Voltage converter and method for operating a voltage converter

Abstract

Voltage converters (10, 20, 30), comprising a controllable switch (11) for clocked operation of the voltage converter (10, 20, 30), and a detection device (12) for detecting a voltage (V SNS ), which depends on a voltage drop along a working path of the switch (11) when it is in an open state, characterized by a determination device (13) for determining a plurality of different fault cases of the voltage converter (10, 20, 30) depending on the detected voltage (V) SNS ), wherein the determination device (13) is configured to identify each of the multiple different fault cases of the voltage converter (10, 20, 30) by comparing the detected voltage (V SNS ) with each one from a given plurality of different threshold values ​​(T OVP ; T UVP ; TOPP ; T UPP ) to determine, wherein the determining device (13) is configured to perform a comparison depending on a digitized recorded voltage (V) SNS to carry out.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a voltage converter which can be used, for example, for operating lighting devices, in particular LED lighting devices, and to a method for operating a voltage converter. BACKGROUND OF THE INVENTION

[0002] LED lamps have established themselves in recent years as an energy-efficient and environmentally friendly alternative to incandescent bulbs and compact fluorescent lamps. They are operated behind ballasts that use voltage converters to set a defined operating point at a low-voltage DC voltage and a corresponding current. Significant deviations from this operating point can result in faults, which can, for example, lead to the extinction or destruction of the LED lamps.

[0003] Ensuring the proper operation of LED lighting therefore requires the evaluation and monitoring of the supplied electrical variables, particularly the electrical voltage and the electrical power consumption, with regard to various fault scenarios. The additional effort required for this in terms of circuit components and complexity is reflected significantly in the unit costs for mass-produced products such as LED lighting systems. Among other things, the evaluation of a multitude of different fault scenarios requires the integrated circuits (ICs, ASICs) used in the ballasts to be equipped with a larger number of connections (pins).

[0004] US 3 784 893 A discloses a current and voltage regulated DC-DC converter designed for parallel operation with similar DC-DC converters and having integrated protection functions against overcurrent and overvoltage.

[0005] US 5 122 726 A discloses a protection circuit against overvoltage and component failures for parallel operated, redundant, current-regulated power supplies. SUMMARY OF THE INVENTION

[0006] The present invention is therefore based on the object of providing an improved voltage converter and a correspondingly designed method for operating a voltage converter, whereby an improved evaluation of electrical variables occurring during operation with an electrical load, in particular an LED lamp, is possible using simple means.

[0007] This object is achieved according to the invention by a voltage converter having the features of patent claims 1 and 8, respectively, and by a method for operating a voltage converter having the features of patent claims 10 and 11, respectively. The dependent claims define preferred or advantageous embodiments of the invention.

[0008] According to exemplary embodiments of the invention, voltage converters and methods for operating a voltage converter are provided, which, in particular, reduce the effort required to evaluate electrical variables such as the electrical voltage and the electrical power consumed. This lowers the unit costs of the voltage converters and simultaneously ensures a long service life for the loads operated with them.

[0009] A voltage converter according to a first aspect comprises a controllable switch for clocked operation of the voltage converter, a detection device for detecting a voltage which is dependent on a voltage dropping along an operating path of the switch in an open state of the switch, and a determination device for determining a plurality of different fault cases of the voltage converter as a function of the detected voltage, wherein the determination device is configured to determine a respective one of the plurality of different fault cases of the voltage converter by comparing the detected voltage with a respective one of a predetermined plurality of different threshold values, wherein the determination device is configured to carry out a comparison as a function of a digitized detected voltage.

[0010] Each of the many different fault scenarios is reflected in the voltage detected along the operating path of the switch in its open state. The detection device can therefore be kept simple. This also applies to the determination device, which only has to evaluate a single electrical quantity, namely the detected voltage, and only needs to have one connection or pin for evaluating the voltage, from which a statement about the various fault scenarios can be derived. Overall, the circuitry required to determine the many different fault scenarios is thus minimized, which reduces the unit cost of the voltage converter on the variable cost side.

[0011] In addition, a more comprehensive evaluation and monitoring of the electrical quantities, in particular the electrical voltage and the electrical power, based solely on the detected voltage ensures proper operation and a long service life of the electrical consumer connected to the voltage converter.

