Light source converters with balanced output currents and methods for balancing them

Abstract

Lamp converter with an LLC resonant circuit, from whose secondary side lamps (LED), such as in particular an LED line, can be supplied, where the LLC resonant circuit comprises: - a half-bridge circuit (HB) with two switches (S1, S2) connected in series, which are controlled by a control circuit (SE), - a resonant circuit (RK) supplied from a midpoint of the two switches (S1, S2), and - a transformer (T1) supplied with AC voltage from an output of the resonant circuit (RK), on the secondary side of which a current path (SP1, SP2) is provided for each of the two polarities of the AC voltage, characterized in that - a detection circuit (ES) is provided which detects a signal (V1, V2) which represents currents (I SP1 , I SP2) in the two current paths (SP1, SP2) and / or their ratio, wherein the detection circuit (ES) has at least one detection branch (EZ1) which detects the signal representing the current through a signal path (SP1), and - the control circuit (SE) adjusts the timing of the two switches (S1, S2) of the half-bridge circuit (HB) depending on the signal (V1, V2) detected by the detection circuit (ES), wherein the at least one detection branch (EZ1) has a sample-and-hold circuit (S3, RH1, CH1).

Description

[0001] The invention relates to a lamp converter for operating at least one lamp, preferably at least one LED or LED array. The invention also relates to a method for operating a lamp converter. The invention further relates to a lamp converter with an LLC circuit in which an AC voltage is used to supply a (series) resonant circuit, which in turn serves to supply another converter stage for directly supplying a lamp. The supply voltage supplied to the lamp must then typically be converted into a DC voltage. This can generally be achieved, for example, using a full-bridge rectifier. However, with regard to energy advantages, rectification starting from a transformer is recommended.

[0002] A “lamp converter” is an electrical circuit that can be supplied with an input voltage and to which lamps, such as one or more LEDs, can be connected in order to be electrically operated in a defined manner.

[0003] From the prior art, for example, the document WO 2014 / 060899 A2 is known, in which a lamp converter in Fig. 1, which can serve as a starting point for the invention. A similar lamp converter is also described in Fig. 1. A control circuit SE controls an inverter half-bridge HB with two switches S1, S2 connected in series. As shown in Fig. As shown in Figure 1, the half-bridge circuit HB is supplied by an input voltage, which is exemplified as the bus voltage V BUSInstead of a bus voltage, which is normally a DC voltage, a rectified AC voltage can also be used to supply the half-bridge.

[0004] Starting from a midpoint of the half-bridge HB, or the two switches S1, S2, a resonant circuit is now supplied, which is formed in particular from a series connection of a capacitor C1, an inductor L1 and a second inductor L2a. Starting from the inductor L2a, a transformer T1 is now fed with an alternating voltage, i.e. an AC voltage. The transformer T1 has the electromagnetic inductors, coils or windings L2a, L2b, L2c. The inductors L2b and L2c are arranged on the secondary side of the transformer T1. The inductors L2b and L2c are shown as separate inductors because a center tap M1 is provided on the secondary side of the transformer T1.

[0005] Starting from the inductors L2b and L2c, a current path SP1 and SP2 is then supplied. The current paths SP1 and SP2 thus each connect one side of the inductor L2b and L2c to a connection point CP, with each current path having a diode for rectification.

[0006] The first current path SP1 has the diode D1, while the second current path SP2 has a second diode D2. An induced current I SP1 transmitted, an induced current I SP2 . On the other hand, an output terminal E1 of the lamp converter is connected to the connection point CP, to which, for example, a load LED, e.g. a lamp and in particular at least one LED, can be connected.

[0007] Between the connection point CP and the output terminal E1, a smoothing capacitor C2 is further connected with its higher potential side, whereby the lower potential side of the second capacitor C2 can be at the secondary ground potential of the transformer.

[0008] The control circuit SE controls the higher-potential switch S1 of the half-bridge HB via a control signal HS ("high-side" signal), while controlling the lower-potential switch S2 of the half-bridge with a signal LS ("low-side" signal). The control circuit SE alternately switches the switches S1 and S2, which are preferably transistors, e.g., FETs or MOSFETs, to provide an alternating voltage for the transformer T1 at the midpoint of the half-bridge HB.

