DE102012007451A1 - Transducer e.g. LLC resonant converter for lighting unit, of LED converter used in lighting system, has control device that is arranged in primary-side circuit, to detect error state at output unit of secondary-side circuit - Google Patents

Abstract

The transducer (19) has primary-side circuits (20), half-bridge circuit with switches (21,22) and LLC resonant circuit. A secondary-side circuit (30) is isolated electrically from the primary-side circuit. The secondary-side circuit is provided with output unit (35) for supplying power to lighting unit (5). A control device (14) is arranged in the primary-side circuit, to detect the error state at the output unit of the secondary-side circuit. An independent claim is included for a method for operating LLC resonant converter for lighting unit.

Description

The invention relates to a converter for supplying a lighting means, an LED converter and a method for operating such a converter. The invention particularly relates to such devices and methods in which a light source, in particular a light source comprising one or more light emitting diodes, with a so-called SELV ("Separated Extra Low Voltage" or "Safety Extra Low Voltage") - device with Energy is supplied.

Transducers with electrical isolation serve for galvanically decoupled transmission of electrical energy from an input side to an output side. Such converters are used in various applications for power or voltage supply, such as in switched mode power supplies. In clocked converters, controllable switches, which may be in the form of circuit breakers, are used and clocked to transfer electrical energy to the output side. A galvanically decoupled energy transfer can be achieved by using a transformer or other transformer. Such a galvanic separation or potential separation is required for safety reasons in operating devices for lighting to separate an ELV ("extra low voltage") - area by a so-called potential barrier or SELV barrier of areas with higher supply voltage, especially mains voltage.

For operating light sources, it is possible to use transducers which are designed as so-called resonant transducers which have a resonance circuit. The resonant circuit may be a series or parallel resonant circuit. In the design of converters, the goal is to keep losses low. Resonant transducers comprising an LLC resonant circuit with two inductances and one capacitance can be controlled on the primary side resonantly or quasi-resonantly. Such converters have the advantage that energy-efficient operation with relatively low switching losses is possible.

For safety reasons, the operation of a converter should allow to detect at least certain operating states, for example open circuit or short circuit at the output of the SELV range. A conventional approach for this purpose uses a direct measurement, for example, of the output voltage, which is carried out in the secondary-side circuit. The voltage detected on the secondary side can then be returned to the primary side via an isolator. The bridging of the SELV barrier requires appropriate components which increase the installation space and / or costs of the operating device. The US 2012/0033453 A1 describes an example of a resonant converter comprising a half-bridge and an LLC circuit and in which an isolator is provided to return an output-measured quantity to the input side.

There is a need for devices and methods that provide improvements for detection of certain operating conditions, particularly output short circuit and / or open circuit output. In particular, there is a need for devices and methods in which the circuitry complexity and / or costs associated with conventional SELV barrier bridging devices can be reduced or avoided. There is also a need for such devices and methods that have low switching losses.

According to the invention, a method, a converter and an LED converter are provided with the features specified in the independent claims. The dependent claims define embodiments.

According to embodiments of the invention, an LLC resonant converter comprising a primary-side half-bridge circuit and an LLC resonant circuit has a control device which, depending on a phase relationship of a current in the primary-side circuit, determines certain operating conditions such as a short circuit at the output of the secondary side and / or an open circuit Detect circuit at the output of the secondary side. The controller performs the detection of error conditions concerning the output of the secondary side based on a measurand detected in the primary-side circuit.

To detect a fault condition, a time may be detected at which a current flowing between the LLC resonant circuit and ground has a zero crossing. It can be determined whether this time lies within an interval by a reference time. The reference time may be the middle between a first switching time, before the zero crossing, a first switch of the half-bridge circuit is switched last in the off state, and a second switching time, after the zero crossing, a second switch of the half-bridge circuit for the first time in the off state will be switched.

The devices and methods can detect in particular an open circuit and / or a short circuit at the output of the secondary side. The devices and methods utilize that, in the LLC resonant converter, primary side sensed measurements representing current in the primary side may provide information as to whether an open circuit or a short circuit present at the output of the secondary side. This allows, even without measurement in the secondary side circuit to detect an open circuit and / or a short circuit at the output of the secondary side circuit.

