WO2011130770A1

WO2011130770A1 - Operating circuit for light-emitting diodes

Info

Publication number: WO2011130770A1
Application number: PCT/AT2011/000204
Authority: WO
Inventors: Horst Knödgen
Original assignee: Tridonic Gmbh & Co. Kg
Priority date: 2010-04-21
Filing date: 2011-04-21
Publication date: 2011-10-27
Also published as: DE112011101416A5

Abstract

The invention relates to a method for operating at least one LED by means of a switching-regulator circuit, a supply voltage being provided for at least one LED by means of a coil (L1) and a switch (S1) clocked by an open-loop/closed-loop control unit (SR), characterized in that the current through the LED is monitored by a Hall sensor as a sensor unit (SE2), said sensor unit (SE2) outputs a feedback signal, and an open-loop/closed-loop control unit (SR) controls the switch (S1) according to the feedback signal of the sensor unit (SE2).

Description

Operating circuit for LEDs

The invention relates to an operating circuit with

Light-emitting diodes according to the preamble of patent claims 1 and 4 and a method for operating light-emitting diodes according to the preamble of patent claim 13.

Technical area

Semiconductor light sources such as light emitting diodes have become increasingly interesting for lighting applications in recent years. The reason for this is, among other things, that crucial technical

Innovations and great progress both in the

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

Not least due to the comparatively long service life, LEDs have become an attractive alternative to conventional light sources such as incandescent or

Develop gas discharge lamps. -

PRIOR ART Semiconductor light sources are well known from the prior art and are abbreviated hereafter to LED (Light Emitting Diode). This term is intended in the

Following both light emitting diodes of inorganic

Materials as well as light emitting diodes from organic

Materials include. It is known that the

Light emission from LEDs correlates with the current flow through the LEDs. For brightness control, LEDs are therefore always operated in a mode in which the current flow through the LED is controlled.

In practice, to drive an arrangement

One or more LEDs, preferably switching regulator, such as step-down converter or buck

Converter). Such a switching regulator is

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

In this case, a control unit controls a high-frequency clocked switch (for example, a

Power transistor). When the switch is turned on, current flows through the LED assembly and a coil, which is charged by it. The

cached energy of the coil discharges in the off state of the switch via the LEDs

(Freewheeling phase). The current through the LED arrangement shows a zigzag time course:. at

If the switch is switched on, the LED current shows a

Rising edge, when the switch is off there is a falling edge. The time average of the LED current represents the RMS current through the LED arrangement and is a measure of the brightness of the LEDs. By appropriate timing of the circuit breaker, the average, effective current can be controlled.

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

(typically in the range above 10 kHz), as small as possible. A large fluctuation range of the current (ripple or ripple) has a disadvantageous effect particularly with LEDs, since the spectrum of the emitted light can change as the current amplitude changes.

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

vary, but to apply a so-called PWM (pulse width modulation) method. In this case, the LEDs are supplied by the operating device with low-frequency (typically with a frequency in the range of 100-1000 Hz) pulse packets with (in the time average) constant current amplitude. The current within a pulse packet is superimposed on the above-mentioned high-frequency ripple. The brightness of the LEDs can now be adjusted by the frequency of the

Pulse packets are controlled; the LEDs can

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 flexibly and versatile as possible, for example, regardless of how many LEDs are actually connected as a load and should be operated. The load may also change during operation if, for example, an LED fails.

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

operated in non-leaking mode. This method is explained in more detail with reference to FIG. 1a and FIG. 1b (prior art). In the example shown in FIG. 1a, a buck converter (buck converter) for the operation of at least one LED (or a plurality of LEDs connected in series), which has a first switch S1, is shown as the basic circuit. The operating circuit is supplied with a DC voltage or a rectified AC voltage U0.

In the on state of the first switch Sl

(During the period t_on) energy is built up in the coil LI, which discharges in the switched-off state of the first switch Sl (time t_off) via at least one LED. The resulting temporal current profile is shown in Figure lb (prior art). Two pulse sequences of the PWM are shown here. The current flow within a pulse packet is also shown enlarged. For reasons of color consistency, the amplitude of the rib should be as small as possible within a pulse packet. This can be done by a suitable choice of the switch-on time tO and

Off time tl done. So can these

For example, timings may be selected such that the first switch Sl is turned on when the current falls below a certain minimum reference value and the switch is turned off when the current exceeds a maximum reference value. However, this method has several disadvantages: First, in order to achieve the lowest possible ripple, a rapid sequence of inputs and AusHaltVorgängen is necessary. The slope

(Positive or negative edge) of the current is namely not controlled by the operating device and considered to be given, since it is determined inter alia by the inductance of the coil LI and the power consumption of the LEDs. To reduce the ripple, would have to

more switching operations within one time period

take place, which naturally involves switching losses. On the other hand, these switching losses in the continuous conduction mode are particularly high.

