[introduction] the main good point that low side detects is to be able to use relatively simple configuration to magnify billabong resistor the voltage of two end. For example, the cost that the blame of current operation amplifier turns over suitable buy to be able to become need to be able to compete in consumptive market space is sensitive model the utility preference that electric machinery control applies.

In low side electric current Chanduan amplifier is used in detecting

The main good point that low side detects is to be able to use relatively simple configuration to magnify billabong resistor the voltage of two end. For example, the cost that the blame of current operation amplifier turns over suitable buy to be able to become need to be able to compete in consumptive market space is sensitive model the utility preference that electric machinery control applies.

If the graph is shown 1 times,the circuit that is based on inphase configuration pursues.

Graph 1.

However, solution of this kind of low cost may get the influence of a variety of different mistakes. For accurate measure electric current, we need to consider any likelihoods to affect circuit accessible node (for example amplifier is inputted) be not ideal effect. We will be in below in more detail discusses this issue.

Minim resistor

A serious mistake is the parasitism resistor of the PCB trace that establishs ties with R Shunt. Because R Shunt is in,fine long hair has very little value inside Europe limits, because any parasitism resistance of this and R Shunt series connection are possible,bring about showing an error. Build a model to this parasitism resistor through R stray, we get 2 medium principles pursue pursueing.

Graph 2.

Basis application, I load can be as high as hundreds. Accordingly, even if lesser R Stray value also can produce quite big error voltage V Error. This error voltage will be magnified by the gain of amplifier and appear in output to carry.

Because the temperature coefficient of cupreous resistor is quite tall (make an appointment with 0.4%/ ° C) , the value of R can produce stray, because this error voltage is met,change along with temperature very big. Accordingly, stray resistor can be in bear the error related the generation in the system that bigger temperature changes and temperature. To reduce error voltage V Error, we should avoid a line to grow too, reduce R stray with limit ground.

Be worth what carry is, the more effective solution that eliminates R stray error is use different amplifier and not be inphase configuration. From the graph 2 in can see, inphase configuration has Chan Duan to input. It detects node A point is opposite the voltage at the ground. However, the amplifier that need branch has the input that need branch and feel measure R Shunt the voltage of two end. This is shown 3 times like the graph.

Graph 3.

The transfer function of the amplifier that need branch gives out by next type:

[} of spreader of V_{out}=frac{R_{2}}{R_{1}}left(v_{A}-v_{B} Ight)=frac{R_{2}}{R_{1} }V_{]

Because the difference of amplifier divides an input to detect,divide galvanic block the voltage of two end, PCB walks along the resistor of the line to won’t produce an error. We will study in the in more detail in the following article the amplifier that need branch is configured.

Block solder sex

Another error source is with detect the soldering tin resistor that resistor establishs ties. This is in graph 4 in undertook demonstrative.

Graph 4.

In pursueing here, direction of arrowhead of red of load current edge from left flow right. Perpendicular trace receives billabong resistor amplifier to input end repeatedly (In+ and In- ) . Accordingly, meeting feeling measures amplifier the voltage between A dot and B dot is poor. Feeling the real value that measures resistor is R Shunt +2R Solder. Solder resistor can be inside the limits of hundreds of microhm.

The error becomes showing, when should using small billabong resistor especially. For example, shed resistor and I load = 20 A to the cent of 0.5 M Ω , solder the error of resistor may be as high as 22% . To solve this problem, amplifier input should receive billabong resistor repeatedly directly and not be to carry shed trace. Graph 5 indicated position of a give typical examples, can provide more accurate result.

Graph 5.

Below this kind of circumstance, have solder of two pairs of PCB dish: Arrive to be being used at joining R Shunt laden, another pair is used at joining R Shunt amplifier is inputted. In application of big electric current, the electric current of amplifier derive (I Amp) is far be less than I Load. This is why the account that afore-mentioned layout can reduce block solder error.

To understand this technology better, let us compare what two kinds of circumstances fall to detect voltage. The position that use graph shows 4 times, the voltage that detects is:

[V_{A}-v_{B}=left(R_{shunt}+2R_{solder1} Ight) Imes Left(I_{load}+I_{amp} Ight) ]

Because I Amp is smaller than I Load much, we have:

[} of to load of V_{A}-v_{B}approxleft(R_{shunt}+2R_{solder1} Ight) Imes I_{load}=R_{shunt}I_{load}+2R_{solder1}I_{]

Equality 1.

This gave out the error voltage of 2R Solder1 I Load. Graph 5 medium layout how? The circuit graph of this kind of layout is shown as follows:

Graph 6.

Ask an attention, voltaic I Load does not return its source through R Solder2. Measures voltage is:

[V_{C}-v_{D}=R_{shunt} Imesleft(I_{load}+I_{amp} Ight)+2R_{solder2}I_{amp}approx R_{shunt}I_{Load}+R_{solder2}I_{amp} ]

Below this kind of circumstance, the error is 2R Solder2 I Amp, it is far be less than formula the error of 1, because I Amp is far,be less than I Load. This kind of technology is called normally Er Wen Chuangan, get use in a lot of application domains. It makes we can accurate measure impedance. Graph 7 indicated a few other PCB position that use Er Wen Chuangan technology.

Graph 7. Picture (adapt) offer by TI.

You can be in of Analog Devices ” the solder that sheds resistor through improving low cost to divide dish layout will optimize tall electric current to detect precision ” in find more complex article opening Er join layout give typical examples.

May you want to know a picture 5 with the graph 7 in in 3 kinds of depicted position which kind of can you bring about more accurate measurement? What should notice is, answer this question very hard, the resistor that because the result depends on,you use in the design. Different resistor manufacturer is in of resistor nominal different measurement may be used when the value the position.

For example, if resistor manufacturer measured solder dish internal resistance, so the layout in graph 7(a) can be offerred for us more accurate measure an outcome.

Noisy ground

Graph 8 showed another error cause: Noise ground connection.

Graph 8.

We had discussed, because be the same as suitable buy to have Chan Duan to input, it measures node A photograph the voltage to the ground. Suppose our circuit board have an appropriative ground level. We can be in special the place that stands by R spreader places to cross aperture, ground potential is received in the system with holding B place, and the error that limit ground reduces PCB to take line resistance. Another sensitive node is node C. Any coupling can be magnified to the signal of node C and appear in output to carry. Accordingly, we also need to hold node C potential.

However, hypothesis ground has noise and a few electric current had shed ground connection layer, if pursue,8 are shown. This will bring about node voltage exists between B and C, and we hope they have same potential below good case.

Hypothesis node B holds potential, the voltage difference that sorts with terrestrial electricity will appear in node C and in output end introduces an error. To avoid this mistake, the proposal uses ambassadorial dot B and C each other layout of special close PCB.

Put them together

Pursue the position of 9 give typical examples that showed one considered afore-mentioned notes. Layout of this give typical examples is based on the operation amplifier that uses SOT 23 to enclose.

Graph 9.

Ask an attention, join of article opening Er is used at detecting billabong resistor the voltage of two end. Ask an attention additionally, the ground connection side of R 1 and R spreader each other special stand by. Remember please, join of article opening Er has a few kinds of different solder dish layout. You may need to seek advice from resistor manufacturer or undertake a few experiments suit the overall arrangement that you devise in order to decide.

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