Circuit and system for adjusting a coil current

Abstract

Circuit (10) for adjusting a current (I) through a coil (1) for a solenoid valve, comprising: - a control input (10a) for receiving a control signal (PWM) and a control output (10b) for connection to a first electrode of the coil (1), - a first and second supply terminal (11a, 11b) for connection to a first voltage source (V1), - a flip-flop (5) with a data input (D), a clock input (CLK), a flip-flop output (Q) and a reset input (R), - a comparator unit (7) with an inverting comparator input (8a), a non-inverting comparator input (8b), and an output electrode (7a), - a switching element (T1) with a control electrode (T1G), a drain electrode (T1D) and a source electrode (T1S) and - a measuring resistor (R_Sens), wherein - the flip-flop (5) with its clock input (CLK) is connected to the control input (10a),with its data input (D) and its reset input (R) to the output electrode (7a) and with its flip-flop output (Q) to the control electrode (T1G),- the comparator unit (7) with its non-inverting comparator input (8b) to the control input (10a) and with its inverting comparator input (8a) to the source electrode (T1S),- the switching element (T1) with its outflow electrode (T1D) to the control output (10b) and with its source electrode (T1S) via the measuring resistor (R_Sens) to the second supply terminal (11b), and- the first supply terminal (11a) is provided for connection to a second electrode of the coil (1), wherein the circuit further comprises a first optocoupler (9a) which, on the input side, receives an external PWM control signal (PWM) and, on the output side, outputs the control signal at the control input (PWM) is set up.

Description

The coil current I (Fig. 1 bottom) in a solenoid valve is often adjusted by pulse-width modulation of the supply (Fig. 1 top). The valve coil 1 (Fig. 2) is periodically connected (period TPMW) to and disconnected from a supply voltage V1. This is achieved using a switching element, e.g., a transistor T1. In the connected state (state PWM_1), the coil current I increases steadily with time t; in the disconnected state (state PWM_2), it decreases steadily. A diode D1 allows current to continue flowing when transistor T1 is switched off. By changing the ratio of on-time to off-time (duty cycle), the value of the coil current I can be changed / adjusted. The PWM control signal for transistor T1 is generated, for example, using a microcontroller 3, which outputs a frequency signal with a variable duty cycle (PWM signal) via a digital output 3a. This is the reference input in the current controller. Furthermore, a level conversion of the microprocessor's digital output signal (e.g. 0 / 5 V) to the PWM control signal with an amplitude level suitable for controlling transistor T1 can be provided (not shown). For current control, the coil current I must also be measured and compared to a setpoint. This measurement is performed, for example, via the voltage drop across the current-sense resistor R_Sense. The (analog) measured value of the voltage applied to input 3b of the microcontroller 3, which is representative of the coil current I given a known current-sense resistor R_Sense, is acquired via an analog-to-digital converter (ADC) in the microcontroller 3. A software control algorithm compares the digitized actual value of the coil current I with a setpoint and modifies the duty cycle of the PWM control signal so that the actual value and the setpoint are as close as possible. Compared to linear control with a variable or controllable resistor inserted in series with coil 1 in the circuit, the system and circuit shown in Fig. 2 achieve a relatively high efficiency. In an electric or hybrid vehicle, there are usually at least two separate voltage systems; for example, the common 12 V on-board electrical system and a high-voltage (HV) system with, for example, 300 V for the drive system. If microcontroller 3 and the solenoid valve (with its power supply) are located in different voltage systems, the reference signal from microcontroller 3 to transistor T1 and the measured value from the valve back to microcontroller 3 must be transmitted across the potential boundaries. Isolation transformations used for this purpose in the analog domain are expensive and unsuitable for converting a DC voltage measurement back to the other voltage. German patent application DE 10 2007 006 179 A1 relates to a circuit arrangement for operating an inductive load, in particular a solenoid valve of a fuel injection system of an internal combustion engine. The circuit arrangement comprises current-supplying means for energizing the load, which are configured to apply a first operating voltage to the load during a first operating phase and to apply a second operating voltage, which is lower than the first operating voltage, intermittently to the load during a subsequent second operating phase. Furthermore, the circuit arrangement comprises control means for controlling the intermittent operation of the current-supply means during the second operating phase in order to set a desired load current by appropriately switching the second operating voltage on and off at the load.Furthermore, the circuit arrangement includes monitoring means for monitoring the achievement of the desired load current during the second operating phase, as well as adjustment means for adjusting the second operating voltage based on the result of the monitoring. German patent application DE 35 29 742 