CN104076181A - Current detection circuit - Google Patents

Abstract

The embodiment of the invention discloses a current detection circuit, which comprises: the circuit comprises a sampling resistor, an amplifying circuit and a common-mode voltage clamping circuit, wherein the sampling resistor is connected in series on a current loop to be detected; the amplifying circuit is used for amplifying the voltage difference between the two ends of the sampling resistor, the first input end of the amplifying circuit is connected with the first end of the sampling resistor, the second input end of the amplifying circuit is connected with the second end of the sampling resistor, and the output end of the amplifying circuit outputs the amplified voltage difference; the first input end of the common mode voltage clamping circuit is connected to the first input end of the amplifying circuit, the second input end of the common mode voltage clamping circuit is connected to the grounding end of the amplifying circuit, and the common mode voltage clamping circuit is used for clamping the voltage between the first input end and the second input end of the common mode voltage clamping circuit within the common mode threshold range. The invention can detect the high-end current in a large common-mode voltage range.

Description

A current detection circuit

technical field

The invention relates to the field of electronic circuits, in particular to a current detection circuit.

Background technique

Current detection is the basis of various protection circuits and control circuits. High-precision current detection can ensure reliable operation of protection circuits and precise control of control circuits. At present, the common current detection method is to connect a small resistance high-precision sampling resistor in series in the current loop to be detected, and amplify the voltage difference across the sampling resistor through a differential integrated operational amplifier or a special current detection chip. output, and then divide the amplified voltage difference by the product of the amplification factor and the resistance value of the sampling resistor to obtain the magnitude of the current to be detected. In order to ensure that all current faults from the load to the ground can be detected and reduce the interference of the ground, it is generally necessary to set the sampling resistor between the output of the power supply and the load, which is called high side current sense. However, because the high-end current detection is close to the output end of the power supply, the common-mode voltage at the two ends of the sampling resistor is high. This high-side current-sensing technique cannot be used without current sensing at analog voltages.

Contents of the invention

The embodiment of the present invention provides a current detection circuit capable of detecting high-end current within a large common-mode voltage range.

The current detection circuit provided by the present invention includes a sampling resistor, an amplification circuit and a common-mode voltage clamping circuit, wherein,

The sampling resistor is connected in series on the current loop to be detected;

The amplifying circuit is used to amplify the voltage difference across the sampling resistor, the first input end of the amplifying circuit is connected to the first end of the sampling resistor, and the second input end of the amplifying circuit is connected to the sampling resistor At the second end, the output end of the amplifying circuit outputs the amplified voltage difference;

The first input terminal of the common-mode voltage clamping circuit is connected to the first input terminal of the amplification circuit, the second input terminal of the common-mode voltage clamping circuit is connected to the ground terminal of the amplification circuit, and the The common-mode voltage clamping circuit is used to clamp the voltage between the first input terminal and the second input terminal of the common-mode voltage clamping circuit within the common-mode threshold range.

Optionally, the common-mode voltage clamping circuit includes a Zener diode, a first resistor and a triode, wherein:

The cathode of the Zener diode is connected to the first input end of the common-mode voltage clamping circuit to the first input end of the amplification circuit, and the anode of the Zener diode is connected to the first input end of the first resistor. terminal, the second terminal of the first resistor is connected to the ground point, the base of the triode is connected to the first terminal of the first resistor, and the emitter of the triode is the first terminal of the common-mode voltage clamping circuit. The two input ends are connected to the ground end of the amplifying circuit, and the collector of the triode is used to be connected to the ground point.

Optionally, the amplifying circuit includes a high-side current detection chip and a second resistor, wherein the first input terminal and the second input terminal of the high-side current detection chip are respectively the first input terminal and the second input terminal of the amplifying circuit. The second input end, the first end of the second resistor is connected to the output end of the high-side current detection chip, the second end of the second resistor is used to connect to the ground point, and the second end of the second resistor The first end is the output end of the amplifying circuit.