Although a real semiconductor switch switches very quickly, it does not switch infinitely fast. The at

Switching process dissipated energy is greater, the longer the switching process lasts and the higher the power is applied to the switch during the switching operation. In non-leaking operation, the switching losses are now

particularly high, since the switching operations take place while high currents are applied.

Presentation of the invention

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

Operating circuit for at least one LED and a

Method for operating at least one LED

to provide, which allows in a simple manner, the constancy of the current and thus the LED power.

This object is achieved by the features of the independent claims. The dependent claims further form the central idea of the invention in a particularly advantageous manner. According to a first aspect of the invention, the

Operating circuit for at least one LED a

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

Control unit clocked first switch

provides, is cached when the first switch in the coil, an energy that discharges when switched off the first switch via a diode and the at least one LED.

According ^'to the invention is provided a sensor unit which monitors the current flow through the LED and produces a sensor signal. The sensor signal is supplied to the control unit and processed there, the

Control unit, the switch according to the

Current monitoring by means of the sensor unit controls the sensor unit is a Hall sensor. The invention also relates to an operating circuit for at least one LED, which is supplied with a supply voltage, comprising at least one coil and at least one clocked by a control / regulating unit switch, wherein the operating circuit is a supply voltage for

provides at least one LED, wherein at

switched on switch in the coil an energy

is cached, which discharges when the switch is switched off via a diode, wherein a

Sensor unit is present, which monitors the current flow through the LED and generates a sensor signal depending on the current flow through the LED, and that the Se sorsignal the control / regulating unit is supplied and processed there, wherein the control unit drives the switch according to the supplied sensor signal, wherein the

Sensor unit is formed by a Hall sensor. The operating circuit preferably includes a capacitor disposed in parallel with the at least one LED and which maintains the current through the LED during the phase of demagnetization of the coil so that the current through the LEDs is smoothed.

In a preferred embodiment of the invention, the operating circuit has a further sensor unit (referred to as first) which generates a further (first) sensor signal dependent on the current flow through the first switch, and the sensor unit (referred to as second) designed as a Hall sensor, which detects the Current flow through the coil, preferably the achievement of the demagnetization of the coil detected and generates a sensor signal. The sensor signals are supplied to the control unit. and edited.

The invention also relates to a method for operating at least one LED by means of a

Switching regulator circuit, wherein a supply voltage for at least one LED is provided by means of a coil and a switch clocked by a control / regulating unit,

characterized in that the current flow through the LED is monitored by a Hall sensor as a sensor unit, this sensor unit outputs a feedback signal and a control / regulating unit switches the switch depending on the

Feedback signal of the sensor unit activates. According to the invention, the control unit changes the

Switching ratio and / or the driving frequency of the switch depending on the feedback signal of the designed as a Hall sensor sensor unit .:

Preferably, 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 to determine the on and / or off timing of the first switch.

Preferably, the control unit turns off the first switch when the current through the first switch exceeds a maximum reference value, and turns on again at the time when the current flow through the LED falls below a minimum reference value.

In a preferred embodiment of the invention, the first sensor unit is a measuring resistor (shunt).

According to the second Sehsoreinheit is a

Hall sensor.

In a further embodiment, the second recognizes

Sensor unit reaching the demagnetization of the coil, putting the voltage above the first

Switch monitored by means of a (ohmic) voltage divider. Further preferred embodiments and further developments of the invention are the subject of further subclaims. The present invention will be described below

preferred embodiments with reference to the accompanying drawings. Figure la shows a circuit arrangement according to the

known prior art

FIG. 1 b shows a diagram with the time profile of the LED current in the circuit arrangement of FIG. 1 a (prior art)

FIG. 2 a shows a first example of an operating circuit (buck) according to the invention for LEDs. FIG. 2 b shows a diagram which is time-dependent

Current curves and control signals in the in Fig. 2a

represents a circuit arrangement shown

Figure 3 and Figure 4 show special operating circuit (Buck) for LEDs

FIG. 5 shows a modification of the circuit of FIG. 2a (Buck Boost).

