CN102768300A - Current detecting circuit - Google Patents

Abstract

The invention provides a current detecting circuit which comprises a grid driving circuit, a first NMOS (N-channel metal oxide semiconductor) tube, a second NMOS tube, a first resistor, a second resistor, a comparator, a constant current source and an adjusting device. The adjusting device is used for adjustment according to different working areas of the NMOS tubes so that overcurrent threshold values of a chip are equal when the output NMOS tubes are positioned in the different working areas. The current detecting circuit solves the problem that working areas of output MOS (metal oxide semiconductor) tubes of a current detecting circuit of a chip in the prior art are not considered, and the overcurrent threshold values of the chips are consistent when the output MOS tubes work in saturation areas and linear areas.

Description

Current detection circuit

Technical field

The present invention relates to electronic circuit field, in particular to a kind of current detection circuit.

Background technology

In electronic circuit,, often need the working current of chip be detected for fear of chip is damaged.

The conventional current testing circuit is as shown in Figure 1, and in Fig. 1, NMOS manages M _NpBe the output device in the chip, for output load provides curtage, NMOS manages M _NpAnd M _NsGate voltage provide by gate driver circuit.In the circuit working process, M _NsM is flow through in detection _NpElectric current because M _NpAnd M _NsV _GsVoltage is equal, so

Wherein W is the metal-oxide-semiconductor width, and L is a metal-oxide-semiconductor length.Detect electric current I _SBe the output device electric current I of flowing through _PL/n.In order to guarantee the efficient of chip, common n＞＞1.When the chip operate as normal, I _SElectric current is very little, makes B point voltage V _BGreater than A point voltage V _A, wherein, V _ABe fixed voltage, equal V _A=V _In-I _Set* R _Set, comparing A and B two point voltages through comparer, the output CL of comparer is a low level, CL is in normal operating conditions for low expression chip.When chip is exported shorted to earth or is connect than heavy load, I _SIncrease, make V _BLess than V _A, the output CL of comparer is a high level, CL is that high level representes that chip is in over-current state.

Yet this testing circuit is not considered NMOS pipe M _NpThe zone of work:

Suppose M _NpConducting resistance be R _On, M _NpAnd M _NsW/L than for n=1000.

Work as M _Np(V when being operated in the saturation region _OutFrom V _InFar away) because M _NpAnd M _NsConducting resistance much larger than R _Sense, therefore, R _SenseCan ignore M _NpAnd M _NsForm current-mirror structure, so detect electric current

CL is by the low M that flows through when uprising _NpElectric current

Work as M _Np(V when being operated in linear zone _OutNear V _In), because M _NpAnd M _NsConducting resistance smaller can and R _SenseCompare, so detect electric current

CL is by the low M that flows through when uprising _NpElectric current $I_{P2}=\frac{({1000R}_{\mathrm{On}}+R_{\mathrm{Sense}})}{R_{\mathrm{On}}}*\frac{I_{\mathrm{Set}}*R_{\mathrm{Set}}}{R_{\mathrm{Sense}}}.$

If R _On≈ 100mohms, R _Sense≈ 50ohms, so

M _NpDetection electric current when being operated in linear zone can be littler by 50% than the detection electric current that is operated in the saturation region, M _NpBe operated in linear zone, the I of CL during by low uprising _PCan be greater than 50% of saturation region.Pass through I like fruit chip _SetAnd R _SetThe overcurrent threshold value of setting the saturation region is 3A, M so _NpOvercurrent threshold value when being operated in linear zone will become 4.5A, and the electric current of 4.5A will cause fatal influence to chip itself or load.

Do not consider the problem of the perform region of output mos pipe not propose effective solution at present as yet to the current detection circuit of correlation technique chips.

Summary of the invention

The invention provides a kind of current detection circuit, do not consider the problem of the perform region of output mos pipe with the current detection circuit that solves chip.

