Voltage-limiting circuit and field device comprising such a voltage-limiting circuit
Patent Information
- Application Number
- EP2023833017
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-12-16
- Filing Date
- 2023-12-13
- Publication Date
- 2025-10-22
AI Technical Summary
Existing voltage limiting circuits for explosion protection in process automation, specifically those using triple limiting designs, have high space requirements and relatively high power consumption, which is inefficient for field devices in potentially explosive areas.
A voltage limiting circuit utilizing two monolithic voltage limiter modules in semiconductor technology, connected in shunt to a supply voltage source, with each module featuring a transistor, voltage divider, and freewheeling diode, designed to minimize space and power consumption while maintaining 'ia' level protection, achieving a footprint reduction and lower power usage.
The dual monolithic design significantly reduces the footprint and power consumption of the voltage limiting circuit, allowing for efficient operation within the 'ia' explosion protection class, with a power consumption of up to 1.4 W and a transistor temperature not exceeding 150°C, while maintaining effective voltage regulation and safety.
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Abstract
Description
[0001] Voltage limiting circuit and field device with such a voltage limiting circuit
[0002] The present invention relates to a voltage limiting circuit and a field device of process automation technology with such a voltage limiting circuit.
[0003] In process automation technology, field devices are often used to record and / or influence process variables. Sensors such as level gauges, flow meters, pressure and temperature gauges, pH redox potential meters, conductivity meters, etc. are used to record process variables and record the corresponding process variables: level, flow, pressure, temperature, pH value or conductivity. Actuators such as valves or pumps are used to influence process variables and can be used to change the flow of a liquid in a section of pipe or the fill level in a container. In principle, field devices are all devices that are used close to the process and that supply or process process-relevant information. In the context of the invention, field devices also include, in particular, remote I / Os, radio adapters and / orgenerally understood to mean devices that are arranged at the field level. Many field devices are available as so-called 2-wire devices. In this case, the field device is powered via the same cable pair (two-wire) as is used for communication, particularly of the measured values. In process automation technology, physical or technical quantities must often be measured or determined by the field devices in potentially explosive areas where there is a risk of explosion due to the process media. By taking suitable measures in the field devices and evaluation systems (such as voltage and current limitation), the electrical power of the signals to be transmitted can be limited so that they cannot trigger an explosion under any circumstances (short circuits, interruptions, thermal effects, etc.). Appropriate protection principles for this have been defined, for example, in IEC EN DIN 60079-ff.According to this standard, design and circuitry measures for field devices for use in potentially explosive atmospheres are defined based on the applicable types of protection. One of these types of protection is the "intrinsic safety" type of protection (marking Ex-i, IEC EN DIN 60079-11, published June 2012). The "intrinsic safety" type of protection is based on the principle of current and voltage limitation in an electrical circuit. The energy in the circuit that could ignite an explosive atmosphere is limited in such a way that neither sparks nor excessive heating of the electrical components can ignite the surrounding explosive atmosphere. The "intrinsic safety" type of protection defines three protection levels: Ex-ia, Ex-ib and Ex-ic.Level a is defined as the highest level at which two countable errors in combination must not lead to a malfunction and thus cause ignition (2-fault safety). Level b defines that one countable error must not lead to a malfunction and thus cause ignition (1-fault safety). Correspondingly, no fault safety is defined at level c, so that even a malfunction can cause ignition (0-fault safety). Circuitry measures to achieve intrinsic safety generally include current limitation, voltage limitation and the associated power limitation, whereby this is usually achieved by limiting circuits with a triple design. Such voltage limiting circuits are disclosed, for example, in DE 10 2006 056 591 A1.
[0004] The disadvantage of triple-circuit limiting circuits is, on the one hand, their increased space requirement and, on the other hand, their relatively high power consumption. The object of the present invention is to remedy this.
[0005] The object is achieved according to the invention by the voltage limiting circuit according to claim 1 and the field device according to claim 10.