FIG. 6 shows a further specific embodiment of the invention

Figure la and Figure lb show the state of the art. If a secondary winding is shown in the figures as a tap on the coil LI, this secondary winding is shown symbolically instead of the Hall sensor (second sensor unit SE2), which can be coupled to the coil LI and monitor the current through the LED.

The circuit arrangement shown in FIG. 2a serves for the operation of at least one (or a plurality of LEDs connected in series and / or in parallel). In the example shown, for example, two LEDs are connected in series, it may of course be only one or more LEDs. The LED or the serially and / or parallel-connected LEDs are also referred to below as the LED track. An advantage of the present invention is that the operating circuit adapts very flexibly to the type and number of serially connected LEDs. The circuit is supplied with a DC voltage U0, which of course can also be a rectified AC voltage. The LEDs are connected in series with a coil LI and a first switch Sl.

In addition, the circuit arrangement has a diode D1 (the diode D1 is parallel to the LEDs and the coil LI

switched) and a parallel to the LEDs connected capacitor Cl. In the switched-on state of the first switch S1, current flows through the LEDs and through the coil LI, which is thereby magnetized. in the

switched off state of the first switch Sl discharges stored in the magnetic field of the coil energy in the form of a current through the diode Dl and the LEDs. In parallel with this, at the beginning of the switching on of the first switch S1, the capacitor C1 is charged. During the turn-off of the first switch Sl

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

As the first switch Sl is preferably a

Field effect transistor or bipolar transistor

used. The first switch Sl is switched to high-frequency, typically in a frequency range of about 10 kHz.

An advantage of the invention is that the first switch Sl is spared in operation, as it is preferably switched on, as explained later, when the power applied to it is almost zero. In the state of

Technology, on the other hand, where the switching operations under high

Run power, must be used for the first switch Sl a high-quality device with a very short switching time to the switching losses in one

tolerable framework.

An advantage of the circuit according to the invention is that for the first switch Sl and the diode Dl quite a comparatively cheaper device with a comparatively slightly longer switching time or longer Ausräumzeit can be used.

In the circuit of Figure 2a, a control and / or regulating unit SR is further provided, which specifies the timing of the first switch S1 for controlling the LED power. The control unit SR uses to set the exact turn-on and turn-off timing of the first one

Switches 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

Switch Sl arranged and detects the flow of current through the first switch Sl. This serves to monitor the current flow through the first switch Sl. If the current flow through the first switch Sl exceeds a certain maximum reference value, the first switch S1 is switched off. In an advantageous embodiment, the first sensor unit SEI may be, for example, a

Measuring resistor (shunt or current measuring resistor) act.

The sensor unit SE2 can also perform the function of

Sensor unit SEI take over by exceeding or reaching a maximum value for the LED current i_LED or the coil current i_L is detected and the

Control unit SR is signaled. To monitor the current flow can now the

Voltage drop at the measuring 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, the first switch Sl is turned off. The second sensor unit SE2 is arranged within the current branch, which is traversed by the current during the free-wheeling hare, preferably in the vicinity or on the coil LI. With the aid of the second sensor unit SE2, the control unit / control unit SR a

set appropriate time for the switch-on of the first switch Sl. According to the invention, the first switch Sl

preferably switched on when the current through the coil LI has fallen below a certain value or for the first time is zero (or at least very low). In the latter case, this time is

preferably in the time domain, when the diode Dl shuts off at the end of the freewheeling phase. According to the invention lies to

Switching time of the first switch Sl the lowest possible current at the switch Sl. By recognizing the

Current zero crossing through the coil LI allows almost lossless switching.

According to an advantageous embodiment of the invention, the current through the LEDs shows only slight ripple and does not vary greatly. This can be achieved by virtue of the fact that the LED current can be kept in a predetermined range due to the inventive monitoring of the LED current through a Hall sensor. Preferably, the control unit SR turns off the first switch when the current through the first switch, a

maximum reference value and turns on at the time when the current flow through the LED falls below a minimum reference value. As already explained, the Hall sensor as the second sensor unit SE2 can also serve to detect a demagnetization of the coil LI. In addition, the smoothing effect of a parallel to the LEDs connected capacitor Cl can be used.

During the phase of a low coil current, the capacitor Cl can take over the supply of the LED. The individual current courses and the optimal

Turn-on time of the first switch Sl are to be explained in more detail with reference to the diagram in Figure 2b.

Analogous to the diagram in FIG. 1b, the time profile of the current i_L is shown over two pulse packets.