A kind of current detection circuit comprises: gate driver circuit is used to export gate drive voltage; The one NMOS pipe, the grid of NMOS pipe is connected with gate driver circuit; The 2nd NMOS pipe, the grid of the 2nd NMOS pipe is connected with the grid of NMOS pipe; First resistance, first end of first resistance is connected with the drain electrode of the 2nd NMOS pipe, and second end of first resistance is connected with supply voltage with the drain electrode of NMOS pipe respectively; Second resistance, first end of second resistance is connected with the drain electrode of NMOS pipe; Comparer, the first input end of comparer is connected with the drain electrode of the 2nd NMOS pipe, and second input end of comparer is connected with second end of second resistance; Constant current source, first end of constant current source is connected with second input end of comparer, second input end grounding of constant current source; And adjustment device; First end of adjustment device is connected with the grid of NMOS pipe; Second end of adjustment device is connected with second resistance, and the 3rd end of adjustment device is connected with supply voltage with the drain electrode of said NMOS pipe, be used for according to a NMOS manage that residing different operating zone is adjusted so that a NMOS manage be in different operating when regional the overcurrent threshold value of chip equal; Wherein, zones of different comprises saturation region and linear zone.

Further, the adjustment device comprises: the 3rd NMOS pipe, and the grid of the 3rd NMOS pipe is connected with the grid of NMOS pipe with the 2nd NMOS pipe, and the drain electrode of the 3rd NMOS pipe is connected with supply voltage, and the source electrode of the 3rd NMOS pipe is connected with second end of second resistance.

Further, the conducting resistance of the 3rd NMOS pipe be the 2nd NMOS pipe conducting resistance m doubly, the resistance of second resistance be first resistance resistance m doubly; The conducting resistance of the one NMOS pipe is the l/n of the conducting resistance of the 2nd NMOS pipe; Wherein, m is a natural number, and n is the W/L of NMOS pipe and the ratio of the W/L of the 2nd NMOS pipe; W represents the wide of NMOS pipe, and L represents the length of NMOS pipe.

Further, the first input end of comparer is a negative pole, and second input end of comparer is anodal.

Further, the first input end of comparer is anodal, and second input end of comparer is a negative pole.

Further, this circuit also comprises: control device, be connected with the output terminal of comparer, and be used for other circuit execution corresponding action according to the output level control chip of comparator output terminal.

Further, this circuit also comprises: load circuit is connected with the source electrode of NMOS pipe.

Through the present invention, on the basis of traditional current detection circuit, increase the adjustment device; Detect the duty of output mos pipe through the adjustment device; When the output mos plumber did at linear zone, the adjustment device was operated in linear zone, when the output mos pipe is operated in the saturation region; The adjustment device turn-offs; Adjust so that a NMOS is in the overcurrent threshold value of different operating when zone chip according to the residing different operating of output mos pipe zone and to equate that the current detection circuit that has solved the correlation technique chips is not considered the problem of the perform region of output mos pipe, has realized that the overcurrent threshold value of the chip that the output mos pipe detects when being operated in the saturation region with linear zone is consistent.

Description of drawings

Accompanying drawing described herein is used to provide further understanding of the present invention, constitutes the application's a part, and illustrative examples of the present invention and explanation thereof are used to explain the present invention, do not constitute improper qualification of the present invention.In the accompanying drawings:

Fig. 1 is a kind of circuit connection synoptic diagram according to the current detection circuit of correlation technique; And

Fig. 2 is a kind of preferred circuit connection synoptic diagram according to the current detection circuit of the embodiment of the invention.

Embodiment

Hereinafter will and combine embodiment to specify the present invention with reference to accompanying drawing.Need to prove that under the situation of not conflicting, embodiment and the characteristic among the embodiment among the application can make up each other.

