Operating circuit for leds, having dimming signal comprising high-frequency modulated pulse packet signal with harmonised frequencies

Translation of description of equivalent WO 2013138829 A1

OPERATING CIRCUIT FOR LEDS, WITH dimming signal OFF at high frequency modulated IMPULSPAKETE- SIGNAL, WITH COORDINATED FREQUENCIES

The invention relates to an operating circuit with

Light-emitting diodes according to the preamble of claim 1 and a method according to the preamble of

Patent claim 10.

Technical field

Semiconductor light sources such as LEDs have become increasingly interesting in recent years for lighting applications. The reason for this is, inter alia, that the crucial technical

Innovation and great progress both in

Brightness as well as the light efficiency (light output per watt) of these light sources could be obtained.

Not least because of the relatively long life light-emitting diodes could become an attractive alternative to conventional light sources such as incandescent or

Gas discharge lamps develop.

The prior art semiconductor light sources are known from the prior art and are referred to as LED

(Light-emitting-diode) abbreviated. This term is hereinafter both LEDs of inorganic

Materials as well as light emitting diodes made of organic

Materials include. It is known that the

Light output of LEDs with the current flow through the LEDs correlated. To be dimming. LEDs therefore basically operated in a mode in which the current flow is controlled by the LED. In practice, for controlling an array of one or more LEDs, preferably switching regulator, for example, step-down converter (step-down or buck

Converter) is used. Such a switching regulator is

for example, known from DE 10 2006 034 371 AI.

Here one clocked at high frequency switch (a control unit controls, for example a

Power transistor) on. In the switched state of the switch current through the LED assembly and a coil that is charged thereby flows. The

between stored energy of the coil is discharged in the off state of the switch on the LEDs

. (Freewheeling phase} The current through the LED array shows a zigzag over time: at

the switch is shown by the LED current one

rising edge, when the switch is off there is a falling edge. The time average of the LED current represents the effective current is through the LED array and is a measure of the brightness of the LEDs. the mean effective current can be controlled by appropriate timing of the circuit breaker.

The function of the operating device is now to set a desired average current flow through the LEDs and the temporal variation of the current, due to the high-frequency switching on and off of the switch

{Tpyischerweise in the range above 10 kHz} to minimize. Sine large variation of the current {waviness or ripple) is particularly noticeable with LEDs disadvantageous because of change in the current amplitude may change the spectrum of the emitted light.

In order to keep the emitted light spectrum during operation as constant as possible, it is known in brightness LEDs for arrangements not the current amplitude to

vary, but a so-called PWM (pulse-width- modulation) - procedures apply. Here the stream within a pulse packet to LEDs (typically supplied by the operating unit low at a frequency in the range of 100-1000 Hz} pulse Packages (constant in time average} current amplitude. Is the top services mentioned above high frequency ripple superimposed. The brightness of the LEDs can now by the frequency of

Pulse packets are controlled; the LEDs may

for example, be dimmed by the time interval between the pulse packets is increased.

A practical requirement of the operating device is that it can be used as flexible and versatile, for example, regardless of how many LEDs are a burden actually connected and to be operated. The load also may change during operation, for example, when an LED fails.

In conventional technologies, the LEDs are in a so-called 'continuous conduction mode' or

nichtlückendem operation operated. This method is based on Figure la and Figure lb explained (prior art}. In the example shown in Figure la is a basic circuit of a step-down converter (buck converter) for operating at least one LED (or more series-connected LEDs) shown having a first switch Sl. The operation circuit is supplied with a DC voltage or a rectified alternating voltage U0.

In the switched-on state of the first switch Sl

(During the time period t_on) is built up in the coil LI energy propagating in the off state the first switch Sl (duration t_joff) discharges through at least one LED. The resulting temporal current curve is shown in Figure lb ready (prior art). Two pulse packets of the PWM are shown. The current waveform within a pulse packet is also enlarged. For the sake of color constancy, the amplitude of Rippeis should be minimal within a pulse packet. This can by a suitable choice of the power is turned ON TO and

carried Ausschaltzeitpunkts tl. Thus, this

Time points are chosen, for example so that the first switch Sl is turned on, when the current falls below a predetermined minimum reference value, and the switch is turned off when the current exceeds a maximum reference value. However, this method has several disadvantages: On the one hand, to achieve a very low ripple, a rapid succession of inputs and Auschaltvorgängen is necessary. The slope

(Positive or negative edge) of the current is in fact not the ballast controllable and to be regarded as given, as they imitate including through the inductance of the coil LI and the power con of LEDs is determined. Due to tolerances in the components of

Operating circuit and also due to the limited

Resolution of the clock units may be

Flickers or other disturbances come.

Summary of the Invention

It is the object of the present invention, improved over the prior art

Operating circuit for at least one LED and a

A method for operating at least one LED

provide, which makes it possible in a simple manner, the maintenance of a constant current and thus the LED power.

This object is achieved by the features of the independent claims. The dependent claims develop the central idea of ​​the invention in a particularly advantageous way on.

