A direct voltage measuring circuit

Abstract

The application discloses a direct-current voltage measurement circuit, and belongs to the technical field of measurement of electrical variables, which comprises: a voltage sampling circuit, which is used for sampling a direct-current voltage to be measured and outputs a sampling voltage; a first protection unit, which is connected with the voltage sampling circuit; a voltage protection ring, which is arranged outside the voltage sampling circuit; a voltage buffer, which is used for transmitting the sampling voltage to the voltage protection ring; and a processor, which receives and processes the sampling voltage through a switching circuit. The circuit transmits the sampling voltage to the voltage protection ring through the voltage buffer by arranging the voltage protection ring, so that the voltage protection ring is subjected to a voltage value with the same amplitude as the sampling voltage, a protection ring with the same voltage is formed outside the voltage sampling circuit, and the problem that the sampling voltage is lost due to the leakage of the voltage sampling circuit caused by the stray capacitance of the circuit board can be avoided.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of measuring electrical variables, and particularly relates to a direct-current voltage measurement circuit. BACKGROUND

[0002] In high-precision direct-current voltage measurement, if leakage and leakage temperature drift of the protection device on the sampling circuit occur, the accuracy and stability of the measurement result will be seriously affected. If the protection device on the sampling circuit is removed, the accuracy of the direct-current voltage measurement result will not be affected within a certain range, but when there is an over-range voltage input, the measurement device will face the risk of damage due to the lack of protection devices. SUMMARY

[0003] The present application proposes a direct-current voltage measurement circuit to solve the above problems.

[0004] To solve the above technical problems, the present application adopts the following technical solutions:

[0005] A direct-current voltage measurement circuit comprises:

[0006] a voltage sampling circuit for sampling a direct-current voltage to be measured and outputting a sampling voltage;

[0007] a first protection unit connected with the voltage sampling circuit, for clamping the voltage at both ends when the sampling voltage exceeds a threshold range;

[0008] a voltage protection ring arranged outside the voltage sampling circuit;

[0009] a voltage buffer for transmitting the sampling voltage to the voltage protection ring;

[0010] a processor for receiving and processing the sampling voltage through a switching circuit to obtain the amplitude of the direct-current voltage to be measured.

[0011] In some embodiments, the switching circuit is a multiplexer, which comprises a control end, an output end and a plurality of input ends, the third input end of the multiplexer is connected with the sampling circuit for receiving the sampling voltage;

[0012] the processor is connected with the output end of the multiplexer through a conditioning circuit;

[0013] the processor outputs a selection signal to the multiplexer through the control end of the multiplexer.

[0014] In some embodiments, the multiplexer further comprises a fourth input adjacent to the third input, and one of the outputs of the voltage buffer is connected to the fourth input.

[0015] In some embodiments, the DC voltage measurement circuit further comprises a second protection unit, an input of the second protection unit is connected to an input of the voltage buffer, an output of the second protection unit is connected to an output of the voltage buffer, and a ground of the second protection unit is connected to a ground.

[0016] The DC voltage measurement circuit further comprises:

[0017] a clamping unit, one end of the clamping unit is connected to the fourth input, and the other end of the clamping unit is connected to the ground;

[0018] When the sampling voltage is out of the threshold range, the processor controls the fourth input of the multiplexer to be selected by the output thereof.

[0019] In some embodiments, the DC voltage measurement circuit further comprises:

[0020] a second voltage source, the voltage outputted by the second voltage source is lower than the clamping voltage of the clamping unit, and higher than the maximum value of the sampling voltage allowed to be received;

[0021] a comparator, one input of the comparator is connected to the second voltage source, the other input of the comparator is connected to the output of the voltage buffer, and the output of the comparator is connected to the processor.

[0022] In some embodiments, the voltage sampling circuit comprises a voltage sampling unit and a sampling switch connected in series.

[0023] The DC voltage measurement circuit further comprises:

[0024] an isolation voltage source, a positive pole of the isolation voltage source is connected to a control end of the sampling switch, and the isolation voltage source is used to provide an opening voltage;

[0025] a discharge resistor, the discharge resistor is connected between an output of the voltage sampling unit and a switch circuit;

[0026] a protection switch, a control end of the protection switch is connected to the voltage sampling circuit, an input of the protection switch is connected to the positive pole of the isolation voltage source, and an output of the protection switch is connected to a negative pole of the isolation voltage source through the discharge resistor;

[0027] the first protection unit is connected at two ends thereof in the voltage sampling circuit, and one of the two ends of the second protection unit is connected close to an upstream of transmission of the sampling voltage, and the other end is connected close to a downstream of transmission of the sampling voltage.