[0012] A voltage converter is understood in particular to mean a device which converts a supplied direct voltage into another direct voltage with or without an alternating voltage component, for example in order to adjust the operating point of an electrical consumer, in particular an LED lamp.

[0013] Controllable switches are, in particular, switches that establish or break a conductive electrical connection in an electronic circuit upon external initiation, for example, by an integrated circuit or a processor. Examples of controllable switches include semiconductor transistors and relays.

[0014] The majority of different fault cases can include an overvoltage.

[0015] An analysis of the detected voltage for an overvoltage fault allows the voltage converter to be shut down (“Over Voltage Protection” (OVP) before the connected load is destroyed, or the operating point to be adjusted to counteract the fault. Furthermore, this ensures that in the event of a fault, the output voltage of a SELV device does not exceed the SELV limit, thus preventing life-threatening situations.

[0016] An overvoltage is defined in particular as the measured voltage exceeding a specified upper limit. The latter can thus ensure the long service life of a connected load.

[0017] The majority of different fault cases can also include undervoltage.

[0018] An evaluation of the detected voltage for an undervoltage fault allows the voltage converter to be shut down (“Under Voltage Protection”, UVP or “Short Circuit Protection”, SCP) before the connected load enters undefined lighting states. Alternatively, the load's operating point can be adjusted to counteract the fault.

[0019] In this context, an undervoltage is understood to occur when the detected voltage falls below or does not exceed a specified lower limit. This lower limit can thus ensure the proper operation of the connected load.

[0020] The majority of different error cases can also include overperformance.

[0021] Similar to the case of an overvoltage fault, an evaluation of the detected voltage with regard to an overpower fault enables the voltage converter to be switched off (“Over Power Protection”, OPP) before the connected load is damaged, or the operating point to be regulated in a manner directed against the fault, whereby information about a current occurring during operation of the voltage converter is also taken into account.

[0022] Overpower occurs in particular when the absorbed power determined as a function of the detected voltage exceeds a specified upper limit.

[0023] The majority of different error cases may also include underperformance.

[0024] An evaluation of the recorded voltage with regard to an underpower fault enables, analogously to the undervoltage fault, a shutdown of the voltage converter (“Under Power Protection”, UPP) before the connected load assumes undefined operating states, or a regulation of the load’s operating point directed against the fault, whereby additional information about a current occurring during operation of the voltage converter is taken into account.

[0025] In particular, underpower occurs when the absorbed power determined as a function of the detected voltage falls below or does not exceed a specified lower limit.

[0026] Each of the majority of different error cases can generally be determined by a simple comparison with a designated threshold value, which requires only minimal circuitry effort. Each of the majority of different error cases can, in principle, be determined independently of and simultaneously with every other of the majority of different error cases. This makes it particularly possible to monitor the occurrence of several of the majority of different error cases simultaneously.

[0027] A threshold comparison is possible using analog or digital signals and can be implemented, for example, using an analog comparator or an integrated digital circuit designed for this purpose.

[0028] The determination device is designed to carry out the comparison as a function of a digitized detected voltage.

[0029] This makes it possible, in principle, to digitally determine most of the different fault scenarios. Digitizing the measured voltage, for example, using an analog-to-digital converter (ADC), opens up potentially more precise detection and processing, for example, using a microcontroller or microprocessor.

[0030] According to one embodiment of the invention, the determining device can be configured to carry out the comparison as a function of a peak value of the detected voltage.

[0031] This makes it easy to identify over- or under-power faults in voltage converters where the information about the voltage supplied to the load, especially an LED light source, is contained in a peak value of the detected voltage. These faults can then be determined by simple comparisons with designated threshold values, which include the peak value of the detected voltage.

[0032] A resonant converter (“LLC converter”) is an example of a voltage converter in which the information about the supplied voltage can be contained in the peak value of the detected voltage.

[0033] The peak value can be provided by a tracking comparator, to which the detected voltage is fed on the input side.

[0034] According to one embodiment, the determining device can also be configured to carry out the comparison as a function of a detected voltage scaled with a predetermined factor.

