DE102009017139A1 - LED e.g. organic LED, regulating method for illumination system, involves utilizing measured actual value as feedback variable for regulation of LED, where actual value is compared with reference value - Google Patents

Abstract

The method involves interconnecting an LED e.g. organic LED, in an output circuit, and magnetizing an inductor (L1) if a switch (S1) is clocked actively. A measured actual value representative for average value of LED current is utilized as a feedback variable for regulation of the LED, where the actual value is compared with a reference value. The actively clocked switch is switched on at one time if the indirectly or directly detected current is degraded to zero. A pulse-width repetition rate of the switch is changed as a control variable over the time of switching off of the switch. Independent claims are also included for the following: (1) a circuit for regulation of power of an LED (2) an illumination system.

Description

The The present invention relates to a circuit arrangement for operating of light emitting diodes (LED), in particular of inorganic light emitting diodes or organic light-emitting diodes, which in electronic ballasts for corresponding LEDs is used.

The The invention also relates to a lighting system.

at In the prior art, the switch-off time of the switch determined by the fact that the LED current is a fixed Abschaltschwellenwert reached. This leads to inaccuracies, since the negative current flow range directly after switching on the switch may vary, causing the power control makes inaccurate.

The The object of the invention is now, the power control of an LED in a converter such as a buck converter or buck boost To make the converter more accurate.

These Task is solved by the characteristics of the independent Claims. Make the dependent claims the central idea of the invention in particularly advantageous Continue.

One The first aspect of the invention relates to a method of regulation, in particular for power control of an LED in a converter with a switch.

Of the Converter is powered by an active switch and passive Energy storage elements formed with, for example, an inductance. For example, such a converter may be a Buck Converter, Buck Boost Act converter or flyback converter.

The LED is connected in the output circuit. An inductance is magnetized when the switch is actively clocked and over the closed switch and the inductance a current flow takes place. As feedback variable for the control will be a for the mean value of the LED current representative measured actual value used, which is compared with a reference value as a setpoint.

Depending on a difference between the actual value and the desired value, the duty cycle of the current Switching of the active clocked switch and / or a following power-up can be set.

there can the duty cycle of the active clocked switch only every n-th switch-on changed become, with n larger or equal to 2.

The duty cycle the active clocked switch can, for example, on the time of off the active clocked switch can be changed as a control variable.

The duty cycle can be measured by adaptive specification of a switch-off level of a measured for the LED power representative sizes be set, wherein upon reaching the switch-off of the active clocked switch is turned off.

When control variable The power control may alternatively or in addition to the timing of the active clocked switch the level of the DC bus voltage supplying the converter uses become.

The Bus voltage can be generated by means of an active PFC circuit, wherein the level of the generated bus voltage by change the timing of a switch of the PFC circuit is executed.

When for the Mean value of the LED current more representative measured actual value can be a sample of the LED current, preferably measured at half the Einschatzeitdauer the active clocked switch.

Of the for the Mean value of the LED current representative Actual value can be determined by a continuous measurement of the LED current (or a for that representative Size) be determined.

Of the continuously measured LED current can be compared with a reference value be and for the mean representative Actual value can be the duty cycle of the comparative value the turn-on period of the active switch.

The duty cycle can be determined using a bidirectional digital counter.

Of the Reference value may be from a predetermined dimming value and / or the measured LED voltage depend.

The The invention also relates to an integrated circuit, in particular ASIC to carry out a method as set forth above is.

Farther The invention relates to an operating device for an LED, comprising a such integrated circuit.

Also according to the invention a circuit for power control of an LED provided, which has a Converter having a switch, wherein the LED in the output circuit is interconnectable. A control unit activates the switch, causing the switch takes over the current flow and the inductance magnetized, causing the LED with a high-frequency voltage is supplied. The control unit becomes representative of the mean value of the LED current measured actual value, the is compared with a reference value.

The Control unit may be dependent from a difference between the actual value and the setpoint, the duty cycle of current switch-on of the active clocked switch and / or of a subsequent switch-on process.

The Control unit can change the duty cycle of the active clocked switch only every n-th switch-on change, where n is greater or equal to 2.

The Control unit can change the duty cycle of the active clocked switch over Change the time of switching off the active clocked switch as a control variable.