[0009] In the Fig. 1, the primary winding L2a of the transformer T1 is connected on its lower-potential side to the primary-side ground, as is the lower-potential side of the half-bridge switch S2. The current or voltage through the primary-side inductance L2a is transferred by the transformer T1 to the secondary side, whereby the current I in the first current path SP1 SP1 and in the second current path SP2 the current I SP2 is induced.

[0010] The center tap between the secondary-side inductors L2b and L2c, however, serves to provide currents or voltages at the connection point CP that are essentially symmetrical around a zero point.

[0011] Diodes D1 and D2 provide a direct current or voltage at the junction point CP to drive the load LED. The secondary ground can either be connected to the primary ground or isolated from it.

[0012] Overall, the voltage at the output terminal E1 or the current I SP1 or I SP2 on the voltage applied to the primary-side inductance of transformer T1 or the voltage waveform. These can be adjusted by changing the timing or switching frequency of switches S1, S2 or a duty cycle of the half-bridge circuit HB, ie, in particular, by changing the on-time duration of switches S1, S2.

[0013] Based on the Fig. The circuit shown in Figure 1 presents the problem that the inductors L2b, L2c on the secondary side of transformer T1 (which, in particular, represent two halves of a single secondary-side inductor) are not exactly symmetrical and do not have the same electrical or symmetrical parameters. This leads to an asymmetrical load on the components downstream on the secondary side of transformer T1, and in particular on diodes D1 and D2. It may even happen that only one of the current paths SP1, SP2, and thus a diode D1 / D2, is loaded.

[0014] EP 1257048 A2 discloses a control device for a resonant converter.

[0015] DE 102014214746 A1 discloses an active circuit for detecting a lamp current.

[0016] DE 102013224749 A1 discloses a driver circuit for lighting devices.

[0017] The invention now provides a solution that allows an exact symmetry of the currents output on the secondary side, i.e., the current at the connection point CP or at the output terminal E1, to be achieved even with unequal or asymmetrical inductances L2b, L2c on the secondary side of the transformer T1. For this purpose, the invention provides a lamp converter and a method for operating a lamp converter according to the independent claims. Further developments of the invention are the subject of the dependent claims.

[0018] In a first aspect, a lighting converter with an LLC resonance circuit is provided, from the secondary side of which lighting means, such as an LED strip, can be supplied. The LLC resonance circuit has: a half-bridge circuit with two switches connected in series, which are controlled by a control circuit; a resonance circuit supplied from a midpoint of the two switches; and a transformer supplied with AC voltage from an output of the resonance circuit, on the secondary side of which a current path is provided for each of the two polarities of the AC voltage. A detection circuit is provided which detects a signal that represents currents in the two current paths and / or their ratio, and the control circuit adjusts the clocking of the two switches of the half-bridge circuit depending on the signal detected by the detection circuit.

[0019] The detection circuit has at least one detection branch which detects the signal representing the current through at least one signal path.

[0020] The at least one detection branch can evaluate a rectified mixed signal.

[0021] The at least one detection branch comprises a sample and hold circuit.

[0022] The detection circuit may have a detection branch for each current path.

[0023] The at least one detection branch may comprise a switch that is clocked synchronously with one of the two switches of the half-bridge circuit.

[0024] A voltage and / or a voltage value that is proportional to the current through one of the current paths can be detected on the at least one detection branch.

[0025] Depending on the signal supplied to the control circuit, the control circuit can change a duty cycle of the half-bridge circuit and, in particular, shorten or lengthen a switch-on time of at least one of the two switches of the half-bridge circuit.

[0026] The secondary side of the transformer may have a center-tapped winding coupled to a primary winding of the transformer, from which the current paths are supplied.

[0027] Each current path may include a detection inductance that is electromagnetically coupled to at least one third detection inductance of the detection circuit. The at least one detection branch of the detection circuit may be arranged between a rectifier and filter circuit.

[0028] The control circuit can change the control of the two switches of the half-bridge circuit by changing the timing until the signal supplied to the control circuit corresponds to a desired value and / or signals supplied to the control circuit are in particular substantially the same, e.g. have the same signal values.

