CN210665853U - Sampling circuit for sensor to output 4-20mA current - Google Patents
Sampling circuit for sensor to output 4-20mA current Download PDFInfo
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- CN210665853U CN210665853U CN201921287552.XU CN201921287552U CN210665853U CN 210665853 U CN210665853 U CN 210665853U CN 201921287552 U CN201921287552 U CN 201921287552U CN 210665853 U CN210665853 U CN 210665853U
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Abstract
The utility model relates to the technical field of circuits, specifically disclose a sampling circuit for sensor output 4~20mA electric current, wherein, a sampling circuit for sensor output 4~20mA electric current includes: the battery charging device comprises a first diode, a second diode, a switch tube, a first resistor and a second resistor, wherein the anode of the first diode is connected with the output end of the sensor and used for inputting 4-20mA current, the cathode of the first diode is connected with the first end of the switch tube, the second end of the switch tube is connected with one end of the first resistor, the other end of the first resistor is connected with a signal ground, the driving end of the switch tube is connected with one end of the second resistor, the other end of the second resistor is connected with the voltage end of the battery, the driving end of the switch tube is connected with the cathode of the second diode, the anode of the second diode is connected with the signal ground, and the second end of the switch tube is a voltage. The utility model provides a sampling resistor that is used for sampling circuit of 4~20mA electric currents of sensor output to adopt is small with low costs, can satisfy customer's demand.
Description
Technical Field
The utility model relates to the technical field of circuits, especially, relate to a sampling circuit for sensor output 4~20mA electric current.
Background
As shown in FIG. 1, a current-type sampling circuit for a sensor outputs 4-20mA according to application requirements, outputs 1-5V after passing through the sampling circuit, and determines that the resistance of a sampling resistor R1 is fixed to 250R and cannot be adjusted. The signal input needs to be able to withstand shorting to the battery without damage, as required by automotive industry standards. When the current input signal Iipput is short-circuited to the battery voltage (32V), R1 is caused to generate heat greatly (the power is larger than 4W), and then in consideration of design derating, R1 needs to adopt a high-power (more than 8W) precision resistor, so that the product is large in size and high in cost, and cannot meet the requirements of customers.
Disclosure of Invention
The utility model provides a sampling circuit for 4~20mA electric currents of sensor output solves the big problem with high costs of the sampling resistance volume that exists among the correlation technique.
As an aspect of the utility model, a sampling circuit for sensor output 4~20mA electric current is provided, wherein, a sampling circuit for sensor output 4~20mA electric current includes: a first diode, a second diode, a switch tube, a first resistor and a second resistor,
the anode of the first diode is connected with the output end of the sensor and used for inputting 4-20mA current, the cathode of the first diode is connected with the first end of the switch tube, the second end of the switch tube is connected with one end of the first resistor, the other end of the first resistor is connected with a signal ground, the driving end of the switch tube is connected with one end of the second resistor, the other end of the second resistor is connected with the voltage end of the storage battery, the driving end of the switch tube is connected with the cathode of the second diode, the anode of the second diode is connected with the signal ground, and the second end of the switch tube is a voltage output end.
Further, the switch tube includes an NMOS tube, a first end of the NMOS tube is a drain end, and a second end of the NMOS tube is a source end.
Further, the second diode includes a zener diode.
Further, the voltage range output by the voltage output end is 1V-5V.
By the sampling circuit for outputting the 4-20mA current by the sensor, for a normally input 4-20mA signal, the voltage on R1 is less than 5V, and the voltage Vgs of a control electrode loaded to a switch tube Q1 is greater than the opening voltage V of a switch tube Q1GS(Plateau)Therefore, the switching tube Q1 is turned on, the current of 4-20mA can be normally input to the sampling resistor R1, when the input signal Iipnput is short-circuited to the battery voltage, the current flowing through R1 is rapidly increased, the control signal of the switching tube is rapidly reduced, and the voltage V reaches the Miller platform voltage VGS(Plateau)At this time, the switching tube is switched from the on state to the off state, and finally stays in the middle transconductance region (linear amplification region), and at this time, the voltage on the sampling resistor R1 is VZ(D2)- VGS(Plateau)And the short-circuit voltage is about 1/4 of 32V between 7V and 8V, so that the heat generation of the whole protection circuit is reduced to 1/4 of the scheme shown in figure 1, and the heat generation of the sampling resistor is reduced to 1/16 of the scheme shown in figure 1 in a short-circuit state, so that the sampling circuit for outputting 4-20mA current by the sensor not only solves the heat generation problem when the battery is in a short circuit, but also has small volume and low cost by the sampling resistor, and can meet the requirements of customers.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
fig. 1 is a prior art current-mode sampling circuit diagram of a sensor output.