According to a first aspect of the invention, the

Operating circuit for at least one LED, a

DC or rectified AC voltage is supplied. A supply voltage for at least one LED by means of a coil and a by a

Control unit clocked first switch provides, wherein when the first switch in the coil energy is temporarily stored, which are connected via a diode and discharging the at least one LED is turned off first switch. The control unit controls the first switch with a dimming signal, the dimming signal by a

Linking a low-frequency signal and a high frequency signal is generated, and this linkage is preferably located within the control unit. The pulse width TON {* LF) and / or the period of the low frequency signal to be an integer

elected or estgelegt multiple of the period of the high frequency signal.

A change in the brightness of the LED can be done by changing the frequency of the low frequency signal. The change in frequency is done by changing the off time of the low frequency signal.

Preferably, the off period of the low frequency signal is increased when the Hellgikeit is to be reduced, and reducing the off time of the low frequency signal when the

Hellgikeit to be increased.

The controller may select the switch-off of the first switch so that the lowest possible switching losses occur while the current flow through the at least one LED lowest possible ripple on eist.

For example, the operating circuit includes a first sensor unit which generates a that is dependent from the current flow through the first switch first sensor signal, and / or a second sensor unit that the achievement

detects demagnetization of the coil and generates a second sensor signal. The second sensor unit may, for example, the voltage or the current through the detect LED and dependent thereof generate a second sensor signal. The sensor signals are fed and processed to the control unit. For example, the control unit uses a signal of the first sensor unit or a signal of the second

Sensor unit or a combination of both signals for defining the input and / or Ausschaltzeitpunkts and / or the duty cycle of the first switch.

For example, the control unit switches the first

Switch, when the current exceeds a maximum reference value by the first Sehalter and optionally switched at the time again when the current falls below the LED a minimum reference value, for example when the coil is demagnetized and / or the diode blocks. The date of iedereinschaltens can also be determined by a predetermined frequency. In a preferred embodiment of the invention the first sensor unit is a measuring resistor (shunt).

In a further embodiment of the invention the second sensor unit is inductively to the coil

coupled secondary coil or a Hall sensor or the second sensor unit detects the reaching of the

Demagnetization of the coil by monitoring the voltage is above the first switch by means of a (non-reactive) voltage divider. In a further embodiment of the invention, the operating circuit for at least one LED by a resonant or quasi-resonant circuit is formed. A Supply voltage for at least one LED is by means of providing at least a clocked by a control unit of the first switch, the first switch in the

switched-on state supplies a resonance circuit, which preferably comprises at least one coil as an inductor. In the resonant circuit, preferably in the coil energy is temporarily stored, viewed through a diode and discharges in off the first switch at least one LED. a capacitor may be connected as a smoothing capacitor between the diode and the LED which is arranged directly or indirectly parallel to the LED. The resonant circuit may also include a resonant capacitor. The coil can also be part of a transformer or it may be in addition to the coil, a transformer in the resonant circuit

be arranged. The first switch may also be part of an inverter, for example, an alternately clocked half-bridge. The invention also relates to a method for driving at least one LED.

Further preferred embodiments and developments of the invention are the subject matter of further subclaims.

The present invention is explained below with

of preferred embodiments with reference to the accompanying drawings described below. Figure la shows a circuit arrangement in accordance with the

prior art Figure lb shows a diagram with the time course of LEDstroms in the circuit arrangement of FIG North la {prior art)

2a shows a first example of an operating circuit (Buck) for LEDs

Figure 2b shows a diagram, the time-dependent

Current waveforms and control signals as shown in FIG 2a

represents circuitry shown

Figure 3 and Figure 4 show specific embodiments of an operating circuit

Figure 5 shows a modification of the circuit of Figure 2a (buck-boost)

Figure 6 shows a further special embodiment of an operating circuit

Figure 7 shows a first example of an inventive embodiment of a control unit SR

Figure 8 a shows an example of the invention

Control of an operating circuit for LEDs

Figure 8 b shows an example of control of an operating circuit for LEDs according to the prior art Figure 9 shows another embodiment of a

operating circuit

Figure la and Figure lb showing the prior art.

The circuit arrangement shown in Figure 2a is used to operate at least one (or more in series and / or parallel geschaltenen) LED. In the example shown two LEDs are connected in series, for example, there can also be only one or more LEDs. The LED or the serial and / or parallel geschaltenen LEDs are also hereinafter referred to as LED track. An advantage of the present invention is that the operating circuit flexibly adapts to the type and number of series connected LEDs. The circuit is a DC voltage UO supplied, which may be a rectified AC voltage course. Preferably, the DC voltage UO is, however, a constant DC voltage as possible, but it may have a low

AC component having a Ippel. The LEDs are connected in series with a coil LI and a first switch Sl.

In addition, the circuit arrangement includes a diode Dl {diode Dl is in parallel to the LEDs and the coil LI switched) and optionally one of the LEDs connected in parallel with capacitor Cl to. When switched on

State of the first switch Sl current flows through the LEDs, and through the coil LI, which is magnetized characterized. In the off-state of the first switch Sl is stored in the magnetic field of the coil energy is discharged in the form of a current through the diode Dl and the LEDs. In parallel, the capacitor C is charged at the beginning of turning on the first switch Sl.