A1 relates to a device for regulating the current through an inductive load, in particular a control valve, comprising a current measuring device and a switching device in the load circuit, a current comparator, and a constant frequency clock generator. The switching device can be switched on by the constant frequency clock generator and switched off by the output signal of the comparator. It is an object of the present invention to provide a circuit and a system for adjusting a current through a coil for a solenoid valve, which allows reliable operation in a system with different voltage networks. The problem is solved by the subject matter of claim 1. Advantageous embodiments are characterized in the dependent claims. The invention relates to a circuit for adjusting the current through a coil for a solenoid valve. The circuit comprises a control input for receiving a control signal and a control output for connection to a first electrode of the coil. Furthermore, the circuit includes a first and second supply terminal for connection to a first voltage source, as well as a flip-flop with a data input, a clock input, a flip-flop output, and a reset input. The circuit also includes a comparator unit with a non-inverting comparator input, an inverting comparator input, and an output electrode. In addition, the circuit includes a measuring resistor and a switching element, in particular a transistor such as a MOSFET, for example, a normally-off n-channel MOSFET, wherein the switching element has a control electrode, a discharge electrode, and a source electrode. The flip-flop is coupled to the control input of the circuit via its clock input, specifically directly connected. The flip-flop is further coupled to the output electrode of the comparator unit via its data input. Its reset input is also coupled to the output electrode of the comparator unit via its reset input, specifically directly connected. Finally, its flip-flop output is coupled to the control electrode of the switching element via its control electrode, specifically directly connected. The comparator unit is coupled to the control input of the circuit via its non-inverting comparator input. Furthermore, the comparator unit is coupled to the source electrode of the switching element via its inverting comparator input. The switching element is coupled to the control output of the circuit via its outflow electrode, in particular directly connected. Furthermore, the switching element is coupled to the second supply terminal of the circuit via the measuring resistor via its source electrode, in particular directly connected to the second supply terminal of the circuit via the measuring resistor. The first supply connection of the circuit is ultimately intended for connection to a second electrode of the coil, in particular for direct connection. The fact that one element is coupled to another element includes both a direct or immediate electrical connection between the two elements and an indirect or mediated electrical connection between the two elements. The coil in question is, for example, the coil of a solenoid valve. In particular, it could be a proportional valve for the compressor of an air conditioning compressor, for example, in a motor vehicle. The reset input (also called "reset") of the flip-flop is specifically an inverted input, meaning the flip-flop is reset when a negative pulse is applied to the reset input. The flip-flop could, for example, be a type 74HC74 with inverted set and reset inputs. The comparator unit can advantageously have an open collector output. For example, the comparator unit is a type LM 393. The circuit further comprises a first optocoupler, which is configured on its input side to receive an external PWM control signal and on its output side to output the control signal at the control input of the circuit. In other words, an external control signal, in particular a PWM signal generated by a microcontroller, can be supplied to the circuit via the first optocoupler and made available at the control input, even across different potential boundaries of the external microcontroller and a power supply to the circuit. In an advantageous embodiment, the circuit according to the invention includes a third supply connection for connection to a second voltage source. The first and second voltage sources are, in particular, coupled together with the second supply connection. For example, the first voltage source is a 12 V vehicle electrical system and the second voltage source is a 5 V supply voltage derived from it. In a further advantageous embodiment, the circuit according to the invention comprises two first resistors and a first capacitor. The fact that there are two first resistors refers here and in the following only to a functional grouping of the two resistors; the two resistors may, in particular, have different parameters. In this configuration, the control input is coupled to the non-inverting comparator input via one of the first two resistors, in particular directly connected, while the first capacitor is connected in parallel with the other first resistor and couples the non-inverting comparator input to the second supply terminal, in particular directly connected. The first two resistors form a voltage divider; advantageously, a low-pass filter is implemented together with the first capacitor, the output of which is coupled to the non-inverting comparator input and which is configured to supply the averaged control signal applied to the