Abstract: A device for operating a discharge lamp of the alternating current operating type has a high pressure discharge lamp with a silica glass discharge vessel in which a pair of opposed electrodes are located and on which a trigger electrode is located, a feed device which supplies an alternating discharge current to the high pressure discharge lamp, the feed device having a starter circuit, an inverter circuit with at least two switching devices; a coil which is located downstream of the inverter circuit and is series-connected to the discharge lamp; and a control element which produces on/off driving in alternation with a dead time, and in which the inductance of the coil is at most 210 ?H.

Abstract: An incandescent lamp includes a lamp voltage conversion circuit within the lamp and connected to a lamp terminal, where the voltage conversion circuit converts a first line voltage at the lamp terminal to a second RMS load voltage usable by a light emitting element of the lamp. The voltage conversion circuit includes a triac phase-controlled dimming circuit, which in turn includes plural resistors connected to each other in parallel, each of the resistors being series-connected to a respective fuse, each of which has a different breaking current corresponding to voltage present at the line. A resistance in the phase-controlled dimming circuit is fixed by breaking at least one fuse in response to the first voltage. The voltage conversion circuit may be an integrated circuit that is in the lamp base and connected between the lamp terminal and the light emitting element.

Abstract: A step-up converter has a power factor correction, has an input for connection to a supply voltage, in particular a rectified AC voltage; an inductor, a diode and a storage capacitor, which are coupled in a series arrangement between the input and the output, in which the voltage that is dropped across the storage capacitor is provided at the output; a switch, which is coupled between a junction point between the inductor and the diode, on the one hand, and a reference potential, on the other hand; and a drive circuit for the switch which controls the times for which the switch remains closed and open; the drive circuit being designed to control the time for which the switch remains closed as a function of the freewheeling time of the inductor. A method for operating such a step-up converter is also disclosed.

Abstract: This invention relates to new soft-switching techniques for minimizing switching losses and stress in power electronic circuits using inverter legs. By choosing the switching frequency with specific relationships with the resonant frequency of the power electronic circuits, the proposed switching technique enables the power electronic circuits to achieve soft switching under full load and short-circuit conditions at the defined frequencies for both capacitive and inductive loads. This technique can be applied to an electronic circuit with two switches connected in totem pole configuration between two dc voltage rails or commonly known as a power inverter leg or inverter arm. Examples of these circuits are class-D power converter, half-bridge power converters and full-bridge power converters or inverters. The proposed techniques allow inverter circuits with resistive, capacitive and inductive loads to achieve soft switching.

Abstract: The present invention relates to a high-efficiency controller of a gas-filled light producing tube; the controller can produce signals in a form of outputs of high-frequency sine wave to soft-start a gas-filled light producing tube according to the principle of modulation and oscillation of pulse (P.W.M.) so that the gas-filled tube produces light, and that service light of the gas-filled tube can be lengthened. If abnormal conditions happen, e.g. people's touching the gas-filled tube, and the tube breaking, the controller will make the transformer stop working immediately, preventing sparks from being produced to hurt people, making the gas-filled light producing tube safe to use.

Abstract: A voltage is applied across the positive electrode and negative electrode of a flash discharge tube (xenon flash lamp) to emit light by a charge and discharge capacitor. This voltage application accumulates energy in a residual inductance existing in the circuit constructed by the flash discharge tube and the power supply circuit for the flash discharge tube. This energy is made to flow as surge current into a series circuit comprising the flash discharge tube, a surge current diode and a diode protecting resistor.

Abstract: The invention is to provide a projector of external power supply, which comprises: a DC (direct current) power supply port, a step-up circuit, a voltage regulation circuit, a lamp, and an igniter. Wherein, a DC voltage provided from outside is received by the DC power supply port and is converted to a first electric potential by the step-up circuit. The first electric potential may actuate the igniter to light up the lamp and, after the lamp is lighted up, the step-up circuit regulates the working voltage of the lamp to a second potential voltage. Wherein, the first electric potential is higher than the second electric potential.

Abstract: A method and apparatus for illuminating lighting elements in one or more predetermined patterns. A preferred frequency controlled lighting system implementing this method includes a motion switch, a controller, and lighting elements. The motion switch creates an activation signal in response to movement of the motions switch, the activation signal indicating at least one of duration of electrical engagement or frequency of electrical engagement within the motion switch. The controller detects the activation signal generation and uses a signal analysis system to analyze the activation signal.