[0029] The control circuit can change the control of the two switches of the half-bridge circuit by changing the timing until a setpoint value for a signal supplied to the control circuit is reached, which in particular represents a ratio of two voltage values.

[0030] The detection circuit can have two detection branches, each of whose switches is clocked synchronously with one of the two switches of the half-bridge circuit.

[0031] The detection circuit may supply two signals to the control circuit, each signal indicating an electrical parameter representing the current through a current path, and / or relate the two signals and transmit information about the relationship to the control unit.

[0032] In a further aspect, a method is provided for balancing the current flows at the output of an LLC resonant circuit, from the secondary side of which lighting means, such as an LED path, can be supplied, wherein a control circuit controls two series-connected switches of a half-bridge circuit, and wherein the half-bridge circuit supplies a resonant circuit from a midpoint of the two switches, and a transformer is fed with AC voltage from an output of the resonant circuit, on the secondary side of which a current path is provided for each of the two polarities of the AC voltage.A detection circuit detects a signal representing currents in the two current paths and / or their ratio, wherein the detection circuit has at least one detection branch that detects the signal representing the current through a signal path, and the control circuit adjusts the timing of the two switches of the half-bridge circuit depending on the signal detected by the detection circuit, wherein the at least one detection branch has a sample-and-hold circuit.

[0033] The invention will now be described with reference to the figures, in which: Fig. 1 a circuit arrangement according to the prior art; Fig. 2 schematically shows a circuit arrangement according to the invention; Fig. 3 shows an example of a circuit arrangement according to the invention; Fig. 4 exemplary recording values.

[0034] Fig. Figure 2 schematically shows a circuit according to the invention. A half-bridge circuit HB is supplied from a supply V, in particular a direct voltage or a rectified alternating voltage, e.g., a rectified mains voltage, which supplies a resonant circuit RK with an alternating voltage.

[0035] The half bridge has, as for Fig. 1, preferably comprises at least two switches S1 and S2 connected in series, which are controlled by a control unit SE. The higher-potential switch can be controlled via the control signal HS, and the lower-potential switch can be controlled via the control signal LS.

[0036] The primary winding of transformer T1 is connected to the resonant circuit RK. At least one current path is supplied from the secondary winding of transformer T, which has a center tap that essentially divides the secondary inductance into two inductances. A detection circuit ES is integrated into this current path, which detects at least one signal representing the current in the at least one current path, preferably the currents in two current paths or their ratio. Information representing the signal(s) or the ratio is then fed to the control circuit SE, which, depending on this information, changes the duty cycle or clocking of the switches of inverter HB by changing the control signals HS and / or LS.

[0037] In Fig. Figure 2 shows the signals V1 and V2, which are fed from the detection circuit ES to the control circuit SE. It should be understood that if only a signal representing the ratio of the current values ​​or only one signal is transmitted to the control unit SE, only this signal needs to be fed from the detection circuit ES to the control circuit SE. The load LED can be electrically supplied from the transformer T.

[0038] Details of the circuit according to the invention will now be explained with regard to the Fig. 3a and Fig. 3b.

[0039] In Fig. 3A is essentially one of the Fig. 1 corresponding circuit is shown. Accordingly, the same reference numerals designate Fig. 1 also essentially the same parts of the circuit in Fig. 3a. The electrical supply V is in Fig. 3a again as voltage V BUSThe key difference here is that a first detection inductance L3a is connected in the first current path SP1 between the diode D1 and the connection point CP. Furthermore, a second detection inductance L3b is provided in the second current path SP2 between the diode D2 and the connection point CP. Electromagnetically coupled to the first and second detection inductances L3a and L3b is a third detection inductance L3c, which is preferably on the primary side with respect to the resonant circuit RK, the LLC resonant circuit, or the transformer T1.

[0040] The first detection inductance L3a and the second detection inductance L3b, together with the third detection inductance L3c, form the converter W1 and, in particular, a further transformer. Therefore, a current dependent on the current through the first detection winding L3a is detected at the third detection winding L3c when a current I SP1flows through the first current path SP1, while a current I SP2 through the second current path SP2 dependent current is detected when the current I SP2 flows through the second current path SP2. Consequently, a current path for the induced currents is provided on the secondary side for each polarity of the primary AC voltage.