[0035] This makes it easy to determine, for example, the overpower fault scenario. The product of the measured voltage, which can be analog or digital and possibly as a peak value, multiplied by the specified factor, in particular a specified current, preferably yields the power supplied to the load. The overpower fault scenario can then be determined by a simple comparison with a designated threshold value.

[0036] A product can be formed, for example, using an analog multiplier or multiplier logic.

[0037] A voltage converter according to a second aspect comprises a controllable switch for clocked operation of the voltage converter, a detection device for detecting a voltage which is dependent on a voltage dropping along an operating path of the switch in an open state of the switch, and a power determination device for determining a power consumed by the voltage converter as a function of a detected voltage scaled with a predetermined factor, wherein the voltage converter is designed for use in an operating circuit for a lighting device.

[0038] This allows the power supplied to the load, in particular an LED light source, to be determined using simple means. The power supplied to the load is preferably the product of the specified factor, in particular a specified current, and the measured voltage, which can be in analog or digital form and, if necessary, as a peak value.

[0039] A suitable power detection device can be designed, for example, as an analog multiplier or as multiplier logic.

[0040] According to a preferred embodiment, the voltage converter may be an inductive voltage converter selected from the group comprising flyback converters, step-down converters and resonant converters.

[0041] According to a preferred embodiment of the invention, the voltage converter is designed for operation with a lighting means, in particular an LED lighting means, although the invention is not limited to this preferred application of an operating circuit for a lighting means.

[0042] A method for operating a voltage converter according to a first aspect of the invention comprises: clocked operation of the voltage converter by means of a controllable switch; detecting a voltage which is dependent on a voltage falling along an operating path of the switch when the switch is open, by means of a detecting device; determining a plurality of different fault cases of the voltage converter as a function of the detected voltage by means of a determining device; determining a respective one of the plurality of different fault cases of the voltage converter by comparing the detected voltage with a respective one of a predetermined plurality of different threshold values ​​by means of the determining device, and performing the comparison as a function of a digitized detected voltage by means of the determining device.

[0043] A method for operating a voltage converter according to a second aspect of the invention comprises: clocked operation of the voltage converter by means of a controllable switch, detecting a voltage which is dependent on a voltage falling along an operating path of the switch in an open state of the switch by means of a detection device, and determining a power of the voltage converter as a function of a detected voltage scaled with a predetermined factor by means of a power determination device, wherein the voltage converter is designed for use in an operating circuit for a lighting device.

[0044] The power of the voltage converter can be determined, in particular, as a function of a peak value of the detected voltage. Thus, the method can be used, in particular, with voltage converters in which the information about the voltage supplied to the load, in particular an LED lamp, is contained in the peak value of the detected voltage.

[0045] The method according to the first or second aspect of the invention can each comprise method features that correspond to the previously described features of the voltage converter according to the first or second aspect of the invention. Accordingly, the previously mentioned device features of the voltage converter of the present invention can be used analogously in the method, and the method has the advantages already described in connection with the corresponding device features. SHORT DESCRIPTION OF THE CHARACTERS

[0046] The invention is explained in more detail below using preferred embodiments and with reference to the drawings, wherein the same reference numerals designate the same or similar elements. Fig. 1 shows a schematic block diagram of a voltage converter according to an embodiment; Fig. 2 shows a circuit diagram of an exemplary flyback converter according to the embodiment; Fig. 3 shows a circuit diagram of an exemplary buck converter according to the embodiment; Fig. 4 shows a circuit diagram of an exemplary resonant converter according to the embodiment; Fig. 5 shows a table with exemplary determination devices for various voltage converters according to the embodiment; and Fig. 6 shows method steps of a method for operating the voltage converter according to the embodiment. DETAILED DESCRIPTION OF EMBODIMENTS

[0047] The present invention is explained in more detail below using preferred embodiments and with reference to the drawings.

[0048] The figures are schematic representations of various embodiments of the invention. Elements depicted in the figures are not necessarily drawn to scale, but rather are depicted in such a way that their function and purpose will be understood by those skilled in the art.

[0049] Fig. 1 shows a schematic block diagram of a voltage converter 10, 20, 30 according to an embodiment.

