DE102014202665A1 - Driver circuit for leds - Google Patents

Driver circuit for leds

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Publication number
DE102014202665A1
DE102014202665A1 DE102014202665.2A DE102014202665A DE102014202665A1 DE 102014202665 A1 DE102014202665 A1 DE 102014202665A1 DE 102014202665 A DE102014202665 A DE 102014202665A DE 102014202665 A1 DE102014202665 A1 DE 102014202665A1
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Germany
Prior art keywords
driver circuit
circuit
pwm
signal
current
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
DE102014202665.2A
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German (de)
Inventor
Thomas Küng
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Tridonic GmbH and Co KG
Original Assignee
Tridonic GmbH and Co KG
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Publication date
Application filed by Tridonic GmbH and Co KG filed Critical Tridonic GmbH and Co KG
Priority to DE102014202665.2A priority Critical patent/DE102014202665A1/en
Publication of DE102014202665A1 publication Critical patent/DE102014202665A1/en
Pending legal-status Critical Current

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    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHTING NOT OTHERWISE PROVIDED FOR
    • H05B45/00Circuit arrangements for operating light emitting diodes [LED]
    • H05B45/30Driver circuits
    • H05B45/37Converter circuits
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHTING NOT OTHERWISE PROVIDED FOR
    • H05B45/00Circuit arrangements for operating light emitting diodes [LED]
    • H05B45/30Driver circuits
    • H05B45/37Converter circuits
    • H05B45/3725Switched mode power supply [SMPS]
    • H05B45/382Switched mode power supply [SMPS] with galvanic isolation between input and output

Abstract

The invention relates to a driver circuit (1) for lighting means, in particular for one or more LEDs, comprising: - a circuit (2) which can be supplied with voltage (Vdc) and clocked by means of at least one switch (LS, HS), which supplies one - a control circuit for controlling the lamp current having a regulator (10), the controller (10) depending on a feedback signal (Im), which reflects the current through the lighting means, and a signal (ILS), which represents a setpoint for the luminous flux, generates a manipulated variable (ASF) for controlling the luminous flux, - a PWM modulator (11) for modulating the manipulated variable (ASF) with a PWM signal ,