[0041] The current detected at the third detection winding L3c is then fed to a rectifier GR, which then produces a rectified current I sense According to the invention, the current signal I sense evaluated with regard to an asymmetry of the current component through the current paths SP1, SP2 or through the diodes D1, D2.

[0042] As in Fig. As shown in Figure 3b, the current signal I sense from the rectifier to a known filter circuit FS, consisting of a filter resistor RF, a filter capacitor CF and a sampling resistor R SENS, and evaluated with regard to averaging, so that ultimately the mean I sense_avg of the current flowing on the secondary side of transformer T1 can be used as a representative signal for regulating the LED current. The mean value signal I sense_avg is then used for current control, where it is used as an actual signal and can be used as a control variable for the timing of the switches S1, S2 of the inverter HB. Accordingly, the mean value signal I sense_avg fed to the control circuit SE as a signal (3).

[0043] According to the invention, it is now provided that before the averaging, the combined current signal I senseis split into values ​​that are representative of the current through the current paths SP1 and SP2, or the currents occurring at the diodes D1 and D2. For this purpose, a first detection branch EZ1 is provided, consisting of a series circuit formed by a third switch S3, which is connected by its higher-potential side to the rectifier GR and the filter resistor RF, and a first resistor RH1 and a first capacitor CH1. A voltage signal V1 is detected between the first resistor RH1 and the first capacitor CH1, which represents the voltage drop across the first capacitor CH1.

[0044] A second detection branch EZ2, consisting of a series circuit of a fourth switch S4, a second resistor RH2, and a second capacitor CH2, is also connected between the rectifier GR and the filter circuit. The higher-potential terminal of the fourth switch S4 is connected to the rectifier GR and the filter resistor R F connected, while its lower-potential side is connected to one side of the second resistor RH2. The second capacitor CH2 is connected to the other side of the second resistor RH2, which is also at ground potential. The measurement signal V2, which represents a voltage drop across the second capacitor CH2, is recorded between the second resistor RH2 and the second capacitor CH2.

[0045] In the first detection branch EZ1, the current I2 flows when the third switch S3 is activated, and in the second detection branch EZ2, the current I2 flows when the fourth switch S4 is activated.

[0046] What is crucial now is that the third switch S3 and the fourth switch S4 are controlled synchronously with the switches S1 and S2 of the half-bridge HB. For example, the third switch S3 is controlled synchronously with the higher-potential switch of the half-bridge S1, while the fourth switch S4 is controlled synchronously with the lower-potential switch S2 of the half-bridge HB. Accordingly, the third switch S3 is controlled by the control signal HS from the control circuit SE, while the fourth switch S4 is controlled by the control signal LS, or vice versa.

[0047] The basic idea of ​​the invention is that the currents through the diodes D1 and D2 can be evaluated separately. In this case, the current signal I is subsequently split. sense , since the combination of the two currents I SP2 and I SP1 is already provided for averaging.

[0048] Alternatively, a separate third or fourth detection inductance coupled to the first detection inductance L3a and the second detection inductance L3b could be provided for evaluation. A corresponding voltage or current signal could then also be transmitted to the control circuit SE. Furthermore, the detection circuit ES can determine a ratio from the detection signals V1 and V2 and transmit this ratio as a single signal to the control circuit SE. For this purpose, a corresponding circuit for forming the ratio value can be provided in the detection circuit ES.

[0049] Knowing the at least one signal which is supplied from the detection circuit ES to the control circuit SE and which represents the currents through the diodes D1 and D2, an asymmetry of the secondary-side inductances L2b, L2c of the transformer T1 can now be eliminated not mechanically but in a control-technical manner by using the supplied value to change the timing of the half-bridge switches S1, S2 and in particular to change the duty cycle of the half-bridge HB by way of a feedback control for this asymmetry.

[0050] In Fig. In the embodiment shown in Figure 3b, the detection signals V1 and V2, which are voltage signals representing the currents through the diodes D1 and D2, respectively, are evaluated by the control circuit SE (in particular, IC, ASIC, microcontroller), which then controls the switches S1, S2 of the half-bridge HB accordingly. Furthermore, the detection circuit ES can have its own microcontroller, ASIC, or IC, which feeds the feedback signal to another control unit, whereupon this control unit then changes the control of the inverter switches S1, S2.

