CN100547410C - Power tube current detection circuit - Google Patents

Abstract

The invention relates to a power tube current detection circuit, which includes: a power tube to be tested, a power tube that matches the power tube to be tested and has a certain width-to-length ratio, and the power tube current detection circuit also includes a power tube A current mirror circuit, the current mirror circuit includes several detection power tubes, and detects the current of the power tube to be tested by the current flowing through the detection power tubes. The technical scheme of the invention has simple structure, high detection current accuracy, fast current limiting response speed, and low power consumption and manufacturing cost.

Description

Power tube current detection circuit

[technical field]

The present invention relates to a kind of testing circuit, particularly a kind of power tube current detection circuit.

[background technology]

DC-DC (DC-to-dc) Switching Power Supply, LDO (linear voltage decreasing regulator), Charger power management chips such as (chargers), begin to power up just, in output terminal short circuit or the loop feedback during required power tube current, often need more accurate ground detection power tube current to handle these situations.If at chip power such as DC-DC, LDO or when the output short circuit occurring, do not have timely switch-off power pipe or take other current-limiting modes, chip may burn in a short period of time.

Relatively the scheme of several detection electric currents commonly used has following several at present:

1. adopt the precision resistance scheme

See also Fig. 1, this technical scheme uses a precision resistance to connect with power tube, comes the electric current of detection power pipe by the voltage of measuring the precision resistance two ends.Its principle of work is as follows, and resistance R sense is a precision resistance that resistance is very little, for example 0.1 or 0.2 Ω.Flow through resistance R sense during to power tube Q1 when electric current, and the pressure drop at the Rsense two ends is:

V _Rsense＝I _Rsense*Rsense (1)

Because the empty fugitive of amplifier answered, its input terminal voltage keeps equating (get R1 in the circuit and equal R2), thereby the voltage at R2 two ends equals V _RsenseThereby the electric current of the R2 that can obtain flowing through is directly proportional with Isense, can obtain the voltage Vsense that is directly proportional with Isense equally, and its size is:

$\mathrm{Vsense}=\frac{R3*\mathrm{Rsevse}*\mathrm{Isense}}{R2}---\left(2\right)$

The Vsense that obtains from above analysis has realized the detection to power tube voltage, can be by current limliting being done in the processing of Vsense or being used for the feedback control loop of current DC-DC.A very big shortcoming of this method is to need external resistance, has increased the cost of design, and in addition, resistance is in the current loop all the time, and the utilization ratio of power supply is reduced.

2. adopt power tube self internal resistance scheme

See also Fig. 2, the advantage of this circuit is not need the precision resistance that uses in the option A, directly uses the resistance of power tube self to detect its electric current.The principle of circuit is similar to scheme 1, supposes that power tube resistance is R _Q1, resistance R 1 equals R2, and then we can obtain:

$\mathrm{Vsense}=\frac{R3*R_{Q1}*\mathrm{Isense}}{R2}---\left(3\right)$

But because the internal resistance of power tube Q1 is to be determined by formula (4):

$R_{Q1}=\frac{1}{{\mathrm{\μ}}_n{C}_{\mathrm{ox}}\frac{L}{W}(V_{\mathrm{GS}}-V_{\mathrm{TH}})}---\left(4\right)$

Its resistance changes with supply voltage or its gate source voltage, thereby is not very accurate by the detected electric current of this scheme.

3. adopt tubule scheme with the power tube coupling

See also Fig. 3, this circuit adopts the tubule MP2 that mates with power tube MP1 to detect electric current.Get in the circuit:

$\frac{\mathrm{<figure-callout\; id="2"\; label="W\; L\; MP"\; filenames="C20061006314800081.png"\; state="\{\{state\}\}">W</figure-callout>}}{L_{\mathrm{MP}}}=\frac{\mathrm{<figure-callout\; id="2"\; label="W\; L\; MS"\; filenames="C20061006314800081.png"\; state="\{\{state\}\}">W</figure-callout>}}{L_{\mathrm{MS}}}=\frac{1}{N}\frac{W}{L_{\mathrm{MP}1}}---\left(5\right)$

As VQ when being low, switching tube MP1 and MS1 open, because the clamping action of amplifier, voltage VA equals VB, so can obtain:

${\mathrm{<figure-callout\; id="2"\; label="I\; MP"\; filenames="C20061006314800081.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{MP}}=I_{\mathrm{<figure-callout\; id="2"\; label="MS"\; filenames="C20061006314800081.png"\; state="\{\{state\}\}">MS</figure-callout>}2}=\frac{1}{N}{I}_{\mathrm{MP}1}---\left(6\right)$

I _sen＝I _MP2 (7)

V _add＝I _sen*R (8)

By above analysis, can obtain the voltage V that is directly proportional with power tube MP1 electric current _Add, thereby it can be used for current limliting or be used for current feedback loop.The ratio of precision scheme 1 of this electric circuit inspection electric current is hanged down a bit, but can save an off chip resistor, and its shortcoming is that the structure of amplifier shows complicated slightly, and power consumption is bigger.