[0028] In some embodiments, the discharge resistor has two, namely a first discharge resistor and a second discharge resistor;

[0029] The protection switch has two, namely a first protection switch and a second protection switch;

[0030] The first discharge resistor and the second discharge resistor are connected in sequence in the voltage sampling circuit, and the negative electrode of the isolated voltage source is connected between the first discharge resistor and the second discharge resistor;

[0031] The control end of the first protection switch is connected in the voltage sampling circuit, and the connection point is close to the transmission upstream of the sampling voltage, the input end of the first protection switch is connected with the positive electrode of the isolated voltage source, and the output end of the first protection switch is connected with the negative electrode of the isolated voltage source through the second discharge resistor;

[0032] The control end of the second protection switch is connected in the voltage sampling circuit, and the connection point is close to the transmission downstream of the sampling voltage, the input end of the second protection switch is connected with the positive electrode of the isolated voltage source, and the output end of the second protection switch is connected with the negative electrode of the isolated voltage source through the first discharge resistor.

[0033] In some embodiments, the sampling switch has two, namely a first sampling switch and a second sampling switch;

[0034] The control ends of the first sampling switch and the second sampling switch are connected with the positive electrode of the isolated voltage source respectively, the first sampling switch is connected between the output end of the voltage sampling unit and the first discharge resistor, and the second sampling switch is connected between the switch circuit and the second discharge resistor.

[0035] In some embodiments, the direct current voltage measurement circuit further comprises a voltage calibration circuit, and the voltage calibration circuit comprises:

[0036] A precision voltage source for outputting a calibration voltage within a set threshold range of fluctuation;

[0037] A calibration voltage source, the output end of which is connected with the first input end of the multiplexer;

[0038] An isolation circuit, the precision voltage source transmits the calibration voltage to the calibration voltage source through the isolation circuit;

[0039] The processor is configured to calibrate the gain error when the first input end of the multiplexer is selected and its output end is gated.

[0040] In some embodiments, the isolation circuit comprises:

[0041] A capacitor;

[0042] a first switch, a common terminal of which is connected to the positive terminal of the capacitor, one of the moving terminals of the first switch is connected to the positive terminal of the precision voltage source, and the other moving terminal is connected to the positive terminal of the calibration voltage source;

[0043] a second switch, a common terminal of which is connected to the negative terminal of the capacitor, one of the moving terminals of the second switch is connected to the negative terminal of the precision voltage source, and the other moving terminal is connected to the ground terminal, and the negative terminal of the calibration voltage source is connected to the ground terminal;

[0044] an oscillator for controlling the gating state of the first switch and the second switch.

[0045] In some embodiments, the processor controls the second input terminal of the multiplexer to be gated with the output terminal thereof when calibrating the misadjustment error.

[0046] Compared with the prior art, the direct current voltage measurement circuit has the advantages and positive effects that when an over-range voltage is input, the first protection unit is turned on to clamp the voltage, thereby ensuring the safety of the rear-end measurement device.

[0047] The voltage protection ring is driven by the voltage buffer to transmit the sampling voltage to the voltage protection ring, so that the voltage protection ring is applied with a voltage value of the same amplitude as the sampling voltage, and since the voltage protection ring is arranged outside the voltage sampling circuit, i.e., a voltage protection ring of the same voltage is formed outside the voltage sampling circuit, the problem of loss of sampling voltage due to leakage of the voltage sampling circuit caused by the stray capacitance of the circuit board can be avoided.

[0048] The voltage protection ring is driven by the voltage buffer, so that the output voltage can follow the input voltage without amplitude change, and the voltage protection ring can also be driven without load.

[0049] Other features and advantages of the present application will become more apparent after reading the detailed description of the embodiments of the present application in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 is a principle block diagram of an embodiment of the direct current voltage measurement circuit proposed by the present application;

[0051] Figure 2 is a circuit principle diagram of an embodiment of the direct current voltage measurement circuit proposed by the present application. DETAILED DESCRIPTION

[0052] The specific embodiments of the present application will be further described in detail below in conjunction with the accompanying drawings.

[0053] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0054] The terms "first", "second" are only for descriptive purpose, and cannot be understood as indicating or implying relative importance. In the description of the present application, the meaning of "multiple" is two or more than two, unless otherwise explicitly and specifically limited.

[0055] Embodiment one, refer to Figure 1 As shown in the figure, the direct current voltage measurement circuit of the embodiment includes a voltage sampling circuit, a first protection unit, a voltage protection ring A, a voltage buffer and a processor.

[0056] The voltage sampling circuit is used for sampling the direct current voltage to be measured and outputting a sampling voltage Vin. The processor receives the sampling voltage Vin for processing and outputs a voltage detection result.

[0057] The first protection unit is connected with the voltage sampling circuit, and is used for clamping the second protection unit first when the sampling voltage exceeds a threshold range, and then a voltage difference appears between the two ends of the first protection unit, and the first protection unit is clamped. Thus, the latter circuit is protected.

[0058] In the steady state process of voltage measurement, there is no current in the voltage sampling circuit. Therefore, each device in the voltage sampling circuit does not produce a voltage drop. The voltage at both ends of the first protection unit is equal to the amplitude of the sampling voltage Vin, and the first protection unit does not act.

