DE102017221786A1 - Lamp operating device with converter in the DCM - Google Patents

Abstract

The invention relates to an operating device for the dimmable operation of lighting means, in particular one or more LED (s), comprising a control circuit having a converter circuit with an energy storage element and at least one switch which is driven by the control circuit. The control circuit is designed to do so to operate by driving the switch, the converter circuit optionally at least in critical mode or in the mode with lückendem current operation. In the latching operation, the reclosing time is set in discrete increments in the range of a rising zero crossing of the current through the memory element. The control circuit is designed to control a parameter influencing the luminous flux by an indirect or direct change in the case of an incremental change of the reclosing time the switch-on period of the switch.

Description

The present invention relates to a lamp operating device, which is designed in particular for the dimmable operation of light sources, such as LEDs. Of course, LEDs also mean organic LEDs (OLEDs).

More specifically, the invention relates to dimmable control gear for lighting devices that use an active clocked converter. In this case, a control circuit controls a switch of the clocked converter, such that in the switched (conductive) state of the switch, an energy storage element (for example, an inductance) is charged, which energy storage element in the off state of the switch (non-conductive state of the switch) again on the Lamp path discharges or preferably a further energy storage device (eg, capacitor) loads, which in turn feeds the LED track with a ripple afflicted with DC voltage. Thus, ultimately, there is an increasing and decreasing current flow through the energy storage element (inductance).

Of course, if a relatively high average light output is desired, the current drop through the inductor is limited to a value greater than zero, and the switch is again rendered conductive before the current through the inductor has dropped to zero. Meanwhile, for example, if the light output is to be decreased for dimming, the restart threshold (or the corresponding time switch-on time) is correspondingly reduced (or the reconnection time extended), until finally the state is reached that the current through the inductance actually drops to zero may before the switch is again switched conductive and the current thus rises again.

This mode of operation (restarting on reaching the zero level) is typically called "critical mode" or "borderline mode".

Of course, if it is to be further reduced starting from this critical mode, a dead time must naturally be introduced between the drop of the current through the inductance to zero and the reconnection of the switch. This mode is accordingly called "discontinuous mode" (DCM).

It is advantageous, however, not to perform the reclosing in the lapping current mode at arbitrary times, but only when the current that trails after the first zero crossing (due to resonance effects) and thus crosses the zero line several times through the inductor makes a rising zero crossing , Only when the switch is turned on again in these time ranges of the positive zero crossing of the current through the inductance, a zero-voltage switching (ZVS) can be achieved.

The time ranges of the positive zero crossings can be detected by measuring (for example, the current through the inductance), or can be predicted on the basis of the resonant frequency known from the dimensioning of the components.

Thus, there is thus the problem that in the intermittent operation or in the transition from the critical mode into the lopsided operation, the luminous power can not be changed continuously by continuously changing the reconnection time, but only in increments ("valley switching") between one or more positive zero crossings of the current through the inductance, which can lead to jumps in the light output, which can also be perceived optically as flickering during a dimming ramp.

The invention now addresses this problem and provides a technique which, when dimming in the leaky mode or transitioning from the critical mode to the spanning mode, at least reduces the problem of jumps in the output power of the converter, even if the reconnection only to the Time points of the positive zero crossings of the current through the inductance takes place.

As a further aspect, the embodiment should be such that an ASIC is not necessarily required as a control device, but that a microcontroller can also initiate the corresponding activation of the switch.

This object is solved by the features of the independent claims. The dependent claims further advantageously form the central idea of the invention.

A first aspect of the invention relates to an operating device for the dimmable operation of lighting devices, in particular one or more LED (s). It has a control circuit which has a clocked converter circuit with an energy storage element, in particular at least one inductance, and at least one switch, which is clocked starting from the control circuit. The converter circuit can be, for example, a buck converter or a boost converter.

The control circuit is designed such that, by activating the switch, the converter circuit can be operated selectively, in particular by a signal specifying the power, at least in the critical mode or in the mode with a gaping current. In a first dimming range, therefore, there is an operation in the latching mode, and in another separate dimming range, there is an operation in the critical mode. These two modes may be adjacent to each other, however, a hybrid mode may also be provided between them, in which the gaping or critical mode is temporally multiplexed. (Optionally, the critical mode can also be connected to a continuous mode).

In the latching operation, the control circuit sets the switch-on instant of the switch in discrete increments into one of the time ranges after the first zero crossing, in which the current during the discharge of the energy storage element performs a rising zero crossing. In this case, the control circuit is designed to regulate a feedback variable influencing the luminous flux power in the event of an incremental change in the reconnection time by direct or indirect change in the switch-on duration of the switch.

• - bei einer inkrementellen Verlängerung des Wiedereinschaltzeitpunkts inkrementell bzw. sprunghaft die Einschaltzeitdauer zu verlängern und dann eine Regelung mit der Steuergrösse „Einschaltzeitdauer“ durchzuführen und,
• - bei einer inkrementellen Verringerung des Wiedereinschaltzeitpunkts inkrementell bzw. sprunghaft die Einschaltzeitdauer zu verkürzen und dann eine Regelung mit der Steuergrösse „Einschaltzeitdauer“ durchzuführen.

The control circuit can be designed to

• incrementally or step-by-step, with an incremental extension of the reconnection time, the switch-on time duration and then carry out a control with the control variable "switch-on time duration" and
• - Incremental or abruptly shortening the switch-on period when there is an incremental reduction in the reclosing time, and then carry out a control with the "switch-on duration" control variable.

