CN101846702A - Inductive current detection circuit - Google Patents

Abstract

The invention discloses an inductive current detection circuit, which comprises an inductor, a detection coils and a differential amplifying circuit and is characterized in that the inductor is formed by a power coil and a magnetic core, wherein the detection coil and the power coil of the inductor have the same turn number and are closely coupled; the output of the detection coil is connected to the in-phase end of a differential operational amplifier in the differential amplifying circuit for amplifying in phase; meanwhile, inductive voltage is connected to the inverting end of the differential operational amplifier for inversely amplifying; the inductive voltage can be completely eliminated by adjusting in-phase and inverting amplifier parameters according to a coupling coefficient; and an amplifying signal with direct current equivalent resistance and voltage of the power coils of the inductor can be obtained at the output of the differential operational amplifier and the current of the overcurrent inductor can be accurately detected.

Description

A kind of inductive current detection circuit

Technical field

The present invention relates to electronic circuit field, particularly current detection circuit is a kind of inductive current detection circuit specifically.

Background technology

Switching Power Supply output filtering need use inductance, and the direct current equivalent resistance pressure drop by inductance detects inductive current, and functions such as the overcurrent protection of realization Switching Power Supply, short-circuit protection have advantages such as harmless, high-level efficiency, saving volume.

United States Patent (USP) 3,733,536 have provided the method (with reference to Fig. 1) of utilizing magnetic test coil to come the detection power inductive current: magnetic test coil 9 has the identical number of turn, magnetic coupling with filter inductance 1, has the relation of voltage offset.But in side circuit, because the relation of the coupling coefficient of coil, identical number of turn magnetic test coil and filter inductance voltage can not be offset fully.Therefore, the output signal that detects winding comprises also comprise the inductive drop of not offset fully except that being proportional to the current signal that flows through filter inductance.The inductive drop of being offset fully can be covered and be proportional to the current signal that flows through filter inductance, has limited the use of this testing circuit.

Summary of the invention

The problems referred to above that the prior art that the present invention will solve exists aim to provide a kind of inductive current detection circuit, can eliminate the inductive drop of not offset fully that causes owing to coupling coefficient, are flow through the current signal of inductance accurately.

For this reason, the present invention is by the following technical solutions: a kind of inductive current detection circuit, comprise an inductance, a magnetic test coil and a differential amplifier circuit, it is characterized in that described inductance is made of power coil and magnetic core, the power coil equal turn numbers and the close-coupled of described magnetic test coil and described inductance; The output of magnetic test coil is connected to the in-phase end of differential operational amplifier in the differential amplifier circuit, carries out homophase and amplify, simultaneously inductive drop is connected to the end of oppisite phase of differential operational amplifier, carry out anti-phase amplification; According to coupling coefficient, adjust homophase, inverting amplifier parameter, eliminate inductive drop, obtain the amplifying signal of the direct current equivalent resistance voltage of electric inductance power coil in the output of differential operational amplifier.

Principle of work is: the coupling coefficient that has between the power coil of the identical number of turn, closely-coupled magnetic test coil and inductance equals 1 in theory, but actual for less than but approach 1, magnetic test coil voltage can not be offset inductive drop fully, the output of magnetic test coil except the direct current equivalent resistance voltage of the power coil that comprises inductance, the inductive drop that is not cancelled in addition.The output of magnetic test coil is connected to the in-phase end of differential operational amplifier, carries out homophase and amplify; Simultaneously inductive drop is connected to the end of oppisite phase of differential operational amplifier, carries out anti-phase amplification.According to coupling coefficient, adjust homophase, inverting amplifier parameter, can eliminate inductive drop fully, obtain the amplifying signal of the direct current equivalent resistance voltage of electric inductance power coil in the output of differential operational amplifier, detect the electric current of overcurrent inductance exactly.

