filenames="Y20082009209800112.png"\; state="\{\{state\}\}">I</figure-callout>}}_d=\frac{I_{d2}}{N}.$

Adopt described method to reduce loss, but owing to the reasons such as finite gain of process deviation, amplifier, make that the current ratio on current sample pipe M1 and the power tube M2 can not strictness equal 1: can there be an error in N.

By above analysis as can be seen, described detection method all has the limitation such as input/output port that power consumption is big, the circuit realization is complicated, need be extra.

Summary of the invention

The purpose of this utility model is to provide a kind of inductive current detection circuit, and this circuit also will make and realize that circuit is simple as far as possible when accurately detecting inductive current, and not needing increases extra input/output port, and is not subjected to the influence of extraneous factors such as temperature.

A kind of inductive current detection circuit that is used for Switching Power Supply, this circuit comprise the power tube MP1 in the switch power supply system, continued flow tube MN1, inductance L and capacitor C ₀, wherein, power tube MP1 and continued flow tube MN1 series connection, inductance L and capacitor C ₀Series connection, this circuit also comprises two switching tube MS1 and MS2, reference current source I ₁Sample rate current pipe MR, and NMOS pipe M1, the M2 and the M3 that connect by three mirror images, two current detecting pipe MP2 and MP3 that mirror image connects, and the mirror image circuit formed of the PMOS pipe M4 that connects by two mirror images and M5, wherein, current detecting pipe MP2, PMOS pipe M4, NMOS manage M3 and connect successively in the described three arrangement of mirrors image tubes, current detecting pipe MP3, PMOS pipe M5, NMOS pipe M2 connects reference current source I successively ₁Connecting with NMOS pipe M1 provides the electric current of described mirror image pipe; Switching tube MS1 and power tube MP1 series connection and after grid are connected altogether, be connected in parallel with switching tube MS2 and grid voltage opposite, sample rate current I _SenFrom the drain electrode output of sample rate current pipe MR, the source electrode of described sample rate current pipe MR is connected the drain electrode of current detecting pipe MP2, and grid links to each other with the drain electrode of PMOS pipe M5.

Described circuit also comprises a building-out capacitor C _C, this building-out capacitor C _CThe source electrode and the PMOS that are connected in current detecting pipe MP3 manage between the drain electrode of M5.

The technological parameter that three NMOS that described mirror image connects manage M1, M2 and M3 is identical, and breadth length ratio is identical.

The technological parameter that two PMOS that described mirror image connects manage M4 and M5 is identical, and breadth length ratio is identical.

Two current detecting pipe MP2 that described mirror image connects are identical with the technological parameter of MP3, and breadth length ratio is identical.

Described two PMOS pipe MS1 and MS2 are breadth length ratio greater than 50 switching tube.

Described reference current source I ₁Output is less than 50 microamperes electric current.

The beneficial effects of the utility model are: simple in structure, and only need just can accurately the sample size of inductive current of the metal-oxide-semiconductor of several mirror images and resistance, and obtain sample rate current I by the current detecting pipe MP2 of mirror image and the breadth length ratio of current detecting pipe MP3 _SenWith the ratio of inductive current, there is not the influence of temperature characterisitic, and low in energy consumption, can effectively improve the efficient of Switching Power Supply, have the accuracy of detection height, good temp characteristic is easy to integrated advantage.

Description of drawings

Fig. 1 is the circuit structure diagram of cited current mode DC/DC step-down controller in the utility model embodiment.

Fig. 2 (a) is the partial circuit diagram that resistance in series detection method described in the utility model background technology detects inductive current.

Fig. 2 (b) is the partial circuit diagram that the method for detection power tube voltage drop described in the utility model background technology detects inductive current.

Fig. 2 (c) is the partial circuit diagram that equal proportion electric current testing described in the utility model background technology detects inductive current.

Fig. 3 is the circuit diagram that inductive current described in the utility model detects.

Embodiment

Current detection circuit can be used for multiple field, in the circuit that especially needs circuit is protected.The utility model is an example with the DC/DC step-down controller of current mode, in conjunction with the accompanying drawings embodiment of the present utility model is described in detail, but should limit protection domain of the present utility model with this.

