A circuit having a current output driver that outputs an output current to a load

Abstract

A circuit is proposed, which has a microcontroller, a digital-to-analog converter and a DC transformer. The digital-to-analog converter has a current output driver for outputting an output current that can be predetermined by process data to a load. The microcontroller outputs a control signal (such as a PWM signal) for setting the supply voltage of the current output driver to the DC transformer based on the output voltage.

Description

Technical Field

[0001] The present invention relates to a circuit for an input / output module (I / O module), the circuit having a microcontroller and a digital-to-analog converter, the digital-to-analog converter having a current output driver for outputting an output current to a load. The present invention particularly relates to a circuit for an I / O module having a microcontroller, the microcontroller measuring an output voltage and adjusting a supply voltage of the digital-to-analog converter based on the measured output voltage in order to reduce power loss. Background Art

[0002] The power loss of an analog current output module is mainly determined by the current output driver and its supply circuit. In order to reduce the power loss, the supply voltage can be continuously regulated according to the output voltage. If, for example, only a relatively small output current flows, the supply voltage of the current output driver can be reduced. Thereby, the voltage drop across the current output driver is lower and the current supply circuit has to provide less power. Thus, the power loss of the current output driver and the current supply circuit is reduced overall. Summary of the Invention

[0003] The circuit according to the present invention includes a communication unit for receiving process data, a microcontroller, a load, a digital-to-analog converter, and a first DC transformer. The communication unit can be connected to a bus for communication. The microcontroller is connected to the communication unit. The digital-to-analog converter has a current output driver for outputting an output current to a load. The microcontroller is connected to the digital-to-analog converter via a digital interface and is configured to set an output current of the digital-to-analog converter based on received process data via the digital interface.

[0004] The digital-to-analog converter has an analog-to-digital converter and is configured to convert an output voltage into a digital voltage value by means of the analog-to-digital converter and transmit it to the microcontroller via the digital interface. The microcontroller is connected to the first DC transformer via a control interface, wherein the first DC transformer is configured to generate a first supply voltage for supplying the current output driver of the digital-to-analog converter. The microcontroller is configured to output a control signal for setting the first supply voltage to the first DC transformer via the control interface based on the output current and the digital voltage value.

[0005] Herein, the concept of "circuit" used in this text is particularly understood as an arrangement structure in which electrical components and / or electronic components are connected together to conform to a function. In addition, the concept of "microcontroller" used in this text is particularly understood as a semiconductor chip having a processor and a memory. In addition, the concept of "digital-to-analog converter" used in this text is particularly understood as a circuit that, for example, receives binary-coded information and derives the intensity of the voltage or current to be output from the binary-coded information.

[0006] Furthermore, the concept of "current output driver" used herein is particularly understood as a circuit that outputs, at the output end, a current derived from a voltage applied at the input end. Furthermore, the concept of "DC transformer" used herein is particularly understood as a circuit that is supplied with a first voltage at the input end and outputs a second voltage at the output end, wherein the voltage at the input end and the voltage at the output end are at least partially different. Furthermore, the concept of "digital interface" used herein is particularly understood as an interface that transmits binary-encoded information, for example, from a microcontroller to a digital-to-analog converter and vice versa.

[0007] Furthermore, the concept of "analog-to-digital converter" used herein is particularly understood as a circuit that derives binary-encoded information, for example, from the intensity of an input voltage or an input current. The concept of "digital voltage value" used herein is particularly understood as a voltage value that is interpreted by compensating the voltage value within a certain value range and assigning the voltage value to its corresponding value range.

[0008] Herein, the concept of "I / O module" used within the scope of this document is particularly understood as a device that can be serially connected to another I / O module or a front end or serially connected during operation, which connects one or more field devices to the front end and, if necessary, (through the front end) to a superior control unit. In this regard, the concept of "field device" used within the scope of this document is particularly understood as sensors and / or actuators that are (signal-technologically) connected to an I / O module (for example, switched on an I / O module).

[0009] Furthermore, the concepts of "input end" and "output end" used within the scope of the current specification are particularly understood as electrical connectors, such as connection posts. Furthermore, the concept of "front end" used within the scope of the current specification is understood as a component of a modular fieldbus node, the task of which is to make the data and / or services of the I / O modules serially connected to the front end available to other fieldbus user devices (such as a superior control unit) through a bus interface and a fieldbus connected to the bus interface.