The invention clamps the common-mode voltage at the input end of the amplifying circuit within a common-mode threshold range through the common-mode voltage clamping circuit, so that the current detection circuit can detect the high-end current within a large common-mode voltage range.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

FIG. 1 is a circuit diagram of a current detection circuit provided by an embodiment of the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

Please refer to FIG. 1. FIG. 1 is a circuit diagram of a current detection circuit provided by an embodiment of the present invention, including:

Sampling resistor R _sense 101, amplifier circuit 102 and common mode voltage clamping circuit 103, wherein,

The sampling resistor R _sense is connected in series on the current loop to be detected.

Specifically, in order to improve the accuracy of current detection, the sampling resistor R _sense is a precision resistor. In order to reduce the power loss caused by the sampling resistor R _sense to the circuit, the sampling resistor should choose a resistor with a small resistance, preferably 0.1Ω～1.5Ω , the sampling resistor R _sense is connected in series between the output terminal of the power supply and the load or other high-end sampling positions.

The amplifying circuit 102 is used to amplify the voltage difference between the two ends of the sampling resistor R _sense , the first input end of the amplifying circuit is connected to the first end of the sampling resistor R _sense , the second input end of the amplifying circuit is connected to the second end of the sampling resistor R _sense , and the amplifying The output end of the circuit outputs the amplified voltage difference.

Optionally, the amplifying circuit 102 may be a voltage amplifying circuit composed of an integrated operational amplifier and other electronic components, or a voltage amplifying circuit composed of a high-side current detection chip and a second resistor and other electronic components.

Optionally, the amplifying circuit includes a high-side current detection chip U and a second resistor R ₂ , wherein the first input terminal and the second input terminal of the high-side current detection chip U are respectively the first input terminal and the second input terminal of the amplifying circuit. Input end, the first end of the second resistor _R2 is connected to the output end of the high-side current detection chip, the second end of the second resistor _R2 is used to connect to the ground point, and the first end of the second resistor _R2 is an amplifier circuit 102 output.

The high-end current detection chip can be MAX9928, MAX4172 of MAXIM Company, TSC101, TSC102 of ST Company, etc. This embodiment uses MAX9928 as an example for illustration, but it does not mean that the high-end current detection chip in this embodiment is limited to MAX9928.

The first input terminal of the common mode voltage clamping circuit 103 is connected to the first input terminal of the amplifying circuit 102, and the second input terminal of the common mode voltage clamping circuit 103 is connected to the ground terminal of the amplifying circuit 102, and the common mode voltage clamping circuit 103 is used to clamp the voltage between the first input terminal and the second input terminal of the common-mode voltage clamping circuit within the common-mode threshold range.

Optionally, the common-mode voltage clamping circuit 103 includes a Zener diode D, a first resistor _R1 and a triode Q, wherein:

The negative pole of the Zener diode D is connected to the first input end of the common-mode voltage clamping circuit 103 to the first input end of the amplification circuit 102, and the positive pole of the Zener diode D is connected to the first end of the first resistor _R1 , the first The second end of the resistor _R1 is connected to the ground point, the base of the transistor Q is connected to the first end of the first resistor _R1 , and the emitter of the transistor Q is connected to the second input end of the common-mode voltage clamping circuit 103 to the amplifier circuit The ground terminal of 102, the collector of the transistor Q is used to connect to the ground point. Wherein, the transistor Q is a PNP transistor.

As shown in Figure 1, assuming that the sampling resistor R _sense is connected in series between the 120V DC power supply and the load, since the current of the power supply line, that is, the current value to be detected is very large, even reaching several amperes, in order to reduce the current on the sampling resistor R _sense For power consumption, the resistance value of the sampling resistor R _sense must be very small, and 0.1Ω is selected in this embodiment. According to the chip data of MAX9928, the maximum common-mode voltage that the RS+ and RS- pins can withstand is 36V. In this embodiment, the Zener diode D with a 24V voltage drop and the PNP transistor Q with a high amplification factor are used to clamp the RS+ pin and the GND pin of the MAX9928 within the common-mode threshold, where the common-mode threshold is 24V minus The base-emitter voltage drop of the triode Q is 0.7V, which is about 23.3V. Through the common-mode voltage dislocation circuit of this embodiment, although the power supply voltage reaches 120V, the common-mode voltage borne by the current detection chip U is clamped at 23.3V. V, less than the highest voltage that the current detection chip can withstand.