Fig. 1 is the DC/DC step-down controller circuit structural drawing at inductive current detection circuit described in the utility model place, and this circuit structure comprises inductance L, error amplifier EA, current detection circuit, comparer comp, RS latch, power tube MP1 to be measured, continued flow tube MN1, resistance R _f, capacitor C _oWith feedback resistance R1 and R2.Wherein, input voltage V _InThrough the power tube MP1 and the continued flow tube MN1 ground connection of series connection, two feedback resistance R1 and R2 series connection back and capacitor C _oParallel connection, described parallel branch are connected with inductance L and are connected on continued flow tube MN1 drain-source end.Wherein, the voltage at two of series connection feedback resistance R1 and R2 two ends is the output voltage V of described DC/DC step-down controller _o

The input termination reference voltage source V of described error amplifier EA _Ref, another input end is connected between two feedback resistance R1 and the R2, the positive input terminal of the output termination comparer comp of this error amplifier EA, and the negative input end of this comparer comp is connected on the output terminal and the resistance R of current detection circuit _fBetween.

The output terminal of described comparer comp inserts the R end of rest-set flip-flop, the S end input clock signal clock of this rest-set flip-flop, and the inverse output terminal of described rest-set flip-flop connects the grid of power tube MP1 and continued flow tube MN1, and the grid of promptly described two pipes links to each other.

In the described DC/DC step-down controller circuit, supply voltage V _InGive capacitor C by power tube MP1 through inductance L _oCharging obtains output voltage V _o, obtain and inductive current I by current detection circuit _LProportional detection electric current I _SenThrough resistance R _fVoltage that obtains and error voltage V _EaRelatively the back produces control signal V _Reset, this control signal V _ResetThe shutoff of power controlling pipe behind rest-set flip-flop, thus capacitor C passed through _oDischarge and recharge control output voltage V _oSize.Therefore, in the described circuit, if current detection circuit can be exactly with inductive current I _LSample sample rate current I _Sen, then power controlling pipe MP1 rapidly obtains more stable output voltage V _o

Fig. 3 is the circuit diagram of the utility model embodiment, and described circuit comprises inductance L and capacitor C ₀, the PMOS that the current detecting pipe MP2 that two switching tube MS1 and MS2, the NMOS pipe M1, the M2 that are connected by three mirror images and M3, two mirror images are connected and MP3 and two mirror images are connected manages mirror image circuit, the reference current source I that M4 and M5 form ₁, sample rate current pipe MR, power tube MP1, and continued flow tube MN1.

Wherein, current detection circuit place DC/DC step-down controller partial inductance L and capacitor C _oSeries connection, power tube MP1 and continued flow tube MN1 series connection, current detecting pipe MP2, PMOS pipe M4, NMOS pipe M3 connects successively in the described three arrangement of mirrors image tubes, and current detecting pipe MP3, PMOS pipe M5, NMOS pipe M2 connects reference current source I successively ₁Connecting with NMOS pipe M1 provides the electric current of described mirror image pipe; Switching tube MS1 and power tube MP1 series connection and after grid are connected altogether, be connected in parallel with switching tube MS2 and grid voltage opposite, sample rate current I _SenFrom the drain electrode output of sample rate current pipe MR, the source electrode of described sample rate current pipe MR is connected the drain electrode of current detecting pipe MP2, and grid links to each other with the drain electrode of PMOS pipe M5.

In addition, described circuit also comprises a building-out capacitor C _C, this building-out capacitor C _CThe source electrode and the PMOS that are connected in current detecting pipe MP3 manage between the drain electrode of M5.

In the described circuit shown in Figure 3, the testing process of inductive current is divided into following two kinds of situations:

Work as V _Q=0 o'clock, thus inductive current obtained by the electric current of detection power pipe MP1.Below the concrete implementation method of described testing circuit is made labor.

Because V _QFor low, then power tube MP1 and the equal conducting of switching tube MS1, continued flow tube MN1 and switching tube MS2 all end, because current detecting pipe MP2 is connected with current detecting pipe MP3 mirror image, PMOS pipe M4 is connected with the M5 mirror image simultaneously, and NMOS pipe M1, M2 are connected with M3 also mirror image, and current detecting pipe MP2, PMOS pipe M4, NMOS pipe M3 connects successively, also series connection successively of current detecting pipe MP3, PMOS pipe M5, NMOS pipe M2, reference current source I ₁Connect with NMOS pipe M1, by the characteristic of mirror image circuit as can be known, reference current source I ₁Current mirror on NMOS pipe M2 and NMOS pipe M3, the electric current that then flows through two PMOS pipe M4 and M5 also equates, because the technological parameter of two NMOS pipe M2 and M3, two PMOS pipe M4 and M5 is all identical respectively, and it is also identical respectively to get its breadth length ratio in the present embodiment, then the source voltage V of PMOS pipe M4 _ASource voltage V with PMOS pipe M5 _BEquate.