According to one embodiment, a converter for a light source is specified. The converter comprises a primary-side circuit and one of them galvanically isolated secondary side. The primary-side circuit comprises a half-bridge circuit comprising a first switch and a second switch, and an LLC resonant circuit connected to a node between the switches of the half-bridge. The secondary side has an output for supplying energy to the luminous means. The converter comprises a control device that is set up to detect a fault condition at the output of the secondary side, depending on a phase position of a current in the primary-side circuit.

The controller may be configured to generate control signals for clocked switching of the two switches of the half-bridge. The control device can be set up to detect the error state at the output of the secondary side as a function of a phase position of the primary-side current relative to the control signals.

The primary-side circuit may be configured to tap a voltage across a sense resistor connected between a switch of the half-bridge circuit and ground to sense the current. The sense resistor may be connected between the switch disposed on the low potential side of the half bridge and ground. A shunt resistor can be used as a measuring resistor at the same time. In this way, a simple and cost-effective detection of the primary-side current can be realized.

The controller may be configured to detect the error condition depending on a time of zero crossing of the current.

A comparator may have an input for receiving a measurement signal proportional to the current. The controller may be coupled to an output of the comparator to determine the time of zero crossing. This makes a simple and cost-effective monitoring of the zero crossing of the current possible.

The control device may be configured to determine a deviation between the time of the zero crossing and a reference time and to detect the error state as a function of a threshold value comparison of the deviation.

The control device may be configured to set the reference time as a function of a first switching time, in which a first switch of the half-bridge circuit is switched to an off state, and a second switching time, in which a second switch of the half-bridge circuit is switched to an off state, to determine. The first switching time may correspond to the last switching operation of the first switch to the off state before the corresponding zero crossing of the current, and the second switching time may correspond to the first switching operation of the second switch to the off state after the corresponding zero crossing of the current. The first switching time may correspond to the Nth switching of the first switch to the off state before the corresponding zero crossing of the current, and the second switching time may correspond to the Nth switching of the second switch to the off state after the corresponding zero crossing of the current where N is a natural number.

The first switch may be connected between a supply connection of the primary-side circuit and the LLC resonance circuit. The second switch may be connected between the LLC resonant circuit and a reference potential, in particular ground. Ie. the first switch may be the switch on the high potential side of the half bridge circuit, and the second switch may be the switch on the low potential side of the half bridge circuit.

The control device may be arranged such that the reference time is the middle between the first switching time and the second switching time.

The control device may be configured to generate a first clocked control signal and a second clocked control signal for controlling the half-bridge circuit. The controller may be configured to determine the reference time depending on both the first clocked control signal and the second clocked control signal.

The control device may be configured to compare, for performing the threshold comparison, the deviation between the time of the zero crossing and the reference time with a threshold which is smaller than a period of the first clocked control signal and the second clocked control signal. The threshold may depend on a switching frequency at which the controller switches the switches of the half-bridge circuit.

The control device may be configured to detect an open circuit or a short circuit at the output of the secondary side based on the phase position of the current.

According to a further embodiment, an LED converter is provided which comprises the converter according to an embodiment.

According to a further embodiment, a lighting system is specified which comprises the LED converter and a light source coupled thereto. The lighting means may comprise one or more light-emitting diodes (LEDs). The LEDs may include inorganic and / or organic LEDs. The LEDs can be integrated into an LED module that is separate from the LED converter. The lighting system may further comprise a central controller arranged to transmit dimming commands to the LED converter or to evaluate signals transmitted by the LED converter.

In accordance with another embodiment, a method of operating an LLC resonant converter for a lighting device is provided. The LLC resonant converter includes a primary side circuit and one of them galvanically isolated secondary side. The primary-side circuit comprises a half-bridge circuit comprising a first switch and a second switch, and an LLC resonant circuit connected to a node between the switches of the half-bridge. The secondary side has an output for supplying energy to the luminous means. In the method, a measured variable in the primary-side circuit is detected, which depends on a current in the primary-side circuit. An error condition at the output of the secondary side is detected based on a phase position of the current.

To detect the error condition, a deviation between a time of a zero crossing of the current and a reference time can be determined. The deviation can be compared to a threshold.