During the switch-off of the first switch Sl

{Freewheeling phase) discharges the capacitor Cl and contributes to the current flow through the LED track at. With suitable dimensioning of the capacitor Cl, this results in a smoothing of the current through the LEDs.

As the first switch Sl is a preferably

Field-effect transistor or bipolar transistor used. The first switch Sl is switched at high frequency, typically in a frequency range above 10 kHz, preferably above 50kHz.

An advantage of this mode is that the first

Sl switch is spared in operation when it is carried out later, preferably then turned on when the voltage across it is nearly zero power. In the prior art, by contrast, where the switching operations at high

run performance, a high-quality component with a very short switching time must be used for the first switch Sl to the switching losses in a

keep tolerable framework.

An advantage of this mode is that for the first switch Sl and the diode Dl also very much a

comparatively cheaper component with comparatively little longer shift duration or longer Ausräumzeit can be used.

In the circuit of Figure 2a is a further

Controller SR provided the performance dictates the timing of the first switch Sl for regulating the LED.

The control unit SR used to determine the exact power-on and output timing of the first switch Sl as input signals from a first sensor unit SEI and / or signals from a second sensor unit SE2.

The first sensor unit SEI is in series with the first

arranged switches Sl and detects the current flow through the first switch Sl. This serves to monitor the

Current flow through the first switch Sl. exceeds the current flow through the first switch Sl a certain maximum reference value, the first switch Sl is turned off.

In an advantageous embodiment, it may for example be a measuring resistor (shunt or current sensing resistor) at the first sensor unit SEI.

For monitoring of the current flow is now the

Voltage drop across the sense resistor (shunt) are tapped and compared for example by means of a comparator with a reference value.

Exceeds the voltage drop at the measuring resistor

(Shunt) a certain value, so the first switch Sl is switched off.

The second sensor unit SE2 is within the

Current branch, which is flowed through by the current during the freewheeling hase, arranged, preferably near or at the coil L or in series or in parallel to the LED (for example, as a current mirror}. With the help of the second sensor unit SE2, the controller unit SR a suitable set the time for the switch-on of the first switch Sl. in a possible operating mode of the first switch Sl preferably is then turned on when the current through the coil LI is for the first time zero or at least very low, that is, preferably in the time range when the diode D blocks at the end of the freewheeling phase. In this case, the switching-on of the first

Switch S a möglichs low power to the switch Sl. By detecting the current zero through the coil LI a nearly lossless switching is enabled.

Preferably, the current through the LEDs shows only low ripple and does not fluctuate greatly. This is due to the smoothing effect of the LEDs connected in parallel with capacitor Cl. While the phase of a low coil current the capacitor Cl takes over feeding of the LED. The off-time of the switch S can also be specified by a fixed predetermined frequency. In this case, the off-time of the switch S results from the remaining time of the period of

Clock frequency of the switch Sl (hereinafter also referred to as high-frequency signal), that is, the difference of period duration and on period of the switch Sl.

The individual current waveforms and the optimal

Switch-on of the first switch Sl to be explained in more detail in Figure 2b with reference to the diagrams.

Analogously to Diagram in Figure 1b shows two pulse packets of the temporal profile of the current i__L. The enlarged view shows the current flow within a PW pulse packet: It is the temporal profile of the current i_L through the coil LI, the temporal profile of the current i__LED by the LEDs and the time course applied the condition of the first switch Sl (at 0, is the first switch Sl is turned off, in the state 1 of the switch is closed, and the signals for the state of the switch Sl corresponds to the Drive signal (ie at the gate) of the switch S). To the

Time t_0, the first switch Sl is closed and starts a current through the LED and the coil LI to flow. The current i_L shows an increase according to an exponential function, whereby the interest here

Area is to recognize a quasi-linear increase in the current i_L.

i_LED differs from i_L in that part of the current i_L for charging the capacitor Cl contributes. The opening of the first switch Sl at the time t_l {example when a desired maximum

is reached reference value) has the consequence that discharges stored in the magnetic field of the coil energy via the diode Dl and the LED's or the capacitor Cl. The current flows in the same direction i_L further, but continuously decreases and can even reach a negative value. A negative current (ie, a current flow having the reverse direction) as long as available as long as the charge carriers previously accumulated in the conductively poled diode Dl, are eliminated from the junction of the diode Dl.

The current i_LED contrast decreases only slightly and is maintained, since the capacitor Cl has a smoothing effect. At the time t_2 the diode. The current i_JL decreases {but is still negative) and is close to zero. In this phase, parasitic capacitances at the diode Dl and other parasitic capacitances are reloaded in the rest of the circuit.

The voltages at the node Ux above the first

Switch S and the coil LI change in this Period very quickly. The voltage at node Ux drops to a low value (due to the blocking of the diode Dl). An advantageous iedereinschaltzeitpunkt t_3 for the first switch Sl is now given when the current i__L the zero crossing, or at least close to the

Zero crossing achieved. At this time, the coil LI is not or hardly magnetizable.