This a kind of preferred circuit that preferred embodiment provides a kind of current detection circuit, Fig. 2 that this circuit is shown connects synoptic diagram, and this circuit comprises like lower component: gate driver circuit 202 is used to export gate drive voltage; The one NMOS manages M _Np, a NMOS manages M _NpGrid be connected with the output terminal of gate driver circuit 202; The 2nd NMOS manages M _Ns, the 2nd NMOS manages M _NsGrid and NMOS pipe M _NpGrid connect; First resistance R _Sense, first resistance R _SenseFirst end and the 2nd NMOS pipe M _NsDrain electrode connect first resistance R _SenseSecond end respectively with NMOS pipe M _NpDrain electrode and supply voltage V _InConnect; Second resistance R _Set, second resistance R _SetFirst end and NMOS pipe M _NpDrain electrode connect; Comparer 204, the first input end of comparer 204 and the 2nd NMOS pipe M _NsDrain electrode connect, second input end of comparer 204 is connected with second end of second resistance; Constant current source I _Set, constant current source I _SetFirst end be connected constant current source I with second input end of comparer 204 _SetSecond input end grounding; And the adjustment device, first end of adjustment device is connected with the grid of NMOS pipe, and second end of adjustment device is connected with second resistance, the drain electrode and the supply voltage V of the 3rd end of adjustment device and said NMOS pipe _InConnect, be used for according to the residing different operating of NMOS zone adjust so that a NMOS when being in the different operating zone overcurrent threshold value of chip equate, wherein; Zones of different comprises saturation region and linear zone; Preferably, in Fig. 2, the adjustment device is the 3rd NMOS pipe M _Nt, the 3rd NMOS manages M _NtGrid and NMOS pipe M _NpWith the 2nd NMOS pipe M _NsGrid connect, the 3rd NMOS manages M _NtDrain electrode and supply voltage V _InConnect, the 3rd NMOS manages M _NtThe source electrode and second resistance R _SetSecond end connect.Need to prove, here the 3rd NMOS pipe M here _NtAdjust the preferred embodiment a kind of of device as just invention, the present invention is not constituted qualification improperly.

The present invention also provides a kind of above-mentioned NMOS pipe M _Np, the 2nd NMOS manages M _NsWith the 3rd NMOS pipe M _NtThe relation of conducting resistance, and first resistance R _SenseWith second resistance R _SetRelation, specifically, the conducting resistance of the 3rd NMOS pipe be the 2nd NMOS pipe conducting resistance m doubly; The resistance of second resistance be first resistance resistance m doubly, the conducting resistance of NMOS pipe is the l/n of the conducting resistance of the 2nd NMOS pipe, wherein; M is a natural number; N is the W/L of NMOS pipe and the ratio of the W/L of the 2nd NMOS pipe, and W represents the wide of NMOS pipe, and L represents the length of NMOS pipe.Specify below in conjunction with example:

If a NMOS manages M _Np, the 2nd NMOS manages M _NsWith the 3rd NMOS pipe M _NtConducting resistance be respectively

R _OnAnd mR _On, first resistance R _Sense=R, second resistance R _Set=mR, m are natural number.

As NMOS pipe M _Np(V when being operated in linear zone _InAnd V _OutMore approaching), M _NtV _GsGreater than V _Th, M _NtFollow M _NpAlso be operated in linear zone, the voltage that A is ordered is by I _Set, R _SetAnd M _NtCommon decision, when making CL by low uprising

Wherein, mR||mR _OnBe mR and mR _OnParallel connection.

Work as M _Np(V when being operated in the saturation region _InAnd V _OutDistant), M _NtV _GsLess than V _Th, M _NtTurn-off, the voltage that A is ordered is by I _SetAnd R _SetDecision, the I when making CL by low uprising _P=mn*I _Set

Pass through M like this _NtAdding just solved M _NpBe operated in saturation region and linear zone, the I of comparator output terminal CL during by low uprising _PInconsistent problem.

In an embodiment of the invention; The first input end of comparer is a negative pole; Second input end of comparer is anodal (like the connected mode among Fig. 2), and comparator output terminal CL output low level characterized chip operation and was in normal condition this moment; Comparator output terminal CL exports high level, characterizes chip and is in over-current state; In an embodiment of the invention, the first input end of comparer is anodal, and second input end of comparer is a negative pole; This moment comparator output terminal CL output low level; Characterize chip operation and be in over-current state, comparator output terminal CL exports high level, characterizes chip and is in normal condition.