[0010] The microcontroller can be configured to store the output range having a minimum current value and a maximum current value received through the communication unit and set a first supply voltage based on the minimum current value and / or the maximum current value.

[0011] Furthermore, the microcontroller can be configured to initially set the first supply voltage to a maximum voltage value and set the first supply voltage based on the output current and the digital voltage value after receiving process data.

[0012] Furthermore, the microcontroller can be configured to set the first supply voltage based on the output current when the output current included in the process data is within a predetermined current range.

[0013] In addition, the microcontroller can be set to set the first supply voltage based on the output current when the digital voltage value is within a predetermined voltage value range.

[0014] The microcontroller can be set to set the first supply voltage by means of a function, where the function has the maximum current value, the output current, and the digital voltage value as input variables.

[0015] The microcontroller can also be set to additionally set the first supply voltage based on the bias voltage.

[0016] The microcontroller can, for example, be set to set the first supply voltage by means of a function, and the function is:

[0017] V1 = Imax × Vdig / I + Voff

[0018] where Imax is the maximum current value, V1 is the first supply voltage, Vdig is the digital voltage value, I is the output current, and Voff is the bias voltage.

[0019] The microcontroller can also be set to adjust the bias voltage according to the time value and / or the measured value.

[0020] The microcontroller can be set to determine the control signal for setting the first supply voltage multiple times and output it to the first DC transformer through the control interface, where the determination is made for two (different) time-interval measurements of the second supply voltage.

[0021] The microcontroller can also be set to re-determine the first supply voltage of the first DC transformer when the circuit is accessed.

[0022] The microcontroller can also be set to generate a control signal through which the first DC transformer can be controlled.

[0023] For example, the microcontroller can be set to set the first supply voltage by means of pulse-width modulation (PWM) of the control signal, or the switching signal can conform to a percentage value from which a PWM signal or an analog signal conforming to the percentage value can be derived.

[0024] The calculation of the switching signal or the percentage value can be determined by the microcontroller based on the current value of the output current (which is, for example, already digitally present in the microcontroller) and the digital voltage value (which is, for example, transmitted to the microcontroller via SPI). If the load behaves as an ohmic resistor (i.e., linear), one sampling point (including the current value and the associated digital voltage value) is sufficient. In the case of a non-linear resistor, multiple sampling points can be detected and the switching signal or the percentage value can be inferred.

[0025] The memory of the microcontroller has a data structure for distributing a first supply voltage for a pulse width.

[0026] The circuit may include a second DC transformer supplied with a second supply voltage, wherein the second DC transformer is integrated in a digital-to-analog converter and is arranged to generate a third supply voltage for a current output driver, and wherein the microcontroller is arranged to set the third supply voltage via a digital interface based on the voltage and the output current at the current output.

[0027] The first and third supply voltages may have different signs. For example, the first supply voltage may be a negative voltage and the third supply voltage may be a positive voltage.

[0028] The microcontroller and the first DC transformer may be electrically isolated.

[0029] The microcontroller and the current output driver may be electrically isolated.

[0030] The microcontroller may be arranged to receive process data via a bus interface and to derive the current value to be output at the current output from the process data.

[0031] Here, it is to be understood that the steps performed by the circuit may be understood as steps of a corresponding method implemented in the case of using the circuit, and vice versa. Description of the Drawings

[0032] The invention is subsequently explained in detail by means of embodiments, wherein, with reference to the drawings, in which:

[0033] Figure 1 a block diagram of a circuit according to the invention is shown;

[0034] Figure 1a and Figure 1b shows Figure 1 the output voltage and the first supply voltage in;

[0035] Figure 1c and Figure 1d shows a possible determination of the first supply voltage and the third supply voltage;

[0036] Figure 2 shows Figure 1 a modification of the circuit according to the invention shown in;

[0037] Figure 2a and Figure 2b shows Figure 2 the output voltage and the first supply voltage in;

[0038] Figure 3 shows Figure 2A modification of the circuit according to the invention as shown;

[0039] Figure 3a and Figure 3b shows Figure 3 the output voltage, the first supply voltage and the third supply voltage in;

[0040] Figure 4 shows Figure 3 a modification of the circuit according to the invention as shown in;

[0041] Figure 4a and Figure 4b shows Figure 4 the output voltage, the first supply voltage and the third supply voltage in;

[0042] Figure 5 shows the structure of a modular fieldbus node in which the circuit is used;

[0043] Figure 6 schematically shows the structure of a fieldbus system;

[0044] Figure 7 shows a flow chart which shows the application of the circuit according to the invention.