The first switch Sl may be turned on at this time with very low losses, since hardly any current flows through the coil LI. A restart is possible but also already at the time t_2 or shortly before, because the current through the coil LI is very low in this time range. To detect the beneficial power is turned ON for the first switch Sl is now serving a second sensor unit SE2. In a first embodiment, the current i__L example, can be detected by the coil LI. This requires relatively complex circuits. The current through the coil LI i_L example, can be detected by a Hall sensor. Additionally or alternatively, therefore further / other sizes can be used which are suitable for the detection of an advantageous power is turned ON.

In a further embodiment, for example, the magnetization state of the coil LI are recorded. It may be, for example, in the second sensor unit SE2 to a secondary winding L2 of the coil LI that taps the voltage across the coil LI. The monitoring of temporal voltage profile across the coil LI (in particular the 'slump¹ shortly after disabling the diode Dl after Time t_2) makes a statement about the

vorteilhaf en reclose timing of the first

Switch Sl. In a simple embodiment, a comparator would be enough, the achievement

Demagnetization (and thus the zero-crossing) on ​​the basis of Uber- or falling below a threshold detect kan.

Instead of or in addition to voltage monitoring at the coil LI, for example, to monitor the voltage at the node Ux above the first switch Sl. The voltage at node Ux falls in blocking of the diode from a high value to a low value significantly. The signal for turning the first

Switch S can therefore be triggered when falling below the voltage Ux below a certain threshold. The SR control unit switches the first switch Sl at the time again when the coil LI is demagnetized and / or the diode Dl blocks. The second sensor unit SE2 can consist of an inductively to the coil LI

coupled secondary winding L2 or from a

Voltage divider (Rl, R2) exist at the node Ux.

but for the operation of the operating circuit and the adjustment of the current through the LED, other

Control mechanisms conceivable, so can the beipieisweise

Falls below a predetermined threshold value for the LED current to be a condition for the reconnection. It would also be a scheme only on the basis of the detected during the activation of the switch Sl current through the measurement resistor (shunt) RS possible, for example, the time of the switch Sl in this case fixed clock frequency can be changed or it may be the LED current can be regulated on the basis of the time-averaged flow. The SR control unit uses the information from the first sensor unit SEI and / or the second

Sensor unit SE2 establishing the training and

Power is turned ON the first switch Sl, thus generating a high frequency signal for direct or

indirect regulation of the LED current. It is also a power control means of the evaluation of the

Operating circuit power supplied conceivable.

The setting of the brightness can be done by setting the time-averaged LEDleistung by the controller SR, preferably in the form of low-frequency PWM signals. The frequency of the low frequency PWM

is the signal for adjusting the brightness

typically in the order of 100 - 1000 Hz.

The Fig. 8 b shows an example of the prior

Technique where a pulse packet {as shown in Fig. Lb already explained) by high-frequency pulses by the end of the pulse width of the low-frequency pulse is cut off, and at a time where a period of a

high-frequency pulses is not completed. The pulse width of the low-frequency pulse determines the width of the pulse packet. There, such a performance during both a falling and a rising edge of a high-frequency pulse occur. The example of FIG. 7 shows the inventive

Actuation of the switch Sl by the control unit SR, as it is applicable for example to the circuit of the example of FIG. 2. In Fig. 8 a are the

low-frequency signal (LF) and the high frequency signal (RF) and the resulting dimming signal (FET) shown in their exemplary time course, the exact mode of operation is explained below using the example of FIG. 7.

A possible implementation of the invention within a control unit SR is illustrated in Fig. 7. The SR control unit controls the first switch Sl with a dimming signal, the dimming signal by a

shortcut ^'a low-frequency signal and a high frequency signal is generated.

The low-frequency signal and the high frequency signal can be linked internally in the control unit and SR are output to an output of the control unit SR.

The low-frequency signal from a

PW low frequency unit (Low Frequency PWM unit) can be generated, and the high frequency signal which can be generated by a high frequency PWM unit (High Frequency PWM unit), can be linked via a coupling member. The coupling member may be formed by a logic operation. In the example of FIG. 7, the AAS low frequency signal from a

low frequency PWM unit (Low Frequency PWM unit) is generated, supplied to the D input of a D-flip-flops.

The high-frequency signal, which is generated by a high frequency PWM unit {High frequency PWM unit) is a C input of the D flip-flop supplied. The signal at the output Q of the D flip-flop resulting signal is supplied to an OR operation. Also, the low frequency signal, which is generated by a low-frequency PWM unit {Low frequency PWM unit), the OR is

Linking fed. The output of the OR

Link is supplied to an AND operation. The AND operation is also high-frequency signal (high frequency PWM unit) is generated by a hig equenten PWM unit supplied. This is the output of the AND

Linkage resulting signal is the dim signal, which is supplied to the gate driver input (gate driver input) of the control unit SR, and thus the gate of the switch Sl.

The linking of low-frequency signal and

but a high-frequency signal can also take place via a calculation of the parameters for the low-frequency signal on the basis of parameters such as the period duration (T__HF) of the high-frequency signal, for example in a digital

System.