[0059] In some embodiments, the direct current voltage measurement circuit further includes a second protection unit, an input end of the second protection unit is connected with an input end of the voltage buffer, an output end of the second protection unit is connected with an output end of the voltage buffer, and a ground end o of the second protection unit is connected with a ground end GND1. The second protection unit is used for overvoltage protection of the input and output ends of the voltage buffer, and clamps the overvoltage.

[0060] The sampled voltage Vin is transmitted downstream along the voltage sampling circuit. Since the output sampled voltage Vin is not an ideal step signal when the voltage signal is transmitted in the voltage sampling circuit, but rather a signal that ramps from 0V to the maximum voltage amplitude, the transient transmission of the sampled voltage Vin upstream is a simultaneous rise from 0V along the ramp and downstream. When the sampled voltage Vin exceeds the maximum allowable range of the voltage measurement circuit relative to the GND1 network, or when a large surge signal is superimposed on the sampled voltage Vin, and the voltage amplitude across the second protection unit exceeds the threshold voltage of the second protection unit, the two ends of the second protection unit are connected to ground. Clamping occurs between the input voltage of the second protection unit and ground. At this time, the sampled voltage Vin exceeds the maximum allowable input value. Because the clamping voltage of the second protection unit is lower than the amplitude of the sampled voltage Vin, it protects the downstream circuitry.

[0061] In this embodiment, the sampling voltage Vin is transmitted from upstream to downstream according to the transmission direction.

[0062] A voltage protection ring A is arranged around the outside of the voltage sampling circuit.

[0063] In some embodiments, the voltage protection ring A may be formed by, but is not limited to, PCB wiring surrounding the voltage sampling circuit.

[0064] A voltage buffer is connected between the voltage sampling circuit and the voltage protection ring A to transmit the sampled voltage from the sampling circuit to the voltage protection ring A. This ensures that the voltage protection ring A has the same voltage amplitude as the sampled voltage. Since the voltage protection ring is positioned around the outside of the voltage sampling circuit, forming a protective ring with the same voltage, it avoids the problem of leakage current in the voltage sampling circuit and loss of sampled voltage due to capacitive effects caused by circuit board characteristics and wiring layout.

[0065] By driving the voltage protection ring A through a voltage buffer, it can be ensured that the output voltage can follow the input voltage without any change in amplitude, and at the same time, the voltage protection ring A can be driven without generating a load on the input voltage.

[0066] The processor receives the sampled voltage Vin sent by the voltage sampling circuit through the switching circuit, processes it, and calculates the amplitude of the DC voltage to be measured.

[0067] In some embodiments, such as Figure 2 As shown, the switching circuit is a multiplexer, which includes a control terminal P26, an output terminal P25, and multiple input terminals. The third input terminal P23 of the multiplexer is connected to the sampling circuit to receive the sampling voltage Vin.

[0068] The processor is connected with the output terminal P25 of the multiplexer through the conditioning circuit.

[0069] The processor outputs a gate signal to the multiplexer through the control terminal of the multiplexer, so as to control the connection between one of the input terminals of the multiplexer and the output terminal of the multiplexer.

[0070] When the third input terminal P23 is gated with the output terminal P25 of the multiplexer, the sampling voltage Vin is transmitted to the conditioning circuit through the two pins, and then transmitted to the processor for processing by the conditioning circuit.

[0071] The switch circuit can be implemented by the multiplexer. When the sampling voltage Vin exceeds the maximum allowable range, the processor can control the action of the multiplexer to disconnect the terminal outputting the sampling voltage, so that the high voltage cannot be transmitted to the processor and the front-end circuit of the processor through the switch circuit, thereby protecting the measurement device with the processor as the core.

[0072] In some embodiments, the multiplexer includes a fourth input terminal P24 adjacent to the third input terminal P23, and one of the output terminals of the voltage buffer is connected with the fourth input terminal. After the fourth input terminal is connected with the voltage protection ring, the voltage value of the fourth input terminal is equal to the voltage value of the third input terminal, so that the leakage between the adjacent metal pins of the multiplexer is suppressed.

[0073] By connecting the output terminal of the voltage buffer with the fourth input terminal P24, the voltage buffer can also transmit the sampling voltage to the fourth input terminal P24. Since the fourth input terminal P24 is adjacent to the third input terminal P23, the fourth input terminal P24 and the third input terminal P23 are at the same potential in normal testing, and the leakage between the pins is also suppressed, thereby avoiding the leakage of the sampling voltage input by the third input terminal P23 through the fourth input terminal P24.

[0074] When the sampling voltage Vin is normal, since the output terminal of the voltage buffer is connected with the voltage protection ring A, and the second protection unit is also connected with the voltage protection ring A, the leakage of the second protection unit will not affect the amplitude of the sampling voltage Vin input to the third input terminal P23.

[0075] In some embodiments, the direct current voltage measurement circuit further includes a clamping unit, one end of which is connected with the fourth input terminal P24, and the other end is connected with the ground terminal GND1.