control input as the reference voltage for the comparator unit. In a further advantageous embodiment, the circuit according to the invention further comprises a first diode that couples the control output of the circuit in the forward direction to the first supply terminal of the circuit, in particular directly. The first diode is provided, in particular, for a parallel connection with the coil in order to allow current flow when the switching element is blocked. In a further advantageous embodiment, the circuit according to the invention further comprises a second resistor and a second capacitor. The inverting comparator input is coupled to the source electrode of the switching element via the second resistor, in particular directly connected. The inverting comparator input is also coupled to the second supply terminal of the circuit via the second capacitor, in particular directly connected. Specifically, the second resistor and the second capacitor form a low-pass filter. This advantageously filters out voltage spikes when the switching element is switched, thus preventing faulty switching of the comparator unit. In a further advantageous embodiment, the circuit according to the invention further comprises a third resistor and a third capacitor. The output electrode of the comparator unit is coupled to the control input of the circuit via the third capacitor, which is connected in series with the third resistor. In particular, the output electrode is directly connected to the control input via a series circuit consisting of the third capacitor and the third resistor. In particular, the third resistor and the third capacitor form a differentiator.Advantageously, in this way, corresponding to a switching operation of the control signal at the control input of the circuit, in particular during a level change from high to low, a (negative) voltage pulse can be generated at the reset input of the flip-flop, by means of which the flip-flop can be reset, provided that this has not already been done by the signal output by the output electrode of the comparator unit. In a further advantageous embodiment, the circuit according to the invention further comprises a second diode that couples the output electrode of the comparator unit in the forward direction to the data input of the flip-flop, in particular directly connecting it. Advantageously, this allows a voltage pulse to be limited corresponding to a switching operation of the control signal at the control input of the circuit, in particular during a level change from low to high. In a further advantageous embodiment, the circuit according to the invention further comprises a fourth resistor that couples, in particular directly connects, the output electrode of the comparator unit to the data input of the flip-flop. Advantageously, the output electrode of the comparator unit can thus be brought to a high level at the data input of the flip-flop as long as the potential at the non-inverting comparator input is higher than at the inverting comparator input. In a further advantageous embodiment, the circuit according to the invention further comprises a third supply connection. The flip-flop has a set connection which is coupled to, and in particular directly connected to, the third supply connection of the circuit. Alternatively or additionally, the comparator unit comprises a comparator and an output transistor, in particular a bipolar transistor such as an NPN bipolar transistor. The comparator has a non-inverting comparator input and an inverting comparator input. Furthermore, the comparator has a first and second comparator supply connection and a comparator output. The output transistor is coupled to the comparator output of the comparator via its base electrode, in particular directly connected. Furthermore, the output transistor is coupled to the output electrode of the comparator unit via its collector electrode, in particular directly connected, and to the second comparator supply terminal of the comparator via its emitter electrode, in particular directly connected. Finally, the first comparator supply terminal of the comparator is coupled to the third supply terminal of the circuit, in particular directly connected. In a further advantageous embodiment, the circuit according to the invention further comprises a control terminal and a second optocoupler. The second optocoupler is coupled to the control electrode on its input side for receiving an internal control signal and is configured to output the control signal at the control terminal on its output side. In other words, an internal measured value, which is particularly representative of a PWM signal for controlling the switching element, can be provided at the control terminal of the circuit via the second optocoupler and supplied, for example, to an external control device such as the aforementioned microcontroller, across different potential boundaries of the external microcontroller and a power supply to the circuit. The invention also relates to a system comprising the circuit according to the invention, a microcontroller, a coil for a solenoid valve and a first and a further voltage source. The microcontroller is coupled to the control input, in particular via the first optocoupler. The microcontroller is configured to provide an external control signal at the control input. Furthermore, the coil is coupled with its first electrode to the control output of the circuit, in particular directly connected, and with its second