Abstract: The invention relates to a method and a circuit for starting or operating discharge lamps which are designed for dielectrically impeded discharges. In this case, it is established in advance, with the aid of an overvoltage protection circuit and test power pulses, whether the discharge lamp is connected.

Abstract: FA ballast (20) for powering a gas discharge lamp (70) comprises an inverter (200) and an arc protection circuit (600). Arc protection circuit (600) monitors an electrical signal within the ballast. In response to occurrence of a disturbance in the signal, such as what occurs during output arcing, arc protection circuit (600) disables the inverter (200) for a timed shutdown period. Arc protection circuit (600) provides a timed starting period for igniting the lamp, during which time any disturbance in the electrical signal is essentially ignored and inverter (200) is allowed to continue to operate. Arc protection circuit (600) also provides a restart function for periodically attempting to ignite and operate the lamp. Arc protection circuit (600) is preferably realized using a timer integrated circuit (U1) with associated discrete circuitry, and may be adapted for use with ballasts having self-oscillating or driven type inverters.

Abstract: In a voltage source according to the present invention, a switching transistor (Q1) is turned on when the voltage of an electrolytic capacitor (C1) exceeds a predefined positive voltage level (E1), to keep the electrolytic capacitor (C1) at the predefined voltage level (E1), and turned off when the voltage of the electrolytic capacitor (C1) is reduced below the predefined voltage level (E1). A switching transistor (Q2) is turned on when the voltage of an electrolytic capacitor (C2) is reduced below a predefined negative voltage level (?E2), to keep the electrolytic capacitor (C2) at the predefined voltage level (?E2), and turned off when the voltage of the electrolytic capacitor (C2) exceeds the predefined voltage level (?E2). Therefore, an output voltage (V3) is controlled between the predefined voltage level (E1) as an upper limit and the predefined voltage level (?E2) as a lower limit.

Abstract: A high intensity discharge (HID) driver for a HID lamp which can be used as a HID ballast is provided. The HID driver at least includes an input processor connected to an input power for suppressing a transient and an in-rush current of the input power, a main driver connected to the input processor and a HID lamp for driving and amplifying the input power; and a protection circuit connected to the main driver and the HID lamp for controlling a timing of starting after a failure condition. Moreover, the HID driver can further includes a timing circuit connected to the main driver for controlling a timing, and a starting circuit connected to the timing circuit and the HID lamp for starting the HID lamp. The HID driver can be applied to a high pressure sodium (HPS) lamp or a metal halide lamp (HML).

Abstract: Disclosed is a control circuit of an electronic ballast for a fluorescent lamp, wherein the control circuit comprises a protection circuit and an automatic re-lamp circuit. The protection circuit detects an abnormal voltage condition resulted from a defective lamp tube, stops an oscillation circuit of the electronic ballast from generating high voltage output, and thereby protects a worker from an electric shock when the worker attempts to replace the defective lamp tube. The automatic re-lamp circuit turns on a newly installed lamp tube without switching off and on a power supply to the fluorescent lamp first.

Abstract: An electrical load power control device is described that reduces the power consumption of inductive and inductive-dissipative loads, including for example fluorescent lighting. The power circuit of the invention interrupts AC power supply to the load during a plurality of intervals within each half cycle of the AC mains signal frequency whilst providing an alternate path for current flow during the interruption to maintain a sinusoidal-like current to the load. During a crossover lag zone encompassing zero crossing points of the voltage and current and during which the voltage and current have opposite polarities, both elements of the power switch are switched to the “on” condition, one element of the circulating switch is switched to the “on” condition when a positive current is flowing in the load and the other element of the circulating switch is switched to the “on” condition when a negative current is flowing in the load.

Abstract: In a phase controller used in a light control of an incandescent lamp, noise reduction, prevention of elements from damage due to short circuit current, downsizing and lower cost are purposed. A CPU circuit of a control circuit sets a gradual increase term during which a load voltage applied to the incandescent lamp is gradually increased by driving a self-quenching type switching device such as an IGBT. After passing the gradual increase term, a main switching device such as a TRIAC is turned on. The phase controller further comprises a current sensor such as a shunt resistor for sensing a value of the load current flowing through the self-quenching type switching device, according to need. The CPU circuit compares the sensed value of the load current with at least one reference value, and selects driving manner of the main switching device and the self-quenching type switching device corresponding to the result of comparison.