Description

  • The present invention relates in particular to a control circuit and a converter for the operation of at least one light source, for. B. a driver circuit for the operation of at least one LED, and a corresponding method for operating a lighting means.
  • A driver circuit for operating LEDs is basically known from the prior art. Such a driver circuit is powered by an electrical supply source, and includes a resonant circuit, such. B. an LLC converter, which is responsible for transmitting electricity via a galvanic barrier or galvanic barrier from a primary side to a secondary side of the galvanic barrier. The purpose of this transfer of electrical energy is the supply of a switched on the secondary side LED track with electricity.
  • The invention is based on such LLC topology z. B. includes a half-bridge inverter with the following resonant circuit. The resonant circuit feeds a transformer, starting from the secondary side in turn an LED track can be supplied.
  • From the prior art, however, it is known to detect the current through the primary side of the transformer as the actual value of the LED current for constant control of the LED current. However, this measurement is subject to the uncertainty of the magnetization current whose exact size is not determined in this topology.
  • In this case, there is a known correction of this measurement is that on the secondary side, the voltage across the LED track is measured and, if necessary, with other measurements such. As the temperature is sent from a secondary side microcontroller via the SELV barrier to the microcontroller on the primary side. This microcontroller thus corrects the primary current measurement by this correction contribution, which is calculated using empirical, e.g. B. in a look-up table stored measured values is determined based on the secondary-side LED voltage measurement. Finally, the microcontroller controls the frequency of the half-bridge depending on the current and voltage measurement via an ASIC as manipulated variable. The disadvantage here is that the look-up table for determining the correction value can only approximately determine the correct correction contribution. In addition, the solution is relatively expensive in terms of components, in particular to overcome the SELV barrier.
  • With such a driver circuit, dimming of the LED path can be achieved by briefly switching off the high-frequency clocking of the switches of the half-bridge. This is achieved by a low-frequency PWM modulation. However, it is problematic here that the levels of PWM modulation are limited. The resolution of the stages of PWM modulation, z. 7-bit causes so-called dithering, d. H. The frequency of the LLC converter can not be controlled precisely enough. Consequently, the desired LED current and thus the desired brightness can only be approximately adjusted.
  • The invention is based on the technical problem of specifying a control circuit or driver circuit for operating light sources, in particular LEDs, in which a desired value for the brightness is better implemented.
  • This problem underlying the invention will now be solved by the combination of the features of the independent claims. The dependent claims further advantageously form the central idea of the invention.
  • According to a first aspect of the invention, a driver circuit for lighting means is provided, in particular for one or more LEDs. The driver circuit comprises a voltage-supplyable circuit which is clocked by means of at least one switch and supplies a resonant circuit for supplying the lighting means with power. The driver circuit further comprises a control circuit for controlling the luminous flux, comprising a regulator. The controller generates a manipulated variable for controlling the luminous flux in response to a feedback signal representing the current through the luminous means and a signal representing a setpoint value for the luminous flux. The driver circuit comprises a PWM modulator for modulating the manipulated variable with a PWM signal.
  • Preferably, the control loop is activated continuously and in particular also in the turn-off periods of the PWM signal. The modulation of the manipulated variable by the PWM signal preferably results in the control circuit being activated continuously and in particular also in the turn-off periods of the PWM signal.
  • Preferably, the control circuit has a time constant that is slower than the time duration of a period of the PWM modulation.
  • Preferably, the time constant of the control loop is much slower than the duration of a period of the PWM modulation, z. At least 5 times slower, especially between 5 and 10 times slower.
  • The driver circuit preferably has a low-pass filter for filtering the feedback signal. Thus, the controller sets the manipulated variable depending on the low-pass filtered feedback signal.
  • Preferably, the time constant of the low-pass filter is slower than the duration of a period of the PWM modulation.
  • At this time, the time constant of the control loop may be slower than the period of one period of the PWM modulation that the time constant of the low-pass filtering by the low-pass filter is slower than the period of one period of the PWM modulation.
  • Preferably, the time constant of the control algorithm implemented in the controller is slower than the duration of a period of the PWM modulation.
  • The time constant of the control loop can thereby be slower than the time duration of a period of the PWM modulation that the time constant of the control algorithm implemented in the control algorithm is slower than the duration of a period of the PWM modulation.
  • Preferably, the PWM modulation due to the slow time constant, in particular due to the slowdown by the low-pass filter, by the control loop is not adjustable.
  • Preferably, the driver circuit comprises a PWM dimming unit for setting a duty ratio for the PWM modulation depending on a dimming command. DB). The duty cycle is preferably set independently of feedback variables, in particular from the area of the driver circuit.
  • In this case, the PWM modulation can be done in particular open-loop. Ie. the PWM signal is modulated only by control and not by control on the manipulated variable. In other words, the PWM modulation is done without feedback.
  • The driver circuit preferably has an amplitude dimming unit for determining the setpoint value for the luminous flux in dependence on the dimming command.
  • The setpoint can be set independently of the set duty cycle for the PWM modulation.
  • Preferably, in a first dimming range of the dimming command, the duty cycle for the PWM modulation is 100%. lies. Preferably, in a second dimming range, the duty cycle is reduced stepwise or continuously (continuously or quasi-continuously esp. In a digital embodiment).
  • Preferably, a cascade control is provided. The first control circuit comprising the regulator for regulating the luminous flux is interleaved with a second control circuit having a further regulator. The second control loop may have a faster time constant than the first control loop. The second control circuit can in particular serve to regulate a residual ripple of the voltage.
  • The driver circuit preferably has a transformer following the resonance circuit for transmitting electrical energy from a primary winding coupled to the resonance circuit to a secondary winding, from which the lighting means can be supplied with power.
