Power supply circuit for an analog output

Abstract

The present invention relates to a power supply circuit (1.1) for a first analog output (5.1), comprising a DC-DC converter (2) with a supply output (2.1), an internal or external reference voltage (2.2), and a feedback terminal (2.3) for providing a DC supply voltage (8) at the supply output (2.1), a first p-channel MOSFET (3) with a first gate terminal (3.1), a first source terminal (3.2), and a first drain terminal (3.3), and a first signal input (5.3) through which the voltage value (9.1) present at the first analog output (5.1) is supplied to the power supply circuit (1.1) and sampled from the first gate terminal (3.1), wherein the first source terminal (3.2) is connected to the supply output (2.1) via a first resistor (4.1), and the first drain terminal (3.3) is connected to the feedback terminal (2.3) via a second resistor. (4.2) is connected to 0 volts and wherein the value of the supply DC voltage (8) is formed by adding a constant voltage excess (10) to the sampled voltage value (9.1). The invention further relates to a corresponding voltage supply circuit (1.2) with two p-channel MOSFETs (3, 11) connected in series and a measuring device with one of the aforementioned voltage supply circuits (1.1, 1.2).

Description

Technical FieldThe present invention relates to a voltage supply circuit for an analog output, in particular of a measuring device. The present invention furthermore relates to a measuring device having a sensor element and at least one such voltage supply circuit.BACKGROUND OF THE INVENTIONElectronic devices such as measuring devices with analog outputs are already known from the prior art. At the analog output, a value, in particular a measured value, for example a measured value recorded by means of a sensor element, is linearly mapped to an electrotechnical variable, in particular to a current intensity or a voltage in a specific range of the variable such as, for example, 4-20 mA for the current intensity. The electrotechnical variable is then tapped off, for example, from a controller as a signal and further processed, for example, in a process controller.It is known from the prior art that the electrical engineering variable is adjusted on the basis of an operating voltage present in the measuring device as a function of the measured value. For example, a current intensity signal is directly adjusted from the operating voltage by a current regulator or a voltage signal is directly adjusted from the operating voltage by a voltage regulator. However, disadvantageously, there is often an unfavorable ratio between the operating voltage, the load present at the analog output and the electrotechnical variable to be controlled in such a way that the control of the variable can only take place with high power loss. For example, such a ratio is present if the burden is very low, for example is approximately 0 ohm, in the case of a 36 V operating voltage and a mapping of the measured value to a 4-20 mA current strength signal.DESCRIPTION OF THE INVENTIONProceeding from this situation, it is an object of the present invention to propose a circuit for supplying voltage, on the basis of which the electrical engineering variable can be provided at the analog output with low power loss.The object of the invention is achieved by the features of the independent main claims. Advantageous embodiments are specified in the dependent claims. Insofar as technically possible, the teachings of the subclaims can be combined as desired with the teachings of the main and dependent claims.Advantages of the claimed aspects of the invention are explained below and preferred modified embodiments of the aspects of the invention are described below. Explanations, in particular regarding advantages and definitions of features, are basically descriptive and preferred, but non-limiting examples. Where an explanation is limiting, this is expressly mentioned. In particular, the invention is explained with reference to a measuring device, wherein the value mapped to the signal is, for example, a measured value. However, it is expressly understood that with respect to another device, the value may be other than a measurement value, for example, any value of a control loop.If elements are designated with the aid of a numbering, i.e. for example "first element", "second element" and "third element", this numbering is provided purely for differentiation in the designation and does not represent a dependence of the elements on one another or a obligatory sequence of the elements. This means in particular that, for example, a device or a method does not have to have a "first element" in order to be able to have a "second element". The device or the method can also have a "first element" and a "third element", but without necessarily having a "second