The low-frequency signal and the high frequency signal are preferably linked internally to the dimming signal and the dimming signal at an output of the control unit

{SR) is output. The control unit (SR) preferably comprises means for combining the low-frequency signal and the high frequency signal to select or set the pulse width {TON * LF) of the low-frequency signal as an integer multiple of the period (T_HF) the high frequency signal. It would also be possible that a to the control unit (SR) external microcontroller generates the low-frequency signal by the microcontroller has a low-frequency PWM unit (Low Frequency PWM Unit). This low-frequency signal can be supplied to the control unit SR, said SR control unit, only the high requente PWM unit (High Frequency PWM unit) for generating the high-frequency signal and the coupling member to

may include linking of low-frequency signal and hig equentem signal. Such a system is explained as an example in Fig. 6.

During dimming of the LED, the frequency of the low-frequency signal can be changed. The change in the frequency of the low-frequency signal can be selected depending on the change in the pulse width TON * {LF} of the low frequency signal. The change in frequency results from an adjustment of the off period of the low frequency signal. Preferably, the length of the off period of the low frequency signal is increased to reduce the brightness or the dimming level.

The change of the frequency and the pulse width (TON * LF) of the low-frequency signal can be done such that the duty ratio of the signal at constant niederf equenten dimming level or brightness level remains constant.

Preferably, the low frequency signal is a

a low frequency pulsed, in particular PWM signal, in particular in the range of about 100 Hz to 1000 Hz, preferably in the range of 500 Hz to 1000 Hz. A to Dimming or changing the brightness required change in frequency of the low-frequency signal may be in the range of for example 100 Hz to 200 Hz.

Preferably, the high-frequency signal is a high frequency, pulsed, in particular P-M signal, for example in the range of about 50 kHz or above.

Due to the linking of the low-frequency signal with the high frequency signal it may be necessary that, for a permanent change of Frequnez; of

high-frequency signal a permanent collection and

Adjustment of the low-frequency signal must be carried out with regard to its pulse width. Due to the combination of the niederf equenten signal with the high frequency signal, it may be necessary that the pulse width of niederf equenten signal is changed only incrementally during dimming or changing the brightness, the incremental length a full period or a multiple of the full period of the high-frequency signal is. An exact graduation of the adjustment of brightness or dimming level of the can then be performed over the length of the off period of the low frequency signal.

The dimming signal, via which the brightness of the LED is adjusted is thus formed of pulse packets, preferably pulsed as a resultant,

in particular PWM signal, the pulse packets are interrupted by longer breaks. The dimming signal can be dependent on a given from the outside, for example by a user brightness setting. This brightness setting, by the supplied low-frequency signal

The low-frequency signal may be of the desired dimming level of LED depends. The low-frequency signal may also be of another integrated control circuit such as a microcontroller, which is arranged as a central controller, preset and are only looped from the control unit SR. The

low-frequency signal may also be of another

Microcontroller which is arranged as a central controller, are predefined and need not necessarily be issued or looped through from controller SR.

The high-frequency signal may be the current and / or voltage through the LED dependent. The high-frequency signal is dependent on a control loop, wherein a function of at least a predetermined set value for a current and / or voltage within the

Operating circuit and to the comparison with an actual value at least the first switch Sl is clocked by a high frequency driving. For example, the

Operating circuit operated in Hysteritischen mode, the switch S switched on depends on the achievement of threshold values ​​on and off (eg in a switch of the switch S after reaching the zero point of the current through the coil LI or below a lower limit value for the LED power on and off the switch Sl is exceeded a current through the switch Sl). According to the invention has in this Control loop no consideration to the actual brightness of the LED to be taken.

Therefore through the invention has the advantage that the control loop can be decoupled for regulating the current through the LED on the preset brightness and can still drive to the switch via a single drive signal is possible (the

Link from the RF signal of the control loop with the low-frequency signal for the brightness preferably internally of the control unit is linked SR).

The control loop for controlling the current through the LED, and thus the high-frequency signal can be also used in order occurring variations in the

to compensate DC UO. For example, the DC voltage UO have a ripple at double the mains voltage when the DC voltage UO example of a 230V AC with 50 Hz power frequency over a

Rectifier and an optional intermediate

Power factor correction circuit is fed. The DC voltage U0, for example, a 100 Hz ripple with about 10% in this case comprise amplitude compared to the amplitude of the DC component. The

Operating circuit with its control loop can be now configured such that the high frequency signal is adjusted so that it is not passed 100 Hz ripple on the LED but is mitigated. This may for example be carried out directly by a fast loop or by the disclosure of information about the current amplitude of the DC voltage U0, which depends on the current amplitude of the DC voltage U0 the frequency of the hig equenten signal can be adjusted. Such control is also called, Feed

Forward 'means control. Since the period of the high frequency signal thus synchronized to the amplitude of the DC voltage U0 Rippeis (modifies the fluctuation of the DC voltage U0}, and this is done continuously, can in determining the

Pulse width (TON * LF) of the low-frequency signal and the current amplitude of the DC voltage U0 be considered. It may also in regard to the course of the

Fluctuation of the DC voltage UE0 an adaptation of

Pulse width TON {* LF) carried out the low frequency signal depending on the current course of the DC voltage U0. It can therefore in determining the pulse width (TON * LF) of the low-frequency signal and the current amplitude of the DC voltage U0 and / or the current profile of the direct voltage U0 be considered. By the invention it is thus ensured that a pulse packet of high frequency pulses is not cut off by the end of the pulse width of the low frequency pulse, but it is adjusted the pulse width of the low pulse to the duration of the pulse packet of high-frequency pulses.