The reference time may be determined from a middle between a first switching time, at which the first switch is switched to the off state before the zero crossing, and a second switching time, at which the second switch is switched to the off state after the zero crossing. The first switching time may correspond to the last switching operation of the first switch to the off state before the corresponding zero crossing of the current, and the second switching time may correspond to the first switching operation of the second switch to the off state after the corresponding zero crossing of the current. The first switching time may correspond to the Nth switching of the first switch to the off state before the corresponding zero crossing of the current, and the second switching time may correspond to the Nth switching of the second switch to the off state after the corresponding zero crossing of the current where N is a natural number.

The detection of the fault condition may include a detection of an open circuit at the output or a short circuit at the output of the secondary side based on the phase position.

Embodiments of the method according to advantageous or preferred embodiments as well as the effects achieved thereby correspond to the embodiments described with reference to the devices. The method can be carried out automatically with a converter or LED converter according to an embodiment.

The invention will be explained in more detail with reference to the accompanying drawings with reference to preferred embodiments.

1 shows a schematic representation of a lighting system with an LED converter according to an embodiment.

2 shows a circuit diagram of a converter according to an embodiment.

3 shows a simplified circuit diagram of the converter to explain the operation.

4 illustrates control signals for half-bridge driving, which generates a control device of the converter according to an embodiment in a first operating mode.

5 illustrates the operation of the controller in detecting a fault condition based on a phase relationship of a current in the primary-side circuit.

6 shows a circuit diagram of a converter according to another embodiment.

7 is a flowchart of a method according to an embodiment.

The features of the various embodiments described below can be combined with each other, unless this is expressly excluded in the following description.

1 shows a lighting system 1 in which a control gear 2 after one Embodiment LEDs 3 energized. The operating device 2 can be configured as an LED converter. The LED converter 2 can be designed as a constant current source. The LED converter 2 can be designed so that the brightness of the LEDs 3 via commands, for example via a bus 4 or wirelessly transmitted, is adjustable. The LED converter 2 may include a corresponding interface for communication with a central controller and be configured to receive dimming commands via the interface.

The LED converter 2 may be configured as a SELV device in which a primary-side circuit (for example, a non-SELV side) and a secondary-side circuit (for example, a SELV side) are galvanically isolated. The LED converter 2 can be an AC / DC converter 10 include. The AC / DC converter 10 can be set up to be coupled on the input side with a mains voltage. The AC / DC converter 10 may be configured as a so-called smoothing circuit or power factor correction (PFC) circuit. The AC / DC converter 10 provides a bus voltage Vbus to a converter, which has an input-side or primary-side circuit 11 and one of them galvanically isolated output side or secondary side circuit 13 having. A galvanic isolation is done by a transformer 12 or other translators.

The LED converter 2 has a control device 14 on. The control device 14 may be a semiconductor integrated circuit, in particular an application-specific integrated circuit (ASIC). The control device 14 can be in the primary-side circuit 11 be integrated. The control device 14 may be on the non-SELV side of the LED converter 2 are located.

The LED converter 2 is configured such that the control device 14 Automatically detects fault conditions in which at the output of the LED converter 2 an open circuit or a short circuit is present. For this purpose, the control device 14 the detection of the fault condition, such as an open circuit or a short circuit on the secondary side output of the LED converter 2 , based on a phase relationship of a current in the primary-side circuit. The control device 14 In particular, it can detect the fault condition by comparing, for determining the phase position, a time at which the current has a zero crossing with a reference time which is determined by clocked control signals for the half-bridge triggering.

As in 1 is shown schematically, in the LED converter 2 the controller 14 Automatically detect fault conditions, such as an open circuit or a short circuit at the output of the secondary side, without having to carry out a measurement on the secondary side. It is not absolutely necessary to provide on the secondary side corresponding components for detecting an open circuit or a short circuit at the output of the secondary side. It is also not absolutely necessary to acquire values on the secondary side via the SELV barrier to the control device 14 to have to return. If the controller 14 detected a fault condition, it can automatically a corresponding operating mode of the LED converter 2 initiate. Such an operating mode may include, for example, a safety shutdown and / or the output of signals indicating the presence of an error condition. A corresponding control of the LED converter 2 can again be done on the primary side. The control device 14 can be the AC / DC converter 10 and / or the input side 11 for an operating mode in the event of a fault, for example, to effect a safety shutdown and / or the output of signals indicating the presence of an error condition.