Abstract: The following circuit is proposed for discharge lamps having a particularly high starting voltage. An a.c. voltage generator (1) provides a corresponding a.c. voltage. A starting voltage generating device, which comprises a piezo transformer (2), is connected to the a.c. voltage generator (1) and can be connected at its output to a discharge lamp (4), generates a starting voltage from the a.c. voltage. The starting voltage generating device in this case comprises at least one diode (3) which is connected in parallel with the output of the starting voltage generating device. A zero-order pump circuit is thus integrated in the starting circuit. Advantageous here is the use of higher-order pump circuits.

Abstract: A multi-function feedback sense input in an electronic ballast control indicates a number of lamp faults on the basis of lamp parameters exceeding specified thresholds. An end of life detection is achieved by conditioning a lamp feedback with a DC offset to provide a simple threshold comparison to determine if the lamp exceeds specified operational boundaries. An open filament, absent lamp or broken cathode is detected on the same feedback sense by detecting an open circuit in the lamp filament and driving the sense feedback to a shutdown state in the event of a filament open circuit. The ballast control includes a current sense feedback for detecting overcurrent conditions as well as lamp faults so that the control detects an end of life condition, lamp absence, broken lamp, open filament, broken cathode, overcurrent, hardswitching or failure to ignite fault with a minimum number of feedback sensors.

Abstract: The present invention provides a high frequency electronic ballast with low voltage output, comprising a high voltage power supply (200) generating high voltage power (234) at a voltage and a frequency; a low voltage microcontroller (214) which is responsive to the voltage and the frequency of the high voltage power (234) and generates a low voltage drive signal (240); and a switch (216) operably connected to the high voltage power supply (200) and responsive to the low voltage drive signal (240). The low voltage output of the switch (216) can be used to drive auxiliary low voltage loads (220), such as a back-up incandescent lamp (116). The low voltage output can be responsive to HID lamp power, so that the backup incandescent lamp (116) is energized when the HID lamp is not providing illumination.

Abstract: In a phase controller used in a light control of an incandescent lamp, noise reduction, prevention of elements from damage due to short circuit current, downsizing and lower cost are purposed. A CPU circuit of a control circuit sets a gradual increase term during which a load voltage applied to the incandescent lamp is gradually increased by driving a self-quenching type switching device such as an IGBT. After passing the gradual increase term, a main switching device such as a TRIAC is turned on. The phase controller further comprises a current sensor such as a shunt resistor for sensing a value of the load current flowing through the self-quenching type switching device, according to need. The CPU circuit compares the sensed value of the load current with at least one reference value, and selects driving manner of the main switching device and the self-quenching type switching device corresponding to the result of comparison.

Abstract: A fluorescent lamp end-of-life protection circuit in an illuminating electric appliance, includes a rectifying effect protection circuit for a lamp tube and an overvoltage protection circuit for the lamp tube, in which a circuitry of two series resistors and a capacitor in series is connected in parallel with the lamp tube. A cathode of a transient voltage suppresser is connected to one end of the lamp tube, its anode is connected to an anode of a diode, and a cathode of the diode is connected to a common node of two series resistors. One end of a trigger diode is connected to a common node of the capacitor and the resistor, and the other end thereof is connected to a gate terminal G of a triac, a first electrode and a second electrode of of which are connected to two ends of the lamp tube respectively.

Abstract: A hybrid electronic ballast circuit includes a ballast control, half-bridge driver, and a power switch half-bridge in a single package. The ballast circuit includes a number of fault protections and safety features and is self-oscillating to drive a resonant circuit including a fluorescent lamp. Internal feedback and control signals are provided for a number of modes of operation, including startup, preheat, normal run mode and fault protection response mode. A voltage controlled oscillator adjusts the switching frequency of the switching half-bridge to maintain zero volt switching and minimum current switching. The entire ballast control may have only three external connections, and may be implemented in a TO220 package.

Abstract: A method of preventing acoustic arc resonance (AAR) in a high frequency electronic ballast for a High-Intensity-Discharge (HID) lamp, includes the step of providing a phase modulated signal to the HID lamp, the phase modulated signal being provided by a pulse source working at a Pulse-Phase-Modulation (PPM) mode with a fixed frequency.