The enlarged view shows the current flow

within a PWM pulse packet: The time profile of the current i_L through the coil LI, the time profile of the current i_LED by the LEDs and the time profile of the state of the first switch S1 are plotted (in state 0, the first switch S1 is off, im Level 1, the switch is closed, the signals for the state of the switch Sl correspond to the

Control signal (ie at the gate) of the switch Sl). To the

At time t_0, the first switch Sl is closed and current begins to flow through the LED and the coil LI. The current i_L shows an increase according to an exponential function, with the one of interest here

Area a quasi-linear increase of the current i_L can be seen. i_LED Differs from i_L in that part of the current i_L contributes to the charge of the capacitor Cl.

The opening of the first switch Sl at time t_l (for example, when a desired maximum

Reference value is reached) has the consequence that the stored energy in the magnetic field of the coil via the diode Dl and the LEDs or the capacitor Cl discharges. The current i_L continues to flow in the same direction, but decreases continuously and can even reach a negative value. A negative current (i.e., a reverse current flow) is present as long as the carriers previously accumulated in the conductively polarized diode Dl are removed from the barrier layer of the diode D1.

The current i_LED, on the other hand, decreases only weakly and is maintained, since the capacitor Cl has a smoothing effect. At time t_2, the diode blocks. The current i_L decreases (but is still negative) and goes to zero. In this. Phase are reloaded parasitic capacitances at the diode Dl and other parasitic capacitances in the remaining circuit. The voltages at node Ux above the first

Switch Sl and the coil LI change very quickly during this period. The voltage at the node Ux drops to a low value (due to the diode Dl blocking). An advantageous switch-on time t_3 for the first switch Sl is now given when the current i_L reaches the zero crossing, or at least the vicinity of the zero crossing. At this time, the coil LI is not or hardly magnetized.

The first switch Sl can be turned on at this time with very low losses, since hardly any current flows through the coil LI. A reconnection is also already possible at the time t_2 or shortly before, because the current through the coil LI is very low in this time range.

For detecting the advantageous switch-on time for the first switch Sl, a second sensor unit SE2 is now used. In a first embodiment, for example, the current i_L can be detected by the coil LI. However, this requires relatively complicated circuits. The current i_L through the coil LI and the LED can be detected, for example, by means of a Hall sensor. Additionally or alternatively, therefore, other / other variables can be used, which are for the detection of an advantageous

Einschaltzeitpunkts are suitable. If the capacitor Cl is not present or has only a very small capacitance, the current i_L (which flows through the coil LI) corresponds to the current i_LED through the LED, whereby current is monitored by monitoring the current i_L (which flows through the coil LI) i_LED can be monitored or recorded by the LED. In a further advantageous embodiment, for example, the magnetization state of the coil LI can be detected. The second sensor unit SE2 may be a Hall sensor, which is coupled to the coil LI or integrated in it.

The monitoring of the current flow at the coil LI

(In particular, the 'break-in' shortly after blocking the diode Dl after the time t_2) allows a statement about the advantageous reclosing time of the first switch Sl.

In a simple execution variant would be a

Range comparator, which can detect the exceeding or falling below a threshold value for the current through the LED i_LED or the coil current i_L.

Instead of or in addition to the current monitoring on the coil LI, for example, the voltage at the node Ux above the first switch Sl can be monitored. The voltage at node Ux drops significantly from a high value to a low value when the diode is turned off. The signal to turn on the first

Switch Sl can therefore be triggered below the voltage Ux below a certain threshold. The

Control unit SR turns on the first switch Sl again at the time when the coil LI

is demagnetized and / or the diode Dl blocks.

The second sensor unit SE2 can consist of a inductively coupled to the coil LI secondary winding L2 or from a voltage divider (Rl, R2) at the node Ux. The control unit SR uses the information from the first sensor unit SEI and / or the second

Sensor unit SE2 for defining the off and on

Turn-on time of the first switch Sl.

The regulation of the ^" (time-averaged) current through the LED and thus the LED power through the

Control / regulation unit SR can take place, for example, in the form of PWM signals. The frequency of the PWM signal is typically on the order of more than 100 Hz up to the MHz range.

Figure 3 and Figure 4 show specific embodiments of the invention.