In the LED converter 2 can the controller 14 fulfill additional functions. The control device 14 For example, can perform an overcurrent protection function, in which by changing the timing of the switch of the half-bridge, the primary-side and / or output-side current is reduced, even if there is no short circuit. The control device 14 can also perform conventional functions of controlling an LED converter, such as the implementation of commands over a bus 4 or via a wireless interface to adjust the brightness of a light source.

The operation and construction of transducers according to embodiments will be described with reference to FIG 2 - 7 described in more detail.

2 is a circuit diagram of a converter 19 according to an embodiment. The converter 19 includes a primary-side circuit 20 and a secondary side 30 , There is potential separation between the primary-side circuit 20 and the secondary side 30 in front. For separation, a transformer with a primary coil 28 and a secondary coil 29 be provided. The converter 19 can with the LED converter 2 or in another operating device for operating LEDs to perform the functions of in 1 illustrated primary-side circuit 11 , the galvanic isolation 12 and the secondary side 13 to fulfill. The converter 19 acts as a DC / DC converter. The secondary side 30 may be a SELV region that passes through a SELV barrier 39 is separated from the primary-side area. The primary-side circuit 20 can contain all components that are not part of the SELV range.

The primary-side circuit 20 includes an LLC resonant circuit configured as a series resonant circuit. The LLC resonant circuit has a first inductance 25 , a second inductance 26 and a capacity 27 in a series connection. In accordance with the general terminology in this technical field, the term "LLC resonant circuit" or "LLC resonant converter" is used to refer to a resonant circuit with two inductors and a capacitance or a corresponding converter, which does not matter, whether the inductance 26 between the inductance 25 and the capacitor 27 is switched or the capacitor 27 between the inductive elements 25 and 26 is switched. The symbolically represented second inductance 26 can the magnetization inductance of the primary coil 28 be the transformer. The primary coil 28 and secondary coil 29 should illustrate in this illustration, only the winding ratio and the galvanically coupled energy transfer of the transformer. Alternatively or additionally, also the first inductance 25 be integrated as stray inductance in the transformer. The second inductive element 26 may be the main inductance of the resonant circuit whose inductance is greater than the first inductance 25 is. Other embodiments of the LLC resonant circuit are also possible. For example, the capacity 27 between the inductors 25 and 26 be switched, in the LLC resonant circuit can also resistors 24 be present in 2 are shown schematically and which may be parasitic resistors of circuit elements and / or hold resistors.

The primary-side circuit 20 includes a half bridge with a first switch 21 which may be a circuit breaker and a second switch 22 which can be a circuit breaker. The first switch 21 and the second switch 22 may be identical, and the half bridge may be formed as a symmetrical half bridge. The switches can be designed as field-effect transistors, for example as MOSFETs. The resonant circuit is connected to a node between the first switch 21 and the second switch 22 connected. The resonant circuit is at the middle of the half-bridge between the two switches 21 and 22 connected. A first connection of the first inductance 25 of the resonant circuit can be connected to the node between the first switch 21 and the second switch 22 be connected to the half-bridge circuit. A second terminal of the first inductance 25 may be connected to a first terminal of the second inductance 26 be connected to the resonant circuit. A second terminal of the second inductance 26 of the resonant circuit can with a first connection of the capacity 27 be connected. A shunt resistor 23 can be between the second switch 22 and a reference potential, such as ground, to be switched to enable an error shutdown and, for example, to keep shutdown times sufficiently short in the event of a fault trip. As will be described in more detail, during operation of the converter 19 one over the shunt resistor 23 or a voltage drop across another measuring resistor of the primary-side circuit is detected in a time-resolved manner. As a result, the phase position of the current can be determined by the second switch 22 flows when the second switch 22 is in the on state.

In the operation of the converter 19 controls the controller 14 the first switch 21 and the second switch 22 , In this case, each of the switches can each be switched with the same switching frequency. The control device 14 controls the first switch 21 and the second switch 22 such that at most one of the two switches is turned on at a maximum. To adjust the brightness, the controller 14 For example, change the switching frequency to the value of the frequency-dependent transfer function or gain of the converter 19 adjust.

3 shows a simplified representation of the converter 49 to explain the operation of the control device 14 , The primary-side circuit 50 with the control device 14 has an arrangement with which zero crossings of a current in the primary-side circuit can be detected.