[0006] The voltage limiting circuit according to the invention is a voltage limiting circuit for ignition protection type “ia” with exactly two monolithic voltage limiter modules, wherein the voltage limiter modules each have: a supply voltage connection; a circuit ground connection; a voltage divider for providing a divider voltage, wherein the voltage divider is arranged between the supply voltage connection and circuit ground; a regulator with a regulator signal output for outputting a regulator signal;an actuator with an actuator signal input and a current channel whose resistance value depends on the controller signal applied to the actuator signal input, wherein the current channel runs parallel to the voltage divider between the supply voltage connection and circuit ground, wherein an input of the controller is supplied with the divider voltage of the voltage divider, wherein the controller signal output is connected to the actuator signal input, wherein in particular both voltage limiter modules are to be arranged with their supply voltage connection and their circuit ground connection in shunt connection to a supply voltage source;
[0007] In one embodiment of the invention, the actuator comprises a transistor, wherein the actuator signal input comprises a base terminal of a bipolar transistor or a gate terminal of a field-effect transistor. In one embodiment of the invention, the voltage limiter modules each further comprise a freewheeling diode connected in parallel with the current channel of the actuator.
[0008] In a further development of the invention, the controller comprises an operational amplifier and a reference voltage source, in particular a bandgap voltage reference, wherein a first input of the operational amplifier is supplied with the divider voltage of the voltage divider, wherein a second input of the operational amplifier is connected to the reference voltage source, and wherein an output of the operational amplifier is the controller signal output.
[0009] In a further development of the invention, the voltage limiter modules each further comprise a resistance element arranged between the controller signal output and the supply voltage connection.
[0010] In a further development of the invention, the voltage limiter modules each have a base area of no more than 18 mm 2 in particular not more than 12 mm 2 on.
[0011] In a further development of the invention, the actuators have the largest area share of all the functional elements of the voltage limiter modules mentioned.
[0012] In a further development of the invention, transistors of the voltage limiter modules each have a barrier layer, wherein the barrier layers have a temperature of not more than 150 °C at an ambient temperature of the voltage limiting circuit of up to 85 °C and a power consumption of the voltage limiter modules of up to 1.4 W each.
[0013] In a further development of the invention, the transistors of the voltage limiter modules each have a barrier layer, wherein the barrier layer has a power-dependent temperature increase of not more than 60 °C / W, in particular not more than 45 °C / W, at an ambient temperature of the voltage limiting circuit of up to 85 °C and a power consumption of the voltage limiter modules of up to 1.4 W.
[0014] The process automation field device according to the invention comprises: a sensor; a measuring and operating circuit for operating the sensor and for processing signals from the sensor; and a supply circuit comprising a supply voltage source for supplying the measuring and operating circuit, and a voltage limiting circuit according to one of the preceding claims, wherein the voltage limiter modules are connected in shunt to the supply voltage source. The invention will now be explained in more detail with reference to the exemplary embodiments illustrated in the drawings. It shows:
[0015] Fig. 1 : a schematic representation of a field device with a voltage regulator circuit according to the prior art;
[0016] Fig. 2: a schematic representation of an embodiment of a field device according to the invention with a first embodiment of a voltage regulator circuit according to the invention; and
[0017] Fig. 3: a schematic representation of an embodiment of a field device according to the invention with a second embodiment of a voltage regulator circuit according to the invention.
[0018] The prior art field device shown in FIG. 1 comprises a supply circuit 150, a voltage limiting circuit 140, a measuring and operating circuit 170, and a sensor 180 operated by the measuring and operating circuit 170, which receives and processes measurement signals from the sensor 180. The voltage limiting circuit 140 comprises three discretely constructed voltage limiter modules 140a, 140b, 140c, which are connected to a supply voltage terminal 152 of the supply circuit 150 in shunt connection to the measuring and operating circuit. The discrete structure of the voltage limiter modules requires a triple design in order to comply with explosion protection class “ia”. The voltage limiter modules 140a, 140b, 140c each comprise a transistor 145a, 145b, 145c as an actuator, the current channel of which runs between the supply voltage connection 152 and circuit ground.A supply voltage whose base is connected via a resistor element 160a, 160b, 160c to the output of a regulator 148a, 148b, 148c, which here has a controllable voltage source 142a, 142b, 142c. A control signal for the voltage source is provided by the output or center tap of a voltage divider 146a, 146b, 146c. The voltage limiting circuit 140 fulfills its purpose, but is disadvantageous in that the discretely constructed voltage limiter modules 140a, 140b, 140c each have an area of 36 mm. 2 to a large total space requirement of 108 mm 2 In addition, the resistance elements 160a, 160b, 160c contribute to limiting the base current of the transistors 145a, 145b, 145c and the power consumption of the voltage limiting circuit 140.