Fig. 2 is the utility model provides a circuit structure chart that is used for sensor output 4~20mA electric current's sampling circuit.
Detailed Description
It should be noted that the embodiments and features of the embodiments of the present invention may be combined with each other without conflict. The present invention will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
In order to make the technical solution of the present invention better understood, the technical solution of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative efforts shall belong to the protection scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged under appropriate circumstances for purposes of describing the embodiments of the invention herein. Furthermore, the terms "comprises," "comprising," and any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
In this embodiment, a sampling circuit for outputting 4 to 20mA current from a sensor is provided, fig. 2 is a circuit structure diagram of the sampling circuit for outputting 4 to 20mA current from a sensor, as shown in fig. 2, including: a first diode D1, a second diode D2, a switch tube Q1, a first resistor R1 and a second resistor R2,
an anode of the first diode D1 is connected to an output end of a sensor and is used for inputting 4-20mA current, a cathode of the first diode D1 is connected to a first end of the switch tube Q1, a second end of the switch tube Q1 is connected to one end of the first resistor R1, the other end of the first resistor R1 is connected to a signal ground GND, a driving end of the switch tube Q1 is connected to one end of the second resistor R2, the other end of the second resistor R2 is connected to a voltage end Vbat of a storage battery, a driving end of the switch tube Q1 is connected to a cathode of the second diode D2, an anode of the second diode D2 is connected to the signal ground GND, and a second end of the switch tube Q1 is a voltage output end Vout.
By the sampling circuit for outputting the 4-20mA current by the sensor, for a normally input 4-20mA signal, the voltage on R1 is less than 5V, and the voltage Vgs of a control electrode loaded to a switch tube Q1 is greater than the opening voltage V of a switch tube Q1GS(Plateau)Therefore, the switching tube Q1 is turned on, the current of 4-20mA can be normally input to the sampling resistor R1, when the input signal Iipnput is short-circuited to the battery voltage, the current flowing through R1 is rapidly increased, the control signal of the switching tube is rapidly reduced, and the voltage V reaches the Miller platform voltage VGS(Plateau)At this time, the switching tube is switched from the on state to the off state, and finally stays in the middle transconductance region (linear amplification region), and at this time, the voltage on the sampling resistor R1 is VZ(D2)- VGS(Plateau)And the short-circuit voltage is about 1/4 of 32V between 7V and 8V, so that the heat generation of the whole protection circuit is reduced to 1/4 of the scheme shown in figure 1, and the heat generation of the sampling resistor is reduced to 1/16 of the scheme shown in figure 1 in a short-circuit state, so that the sampling circuit for outputting 4-20mA current by the sensor not only solves the heat generation problem when the battery is short-circuited, but also has small volume and low cost by the sampling resistor, and can meet the requirements of customers.
Specifically, the switching tube Q1 includes an NMOS tube, where a first terminal of the NMOS tube is a drain terminal, and a second terminal of the NMOS tube is a source terminal.
Preferably, the second diode D2 includes a zener diode.
Specifically, the voltage range output by the voltage output end Vout is 1V-5V.
The working principle of the sampling circuit for outputting 4-20mA current by the sensor provided by the embodiment is described in detail with reference to FIG. 2.
As shown in FIG. 2, a current signal Iinput of 4 to 20mA is inputted to the anode of a first diode D1, and the cathode of D1 is connected to the drain of an N MOS transistor Q1. The source of Q1 is connected to one end of a sampling resistor R1, and the other end of R1 is connected to ground. The grid of Q1 is connected to one end of R2 and the cathode of zener diode D2, the other end of R2 is connected to battery voltage Vbat, and the anode of D2 is grounded.