According to the present invention, a typical prioritization scheme is: described differential amplifier circuit comprises first resistance, second resistance, the 3rd resistance, the 4th resistance, the 5th resistance and integrated operational amplifier, the end of the same name of the power coil of described magnetic test coil and described inductance links to each other with an end of the 5th resistance, the different name end of described magnetic test coil is connected and is connected to the in-phase input end of integrated operational amplifier and an end of the 3rd resistance behind first resistance, the other end of the 3rd resistance is connected to reference to ground, the different name end of described power coil is connected and is connected to the inverting input of integrated operational amplifier behind second resistance, one end of the other end of the 5th resistance and the 4th resistance, the other end of the 4th resistance is connected to the output of integrated operational amplifier.

Description of drawings

The present invention is further described below in conjunction with drawings and Examples.

Fig. 1 is the prior art synoptic diagram.

Fig. 2 is the synoptic diagram of a kind of inductive current detection circuit first embodiment of the present invention.

Fig. 3 is the schematic equivalent circuit of Fig. 2.

Fig. 4 is the synoptic diagram of a kind of inductive current detection circuit second embodiment of the present invention.

Fig. 5 is the synoptic diagram of a kind of inductive current detection circuit the 3rd embodiment of the present invention.

Embodiment

With reference to Fig. 2,100 parts comprise 10, one magnetic test coils 02 of an inductance, and inductance 10 is by power coil 01, and magnetic core 03 is formed.Described power coil 01 is wound on the same magnetic core 03 with described magnetic test coil 02, number of turn equal turn numbers, close-coupled, coupling coefficient k equals 1 in theory, actual less than but approach 1; Described power coil 01 has common node A with described magnetic test coil 02, and this node is an end of the same name simultaneously, and described power coil 01 has different name end node B, node C respectively with described magnetic test coil 02.200 parts are differential amplifier circuit, comprise first resistance R 1, second resistance R 2, the 3rd resistance R 3, the 4th resistance R 4, the 5th resistance R 5 and an integrated operational amplifier IC1.The different name end node C of magnetic test coil 02 is connected to the in-phase input end of integrated operational amplifier IC1 by first resistance R 1, this in-phase input end also is connected to reference to ground by the 3rd resistance R 3, the different name end node B of described power coil 01 is connected to the inverting input of integrated operational amplifier IC1 by second resistance R 2, end node A of the same name is connected to the inverting input of integrated operational amplifier IC1 by the 5th resistance R 5, the 4th resistance R 4 one terminates at the anti-phase input of integrated operational amplifier IC1, and the other end is connected to the output of integrated operational amplifier IC1.

The principle of work of Fig. 2 will illustrate by its equivalent electrical circuit Fig. 3.

With reference to Fig. 3, power coil 01 equivalence is that an inductance L 01 is connected with resistance R 01, this resistance in series is the direct current equivalent resistance of this power coil 01, magnetic test coil 02 also equivalence is an inductance L 02 R02 that connects with resistance, this resistance in series is the direct current equivalent resistance of this magnetic test coil 01, magnetic test coil 01 with etc. the coupling coefficient of number of turn power coil 02 be k, k equals 1 in theory, actual less than but approach 1.

When electric current I in flowed through port A, port B by power coil 01, the pressure drop on the direct current equivalent resistance of power coil 01 was:

V _Ro1＝R ₀₁·Iin (1)

Voltage can equivalence be the inductive drop V of power coil 01 between port A, the B _L01And direct current equivalent resistance voltage drop V _R01Sum:

V _AB＝V _L01+V _R01 (2)

Therefore the great integrated operational amplifier of input impedance because detection winding dc has connected in the loop flows through the electric current that detects winding 02 and can ignore its direct current equivalent resistance pressure drop V _R02Can ignore, the voltage between port A and the port C is the voltage of coming from the equivalent inductance L01 coupling of power winding 01 by the equivalent inductance L02 that detects winding 02 so:

V _AC＝V _L02＝k·V _L01 (3)

The voltage that can be got between port C and the port B by formula (2) and formula (3) is:

V _CB＝V _AB-V _AC＝V _L01+V _R01-k·V _L01＝(1-k)·V _L01+V _R01 (4)