  • Preferably, the feedback signal indirectly reflects the luminous flux, in which it is inductively coupled out on the secondary side of the transformer.
  • The driver circuit preferably has a driver for output, based on the PWM-modulated manipulated variable, at least one on / off drive signal for controlling the at least one switch of the clocked circuit.
  • The manipulated variable preferably reproduces the frequency and / or the duty ratio of the control of the at least one switch of the clocked circuit.
  • According to a further aspect of the invention, a control unit is provided for operating a driver circuit for lighting means, in particular for one or more LEDs. The control unit comprises an input for a return signal representing the current through the lighting means. The control unit comprises a control circuit for regulating the luminous flux, comprising a regulator. The controller generates a manipulated variable for the regulation of the luminous flux as a function of the feedback signal and of a signal representing a setpoint value for the luminous flux. The control unit comprises a PWM modulator for modulating the manipulated variable with a PWM signal.
  • Preferably, the control unit is in the form of an integrated circuit, in particular ASIC or microcontroller or a hybrid version thereof.
  • According to another aspect of the invention is a method for controlling the current through Light source, in particular by one or more LEDs provided. A return signal representing the current through the lamps is tapped off. Depending on the feedback signal and of a signal representing a setpoint for the luminous flux, a manipulated variable for the regulation of the luminous flux is generated. A PWM signal is modulated onto the manipulated variable.
  • The aspects mentioned above with respect to the driver circuit are also applicable to the control unit and to the method.
  • The invention thus preferably proposes that the PWM signal does not temporarily switch off the control loop or modulate the entire half-bridge driver, but rather modulate the output signal of the half-bridge control loop.
  • Preferably, a control of the LED current by changing the frequency of the half-bridge drive is present. This control loop runs constantly, ie also in the turn-off periods of the PWM modulation. This control has a time constant that is significantly slower than the frequency / duration of the PWM modulation.
  • In a preferred embodiment, the targeted, slowing 'by the low-pass filtering of the feedback signal before the comparator with the desired signal. However, this time constant can also be implemented after the comparator or in the control algorithm itself.
  • Overall, there is preferably a type of combined PWM / AM dimming. However, since the feedback signal is low-pass filtered and the control loop is continuously active, the LED current remains substantially constant over a period of PWM modulation, resulting in improved color continuity of the LED path.
  • The invention will also be described below with reference to the figures.
  • 1 shows schematically the structure of a driver circuit according to the invention for the supply of lighting means, in particular for the supply of LEDs or an LED track,
  • 2 shows an alternative embodiment of the driver circuit according to the invention,
  • 3 shows an alternative embodiment of the driver circuit according to the invention,
  • 4 shows an alternative embodiment of the detection of the current through the LEDs in the driver circuit according to the invention
  • 5 shows the influence of a dimming value on parameters of the control according to the invention, and
  • 6 another embodiment of a driver circuit according to the present invention.
  • In 1 is an embodiment of a driver circuit 1 shown for the supply of light sources, in particular in the form of an LED converter for the supply of LEDs or an LED track.
  • The driver circuit 1 is fed on the input side by an input voltage Vdc. The input voltage Vdc is preferably a rectified, and optionally filtered, AC voltage or mains voltage. Preferably, this rectified mains voltage according to a converter in the form z. B. a power factor correction circuit (not shown) supplied before the driver circuit 1 provided. The input voltage Vdc is in this case an approximately constant bus voltage possibly having a residual ripple. In the embodiment of 1 The input voltage Vdc has an amplitude of 400V. The input voltage can also be called bus voltage or DC link voltage. Alternatively, the input voltage Vdc also a DC voltage or a constant voltage such. B. a battery voltage.
  • The input side is in the driver circuit 1 a switching regulator is provided, which is fed by the input voltage Vdc. The input voltage Vdc supplies in particular a clocked circuit or an inverter, the z. B. in the form of a half-bridge circuit 2 can be designed. The half-bridge circuit shown 2 has a potential lower switch LS and a higher potential switch HS. According to the invention, the inverter 2 at least one switch on. As an inverter with a switch can z. B. a flyback converter (not shown) may be provided.
  • The series-connected switches LS, HS of the half-bridge circuit 2 can be used as transistors, z. B. FET or MOSFET be configured. The switches LS, HS are derived from respective control signals S / LS, S / HS from a half-bridge driver 12 a control unit ST controlled. Preferably, the switches LS, HS by the control signals S / LS, S / HS or by the half-bridge driver 12 alternately on and off. The mean value of the current through the LEDs can be adjusted by changing the drive frequency ASF of the switches LS, HS, and / or by changing the duty cycle of the drive. The potential-lower switch LS is connected to a primary-side ground. At the half-bridge circuit 2 the input voltage Vdc is applied.
  • Between the two switches LS, HS, ie at the midpoint of the half-bridge circuit 2 , is a resonant circuit 3 in the form of z. B. a series resonant circuit connected. Alternatively, at the midpoint of the half-bridge circuit 2 According to the invention, a parallel resonant circuit be connected. The in 1 shown resonant circuit 3 is designed as a series resonant circuit and includes inductance and capacitance elements. In particular, between the primary-side ground and the center of the half-bridge circuit 2 a series circuit comprising a first coil Lr, a second coil La and a capacitor Cr. The resonant circuit 3 is referred to in this case as the LLC resonant circuit. The coil Lr and the capacitor Cr preferably form an LC resonant circuit and are referred to as a resonant coil and a resonant capacitor.
  • The second coil La connected in series with the coil Lr and the capacitor Cr is preferably the primary winding of a transformer T serving as a transformer for galvanic isolation. The transformer T is an example of a galvanic barrier used in 1 as a safety extra-low voltage barrier or SELV barrier 7 (English: Safety Extra Low Voltage) is shown. The transformer T forms a total of a galvanic barrier between a primary side having the primary winding La and a secondary side comprising the secondary winding Lb of the transformer T. In 1 the transformer T is shown as an ideal transformer, wherein the primary winding of the real transformer T can have a leakage inductance and a main inductance for guiding the magnetizing current.