[0051] The resonant circuit or LLC resonant circuit is used with the transformer T1 with center tap to achieve a somewhat higher efficiency. The problem solved by the invention therefore addresses that depending on the operating point, the current through the secondary windings L2b, L2c can vary. In particular, the invention prevents the entire output current of the transformer T1 from flowing via only one of the current paths SP1, SP2, i.e. via one of the secondary-side inductors L2b, L2c, which also represents a considerable electrical and thermal load on the transformer T1. While typically the half-bridge HB operates with a duty cycle of 50%, i.e.that the switches S1, S2 of the half-bridge are active essentially in equal parts, possibly taking into account a dead time, the solution according to the invention compensates for any asymmetry by correcting the duty cycle of the half-bridge HB and, in particular, changing a switch-on time and / or switch-off time of the half-bridge switches S1, S2.

[0052] Fig. 4a-c schematically show how, in the case of an asymmetry with essentially the same control of the half-bridge switches S1, S2 by the control signals LS and HS, different currents can result in the current paths SP1, SP2.

[0053] While the detection circuit ES determines the detection signal V1 on the first detection branch EZ1 when, as in Fig. 4a and Fig. 4b, the switch S1 and the third switch S3 are activated by means of the signal HS, the second detection branch EZ2 detects the detection signal V2 when, as shown in Fig. 4a and Fig. 4c, the switch S2 and the fourth switch S4 are activated by control by means of the signal LS.

[0054] Accordingly, as in Fig. 4d, a deviation ΔV reflecting the asymmetry is obtained from the detection signals V1 and V2. Accordingly, by changing the control of the half-bridge switches S1, S2 by changing the control signals LS, HS, a change in the currents I SP1 , I SP2 in the current paths SP1, SP2. In particular, the value ΔV can be used as an actual value for the asymmetry, which can then be used by the control circuit SE, which is responsible for controlling the half-bridge switches S1, S2.

[0055] The current of the secondary inductors L2b, L2c of the transformer T1 is thus detected via the detection inductors L3a to L3c. As in Fig. As shown in Figure 3b, this alternating current signal is rectified by a rectifier GR, in particular a bridge rectifier. By clocking the switches of the detection branches EZ1, EZ2, the signals V1, V2 are obtained, as shown in the Fig. 4b and Fig. 4c. The current in the inductors L3a to L3c behaves synchronously with the switching of the half-bridge switches S1, S2, which are controlled by the control signals LS and HS.

[0056] It should be noted that the first resistor RH1 and the first capacitor CH1 constitute a sample-and-hold circuit. The same applies to the second resistor RH2 and the second capacitor CH2. Thus, the measurement signal acquired via the third and fourth switches S3 and S4, respectively, is fed to a sample-and-hold stage. This produces the acquisition signal V1, i.e., the voltage V1 at acquisition point (1), while the acquisition signal V2, or the voltage signal, is generated at acquisition point (2). The signal at point (1) is proportional to the current through the first acquisition inductance L3a, while the acquisition signal V2 is proportional to the current through the second acquisition inductance L3b.

[0057] The detection signals can then be evaluated, for example, with the analogue digital converter of a microcontroller, which then changes the duty cycle of the inverter HB until the detection signal V1 at point (1) corresponds to the detection signal V2 at point (2).