FIG. 3 shows a special embodiment of the above-described switching arrangement (a Buck converter). The advantageous one

Switch-off is detected by detecting the voltage at the node Ux above the first switch Sl. This is done by the ohmic

Voltage divider Rl and R2. The node Ux is located between the coil LI, the diode Dl and the switch Sl. As a voltage divider is, for example, a

capacitive voltage divider or combined

Voltage divider consisting of resistance and capacity

is built up, possible. The measuring resistor (shunt) RS is used for current detection by the first switch Sl. The monitoring of the temporal voltage curve on

Node Ux (in particular of the 'break-in' shortly after the diode Dl is blocked near the instant t_2) makes it possible to say something about the advantageous one

Reclosing time of the first switch. Sl.

Instead of or in addition to a 'current monitoring on the coil LI, for example, the voltage at the node Ux above the first switch Sl can be monitored. The _. Voltage at node Ux drops significantly from a high value to a low value when the diode is turned off. The signal to turn on the first

Switch Sl can therefore be triggered below the voltage Ux below a certain threshold.

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

Capacitor Cl is arranged. The second switch S2 is selectively / independently controllable and may for example be a transistor (MOSFET or bipolar transistor). If the second switch S2 is closed, the

Discharge process of the capacitor Cl accelerates. Due to the accelerated discharge of the capacitor Cl is achieved that the current flow through the LED goes to zero as quickly as possible. This is desirable, for example, at the end of a PWM packet, where the current flow through the LED

should fall as quickly as possible ie the falling edge of the current flow should be as steep as possible (for reasons of color constancy). Preferably, the second switch S2 can be activated and driven at a low dimming level, where the PWM packets are very short and it is important that the current through the LED rapidly approaches zero at the end of a pulse packet. For example, an even lower dimming level can be achieved by suitable activation of the second switch S2.

Another function of this second switch S2 is that it bridges the LEDs when switched on. This is required, for example, when the LEDs are to be turned off, i. should not emit light, but the supply voltage U0 is still present. Without bridging by the second switch S2, a (smaller) current would flow across the LEDs and resistors R1 and R2, and the LEDs would (slightly) light up.

It should be noted that the arrangement of a second

Switch S2 parallel to the LEDs and the capacitor Cl for accelerated discharge of the capacitor Cl or for bridging the LED not only on the specific

Embodiment of the circuit arrangement of Figure 3 is limited, but in all embodiments of the r

Invention can be applied.

FIG. 4 shows a modification of the circuit in FIG. 3 in that current monitoring takes place on the coil LI. The current at the coil LI can be detected, for example, by means of the Hall sensor, which is coupled to the coil Sl. To detect the advantageous switch-on time for the first switch Sl, the Hall sensor is now used as

Sensor unit SE2 The monitoring of the temporal voltage curve on the coil LI (in particular of the 'break-in ¹ in the vicinity of the blocking of the diode Dl after the time t_2) makes it possible to say something about the advantageous reclosing time of the first switch S1. This monitoring can, as already mentioned, using a Hall sensor as

Sensor unit SE2 take place, which is symbolically represented as a secondary winding L2 as already explained.

As already mentioned, the determination of the time for switching the switch S1 back on may also take place by means of a threshold value monitoring (to the undershooting or exceeding of a threshold value, to monitoring by means of a Hall sensor). It should be noted that the method for detecting an advantageous switch-on time for the first switch Sl by means of Hall sensor, of course, to others

Circuit topologies can be applied, so

for example, for a so-called flyback converter or buck-boost converter or a so-called

Forward converter or forward converter.

FIG. 5 shows a modification of the circuit of FIG. 2a in that the arrangement of the coil LI, the diode D1 and the orientation of the LED path

is modified (forms a flyback converter or buck-boost converter). A development of the invention is shown in FIG. 6

shown. The recognition of the achievement of

Demagnetization of the coil LI by monitoring the Hall sensor (shown as winding L2) can be performed by a standard available control circuit IC.

This control circuit IC (Integrated Circuit), as a specific embodiment of the control unit SR shown in FIGS. 2 to 5, has one

Input for detecting the achievement of demagnetization of a sink LI by monitoring to the coil LI

coupled Hall sensor. Furthermore, the

Control circuit IC via an output for controlling a switch and via further monitoring inputs. A first of these monitoring inputs can be used for specifying a reference value, such as a reference voltage. A second monitoring input can be used to monitor the reaching of a maximum voltage or also by means of a voltage measurement on a

Resistance to monitor the achievement of a maximum current can be used. A third monitoring input can be used to monitor a further voltage or to activate and deactivate the control circuit IC or the control of the control circuit IC

controlled switch can be used.