[0019] The present invention is based on Section 7.5.2 "Shunt Voltage Limiter Circuits" of the IEC EN DIN 60079-11 standard, published in June 2012, which states that a dual voltage limiter circuit design is acceptable if it comprises two monolithic voltage limiter modules, each implemented entirely in semiconductor technology. This minimizes both the space requirement and the power consumption of the voltage limiter circuit.
[0020] The exemplary embodiment of a field device 1 according to the invention with a voltage limiting circuit 40 according to the invention shown in FIG. 2 comprises a supply circuit 50, a voltage limiting circuit 40, a measuring and operating circuit 70, and a sensor 80 operated by the measuring and operating circuit 70, the latter receiving and processing measurement signals from the sensor 80. The voltage limiting circuit 40 comprises only two monolithic semiconductor voltage limiter modules 40a, 40b, which are connected in shunt to the measuring and operating circuit to a supply voltage terminal 52 of the supply circuit 50. The monolithic implementation of the voltage limiter modules enables a dual design to comply with explosion protection class "ia."The voltage limiter modules 40a, 40b each comprise a transistor 45a, 45b as an actuator, whose current channel is shunted between the supply voltage terminal 52 and circuit ground, and whose base is connected to the output of a regulator 48a, 48b, which in this case has an adjustable shunt voltage regulator 42a, 42b. A control signal for the shunt voltage regulator is provided by the output or center tap 47a, 47b of a voltage divider 46a, 46b, which is also shunted between the supply voltage and circuit ground. If the voltage rises above a setpoint, the current flow through the transistor 45a, 45b is increased by controlling the base of the transistor until the voltage is reduced to the setpoint again.
[0021] The voltage limiter modules 40a, 40b are designed such that, at a power consumption of 1.4 W, which corresponds to 1.5 times the maximum possible power to be handled, and at an ambient temperature of 85 °C, the junction of the transistor does not exceed a temperature of 150 °C. Furthermore, the voltage limiter modules 40a, 40b are designed such that the current channel can carry a current of 150 mA, which corresponds to 1.5 times the maximum possible current. This is achieved in particular by the fact that the transistors 45a, 45b each have a relatively large area share of the total area of a voltage limiter module 40a, 40b. The voltage limiter modules 40a, 40b can each have a base area of 9 mm 2 Since only two such voltage limiter modules are required, the entire voltage limiting circuit 40 has a footprint of only 18 mm 2, which corresponds to approximately one-sixth of the footprint of a discrete voltage limiting circuit according to the prior art. The voltage limiter modules also each include a freewheeling diode 60a, 60b to absorb voltage surges of opposite sign to the supply voltage, for example, due to inductances.
[0022] The exemplary embodiment of a field device 201 according to the invention with a voltage limiting circuit 240 according to the invention, shown in FIG. 3, comprises a supply circuit 250, a voltage limiting circuit 240, a measuring and operating circuit 270, and a sensor 280 operated by the measuring and operating circuit 270, the latter receiving and processing measurement signals from the sensor 280. The voltage limiting circuit 240 comprises only two monolithic semiconductor voltage limiter modules 240a, 240b, which are connected in shunt to the measuring and operating circuit to a supply voltage terminal 252 of the supply circuit 250. The monolithic implementation of the voltage limiter modules enables a dual design to comply with explosion protection class "ia."The voltage limiter modules 240a, 240b each comprise a field-effect transistor 245a, 245b as an actuator, whose current channel is shunted between the supply voltage terminal 252 and circuit ground, and whose gate is connected to the output of a regulator 248a, 248b, which here has an operational amplifier 242a, 242b. An input signal for a first input of the operational amplifier is provided by the output or center tap 247a, 247b of a voltage divider 246a, 246b, which is also shunted between the supply voltage and circuit ground. A voltage reference signal 244a, 244b is present at the second input of the operational amplifier 248a, 248b, which is provided in particular by a bandgap voltage reference.In case the voltage rises above a set value, the current flow via the field effect 245a, 245b is increased by driving the gate of the transistor until the voltage is reduced again to the set value.