  • The secondary winding Lb of the transformer T has a tapping, in particular a center tap or center tap, this center tap can serve as a secondary side ground. Alternatively, the secondary winding Lb may consist of two separate windings, in which case the center of these separate windings corresponds to the center tap.
  • One terminal of the secondary winding Lb is connected to a first detection winding L1, and the other terminal of the secondary winding Lb is connected to a second detection winding L1 '. The first detection winding L1 and the second detection winding L1 'are preferably identical. Preferably, the respective number of turns nL1_sec, nL1'_sec of the detection windings L1, L1 'are the same. In series with the first detection winding L1, a first diode D1 is connected. In series with the second detection winding L1 ', a second diode D1' is connected. The detection coils L1, L1 'are connected to the anode of the diodes D1, D1'.
  • The respective cathodes of the diodes D1, D1 'are brought together so that these diodes D1, D1' form a rectifier circuit 4 form. During operation, an AC current, ie an alternating current, preferably flows through the secondary winding Lb of the transistor T. Depending on the direction of this alternating current, a current flows through the first diode D1 or through the second diode D1 '. At the output of the rectifier circuit 4 , ie at the connection point of the diodes D1, D1 ', thus flows a rectified current. The rectifier is also referred to as the center rectifier.
  • The rectifier circuit 4 On the output side it feeds a storage capacitor C2. This storage capacitor C2 is preferably connected between the connection point of the diodes D1, D1 'and the center tap of the secondary winding Lb. As storage capacitor C2, an electrolytic capacitor can preferably be used because of its comparatively high capacity. The secondary-side current through the detection windings L1, L1 'is thus used to operate the LEDs first by the rectifier circuit 4 rectified and then preferably filtered or low-pass filtered.
  • Parallel to the storage capacitor C2, the lighting means, preferably LEDs or an LED track, are connected. The driver circuit 1 has correspondingly two output terminals K1, K2 for connecting the LEDs. In 1 the illustrated LED should be representative of one or more LEDs. Preferably, that of the driver circuit 1 operated LED track have a series circuit of multiple LEDs. Alternatively, parallel LEDs or a combination of LEDs connected in parallel and in series can also be supplied.
  • At the output of the rectifier circuit 4 or of the storage capacitor C2, further components may be provided for filtering. Exemplary is in this 1 a coil L2 shown. This coil L2 may preferably be arranged in series with the LEDs, this series circuit being connected in parallel with the capacitor C2. The coil L2 is preferably connected between the output terminal K1 on the one hand and the connection point of the diodes D1, D1 'on the other hand. Between two output terminals K1, K2, the driver circuit may have a further storage or filter capacitor C3. In addition, a resistor R3 may be provided between the output terminal K2 and the center tap of the secondary winding Lb.
  • The detection windings L1, L1 'are coupled to a primary side winding L1 ". The alternating current flowing through the secondary winding Lb of the transistor T is thus supplied from the secondary-side detection windings L1, L1 'in FIG a primary-side current flowing through the winding L1 "is transformed. These three windings L1, L1 ', L1 "form a detection transformer or a preferably electrically isolated detection transformer T1. The current through the primary-side winding L1 "gives the current through the secondary-side windings L1, L1 ', ie also the current through the LEDs. At least averaged over time, the current through the primary-side winding L1 "is a representation of the mean value of the current through the LEDs. Of course, the ratio of the number of turns of the corresponding primary and secondary windings to each other is taken into account. Preferably, the number of turns nL1 "_ prime, nL1_sec, nL1'_sec of the primary and secondary side detection windings L1", L1, L1 'are equal.
  • Preferably, the secondary winding Lb on the one hand and the detection windings L1, L1 'on the other hand are formed as separate windings. Ie. the secondary winding Lb and the sense windings L1, L1 'form two separate transformers. This results in particular from the requirement that the detection transformer L1, L1 ', L1' 'is designed as a current transformer. The windings of the detection transformer are in particular designed to enable as loss-free detection of the secondary-side alternating current. By suitable choice of the windings, the detection transformer L1, L1 ', L1 "designed as a current transformer can have the lowest possible impedance.
  • The alternating current through the detection windings L1, L1 'generates an alternating current in the coupled primary-side detection winding L1 ". An evaluation circuit 6 is connected to the primary-side detection winding L1 "to generate a measured value Im for the current through the LEDs. This measured value Im is fed back to the control circuit ST. On the basis of the obtained feedback value Im, the control circuit ST generates the control signals S / LS, S / HS for the switches LS, HS. Based on the actual value Im, the control circuit ST performs a current control to a desired setpoint ILS, in which the half-bridge circuit 2 is clocked accordingly.
  • The evaluation circuit 6 serves in principle to evaluate the information supplied by the detection winding L1 '' information about the current through the LEDs or process and then returned to the control circuit ST. On the secondary side, therefore, a signal reproducing the current through the secondary side is inductively coupled out and transferred to the primary side, where it is rectified, averaged and then supplied to the control circuit ST. The detection winding L1 "is for this purpose with a rectifier 5 connected. The rectifier 5 can z. B. in the form of a full-bridge rectifier having four diodes (not shown) to be configured.
  • At the output of the rectifier 5 In turn, a resistor Rshunt is connected, which reflects the current through the secondary side and through the LEDs. After a low-pass filtering by a low-pass filter LPF, the actual value signal Im of the LED current of the control circuit ST is fed back. The low-pass filter LPF can, for. B. be designed as an RC element with a resistor and a capacitor, wherein the capacitor is preferably connected in parallel to the filtered signal Im. This filtered actual value Im represents the mean value of the LED current. The analog average actual value Im of the LED current is preferably converted by an analog-to-digital converter ADC into a digital actual value. The analog-to-digital converter ADC is preferably designed as a 12-bit converter.
  • The measured actual value Im of the LED current is subtracted from the control unit ST a setpoint value for the LED current ILS. The control unit ST comprises means such. B. a comparator 9 for comparing the setpoint value ILS and the actual value Im or for forming the difference of these values. This results in a control difference RDF for controlling the current through the LEDs.