The control circuit can be designed to carry out an incremental prolongation of the reconnection time if the control with the control variable "switch-on time" results in predetermined minimum or maximum values of the switch-on duration or a variable influencing them, that is to say this control by means of the change of the switch-on period to theirs Limits pushes.

The control circuit may be configured to specify the change in the switch-on period of the switch indirectly by specifying a switch-off threshold for the current through the switch or directly by specifying the switch-on period.

The control circuit may be configured to, in the event of a transition from the critical mode to the latching current mode, suddenly increase the value for the switch-on time duration of the switch.

The converter circuit can be, for example, a boost, buck, buck / boost or flyback converter.

A further aspect of the invention relates to a method for the dimmable operation of light sources, in particular one or more LED (s),
using a control circuit having a clocked converter circuit with an energy storage element and at least one switch, which is driven by the control circuit. In this case, the converter circuit is operated in at least a partial area of the total dimming range in the mode with a gaping current. In the latching mode, the reclosing time is set in discrete increments in the range of a rising zero crossing of the current through the memory element.

• - eine zu dem einzustellenden Dimmwert vordefinierte Abschaltschwelle für den Strom durch den Schalter oder eine Einschaltzeitdauer des Schalters festgelegt,
• - ein steigender Nulldurchgang als tatsächlichen Wiedereinschaltzeitpunkt eingestellt, der demjenigen theroretischen Wiedereinschaltzeitpunkt am nächsten kommt, der sich aus der Abschaltschwelle bzw. der Einschaltzeitdauer und dem einzustellenden Dimmwert ergibt, und
• - die Abschaltschwelle oder die Einschaltzeitdauer abhängig von der Abweichung des tatsächlichen Wiedereinschaltzeitpunkts von dem theoretischen Wiedereinschaltzeitpunkt, verändert.

To set a dimming value

• a fixed switch-off threshold for the current through the switch or a switch-on time duration of the switch is predefined for the dimming value to be set,
• a rising zero crossing is set as the actual reclosing time, which comes closest to the theoretical reconnection time resulting from the shutdown threshold or the set duration and the dimming value to be set, and
• the switch-off threshold or the switch-on duration is changed depending on the deviation of the actual switch-on time from the theoretical switch-on time.

The predefined switch-off threshold for the current through the switch or a switch-on time duration of the switch can depend not only on the dimming value to be set, but on at least one further parameter, such as, for example, the voltage across the lighting means.

The invention also relates to a control circuit, for example. ASIC or microcontroller, which is designed for such a method. Another aspect of the invention relates to a circuit for detecting the zero crossing of the current through the inductance of a buck converter, in particular a buck converter in an operating device of the type described above,
having one with the potential at a connection point of the diode of the Buck converter and a switch of the Buck converter connected diode circuit which generates a preferably digital detection signal whose preferably logic level changes at a zero crossing of the current through the inductance.

This circuit may comprise a software-moderate or hardware-trained block, which prevents the level of the detection signal after a first zero crossing changes at further zero crossings.

This circuit may comprise a control circuit, preferably a microcontroller, to which the detection signal is supplied.

A defined level change of the detection signal can trigger a counter in the microcontroller.

A further aspect of the invention relates to a circuit for detecting the lower reversal point of the current through the inductance of a buck converter,
having a magnetically coupled to the inductance of the buck converter auxiliary winding which generates a signal which switches a detection signal generating transistor when the current through the inductor reaches its lower reversal point.

Yet another aspect of the invention relates to an operating device for lighting means, comprising a converter clocked on the primary side by means of a switch, in particular a buck converter,
comprising a control circuit, which switches the switch non-conductive again after a predetermined time period, ton, or upon reaching a cut-off value of the rising switch current,
wherein the control circuit is supplied with a feedback signal, which reproduces the voltage via the lighting device supplied by the operating device,
wherein the control circuit sets the duration of time ton or the cut-off value depending on the feedback signal.

In this case, preferably the time duration ton or the switch-off value is set lower at the lower voltage across the lighting means than at the higher voltage across the lighting means.

• 1 zeigt eine schematische Ansicht eines bekannten Buck-Konverters zum Betrieb einer LED-Strecke.
• 2 zeigt die Strom- und Spannungsverläufe in einem derartigen Konverter von 1.
• 3 zeigt die Anwendung des sog. Valley Switch in einem ausgewählten Dimmbereich.
• 4 zeigt ein Blockschaltbild zur Ausführung der Erfindung.
• 5 zeigt Signalverläufe bei der Ausführung der Erfindung.
• 6 zeigt eine Implementierung der Erfindung mit zwei möglichen Zero-Cross Erfassungsschaltungen.
• 7 bis 10 zeigen Signal- und Stromverläufe sowie eine schematische Schaltung (9) zur Kompensation der Ausschaltverzögerung bei der Peak-Strom Erfassung in getakteten Wandlern

Further features, properties and advantages of the invention will now be explained with reference to embodiments and the accompanying figures of the drawings.

• 1 shows a schematic view of a known buck converter for operating an LED track.
• 2 shows the current and voltage waveforms in such a converter of 1 ,
• 3 shows the application of the so-called valley switch in a selected dimming range.
• 4 shows a block diagram for carrying out the invention.
• 5 shows waveforms in the practice of the invention.
• 6 shows an implementation of the invention with two possible zero-cross detection circuits.
• 7 to 10 show signal and current characteristics as well as a schematic circuit ( 9 ) to compensate for the off delay in the peak current detection in clocked converters

In 1 schematically is a known buck converter for operating a light source path 6 shown.