electrode to the first supply terminal of the circuit, in particular directly connected. In addition, the first voltage source is coupled with one pole to the first supply terminal of the circuit, in particular directly connected, and with its second pole to the second supply terminal of the circuit, in particular directly connected. Finally, the microcontroller is coupled to the second voltage source for its supply. The first and subsequent voltage sources are specifically different voltage sources in separate voltage networks. For example, the first voltage source is a 12 V vehicle electrical system. The subsequent voltage source is, for example, a 300 V high-voltage network. Exemplary embodiments of the invention are explained in more detail below with reference to the schematic drawings. Figure 1 shows a control signal and a resulting coil current in a solenoid valve when the coil current is adjusted using a circuit according to Figure 2. Figure 2 shows a system with a circuit for adjusting the coil current for operation in a voltage network. Figure 3 shows a system with a circuit for adjusting the coil current for operation in different voltage networks. Figure 4 shows a control signal and a resulting coil current in a solenoid valve when the coil current is adjusted using a circuit according to Figure 3, as well as further signal waveforms within the circuit. Elements of the same construction or function are provided with the same reference symbols across all figures. Technical implementation The system 100 shown in Fig. 3 comprises a circuit 10 for adjusting a coil current I through a coil 1 of a solenoid valve for a motor vehicle and a microcontroller 3. The circuit 10 is connected via a first supply terminal 11a to a first terminal of a first voltage source V1. For example, the first voltage source V1 is a 12 V vehicle electrical system. The circuit 10 is also connected via a second supply terminal 11b to a second terminal of the first voltage source V1. This terminal is, for example, ground. A third supply terminal 11c of the circuit 10 is also connected to a terminal of a second voltage source V2. For example, the second voltage source V2 is a 5 V connection, which is taken directly from the first voltage source V1, for example via a linear regulator. The first and second voltage sources V1, V2 are assigned to a first voltage network N1. In contrast, the microcontroller 3 is connected to a second voltage network N2 for power supply, for example a 300 V high-voltage network, via a further voltage source (not shown in detail). The microcontroller 3 is connected via a digital output 3a to a first optocoupler 9a of the circuit 10, through which a pulse-width modulated control signal (PWM) is provided at the control input 10a of the circuit 10. Advantageously, this enables the coil current I to be adjusted across the different potential limits of the voltage networks N1 and N2. Circuit 10 comprises a transistor T1 as a switching element, a flip-flop 5, and a comparator unit 7 with a comparator 8 and an output transistor T2. A clock input CLK of flip-flop 5 is connected to the control input 10a of circuit 10. A flip-flop output Q of flip-flop 5 is connected to a control electrode T1G of transistor T1. A first diode D1 is connected in parallel to the coil 1 and couples a discharge electrode T1D of the transistor T1 in the forward direction with the first supply terminal 11a. A source electrode T1S of transistor T1 is coupled to the second supply terminal 11b via a measuring resistor R_Sens. The control input 10a is coupled to a non-inverting comparator input 8b of comparator 8 via a first resistor R1a. The non-inverting comparator input 8b is further coupled to the second supply terminal 11b via a parallel circuit consisting of another first resistor R1b and a first capacitor C1. This advantageously implements a low-pass filter that supplies the averaged PWM control signal to comparator 8 as a reference voltage Vref. An inverting comparator input 8a of comparator 8 is coupled to the source electrode T1S of transistor T1 via a second resistor R2 and to the second supply terminal 11b via a second capacitor C2. A low-pass filter formed by the second resistor R2 and the second capacitor C2 filters voltage spikes that occur when transistor T1 switches. This prevents faulty switching of comparator 8. A first comparator supply terminal 8c of comparator 8 is connected to the third supply terminal 11c, a second comparator supply terminal 8d of comparator 8 is connected to the second supply terminal 11b and to an emitter electrode T2E of output transistor T2. A comparator output 8e is connected to a base electrode T2B of output transistor T2, a collector electrode T2C of output transistor T2 is connected to output electrode 7a. The comparator 8 reacts to a peak value of a voltage representative of the coil current I, applied to the inverting comparator input 8a, not to its RMS value. However, with a suitable PWM control signal frequency, the resulting error is small or tolerable. Since only the aforementioned peak value is relevant, circuit 10 can be simplified such that transistor T1 switches relative to ground potential. It can therefore be driven directly from the flip-flop output Q, thus eliminating the need for the level shift mentioned in relation to Fig. 2, which is not shown in detail. A comparator unit 7 with an open-collector output, such as an LM393, can advantageously be used. As long as the potential at the non-inverting comparator