[0076] The clamping unit has a threshold value, which is lower than the clamping voltage of the second protection unit. When the input voltage of the clamping unit exceeds the threshold value, the clamping unit clamps the input voltage to a smaller voltage amplitude.

[0077] If the sampling voltage Vin exceeds the maximum allowable range of the voltage measurement circuit relative to the GND1 network, or a large surge signal is superimposed on the sampling voltage Vin, when the voltage amplitude across the second protection unit exceeds the threshold voltage of the second protection unit, the input end m and the output end n of the second protection unit are connected to the ground end o, the ground end o is connected to the ground, and the clamping between the m end and the ground end o of the second protection unit will occur, and the clamping voltage is lower than the amplitude of the voltage signal Vin.

[0078] Since the clamping voltage of the second protection unit is higher than the clamping voltage threshold of the clamping unit, the potential of point 6 is further clamped to a lower amplitude level.

[0079] When the sampling voltage exceeds the threshold range, the processor controls the fourth input end P24 of the multiplexer to be selected with the output end P25 thereof. The voltage of the fourth input end P24 is the clamping voltage, and since the clamping voltage of the clamping unit is lower than the highest input voltage of the subsequent circuit, the subsequent circuit is protected.

[0080] In some embodiments, the direct current voltage measurement circuit further comprises a second voltage source V2 and a comparator, the voltage value output by the second voltage source V2 is lower than the clamping voltage of the clamping unit, and higher than the maximum value of the sampling voltage allowed to be received.

[0081] One input end of the comparator is connected with the second voltage source V2, and the other input end is connected with the output end of the voltage buffer, and the output end of the comparator is connected with the processor.

[0082] In combination Figure 2 As shown, if the voltage source V2 and the reverse end of the comparator are connected, the comparator outputs a high level, and when the sampling voltage exceeds the threshold range, the amplitude of the voltage source V2 is lower than the amplitude of the clamping voltage of the clamping unit, and higher than the highest amplitude of the normal voltage signal to be measured, so at this time the comparator outputs a high level signal to the processor, and the processor controls the fourth input end P24 of the multiplexer to be selected with the output end P25 thereof.

[0083] In some embodiments, the voltage sampling circuit comprises a voltage sampling unit and a sampling switch connected in series, the voltage sampling unit is used for sampling the direct current voltage to be measured, and the voltage sampling unit can be composed of a voltage dividing resistor, and outputs a sampling voltage Vin.

[0084] In the steady state of the voltage measurement, the sampling switch is on, and the sampling voltage Vin is transmitted along the path surrounded by the voltage protection ring A to the third input terminal P23 of the multiplexer. When the third input terminal P23 of the multiplexer is not on with the output terminal P25, the third input terminal P23 presents high resistance to the output terminal P11 pin of the sampling voltage Vin. When the third input terminal P23 of the multiplexer is on with the output terminal P25, the input terminal of the conditioning circuit also presents high resistance to the output terminal P11 pin of the sampling voltage Vin. Therefore, in the steady state of the voltage measurement, there is no current in the transmission path of the sampling voltage Vin. Therefore, the on-resistance of the sampling switch does not produce a voltage drop.

[0085] In some embodiments, the direct current voltage measurement circuit further comprises an isolated voltage source V1, the positive electrode of the isolated voltage source V1 is connected to the control terminal of the sampling switch, and the isolated voltage source V1 is used to provide an on voltage for the sampling switch.

[0086] In some embodiments, the direct current voltage measurement circuit further comprises a discharge resistor and a protection switch, and the discharge resistor is connected in the voltage sampling circuit. In the steady state of the voltage measurement, there is no current in the transmission path of the sampling voltage Vin. Therefore, no voltage drop is generated on the discharge resistor.

[0087] The control terminal of the protection switch is connected to the voltage sampling circuit, the input terminal of the protection switch is connected to the positive electrode of the isolated voltage source V1, and the output terminal of the protection switch is connected to the negative electrode of the isolated voltage source V1 through the discharge resistor.

[0088] When the sampling voltage Vin is within the normal range, the voltage at the control terminal of the protection switch and the voltage at the emitter are equal to the amplitude of the sampling voltage Vin, the protection switch is off, the connection between the positive electrode of the isolated voltage source V1 and the discharge resistor and the negative electrode of the isolated voltage source V1 cannot form a discharge circuit.

[0089] When the sampling voltage Vin exceeds the normal range, the protection switch is on, the positive electrode of the isolated voltage source V1 is connected to the negative electrode of the isolated voltage source V1 through the discharge resistor, the isolated voltage source V1 discharges through the discharge resistor, at this time the level of the control terminal of the sampling switch is pulled low and is less than the on threshold of the sampling switch, the sampling switch is off, and the voltage sampling circuit is disconnected, so that the entire voltage measurement circuit is protected.