It is based on a DC bus voltage 1 , also with V _bus when conducting, a semiconductor switch is turned on 2 an inductance 4 charged in the off state 3 of the switch 2 over a capacitor 5 (or alternatively directly via a lamp load) discharges.

Starting from the capacitor 5 So is a DC operating voltage V _LED for a light path 6 provided. In the switched-on state of the switch 2 the tension increases V _LED by charging the capacitor while in the off state of the switch 2 decreases. Thus, there is a varying course of the current I _LED through the light path 6 , wherein the human eye with appropriate high-frequency control of the switch 2 only perceives the time average.

The desk 2 is replaced by an in 1 not shown control circuit via a signal input 3 driven. The control circuit may be an ASIC or preferably a microcontroller.

2 shows corresponding signal, - voltage and current characteristics.

The signal HS is the level at the control input 3 of the switch 2 , During a period of time ton, this switch is turned on while it is in the periods t _off and _dead is not switched on.

In the period t _off is the diode 7 in 1 conductive.

The lowest curve in 2 Finally, the current flow through the inductance 4 , of the denoted by IL. During the switch-on period t _on of the switch 2 this current increases while in the off-time period t _off decreases until it makes a first (falling) zero crossing. Due to resonance effects, a vibration course then occurs during the time duration _dead , A reconnection in this current gap is carried out according to the invention always to a temporal range in which the current IL through the inductance 4 performs a rising zero crossing.

The switch-on period t _on can be timed out by a control circuit. The turn-on time ton can, however, also be the result of a hysteresis control in which the switch 2 is switched non-conductive, as soon as the rising switch current a predetermined upper Abschaltwert I _peak has reached.

As already mentioned at the beginning, reclosing only in discrete increments to the positive zero-crossing ranges of the current causes leaps in the light output in the intermittent operation or at the transition from the critical mode to the mode with intermittent operation, since there is no continuous change in the light output Wiederschaltschaltzeitpunkts should take place and thus the supply of the transistor could not be constant.

If, for example, the luminous flux power is to be reduced in intermittent operation, it is necessary to suddenly trigger a higher-time reclosing time for the switch. According to the invention, the thus-threatening power jump is now compensated for by maintaining a tone-time control when the switch-off period is held. That is, in a choice of an increment of the positive zero crossings of the current IL by the inductance deviating from the current state 4 is simultaneously estimated by the control circuit, as for maintaining a continuous power reduction t _on -Zeit must first be extended abruptly to a new operating point (as I said, either by a real time specification or by increasing the switch-off threshold in a hysteresis control), before then at this estimated working time around a ton-time control is performed.

In contrast to the prior art, the on-duration time ton is not recorded in intermittent operation, but designed adaptive and a t _on -Time control maintained.

This has control technology beyond the advantage that a continuous t _on -Time control is maintained, so both in intermittent operation as well as in critical mode or possibly also in the continuous mode of operation.

Conversely, if, for example, to perform a dimming, the light output is to be increased again, first the dead time _dead reduced by a jump of the zero-crossing increments down, and at the same time the leaps t _on Time is reduced to an estimated operating point to avoid light power jumps, then at this estimated operating point, the sound-time control is continued.

It is important to emphasize again that the switch-on time t _on of the switch 2 either directly from a tone-time control, but also indirectly, namely in particular by setting a switch-off threshold I _peak can allocate for the switch current. The new operating point can thus be a new switch-on time or a new switch-off threshold.

A jump in the dead time increment, ie the selected positive zero crossing during the time _dead , can also be triggered when the tone-time control or the Abschaltschwellenregelung at an upper or lower predetermined limit for the t _on Time or the switch-off threshold I _peak encounters.