element". It is also possible to provide a plurality of units of an element of a single numbering, that is to say, for example, a plurality of "first elements".According to a first aspect of the invention, the object is achieved by a voltage supply circuit for a first analog output, in particular a measuring device, having a DC-to-DC converter with a supply output, an internal or external reference voltage reference and a feedback connection, wherein the DC-to-DC converter is configured to provide a supply DC voltage at the supply output. The voltage supply circuit further comprises a first p-channel MOSFET having a first gate terminal, a first source terminal and a first drain terminal and a first signal input, by means of which the voltage value present at the first analog output is supplied to the voltage supply circuit and sensed by the first gate terminal. In this case, the first source terminal is connected via a first resistor to the supply output and the first drain terminal is connected to the feedback terminal and via a second resistor to 0 volt, also referred to as ground or GND, and the value of the DC supply voltage is formed by adding a constant voltage excess to the sampled voltage value.Insofar as the voltage supply circuit is provided for an analog output stage, it is configured to supply the electronic components assigned to the analog output stage with the DC supply voltage. This is, for example, a current regulator or a voltage regulator, by means of which the measured value is mapped to a corresponding electrical quantity at the analog output.A DC-DC converter, also called a DC-DC converter, denotes an electrical circuit which converts a DC voltage supplied at the input into a DC voltage with a higher, lower or inverted voltage level with high efficiency compared to a linear voltage regulator. Insofar as the DC-to-DC converter has an internal or external reference voltage reference and a feedback terminal, it is set up in such a way that the voltage present at the feedback terminal is exactly equal to that of the internal or external reference voltage reference via the DC supply voltage. In particular, the reference voltage reference and the feedback connection lead to inputs of an operational amplifier of the DC-DC converter.A p-channel MOSFET is a metal oxide semiconductor field effect transistor (MOSFET) in which positively charged charge carriers (holes, holes) as majority charge carriers take over the conduction of the electric current in the channel, that is to say between the source terminal and the drain terminal. In this case, the internal resistance of the drain-source path is controlled with the voltage between the gate terminal and the source terminal. The p-channel MOSFET is, in particular, an enhancement type p-channel MOSFET.Insofar as two connections or electronic components are connected to one another, this is understood to mean that the connections or electronic components are electrically conductively connected to one another.The first aspect of the invention described above comprises the technical teaching that the supply DC voltage provided by the DC-to-DC converter is fed back to the feedback connection via the first resistor, the first p-channel MOSFET and the second resistor, wherein the output voltage of the first analog output dependent on the signal is present at the first gate connection. In this way, the DC supply voltage is tracked to the signal, wherein it always exceeds the output voltage by a constant voltage excess. The constant voltage excess arises from the voltage drop across the first resistor, which is formed by the constant current through the complete feedback path and is supported on the source terminal of the first MOSFET, wherein the largely constant gate-source voltage of the MOSFET additionally adds to the analog signal voltage. The constant current through the feedback path is predefined by the magnitude of the reference voltage and the value of the second resistor at the feedback terminal. The DC supply voltage is adjusted so that exactly this current flows. Advantageously, the constant voltage excess can then be set at least approximately corresponding to the voltage drop at the regulator for providing the signal, so that the DC supply voltage always corresponds to the DC supply voltage required at the regulator for providing the signal with minimal power loss. In other words, the DC supply voltage equals the amount of the sum of the voltage value at the analog output and the voltage requirement at the regulator which adjusts the signal output at the analog output, and in this respect enables the adjustment of the signal output at the analog output with the smallest possible power loss.The first aspect of the invention provides a DC supply voltage for a single analog output. According to a second aspect of the