Of the present invention one preferred embodiment in, also foregoing circuit is optimized, specifically; Increase control device, this control device is connected with the output terminal CL of comparer, is used for other circuit execution corresponding action according to the output level control chip of comparator output terminal; For example; When chip is in over-current state, the output mos pipe is closed, to reach the effect of protection chip.In addition, the source electrode of NMOS pipe of the present invention also is used to connect load circuit, for load circuit provides voltage or electric current.

From above description; Can find out that the embodiment of the invention increases the adjustment device on the basis of traditional current detection circuit; Detect the duty of output mos pipe through the adjustment device; When the output mos plumber did at linear zone, the adjustment device was operated in linear zone, when the output mos pipe is operated in the saturation region; The adjustment device turn-offs; Adjust so that a NMOS is in the overcurrent threshold value of different operating when zone chip according to the residing different operating of output mos pipe zone and to equate that the current detection circuit that has solved the correlation technique chips is not considered the problem of the perform region of output mos pipe, has realized that the overcurrent threshold value of the chip that the output mos pipe detects when being operated in the saturation region with linear zone is consistent.

The above is merely the preferred embodiments of the present invention, is not limited to the present invention, and for a person skilled in the art, the present invention can have various changes and variation.All within spirit of the present invention and principle, any modification of being done, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (7)

1. a current detection circuit is characterized in that, comprising:

Gate driver circuit is used to export gate drive voltage;

The one NMOS pipe, the grid of said NMOS pipe is connected with said gate driver circuit;

The 2nd NMOS pipe, the grid of said the 2nd NMOS pipe is connected with the grid of said NMOS pipe;

First resistance, first end of said first resistance is connected with the drain electrode of said the 2nd NMOS pipe, and second end of said first resistance is connected with supply voltage with the drain electrode of said NMOS pipe respectively;

Second resistance, first end of said second resistance is connected with the drain electrode of said NMOS pipe;

Comparer, the first input end of said comparer is connected with the drain electrode of said the 2nd NMOS pipe, and second input end of said comparer is connected with second end of said second resistance;

Constant current source, first end of said constant current source is connected with second input end of said comparer, second input end grounding of said constant current source; And

The adjustment device; First end of said adjustment device is connected with the grid of said NMOS pipe; Second end of said adjustment device is connected with said second resistance, and the 3rd end of said adjustment device is connected with said supply voltage with the drain electrode of said NMOS pipe, be used for according to a said NMOS manage that residing different operating zone is adjusted so that said NMOS pipe when being in the different operating zone overcurrent threshold value of chip equal; Wherein, said zones of different comprises saturation region and linear zone.

2. circuit according to claim 1 is characterized in that, said adjustment device comprises:

The 3rd NMOS pipe; The grid of said the 3rd NMOS pipe is connected with the grid of said NMOS pipe and said the 2nd NMOS pipe; The drain electrode of said the 3rd NMOS pipe is connected with said supply voltage, and the source class of said the 3rd NMOS pipe is connected with second end of said second resistance.

3. circuit according to claim 1 is characterized in that, the conducting resistance of said the 3rd NMOS pipe be said the 2nd NMOS pipe conducting resistance m doubly; The resistance of said second resistance be said first resistance resistance m doubly, the conducting resistance of said NMOS pipe is the l/n of the conducting resistance of said the 2nd NMOS pipe, wherein; M is a natural number; N is the W/L of said NMOS pipe and the ratio of the W/L of said the 2nd NMOS pipe, and W represents the wide of NMOS pipe, and L represents the length of NMOS pipe.

4. circuit according to claim 1 is characterized in that, the first input end of said comparer is a negative pole, and second input end of said comparer is anodal.

5. circuit according to claim 1 is characterized in that, the first input end of said comparer is anodal, and second input end of said comparer is a negative pole.

6. circuit according to claim 1 is characterized in that, also comprises:

Control device is connected with the output terminal of said comparer, is used for other circuit execution corresponding action according to the output level control chip of comparator output terminal.

7. circuit according to claim 1 is characterized in that, also comprises:

Load circuit is connected with the source electrode of said NMOS pipe.

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