[0050] The voltage converter 10, 20, 30 comprises a controllable switch 11, a detection device 12 and a determination device 13 and is designed in particular for use in an operating circuit for a lighting device, for example an LED lighting device.

[0051] The controllable switch 11 is periodically opened and closed to operate the voltage converter 10, 20, 30. When the switch 11 is closed, energy supplied to the voltage converter 10, 20, 30 on the input side in the form of a direct voltage is stored in an energy storage device of the voltage converter 10, 20, 30, while when the switch 11 is open, the energy stored in the energy storage device is delivered to a load connected to the output side, for example, to an LED lamp. When the switch is open, a voltage builds up along its operating path, which voltage can be detected by the detection device 12. The determination device 13 serves to determine a plurality of different fault cases of the voltage converter depending on the detected voltage. These statements apply equally to the following with reference to Fig. 2 - 4 described voltage converters 10, 20, 30.

[0052] Fig. 2 shows a circuit diagram of a flyback converter 10 according to the embodiment.

[0053] The flyback converter 10 comprises primary and secondary storage inductances L as energy storage devices. P and L S with a common magnetic flux. The controllable switch 11 is designed, for example, as a semiconductor power switch. In the closed state of the switch 11, a voltage in the form of a DC voltage V IN supplied energy via the inductance L P , stored there in the form of a developing magnetic field and fed to a ground potential via switch 11. In the open state of switch 11, the stored energy is transferred via the inductance L Sand delivered to LED lamps connected on the output side. In the case of the flyback converter 10, the detection device 12 comprises an auxiliary inductance L A , which is also connected to the common magnetic flux of the storage inductances L P and L S This means that a voltage is branched off from the energy storage device, which voltage depends on the voltage drop along the operating path of the switch 11 when it is open, and allows a conclusion to be drawn about the voltage supplied to the load connected to the output side. The branched voltage is applied to a voltage divider comprising ohmic resistors R1 and R2, with a partial voltage thereof being applied as the detected voltage to a resistor connected to V SNS The determination device 13 is coupled to this connection, which in connection with Fig. 5 is explained in more detail. V DD,HV referred to in Fig. 2 a supply voltage obtained from the flyback converter for the determination or evaluation device 13, which is preferably designed in the form of an integrated circuit.

[0054] Fig. 3 shows a circuit diagram of a step-down converter 20 according to the embodiment.

[0055] The buck converter 20 comprises a storage inductance L and a storage capacitance C as energy storage. The controllable switch 11 is a semiconductor power switch. In the closed state of the switch 11, the buck converter 20 is supplied with a DC voltage V INsupplied energy, which operates the LED lamps connected on the output side via the switch 11 and the storage inductance L and charges the storage capacitance C connected in parallel. In the open state of the switch 11, the energy stored in the form of magnetic or electric fields is retrieved from the inductance L and the capacitance C in order to operate the LED lamps connected on the output side. In the case of the step-down converter 20, the detection device 12 comprises an auxiliary inductance L A , which is connected to the magnetic flux with the storage inductance L. This results in a voltage being branched off from the magnetic energy storage device, which voltage depends on the voltage drop along the working path of the switch 11 when it is open and allows a conclusion to be drawn about the voltage supplied to the load connected to the output side. Similar to the flyback converter 10 of Fig. 2 is a partial voltage of the branched voltage as detected voltage at terminal V SNS This, in turn, forms the starting point for the determination device 13, which is described in detail below.

[0056] Fig. 4 shows a circuit diagram of a resonant converter 30 according to the embodiment.

[0057] The resonant converter 30 has an input-side resonant circuit with an inductance L R and a capacity C R which is connected to the terminal V INby means of a direct voltage and is excited to oscillate by the alternating periodic opening and closing of controllable semiconductor power switches 11, 11', particularly in the range of its resonant frequency. This oscillation is transmitted via the isolating inductors L and a rectifier circuit to a resonance-matched resonant circuit on the output side, which feeds the connected LED lamp. In the case of the resonant converter 30, the detection device 12 comprises an auxiliary inductor L A , which is permeated by the same magnetic flux as the isolating inductances L. The voltage branched off across it depends on a voltage drop along the operating path of the switch 11 when it is open and allows a conclusion to be drawn about the voltage supplied to the load connected to the output side. In the manner described above, a partial voltage of this voltage is measured at a voltage marked VSNS designated connection is provided, to which in turn the determination device 13 explained in more detail below is connected.