Abstract: A voltage is applied across the positive electrode and negative electrode of a flash discharge tube (xenon flash lamp) to emit light by a charge and discharge capacitor. This voltage application accumulates energy in a residual inductance existing in the circuit constructed by the flash discharge tube and the power supply circuit for the flash discharge tube. This energy is made to flow as surge current into a series circuit comprising the flash discharge tube, a surge current diode and a diode protecting resistor.

Abstract: A CCFL power converter circuit is provided using a high-efficiency zero-voltage-switching technique that eliminates switching losses associated with the power MOSFETs. An optimal sweeping-frequency technique is used in the CCFL ignition by accounting for the parasitic capacitance in the resonant tank circuit. Additionally, the circuit is self-learning and is adapted to determine the optimum operating frequency for the circuit with a given load. An over-voltage protection circuit can also be provided to ensure that the circuit components are protected in the case of open-lamp condition.

Abstract: The invention relates to a novel operating circuit for a low-pressure discharge lamp 1 with early EOL detection via a measurement of the DC voltage between the electrodes 2, 3. In this case, the DC voltage can be modified by an offset voltage 10 such that only one polarity has to be taken into account during measurement.

Abstract: A switched mode controller for properly handling an under-voltage condition in a power line which includes a current mirror for receiving current from the power line; a reference current source coupled to the current mirror for supplying a reference current; and a power transistor coupled to the reference current source, the power transistor generating a pulse width modulated signal when current from the power line exceeds the reference current, the power transistor being disabled when current from the power line is less than the reference current.

Abstract: The invention relates to an interface circuit which is suitable for operating capacitive loads such as electric ballasts for lamps at a mains supply circuit, in particular a phase gating dimmer. The interface circuit according to the invention short-circuits the load input if the mains supply circuit does not carry out a load supply.

Abstract: An apparatus is provided including an image projection lighting device. The image projection lighting device may be comprised of a base housing, a yoke, and a lamp housing. The lamp housing may be comprised of a lamp and a first light valve. The image projection lighting device may be further comprised of a communications port, a processing system, and a memory. A cutoff value representing an amount of accumulated operating time at which the lamp may begin to operate improperly may be stored in the memory. An accumulated value representing an actual accumulated amount of operating time of the lamp may also be stored in the memory. The processing system may prevent the lamp from operating when the accumulated value is within a limit of the cutoff value, unless the processing system grants a request for a variance.

Abstract: High voltage and low voltage switch mode circuits and methods serve to recover the charge stored on electro-luminescent lamp panels that would otherwise be dissipated during the discharge cycle of a drive circuit. The high voltage circuits and methods operate to transfer the charge to the high voltage rail, while the low voltage circuits and methods operate to transfer the charge to the source of low drive voltage.

Abstract: The invention relates to a ballast for a lamp having an inverter which includes at least one switch (S1; S2), and having a drive circuit (10) for alternately opening and closing the at least one switch (S1; S2) wherein the drive circuit (10) is designed to drive the at least one switch (S1; S2) alternately at at least two different frequencies (&ohgr;a, &ohgr;b). It also relates to a method for operating a ballast for a lamp having an inverter which comprises at least one switch (S1; S2), and having a drive circuit (10) for alternately opening and closing the at least one switch (S1; S2) wherein the drive circuit drives the at least one switch (S1; S2) alternately at at least two different frequencies (&ohgr;a, &ohgr;b).

Abstract: A twinkle bulb light set includes, alternately from one end of the light set to an opposite end of the light set, a plurality of standard bulb sockets, each configured and dimensioned to operatively receive a standard bulb, whether a steady burning bulb or twinkle bulb, and at least one fuse bulb socket configured and dimensioned to operatively receive a fuse bulb. The standard bulb sockets are configured and dimensioned to releasably operatively receive only standard bulbs, and the fuse bulb socket is configured and dimensioned to non-releasably operatively receive a fuse bulb.

Abstract: A simple, low-cost ballast circuit for adjusting the lumen output of a gas lamp. A number of ballast circuits are provided for a gas lamp, such as a fluorescent lamp. Specifically, a variable resistor is provided in each of the ballast circuits. The variable resistor is included in the resonant control circuit to adjust the switching frequency of the ballast circuit, thereby controlling the lumen output or brightness of a gas lamp. Additional components, such as a fixed resistor or an inductor may be added to the ballast circuit to limit the maximum switching frequency.