The control unit can SR by a microcontroller, FPGA, PAL, or an application-specific

integrated circuit (ASIC) are formed.

The control of the present invention is not limited to the

Topology or circuit arrangement of Fig. 3 is limited, it are as implementations in accordance with the circuits of FIGS. 1 to 6 is possible. For example, this invention in a buck converter, boost converter, inverter

{Buck-boost converter), isolated flyback converter {Flayback-), Cuttlefish converters, half-bridge converter or other topologies and circuits are applied.

The invention relates generally to drive circuits for at least one LED that Sl by means of a switching regulator via at least one clocked first switch

is provided, wherein on the frequency and / or the duty cycle of the clocked switch Sl, the current is influenced by the LED, and the frequency and / or the duty cycle of the clocked switch S is specified by a control unit SR by means of a dimming signal as the drive signal, wherein the dimming signal is generated by a combination of a low-frequency signal and a high frequency signal. The

low-frequency signal (LF) and the high-frequency signal (HF) are preferably linked via a coupling member. The control unit SR, the pulse width (TON * LF) and / or the period of the low frequency signal as an integer multiple of the period of

select high-frequency signal. The coupling member thus provides an example of means for linking the

low frequency signal (LF) and the high frequency

{Signal HF). The examples of FIG. 7 or 8 (and the others of course) can be extended to multiple operating circuits available according to the figures 7 and 8 are. The control units of the individual SR

Operating circuits of a common

Microcontrollers are driven out. However, it would also be possible the function of the central control of the individual drive circuits by a central

And the controller controlling the operation of the

Operating circuits by the control units SR to be arranged in a common micro controller. The individual operating circuits, for example, LED ~ drive strands of different wavelength or color. The control of the microcontroller can have a

Interface (wireless or wired} occur. In this case, control signals for adjusting the brightness or color, or status information about the

Interface are transmitted.

The invention thus also provides a method for driving at least one LED, wherein the controller controls the switch Sl SR with a dimming signal, and wherein the dimming signal is generated by a combination of a low-frequency signal and a high frequency signal. The pulse width (TON * LF) and / or the period of the low-frequency signal is in this case as an integral multiple of the period of

high-frequency signal selected.

In a further embodiment, the

Operating circuit are formed for at least one LED by a resonant or quasi-resonant circuit (F g. 9) · A power supply voltage for at least one LED is provides by means of at least one clocked by a control unit first switch Sl, the first switch Sl in total switched off a

The resonant circuit input, the preferably at least one coil LI has as an inductor. In the resonant circuit, preferably in the coil LI is an energy

buffered, viewed through a diode Dl and the discharges in off the first switch Sl at least one LED. may also be a capacitor C as a smoothing capacitor between the diode D and the LED

be connected, which is arranged directly or indirectly parallel to the LED. The resonant circuit may also include a

Resonance capacitor Cr have. The coil LI may also be part of a transformer or it may be in addition to the coil, a transformer {28, 29) in the

be arranged resonant circuit. The first switch Sl may also be part of an inverter, for example, an alternately clocked half-bridge with the two

Switches Sl and S3. In the example of FIG. 9 is an example of a so-called LLC converter

(Serienresonanter insulated LLC -Halbbrückenwandler) shown. The half-bridge with alternating

clocked switches Sl and S3 can be controlled according to the invention with the dimming signal, the two switches Sl and S3 respectively with 50% duty cycle at high frequency during the pulse width (TON * LF) of be down requenten signal activated. The frequency of the high frequency signal may result from a rule grinding or the set value for the operating circuit, for example, dependent on the current through the first sensor unit, which is preferably the current through the LED, by one of the two switches Sl or S3 or in the resonant circuit preferably through the coil LI, captured. The pulse width (TON * LF) and / or the period of low-frequency signal is selected ■ as an integral multiple of the period {T_HF) the high frequency signal. The operating circuit may also filter or smoothing members comprise at the output, for example, an inductor 33. The transformer can

secondary side at its secondary winding 29 also have a plurality of taps, and it can thus also

Diode like the diode Dlb be arranged to allow a higher utilization of the transmitted energy.

Figure 3 and Figure 4 show special More

Embodiments of the invention.

3 shows a specific embodiment of the switch arrangement (a buck converter or buck converter} described above is shown.

The advantageous off time is in this case detected by means of detecting the voltage at node Ux above the first switch Sl. This is done by the resistive voltage divider Rl and R2. The node Ux is between the coil LI, the diode Dl and the switch

When voltage divider, for example, is also a

capacitive voltage divider or combined

Voltage divider comprising resistance and capacitance

is constructed possible. The measuring resistor (shunt) RS is used for current detection by the first switch Sl. The monitoring of temporal voltage profile at

Node UEX (especially the 'slump' shortly after disabling the diode D in the vicinity of the time t_2) makes a statement about the beneficial iedereinschaltzeitpunkt the first switch Sl. Instead of or in addition to monitoring a voltage across the coil LI, for example, the voltage at node Ux above the first switch Sl can be monitored. The voltage at node Ux falls in blocking of the diode from a high value to a low value significantly. The signal for turning the first

Switch S can therefore be triggered when falling below the voltage Ux below a certain threshold.