invention, the object is achieved by a voltage supply circuit for two analog outputs, preferably reciprocal to one another, in particular of a measuring device, having a DC-to-DC converter with a supply output, an internal or external reference voltage reference and a feedback connection, wherein the DC-to-DC converter is configured to provide a supply DC voltage at the supply output. The voltage supply circuit further comprises a first p-channel MOSFET having a first gate terminal, a first source terminal and a first drain terminal, and a second p-channel MOSFET having a second gate terminal, a second source terminal and a second drain terminal, and a first signal input, by means of which the voltage value present at a first analog output is supplied to the voltage supply circuit and sensed by the first gate terminal, and a second signal input, by means of which the voltage value present at a second analog output is supplied to the voltage supply circuit and sensed by the second gate terminal. In this case, the first source terminal is connected via a first resistor to the supply output, the first drain terminal to the second source terminal and the second drain terminal to the feedback terminal and via a second resistor to 0 volt, also referred to as ground or GND, and the value of the DC supply voltage is formed by adding a constant voltage excess to the respectively higher of the two sampled voltage values.Insofar as the first analog output and the second analog output are reciprocal to each other, they map the measured value to the same electrotechnical variable in the same size range, but the limits of the size ranges are interchanged with each other. If the signal is mapped to a current intensity of 4-20 mA, for example, at the first analog output, it is mapped to a current intensity of 20-4 mA with an inverse proportionality at the second analog output. The sum of the variables output at the analog outputs is always the same, approximately always 24 mA in the example mentioned above. Two mutually reciprocal analog outputs are provided, for example, in measuring devices which must meet specific safety requirements levels, for example SIL2, the sum of the variables output at the analog outputs then being used as a control value for the functionality of the measuring device. In principle, however, embodiments in which the two analog outputs are not reciprocal to one another are also encompassed by the invention. That is to say, the signals to be output can also be formed completely independently of one another, for example, in that one output represents pressure and the other temperature.The above-described second aspect of the invention includes substantially the same technical teaching as the first aspect of the invention, wherein the first p-channel MOSFET and the second p-channel MOSFET are connected in series between the first resistor and the second resistor.The DC supply voltage is in this way always determined by the higher of the two voltages present at the analog outputs and is thus sufficient at all times for the supply of both analog outputs.The first aspect of the invention has a further advantage if the signal output at the first analog output is mapped onto an output voltage. In this case, it is necessary to provide a current limitation in order to brake the output current as the load rises up to a short circuit on the load side. Advantageously, the braking of the output-side current from the DC supply voltage can then take place with low power loss, in particular compared to a substantially higher operating voltage of the measuring device which is otherwise possible for the supply of the analog output.According to a further aspect of the invention, the object is achieved by a voltage supply circuit according to the first or second aspect of the invention, with the difference that a pnp Darlington circuit is used instead of a p-channel MOSFET or two p-channel MOSFETs, wherein a base of the Darlington circuit corresponds in each case to a gate terminal of a p-channel MOSFET, an emitter of the Darlington circuit corresponds to a source terminal of a p-channel MOSFET and a collector of the Darlington circuit corresponds to a drain terminal of a p-channel MOSFET. It is also possible, instead of p-channel MOSFET or pnp Darlington circuit, to use a pnp transistor with a high current amplification if a diode or a resistor is connected in series with the base terminal, since otherwise at zero volts at the analog output the feedback voltage cannot reach the level of the reference voltage reference.The embodiments of the voltage supply circuit described below can relate to any of the above-described aspects of the invention. Insofar as features described relate only to one of the described aspects of the invention, this is expressly stated or arises directly from the terms used.In