[0058] Fig. 5 shows a table with exemplary embodiments for the Fig. 1 - Fig. 5 shown determining devices 13 for the various voltage converters 10, 20, 30.

[0059] In the table of Fig. 5, a column is assigned to the flyback converter 10, the buck converter 20, and the resonant converter 30, and a row is assigned to the detection of overvoltage, undervoltage, overpower, and underpower. Each table cell thus shows an exemplary subcircuit of the determination device 13, with which, for a specific voltage converter type, the detected voltage V SNSA specific one of the many different fault scenarios can be determined. Individual subcircuits can be used for several of the many fault scenarios.

[0060] For example, Fig. 5(a) shows a circuit that can be used as part of the determination device 13 in all three voltage converter types. It compares the detected voltage V SNS with a given threshold value T OVP , which represents a maximum voltage that must not be exceeded. An analog comparator, for example, is sufficient as comparison circuit 14. If the condition V SNS > T OVP If this is the case, the overvoltage fault is determined.

[0061] Fig. 5(b) and Fig. 5(c) shows circuits for determining the undervoltage fault. In this case, the detected voltage V SNS each with a given threshold value T UVPwhich specifies a minimum voltage that must not be undercut or exceeded. In the case of the flyback converter 10, the detected voltage V SNS first digitized by means of an analog / digital converter 15 (cf. Fig. 5(b)). The comparison then requires a digital comparison logic 14. A fall below or failure to exceed the threshold value T UVP determines the undervoltage fault.

[0062] Fig. 5(d) and Fig. 5(e) represent circuits for determining the overpower fault case.

[0063] In the flyback converter 10 and the step-down converter 20, the detected voltage V SNS by means of an analog / digital converter 15. In the case of the resonant converter 30, however, a peak value of the detected voltage V SNSdetermined, since with this type of voltage transformer the information about the voltage or power supplied to the consumer is contained in the peak value of the detected voltage V SNS The peak value is provided by a tracking comparator 16, to which the detected voltage is fed on the input side. The voltage V thus prepared is SNS is always multiplied by a given factor I SEL which represents a current value for overpower detection and is predefined. For this purpose, the desired value for I SEL read from a memory of the determination device 13, which may be configured as an integrated circuit or ASIC, or specified via an external resistor. The product is formed by an analog multiplier 17 in Fig. 5(d) or a digital multiplication logic 17 in Fig. 5(e). The product is then tested with a given threshold value T OPPwhich corresponds to a maximum power. If the threshold T OPP is exceeded, the error case of overperformance occurs.

[0064] Fig. 5(f) and Fig. 5(g) show circuits for determining the underpower fault. They correspond to the circuits of Fig. 5(d) and Fig. 5(e), but in these examples the product formation with I SEL has been omitted, since the power is directly reflected in the recorded voltage V SNS so that a comparison of the recorded voltage V SNS with a correspondingly specified threshold value T UPP is sufficient. This threshold T UPP , which is dependent on the threshold value T UVP may vary, represents a minimum voltage at a given minimum power. If the detected voltage falls below this threshold T UPP, the error is considered to be underperformance.

[0065] Fig. 6 shows schematically the sequence of a method for operating a voltage converter, for example the voltage converter 10, 20, 30 of Fig. 1-5, according to an example embodiment.

[0066] In a first step 110, the voltage converter, for example the voltage converter 10, 20, 30, is switched off by means of a controllable switch, for example the controllable switch 11, Fig. 2-4, periodically clocked in such a way that energy supplied on the input side is delivered via one or more energy storage devices of the voltage converter to a consumer connected on the output side, in particular an LED lamp.

[0067] In a second step 120, by means of a detection device, for example the detection device 12 of Fig. 1-4, a voltage is detected which depends on the voltage drop along the working path of the switch in the open state of the switch (in the closed state of the switch 11, this working path is short-circuited without any appreciable voltage drop).