In circuit arrangement of Figure 3, a second switch S2 is also parallel to the LEDs and the

Capacitor Cl is arranged .. The second switch S2 selectively / independently controlled and can, for example, a transistor (MOSFET or bipolar transistor) be.

If the second switch S2 is closed, then the

Discharging the capacitor Cl accelerated. The accelerated discharge of the capacitor Cl is achieved that the Strotnfluss quickly goes through the LED to zero. This is, for example, at the end of a PWM packet desirable where the current flow through the LED

to drop out as soon as possible that the falling edge of the current profile should be as steep as possible (for reasons of color constancy). Preferably, the second switch S2 can be activated and driven at low dimming levels, where the PWM packets are very short and it is important that the current rapidly passes through the LED at the end of a pulse packet to zero. For example, can be achieved by suitable control of the second switch S2 an even lower dimming level. Another function of this second switch S2 is that it in the switched-

State the LEDs bridged. This is, for example, required when the LEDs are to be turned off, that no light will emit, but the

Supply voltage U0 is applied yet. Without the bypass through the second switch S2 would be a (although smaller} power over the LEDs and resistors Rl and R2 flow and the LEDs (geringf gig) lights.

It should be noted that the arrangement of a second

Switch S2 parallel to the LEDs and the capacitor Cl for the accelerated discharge of the capacitor Cl and to bridge the LED not only to the particular

Embodiment of the circuit is limited by Figure 3, but in different

Embodiments of the invention as an additional

Improvement can be applied.

Figure 4 shows a modification of the circuit in Figure 3 in that the voltage monitoring is performed to the coil LI. The voltage at the coil can Sl

for example by means of a secondary winding L2, which is coupled to the coil Sl, (or an additional coil L2, the inductively coupled to the coil LI) can be detected. To detect the beneficial power is turned ON for the first switch Sl is now a secondary winding L2. Monitoring the temporal voltage erlaufs to the coil LI (in particular of the 'dip' in the vicinity of the locking of the diode Dl to the time t_2) allows a statement about the advantageous

Reclose timing of the first switch Sl. This monitoring can be carried out as already mentioned with reference to a secondary winding L2. The determination of the timing of the zero crossing or the demagnetization can as already mentioned be carried out also by means of a threshold value monitoring (on the lower or exceeding a threshold value, wherein a monitoring means of a secondary winding L2, the polarity of the voltage from the winding sense of the secondary winding L2 to the coil depends LI from).

It should be noted that the method for detecting an advantageous power is turned ON for the first switch Sl can be naturally applied to other circuit topologies, such as a so-called flyback or buck-boost converter or a

so-called forward converter or Forward Converter.

Figure 5 shows a modification of the circuit of Figure 2a in that the arrangement of the throttle LI, the diode D and the orientation of the LED track-modified is (forms flyback or buck-boost converter).

A possible further development of an operating circuit for LED is shown in Fig. 6. The detection of the

Reaching the degaussing coil LI based monitoring of the voltage across winding L2 can be performed by a standard available control circuit IC. This control circuit IC

(Integrated circuit), corresponds to the control unit and contains the SR of FIG. 2 to 5, has an input for detecting the reaching of

applied demagnetization of a coil based monitoring of voltage on one of the spool

Secondary winding. Further features of the control circuit IC via an output for driving a switch and further monitoring inputs.

A first of these control inputs can be used for

Presetting a reference value such as. A

Reference voltage are used.

A second control input can be used for monitoring the attainment of a maximum voltage or a voltage measurement based on a resistor for monitoring the reaching of a maximum current. A third monitoring input can be used for the monitoring of a further voltage or also to activate and

Deactivation of the control circuit IC or the

Controlling the controlled control circuit IC

Switch can be used.

According to FIG. 6, the control circuit IC monitors the current through the first switch Sl during the

Switch the first switch Sl through the

Precision resistor (shunt) Rs and the input 4 am

Control circuit IC. As soon as the voltage across the measuring resistor (shunt) Rs is tapped, a

reaches certain maximum value, the first switch Sl is opened. The specification of the opening of the first

Switch Sl necessary amount of tension can by setting a reference value (ie a

Reference voltage) to be adjusted at the input 3 of the control circuit IC. For example, from a

Microcontroller a reference voltage to be given, specifies the height of the maximum across the measuring resistor (shunt) Rs permissible voltage and thus the maximum admissible through the first switch Sl current. For example, the microcontroller may output a PWM control signal that is then smoothed by a filter 10 (for example an RC circuit) and therefore is present as a direct voltage signal having a specific amplitude at the input 3 of the control circuit IC. By changing the duty cycle of the PWM control signal of the microcontroller, the amplitude of the signal can at

Input 3 of the control circuit IC to be adjusted.