an advantageous embodiment of the respective voltage supply circuit, an input DC voltage is between 18 and 36 V, preferably 24 V. The operating voltage of a measuring device having the voltage supply circuit is then used as the input DC voltage, for example, and a further voltage source or a further voltage level can advantageously be dispensed with. Furthermore, the reference voltage reference is advantageously 0.9 V.In a further, preferred embodiment, the first analog output is configured for the output of a 4-20 mA signal and / or the second analog output is configured for the output of a 20-4 mA signal. The analog outputs are then assigned a current regulator or a current regulator, respectively, which regulates the output signal as a function of a measured value, for example. Advantageously, a 4-20 mA signal or a 20-4 mA signal can be supplied with the voltage supply circuits of the first aspect and / or of the second aspect with particularly low loss, that is to say with particularly low power loss.In a further preferred embodiment, to which reference has already been made in part in the above-described, the voltage supply circuit has at least one current regulator for regulating a signal to be output at the first analog output and / or the second analog output, wherein the current regulator is connected to the supply output. Preferably, the voltage supply circuit has a current regulator per analog output, which is connected to the supply output in each case.Particularly preferably, the first resistor and the second resistor are designed in such a way that the DC supply voltage corresponds to the sum of the output voltage present at the first analog output and a constant voltage excess or to the sum of the output voltage present at the second analog output and the constant voltage excess. The constant voltage excess can then advantageously correspond to the voltage requirement of the current regulators and / or further loads in the voltage supply circuit, which voltage requirement exceeds the voltage amounts present at the analog outputs. The power loss for providing the signal at the analog output or the analog outputs can be particularly widely minimized in this way.In one configuration, the constant voltage excess corresponds to a voltage drop across the at least one current regulator or the two current regulators which are provided for each analog output. The reference level of the constant voltage excess is determined by the output voltage applied to the analog output or to the analog outputs. As a result, the voltage drop across the current regulator or the current regulators and thus the loads to be supplied are taken into account to a sufficient extent in order to achieve a low power loss during the regulation of the signal or the signals.In an alternative embodiment, the constant voltage excess corresponds to the sum of the voltage drop across the first resistor, a gate-source voltage of the first p-channel MOSFET or a gate-source voltage of the second p-channel MOSFET and the voltage value at the first or second analog output, wherein the first p-channel MOSFET belongs to the first analog output and the second p-channel MOSFET accordingly belongs to the second analog output. The gate-source voltage of the respective p-channel MOSFET is added in the voltage supply circuit to the output voltage present at the analog output or at the analog outputs and to the voltage drop at the first resistor. If this is taken into account in the case of the constant voltage excess, the loads to be supplied are taken into account to an even more precise extent in order to achieve a low power loss during the adjustment of the signal or signals.For example, the constant voltage excess is between 3 and 7 V, in particular 5 V, wherein in this voltage range usually a low-loss supply of one or two mutually reciprocal analog outputs is made possible.In a further embodiment, the voltage supply circuit has at least one voltage regulator for converting the supply DC voltage into an additional DC voltage at a load output for a further load. The voltage regulator is in particular a linear regulator such as a low drop out voltage regulator (LDO regulator). A voltage regulator stabilizes an electrical DC voltage as the operating voltage for a circuit in order to compensate for variations in the input voltage within wide ranges. In addition to the analog output or the analog outputs, the DC supply voltage can then also be used to provide a further voltage level at DC voltage for further consumers, in particular if this voltage level is closer to the lowest voltage level of the DC supply voltage than, for example, the operating voltage of a measuring device, the DC input voltage present at the DC voltage converter and / or the reference voltage.According to a third aspect of the invention, the object