The Control unit can through the duty cycle adaptive specification of a switch-off level of a measured for the LED current set representative sizes, wherein the control unit on reaching the switch-off level of the actively clocked Switch off.

The Control unit can in addition to the regulation of the operation of the LED as well to drive a DC link circuit and the DC link circuit feedback signals obtained, the DC link voltage supplying the converter DC bus voltage generated.

The Control unit can be used as a control variable the power control alternatively or in addition to the timing of the active clocked switch the level of the DC bus voltage supplying the converter use.

to Generating the bus voltage can be provided an active PFC circuit, wherein the control unit the level of the generated bus voltage by changing the timing of a switch performs the PFC circuit.

Of the Control unit can act as one for the mean value of the LED current representative measured actual value is a sample of the LED current, preferably measured at half the Einschatzeitdauer the active clocked switch, be returned.

The Control unit can be used to determine the average for the LED current representative actual value continuously measure the LED current (or a representative size).

The Control circuit may include a comparator, which is the continuous measured LED current compared to a reference value and the control circuit as for the mean representative Actual value is the duty cycle the output signal of the comparator used.

The Output signal of the comparator can be a bidirectional digital counter supplied to the control circuit be.

The Control circuit may be the reference value depending on an external or internally specified dimming value and / or the measured and the control circuit supplied Set LED voltage.

The The present invention will be described below with reference to preferred embodiments with reference to the attached Drawing closer described.

1 shows an inventive operating device for connected in a buck converter LED,

2 shows in detail a circuit according to the invention for an LED connected in a buck-boost converter and the measurement signals which can be tapped off therefrom,

3 shows the course of drive signals from a switch of the half-bridge as well as the mid-point voltage U _L3 and the LED current I _LED ,

4 shows the structure of a regulation of the LED current,

5 shows the time course of signals of the control of 4 .

1 shows an electronic ballast for operating LED.

1 shows a converter for operating at least one LED and a power factor correction circuit, wherein both circuits are controlled by a control unit IC.

On the input side the electronic ballast does not supply a mains voltage illustrated rectifier - on, to which the active power factor correction circuit adjoins, which acts as a boost converter.

The PFC circuit essentially has a coil L6 which magnetizes becomes when the switch (transistor) S6 to a drive command S6D is predetermined by the integrated circuit IC is closed.

If the switch S6 is opened becomes, discharges the energy of the magnetized coil L6 via a diode D9 to the storage capacitor C6, so that on the capacitor C6 a high DC voltage Uout (bus voltage Uout) sets a triangular ripple having the frequency of the timing of the switch S6.

At the pin ST2 can open when Switch S6 on the one hand measured the bus voltage Uout at this pin On the other hand, the time of demagnetization can also be the coil L6 can be detected.

On the output side, this includes in 1 shown electronic ballast a converter with a switch S1 and an inductance L1. A description of the other elements will be given below.

Of the Converter has another switch S1 and is a buck converter executed. The current through the switch S1 can by means of a measuring resistor (Shunt) R1 are supplied to the control circuit IC at a pin CS. At the pin S1D, a control signal for the switch S1 through the Control circuit IC output.

at closed switch S1 flows the current through the light-emitting diodes (LED) and an inductance L1 and increases substantially linearly with the magnetization of the inductance L1. When switch S1 is turned off, the energy of inductor L1 builds up a current flow in turn through the LEDs and the freewheeling diode D1 essentially linearly until the switch S1 finally returns is turned on. By means of the voltage divider R5, R6 can a measuring point and pin A2 the time can be determined by the magnetization of the inductance L1 is substantially degraded and thus the current through the freewheeling path (diode D1, LED track, L1) is no longer driven.

The Restarting the active clocked switch S1 can by monitoring of the inductance L1 flowing Branch current iL1 be set. For example, can be monitored be whether the current flowing through the inductor L1 branch current iL1 again has fallen to zero or whether the inductance L1 is demagnetized. This can by means of a secondary winding at the inductance L1 or by means of a monitoring the voltage over take the switch S1. It can also be a reconnect due to the expiration of a certain period of time of a direct Current measurement done in the path of the LED.

The Control IC controls the converter and can continue the Perform PFC control.