Because reference current source I in the utility model ₁Choose little electric current, then compare the electric current I of power tube MP1 less than 50 microamperes _P1Can ignore, therefore can realize detecting described inductive current I by the voltage on the detection power pipe MP1 _L

In addition, because two PMOS pipe MS1 and MS2 are switching tube, set the breadth length ratio of described two switching tube MS1 and MS2 in the utility model greater than 50, then its channel resistance is very little, can ignore the drain-source voltage of switching tube MS1, thereby the drain-source voltage that obtains current detecting pipe MP2 equals the drain-source voltage sum of current detecting pipe MP3 and power tube MP1.

Because current detecting pipe MP2, current detecting pipe MP3, power tube MP1 are operated in linear zone, the resistance of promptly described three pipes is used R respectively _{On_MP1}, R _{On_MP2}, R _{On_MP3}Expression then can obtain formula (3) by Ohm law.

I _p2R _{on_MP2}＝I _p1R _{on_MP1}+I ₁R _{on_MP3} (3)

Wherein, I _P2, I _P1, I ₁Be branch current as shown in Figure 3.Also can obtain the relational expression shown in the formula (4) by top analysis:

I _p2＝I _sen+I ₁ (4)

I wherein _SenBe sample rate current as shown in the figure.With the current relation formula that can obtain in formula (4) the substitution formula (3) as shown in Equation (5):

$I_{\mathrm{sen}}=\frac{R_{\mathrm{on}\_\mathrm{MP}1}}{R_{\mathrm{on}\_\mathrm{MP}2}}{\mathrm{<figure-callout\; id="1"\; label="I\; p"\; filenames="Y20082009209800112.png"\; state="\{\{state\}\}">I</figure-callout>}}_p+(\frac{R_{\mathrm{on}\_\mathrm{MP}3}}{R_{\mathrm{on}\_\mathrm{MP}2}}-1)I_1---\left(5\right)$

Because two current detecting pipe MP2 and MP3 are the metal-oxide-semiconductor of mirror image, and breadth length ratio is identical, equivalent resistance approximately equal when the amplification region then, as shown in Equation (6):

R _{on_MP2}≈R _{on_MP3} (6)

So obtain formula (7):

$I_{\mathrm{sen}}\&ap;\frac{R_{\mathrm{on}\_\mathrm{MP}1}}{R_{\mathrm{on}\_\mathrm{MP}2}}{I}_{p1}---\left(7\right)$

Can use formula (8) expression because be operated in the electric current of the power tube MP1 of degree of depth linear zone again:

$I_D=\frac{1}{2}\mathrm{\&mu;}{C}_{\mathrm{OX}}\frac{W}{L}[2(V_{\mathrm{GS}}-V_T)V_{\mathrm{DS}}-{V_{\mathrm{DS}}}^2]---\left(8\right)$

Wherein μ is the mobility of channel electrons, C _OXBe unit area gate capacitance, V _TBe the threshold voltage of power tube, W, L are respectively the width and the length of raceway groove, V _GSBe the gate source voltage of power tube MP1, V _TBe its threshold voltage.

Because power tube MP1 is operated in linear zone, its drain-source voltage is very little, V _DS＜＜V _GS-V _T, ignore V _DS ²Influence, then formula (8) can be similar to and obtain formula (9).

$I_D=\mathrm{\&mu;}{C}_{\mathrm{OX}}\frac{W}{L}(V_{\mathrm{GS}}-V_T)V_{\mathrm{DS}}---\left(9\right)$

So can obtain the equivalent resistance of described power tube MP1 by Ohm law, shown in formula in the background technology (1), bring formula (7) into and can obtain as shown in Equation (10) proportionate relationship formula, set its ratio and represent with K.