Referring to FIG. 6, the control circuit IC monitors the current through the first switch S1 during the first time

Switch-on of the first switch Sl via the

Measuring resistor (shunt) Rs and the input 4 am

Control circuit IC. As soon as the voltage which is tapped across the measuring resistor (shunt) Rs reaches a certain maximum value, the first switch S1 is opened. The specification of opening the first switch Sl

the required level of voltage may be adjusted by providing a reference value (i.e., a reference voltage) at the input 3 of the control circuit IC.

For example, from a microcontroller a

Reference voltage are given, the height of the maximum over the measuring resistor (shunt) Rs permissible

Voltage and thus the maximum permissible by the first switch Sl current. For example, the microcontroller may output a PWM signal that is then smoothed by a filter 10 (eg, an RC element) and thus as

DC signal with a certain amplitude at the input 3 of the control circuit IC is applied. By changing the duty cycle of the PWM signal of the

Microcontroller can control the amplitude of the signal at

Input 3 of the control circuit IC can be adjusted.

The control circuit IC can via the input 5 based on the monitoring of the current at a coupled to the coil LI Hall sensor reaching the

Detecting demagnetization of the coil LI. This detection can be used as a reclosing signal. Once the demagnetization of the coil LI has been detected by the control circuit IC, the control circuit IC can turn on the first switch Sl by driving through the output 7. The control circuit IC can be activated and / or deactivated by applying a voltage at the input 1. This voltage for activating at input 1 can also change between a high and a low level, wherein at high level, the control circuit IC is activated and at low level, at least the activation of the first

Switch Sl interrupts. This control of the input 1 can be done 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 can be achieved and thus the low-frequency control of the

Operating circuit for dimming the LED. Via the input 1, a further reference voltage for the control circuit IC can also be preset via the amplitude of the signal present at this input. This voltage can, for example, the height of the maximum allowable current through the switch

affect or else the permissible duty cycle of the first switch Sl. The control circuit IC and / or the control circuit IC combined with the

Microcontrollers can together form the control unit SR.

The duty cycle of the first switch Sl can also be determined by another voltage measurement within the

Operating circuit dependent. For example, the control circuit IC can also be supplied with a voltage measurement Vsense. About this voltage measurement can over a

Voltage divider R40 / R47, for example, a monitoring or measurement of the voltage at the junction between coil LI and LED done. This voltage measurement Vsense can either be another input of the

Control circuit IC, as an additional variable additively fed to an already occupied input of the control circuit IC or an input of the microcontroller.

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

Operating device combined with a constant current through the LED. It can be specified by a microcontroller, both the frequency and the duty cycle of a PWM signal for dimming LED, in addition, the height of the maximum allowable current can be specified by the first switch Sl.

The microcontroller can control the dimming of the LED by low-frequency PWM via a signal which is fed to the input 1 of the control circuit IC.

Furthermore, the microcontroller 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 predetermined. The operating circuit may further include another

Switch S2 included, which is arranged so that this second switch S2 can bridge the LED. The second switch S2 may further be arranged so that it can take over the current through an existing high-impedance voltage measuring path or a similar existing high-resistance circuit arrangement of the LED or interrupt it.

By connecting the second switch S2 in parallel to the LED, the latter can bridge the LED and thus

deactivate. This method can be used to adjust the brightness (dimming) of the LED. A possible variant would be that the dimming via the second switch S2, while on the activation of the first

Switch Sl only the current through the LED is set and regulated. However, it can be combined to use the control of the two switches Sl and S2 for an optimized dimming control. For example, the second switch S2 can be additionally used only for dimming to a low dimming level. The operating circuit is designed due to the existing topology and the control circuit so that the output voltage of the operating circuit (ie, the voltage across the LED) is limited to a maximum allowable value. If the LED is bridged by closing the second switch S2, then the operating circuit limits the output voltage such that no excessive current can flow, which can lead to possible destruction. This activation of the second switch S2 can

For example, only be used for dimming to low dimming levels. For example, when the buck converter operates fixedly on current source operation (in the so-called hysteretic mode as described in the embodiments) and operates efficiently, the LEDs can only be dimmed with second plates S2, which should be very low impedance, and the losses are still low.

In addition, the second switch S2 can be controlled so that the current through an existing

high-impedance voltage measuring path or similar

existing high-impedance circuit arrangement can take over from the LED.

For example, if the first switch S1 is not clocked according to FIG. 6, 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, with a desired deactivation of the LED (for example, when no light is to be delivered), the second switch S2 can be closed, so that the current flow through the LED is interrupted or avoided.