is achieved by a measuring device having a sensor element, a voltage supply circuit according to the first aspect of the invention or according to the second aspect of the invention and at least one regulator for regulating a signal to be output at the first analog output and / or a signal to be output at the second analog output and proportional to a measured value detected by means of the sensor element. The measuring device can achieve the advantages described above with respect to the voltage supply circuit accordingly.In a preferred embodiment of the measuring device, the signal is mapped at the first analog output to 4-20 mA and / or at the second analog output to 20-4 mA. The analog outputs are then assigned a current regulator or a current regulator in each case, which regulates the output signal as a function of the measured value. Advantageously, a 4-20 mA signal or a 20-4 mA signal can be supplied with particularly low-loss power in the measuring device according to the third aspect of the invention.In yet another preferred embodiment of the measuring device, the voltage supply circuit has at least one voltage regulator for converting the supply DC voltage into a constant DC voltage at a load output for a further load. The measuring device then has at least one further load connected to the load output. Advantageously, the voltage level of the DC supply voltage can then be used for providing a further voltage level at DC voltage with low loss, in particular a voltage level which is close to the lowest voltage level of the DC supply voltage.Brief Description of the DrawingsThe invention is explained in more detail below with reference to the attached drawings on the basis of preferred exemplary embodiments. The formulation figure is abbreviated with Figure in the drawings.In the drawings, FIG. 1 is a circuit diagram of a power supply circuit according to the first aspect of the invention and other elements; FIG. 2 shows a diagram illustration of the supply voltage and of the output voltage present at the first analog output in the case of a voltage supply circuit according to FIG. 1 ; FIG. 3 is a circuit diagram of a power supply circuit according to the second aspect of the invention; and FIG. 4 shows a diagram illustration of the supply voltage, the output voltage present at the first analog output and the output voltage present at the second analog output in the case of a voltage supply circuit according to FIG. 3.Detailed Description of the DrawingsThe described exemplary embodiments are merely examples which can be modified and / or supplemented in a wide variety of ways within the scope of protection defined by the claims. Each feature described for a particular embodiment may, in this respect, be used independently or in combination with other features in any other embodiment. Each feature described for an embodiment of a particular claim category may also be used in a corresponding manner in an embodiment of a different claim category.FIG. 1 shows a circuit diagram of a voltage supply circuit 1.1 according to the first aspect of the invention, having a DC-DC converter 2, a first p-channel MOSFET 3 and a first resistor 4.1 and a second resistor 4.2. In this case, the DC-to-DC converter 2 has a supply output 2.1, a reference voltage reference 2.2 and a feedback terminal 2.3 and is furthermore connected to an input DC voltage by an input terminal 2.4. The input DC voltage is, for example, an operating voltage of a measuring device and is furthermore, for example, 32 V. At the supply output 2.1, the DC voltage converter 2 outputs a supply voltage following the voltage present at the first analog terminal 5.1, wherein an additive voltage excess depends on the ratio between the resistors 4.1 and 4.2.The first p-channel MOSFET 3 has a first gate terminal 3.1, a first source terminal 3.2 and a first drain terminal 3.3. The first gate terminal 3.1 is connected via the first signal input 5.3 to a first analog output 5.1, wherein here a current signal output at the analog output 5.1 is only shown symbolically by means of a current mirror 6. At the analog output 5.1, a burden 7 is also provided, which thus causes a voltage drop at the analog output 5.1. The voltage applied to the first gate terminal 3.1 is thus determined by the output current signal and the burden 7 and in this way in turn determines the resistance of the drain-source path of the first p-channel MOSFET 3.Furthermore, the first source terminal 3.2 is connected via the first resistor 4.1 to the supply output 2.1 and the first drain terminal 3.3 is connected to the feedback terminal and via a second resistor to 0 volt, also referred to as ground or GND. In this way, a control of the DC supply voltage, which is ultimately dependent on the burden 7 and the current intensity of the signal represented here by means of