Differential amplifier circuit is to V _CBHomophase amplifies, to V _ABAnti-phase amplification, output voltage is:

$V_{\mathrm{CS}}=V_{\mathrm{CB}}\&CenterDot;\frac{R4}{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HSA00000112795500011.png"\; state="\{\{state\}\}">R</figure-callout>}2//R5}-V_{\mathrm{AB}}\&CenterDot;\frac{R4}{\mathrm{<figure-callout\; id="5"\; label="R"\; filenames="HSA00000112795500011.png"\; state="\{\{state\}\}">R</figure-callout>}5}$

$=[(1-k)\&CenterDot;{\mathrm{<figure-callout\; id="01"\; label="V\; L"\; filenames="HSA00000112795500012.png,HSA00000112795500013.png"\; state="\{\{state\}\}">V</figure-callout>}}_L+V_{R01}]\&CenterDot;\frac{R4}{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HSA00000112795500011.png"\; state="\{\{state\}\}">R</figure-callout>}2//R5}-[{\mathrm{<figure-callout\; id="01"\; label="V\; L"\; filenames="HSA00000112795500012.png,HSA00000112795500013.png"\; state="\{\{state\}\}">V</figure-callout>}}_L+V_{R01}]\&CenterDot;\frac{R4}{R5}---\left(4\right)$

$=[(1-k)\&CenterDot;\frac{R4}{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HSA00000112795500011.png"\; state="\{\{state\}\}">R</figure-callout>}2//R5}-\frac{R4}{R5}]\&CenterDot;{\mathrm{<figure-callout\; id="01"\; label="V\; L"\; filenames="HSA00000112795500012.png,HSA00000112795500013.png"\; state="\{\{state\}\}">V</figure-callout>}}_L+(\frac{R4}{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HSA00000112795500011.png"\; state="\{\{state\}\}">R</figure-callout>}2//R5}-\frac{R4}{R5})\&CenterDot;{\mathrm{<figure-callout\; id="01"\; label="V\; R"\; filenames="HSA00000112795500012.png,HSA00000112795500013.png"\; state="\{\{state\}\}">V</figure-callout>}}_R$

According to coupling coefficient k, for selected resistance R 2, R4, R5, usually, R4, R5 be much larger than R2, so, select the resistance of suitable resistance R 5, can so that:

$(1-k)\&CenterDot;\frac{R4}{R2//R5}-\frac{R4}{R5}=0---\left(5\right)$

Then have:

$V_{\mathrm{CS}}=(\frac{R4}{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HSA00000112795500011.png"\; state="\{\{state\}\}">R</figure-callout>}2//R5}-\frac{R4}{R5})\&CenterDot;{\mathrm{<figure-callout\; id="01"\; label="V\; R"\; filenames="HSA00000112795500012.png,HSA00000112795500013.png"\; state="\{\{state\}\}">V</figure-callout>}}_R$

$=(\frac{R4}{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HSA00000112795500011.png"\; state="\{\{state\}\}">R</figure-callout>}2//R5}-\frac{R4}{R5})\&CenterDot;{\mathrm{<figure-callout\; id="01"\; label="R"\; filenames="HSA00000112795500012.png,HSA00000112795500013.png"\; state="\{\{state\}\}">R</figure-callout>}}_{01}\&CenterDot;\mathrm{Iin}---\left(6\right)$

Therefore, detected the electric current that flows through inductance accurately.

Following parameters is a typical application example:

Power coil 01:1 circle, inductance value 0.18uH, direct current equivalent resistance 1m Ω;

Magnetic test coil 02:1 circle, inductance value 0.18uH, direct current equivalent resistance 1 Ω;

The coupling coefficient k=0.99 of power coil 01 and magnetic test coil 02;

The parameter of differential amplifier circuit 200 is: R1=R2=1k Ω, R3=R4=R5=100k Ω.