[0090] In some embodiments, the two ends of the first protection unit are connected in the voltage sampling circuit, and one end of the second protection unit is connected close to the upstream of the transmission of the sampling voltage, and the other end is connected close to the downstream of the transmission of the sampling voltage.

[0091] When the sampling voltage Vin is within the normal range, the voltage at the two ends of the first protection unit is equal to the amplitude of the sampling voltage Vin, and the first protection unit does not act.

[0092] When the sampling voltage Vin exceeds the normal range, the voltage at the end of the first protection unit close to the transmission upstream is still equal to the sampling voltage Vin, and the voltage at the end close to the transmission downstream is the clamping voltage of the second protection unit. The voltage across the first protection unit is no longer the same, and when the voltage difference across the first protection unit is large enough, the first protection unit is turned on to trigger the protection switch to be turned on.

[0093] Since in practice the sampling voltage may exceed the maximum positive voltage range or the maximum negative voltage range, and the sampling voltage may superimpose a positive surge signal or a negative surge signal, in order to protect both directions of abnormality, in some embodiments, the discharge resistor has two, which are the first discharge resistor and the second discharge resistor.

[0094] The corresponding protection switch has two, which are the first protection switch Q1 and the second protection switch Q2. The first discharge resistor and the second discharge resistor are connected in the voltage sampling circuit in turn, and the negative electrode of the isolated voltage source is connected between the first discharge resistor and the second discharge resistor.

[0095] In some embodiments, the transmission upstream of the sampling voltage Vin is located at the front end of the first discharge resistor, and the transmission downstream of the sampling voltage Vin is located at the rear end of the second discharge resistor.

[0096] The control end of the first protection switch Q1 is connected in the voltage sampling circuit and the connection point is close to the transmission upstream of the sampling voltage. The input end of the first protection switch is connected with the positive electrode of the isolated voltage source, and the output end of the first protection switch Q1 is connected with the negative electrode of the isolated voltage source through the second discharge resistor.

[0097] The control end of the second protection switch Q2 is connected in the voltage sampling circuit and the connection point is close to the transmission downstream of the sampling voltage. The input end of the second protection switch is connected with the positive electrode of the isolated voltage source, and the output end of the second protection switch Q2 is connected with the negative electrode of the isolated voltage source through the first discharge resistor.

[0098] In some embodiments, the first protection switch Q1 and the second protection switch Q2 are respectively implemented by an NPN triode. For example, Figure 2As shown, the base of the first protection switch Q1 is the control end, and the connection point of the voltage sampling circuit is close to the transmission upstream of the sampling voltage. The collector of the first protection switch Q1 is the input end, and is connected with the positive pole of the isolation voltage source. The emitter of the first protection switch Q1 is the output end, and is connected with the sampling voltage output end of the second discharging resistor. The base of the second protection switch Q2 is the control end, and the connection point of the voltage sampling circuit is close to the transmission downstream of the sampling voltage. The collector of the second protection switch Q2 is the input end, and is connected with the positive pole of the isolation voltage source. The emitter of the second protection switch Q2 is the output end, and is connected with the sampling voltage input end of the first discharging resistor. In the embodiment, the base of the first protection switch Q1 is connected between the first protection unit and the first discharging resistor, and the base of the second protection switch Q2 is connected between the first protection unit and the second discharging resistor.

[0099] When the sampling voltage Vin is in the normal range, the voltages of the two ends of the protection unit, the bases and the emitters of the first protection switch Q1 and the second protection switch Q2 are the same, and thus no leakage occurs.

[0100] The normal measurement state of the sampling voltage Vin described above refers to a steady state. The transient process of the sampling voltage Vin measurement and the working state of the protection unit will be described in combination with the embodiments.

[0101] When the sampling voltage Vin is a positive voltage relative to the GND1 network and exceeds the maximum allowable value of the voltage measurement circuit, or a large positive surge signal is superimposed on the sampling voltage Vin, according to the foregoing description, the clamping unit clamps the potential of the point 6 (located in the transmission downstream of the sampling voltage) to a lower amplitude level. At the same time, the first sampling switch and the second sampling switch are still in the on state, but the voltages of the two ends of the first protection unit are no longer the same, one end is the voltage signal Vin, and the other end is the clamping voltage of the second protection unit. When the voltage difference of the two ends of the first protection unit is large enough, the first protection unit is turned on, and the voltage of the point 1 (located in the transmission upstream of the sampling voltage) is pulled low. At the same time, the base voltage of the first protection switch Q1 is no longer equal to the emitter voltage, and when the voltage difference is greater than the opening threshold, the first protection switch Q1 is turned on. The positive pole of the isolation voltage source V1 discharges to the negative pole of the isolation voltage source V1 through the first protection switch Q1 and the second discharging resistor. At this time, the control end voltage of the sampling switch is pulled low, and when it is less than the opening threshold voltage, the sampling switch is turned off, and the voltage measurement circuit is protected.