the current regulator 6, is effected by feeding back the DC supply voltage via the p-channel MOSFET 3 to the feedback terminal 2.3. The DC supply voltage is adjusted in this way to a constant voltage excess above the output voltage present at the analog output 5.1.FIG. 2 illustrates this regulation of the supply DC voltage 8, wherein the output voltage 9.1 present at the first analog output 5.1 is likewise illustrated. While the voltage is plotted on the y-axis, the time is plotted on the x-axis. In detail, a change of the signal over time is shown, for example as a result of a changed measured value which is mapped by the signal. If, as a result of the change in the signal, the output voltage 9.1 present at the first analog output 5.1 now rises as illustrated, the voltage at the first gate terminal 3.1 and thus also the voltage at the first source terminal 3.2 also rises as hurdle which must overcome the supply DC voltage 8 in order to be able to generate that current through the resistor 4.1 which is intended to equalize the voltage at the feedback terminal 3.2 to the voltage at the reference voltage reference 2.2 via the voltage drop at resistor 4.2 and thus ultimately causes the supply DC voltage 8 to be set correspondingly higher. In this way, the DC supply voltage 8 is at any point in time spaced apart from the output voltage 9.1 present at the analog output 5.1 by a constant voltage excess 10.FIG. 3 shows a circuit diagram of a voltage supply circuit 1.2 according to the second aspect of the invention, which corresponds in essential parts to the voltage supply circuit 1.1. Repeated explanation is omitted. In contrast to the voltage supply circuit 1.1, the voltage supply circuit 1.2 has a second p-channel MOSFET 11 which is connected in series with the first p-channel MOSFET 3 between the first drain terminal 3.3 and the feedback terminal 2.3 or the second resistor 4.2. The second p-channel MOSFET 11 has a second gate terminal 11.1, a second source terminal 11.2 and a second drain terminal 11.3. While the second source terminal 11.2 of the described intermediate circuit of the second p-channel MOSFET 11 is connected to the first drain terminal 3.3 and the second drain terminal 11.3 is connected to the second resistor 4.2 and the feedback terminal 2.3, the second gate terminal 11.1 is connected to a second analog output 5.2 via a second signal input 5.4. The first analog output 5.1 and the second analog output 5.1 are preferably connected to one another in such a way that mutually reciprocal signals are output on them via the same electrotechnical variable.FIG. 4 illustrates the regulation of the supply DC voltage 8 in the voltage supply circuit 1.2. As in FIG. 2, the voltage is plotted on the y-axis, while the time is plotted on the x-axis. The output voltage 9.1 present at the first analog output 5.1 and the output voltage 9.2 present at the second analog output 5.2 are opposite to each other. Over time, the output voltage 9.1 present at the first analog output 5.1 rises, while the output voltage 9.2 present at the second analog output 5.2 falls by the same amount at the same time. In this case, the supply direct voltage 8 is determined by the higher of the two voltages 9.1, 9.2 in such a way that it is spaced apart from the higher of the two voltages 9.1, 9.2 by a constant voltage excess 10 at any point in time.List of reference characters1.1 Voltage supply circuit 1.2 Voltage supply circuit 2 Direct voltage converter 2.1 Supply output of the direct voltage converter 2.2 Reference voltage reference of the direct voltage converter 2.3 Feedback connection of the direct voltage converter 2.4 Input connection of the direct voltage converter 3 First p-channel MOSFET 3.1 Gate connection of the first p-channel MOSFET 3.2 Source connection of the first p-channel MOSFET 3.3 Drain connection of the first p-channel MOSFET 4.1 First resistor 4.2 Second resistor 5.1 First analog output 5.2 Second analog output 5.3 First signal input 5.4 Second signal input 6 Current mirror 7 Load resistor 8 Direct voltage supply 9.1 Voltage 9.2 present at the first analog output at voltage 10 of constant voltage excess 11 Second voltage present at the second analog output p-channel MOSFET 11.1 gate terminal of second p-channel MOSFET 11.2 source terminal of second p-channel MOSFET 11.3 drain terminal of second p-channel MOSFET

Claims