[0045] Here, the same or functionally similar elements are denoted by the same reference numerals in the figures. Detailed Description

[0046] Figure 1 Shows a circuit 100 having a microcontroller 300 and a digital-to-analog converter 400. The digital-to-analog converter 400 has a current output driver 430 for outputting an output current to a load 500. The microcontroller 300 is connected to the digital-to-analog converter 140 via a digital interface 420 and thereby sets the output current I of the digital-to-analog converter 400. The digital-to-analog converter 400 has an analog-to-digital converter 410 and converts an output voltage V2 into a digital voltage value Vdig by means of the analog-to-digital converter 410, and this digital voltage value is transmitted to the microcontroller 300 via the digital interface 420.

[0047] The circuit 100 further includes a first DC transformer 200 which generates a first supply voltage V1 for supplying the current output driver 430 of the digital-to-analog converter 400. The microcontroller 300 is connected to the first DC transformer 200 via a control interface 310 and derives a control signal S from the output current I and the digital voltage value Vdig, and this control signal is output to the first DC transformer 200 via the control interface 310 for setting the first supply voltage V1.

[0048] If the microcontroller 300 is activated, the microcontroller sends an instruction for outputting a current I to the digital-to-analog converter 400. The output voltage V2 (the voltage across the resistor RL) can be read back as a digital voltage value Vdig via the analog-to-digital converter 410 and a digital interface (such as a Serial Peripheral Interface, SPI). The microcontroller 300 can calculate the value of the resistor RL of the load 500 from the measured value Vdig of the output voltage V2 and the known output current I (RL = Vdig / I). Then, with the resistor value RL and the (current) output range A with a minimum current value Imin and a maximum current value Imax, a first supply voltage V1 can be set based on the minimum current value Imin and / or the maximum current value Imax.

[0049] For example, the required minimum negative first supply voltage V1 (e.g., V1 = (RL × Imin) - 2.5 V)) can be set via the PWM of the first DC transformer 200. For this purpose, the memory of the microcontroller 300 has a data structure that assigns the first supply voltage V1 to a pulse width. The bias voltage Voff of 2.5 volts can be adjusted according to time values and / or measured values. This is advantageous especially when a capacitor or an inductor acts on the output of the circuit 100, for example.

[0050] Thus, it can be ensured that the set first supply voltage V1 for a determined resistor value RL is valid over the entire current output range A to be used. At the same time, the power loss is significantly reduced by the lower negative first supply voltage V1. Since the resistor value RL does not change during continuous operation, the calculation and setting of the negative first supply voltage V1 are only required once when the microcontroller 300 is activated or after a diagnosis is established or after the current output range A is changed. As shown in Figure 1a and Figure 1b it can be seen that the first supply voltage V1 can be adjusted according to the output voltage V2, so that the power loss can be reduced.

[0051] As shown in Figure 1c it can be seen that the first supply voltage V1 can be set to the maximum voltage value Vmax at the beginning and, after receiving the process data 800, if the output current I predetermined by the process data 800 is within the output range A, the first supply voltage is set according to the formula F using the output current I as the input variable E and the digital voltage value Vdig.

[0052] To prevent incorrect setting due to inaccurate digitization of the output voltage V2, it can be stipulated that the first supply voltage V1 is set based on the output current I only when the output current I included in the process data 800 is within a predetermined current range IB or the minimum value is, for example, > 1 mA. Alternatively, it can be stipulated that, as shown in Figure 1dAs shown, the first supply voltage V1 is set based on the output current I only when the voltage value Vdig of the digit is within a pre-determined voltage value range VB.

[0053] A (long-term) change in the resistance RL of the load 500 (e.g., caused by aging of components) can be compensated for by adjusting the control signal S for setting the first supply voltage V1 based on the current output voltage V2 after a specific time and outputting the adjusted control signal S to the first DC transformer 200 via the control interface 310, so that the newer control signal S replaces the old control signal S.