[0102] When the sampling voltage Vin is negative relative to the GND1 network and the absolute value exceeds the maximum allowed value of the voltage measurement circuit, or a negative surge signal with a large absolute value is superimposed on the sampling voltage Vin, the sampling switch is in the on state, and the voltage amplitude of points ⑤ and ⑥ will exceed the threshold voltage of the second protection unit. The input end, output end and ground end of the second protection unit are conductive, and clamping will occur between the input end and the ground end o of the second protection unit, and the absolute value of the clamping voltage is lower than the absolute value of the sampling voltage Vin. The voltage across the first protection unit is no longer the same, one end is the voltage signal Vin, and the other end is the clamping voltage of the second protection unit. When the voltage difference across the first protection unit is large enough, the first protection unit is conductive, and the absolute value of the voltage at point ① is lowered. At the same time, the base-emitter voltage of the second protection switch Q2 is no longer equal, and the second protection switch Q2 is conductive. The positive electrode of the isolation voltage source V1 discharges to the negative electrode of the isolation voltage source V1 through the second protection switch Q2 and the first discharge resistor. At this time, the control end voltage of the sampling switch is pulled low, and when it is less than the opening threshold voltage, the sampling switch is turned off, and the voltage measurement circuit is protected. The other processes are the same as when measuring a positive voltage signal, and will not be described again. The voltage measurement circuit is protected.

[0103] In some embodiments, the sampling switch has two, which are the first sampling switch and the second sampling switch.

[0104] The control end of the first sampling switch and the control end of the second sampling switch are respectively connected to the positive electrode of the isolation voltage source, the first sampling switch is connected between the output end of the voltage sampling unit and the first discharge resistor, and the second sampling switch is connected between the switching circuit and the second discharge resistor.

[0105] The first sampling switch has three signal ports, which are the signal input end a end, the signal output end b end and the switch control end c end. When the c end voltage of the first sampling switch is greater than its conduction threshold, the first sampling switch is conductive.

[0106] The second sampling switch has three signal ports, which are the signal input end h end, the signal output end i end and the switch control end j end. When the j end voltage of the second sampling switch is greater than its conduction threshold, the second sampling switch is conductive.

[0107] In some embodiments, the conduction threshold voltages of the first sampling switch and the second sampling switch are equal.

[0108] The voltage sampling unit is connected with the signal input end a end of the first sampling switch through the P11 pin, the signal output end b end of the first sampling switch is connected with the input end of the first protection unit, the base of the first protection switch Q1, the emitter of the second protection switch Q2, and the input end d of the first discharge resistor at a point ①. The switch control end c end of the first sampling switch is connected with the switch control end j end of the second sampling switch, the collector of the first protection switch Q1, the collector of the second protection switch Q2, and the positive end of the isolation voltage source V1 at a point ④.

[0109] The e end of the first discharge resistor is connected with the f end of the second discharge resistor and the negative end of the isolation voltage source V1 at a point ②.

[0110] The isolation voltage source V1 is isolated from the measurement circuit, and the negative end of the isolation voltage source V1 is connected with the GND2 network. The to-be-measured signal Vin is a voltage signal relative to the GND1 network of the measurement circuit.

[0111] The signal input end h end of the second sampling switch is connected with the output end of the first protection unit, the base of the second protection switch Q2, the emitter of the first protection switch Q1, and the g end of the second discharge resistor at a point ③. The signal output end i end of the second sampling switch is connected with the m end of the second protection unit, the input end k end of the voltage buffer, and the third input end P23 of the multiplexer at a point ⑤.

[0112] The ground end o of the second protection unit is connected with the GND1 network of the measurement circuit. The signal n end of the second protection unit is connected with the output end l end of the voltage buffer, the signal input end of the clamping unit, the fourth input end P24 of the multiplexer, and the signal input end of the comparator at a point ⑥.

[0113] The output signal of the comparator is connected with the input end of the processor, and the processor is connected with the signal output end of the conditioning circuit. The input end of the conditioning circuit is connected with the output end P25 of the multiplexer.

[0114] When the voltage source V2 and the same direction end of the comparator are turned on, the comparator outputs a low level; the on channel of the multiplexer is controlled to change in the order of the second input end P22 and the output end P25 being turned on, the first input end P21 and the output end P25 being turned on, and the third input end P23 and the output end P25 being turned on. In this way, the direct current error of the system and the measurement result drift caused by temperature drift can be corrected.

[0115] The conditioning circuit outputs corresponding data to the processor according to the channel order changed by the multiplexer, and the processor respectively performs the offset error calibration, the gain error calibration, and the calculation of the amplitude of the to-be-measured voltage.

[0116] The direct current error of the system and the drift caused by long time use will affect the accuracy of the measurement result. In order to solve the above problems, in some embodiments, the direct current voltage measurement circuit further comprises a voltage calibration circuit, which is used to input a standard voltage to the system for calibrating the system offset error.

[0117] In some embodiments, the voltage calibration circuit comprises a precision voltage source and a calibration voltage source, and the precision voltage is used to output a calibration voltage with a fluctuation range within a set threshold.