Abstract: A discharge lamp lighting device for lighting a discharge lamp includes an ignitor for applying a starting voltage to the discharge lamp at the time of starting and thus lighting the discharge lamp; a voltage detection circuit for detecting a voltage of the discharge lamp; and a current control circuit section for controlling a current supplied to the discharge lamp on the basis of the detection by the voltage detection circuit, wherein the current control circuit section, after ignition, starts controlling the current supplied to the discharge lamp on the basis of the detection result by the voltage detection circuit and continuously increases the current supplied to the discharge lamp at a predetermined rate. Thus, a discharge lamp lighting device which is inexpensive and highly reliable and enables a longer lifetime of the discharge lamp is provided.

Abstract: In a circuit configuration to operate a gas discharge lamp (LA) the lamp (LA) is arranged in a full bridge circuit. A control circuit in normal operation actuates the four switches (S1-S4) in such a way that it changes over with a first frequency (f1) alternately between a first and a second state (T1, T2), whereby in the first state (T1) the two switches (S2, S3) of a first bridge diagonal are opened, one switch (S1) of the second bridge diagonal is closed and the other switch (S4) with a second frequency (f2), which is higher than the first frequency (f1), is alternately opened and closed. In the second state (T2) the four switches (S1-S4) are actuated in such a way that the lamp (LA) is pole reversed. In a start phase (TS) on the contrary the switch connected to the DC voltage source (S4) of a half-bridge is opened, the second switch (S3) of this half-bridge is closed, and the two switches (S1, S2) of the other half-bridge are with a third frequency (f3) alternately opened and closed.

Abstract: Disclosed is an electronic ballast of a high power factor for a compact fluorescent lamp (CFL) capable of implementing a high power factor and turning on lamps of different capacitances (3W-26W), or selectively turning on two lamps having the same capacitance or one lamp, using one circuit, by separating a lamp power and a circuit driving power.

Abstract: Control and filter circuits for linear power supplies, employing resistance to limit the release of stored energy and simultaneously removing the input mains AC, so as to protect a load device from damage when a high voltage fault occurs. The circuits may be used particularly in output filters for high voltage power supplies for high power transmitting tubes, such as Inductive Output Tubes used in UHF television transmitters, which must be protected from internal arcing by a controlled release of stored energy and a rapid disconnection of input power. The use of the filter circuit combined with rapid solid state switching ensures that the load is not subject to an excessive surge when a high voltage fault occurs.

Abstract: A ballast (10,20) for powering a gas discharge lamp load (30) comprises a protection circuit (300,600) operable to monitor an electrical signal (40) in the ballast and disable the ballast for at least a predetermined period of time in response to a disturbance wherein at least a portion (44) of the electrical signal (40) exhibits a time-rate-of-change that exceeds the time-rate-of-change of the signal during normal operation of the ballast and gas discharge lamp load. Protection circuit (300,600) is capable of disabling the ballast within a response time that is less than twice the period of the electrical signal. In a preferred embodiment that is suitable for ballasts with driven-type inverters, protection circuit (300) comprises a latching device (310) and a triggering circuit (330). In a preferred embodiment that is suitable for ballasts with self-oscillating type inverters, protection circuit (600) comprises a pull-down circuit (640) and a negative voltage source (610).

Abstract: In an electronic ballast equipped with a high-frequency bridge circuit, a microprocessor for controlling lamp operation and a stop circuit for interrupting the operation of the ballast in case of a fault condition, the stop circuit interrupts both the operation of the bridge circuit and the operation of the microprocessor. Unstable operation of the ballast caused by the fault condition is prevented thereby.

Abstract: A power supply system has a battery for supplying power and a lamp having a plurality of filaments therein. Each of the filaments is connected to the battery through a filament power feed line, respectively. A switch is provided on each of the filament power feed line. A fault detection circuit measures a current that flows in a non-active filament and generates a fault signal that shuts off the switch for the filament when the current flows in the non-active filament.

Abstract: A high-intensity discharge lamp lighting apparatus, including a main circuit, which contains an LC oscillation circuit, and to which a high-intensity discharge lamp is coupled, and an electronic ballast for starting up into a lighting state the high-intensity discharge lamp via the main circuit which is coupled to its output side, and it is operated at a resonance frequency of the LC resonance circuit in the main circuit at a no-load time.