input 8b is higher than at the inverting comparator input 8a, the output transistor T2 is switched off. The output electrode 7a is connected to the third supply terminal 11c via a resistor R4 and is thus at a high level. If the potential at the inverting comparator input 8a exceeds the potential at the non-inverting comparator input 8b, the output transistor T2 switches on and the output electrode 7a goes low. A 74HC74, for example, with inverted set and reset inputs S and R, can be used as flip-flop 5. A rising edge at the clock input CLK switches the level at the data input D to the flip-flop output Q. Flipflop 5 can be triggered as long as the inverted set and reset inputs S, R are high.By switching the reset input R to a low level, flip-flop 5 is reset to its initial state, and the flip-flop output Q is then low. Compared to circuit 10 according to Fig. 2, the current waveform differs due to the measuring resistor R_Sens, since current is only detected during the turn-on phase of transistor T1. The falling edge of the PWM control signal can also be used to control the reset input R of flip-flop 5. This ensures that transistor T1 is switched off at the latest when the high level ends within one TPMW period. This is achieved by means of a differentiator consisting of a third resistor R3 and a third capacitor C3 connected in series with it. This differentiator generates a short voltage pulse at the reset input R of flip-flop 5 for each switching operation of the PWM control signal. The differentiator is arranged to connect the control input 10a to the reset input R. The positive pulse generated when the PWM control signal changes from a low to a high level is limited by diode D2. The negative pulse generated when the PWM control signal changes from a high to a low level resets flip-flop 5, unless this has already been done by the signal provided by comparator unit 7. Furthermore, optional feedback of the signal output at the flip-flop output Q to the microcontroller 3 is possible. For this purpose, an analog-to-digital converter assigned to an input 3b of the microcontroller 3 is connected to a control terminal of the circuit 10. In this context, the circuit 10 also includes a second optocoupler 9b, which is connected on its input side via a terminal 10c to the control electrode T1G of transistor T1 and on its output side to the control terminal. Advantageously, this allows continuous monitoring of the system 100 for current control by the microcontroller 3. When the system 100 is functioning correctly, the on-time of the control signal PWM and the on-time of transistor T1 measured at terminal 10c have a fixed ratio, which is only influenced by the supply voltage V1.In the event of an open circuit in coil 1 or a short circuit to ground, both turn-on times are identical. In the case of a short circuit to supply voltage V1, the turn-on time of the fed-back signal is extremely short, as the associated excessive current leads to the immediate switch-off of transistor T1. This also provides self-protection for transistor T1, so further protective measures are unnecessary. Fig. 4 shows: - The control signal PWM, which underlies the signals of series 2-4 (series 1); - the coil current I (series 2); - the voltage applied to the measuring resistor R_Sens (series 3); - the voltage filtered by the low-pass filter from the second resistor R2 and the second capacitor C2 according to series 3, as well as the reference voltage Vref (series 4). Fig. 4 further shows: - The control signal PWM, which underlies the signals of series 6 (series 5); - the coil current I1 at a supply voltage V1 of 12 V and the coil current I2 at a supply voltage V1 of 28 V (series 6). As shown in row 6, the coil current I1, I2 remains approximately constant over a wide range when the supply voltage V1 is changed. At 12 V and 28 V supply voltage V1, the peak values ​​of the coil current I1, I2 are identical, but the RMS values ​​are 710 mA (12 V) and 695 mA (28 V). This corresponds to a variation of 2.1%. Fig. 4 also shows: - The control signal PWM, which underlies the signals of rows 8-9 (row 7); - the signal present at the flip-flop output Q (row 8); and - the signal present at the reset input (R) of the flip-flop 5 (row 9). The reset input (R) of flip-flop 5 is high in its idle state. Flip-flop 5 is reset by negative pulses. A reset pulse up to +2.5V is triggered by comparator unit 7. As soon as a switching threshold of flip-flop 5 is reached, transistor T1 switches off, whereupon the voltage across the measuring resistor R_Sens drops abruptly to 0V. The output electrode 7a of comparator unit 7 then immediately returns to a high level and does not drop further. The reset pulse to 0V is triggered by a falling edge of the PWM control signal. A rising edge of the PWM control signal causes a positive voltage spike, which is limited by diode D2. Circuit 10 operates autonomously and requires only a current value input in the form of a PWM signal. Feedback of the actual current value across the potential boundary is not necessary. Circuit 10 is stable and accurate over a wide supply voltage range. It is intrinsically safe and requires no additional safety measures. It generates a current-corresponding time signal, which is suitable for diagnostic purposes. It does not require expensive special components or additional analog-to-digital converters for feedback of the coil current across the potential boundary. It can be manufactured using particularly inexpensive standard components.