[0118] The output end of the calibration voltage source is connected with the second input end P21 of the multiplexer.

[0119] The voltage calibration circuit further comprises an isolation circuit, and the precision voltage source transmits the calibration voltage to the calibration voltage source through the isolation circuit.

[0120] The processor controls the first input end of the multiplexer to be selected and gated with the output end thereof, and is used to calibrate the gain error of the measurement system.

[0121] The processor controls the second input end of the multiplexer to be selected and gated with the output end thereof, and is used to calibrate the offset error of the measurement system.

[0122] In some embodiments, the precision voltage source preferably adopts a high-precision low-drift voltage reference source.

[0123] In order to isolate the precision voltage source from the measurement circuit and prevent the interference on the circuit from affecting the accuracy of the output voltage of the precision voltage source, in some embodiments, the calibration voltage source is composed of an operational amplifier. The output voltage of the calibration voltage source is in proportional relationship with the output voltage of the precision voltage source. The negative pin of the precision voltage source is not connected with the GND1 network, and the transmission of the voltage amplitude is completed through the isolation circuit.

[0124] In some embodiments, the isolation circuit comprises a capacitor C1, a first switching switch K1, a second switching switch K2 and an oscillator.

[0125] The common end q of the first switching switch K1 is connected with the positive end of the capacitor C1, one of the moving points p of the first switching switch K1 is connected with the positive pole of the precision voltage source, and the other moving point r is connected with the positive pole of the calibration voltage source.

[0126] The common end of the second switching switch K2 is connected with the negative end of the capacitor C1, one of the moving points s of the second switching switch is connected with the negative pole of the precision voltage source, and the other moving point u is connected with the ground end, and the negative pole of the calibration voltage source is connected with the ground end GND1.

[0127] The oscillator is used to output a control signal S1 with a frequency of f1, the first switching switch K1 and the second switching switch K2 are two alternative switches, and the control signal S1 is used to control the gating state of the first switching switch K1 and the second switching switch K2.

[0128] When the control signal S1 is high, the q terminal of the first switch K1 and the p terminal of the first switch K1 are turned on, and the t terminal of the second switch K2 and the s terminal of the second switch K2 are turned on. The positive terminal of the capacitor C1 is connected to the q terminal of the first switch K1, and the negative terminal of the capacitor C1 is connected to the t terminal of the second switch K2. The positive output pin of the precision voltage source is connected to the p terminal of the first switch K1, and the negative output pin of the precision voltage source is connected to the s terminal of the second switch K2. When the control signal S1 is high, the precision voltage source charges the capacitor C1. When the control signal S1 is low, the q terminal of the first switch K1 and the r terminal of the first switch K1 are turned on, and the t terminal of the second switch K2 and the u terminal of the second switch K2 are turned on. The capacitor C1 provides a standard voltage to the input terminal of the calibration voltage source.

[0129] The capacitor C1 is charged at a frequency of f1 and a duty cycle of 0.5, and then provides a standard voltage input to the input terminal of the calibration voltage source.

[0130] The calibration voltage source is composed of an operational amplifier circuit, and the output voltage is proportional to the output voltage of the precision voltage source. The negative pin of the precision voltage source is not connected to the GND1 network, and the voltage amplitude is transmitted through the capacitor C1 and the two-way switch K1 and the two-way switch K2. The purpose of this design is to isolate the precision voltage source from the measurement circuit, preventing interference in the circuit from affecting the precision of the output voltage of the precision voltage source.

[0131] The positive input terminal of the calibration voltage source is connected to the r terminal of the first switch K1, and the negative input terminal of the calibration voltage source is connected to the u terminal of the second switch K2. The output of the calibration voltage source is connected to the first input terminal P21 of the multiplexer, and the second input terminal P22 of the multiplexer is connected to the GND1 network.

[0132] The output of the calibration voltage source is connected to the first input terminal P21 of the multiplexer, and the third input terminal P23 pin of the multiplexer is connected to the sampling voltage transmission network.

[0133] In some embodiments, the second input terminal of the multiplexer is connected to the ground terminal. This is used to eliminate the offset error of the system.

[0134] Of course, the above description is not a limitation of the present application, and the present application is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present application should also be within the scope of the present application.