Claims

[1] Lamp converter with an LLC resonant circuit, from whose secondary side lamps (LED), such as in particular an LED line, can be supplied, where the LLC resonant circuit comprises: - a half-bridge circuit (HB) with two switches (S1, S2) connected in series, which are controlled by a control circuit (SE), - a resonant circuit (RK) supplied from a midpoint of the two switches (S1, S2), and - a transformer (T1) supplied with AC voltage from an output of the resonant circuit (RK), on the secondary side of which a current path (SP1, SP2) is provided for each of the two polarities of the AC voltage, characterized by , that - a detection circuit (ES) is provided which detects a signal (V1, V2) which represents currents (I SP1 , I SP2) in the two current paths (SP1, SP2) and / or their ratio, wherein the detection circuit (ES) has at least one detection branch (EZ1) which detects the signal representing the current through a signal path (SP1), and - the control circuit (SE) adjusts the timing of the two switches (S1, S2) of the half-bridge circuit (HB) depending on the signal (V1, V2) detected by the detection circuit (ES), wherein the at least one detection branch (EZ1) has a sample-and-hold circuit (S3, RH1, CH1). [2] Lamp converter according to claim 1, wherein the at least one detection branch (EZ1) receives a rectified signal (I sense ) evaluates. [3] Lamp converter according to claim 1 or 2, wherein the detection circuit (ES) has a detection branch (EZ1, EZ2) for each current path (SP1, SP2). [4] Lamp converter according to one of claims 1 to 3, wherein the at least one detection branch (EZ1) has a switch (S3, S4) which is clocked synchronously with one of the switches (S1, S2) of the half-bridge circuit (HB). [5] Lamp converter according to one of claims 1 to 4, wherein the at least one detection branch (EZ1) detects a voltage and / or a voltage value which is proportional to the current through the current path (SP1). [6] Lamp converter according to one of the preceding claims, wherein the control circuit (SE) changes a duty cycle of the half-bridge circuit (HB) depending on the signal (V1, V2) supplied to the control circuit (SE) and in particular shortens or lengthens a switch-on time of at least one of the two switches (S1, S2) of the half-bridge (HB). [7] Lamp converter according to one of the preceding claims, wherein each current path (SP1, SP2) has a detection inductance (L3a, L3b) which is electromagnetically coupled to at least one third detection inductance (L3c) of the detection circuit (ES). [8] Lamp converter according to one of claims 1 to 7, wherein the at least one detection branch (EZ1) of the detection circuit (ES) is arranged between a rectifier (GR) and filter circuit (FS). [9] Lamp converter according to one of the preceding claims, wherein the control circuit (SE) changes the control of the two switches (S1, S2) of the half-bridge circuit (HB) by changing the timing until the signal (V1, V2) supplied to the control circuit (SE) corresponds to a desired value and / or signals (V1, V2) supplied to the control circuit are in particular substantially equal, in particular have the same signal values. [10] Lamp converter according to one of the preceding claims, wherein the control circuit (SE) changes the control of the two switches (S1, S2) of the half-bridge circuit by changing the timing until a desired value for the signal (V1, V2) supplied to the control circuit (SE) is reached, which in particular represents a ratio of two voltage values. [11] Lamp converter according to one of the preceding claims, wherein the detection circuit (ES) has two detection branches (EZ2, EZ2), the switches (S3, S4) of which are clocked synchronously with one of the two switches (S1, S2) of the half-bridge circuit (HB). [12] Lamp converter according to one of the preceding claims, wherein the detection circuit (ES) supplies the control circuit (SE) with two signals (V1, V2), each of which has a current (I SP1 , I SP2) through a current path (SP1, SP2), and / or sets the two signals (V1, V2) in a ratio and transmits information about the ratio to the control unit (SE). [13] Method for balancing the current flows at the output of an LLC resonant circuit from whose secondary side lighting means, such as in particular an LED circuit, can be supplied, wherein - a control circuit (SE) controls two series-connected switches (S1, S2) of a half-bridge circuit (HB), and wherein the half-bridge circuit (HB) supplies a resonant circuit (RK) from a midpoint of the two switches (S1, S2), and a transformer (T1) is supplied with AC voltage from an output of the resonant circuit (RK), on the secondary side of which a current path (SP1, SP2) is provided for each of the two polarities of the AC voltage, characterized by , that - a detection circuit (ES) detects a signal (V1, V2) which represents currents (I SP1 , I SP2 ) in the two current paths (SP1, SP2) and / or their ratio, wherein the detection circuit (ES) has at least one detection branch (EZ1) which detects the signal representing the current through a signal path (SP1), and the control circuit (SE) sets the timing of the two switches (S1, S2) of the half-bridge circuit (HB) depending on the signal (V1, V2) detected by the detection circuit (ES), wherein the at least one detection branch (EZ1) has a sample-and-hold circuit (S3, RH1, CH1).

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