[0068] In a third step 130, a plurality of different fault cases of the voltage converter are determined by the detected voltage, for example the voltage in Fig. 2-4 shown voltage V SNS , is fed to a determination device. This is designed to determine all of the plurality of different fault cases depending on the detected voltage, since these are each reflected in the detected voltage and can be detected by appropriate signal processing. The determination device can, for example, be as in Fig. 5 shown.

Claims

[1] Voltage converter (10, 20, 30), comprising a controllable switch (11) for clocked operation of the voltage converter (10, 20, 30), and a detection device (12) for detecting a voltage (V SNS ), which depends on a voltage falling along a working path of the switch (11) in an open state, characterized by a determination device (13) for determining a plurality of different fault cases of the voltage converter (10, 20, 30) as a function of the detected voltage (V SNS ), wherein the determining device (13) is designed to determine a respective one of the plurality of different fault cases of the voltage converter (10, 20, 30) by comparing the detected voltage (V SNS ) with a respective one of a predetermined plurality of different threshold values ​​(T OVP ; T UVP ; T OPP; T UPP ) to determine wherein the determining device (13) is designed to make a comparison as a function of a digitized detected voltage (V SNS ) to be carried out. [2] Voltage converter (10, 20, 30) according to claim 1, characterized by that the majority of different fault cases involve overvoltage. [3] Voltage converter (10, 20, 30) according to claim 1 or 2, characterized by that the majority of different fault cases involve undervoltage. [4] Voltage converter (10, 20, 30) according to one of the preceding claims, characterized by that the majority of different error cases involve overperformance. [5] Voltage converter (10, 20, 30) according to one of the preceding claims, characterized by that the majority of different error cases involve underperformance. [6] Voltage converter (30) according to one of the preceding claims, characterized by that the determining device (13) is arranged to carry out the comparison as a function of a peak value of the detected voltage (V SNS ) to be carried out. [7] Voltage converter (10, 20, 30) according to one of the preceding claims, characterized by that the determining device (13) is designed to carry out the comparison as a function of a factor (I SEL ) scaled detected voltage (V SNS ) to be carried out. [8] Voltage converter (10, 20, 30), comprising a controllable switch (11) for clocked operation of the voltage converter, and a detection device (12) for detecting a voltage (V SNS ), which depends on a voltage falling along a working path of the switch (11) in an open state, characterized by a power determination device (17) for determining a power consumption of the voltage converter (10, 20, 30) as a function of a factor (I SEL ) scaled detected voltage (V SNS ), wherein the voltage converter (10, 20, 30) is designed for use in an operating circuit for a lighting means. [9] Voltage converter (10, 20, 30) according to one of the preceding claims, characterized by that the voltage converter (10, 20, 30) is an inductive voltage converter (10, 20, 30) from the group consisting of flyback converter, step-down converter and resonant converter. [10] A method for operating a voltage converter (10, 20, 30), comprising: clocked operation of the voltage converter (10, 20, 30) by means of a controllable switch (11), and Detecting a voltage (V SNS), which is dependent on a voltage falling along a working path of the switch (11) in an open state, by means of a detection device (12), characterized by Determining a plurality of different error cases of the voltage converter (10, 20, 30) depending on the detected voltage (V SNS ) by means of a determining device (13), Determining a respective one of the plurality of different fault cases of the voltage converter (10, 20, 30) by comparing the detected voltage (V SNS ) with a respective one of a predetermined plurality of different threshold values ​​(T OVP ; T UVP ; T OPP , T UPP ) by means of the determining device (13), Carrying out the comparison depending on a digitized recorded voltage (V SNS ) by means of the determining device (13). [11] A method for operating a voltage converter, comprising: clocked operation of the voltage converter by means of a controllable switch (11), and Detecting a voltage (V SNS ), which is dependent on a voltage falling along a working path of the switch (11) in an open state, by means of a detection device (12), characterized by Determining the power of the voltage converter as a function of a factor (I SEL ) scaled detected voltage (V SNS ) by means of a power determination device (17), wherein the voltage converter is designed for use in an operating circuit for a lighting device. [12] Method according to claim 11, characterized by that determining the power of the voltage converter as a function of a peak value of the detected voltage (V SNS ) is carried out. [13] Method according to claim 11 or 12, characterized by that determining the performance of the voltage converter comprises determining an overperformance or an underperformance of the voltage converter.

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