• - Nach Vorgabe einer Veränderung, insbesondere eines Sprunges für den Sollwert für den mittleren LED-Strom wird von der Steuereinheit zuerst berechnet, wie lange im lückenden Betrieb die Totzeit t_dead sein müsste, um den zeitlich mittleren Strom bei gegebener Abschaltschwelle I_Peak zu erzielen. Diese berechnete Totzeit t_dead wird normalerweise nicht auf einen Nulldurchgang des Stromes mit positiven Gradienten fallen, so dass dann einerseits der nächstliegenden Nulldurchgang mit positiven Gradienten gewählt wird, gleichzeitig aber auch die Differenz zwischen der berechneten Totzeit und der sich durch den nächstliegenden Nulldurchgang bestimmt wird. Aufgrund dieser bekannten Differenz kann dann entsprechend der neue Arbeitspunkt der Abschaltschwelle I_Peak beziehungsweise der t_on -Zeitregelung entsprechend eingestellt werden, worauf dann die t_on -Zeitregelung an diesem Arbeitspunkt fortgeführt wird. Um ein unnötiges Springen zwischen unterschiedlichen Nulldurchgängen („Valleys“) zu verhindern, die gegebenenfalls als Sprung in der Leuchtmittel-Leistung sichtbar sein können, wird immer bei Vorgabe eines neuen Durchschnitts stroms der vorherliegende Wert des Nulldurchgangs berücksichtigt, um ein Springen zwischen zwei unterschiedlichen Nulldurchgängen mit positiven Gradienten durch eine Art Hysterese-Regelung zu verhindern.
• - Es wird somit bei Vorgabe eines neuen Durchschnittswerts für den Strom durch Berechnung oder durch Abgleich über eine Tabelle, etc., zuerst eine neue Abschaltschwelle I_Peak definiert, worauf folgend dann die Totzeit im lückenden Betrieb berechnet wird.
• - Die Umsetzung eines einzustellenden Durchschnittsstromwerts auf eine Abschaltschwelle I_Peak oder t_on -Zeit kann multidimensional sein, derart, dass die Wahl der Abschaltschwelle I_Peak (oder der direkten t_on -Zeit Vorgabe) unter Berücksichtigung weiterer Parameter erfolgt (über den einzustellenden Durchschnittsstromwert hinaus). Diese weiteren Parameter können beispielsweise sein:
  • ◯ Die LED-Spannung, da diese einen Einfluss darauf hat, wie sensitiv der Durchschnittswert des Stroms auf die Veränderung der Abschaltschwelle I_Peak oder der t_on -Zeit reagiert.
  • ◯ Ein weiterer Gesichtspunkt der Erfindung ist es, dass die Festlegung der Abschaltschwelle oder der t_on -Zeit abhängig von dem zu erzielenden Dimmwert (ausgedrückt durch den Durchschnittsstrom) auf die Frequenz des Auftretens der Einschaltvorgänge festlegt. Vorzugsweise wird nunmehr bei einem Dimmsprung (also Sprung des Durchschnittswerts des Stroms I_LED die Abschaltschwelle so gelegt, dass sich möglichst eine konstante Frequenz des Auftretens der Einschaltvorgänge ergibt, also möglichst die Totzeit t_dead konstant gehalten wird.
• - Indessen ist es möglich, dass für unterschiedliche Dimmbereiche unterschiedliche Vorgaben für die einzustellende Schaltfrequenz festgelegt sind, so dass also in unterschiedlichen Dimmbereichen (also unterschiedliche Bereiche des Stroms I_LED ) die konstant zu haltende Frequenz des Auftretens der Einschaltvorgänge des Schalters 2 unterschiedlich vorgegeben sein kann. In 3 ist zu sehen, dass das erfindungsgemäße „Valley Switching“, also das inkrementale Springen zwischen unterschiedlichen Inkrementen an positiven Nulldurchgängen des Stroms durch das Energiespeicherelement (Induktivität 4) bevorzugt nur in einem oberen Dimmbereich, anschließend an 100% Nominalleistung der LED-Strecke ausgeführt wird. Bei einem Herabdimmen von beispielsweise unterhalb von 10% Dimmlevel wird die Totzeit im lückenden Betrieb derart groß, dass das abklingende Nachschwingen des Stroms durch die Induktivität 4 nicht mehr vorhanden ist bzw. keine Rolle mehr spielt. Somit kommt es zu einer Übergangszone, in der unterhalb des Dimmbereichs für das Valley Switching die Wiedereinschaltzeitdauer des Schalters kontinuierlich verstellt werden kann. Dieses kontinuierliche Erhöhen der Totzeit im lückenden Betrieb stößt indessen bei der weiteren Verringerung des Dimmpegels beispielsweise unterhalb von 1% Nominalleistung auf Grenzen, da eine sehr lange Totzeit ggf. zu optisch sichtbaren Effekten führen kann. Daher ist eine maximale Totzeit t_deadmax vorgesehen. Wenn diese erreicht wird, wird die Totzeit festgehalten und eine weitere Verringerung der Lichtmittelleistung kann dann beispielsweise nur durch andere Effekte, wie beispielsweise eine Amplituden-Verringerung erzielt werden. 4 zeigt eine schematische Blockdarstellung zur Ausführung der Erfindung. Ein Block A bezeichnet dabei einen Berechnungsblock zur Berechnung der nominalen Totzeit t_deadnom und der nominalen Abschaltschwelle I_peaknom . Dabei wird für diese Berechnung berücksichtigt:
  • - der vorgegebene Sollwert I_nom für den LED-Strom,
  • - der Wert der DC-Versorgungsspannung für den Konverter Vbus sowie
  • - die Leuchtmittelspannung V_LED .
  Aus diesen Eingangswerten berechnet der Block A in 4 anhand einer Funktion oder einer Abgleichstabelle die nominalen Werte für die Totzeit t_deadnom sowie die Abschaltschwelle I_peaknom (oder die Einschaltzeitdauer t_onnom ). Der Block B dient dann zur Umsetzung der Totzeitregelung ausgehend von diesen berechneten Nominalwerten. In einem ersten Block „select nearest neighbour“ wird dasjenige „valley“ (also der positive Nulldurchgang) gewählt, der der nominalen Totzeit tdeadnom an nächsten kommt. In diesem Block B ist vorab abgelegt die zeitliche Lage der „valleys“, was in 4 mit „valley array“ bezeichnet ist. Das „valley“, dass der tdeadnom am nächsten kommt, wird als einzustellendes „valley“ genommen und entsprechend wird die Totzeit mit dem Wert „new Tdead“ eingestellt. (Anmerkung: Alle Berechnungen im Block A sind außerhalb der eigentlichen Regelschleife und sind somit zeitunkritisch. Sie können somit leicht durch einen Mikrokontroller bewältigt werden.)