The second switch S2 can at least always be triggered following a low-frequency PWM packet in order to bridge or deactivate the LED (during the last discharge edge, that is to say at the end of a PWM

Pulse packets). An interruption of the current through the LED can also be done by arranging the second switch S2 in series with the LED. The example of Fig. 6 (and the others, of course) can be extended to include several

Operating circuits according to Figure 6 are present. The control circuits IC and the control units SR of the individual operating circuits are controlled by a common microcontroller. The single ones

Operating circuits can drive, for example, LED strands of different wavelength or color. The control of the microcontroller can via a

Interface (wireless or wired) take place. This control signals for adjusting the brightness or color or status information on the

Interface are transmitted.

The coil LI may also be a transformer, which is a potential separation of the LED relative to the feeding

Supply (supply voltage) allows. For example, the LED supplying the switching regulator circuit as isolated flyback converter (flyback converter) or

Half-bridge converter with transformer be executed.

Thus, according to the invention, a method for operating at least one LED by means of a

Switching regulator circuit proposed, wherein by means of a coil LI and a clocked by a control / regulating unit SR switch Sl, a supply voltage for at least one LED is provided. The current flow through the LED is monitored by a Hall sensor as the second sensor unit SE2. This second

Sensor unit SE2 outputs a feedback signal and a control unit SR controls depending on the

Return signal of the second sensor unit SE2 to the switch Sl. Preferably, the duty cycle and / or the drive frequency of the switch Sl depends on the feedback signal of the control unit SR

Sensor unit SE2 changed.

The Hall sensor can be on a semiconductor material

based. The Hall sensor can be arranged on an integrated circuit, wherein preferably also an evaluation circuit in the integrated circuit

is arranged. The evaluation circuit may include, for example, an analog-to-digital converter, a current source and / or a digital signal processing circuit (for example a microcontroller, ASIC or DSP). The evaluation circuit with a power supply

be connected, for example, a tap can be provided on the LED path, from which a power supply for the evaluation circuit is tapped. In particular, when using the Hall sensor for current monitoring as the detection signal, the Hall voltage is evaluated. The Hall voltage is typical

proportional to the current flowing through and out of this context can be concluded on the basis of the Hall voltage on the current to be monitored. Preferably, the sensor unit SE2 (containing the Hall sensor) is coupled to the coil LI. The

Sensor unit SE2 can be integrated, for example, in the coil LI. In this way, a good coupling of the Hall sensor and thus a reliable current monitoring of the LED current (corresponding to the coil current) can be achieved.- If the Hall sensor is already integrated in the production of the coil LI in this (for example on the Bobbin or attached to a winding), this can be arranged in a defined position, whereby the distance of the Hall sensor set to the coil LI. is. This is advantageous because the distance has influence on the height of the Hall voltage. But it can also be provided that a kind

Calibration measurement is performed, the

Adjustment of the Hall sensor and by the

Control unit SR to be detected sensor signals SES2 is used.

For example, during manufacturing or

Commissioning the Betriebsschaltuhg a predetermined current in the coil LI are impressed and the resulting sensor signal SES2 be adjusted accordingly. In this case, for example, the control unit SR in a table for different current values (either by the coil LI or the LED, depending on the placement of the sensor unit SE2) assign different values of the sensor signal SES2. It can also be done a zero point adjustment. It can also be compared with the Hall sensor

Temperature fluctuations take place. It may, for example, a temperature sensor in the sensor unit SE2

be present, which is a compensation of

Temperature changes possible.

The sensor unit SE2 (which contains the Hall sensor) may also contain protection circuits, for example against overvoltage. It can be on a compensation for

Shifts at ground potential of the sensor for

Ground potential of the evaluation circuit or the

Operating circuit included.

The sensor unit SE2 can also contain a plurality of Hall sensors. By using at least two

Hall sensors can better compensate for variations due to positioning, temperature, or interference. The sensor unit SE2 may have a common-mode rejection for evaluating the at least one Hall sensor. It may additionally or alternatively in particular at

Using multiple Hall sensors a differential measurement can be applied for evaluation to influence

Reduce interference.

In a particular embodiment, the

Evaluation circuit as a sensor unit SE2 (containing the Hall sensor) data via radio or other wireless connection (such as via an air coil) to the control / SR SR transmitted. It can therefore be the supply of the sensor signals SES2 to the control / regulation unit SR via radio or another

wireless connection. It can be especially useful when using a wireless

Connection between the sensor unit SE2 (which contains the Hall sensor) a connection detection with the

Control / regulation SR done. In particular, a connection detection during commissioning or connection of the supply voltage of the operating circuit can take place. In connection detection, the connection between

Sensor unit SE2 and the control / regulation unit SR to be checked or initialized.