  • Meanwhile, the set value ILS for the LED current can be set internally by the control unit ST. Alternatively, a dimming command B, as in FIG 1 shown, externally specified. For example, the control unit ST may be connected to a line in order to receive the dimming command B via this line and to derive therefrom the current setpoint ILS. In particular, this line may be a data line or a data bus for data transmission between the control unit ST and an external communication unit (not shown). The data transmission can take place analogously or preferably digitally by means of a protocol for the control of photometric operating devices. As a protocol z. As DALI (Digital Addressable Lighting Interface) or DSI (Digital Serial Interface) can be used. The received dim command B is from an amplitude dimming unit 8th converted or converted to the setpoint ILS. The amplitude dimming unit 8th preferably generates a set value ILS in digital form, e.g. B. as a 12-bit value.
  • The control difference RDF becomes a controller 10 in which a control algorithm for the control of the LED current is implemented. The regulator 10 is preferably designed as a digital controller and z. B. be configured in the form of a PI controller. Depending on the supplied control difference RDF, the controller generates a manipulated variable by means of which the half-bridge driver 12 is controlled. As a manipulated variable z. B. the drive frequency ASF the switch LS, HS, and / or the duty cycle of the control of the switches LS, HS may be provided. In this case, the switches LS, HS of the half-bridge 2 high-frequency switching, typically in a frequency range of over 10 kHz. The drive frequency ASF is therefore typically higher than 10 kHz and z. B. be up to a few MHz.
  • The control unit ST comprises parallel to the amplitude dimming unit 8th for determining the setpoint value ILS for the LED current as a function of the dimming command B, a PWM dimming unit 8th' , This PWM dimming unit 8th' serves to convert the received dimming command B into a duty cycle TVH for PWM modulation (Pulse Width Modulation). The frequency of the PWM modulation is low frequency with respect to the drive frequency ASF, typically in the range of 100-1000 Hz. The duty cycle TVH becomes a PWM modulator 11 fed.
  • The PWM modulator 11 receives on the input side, on the one hand, the value of the duty cycle TVH for the PWM modulation and, on the other hand, the manipulated variable ASF or a signal which reproduces this manipulated variable.
  • The duty cycle TVH is preferably dependent only on the dimming command B and in particular not on the set value ILS. In the PWM dimming unit 8th' a look-up table may be provided in which a suitable duty cycle TVH is stored for different dimming commands B.
  • The duty cycle TVH influences the PWM modulation by the PWM modulator 11 but not the current regulation by the regulator 10 , In other words, the controller gets 10 as input only the setpoint ILS for the LED current and not the duty cycle TVH. Thus, the controller becomes 10 also not switched off during a turn-off period of the PWM modulation.
  • There is thus a kind of combined PWM / AM dimming, wherein the PWM dimming by modulating the PWM signal by the PWM modulator 11 takes place and the AM dimming or amplitude dimming by regulating the amplitude of the LED current through the controller 10 he follows. However, since the actual value signal Im is low-pass filtered and the control loop is continuously active, the LED current is higher in the on-time periods than in true AM / PWM dimming, where the control is turned off in a PWM-off period. Thus, the LED current remains substantially constant - except for a sawtooth ripple, resulting in improved color consistency of the LED track.
  • For example, according to the invention, the control loop of the LED current is selected to be between 5 and 10 times slower than the low frequency PWM modulation of the operation of the inverter 2 , This PWM modulation is superimposed on the high-frequency operation of the half-bridge inverter to dim the LED path.
  • The signal representing the LED current is, according to the invention, so low-pass filtered or averaged that the time constant is substantially slower than the frequency of the PWM signal.
  • The controller topology according to the invention is now that the control loop with the actual value signal, low-pass filtered LED current 'and the manipulated variable, frequency of the half-bridge inverter' is continuously activated, ie in particular in the OFF periods of the PWM signal.
  • The PWM signal, which thus stops the operation of the half-bridge during the switch-off periods, is applied to the output of the control algorithm. The control loop is unable to correct the PWM modulation due to the slowdown due to the low-pass filtering of the feedback signal.
  • In the embodiment of 1 the low-pass filter LPF is provided outside the control unit ST. Preferably, the low-pass filter is designed analogously. Alternatively, the low-pass filter can also be connected within the control unit ST. For example, the low-pass filter LPF may be after the analog-to-digital converter ABC, in which case the low-pass filter is implemented digitally. In this case, the low-pass filter may either be between the analog-to-digital converter ADC and the comparator 9 be interconnected, or between the comparator 9 and the controller 10 ,
  • 2 shows an alternative embodiment for the secondary side of the driver circuit. In particular, in this 2 an alternative construction of the rectification of the secondary-side current is shown.
  • The detection winding L1 is, as in the embodiment of 1 , in series with the secondary winding Lb, which in contrast to the embodiment of the 1 is designed as a single winding without center tap. The current through the secondary winding Lb becomes a rectifier circuit 20 supplied, which is thus coupled on the input side to the secondary winding Lb or with the series circuit of the secondary winding Lb and the detection winding L1. The rectifier circuit 20 is designed as a bridge rectifier or full-bridge rectifier with four diodes (not shown).
  • The circuit at the output of the rectifier circuit 20 again corresponds to the circuit at the output of in 1 shown Rectifier circuit 4 , The two output terminals of the rectifier circuit 20 are in particular connected to the storage capacitor C2. The LEDs can be connected to terminals K1, K2.
  • 3 shows a further alternative embodiment for the secondary side of the driver circuit. In particular, in this 3 shown another alternative construction of the rectification of the secondary-side current.
  • Similar to in 2 the detection winding L1 is connected in series with the secondary winding Lb. The terminal of the secondary winding Lb, which is not connected to the detection winding L1, is each provided with two diodes 30 . 31 connected. The secondary winding Lb is connected to the anode of the first diode 30 and with the cathode of the second diode 31 connected. A first storage capacitor C30 is between the cathode of the first diode 30 and the detection winding L1 are switched. A second storage capacitor C31 is connected between the anode of the second diode 31 and the detection winding L1 are switched. The diodes D30, D31 form a rectifier circuit 30 , the rectifier circuit 4 of the 1 equivalent. Depending on the direction of flow of the current flowing through the secondary winding Lb current blocks the first or the second diode D30, D31. The storage capacitors C30, C31 are preferably the same and corresponding to the in 1 shown storage capacitor C2.
  • 4 shows an alternative embodiment of the detection of the current through the LEDs in the driver circuit according to the invention.