If, for example, a new time average for the LED current is to be triggered when a new dimming value is specified, the sequence is as follows:

• - After specification of a change, in particular a jump for the setpoint value for the average LED current, the control unit first calculates how long the idle time lapses _dead would have to be the time average current at a given shutdown threshold I _peak to achieve. This calculated dead time _dead will normally not fall to a zero crossing of the current with positive gradient, so that then on the one hand, the nearest zero crossing is selected with positive gradient, but at the same time the difference between the calculated dead time and is determined by the nearest zero crossing. Due to this known difference can then according to the new operating point of the switch-off I _peak or the t _on Timing be adjusted accordingly, then what the t _on Time regulation is continued at this operating point. In order to prevent unnecessary jumping between different zero-crossings ("valleys"), which may possibly be visible as a jump in the luminous power, always taking into account a new average current, the previous value of the zero crossing is taken into account, to jump between two different zero crossings With to prevent positive gradient by a kind of hysteresis control.
• Thus, when a new average value for the current is specified by calculation or comparison via a table, etc., a new switch-off threshold is first of all established I _peak then the dead time in the gap operation is calculated.
• - The conversion of a set average current value to a switch-off threshold I _peak or t _on -Time can be multidimensional, such that the choice of shutdown threshold I _peak (or the direct t _on Time specification) taking into account further parameters (beyond the average current value to be set). These other parameters can be, for example:
  • ◯ The LED voltage, as it has an influence on how sensitive the average value of the current is to the change in the switch-off threshold I _peak or the t _on Time responds.
  • ◯ Another aspect of the invention is that the determination of the switch-off or the t _on Time depending on the dimming value to be achieved (expressed by the average current) at the frequency of occurrence of the turn-on operations. Preferably, now at a dimming jump (ie jump of the average value of the current I _LED the switch-off threshold is set so that as far as possible a constant frequency of the occurrence of the switch-on results, ie as far as possible the dead time _dead is kept constant.
• - However, it is possible that different specifications for the switching frequency to be set are defined for different dimming ranges, so that therefore in different dimming ranges (ie different areas of the current I _LED ) the constant frequency of occurrence of the switch-on operations of the switch 2 can be specified differently. In 3 It can be seen that the "valley switching" according to the invention, ie the incremental jump between different increments at positive zero crossings of the current through the energy storage element (inductance 4 ) is preferably performed only in an upper dimming range, then at 100% nominal power of the LED track. In a dimming down, for example, below 10% dimming level, the dead time in the lopsided operation is so large that the decaying reverberation of the current through the inductance 4 no longer exists or no longer plays a role. This results in a transitional zone in which below the dimming range for valley switching, the reclosing time of the switch can be continuously adjusted. However, this continuous increase in dead time in lopsided operation encounters limits in the further reduction of the dimming level, for example, below 1% nominal power, since a very long dead time may possibly lead to optically visible effects. Therefore, a maximum dead time t _deadmax intended. When this is achieved, the dead time is recorded and further reduction of the light-emitting power can then be achieved, for example, only by other effects, such as amplitude reduction. 4 shows a schematic block diagram for carrying out the invention. A block A designates a calculation block for calculating the nominal dead time t _deadnom and the nominal shutdown threshold I _peaknom , In doing so, account is taken of this calculation:
  • - the specified setpoint I _nom for the LED power,
  • - The value of the DC supply voltage for the Vbus converter as well
  • - The bulb voltage V _LED ,
  From these input values, block A calculates in 4 using a function or an adjustment table, the nominal values for the dead time t _deadnom as well as the switch-off threshold I _peaknom (or the switch-on period t _onnom ). Block B then serves to implement the dead time control on the basis of these calculated nominal values. In a first block "select nearest neighbor", that "valley" (ie the positive zero crossing) is selected which comes closest to the nominal dead time tdeadnom. In this block B is filed in advance the temporal position of the "valleys", which in 4 denoted by "valley array". The "valley" that comes closest to the tdeadnom is taken as the "valley" to be set and accordingly the dead time is set with the value "new Tdead". (Note: All calculations in block A are outside the actual control loop and are therefore time critical, so they can easily be handled by a microcontroller.)

In block B, the actual current control "current regulator" is provided, which is the setpoint I _nom as well as the currently measured actual value for the LED current I _MEAS is supplied.

Furthermore, a dead-time compensation unit is provided "t _{dead compensator} ", which as input information, the selected Valley of the block "Select nearest neighbor" and the time average of the current through the LED track I _nom receives.

In order to prevent now the deviation and thus a jump in the luminous power, the deviation of the valleys from the calculated nominal dead time t _deadnom is created, the output variable of the current regulation "current regulator" by the dead time compensator t _{dead-compensator} ", Changed to shift the operating point, so that therefrom a new switch-off threshold for the switch current" new I _peak "Results.

These processes are again based on the waveforms of 5 to be shown.

The scenario assumes that at one time T1 a jump in the setpoint specification I _nom for the time average of the current is received. Upon receipt of such a setpoint jump, a computation phase, which is needed to perform the computation that is in 4 is pictured.

As in 5 can be seen, the calculation is carried out for the setting of the new setpoint I _nom necessary nominal dead time tdeadnom. In fact, however, the nearest valley becomes "nearest neighbor" to the nominal deadtime t _deadnom set.

Due to this deviation of the nominal dead time t _deadnom From the time position of the next Valleys results in a compensation value I _PKCOMP from the block "t _{dead compensator} " in 4 is used directly for sudden change in the operating point of the current control. By this erratic adjustment of the operating point so the jumps in the Leuchtmittereistung are actually prevented because on the other hand, the current regulator would also rule out this control error (deviation of the actual dead time of the nominal dead time), the time duration of Ausregelns meanwhile could lead to optically visible effects.

ZX-detection circuits:

Regarding 6 An application of the invention to a buck converter will now be described. There are two possible zero-cross detection circuits 10 . 20 explained, which may alternatively or simultaneously be present in a converter.

In 6 there is shown a buck converter according to the present invention whose power path comprises a buck switch M1 , a buck diode D1 , an output filter capacitor fed by the converter C1 , which may be any low-pass filter, as well as the buck inductance L1 -A and a measuring resistor (shunt) R1 for measuring the buck current.