Claims

1. A direct voltage measuring circuit, characterized in that The direct current voltage measurement circuit comprises: a voltage sampling circuit for sampling a direct current voltage to be measured and outputting a sampling voltage; a first protection unit connected with the voltage sampling circuit; a voltage protection ring arranged outside the voltage sampling circuit, the voltage sampling circuit comprising a voltage sampling unit and a sampling switch connected with each other, the output end of the voltage sampling unit and the sampling switch being located in the voltage protection ring; a voltage buffer for transmitting the sampling voltage to the voltage protection ring; a second protection unit, the input end of the second protection unit being connected with the input end of the voltage buffer, the output end of the second protection unit being connected with the output end of the voltage buffer, and the ground end of the second protection unit being connected with the ground end; a processor for receiving and processing the sampling voltage through a switch circuit to obtain the amplitude of the direct current voltage to be measured; the switch circuit is a multiplexer, the multiplexer comprising a control end, an output end and a plurality of input ends, the third input end of the multiplexer being connected with the sampling circuit for receiving the sampling voltage; the processor is connected with the output end of the multiplexer through a conditioning circuit; the processor outputs a gating signal to the multiplexer through the control end of the multiplexer; in a steady state process of voltage measurement, the sampling switch is turned on, and the voltage sampling unit outputs the sampling voltage which is transmitted along a path surrounded by the voltage protection ring to the third input end of the multiplexer; the multiplexer comprises a fourth input end adjacent to the third input end, the output end of the voltage buffer is connected with one of the fourth input ends, and the fourth input end is connected with the voltage protection ring; the direct current voltage measurement circuit further comprises: an isolated voltage source, the positive pole of the isolated voltage source being connected with the control end of the sampling switch for providing an opening voltage; a discharge resistor; a protection switch, the control end of the protection switch being connected with the voltage sampling circuit, the input end of the protection switch being connected with the positive pole of the isolated voltage source, and the output end of the protection switch being connected with the negative pole of the isolated voltage source through the discharge resistor; the discharge resistor has two, namely a first discharge resistor and a second discharge resistor; the protection switch has two, namely a first protection switch and a second protection switch; the first discharge resistor and the second discharge resistor are connected in the voltage sampling circuit in sequence, and the negative pole of the isolated voltage source is connected between the first discharge resistor and the second discharge resistor; the control end of the first protection switch is connected in the voltage sampling circuit and the connection point is close to the upstream of the transmission of the sampling voltage, the input end of the first protection switch is connected with the positive pole of the isolated voltage source, and the output end of the first protection switch is connected with the negative pole of the isolated voltage source through the second discharge resistor; the control end of the second protection switch is connected in the voltage sampling circuit and the connection point is close to the downstream of the transmission of the sampling voltage, the input end of the second protection switch is connected with the positive pole of the isolated voltage source, and the output end of the second protection switch is connected with the negative pole of the isolated voltage source through the first discharge resistor. The sampling switch has two, namely a first sampling switch and a second sampling switch; The control ends of the first sampling switch and the second sampling switch are connected with the positive pole of the isolation voltage source respectively, the first sampling switch is connected between the output end of the voltage sampling unit and the first discharge resistor, and the second sampling switch is connected between the third input end of the multiplexer and the second discharge resistor, and the third input end of the multiplexer is connected with the input end of the voltage buffer; The two ends of the first protection unit are connected in the voltage sampling circuit respectively, one end of the first protection unit is connected between the first sampling switch and the first discharge resistor, and the other end of the first protection unit is connected between the second sampling switch and the second discharge resistor.

2. The direct voltage measurement circuit according to claim 1, characterized in that The DC voltage measurement circuit further comprises: A clamping unit, one end of which is connected with the fourth input end, and the other end of which is connected with the ground end; When the sampling voltage exceeds the threshold range, the processor controls the fourth input end of the multiplexer to be selected with the output end thereof.

3. The direct voltage measurement circuit according to claim 2, characterized in that The DC voltage measurement circuit further comprises: A second voltage source, the output voltage of which is lower than the clamping voltage of the clamping unit, and higher than the maximum value of the sampling voltage allowed to be received; A comparator, one input end of which is connected with the second voltage source, and the other input end of which is connected with the output end of the voltage buffer, and the output end of the comparator is connected with the processor.

4. The DC voltage measurement circuit according to any one of claims 1-3, characterized in that The DC voltage measurement circuit further comprises a voltage calibration circuit, and the voltage calibration circuit comprises: A precision voltage source, which is used to output a calibration voltage with a fluctuation range within a set threshold value; A calibration voltage source, the output end of which is connected with the first input end of the multiplexer; An isolation circuit, the calibration voltage is transmitted from the precision voltage source to the calibration voltage source through the isolation circuit; When the processor controls the first input end of the multiplexer to be selected with the output end thereof, it is used for calibrating the gain error; When the processor controls the second input end of the multiplexer to be selected with the output end thereof, it is used for calibrating the offset error.

5. The direct voltage measurement circuit according to claim 4, characterized in that The isolation circuit comprises: A capacitor; A first conversion switch, the common end of which is connected with the positive end of the capacitor, one movable point of the first conversion switch is connected with the positive pole of the precision voltage source, and the other movable point is connected with the positive pole of the calibration voltage source; A second conversion switch, the common end of which is connected with the negative end of the capacitor, one movable point of the second conversion switch is connected with the negative pole of the precision voltage source, and the other movable point is connected with the ground end, and the negative pole of the calibration voltage source is connected with the ground end; An oscillator, which is used to control the selection state of the first conversion switch and the second conversion switch.

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