With reference to Fig. 4, another embodiment of the invention, be to omit the 1st resistance R 1 and the 3rd resistance R 3 with Fig. 2,3 embodiment differences, the different name end of described magnetic test coil (02) is connected directly to the in-phase input end of integrated operational amplifier (IC1), and all the other structures and Fig. 2,3 embodiments are identical.

With reference to Fig. 5, another embodiment of the present invention is to omit the 3rd resistance R 3 with Fig. 2,3 embodiment differences, and all the other structures and Fig. 2,3 embodiments are identical.

More than describe the present invention by exemplary embodiments, but the present invention is not limited thereto, and is all in change and the replacement done without prejudice to spirit of the present invention and content, should be regarded as belonging to protection scope of the present invention.

Claims (4)

1. inductive current detection circuit, comprise an inductance (10), a magnetic test coil (02) and a differential amplifier circuit (200), it is characterized in that described inductance (10) is made of power coil (01) equal turn numbers and the close-coupled of described magnetic test coil (02) and described inductance power coil (01) and magnetic core (03); The output of magnetic test coil (02) is connected to the in-phase end of differential operational amplifier (IC1) in the differential amplifier circuit (200), carries out homophase and amplify, simultaneously inductive drop is connected to the end of oppisite phase of differential operational amplifier, carry out anti-phase amplification; According to coupling coefficient, adjust homophase, inverting amplifier parameter, eliminate inductive drop, obtain the amplifying signal of the direct current equivalent resistance voltage of electric inductance power coil in the output of differential operational amplifier.

2. inductive current detection circuit as claimed in claim 1, it is characterized in that described differential amplifier circuit (200) comprises first resistance (R1), second resistance (R2), the 3rd resistance (R3), the 4th resistance (R4), the 5th resistance (R5) and integrated operational amplifier (IC1), the end of the same name of the power coil (01) of described magnetic test coil (02) and described inductance links to each other with an end of the 5th resistance (R5), the different name end of described magnetic test coil (02) is connected and is connected to the in-phase input end of integrated operational amplifier (IC1) and an end of the 3rd resistance (R3) behind first resistance (R1), the other end of the 3rd resistance (R3) is connected to reference to ground, the different name end of described power coil (01) is connected and is connected to the inverting input of integrated operational amplifier (IC1) behind second resistance (R2), one end of the other end of the 5th resistance (R5) and the 4th resistance (R4), the other end of the 4th resistance (R4) is connected to the output of integrated operational amplifier (IC1).

3. inductive current detection circuit as claimed in claim 1, it is characterized in that described differential amplifier circuit (200) comprises second resistance (R2), the 4th resistance (R4), the 5th resistance (R5) and integrated operational amplifier (IC1), the end of the same name of the power coil (01) of described magnetic test coil (02) and described inductance links to each other with an end of the 5th resistance (R5), the different name end of described magnetic test coil (02) is connected to the in-phase input end of integrated operational amplifier (IC1), the different name end of described power coil (01) is connected and is connected to the inverting input of integrated operational amplifier (IC1) behind second resistance (R2), one end of the other end of the 5th resistance (R5) and the 4th resistance (R4), the other end of the 4th resistance (R4) is connected to the output of integrated operational amplifier (IC1).

4. inductive current detection circuit as claimed in claim 1, it is characterized in that described differential amplifier circuit (200) comprises first resistance (R1), second resistance (R2), the 4th resistance (R4), the 5th resistance (R5) and integrated operational amplifier (IC1), the end of the same name of the power coil (01) of described magnetic test coil (02) and described inductance links to each other with an end of the 5th resistance (R5), the different name end of described magnetic test coil (02) is connected and is connected to the in-phase input end of integrated operational amplifier (IC1) behind first resistance (R1), the different name end of described power coil (01) is connected and is connected to the inverting input of integrated operational amplifier (IC1) behind second resistance (R2), one end of the other end of the 5th resistance (R5) and the 4th resistance (R4), the other end of the 4th resistance (R4) is connected to the output of integrated operational amplifier (IC1).

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