In the primary-side circuit 50 a current is monitored or sampled, for example by the second switch 22 and thus by serving as a measuring resistor shunt resistor 23 flows when the first switch 21 by a first control signal ctrl1 in the off state and the second switch 22 is switched to the on state by a second control signal ctrl2.

Due to the clocked switching of the first switch 21 and the second switch 22 In the half-bridge circuit, a current that changes cyclically according to the switching frequency of the switches flows. The resulting time dependence of the current that occurs in the primary-side circuit depends on the load on the output 35 the secondary side. In particular, the phase of the current relative to the timing of the first control signal ctrl1 and the second control signal ctrl2 from the load at the output 35 the secondary side. While the second switch 22 is switched to the on state by the second control signal ctrl2 and the first switch 21 is switched by the first control signal ctrl1 in the off state, a measured variable isns can be detected, the current 52 proportional, that flows, if the second switch 22 in the on state and the first switch 21 is in the off state. The measurand isns can be as voltage across a measuring resistor, such as the shunt resistor 23 be recorded.

The phase of the current can be determined depending on a time at which the current 52 has a zero crossing while the second switch 22 in the on state and the first switch 21 in the off state. For easy detection of the zero crossing, the measured variable proportional to the current can be an input of a comparator 51 be supplied. The other input of the comparator 51 can be coupled to a reference, in particular mass. An output of the comparator 51 is with an input of the control device 14 coupled. A jump in the output signal isns_cmp of the comparator 51 shows the time of the zero crossing of the current 52 from which it can be determined whether at the exit 35 the secondary side is an open circuit or a short circuit.

The control device 14 can be designed as a semiconductor integrated circuit, in particular as a chip, in particular as an ASIC. The same semiconductor integrated circuit which generates the half bridge drive control signals ctrl1 and ctrl2 may be based on the phase angle of the current flowing in the primary side circuit 52 detect whether at the output of the secondary side 35 an open circuit or a short circuit is present.

As with reference to 5 will be described in more detail, a fault condition, in which at the output of the secondary side 35 an open circuit or a short circuit is present, depending on a deviation between the time of a zero crossing of the current and the time center between a first switching time, in which the first control signal ctrl1 before the zero crossing the first switch 21 in the off-state, and a second switching time, wherein the second control signal ctrl2 after the zero crossing the second switch 22 in the off state, be detected.

4 schematically shows that of the controller 14 to the first switch 21 output control signal 61 and that to the second switch 22 output control signal 62 with which the corresponding switch is switched. Both switches are periodically switched at the same switching frequency, the switches being alternately clocked. The control signal may correspond, for example, to a gate voltage applied to the gate electrode of the switches.

One switching cycle duration 65 the control signal 61 for the first switch 21 and a switching cycle duration 65 the control signal 62 for the second switch 22 , which may each be defined as the time between successive rising edges of the control signal, is the same for both switches. The switching cycle duration 65 corresponds to the duration of a switching cycle of the first switch 21 and second switch 22 , The switches 21 and 22 are switched so alternately clocked that only a maximum of one of the switches is turned on. A dead time between turning off one switch and turning on the other switch may be small compared to the inverse of the switching frequency, ie small compared to the switching cycle time 65 a switching cycle. Accordingly, the duration 66 during which the switches are off in each switching cycle, be greater than the time duration 67 during which the switches are on in each switching cycle.

The inverse of the switching cycle time 65 is the switching frequency. The switching frequency may be selected to be greater than the natural frequency of the LLC resonant circuit, for example. The switching frequency can be during normal operation of the converter, in which no open circuit and no short circuit at the output 35 of the transducer is changed to adjust the brightness of the bulb.

5 illustrates the operation of the controller 14 for detecting an error condition in which at the output 35 the secondary side 30 an open circuit or a short circuit is present. In this case, the LLC resonant circuit operates with only a low power consumption, for example due to parasitic resistances 24 can be caused.

If at the exit 35 the secondary side 30 an open circuit or a short circuit, the behavior of the LLC resonant circuit is determined by the inductors or the LLC resonant circuit operates in "inductive mode". In this case, the current flowing from the node between the switches 21 . 22 the half-bridge circuit into the LLC resonant circuit or from the LLC resonant circuit through the switches 21 . 22 the half-bridge circuit flows, have a substantially triangular shape. The phase of the current relative to the control signals for the switches 21 . 22 can be 90 ° or π / 2.