$K=\frac{I_{p1}}{I_{\mathrm{sen}}}=\frac{{\left(\frac{W}{L}\right)}_{\mathrm{MP}1}}{{\left(\frac{W}{L}\right)}_{\mathrm{MP}2}}---\left(10\right)$

Can be obtained by formula (10), the breadth length ratio by design power pipe MP1 and current detecting pipe MP2 just can obtain inductive current I _LWith sample rate current I _SenRatio K, therefore, adopt sample rate current I _SenCome proportional equivalent inductance electric current I _L, the shutoff of power controlling pipe MP1 can be fed back the size of output voltage at high speed, obtains the output voltage of efficient stable.

The another kind of working condition of described testing circuit is for working as V _Q=1 o'clock, at this moment, power tube MP1 and switching tube MS1 ended, switching tube MS2 and continued flow tube MN1 conducting.This moment, discharging and recharging by rest-set flip-flop of electric capacity triggered sample rate current I _SenWith inductive current I _LIrrelevant, promptly do not need to detect inductive current, satisfy following relational expression:

I _P2≈I ₁

Then: I _Sen≈ 0

As can be known from the above analysis, testing circuit described in the utility model can be accurately apace with inductive current I _LThe proportional sample rate current I that affacts _SenThereby, control the break-make of two switching tube MS1 and MS2, just realized the break-make of the indirect gauge tap pipe of inductive current, make the whole power-supply system stable voltage of output fast.

Above content be in conjunction with concrete preferred implementation to further describing that the utility model is done, can not assert that concrete enforcement of the present utility model is confined to these explanations.For the utility model person of an ordinary skill in the technical field, under the prerequisite that does not break away from the utility model design, can also make some simple deduction or replace, all should be considered as belonging to protection domain of the present utility model.

Claims (8)

1, a kind of inductive current detection circuit that is used for Switching Power Supply, this circuit comprises the power tube MP1 in the switch power supply system, continued flow tube MN1, inductance L and capacitor C ₀, wherein, power tube MP1 and continued flow tube MN1 series connection, inductance L and capacitor C ₀Series connection is characterized in that this circuit also comprises two switching tube MS1 and MS2, reference current source I ₁Sample rate current pipe MR, and NMOS pipe M1, the M2 and the M3 that connect by three mirror images, two current detecting pipe MP2 and MP3 that mirror image connects, and the mirror image circuit formed of the PMOS pipe M4 that connects by two mirror images and M5, wherein, current detecting pipe MP2, PMOS pipe M4, NMOS manage M3 and connect successively in the described three arrangement of mirrors image tubes, current detecting pipe MP3, PMOS pipe M5, NMOS pipe M2 connects reference current source I successively ₁Connecting with NMOS pipe M1 provides the electric current of described mirror image pipe; Switching tube MS1 and power tube MP1 series connection and after grid are connected altogether, be connected in parallel with switching tube MS2 and grid voltage opposite, sample rate current I _SenFrom the drain electrode output of sample rate current pipe MR, the source electrode of described sample rate current pipe MR is connected the drain electrode of current detecting pipe MP2, and grid links to each other with the drain electrode of PMOS pipe M5.

2, a kind of inductive current detection circuit that is used for Switching Power Supply according to claim 1 is characterized in that, described circuit also comprises a building-out capacitor C _C, this building-out capacitor C _CThe source electrode and the PMOS that are connected in current detecting pipe MP3 manage between the drain electrode of M5.

3, a kind of inductive current detection circuit that is used for Switching Power Supply according to claim 1 and 2 is characterized in that, the technological parameter that three NMOS that described mirror image connects manage M1, M2 and M3 is identical, and breadth length ratio is identical.

4, a kind of inductive current detection circuit that is used for Switching Power Supply according to claim 3 is characterized in that, the technological parameter that two PMOS that described mirror image connects manage M4 and M5 is identical, and breadth length ratio is identical.

5, a kind of inductive current detection circuit that is used for Switching Power Supply according to claim 4 is characterized in that, two current detecting pipe MP2 that described mirror image connects are identical with the technological parameter of MP3, and breadth length ratio is identical.

6, a kind of according to claim 1 or 5 inductive current detection circuit that is used for Switching Power Supply is characterized in that, described two PMOS pipe MS1 and MS2 are breadth length ratio greater than 50 switching tube.

7, a kind of according to claim 1 or 5 inductive current detection circuit that is used for Switching Power Supply is characterized in that, described reference current source I ₁Output is less than 50 microamperes electric current.

8, a kind of inductive current detection circuit that is used for Switching Power Supply according to claim 6 is characterized in that, described reference current source I ₁Output is less than 50 microamperes electric current.

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