Diode-based circuit 10:

The circuit in 6 on the one hand has a first detection circuit 10 and a second detection circuit 20 , which may be alternative or simultaneous, and each adapted to generate a signal representing the instant at which the inductor current IL through the buck inductor L1 -A crosses the zero line, which in English is called, zero crossing ZX '.

First, let us explain the first detection circuit 10 for the ZX event. This circuit has two diodes D20 . D21 , two ohmic resistors R20 . R21 and a zener diode Z20 ,

This circuit is used to generate a signal indicating the onset of dead time _dead detected, ie the first drop of the inductor current IL to zero. During the switch-off period of the switch M1 the current IL decreases from a maximum value I _PK to zero. During this drop, the voltage at the midpoint (measured from the cathode of the diode D1 against ground potential) at the logic level "low". This means that the signal ZCD_1_filtered, which can be supplied, for example, to a pin of a microcontroller or ASIC, is also pulled low during this time since the diode D20 is conductive.

When the current IL has completed the first zero crossing, the current flow becomes negative, ie the current direction through the inductance L1 -A turns around and the slope at the midpoint increases. That means the diode D20 blocks and thus the signal ZCD_1_filtered is pulled to the potential logic "high", namely by the supplied low-voltage supply voltage V _DD and the resistors R20 . R21 , This rising edge (from low to high) of the signal ZCD_1_filtered then starts in the control circuit (for example, a microcontroller) a counter for the dead time _dead , This counter runs until the desired dead time has elapsed and then the control circuit through the signal 3 again the switch M1 on (conductive) switches.

At the in 6 As shown, the control circuit outputs a signal ZCD_Filter_1_out to a logic high (high) while the counter for the dead time is running, which in turn is passed through the diode D21 the signal ZCD_1_filtered pulls "high". This has the advantage that thereby re-starting the dead time counter is avoided, ie restarting at further rising edges of the signal ZCD_1_filtered are thus prevented or hidden.

However, it is also possible to achieve this suppression of further rising edges (each time in reverse current direction), for example by software solution in a microcontroller, so that then the output of the signal ZCD_Filter_1_out and the diode D21 would not be necessary.

Detection circuit 20 with auxiliary winding and transistor:

It will now be the second detection circuit 20 for the ZX event.

This circuit is used to detect possible reclosing times for the switch M1 to be determined (in the event that as the reconnection times are not stored or calculated in advance due to the known component dimensions).

As is known, low minimum switching losses are achieved when the voltage across the switch M1 is low and as minimal as possible when it is switched on, which means that the midpoint voltage (cathode of the diode D1 ) has a maximum to this area. It is therefore important that those times (counts of the dead time counter) are determined in which the midpoint voltage is as high as possible.

The relationship between voltage across an inductor and current through the inductor is known to be given by: $$u_L\left(t\right)=L*\frac{d{t}_L}{dt}$$

This means that the voltage is above the inductance L1 -A is positive when the slope of the current IL is positive and the voltage is negative when the slope of the current is negative. Due to the 90 ° phase shift between current and voltage at an inductance, a voltage maximum occurs at the positive going zero crossing of the current, or a voltage minimum at the negative going zero crossing of the current. A reversal of the voltage takes place in each case at the maximum and minimum of the current through the inductance.

In order to achieve minimum switching losses, so should the switch M1 be turned on at the positive going zero crossing of the current IL again. A reversal of the voltage across the inductor L1 -A takes place at the current minimum before this positive zero crossing. This reversal of the voltage across the inductor is used in accordance with the invention to detect the optimal reclosing times. More specifically, the detected time in this approach according to the invention is half a half wave of the oscillation of the inductor current IL after its first zero crossing before the optimal time for reconnection.

However, real circuits have turn-on delays between the output of a signal and the actual reconnection of the switch M1 before, so that when triggering the switch-on in the switch M1 at the current minimum, before the positive going zero crossing in practice, then the actual switching on of the switch M1 falls approximately to the optimal time, ie the time range of the positive going zero crossing of the inductor current IL.

As can be seen, an auxiliary winding according to the invention L1-B provided with the actual inductance L1-A is coupled in the power path of the converter.

When the voltage over L1 is positive, the diode blocks D30 and the switch Q30 is on. The signal ZCD_1 which can be supplied to a pin of a control unit is thus logically low. When the voltage over L1 is negative, conducts the diode D30 and the switch Q30 is switched off. Thus, the signal ZCD_1 becomes via the resistor R30 pulled to the potential logic high (high), which corresponds to the potential of the supplied low-voltage power supply VDD.

This means that the falling edges of the signal ZCD_1 represent the times at which the voltage across the inductance changes from negative to positive, which means that the current IL has a minimum, then a positive zero crossing with a certain time delay of the inductance current takes place. For each of these falling edges of the signal ZCD_1, the current counter value of the dead time counter is stored in a memory "Valley array".

The rule algorithm that calculates the target dead time now selects one of the values in this filed valley array. The control algorithm (block B) then selects the valley closest to tdeadnom based on tdeadnom. This tdeadvalley is then set (New Tdead in 4 )

Typically, the calculated dead time will differ from the available Valley values, so a new peak current cut-off threshold is calculated (or a new one) t _on Time) to reach the desired average current with the selected dead time.