5 shows the current 73 as a function of the time taken by the node between the switches 21 . 22 the half-bridge circuit into the LLC resonant circuit or from the LLC resonant circuit through the switches 21 . 22 the half-bridge circuit flows. For detecting the phase position of the current when the second switch 22 is switched to the on state, which can be via a measuring resistor decreasing voltage, for example the voltage V_Shunt across the shunt resistor 23 , be monitored. A time point TN of the zero crossing of the current that occurs while the more potential lower switch 22 the half-bridge is switched to the on-state is detected.

The time zero of the zero crossing of the current is compared with the timing of the time-dependent control signals for the switches of the half-bridge to determine whether an error condition exists. For this purpose, a reference time TM can be determined. If a deviation of the time instant TN of the zero crossing from the reference time TM is smaller than a threshold value, ie, the instantaneous time TN of the zero crossing is in an interval 75 around the reference time TM, an error condition is detected.

The reference time TM can be defined as the time interval between a first switching time T1, at which the higher-potential switch 21 the half-bridge was previously switched to the off state before the zero crossing, and a second switching time T2, at which the potential-lower switch 22 the half-bridge is first switched to the off state after the zero crossing. The thus-defined reference time TM is different from the middle of the off-time of the first switch and the middle of the on-time of the second switch.

For a reference time TM, based on both the flank 71 the first control signal for the first switch as well as based on the edge 72 the second control signal is defined for the second switch, a fault condition can be detected in a simple manner on the basis of the deviation between the time instant TN of the zero crossing of the current and the reference time TM. The reference time TM differs by the same time difference 76 of both the first switching time T1 at which the higher potential switch 21 the half-bridge has been last switched to the off state before the zero crossing, and the second switching time T2, at which the lower-potential switch 22 the half-bridge is first switched to the off state after the zero crossing.

The control device 14 can detect the deviation between the time point TN of the zero crossing and the reference time TM in different ways. In one embodiment, the control device 14 calculate a value indicative of the reference time TM and compare it with the time TN of the zero crossing. The point in time TN of the zero crossing of the current can be, for example, as a jump in the output signal of the comparator 51 be recognized.

In a further embodiment, the control device 14 determine both a value representing the first switching time T1 and a value representing the second switching time T2 and determining the mean value as the reference time TM. The first switching time T1 and the second switching time T2 can by detecting the signal edges 71 . 72 be recognized.

In a further embodiment, the control device 14 a first time difference between the edge 71 of the first control signal and the time instant TN of the zero crossing of the current and a second time difference between the time instant TN of the zero crossing and the edge 72 determine the second control signal. The corresponding signal edges in the control signals or in the output signal of the comparator can serve as trigger signals with which a counter is started and stopped. The difference between the first time difference and the second time difference quantifies the deviation between the time point TN of the zero crossing of the current and the reference time TM.

The reference time TM, with which the instantaneous time TN of the zero crossing of the current in the LLC resonant circuit or the current through a measuring resistor is related, does not have to be dependent on those described in FIG 5 represented signal edges 71 . 72 be determined, which immediately precede or follow the zero crossing. For example, the reference time TM may also be used as the middle between a signal edge of the control signal ctrl1 for the first switch 21 the half-bridge, the N-th signal edge to turn off the first switch 21 before the corresponding zero crossing of the current, and a signal edge of the control signal ctrl2 for the second switch 22 the half-bridge, the Nth signal edge to turn off the second switch 22 after the corresponding zero crossing of the current is to be determined. With reference to 4 can, if the zero crossing of the current, during the period 83 is compared with a reference time, the reference time TM also as the time center between the in 4 represented signal edge 81 the first control signal and the signal edge 82 of the second control signal, which is respectively the second corresponding edge before and after the zero crossing.

When the controller 14 Based on the phase position of the current in the primary-side circuit detects that an error condition exists, for example, an open output or a short circuit at the output, the controller 14 automatically initiate a particular mode of operation of the converter or of the converter containing the converter. For example, a signal indicating the presence of a fault may be output. Alternatively or additionally, a safety shutdown can be performed.

Further embodiments of devices and methods can be realized in other embodiments. For example, the phase angle of the current can not only be determined using the in 3 shown comparator, but also be determined in other ways. For example, the control device 14 be fed to the measured variable, which indicates the current in the primary circuit when the second switch 22 the half-bridge is in the on state. The control device 14 can monitor the current to detect the zero crossing.