The control circuit IC can via the input 5 by monitoring the voltage on a load applied to the coil LI secondary coil L2 to achieve the

detect demagnetization of the coil LI. This detection can be used as a reclosing signal.

Once the demagnetization of the coil LI through the

Control circuit IC has been detected, the

Control circuit IC the first switch Sl through control via the output 7 on.

The control circuit IC can be activated by applying a voltage at the input 1 and / or disabled. This voltage for activating at input 1 may also switch between a high and a low level, being activated at high level, the control circuit IC and at low level at least the driving of the first

Switch S interrupts. This activation of input 1 can be carried out by a microcontroller. For example, in this way, a low-frequency activation and deactivation of the control circuit IC, and thus the

Control of the first switch Sl be achieved and thus the low control

Operating circuit for dimming the LED.

About the input 1 can be given via the amplitude of the signal present at this input signal continues to a further reference voltage for the control circuit IC. This voltage can, for example, the height of the maximum allowable current through the switch

influence or even the permissible Exnschaltdauer the first switch Sl. The control circuit IC, and / or the control circuit IC combined with the

Microcontrollers may jointly form the controller SR. According to the invention, the PWM signal, which corresponds to the

Input 1 of the control circuit IC is supplied, according to the invention via a coupling element, for setting by an ohmic resistance, with the drive signal, which is output at the output 7, linked.

Optional signal PWM can also be linked to the signal of the output 7 and will not be applied to the input. 1

The duty cycle of the first switch Sl can also by a further voltage measurement within the

Operating circuit depend.

For example, the control circuit IC and a voltage measurement Vsense are fed.

About this voltage measurement can have a

Voltage divider R40 / R47, for example, a monitoring or measurement of the voltage at the node between coil LI and LED done. This Spannungsme ung V.sub.sense may be either a further input of the

Control circuit IC, are fed as additional size additively an already busy input of the control circuit IC, and also an input of the microcontroller.

Thus, a system can be constructed in which the one simple control for Bimmen of LED is made possible by low PWM, on the other hand a low-loss high-frequency operation of the possible

Operating device combined with a very constant current through the LED.

It can be determined by a micro controller, both the frequency and the duty cycle of a PWM Singales for dimming LED, may in addition also the height of the maximum allowable current through the first switch Sl can be specified. The microcontroller can be a signal which is fed to the input 1 of the control circuit IC, control the dimming of the LED by low-frequency PWM. Furthermore, the micro controller via a signal which is fed to the input 3 of the control circuit IC, the height of the maximum allowable current through the first switch Sl or the necessary duty cycle of the first switch Sl can be specified.

The operating circuit may further comprise a further

contain switch S2, which is arranged such that this second switch S2 can bridge the LED.

The second switch S2 may be further arranged so as the current through an existing high-impedance Voltage measurement path or a similar existing high-impedance circuitry can take over from the LED or interrupt this. By parallel connection of the second switch S2 to the LED that can bridge the LED, and thus

disable. This method can be used to adjust the brightness (dimming) can be used the LED. A possible alternative option would be that the dimming via the second switch S2 is carried out, while on the actuation of the first switch Sl only the current is set and regulated by the LED.

However, the activation of the two switches Sl and S2 combined for optimized Dimmansteuerung be used. Thus, the second switch S2, for example, be used in addition for the dimming to low dimming level. The operating circuit is designed based on the existing topology, and the control circuit, that the output {that is, the voltage across the LED} is limited to a maximum allowable voltage of the circuit operation. If bridged by closing the second switch S2, the LED, then limits the operating circuit, the output voltage such that no excessive current to flow, which can lead to possible destruction.

This actuation of the second switch S2 can

example, be used only for the dimming to low dimming level.

If the depth etzsteller (Buck Converter) fix on

Current source operation (the so-called Hysteritischen mode as described in the Ausführungsfoeispielen) operates efficiently and is running, the LED can in certain

Brightness ranges or modes of operation are also only with the second switch S2, which should be very low, dimmed, and the losses are still low.

In addition, the second switch S2 can be driven so that they present the current through a

high-impedance voltage measurement path or a similar

existing high-impedance circuitry can take over from the LED.

For example, according to FIG. 6, the first switch Sl is not clocked, no current should flow through the LED. Due to the existing voltage divider R40 / R47, however, a small current can flow through the LED. In this case, at a desired deactivation of the LED (for example, when no light is to be dispensed), the second switch S2 are closed so that the current flow is interrupted or prevented by the LED.

The second switch S2 can at least be always driven further to a low P M package to bypass or disable the LED (during the last Entladeflanke, ie at the end of a PWM

Pulse packet).

An interruption of the current through the LED can be done in series with the LED even by arrangement of the second switch S2. The example of FIG. 6 (and the others of course) can be extended to several

Operating circuits exist as shown in FIG. 6 The IC control circuits or the control units of the individual operating SR circuits are controlled by a common micro controller. The single ones

Operating circuits can be controlled, for example, LED strands of different wavelength or color. The control of the microcontroller can have a

Interface (wireless or wired} occur. In this case, control signals for adjusting the brightness or color, or status information about the

Interface are transmitted.