[0054] As shown in Figure 2 , Figure 2a and Figure 2b shown, the microcontroller 300 and the first DC transformer 200 can be electrically isolated. In addition, the microcontroller 300 and the current output driver 430 are electrically isolated.

[0055] As Figure 3 shown, the circuit 100 includes a second DC transformer 440, which is supplied with a second supply voltage V4. The second DC transformer 440 can be integrated in the digital-to-analog converter 400 and generates a third supply voltage V3 for the current output driver 430. The microcontroller 300 can set the third supply voltage V3 based on the output voltage V2 of the output current I via the digital interface 420. As shown in Figure 3a and Figure 3b shown, the first supply voltage V1 can be a negative voltage and the third supply voltage V3 can be a positive voltage. For example, the load 500 can be replaced with another load 500 during a use pause, and the other load does not require a positive output current I but a negative output current I.

[0056] As shown in Figure 4 shown, the microcontroller 300 can be set to receive process data 800 via a communication unit 700 (e.g., a bus interface) and derive the current value to be output at the current output terminal from the process data 800.

[0057] Figure 5There is shown an exemplary modular fieldbus node 40, including a front end 110 and two modules 100a and 100b connected in series to the front end 110, with a sensor 500a or an actuator 500b connected to the modules. The sensor 500a and / or the actuator 500b can be individually supplied with a corresponding output voltage V2 through circuits 100 provided in the respective modules 100a, 100b. Here, it is to be understood that the modules 100a, 100b can be modified such that multiple sensors 500a and / or actuators 500b can be connected to the modules, and one or more of the sensors 500a and / or actuators 500b are individually supplied with a correspondingly adjusted output voltage V2 through the respective circuits 100.

[0058] During operation, the module 100a supplying the sensor 500a with the output voltage V2 reads in the sensor signal through a separate signal line and generates status data from the sensor signal, and transmits the status signal to the front end 110 through the local bus 120. The front end 110 can locally process the status data and / or (possibly in a modified form) when the modular fieldbus node 40 is part of the fieldbus system 10 as Figure 6 shown, continue to transmit it to the superior unit 20 through the fieldbus 30. The superior unit 20 (or the front end 11 in the case of local processing) can generate control data considering the status data.

[0059] The fieldbus system 10 includes a plurality of fieldbus nodes 40, which are connected to the superior unit 20 through the (field) bus 30. The superior unit 20 can be used not only for monitoring but also for regulating the devices (not shown) monitored or controlled by the fieldbus system 10. When the superior unit 20 monitors the devices, the superior unit 20 can periodically or aperiodically receive status data (which then also becomes the input process image) from the fieldbus nodes 40, the status data describing the status of the devices and generating a fault signal or an alarm signal when the status of the devices deviates (substantially) from the desired / allowed status or status range. When the superior unit 20 (not only monitors but also) regulates the devices, the superior unit 20 can periodically or aperiodically receive status data from the fieldbus nodes 100 and determine the control data transmitted to the fieldbus nodes 40 considering the status data. The control data can be part of the process data.

[0060] Control data generated by the superior unit 20 can be transmitted via the (field) bus 30 to the (same or another) front end 110. The control data transmitted to the front end 110 (or generated by the front end 110) can (possibly in an improved form) continue to be transmitted to the module 100b. The module 100b receives the control data and outputs a control signal corresponding to the control data at the output connected to the actuator 500b. The data communication between the components of the field bus system 10 and the mapping of the sensor signals to the status data and the mapping of the control data to the control signals can be adapted to different usage scenarios by the configuration of the modules 100a and 100b. Within the scope of the said configuration, the minimum current value Imin and the maximum current value Imax can also be transmitted to the microcontroller 300, wherein the first supply voltage V1 and the third supply voltage V3 are set based on the minimum current value Imin and / or the maximum current value Imax.