  • While in the embodiments of the 1 to 3 the secondary-side current is fed back to the primary side via a detection transformer T1, the embodiment of FIG 4 on the detection transformer T1 and thus on the secondary-side detection winding and secondary-side detection windings Lb. A shunt or measuring resistor Rshunt connected in series with the LEDs is used here for current measurement.
  • At the measuring resistor Rshunt a signal is tapped. that reflects the current through the LEDs. This signal is preferably low pass filtered, e.g. B. by an RC element consisting of a capacitor C40 and a resistor R40. Namely, the tapped signal can be used to charge the capacitor C40 serving as an example of implementation of integration of the current.
  • The charging voltage of the capacitor C40 is supplied to a secondary-side control unit ST2 as a signal provided to the LEDs. The secondary-side control unit ST2, which is thus arranged on the secondary side of the transformer T, comprises an analog-to-digital converter 40 for converting the measurement signal into digital data. The analog-to-digital converter 40 is preferably designed as a 12-bit converter. These digital data are z. B. via an optocoupler 41 via the SELV barrier to the primary side of the transformer 7 recycled. Alternative to optocoupler 41 can also z. As a digital isolator such. B. ADUM digital isolator used. In particular, the digital data representing current through the LEDs is fed back to the primary-side control unit ST, which in turn supplies the half-bridge circuit 2 dependent on the one hand of these feedback actual values of the LED current and on the other hand by the current setpoint ILS or by the dimming command B drives.
  • 5 shows an embodiment of the dimming by the amplitude dimming unit 8th and the PWM dimming unit 8th ,
  • Preferably, a dimming of the LED track is now as follows:
    From dimming value 100% to a certain dimming value range DWB of, for example, 35%, the LED current is reduced continuously. Here, the duty cycle TVH preferably remains at 100%, so that the PWM modulator 11 has no influence on the manipulated variable.
  • From a certain dimming value DWB of, for example, 35%, the duty cycle of the PWM modulation is then set below 100%. Ie. between this threshold DWB of 35% and a lower threshold USW of z. B. 1%, the duty cycle TVH is gradually reduced. In the PWM dimming unit 8th is z. B. stored in a look-up table, the correspondence between dimming value B and duty cycle TVH. The duty cycle TVH remains constant for a specific dimming range. For example, in dimming range DWB-USW (35% -x%) the duty cycle is the value y% etc., s. 5 ,
  • Thus, if a dimming value below the dimming value DWB, for example, below 35% is specified, a linearly decreasing setpoint for the LED current is fed to the controller. At the same time starting from this dimming value, the duty cycle of the PWM modulator is reduced starting at 100%.
  • The dimming value specification signal B is thus converted, on the one hand, into a variable PWM duty cycle and, on the other hand, supplied to the control algorithm as a continuously decreasing setpoint value for the time-averaged LED current. The PWM duty cycle and the setpoint preferably do not affect each other. Rather, both values preferably depend only on the dimming value B. This is in 5 recognizable in which the setpoint ILS decreases linearly with the dimming value B. The duty cycle TVH, however, decreases gradually with the dimming value B, preferably from the dimming value DWB, for example, 35%.
  • The PWM modulation is thus modulated open loop. The steadily running controller 10 tries to correct this type of interference, however, this Ausregeln narrow limits due to the low-pass filtering, for example, the actual value signal. 5 shows like the regulator 10 the PWM modulation tries to correct in which the controller 10 the average value of the LED current to the value ILED_R is trying to increase.
  • So it will be the setpoint ILS for the current controller 10 continuously reduced. However, the current through the LEDs remains substantially constant over the turn-on periods of the PWM signal, except for a small sawtooth ripple. However, this ripple is not present in the time course, but considered in continuous dimming, since the controller tries in the steadily shortening dimmer with longer dimming durations to control the average value of the current constant.
  • 6 shows a further embodiment of a driver circuit according to the present invention.
  • The driver circuit 60 of the 6 is basically based on the structure of 1 , Actual value ILED _ist is the secondary-side LED current measured as in 4 shown. Similar to in 1 is the actual value of the setpoint ILS by a comparator 61 deducted and a regulator 62 , z. In the form of a P, PI or PID controller. The output of the regulator 62 is a second comparator or subtractor 63 fed. Alternatively, to measure the LED current, the feedback topology of the 1 be used with the detection transformer T1.
  • An actual value for the current through the LLC resonant circuit, or for the current through the coil Lr, the primary winding La or through the capacitor Cr, is measured.
  • In particular, the primary-side alternating current through the LLC resonant circuit of z. B. a diode D60 rectified. The rectified current value is then passed through an RC element 64 low pass filtered, ie averaged, and from an analog to digital converter 65 converted into a digital actual value, preferably into a 12-bit value.
  • The measured actual value of the primary-side current is from the output of the controller 62 subtracted and the regulator 10 fed. The output of the regulator 10 will be like in 1 the PWM modulator 11 and the half-bridge driver 12 fed.
  • As explained above, the input voltage Vdc of z. B. 400 V have a residual ripple. When rectifying a mains voltage results in particular a ripple of 100 Hz.
  • The first control loop with the regulator 62 preferably refers to a slow regulation of the LED current. As a result, z. B. the influence of temperature, in particular the influence of the ambient temperature on the LEDs can be compensated.
  • The second, nested loop with the regulator 64 however, implements a faster algorithm to B. to correct the ripple of the input voltage Vdc.
  • The interleaving of the two control loops or by the cascade control thus results in even faster compensation options in addition to the relatively slow current control loop. For example, the effect of the 100 Hz ripple in the bus voltage can be detected and compensated or corrected.
  • Advantageously, the PWM modulation according to the invention can be used to limit the maximum switching frequency of the LLC resonant circuit.
  • With the PWM modulation according to the invention, a better efficiency of the converter or the LLC resonant circuit can be achieved.
  • The PWM modulation according to the invention can be used in combination or as an alternative to amplitude dimming without the need for additional circuitry.
  • When employing the PWM modulation according to the invention, color shifts are avoided, in particular in the range of low dimming values. This is because the controller 10 regulated to a higher LED current. This is z. In 5 can be seen where is regulated to a current ILED_R, which is significantly higher than the setpoint ILS, so that the occurring at low current values color shifts can be avoided according to the invention.
  • The low resolution of the PWM modulation is compensated by controlling the mean value of the LED current.