• R40, R41 und C40: Diese dienen zur LED-Spannungsmessung.
• R50, C50: Diese dienen zur Mittelwertbildung der Messspannung an dem Messwiderstand R1, um somit den Durchschnittsstrom zu ermitteln, der dann über einen AD-Wandler der Steuerschaltung zugeführt werden kann.
• R51: Dieses Signal wird mittels eines Komparators mit einem eingestellten Schwellwert verglichen. Wenn der Schwellenwert erreicht wird, wird der Schalter M1 abgeschaltet. Dies ist also eine mögliche Implementierung für eine Schwellenwertabschaltung.

In the illustrated implementation, measurement paths are provided, which can be defined as follows:

• R40, R41 and C40: These are used for LED voltage measurement.
• R50, C50: These are used for averaging the measuring voltage at the measuring resistor R1 In order to determine the average current, which can then be fed via an AD converter of the control circuit.
• R51: This signal is compared by means of a comparator with a set threshold. When the threshold is reached, the switch becomes M1 off. So this is one possible implementation for a threshold shutdown.

Compensation of the switch-off delay in peak current detection in clocked converters

As already described above, in the case of clocked converters with a switch actuated on the primary side, there is the approach that the switch is switched to non-conductive when the current through the switched-on switch has risen to a predetermined switch-off value (peak current).

There is the problem that, due to component-inherent turn-off delays, there is a delay between the actual achievement of the peak current value and the turn-off time.

These turn-off delays are caused for example by a so-called propagation delay from the comparator and the gate driver, as well as edge slopes and parasitic capacitances. The actually flowing peak current and thus the resulting time average is thus corrupted, this deviation depending on the slope of the current dI / dT.

For example, typical turn-off delays may be in the order of several hundred nanoseconds, which may, for example, cause the peak current at 1.2 amps to be turned off instead of a desired switch-off value of 1 amp at a steep current increase dI / dT of switch current.

The present aspect of the invention now addresses this problem. This aspect of the invention may be combined with the aspects mentioned earlier in the present description, but of course apply independently to any other primary side active clocked converter, for example buck converters.

The steepness of the increase in current through the primary-side switch depends inter alia on the voltage across the load, for example an LED load. At low LED voltages, the current increase is very steep, resulting in a large overshoot of the peak current. Conversely, a high LED voltage results in a less steep increase in current when the primary switch of the clocked converter is on, which in turn results in less overshoot of the peak current.

According to the invention, the switch-off threshold value is now set as a function of the detected output-side voltage, in particular a measured LED voltage. In this case, the threshold is relatively little reduced (for example, from 1 ampere to 0.95 amperes) at high detected LED voltage, while being significantly reduced at low detected LED voltage, for example, from a nominal value of 1 ampere to 0.9 amps , so that in fact results in both cases, the desired shutdown threshold of 1 ampere due to the off-delay.

The requirements for the accuracy of keeping the peak current are particularly large when the peak current is calculated, for example as described above. As explained in the present description above, there is the approach that fits a stepwise (incrementally) adjustable dead time _dead a necessary peak current I _{pk comp} calculated and set abruptly to a desired current average I _avg to reach. Any deviation in the real peak current from the calculated desired value I _{pk comp} leads to an error in the mean I _avg , Therefore, it is important that the actual real in the converter adjusting peak current with the calculated (desired) peak current I _{pk comp} matches.

With such a precalculation of a necessary peak current with a sudden change in the dead time _dead (in the discontinuous mode of the converter) compensation of the real switch-off delay is particularly important.

7 shows how a different peak current can actually be set at two different operating points (slope of the current through the buck inductance with a conductive switch). As in 7 It can be seen, for example, a real shutdown threshold of 1.2A or 1.1A can be set at a desired shutdown threshold of 1A depending on the operating point, even if the turn-off delay (which is indeed component-dependent) is constant.

According to the invention, the threshold values are now varied according to the operating point in order to compensate for the switch-off delay.

This is in 8th shown.

In a first case, the shutdown threshold is set to 0.9A and in the second case to 0.8A. Due to the switch-off delay, in both scenarios (with different slope of the current through the inductance), the desired (for example, pre-calculated) switch-off threshold value of 1A results and the switch-off delay is thus compensated in this regard.

In 9 a possible implementation of this compensation of this off-delay is shown.

An example is calculated peak current Ipk_comp, which is calculated, for example, from a desired dimming value (current average) and a selected dead time, this calculated peak current Ipk_comp is easily corrected by the output signal of an example integral controller deltalpk. The sum of both paths then gives a desired peak current of, for example, 1A. Depending on the operating point, a correction value Ipk_overshoot is now deducted from this calculated desired target value. For small LED voltages with a steep current increase (large dI / dt) is corrected with a relatively high value (for example, the value Ipk_overshoot be 0.2A). At high LED voltages with flat current increase (low dI / dt) is corrected accordingly less strong (then, for example, the value of Ipk_overshoot be 0.1A).

After deducting this correction or compensation factor Ipk_overshoot, the digital peak current value is converted into a DA converter in an analog threshold. By means of an optional level adjustment and filtering (by means of the resistors R1 . R2 and the capacitor C1 ), the threshold is passed to a comparator which compares the threshold with the actual voltage drop at, for example, a shunt, the voltage drop across the shunt representing the current through the buck inductor. When the measured current (or the falling voltage) reaches or exceeds the threshold value, the comparator switches its output, which leads to a switch-off of the Buck switch.

According to the invention, the factor "Ipk_overshoot" is determined as a function of the measured LED voltage, for example in accordance with an analytical function or a stored table which, for example, fulfills the function 10 reproduces. However, other possibilities can be used to determine information regarding the slope of the current rise through the switch. In this case, the use of at least one of the value of the inductance L, the input voltage come into question V _bus or the output voltage V _LED as well as any combinations thereof.