• – die Eingangsspannung über einen Abgriff ST1,
• – der Strom durch die Induktivität L6 mittels eines Spannungsteilers ST2 (oder eine Überwachung der Spannung über der Induktivität L6), und
• – die Busspannung Uout über den Spannungsteiler ST2.

The control unit can be returned feedback signals from the range of PFC DC link voltage, such as:

• The input voltage via a tap ST1,
• - The current through the inductor L6 by means of a voltage divider ST2 (or monitoring the voltage across the inductance L6), and
• - The bus voltage Uout via the voltage divider ST2.

The Control unit can adjust the level of output voltage through clocking of the switch S6 and preferably by means of the returned bus voltage digitally regulated.

• – die LED-Spannung V_LED mittels eines Spannungsteilers A2,
• – den LED-Strom I_LED mittels des Shunts R1 (nur während des Einschaltens des aktiv getakteten Schalters S1), und
• – die Spannung über dem Schalter S1 mittels eines Abgriffs A2 (induktiv oder durch Abgriff über dem dem Schalter S1).

The control unit feedback signals from the area of the load circuit containing the LED can be returned to the converter:

• The LED voltage V _LED by means of a voltage divider A2,
• - The LED current I _LED by means of the shunt R1 (only during the switching of the active clocked switch S1), and
• - The voltage across the switch S1 by means of a tap A2 (inductive or tapping over the switch S1).

Preferably is parallel to the LED, a capacitor C1 as a filter or smoothing capacitor in parallel connected. This can smooth the LED voltage during operation and while demagnetization of inductor L1 maintains the LED voltage receive. In this case, the determined via the shunt R1 Electricity not exactly the current flowing through the LED, but also contains one over the current flowing through the capacitor C1. Also this total current can for the power control according to the invention be used, as the current through the shunt R1 again a measure of the current Performance in the output circle represents, if it is assumed that the bus voltage Uout is constant (eg due to the regulation of the PFC) or due to a measurement. Also this total current is therefore referred to below as the LED current.

Between the switch S1 and the negative pole of the DC voltage source is a low-impedance shunt R1 interposed, but only for Measurement of currents serves and on the voltages in the circuit has no measurable influence.

2 shows a converter for operating at least one LED, which circuit is controlled by a control unit IC. The converter may be preceded by a circuit for power factor correction.

Of the Converter has a further switch S1 and is as a buck-boost converter executed. Of the Current through the switch S1 can be detected by means of a measuring resistor (shunt) R1 are supplied to the control circuit IC at a pin CS. At the pin SR becomes a control signal for the switch S1 is output by the control circuit IC.

at closed switch S1 flows the current through an inductance L1 and increases substantially linearly with the magnetization of inductance L1 on. The LED will be during this phase fed by the capacitor C1. When switched off Switch S1, the energy of the inductor L1 is built by a current flow through the LEDs and the freewheeling diode D1 substantially linear, until the switch S1 finally is switched on again. By means of the secondary winding L2 on the inductance L1 can at a measuring point and pin A2 the time to be determined, in the magnetization of the inductance L1 is substantially degraded and thus the current through the freewheeling path (diode D1, LED track, inductance L1) is no longer driven.

The Restarting the active clocked switch S1 can by monitoring of the inductance L1 flowing Branch current iL1 be set. For example, can be monitored be whether the current flowing through the inductor L1 branch current iL1 again has fallen to zero or whether the inductance L1 is demagnetized. This can by means of a secondary winding at the inductance L1 or by means of a monitoring the voltage over take the switch S1. It can also be a reconnect due to the expiration of a certain period of time of a direct Current measurement done in the path of the LED.

The Control IC controls the converter and can continue the Perform PFC control.

• – die LED-Spannung V_LED mittels eines nicht dargestellten, parallel zur LED angeordneten Spannungsteilers,
• – den LED-Strom I_LED mittels des Shunts R1 (nur während des Einschaltens des aktiv getakteten Schalters S1), und
• – die Spannung über dem Schalter S1 mittels eines Abgriffs A2 (induktiv oder durch Abgriff über dem dem Schalter S1)

The control unit feedback signals from the area of the load circuit containing the LED can be returned to the converter:

• The LED voltage V _LED by means of a voltage divider, not shown, arranged parallel to the LED,
• - The LED current I _LED by means of the shunt R1 (only during the switching of the active clocked switch S1), and
• The voltage across the switch S1 by means of a tap A2 (inductive or by tapping over the switch S1)

Preferably is parallel to the LED, a capacitor C1 as a filter or smoothing capacitor in parallel connected. This can smooth the LED voltage during operation and while the magnetization or even during the demagnetization of inductance L1 maintain the LED voltage.