The parameters of the sampling circuit for outputting the 4-20mA current by the sensor meet the following conditions:
VZ(D2)= VGS+ R1 * IPR(th)，
wherein, VZ(D2)Represents the rated regulated voltage, V, of the zener diode D2GSRepresenting the control voltage of the NMOS transistor, IPR(th)An overcurrent threshold (exceeding 20mA for a certain margin, for example 30 mA) indicating that protection is triggered;
for a normally input 4-20mA signal, the voltage on R1 is less than 5V, and the voltage Vgs of a control electrode loaded to an NMOS tube Q1 is greater than the turn-on voltage V of an NMOS tube Q1GS(Plateau)Therefore, the NMOS transistor Q1 is turned on, and the current of 4-20mA can be normally input to the sampling resistor R1.
When the input signal Iinput is shorted to the battery voltage, the current through R1 increases rapidly,
VGS↓= VZ(D2)- R1 * Iinput↑，
leading the control signal of the NMOS tube to be rapidly reduced to reach the voltage V of the Miller platformGS(Plateau)At this time, the NMOS switches from the on state to the off state, and finally stays in the middle transconductance region (linear amplification region), and at this time, the voltage across the sampling resistor R1 is VZ(D2)- VGS(Plateau)Approximately 7-8V, which is approximately 1/4 of the short-circuit voltage 32V, so that the heat generation of the whole protection circuit is reduced to 1/4 of the scheme in FIG. 1; meanwhile, in a short-circuit state, the heating of the sampling resistor is reduced to 1/16 of that of the scheme shown in FIG. 1, so that the sampling resistor R1 with smaller volume and lower cost can be adopted.
In addition, in the embodiment, the NMOS transistor participates in the feedback control, so that the feedback control can be more directAnd more continuous control signal voltage VGS。
It is to be understood that the above embodiments are merely exemplary embodiments that have been employed to illustrate the principles of the present invention, and that the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the spirit and substance of the invention, and these modifications and improvements are also considered to be within the scope of the invention.
Claims (4)
1. A sampling circuit for outputting 4-20mA current by a sensor is characterized by comprising: a first diode, a second diode, a switch tube, a first resistor and a second resistor,
the anode of the first diode is connected with the output end of the sensor and used for inputting 4-20mA current, the cathode of the first diode is connected with the first end of the switch tube, the second end of the switch tube is connected with one end of the first resistor, the other end of the first resistor is connected with a signal ground, the driving end of the switch tube is connected with one end of the second resistor, the other end of the second resistor is connected with the voltage end of the storage battery, the driving end of the switch tube is connected with the cathode of the second diode, the anode of the second diode is connected with the signal ground, and the second end of the switch tube is a voltage output end.
2. The sampling circuit for the sensor to output 4-20mA current according to claim 1, wherein the switch tube comprises an NMOS tube, a first end of the NMOS tube is a drain end, and a second end of the NMOS tube is a source end.
3. The sampling circuit for a sensor outputting 4-20mA current of claim 1, wherein the second diode comprises a zener diode.
4. The sampling circuit for the sensor to output the 4-20mA current according to any one of claims 1-3, wherein the voltage output end outputs the voltage in a range of 1V-5V.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201921287552.XU CN210665853U (en) | 2019-08-09 | 2019-08-09 | Sampling circuit for sensor to output 4-20mA current |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201921287552.XU CN210665853U (en) | 2019-08-09 | 2019-08-09 | Sampling circuit for sensor to output 4-20mA current |
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| Publication Number | Publication Date |
|---|---|
| CN210665853U true CN210665853U (en) | 2020-06-02 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201921287552.XU Active CN210665853U (en) | 2019-08-09 | 2019-08-09 | Sampling circuit for sensor to output 4-20mA current |
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| CN (1) | CN210665853U (en) |
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- 2019-08-09 CN CN201921287552.XU patent/CN210665853U/en active Active
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