Voltage supply circuit (1.1) for a first analog output (5.1), in particular a measuring device, having - a DC-to-DC converter (2) having a supply output (2.1), an internal or external reference voltage reference (2.2) and a feedback terminal (2.3), wherein the DC-to-DC converter (2) is configured to provide a supply DC voltage (8) at the supply output (2.1); - a first p-channel MOSFET (3) having a first gate terminal (3.1), a first source terminal (3.2) and a first drain terminal (3.3); and - a first signal input (5.3), by means of which the voltage value (9.1) present at the first analog output (5.1) is fed to the voltage supply circuit (1.1) and sensed by the first gate terminal (3.1), wherein the first source terminal (3.2) is connected via a first resistor (4.1) to the supply output (2.1) and the first drain terminal (3.3) is connected to the feedback terminal (2.3) and via a second resistor (4.2) to 0 volts; and wherein the value of the DC supply voltage (8) is formed by a constant voltage excess (10) being added to the sensed voltage value (9.1).Voltage supply circuit (1.2) for two analog outputs (5.1, 5.2), preferably reciprocal to one another, in particular of a measuring device, having - a DC voltage converter (2) with a supply output (2.1), an internal or external reference voltage reference (2.2) and a feedback terminal (2.3), wherein the DC voltage converter (2) is configured to provide a supply DC voltage (8) at the supply output (2.1); - a first p-channel MOSFET (3) with a first gate terminal (3.1), a first source terminal (3.2) and a first drain terminal (3.3); - a second p-channel MOSFET (11) with a second gate terminal (11.1), a second source terminal (11.2) and a second drain terminal (11.3); a first signal input (5.3), by means of which the voltage value (9.1) present at a first analog output (5.1) is supplied to the voltage supply circuit (1.1) and is sampled by the first gate terminal (3.1); and a second signal input (5.4), by means of which the voltage value (9.2) present at a second analog output (5.2) is supplied to the voltage supply circuit (1.1) and is sampled by the second gate terminal (11.1); wherein the first source terminal (3.2) is connected via a first resistor (4.1) to the supply output (2.1), the first drain terminal (3.3) to the second source terminal (11.2) and the second drain terminal (11.3) to the feedback terminal (2.3) and via a second resistor (4.2) to 0 volts; and wherein the value of the DC supply voltage (8) is formed by adding a constant voltage excess (10) to the respectively higher of the two sampled voltage values (9.1, 9.2).Voltage supply circuit (1.1, 1.2) according to Claim 1 or 2, wherein the first analog output (5.1) is designed for the output of a 4-20 mA signal and / or the second analog output (5.2) is designed for the output of a 20-4 mA signal.Voltage supply circuit (1.1, 1.2) according to one of the preceding claims, having at least one current regulator for regulating a signal to be output at the first analog output (5.1) and / or the second analog output (5.2); wherein the current regulator is connected to the supply output (2.1).Voltage supply circuit (1.1, 1.2) according to one of the preceding claims, wherein the first resistor (4.1) and the second resistor (4.2) are designed such that the DC supply voltage (8) corresponds to the sum of the voltage (9.1) applied to the first analog output (5.1) and a constant voltage excess (10) or the sum of the voltage (9.2) applied to the second analog output (5.2) and the constant voltage excess (10).Voltage supply circuit (1.1, 1.2) according to claim 5, wherein the constant voltage excess (10) corresponds to a voltage drop across the at least one current regulator.Voltage supply circuit (1.1, 1.2) according to claim 5, wherein the constant voltage excess (10) corresponds to the sum of the voltage drop across the first resistor (4.1), a gate-source voltage of the first p-channel MOSFET (3) or a gate-source voltage of the second p-channel MOSFET (11) and the voltage value at the first or second analog output (5.1, 5.2).Voltage supply circuit (1.1, 1.2) according to one of Claims 5 to 7, wherein the constant voltage excess (10) is between 3 and 7 V, in particular 5 V.Voltage supply circuit (1.1, 1.2) according to one of the preceding claims, having at least one voltage regulator for converting the supply DC voltage (8) into an additional DC voltage at a load output for a further load.Measuring device having a sensor element; a voltage supply circuit (1.1, 1.2) according to one of the preceding claims; and at least one regulator for regulating a signal to be output at the first analog output (5.1) and / or a signal to be output at the second analog output (5.2) and proportional to a measured value detected by means of the sensor element.Measuring device according to claim 10, wherein the signal at the first analog output (5.1) is mapped to 4-20 mA and / or at the second analog output (5.2) to 20-4 mA.Measuring device according to claim 10 or 11, wherein the voltage supply circuit (1.1, 1.2) comprises at least one voltage regulator for converting the DC supply voltage (8) into an additional DC voltage at a load output for a further load; and with at least one further load connected to the load output.

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