Abstract: In the case of circuit arrangements for operating gas-discharge lamps (Lp), a charge pump (D5, D6, C31, C32) is often used for the purposes of power-factor correction. If this is the case, poorly igniting lamps (Lp) experience an increase in voltage across a storage capacitor (C1). This is avoided according to the invention by a PTC (KL) in parallel with diodes (D5, D6) of the charge pump.

Abstract: An electronic ballast for lamps, which has an input stage that is designed as a SEPIC converter. By operating the SEPIC converter in the mode with a discontinuous current profile, a slow microcontroller can be used for the control.

Abstract: An abnormality detection circuit detects abnormality relating to ground fault in secondary winding circuitry of transformer, non-grounding fault of transformer assembly casing or false connection of the AC power source to the transformer assembly in reverse polarity. An interrupter circuit turns a switch off in response to detection of the abnormality by the abnormality detection circuit to interrupt the supply of the AC power to the transformer. When the supply of the AC power is interrupted, the switch is connected to a restart circuit, whereupon the circuit is activated to allow a charging current to flow to a capacitor, which is connected in series in a drive current path of a drive circuit with a time delay on the order of 0.5 to 1.0 second which is determined by a delay circuit thereof. The charging current drives a restoring circuit, which controls the interrupter circuit to its restoring condition temporally so that the switch is turned to its “on” condition only once.

Abstract: A ballast circuit includes an output isolation transformer having a primary winding and first and second secondary terminals coupled to opposing ballast lamp terminals for additively applying potentials on the primary winding and the first and second secondary winding potentials across the lamp and limiting ground fault voltages. The circuit can include a closed loop feedback path from a load to a feedback rectifier for promoting linear operation of an input rectifier.

Abstract: A method an apparatus for efficiently driving a low-voltage device from a wide-range input supply uses and inductor and a diode coupled in parallel to provide a high-efficiency energy storage circuit. The parallel diode/inductor circuit is coupled to a switch for intermittently supplying a current to maintain a level of energy storage in the circuit. The switch is coupled to a control circuit for controlling the switch. The external device be a relay and the inductor may be a coil of the relay. The external device may be one or more LEDs connected in series and the diode may be the series LED circuit. The control circuit may include a fault-tolerant synchronization input for connection to multiple driver circuits, whereby audible noise produced by beat frequencies between the relays is eliminated.

Abstract: A filament cut-back circuit comprises an impedance circuit coupled in series between either an AC voltage source and a primary filament winding, or a secondary filament winding and a filament. In response to an alternating voltage from the AC voltage source when coupled in series thereto or an alternating voltage from the secondary filament winding when coupled in series thereto, the impedance circuit operates as a short circuit when the alternating voltage is at a preheat frequency and operates as an open circuit when the alternating voltage is at an operating frequency.

Abstract: An electronic ballast circuit (FIG. 1) includes a voltage-regulated DC power source and an H-bridge having a plurality of transistors (Q5, Q6, Q7, Q8). The circuit operates a high intensity discharge lamp (50). A regulating circuit electrically connected to the transistors regulates the peak current flowing through the H-bridge by discharging a parasitic capacitance (C parasitic).

Abstract: A discharge lamp device which drives a discharge tube filled with a rare gas and has a first electrode mounted at the inside of the tube and a second electrode mounted at the outside of the tube, includes a driving circuit that applies a voltage between the first and second electrodes. The driving circuit applies a positive rectangular wave voltage to the first electrode with a potential of the second electrode being a reference potential (0V). A backlight includes at least one discharge tube and the discharge lamp device.

Abstract: LED lamp circuitry that emulates an incandescent lamp's behaviour upon remote verification of the LED lamp. The LED lamp circuitry presents an input power switch circuit, a fuse blow-out circuit and a cold filament detection circuit permitting the use of LED lamps in applications, such as railway signal light applications, where there is a need for remote monitoring of the lamps, while keeping the advantageous features of lower power consumption and longer life.

Abstract: The invention relates to a novel operating circuit for a low-pressure discharge lamp 1 with early EOL detection via a measurement of the DC voltage between the electrodes 2, 3. In this case, an electrode interrogation can be carried out by checking a respective connection via the electrodes 2, 3 to a respective reference potential.