Claims (19)

  1. Driver circuit ( 1 ) for lighting means, in particular for one or more LEDs, comprising: - a voltage supply (Vdc) and by means of at least one switch (LS, HS) clocked circuit ( 2 ) which supplies a power supply for supplying the light emitting means resonant circuit ( 3 ), - a control circuit for regulating the luminous flux with a regulator ( 10 ), whereby the controller ( 10 ) generates a manipulated variable (ASF) for regulating the luminous flux, depending on a return signal (Im) representing the current through the luminous means and a signal (ILS) representing a setpoint value for the luminous flux PWM modulator ( 11 ) for modulating the manipulated variable (ASF) with a PWM signal.
  2. Driver circuit ( 1 ) according to claim 1, wherein the modulating of the manipulated variable (ASF) by the PWM signal leads to the fact that the control loop is activated continuously and in particular also in the turn-off periods of the PWM signal.
  3. Driver circuit ( 1 ) according to one of the preceding claims, wherein the control loop has a time constant which is slower than the duration of a period of the PWM modulation.
  4. Driver circuit ( 1 ) according to claim 3, wherein the time constant of the control loop is substantially slower than the duration of a period of the PWM modulation, z. B. at least 5 times slower, especially between 5 and 10 times slower.
  5. Driver circuit ( 1 ) according to one of the preceding claims, comprising a low-pass filter (LPF) for filtering the feedback signal (Im), so that the regulator ( 10 ) sets the manipulated variable (ASF) depending on the low-pass filtered feedback signal (Im).
  6. Driver circuit ( 1 ) according to claim 5, wherein the time constant of the low-pass filter (LPF) is slower than the duration of a period of the PWM modulation.
  7. Driver circuit ( 1 ) according to one of the preceding claims, wherein the time constant of the controller ( 10 ) implemented control algorithm is slower than the duration of a period of PWM modulation.
  8. Driver circuit ( 1 ) according to one of claims 3 to 7, wherein due to the slow time constant, in particular due to the slowing down by the low-pass filter (LPF) in a driver circuit ( 1 ) according to one of claims 5 to 6, the PWM modulation by the control loop is not ausregelbar.
  9. Driver circuit ( 1 ) according to one of the preceding claims, comprising a PWM dimming unit ( 8th' ) for setting a duty cycle (TVH) for the PWM modulation as a function of a dimming command (B), the duty cycle (TVH) preferably being independent of feedback variables, in particular from the region of the driver circuit (FIG. 1 ) is set.
  10. Driver circuit ( 1 ) according to claim 9, comprising an amplitude dimming unit ( 8th ) for determining the target value (ILS) for the luminous flux in dependence on the dimming command (B).
  11. Driver circuit ( 1 ) according to claim 10, wherein in a first dimming range (100% -DWB) of the dimming command (B), the duty cycle (TVH) for the PWM modulation is 100%, and in a second dimming range (DWB-). USW), the duty cycle (TVH) is preferably gradually reduced.
  12. Driver circuit ( 1 ) according to one of the preceding claims, wherein the first control loop comprises the controller ( 10 ) for controlling the luminous flux with a second control circuit comprising a further regulator ( 64 ), wherein the second control loop has a faster time constant than the first control loop, and serves to regulate a residual ripple of the voltage (Vdc).
  13. Driver circuit ( 1 ) according to one of the preceding claims, comprising one on the resonant circuit ( 3 ) following transformer (T) for transmitting electrical energy from one with the resonant circuit ( 3 ) coupled primary winding (La) to a secondary winding (Lb), from which the lamps are supplied with power.
  14. Driver circuit ( 1 ) according to one of the preceding claims, wherein the feedback signal (Im) indirectly reproduces the luminous flux, in which it is inductively coupled out on the secondary side of the transformer (T).
  15. Driver circuit ( 1 ) according to one of the preceding claims, comprising a driver ( 12 ) for outputting, based on the PWM-modulated manipulated variable, at least one on / off control signal (S / LS, S / HS) for controlling the at least one switch (LS, HS) of the clocked circuit ( 2 ).
  16. Driver circuit ( 1 ) according to one of the preceding claims, wherein the manipulated variable (ASF) the frequency and / or the duty cycle of the control of the at least one switch (LS, HS) of the clocked circuit ( 2 ).
  17. Control unit (ST) for operating a driver circuit ( 1 ) for lamps, in particular for one or more LEDs, comprising: An input for a return signal (Im) reproducing the current through the luminous means, a control circuit for controlling the luminous flux comprising a regulator ( 10 ), whereby the controller ( 10 ) generates a manipulated variable (ASF) for regulating the luminous flux, depending on the feedback signal (Im) and a signal (ILS) representing a setpoint for the luminous flux, - a PWM modulator ( 11 ) for modulating the manipulated variable (ASF) with a PWM signal
  18. Control unit (ST) according to claim 17 in the form of an integrated circuit, in particular ASIC or microcontroller or a hybrid version thereof.
  19. Method for controlling the current through light sources, in particular by one or more LEDs, in which A tapping the current through the light emitting return signal (Im) is tapped, - A control variable (ASF) is generated for the regulation of the luminous flux, depending on the feedback signal (Im) and a, a setpoint for the illuminant current reproducing signal (ILS), - A PWM signal is modulated to the manipulated variable (ASF).
DE102014202665.2A 2014-02-13 2014-02-13 Driver circuit for leds Pending DE102014202665A1 (en)