6 shows a converter 89 according to a further embodiment. Elements and devices that correspond in design and function to elements or devices described with reference to 1 - 5 have been described are denoted by the same reference numerals.

The converter 89 has a primary-side circuit 90 on that the non-SELV range of the converter 89 can correspond. The measurand isns, which represents the current that flows between the LLC resonant circuit and ground when the switch 22 is switched to the low-potential side of the half-bridge in the on-state, by an A / D converter 91 A / D converted and the controller 14 be supplied. The control device 14 can query the current value of the current isns at a rate greater than the switching frequency of the switches 21 . 22 the half bridge is. Based on the time-dependent detected current isns, the control device 14 determine by digital signal processing the time TN of the zero crossing and with a reference time TM compare, as in reference to 4 has been described.

7 is a flowchart of a method 100 that from the control device 14 for controlling a converter can be performed. The converter can be designed as a converter according to an embodiment. The converter has a half-bridge drive LLC resonant circuit. The converter has a primary-side circuit and one of them galvanically isolated secondary side. For example, the primary side circuit may be a non-SELV region of the transducer and the secondary side may be the SELV region of the transducer.

at 101 After the start of operation of the converter, the switches of the half-bridge circuit are switched clocked.

at 102 detecting a timing of a zero-crossing of the current flowing between the LLC resonant circuit and ground when the switch on the low-potential side of the half-bridge circuit is switched to an on state.

at 103 a deviation between the time of the zero crossing and a reference time is determined. The reference time may be a time middle between switching operations with which switches of the half-bridge circuit are switched to the off state before and after the zero crossing.

at 104 the deviation can be subjected to a threshold comparison. If the deviation is greater than the threshold, the process returns 101 back. The determination of the phase position of the current in the primary-side circuit need not be done every switching cycle, but can be repeated at certain intervals to detect the occurrence of a fault condition during operation.

If at 104 If it is detected that the deviation is smaller than the threshold value, this indicates an error condition. Accordingly, at 105 an error operating mode is initiated. For this purpose, a signal indicating the presence of an error can be output. Alternatively or additionally, a safety shutdown can be performed.

While embodiments have been described with reference to the figures, modifications may be made in other embodiments. While the evaluation of a phase position of a current detected on the primary side for the purpose of detecting an error state at the output of the secondary side has been described in detail, the methods and devices according to exemplary embodiments can also be used to detect other operating states. For example, not only can it be determined whether the phase of the current relative to the switching cycles of the switches of the half-bridge is approximately 90 °, but the phase angle of the current can be determined quantitatively to detect a load at the output of the converter.

The detection of a quantity representing the current on the primary side need not occur at the shunt resistance. For example, a measuring resistor different from the shunt resistor can be provided.

The control device of the converter and LED converter according to embodiments may be configured as a semiconductor integrated circuit. The control device can be configured as an application-specific special circuit (ASIC) or as another chip.

Inductances and capacitances can each be formed by corresponding inductive or capacitive elements, for example as coils or capacitors. However, it is also possible that smaller inductances, for example a Inductance of the LLC resonant circuit, are designed as stray inductance. Similarly, smaller capacities may be designed as stray capacitors.

Converters and methods according to embodiments can be used in particular for the power supply of LEDs.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2012/0033453 A1 [0004]

Claims (16)