[0023] The voltage limiter modules 240a, 240b are designed such that, at a power consumption of 1.4 W, which corresponds to 1.5 times the maximum possible power to be handled, and at an ambient temperature of 85°C, the junction of the transistor does not exceed a temperature of 150°C. Furthermore, the voltage limiter modules 240a, 240b are designed such that the current channel can carry a current of 150 mA, which corresponds to 1.5 times the maximum possible current. This is achieved in particular by the fact that the transistors 245a, 245b each comprise a relatively large area proportion of the total area of a voltage limiter module 240a, 240b.
[0024] The voltage limiter modules 240a, 240b can each have a base area of 9 mm 2 Since only two such voltage limiter modules are required, the entire voltage limiting circuit 240 has a footprint of only 18 mm 2 , which corresponds to approximately one-sixth of the footprint of a prior art voltage limiting circuit. The voltage limiter modules also each include a freewheeling diode 260a, 260b to absorb voltage surges of opposite sign to the supply voltage, for example, due to inductances.
Claims
Patent claims 1. A voltage limiting circuit (1; 201) for ignition protection type "ia" with exactly two monolithic voltage limiter modules (40a, 40b; 240a, 240b), wherein the voltage limiter modules (40a, 40b; 240a, 240b) each have: a supply voltage connection (52; 252); a circuit ground connection; a voltage divider (46a, 46b; 246a, 246b) for providing a divider voltage, wherein the voltage divider (46a, 46b; 246a, 246b) is arranged between the supply voltage connection and circuit ground; a regulator (48a, 48b; 248a, 248b) with a regulator signal output for outputting a regulator signal; an actuator (45a, 45b; 245a, 245b) having an actuator signal input and a current channel whose resistance value depends on the controller signal applied to the actuator signal input, wherein the current channel runs parallel to the voltage divider between the supply voltage connection and circuit ground, wherein an input of the controller (48a, 48b;248a, 248b) is supplied with the divider voltage of the voltage divider (46a, 46b; 246a, 246b), wherein the control signal output is connected to the actuator signal input, wherein in particular both voltage limiter modules (40a, 40b; 248a, 248b) are to be arranged with their supply voltage connection (252) and their circuit ground connection in shunt connection to a supply voltage source (250); 2. Voltage limiting circuit according to claim 1, wherein the actuator comprises a transistor, wherein the actuator signal input comprises a base terminal of a bipolar transistor or a gate terminal of a field effect transistor.
3. Voltage limiting circuit according to claim 1 or 2, wherein the voltage limiter modules each further comprise a freewheeling diode connected in parallel to the current channel of the actuator.
4. Voltage limiting circuit according to claim 1, 2 or 3, wherein the regulator comprises an operational amplifier and a reference voltage source, wherein a first input of the operational amplifier is supplied with the divider voltage of the voltage divider, wherein a second input of the operational amplifier is connected to the Reference voltage source is connected, and one output of the operational amplifier is the control signal output.
5. Voltage limiting circuit according to claim 1 or 2, wherein the voltage limiter modules each further comprise a resistance element arranged between the regulator signal output and the supply voltage terminal.
6. Voltage limiting circuit according to one of the preceding claims, wherein the voltage limiter modules each have a base area of not more than 18 mm 2 in particular not more than 12 mm 2 have.
7. Voltage limiting circuit according to claim 6, wherein the actuators have the largest area share of all said functional elements of the voltage limiter modules.
8. Voltage limiting circuit according to one of the preceding claims, wherein the transistors of the voltage limiter modules each have a barrier layer, wherein the barrier layers have a temperature of not more than 150 °C at an ambient temperature of the voltage limiting circuit of up to 85 °C and a power consumption of the voltage limiter modules of up to 1.4 W.
9. Voltage limiting circuit according to one of the preceding claims, wherein the transistors of the voltage limiter modules each have a barrier layer, wherein the barrier layer has a power-dependent temperature increase of not more than 60 °C / W, in particular not more than 45 °C / W, at an ambient temperature of the voltage limiting circuit of up to 85 °C and a power consumption of the voltage limiter modules of up to 1.4 W.
10. A field device for process automation technology, comprising: a sensor; a measuring and operating circuit for operating the sensor and for processing signals from the sensor; and a Supply circuit comprising a supply voltage source for supplying the measuring and operating circuit, and a voltage limiting circuit according to one of the preceding claims, wherein the voltage limiter modules are connected in shunt to the supply voltage source.