In this embodiment, the high magnification transistor Q ensures that the current on its emitter (ie, the GND pin of the current detection chip) will not be too large and damage the chip.

In this embodiment, the selection of the resistance value of the grounding resistor _R1 needs to match the working characteristics of the Zener diode D, and the current on D must be set within its optimum working current range to ensure the normal operation of D.

The current detection chip U amplifies the voltage difference between the two ends of the upper R _sense through the internal differential amplifier circuit, and then outputs a current proportional to the load current at the OUT pin:

I _out ＝ G _m R _sense I _load

Among them, I _out is the output current of the OUT pin of MAX9928, G _m is the internal gain of MAX9928, the fixed value is 5μA/mV, R _sense is 0.1Ω, and I _load is the load current.

The second resistor _R2 converts the current signal of the MAX9928OUT pin into a voltage signal, so there is,

V _out = G _m R _sense I _load R ₂

The value of the detected load current I _load can be calculated from the above formula. For example, if V _out is 4.4V, the load current I _load can be obtained to be 4A.

In this embodiment, the common-mode voltage at the input end of the amplifying circuit is clamped within a common-mode threshold range by the common-mode voltage clamping circuit, so that the current detection circuit can detect the high-end current within a large common-mode voltage range.

The above disclosures are only preferred embodiments of the present invention, and certainly cannot limit the scope of rights of the present invention. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope of the present invention.

Claims (6)

1. a current detection circuit, is characterized in that, comprises sampling resistor, amplifying circuit and common mode voltage clamping circuit, wherein,

Described sampling resistor is connected on the current return that will detect;

Described amplifying circuit is for amplifying the voltage difference at described sampling resistor two ends, the first input end of described amplifying circuit connects the first end of described sampling resistor, the second input end of described amplifying circuit connects the second end of described sampling resistor, the described voltage difference after the output terminal output of described amplifying circuit is amplified;

The first input end of described common mode voltage clamping circuit is connected to the first input end of described amplifying circuit, the second input end of described common mode voltage clamping circuit is connected to the earth terminal of described amplifying circuit, and described common mode voltage clamping circuit is used for the voltage clamping between described common mode voltage clamping circuit first input end and the second input end in common mode threshold range.

2. circuit according to claim 1, is characterized in that, described common mode voltage clamping circuit comprises voltage stabilizing diode, the first resistance and triode, wherein:

The negative pole of described voltage stabilizing diode is the first input end that the first input end of described common mode voltage clamping circuit is connected to described amplifying circuit, the positive pole of described voltage stabilizing diode is connected to the first end of described the first resistance, the second end of described the first resistance is connected to earth point, the base stage of described triode is connected to the first end of described the first resistance, the second input end of the very described common mode voltage clamping circuit of the transmitting of described triode is connected to the earth terminal of described amplifying circuit, and the collector of described triode is used for being connected to earth point.

3. circuit according to claim 1 and 2, it is characterized in that, described amplifying circuit comprises high-side current detection chip and the second resistance, wherein, the first input end of described high-side current detection chip and the second input end are respectively described first input end and described second input end of described amplifying circuit, the first end of described the second resistance is connected to the output terminal of described high-side current detection chip, the second end of described the second resistance is used for being connected to earth point, the described output terminal that the first end of described the second resistance is described amplifying circuit.

4. circuit according to claim 3, is characterized in that, described sampling resistor is precision resistance.

5. circuit according to claim 4, is characterized in that, the Standard resistance range of described sampling resistor is 0.1 ohm～1.5 ohm.

6. circuit according to claim 3, is characterized in that, described voltage stabilizing diode is that pressure drop is the voltage stabilizing diode of 24 volts.