For example, this connection detection based on a recording of communication between the

Sensor unit SE2 and the control / regulating unit SR take place, wherein the control / regulating unit SR, for example, a

Query sends to the sensor unit SE2 and waits for a corresponding response by the sensor unit SE2. Additionally or alternatively, a test measurement can be performed by the sensor unit SE2, wherein for the purpose of a

Plausibilisierung the measurement result, the measurement result is transmitted from the sensor unit SE2 to the control / regulation unit SR.

Claims

Operating circuit for at least one LED, which is supplied with a DC voltage or rectified AC voltage and by means of a coil (LI) and a clocked by a control / regulating unit (SR) first switch (Sl) provides a supply voltage for at least one LED, wherein at

switched on the first switch Sl in the coil (LI) an energy is stored, which discharges when switched off the first switch (Sl) via a diode (Dl) and at least one LED,

wherein a sensor unit (SE2) is provided, which monitors the current flow through the LED and a

Sensor signal (SES2) generated, and that the

Sensor signals (SES2) is fed to the control unit (SR) and processed there, wherein the

Control unit (SR) the first switch (Sl) according to the current monitoring by means of

Sensor unit (SE2) controls

characterized in that the sensor unit (SE2) is a Hall sensor.

Operating circuit according to claim 1, characterized in that the sensor unit (SE2) is coupled to the coil (LI).

3. Operating circuit according to claim 2, characterized in that the sensor unit (SE2) is integrated in the coil (LI). Operating circuit for at least one LED, which is supplied with a supply voltage, comprising at least one coil (LI) and at least one by a

Control / regulating unit (SR) clocked switch (Sl), wherein the operating circuit provides a supply voltage for at least one LED, wherein when the switch (Sl) in the coil (LI) an energy is temporarily stored, which is switched off when the switch (Sl) discharges a diode (Dl),

wherein a sensor unit (SE2) is provided which monitors the current flow through the LED and generates a sensor signal (SES2) depending on the current flow through the LED, and that the sensor signal (SES2) is fed to the control unit (SR) and there

is processed, wherein the control / regulating unit (SR) the switch (Sl) according to the supplied

Sensor signal (SES2) controls

characterized in that the sensor unit (SE2) is a Hall sensor.

Operating circuit according to claim 4, characterized in that the sensor unit (SE2) is coupled to the coil (LI).

Operating circuit according to claim 5, characterized in that the sensor unit (SE2) is integrated in the coil (LI). Operating circuit according to one of the preceding

Claims, characterized in that additionally a further (first) sensor unit (SEI),

preferably a measuring resistor (shunt, RS), for monitoring the current through the clocked

Switch (Sl) is present.

Operating circuit according to one of the preceding

Claims, characterized in that the second sensor unit (SE2) reaches the reaching of

Demagnetization of the coil (LI) detects.

Operating circuit according to one of the preceding

Claims, wherein the control unit (SR) is formed by a control circuit (IC) having an input for detecting the arrival of the

Demagnetization of a coil (LI) has and a first switch (Sl) controls.

Operating circuit according to one of the preceding

Claims, comprising a microcontroller which by activating a voltage at one input of the control circuit (IC) activates and / or deactivates the latter and at another input a

Specifies reference voltage for the control circuit IC.

Operating circuit according to one of the preceding

Claims, characterized in that the

Sensor unit (SE2) via a wireless connection, in particular radio link, with, the

Control unit (SR) is connected.

12. Operating circuit according to one of the preceding

Claims, characterized in that between the sensor unit (SE2) and the control / regulating unit (SR) a connection detection is performed,

especially when commissioning or connecting the supply voltage.

13. A method of operating at least one LED

by means of a switching regulator circuit, wherein by means of a coil (LI), and by a

Control unit (SR) clocked switch (Sl) provides a supply voltage for at least one LED,

characterized in that the current flow through the LED is monitored by a Hall sensor as the sensor unit (SE2), this sensor unit (SE2)

Return signal outputs and a control / regulating unit (SR) the switch (Sl) depending on the

Feedback signal of the sensor unit (SE2) controls.

14. Method for operating at least one LED

according to claim 14, characterized in that the control / regulating unit (SR) changes the duty cycle and / or the driving frequency of the switch (Sl) depending on the feedback signal of the sensor unit (SE2).