Therefore, be necessary to provide a kind of simple structure that has, and can accurately detect the power tube current detection circuit of electric current.

[summary of the invention]

Technical matters to be solved by this invention is to provide a kind of testing circuit, particularly a kind of power tube current detection circuit.

For solving the problems of the technologies described above, the technical solution adopted in the present invention is: a kind of power tube current detection circuit, it comprises: a power tube to be measured, one with should be to be measured power tube mate, and with its breadth length ratio be the power tube of certain value, this power tube current detection circuit also comprises a current mirroring circuit, and this current mirroring circuit comprises four detection power pipes, and it is right that described four detection power pipes are formed two groups of detection power pipes; Detect the electric current of described power tube to be measured by the voltage of the detection power pipe of flowing through.

Technical scheme of the present invention is simple in structure, detect the current precision height, and the current limliting response speed is fast, and power consumption and manufacturing cost are lower.

[description of drawings]

Fig. 1 is the circuit diagram of existing detection power tube current scheme 1.

Fig. 2 is the circuit diagram of existing detection power tube current scheme 2.

Fig. 3 is the circuit diagram of existing detection power tube current scheme 3.

Fig. 4 is the circuit diagram of power tube current pick-up unit of the present invention.

[embodiment]

The invention will be further described below in conjunction with accompanying drawing.

Along with the development of semiconductor technology, the required operating voltage of integrated circuit becomes more and more lower, thereby the use of DC-DC (DC-to-dc) Switching Power Supply and LDO (linear voltage decreasing regulator) more and more widely.All adopted power tube in these power supply changeover devices, technical scheme of the present invention can the very accurate electric current that obtains the CMOS power tube, is used for entire circuit is carried out current limliting or is used for current mode PWM (pulse-length modulation) DC-DC loop.

See also Fig. 4, be the new solution of the present invention.The current mirror that adopts detection power pipe M1, M2, M3, M4 to form has replaced the amplifier in the scheme 3, and other structures are basic identical.In the present embodiment, above-mentioned detection power pipe is a metal-oxide-semiconductor.Power tube M wherein _YWith power tube M _xBreadth length ratio is N, and M1, M2 equate respectively with the breadth length ratio of M3, M4, when BUFOUT when low, M1, M2, M3, M4 current mirror are started working, the electric current of the M1 that then flows through, M2, M3, M4, Mc is i _Bias, that is:

$i_1=i_2=i_{\mathrm{bias}}=i_{M_c}---\left(9\right)$

According to formula:

$I=\frac{1}{2}{\mathrm{\&mu;}}_n{C}_{\mathrm{ox}}\frac{L}{W}{(V_{\mathrm{GS}}-V_{\mathrm{TH}})}^2---\left(10\right)$

V _GSM1＝V _GSM2 (11)

Can obtain:

V _x＝V _y (12)

$I_{M_y}=N*I_{M_x}---\left(13\right)$

$I_{M_x}=i_o+i_2=i_o+i_{M_c}=i_s---\left(14\right)$

$V_s=i_s*R_s=\frac{1}{N}{I}_{M_Y}---\left(15\right)$

By above derivation, can obtain the voltage that is directly proportional with power tube current, thereby can realize current limliting or use it in the loop feedback; Promptly detect the electric current of power tube to be measured by the voltage of the detection power pipe of flowing through.

Technical scheme of the present invention is simple in structure, detects the current precision height, has simultaneously the current limliting response speed Hurry up, low in energy consumption, the characteristics of low cost of manufacture.

Claims (3)

1, a kind of power tube current detection circuit, it comprises:

One power tube to be measured;

One with the power tube of described power tube to be measured coupling, the breadth length ratio of itself and described power tube to be measured is a certain value;

It is characterized in that described power tube current detection circuit also comprises a current mirroring circuit, described current mirroring circuit comprises four detection power pipes, and it is right that described four detection power pipes are formed two groups of detection power pipes; Detect the electric current of described power tube to be measured by the voltage of the described detection power pipe of flowing through.

2, power tube current detection circuit as claimed in claim 1 is characterized in that, it is right that described detection power pipe is formed the equal respectively detection power pipe of two groups of breadth length ratios.

3, as any described power tube current detection circuit of claim 1 to 2, it is characterized in that described detection power pipe is a metal-oxide-semiconductor.

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