The relationship between the Ipk_overshoot correction value and the selected parameter is an example of 10 linear (linear dependence of the voltage across the LED range V _LED ). However, this dependence can not be linear.

It is also possible that the correction factor Ipk_overshoot is calculated continuously or at regular intervals. During the off-delay t _doff the buck current increases by one value I _pkOV so that at constant OFF delay therefore at any time to be corrected Overshoot value I _pkOV can be calculated according to the following formula: $$V_{Bus}-V_{LeD}=L*\frac{I_{pk\_Ov}}{t_{dOff}}\to I_{pk\_Ov}=t_{dOff}*\frac{V_{Bus}-V_{LeD}}{L}$$

Of course, if the determination of on-time does not pass indirectly through a comparator threshold, but directly through the on-time setting, then the on-time can easily be reduced by the off-delay tdoff to compensate for the off delay effect.

Claims (18)

Operating device for the dimmable operation of light sources (1), in particular one or more LED (s), comprising a control circuit (2) having a clocked converter circuit (3) with an energy storage element (4) and at least one switch (5) is clocked starting from the control circuit (2), - wherein the control circuit (2) is designed to operate by driving the switch, the converter circuit (3) optionally at least in critical mode or in the mode with lückendem current, - wherein the control circuit in the lückenden Operation sets the reconnection time of the switch (5) in discrete increments in one of the temporal ranges after the first zero crossing, in which the current through the energy storage element (4) performs a rising zero crossing, characterized in that the control circuit (2) is designed to with an incremental change the Wiederschaltschaltzeitpunkts a luminous flux performance affecting feedback size by direct or indirect change of the switch-on of the switch (5) to regulate. Operating device after Claim 1 in which the control circuit (2) is adapted to: - incrementally increase the on-time with an incremental extension of the reclosing time and perform control with the "on period"control; and incrementally reduce the on period with an incremental decrease in the reconnect time, and then to carry out a control with the control value "switch-on time period". Operating device according to one of the preceding claims, in which the control circuit (2) is designed to carry out an incremental extension of the reclosing time if the control with the control value "switch-on time" results in predetermined minimum or maximum values of the switch-on duration or a variable influencing them. Operating device according to one of the preceding claims, in which the control device is designed to specify the change in the switch-on period of the switch (5) indirectly by specifying a switch-off threshold for the current through the switch (5) or directly by specifying the switch-on time. Operating device according to one of the preceding claims, in which the control circuit is designed to increase the value for the switch-on time of the switch in a transition from the critical mode to the mode with latching current operation. Operating device according to one of the preceding claims, wherein the converter circuit is a boost, buck or flyback converter. Method for the dimmable operation of lamps, in particular one or more LED (s), using a control circuit having a converter circuit with an energy storage element and at least one switch, which is driven by the control circuit, wherein the converter circuit operated in the mode with lückendem current is in the latching operation, the reclosing time in discrete increments in the range of a rising zero crossing of the current through the memory element, characterized in that for setting a dimming value - a pre-defined to the set dimming threshold for the current through the switch or a switch-on of the switch is set, - an increasing zero crossing is set as the actual reconnection time, which comes closest to the theoretical reconnection, which is the shutdown and the Einschaltzeitdauer and the ei - the switch-off threshold or the switch-on time depends on the deviation of the actual switch-on time from the theoretical switch-on time is changed. Method according to Claim 7 in which the predefined switch-off threshold for the current through the switch or a switch-on time duration of the switch depends not only on the dimming value to be set but on at least one further parameter, such as the voltage across the lighting means. Control circuit, for example. ASIC or preferably microcontroller, which is designed for a method according to one of the claims. Circuit for detecting the zero crossing of the current through the inductance of a buck converter, in particular a buck converter in an operating device according to one of Claims 1 to 6 comprising a diode circuit connected to the potential at a connection point of the diode of the buck converter and a switch of the buck converter which generates a preferably digital detection signal whose preferably logic level changes at a zero crossing of the current through the inductance. Switching to Claim 10 comprising a software-moderate or hardware-trained block, which prevents the level of the detection signal after a first zero crossing at further zero crossings changed. Operating device having a circuit according to one of Claims 10 or 11 and a control circuit, preferably a microcontroller, to which the detection signal is supplied. Operating device after Claim 12 , wherein a defined level change of the detection signal triggers a counter in the microcontroller. Circuit for detecting the lower reversal point of the current through the inductance of a buck converter, in particular a buck converter in an operating device according to one of Claims 1 to 6 comprising an auxiliary winding magnetically coupled to the inductance of the buck converter which generates a signal that switches a transistor producing a detection signal when the current achieved by the inductor its lower reversal point. Operating device having a circuit according to Claim 14 and a control circuit, preferably a microcontroller, to which the detection signal is supplied. Operating device after Claim 15 , wherein a defined level change of the detection signal triggers a counter in the microcontroller. Operating device for lamps, operating device according to one of Claims 1 to 6 . 12 . 13 . 15 or 16 comprising a clocked on the primary side by means of a switch converter, in particular Buck converter, comprising a control circuit which switches the switch non-conductive after a predetermined period of time ton or upon reaching a Abschaltwerts the rising switch current again, wherein the control circuit, a feedback signal is supplied, the voltage is reflected by the lighting device supplied by the operating device, the control circuit setting the time duration t on or the cut-off value as a function of the return signal. Operating device for bulbs after Claim 17 in which the time duration ton or the switch-off value at lower voltage sets above the lighting means lower than at higher voltage across the lighting means.

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