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DE102014202665.2A DE102014202665A1 (en) 2014-02-13 2014-02-13 Driver circuit for leds
PCT/EP2015/050529 WO2015121011A1 (en) 2014-02-13 2015-01-14 Driver circuit for leds
EP15701700.5A EP3105995B1 (en) 2014-02-13 2015-01-14 Driver circuit for leds

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WO2019238879A1 (en) * 2018-06-14 2019-12-19 Tridonic Gmbh & Co Kg Operating circuits for led loads comprising a half-bridge circuit

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DE102012007449A1 (en) * 2012-04-13 2013-10-17 Tridonic Gmbh & Co Kg A method of operating an LLC resonant converter for a lighting device, converter and LED converter

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US9000673B2 (en) * 2010-05-25 2015-04-07 Virginia Tech Intellectual Properties, Inc. Multi-channel two-stage controllable constant current source and illumination source
TW201249256A (en) * 2011-05-18 2012-12-01 Delta Electronics Inc Frequency-variable dimming control apparatus for light-emitting diodes and method for operating the same
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US20120248998A1 (en) * 2011-03-30 2012-10-04 Sanken Electric Co., Ltd. Led driver and led illuminator having the same
DE102012007449A1 (en) * 2012-04-13 2013-10-17 Tridonic Gmbh & Co Kg A method of operating an LLC resonant converter for a lighting device, converter and LED converter

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019154590A1 (en) * 2018-02-07 2019-08-15 Tridonic Gmbh & Co Kg Synchronous converter having under- and overcurrent protection
WO2019238879A1 (en) * 2018-06-14 2019-12-19 Tridonic Gmbh & Co Kg Operating circuits for led loads comprising a half-bridge circuit

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WO2015121011A9 (en) 2016-09-29
EP3105995B1 (en) 2019-10-09
EP3105995A1 (en) 2016-12-21

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