Claims

Circuit (10) for adjusting a current (I) through a coil (1) for a solenoid valve, comprising: - a control input (10a) for receiving a control signal (PWM) and a control output (10b) for connection to a first electrode of the coil (1), - a first and second supply terminal (11a, 11b) for connection to a first voltage source (V1), - a flip-flop (5) with a data input (D), a clock input (CLK), a flip-flop output (Q) and a reset input (R), - a comparator unit (7) with an inverting comparator input (8a), a non-inverting comparator input (8b), and an output electrode (7a), - a switching element (T1) with a control electrode (T1G), a drain electrode (T1D) and a source electrode (T1S) and - a measuring resistor (R_Sens), wherein - the flip-flop (5) with its clock input (CLK) is connected to the control input (10a),with its data input (D) and its reset input (R) to the output electrode (7a) and with its flip-flop output (Q) to the control electrode (T1G),- the comparator unit (7) with its non-inverting comparator input (8b) to the control input (10a) and with its inverting comparator input (8a) to the source electrode (T1S),- the switching element (T1) with its outflow electrode (T1D) to the control output (10b) and with its source electrode (T1S) via the measuring resistor (R_Sens) to the second supply terminal (11b), and- the first supply terminal (11a) is provided for connection to a second electrode of the coil (1), wherein the circuit further comprises a first optocoupler (9a) which, on the input side, receives an external PWM control signal (PWM) and, on the output side, outputs the control signal at the control input (PWM) is set up. Circuit (10) according to claim 1, further comprising two first resistors (R1a, R1b) and a first capacitor (C1), wherein - the control input (10a) is coupled to the non-inverting comparator input (8b) via one of the two first resistors (R1a), - the first capacitor (C1) is connected in parallel with the other first resistor (R1b) and couples the non-inverting comparator input (8b) to the second supply terminal (11b). Circuit (10) according to one of the preceding claims, further comprising a first diode (D1) which couples the control output (10b) in forward direction to the first supply terminal (11a). Circuit (10) according to one of the preceding claims, further comprising a second resistor (R2) and a second capacitor (C2), wherein the inverting comparator input (8a) is coupled to the source electrode (T1S) via the second resistor (R2) and to the second supply terminal (11b) via the second capacitor (C2). Circuit (10) according to one of the preceding claims, further comprising a third resistor (R3) and a third capacitor (C3), wherein the output electrode (7a) is coupled to the control input (10a) via the third capacitor (C3) connected in series with the third resistor (R3). Circuit (10) according to one of the preceding claims, further comprising a second diode (D2) which couples the output electrode (7a) in the forward direction to the data input (D). Circuit (10) according to one of the preceding claims, further comprising a fourth resistor (R4) that couples the output electrode (7a) to the data input (D). Circuit (10) according to one of the preceding claims, further comprising a third supply terminal (11c), wherein the flip-flop (5) has a set terminal (S) coupled to the third supply terminal (11c), and / or the comparator unit (7) comprises a comparator (8) and an output transistor (T2), wherein the comparator (8) has the non-inverting comparator input (8b) and the inverting comparator input (8a), a first and second comparator supply terminal (8c, 8d) and a comparator output (8e), and the output transistor (T2) is coupled with its base electrode (T2B) to the comparator output (8e), with its collector electrode (T2C) to the output electrode (7a) and with its emitter electrode (T2E) to the second comparator supply terminal (8d), and the first comparator supply terminal (8c) to the third supply terminal (11c) is coupled. Circuit (10) according to one of the preceding claims, further comprising a control connection and a second optocoupler (9b) which is coupled on the input side to receive an internal control signal with the control electrode (T1G) and is configured for outputting the control signal on the output side at the control connection. System (100) comprising a circuit (10) according to one of the preceding claims, a microcontroller (3), a coil (1) for a solenoid valve and a first voltage source (V1) as well as a further voltage source, wherein - the microcontroller (3) is coupled to the control input (10a) and is configured to provide an external control signal (PWM) at the control input (10a), - the coil (1) is coupled with its first electrode to the control output (10b) and with its second electrode to the first supply terminal (11a), - the first voltage source (V1) is coupled with a first pole to the first supply terminal (11a) and with a second pole to the second supply terminal (11b), and - the microcontroller (3) is coupled to the further voltage source for supply.

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