[0061] Similarly, the voltage supplies of the sensor 500a and the actuator 500b can be individually adapted to the sensor 500a or the actuator 500b via the corresponding process data. Here, the process is shown in the Figure 7 flowchart. Once the power supply circuit 100 is provided, the initialization phase starts in step 910, in which the digital-to-analog converter 400 is configured for the current output range (for example, ±22 mA). Then, in step 920, the microcontroller 300 processes the process data 800 (which, for example, predetermines an output current I of -10 mA) and sends the corresponding control signal S (for example, via the serial peripheral interface, SPI) to the digital-to-analog converter 400.

[0062] Then, the microcontroller 300 requests the output voltage V2 in step 930. If the load 500 (or rather the sensor 500a, actuator 500b) produces a resistance of, for example, 200 Ω, the value is measured as V2 = 10 mA × 200 Ω = 2 V and transmitted to the microcontroller 300 as the digital voltage value Vdig. The microcontroller 300 can perform the resistance calculation (RL = Vdig / 10 mA = 200 Ω) and determine the required negative minimum first supply voltage of the current output driver 430 (V1 = (-22 mA × 200 Ω) - 2.5 V = -6.9 V) (the current output driver 430 may, for example, require a constant minimum voltage of -2.5 V to operate within a specific range). The calculated minimum supply voltage (-6.9 V) can be assigned to the empirically determined and stored PWM value in the list. The aforementioned value (for example, PWM = 7%) can be transmitted to the first DC transformer 200, whereby the first supply voltage V1 is adjusted in step 940. The method can also be used to generate the positive third supply voltage V3.

[0063] In the above example, the power loss of the current output driver is, for example, (6.9 V - (200 Ω × 10 mA)) × 10 mA = 49 mW. Without adjusting the negative current driver power, the power loss of the current output driver is (16 V - (200 Ω × 10 mA)) × 10 mA = 140 mW, which is significantly higher. For further operation with a resistance value of 200 Ω, the 6.9 V remains unchanged because the negative supply voltage is set for a maximum current of -22 mA. Only when there is a possibility of rewiring and thus also a change in the resistance value due to a restart or a broken wire, is it necessary to recalculate the resistance RL and the negative first supply voltage V1.

[0064] List of reference numerals

[0065] 10 Fieldbus system

[0066] 20 Higher-level control unit

[0067] 30 Bus

[0068] 40 Modular fieldbus node

[0069] 100 Circuit

[0070] 100a I / O module (including circuit)

[0071] 100b I / O module (including circuit)

[0072] 110 Front end

[0073] 120 Fieldbus

[0074] 200 DC transformer

[0075] 300 Microcontroller

[0076] 310 Control interface

[0077] 400 Digital-to-analog converter

[0078] 410 Analog-to-digital converter

[0079] 420 Communication interface

[0080] 430 Current output driver

[0081] 440 DC transformer

[0082] 500 Load

[0083] 500a Sensor

[0084] 500b Actuator

[0085] 610 Electrical isolation

[0086] 620 Electrical isolation

[0087] 700 Communication unit (e.g., bus interface)

[0088] 800 Process data

[0089] 910 Step

[0090] 920 Step

[0091] 930 Step

[0092] 940 Step

[0093] A Output range

[0094] E Input variable

[0095] F Function

[0096] I Output current

[0097] IB Current range

[0098] S Control signal

[0099] V1 First supply voltage

[0100] V2 Output voltage

[0101] V3 Third supply voltage

[0102] Vdig Digital voltage value

[0103] VB Voltage value range

Claims

1. A circuit (100) for an I / O module, comprising: A communication unit (700) for receiving process data (800), the communication unit being connectable to a bus (30) for communication; A microcontroller (300), the microcontroller being connected to the communication unit (700); A load (500); A digital-to-analog converter (400), the digital-to-analog converter having a current output driver (430) for outputting an output current to the load (500); and A first DC transformer (200); Wherein, the microcontroller (300) is connected to the digital-to-analog converter (400) through a digital interface (420); Wherein, the microcontroller (300) is configured to set the output current (I) of the digital-to-analog converter (400) based on the received process data (800) through the digital interface (420); Wherein, the digital-to-analog converter (400) has an analog-to-digital converter (410) and is configured to convert an output voltage (V2) into a digital voltage value by means of the analog-to-digital converter (410) and transmit it to the microcontroller (300) through the digital interface (420); Wherein, the microcontroller (300) is connected to the first DC transformer (200) through a control interface (310); Wherein, the first DC transformer (200) is configured to generate a first supply voltage (V1) for supplying the current output driver (430) of the digital-to-analog converter (400); Wherein, the microcontroller (300) is configured to output a control signal (S) for setting the first supply voltage (V1) to the first DC transformer (200) through the control interface (310) based on the output current (I) and the digital voltage value (Vdig).