Transducer for a light bulb ( 3 ; 5 ), comprising a primary-side circuit ( 20 ; 50 ; 90 ) with a half-bridge circuit, the two alternately clocked in operation switch ( 21 . 22 ) and with an LLC resonant circuit ( 25 - 27 ), one of the primary-side circuit ( 20 ; 50 ; 90 ) galvanically isolated secondary side ( 30 ) with an output ( 35 ) for the energy supply of the illuminant ( 3 ; 5 ), and a control device ( 14 ), which is arranged to be dependent on a phase relationship of a current ( 52 ; 73 ) in the primary-side circuit ( 20 ; 50 ; 90 ) an error condition at the output ( 35 ) of the secondary side ( 30 ) to recognize. Converter according to claim 1, wherein the primary-side circuit ( 20 ; 50 ; 90 ) is arranged to detect the current ( 52 ; 73 ) a voltage across a measuring resistor ( 23 ), which is located between a switch ( 22 ) of the half-bridge circuit and ground is connected, tap. Converter according to claim 1 or claim 2, wherein the control device ( 14 ) is arranged to determine the error state as a function of a time (TN) of a zero crossing of the current ( 52 ; 73 ) to recognize. Converter according to claim 3, wherein a comparator ( 51 ) an input for receiving a measurement signal associated with the stream ( 52 ; 73 ) is proportional, and wherein the control device ( 14 ) with an output ( 35 ) of the comparator ( 51 ) is coupled to determine the time (TN) of the zero crossing. Converter according to claim 3 or 4, wherein the control device ( 14 ) is arranged to determine a deviation between the time (TN) of the zero crossing and a reference time (TM) and to detect the error state depending on a threshold comparison of the deviation. Converter according to claim 5, wherein the control device ( 14 ) is set to the reference time (TM) depending on a first switching time (T1), in which a first switch ( 21 ) of the half-bridge circuit is switched to an off-state, and a second switching time (T2), in which a second switch ( 22 ) of the half-bridge circuit is switched to an off state. A converter according to claim 6, wherein the first switch ( 21 ) between a supply terminal of the primary-side circuit ( 20 ; 50 ; 90 ) and the LLC resonant circuit ( 25 - 27 ), and wherein the second switch ( 22 ) between the LLC resonant circuit ( 25 - 27 ) and a reference potential, in particular ground, is connected, and wherein the control device ( 14 ) is arranged to determine the reference time (TM) as the middle between the first switching time (T1) and the second switching time (T2). Converter according to one of claims 5-7, wherein the control device ( 14 ) is arranged to provide a first clocked control signal (ctrl1; 61 ) and a second clocked control signal (ctrl2; 62 ) for controlling the half-bridge circuit, and wherein the control device ( 14 ) is arranged to set the reference time (TM) in response to both the first clocked control signal (ctrl1; 61 ) as well as the second clocked control signal (ctrl2; 62 ). Converter according to claim 8, wherein the control device ( 14 ) is arranged to compare the deviation with a threshold value smaller than a period of the first clocked control signal (ctrl1; 61 ) and the second clocked control signal (ctrl2; 62 ). Transducer according to one of the preceding claims, wherein the control device ( 14 ) is set up based on the phase of the current ( 52 ; 73 ) an open circuit or a short circuit at the output ( 35 ) of the secondary side ( 30 ) to recognize. LED converter, comprising the converter ( 19 ; 49 ; 89 ) according to any one of the preceding claims. Method for operating an LLC resonant converter ( 19 ; 49 ; 89 ) for a light source ( 3 ; 5 ), the LLC resonant converter ( 19 ; 49 ; 89 ) a primary-side circuit ( 20 ; 50 ; 90 ) with a half-bridge circuit comprising a first switch ( 21 ) and a second switch ( 22 ) and with an LLC resonant circuit ( 25 - 27 ) as well as one of the primary-side circuit ( 20 ; 50 ; 90 ) galvanically isolated secondary side ( 30 ) with an output ( 35 ) for the energy supply of the illuminant ( 3 ; 5 ), the method comprising: detecting a measurand (isns; 74 ) in the primary-side circuit ( 20 ; 50 ; 90 ), by a stream ( 52 ; 73 ) in the primary-side circuit ( 20 ; 50 ; 90 ) and detecting an error condition at the output ( 35 ) of the secondary side ( 30 ) based on a phase relationship of the current ( 52 ; 73 ). The method of claim 12, wherein detecting the error condition comprises: Determining a deviation between a time (TN) of a zero crossing of the current ( 52 ; 73 ) and a reference time (TM), and comparing the deviation with a threshold. Method according to claim 13, wherein the reference time (TM) is the middle between a first switching time (T1) to which the first switch ( 21 ) is switched to the off state before the zero crossing, and a second switching time (T2) to which the second switch ( 22 ) after the zero crossing is switched to the off state is determined. The method of claim 12, wherein detecting the fault condition comprises detecting an open circuit or a short circuit at the output. 35 ) of the secondary side ( 30 ) based on the phase position. Method according to one of claims 12-15, associated with the transducer ( 19 ; 49 ; 89 ) is carried out according to one of claims 1-10.

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