2. The circuit (100) according to claim 1, Among them, The microcontroller (300) is further configured to: Store an output range (A) having a minimum current value (Imin) and a maximum current value (Imax) received through the communication unit (700), And set the first supply voltage (V1) based on the minimum current value (Imin) and / or the maximum current value (Imax).

3. The circuit (100) according to claim 1 or 2, Among them, The microcontroller (300) is further configured to set the first supply voltage (V1) to a maximum voltage value (Vmax) at the beginning and set the first supply voltage (V1) based on the output current (I) and the digital voltage value (Vdig) after receiving the process data (800).

4. The circuit (100) according to claim 1 or 2, Among them, The microcontroller (300) is further configured to set the first supply voltage (V1) based on the output current (I) when the output current (I) included in the process data (800) is within a predetermined current range (IB).

5. The circuit (100) according to claim 1 or 2, Among them, The microcontroller (300) is further configured to set the first supply voltage (V1) based on the output current (I) when the digital voltage value (Vdig) is within a pre-determined voltage value range (VB).

6. The circuit (100) according to claim 1 or 2, Among them, The microcontroller (300) is further configured to set the first supply voltage (V1) by means of a function (F), wherein the function (F) has a maximum current value (Imax), an output current (I), and a digital voltage value (Vdig) as input variables (E).

7. The circuit (100) according to claim 1 or 2, Among them, The microcontroller (300) is further configured to set the first supply voltage (V1) by means of a function (F), wherein the function (F) is: V1 = Imax × Vdig / I + Voff where Imax is the maximum current value, V1 is the first supply voltage (V1), Vdig is the digital voltage value (Vdig), I is the output current (I), and Voff is the bias voltage.

8. The circuit (100) according to claim 7, Among them, The microcontroller (300) is further configured to additionally set the first supply voltage (V1) based on the bias voltage (Voff), wherein the microcontroller (300) is further configured to adjust the bias voltage (Voff) according to a time value and / or a measured value.

9. The circuit (100) according to claim 1 or 2, Among them, The microcontroller (300) is configured to determine a control signal (S) for setting the first supply voltage (V1) multiple times and output it to the first DC transformer (200) through the control interface (310), wherein the determination is made for two temporally spaced measurements of the output voltage (V2).

10. The circuit (100) according to claim 1 or 2, Among them, The microcontroller (300) is further configured to re-determine the first supply voltage (V1) of the first DC transformer (200) when the circuit (100) is accessed.

11. The circuit (100) according to claim 1 or 2, Among them, The microcontroller (300) is further configured to generate a control signal for controlling the first DC transformer (200); and / or wherein the microcontroller (300) is further configured to set the first supply voltage (V1) by means of pulse width modulation of the control signal.

12. The circuit (100) according to claim 11, Among them, The memory of the microcontroller (300) has a data structure that assigns the first supply voltage (V1) to a pulse width.

13. The circuit (100) according to claim 1 or 2, further comprising: A second DC transformer (440) supplied with a second supply voltage. Wherein, the second DC transformer (440) is integrated in the digital-to-analog converter (400) and is configured to generate a third supply voltage (V3) for the current output driver (430); Wherein, the microcontroller (300) is configured to set the third supply voltage (V3) based on the voltage (V2) at the current output terminal and the output current via the digital interface (420).

14. The circuit (100) according to claim 13, Among them, The first supply voltage (V1) is a negative voltage and the third supply voltage (V3) is a positive voltage.

15. The circuit (100) according to claim 1 or 2, Among them, The microcontroller (300) is electrically isolated from the first DC transformer (200).

16. The circuit (100) according to claim 1 or 2, Among them, The microcontroller (300) is electrically isolated from the current output driver (430).

17. The circuit (100) according to claim 1 or 2, Among them, The microcontroller (300) is configured to receive process data via a bus interface and derive the current value to be output at the current output terminal from the process data.

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