Between the switch S1 and the negative pole of the DC voltage source is a low-impedance shunt R1 interposed, but only for Measurement of currents serves and on the voltages in the circuit has no measurable influence.

In 3 Signal curves are shown during the switching on and off of the switch S1. As can be seen, the switch S1 is actively clocked and switched on between the times T ₃₁ and T ₃₂ (time duration t _ON ). As can be seen, the linearly increasing LED current I _LED can only be detected during the time period t _ON at the shunt R1, during which the switch S1 is switched on. On the other hand, in the period of turning off the switch S1 in which the inductor L1 continues to sink the current through the LED to the lower reversal point, the LED current through the shunt R1 can not be detected.

Of the Switch-on time of the high-frequency clocked switch S1 can by monitoring the through the inductance L1 flowing Branch current iL1 be set. For example, can be monitored be whether by the inductance. L1 flowing branch current iL1 again has fallen to zero or whether the inductance L1 is demagnetized. This can by means of a secondary winding at the inductance L2 or by means of a monitoring the voltage over the switch S1. respectively.

at In the prior art, the turn-off time of the high-frequency clocked switch S1 thereby set when the LED power a specified threshold Ipeak reached. It remains - as already explained at the beginning - any fluctuations of the maximum negative current level ΔI at the reversing point T31 and disregarded, what makes this type of power regulation inaccurate.

According to the invention, the switch-off time of the actively-timed switch (in the example of FIG 2 Switch S1) designed adaptive, so that as a result, the turn-on time t _{ON is} variable. This can be achieved, for example, by adapting the switch-off threshold for the LED current and / or adaptively adjusting the switch-on time duration of the actively-clocked switch.

The Adaptation takes place on the basis of a feedback signal, which is the mean value of the LED current (averaging over one or more switch-on durations of the active clocked switch) representative is. By controlling to the average of the LED current, the lamp power control is essential more accurate.

The mean value of the LED current can be detected by a sample is detected and evaluated at the time t _on / 2, ie half of the _ON time t _{ON of} the active clocked switch. If this is higher than the desired average value, the switch-on time period or the switch-off current threshold can be reduced, namely in the current order in a subsequent switch-on of the active clocked switch.

in the However, an embodiment will be explained below, in which the LED current is continuously detected and sent to the control unit is returned.

As in 4 shown in the control unit of the LED current I _LED is compared by a comparator K1 with a reference value I _{avg_soll} . This reference value I _{avg_soll} thus provides the desired mean value for the LED current and may, for example, depend on an external or internal dimming value specification and / or the magnitude of the LED voltage. This reference value I _{avg_soll} is a measure of the nominal power.

In order to achieve a constant lamp power, when the LED voltage V _LED fluctuates, the setpoint value for the mean value of the LED current must be inversely adjusted, so that the resulting product of LED current and LED voltage remains constantly regulated. Of course, with a constant LED voltage, a medium current control corresponds exactly to a lamp power control.

In this embodiment, the purpose of the control is that the duty cycle of the output of the comparator K1 during a turn-on period t _{ON of} the active clocked switch is 50%. In the embodiment, for this purpose, the output signal of the comparator is supplied to a digital up / down counter COUNTER, which is clocked by a timer of the control unit (clock signal CNT_CLK). As in 5 it can be seen that the counter COUNTER counts in one direction, as long as the LED current I _{LED is} below the reference value I _{avg_soll} , and in the opposite direction, as soon as the LED current I _LED exceeds the reference value I _{avg_soll} . If the actual value of the mean value of the LED current I _LED exactly corresponds to the reference value _{specification} I _{avg_soll} , the duty cycle of the comparison signal supplied to the counter COUNTER will be 50% and thus at the end of a switch-on period the counter reading will exactly correspond to its initial level.

• – Busspannung,
• – adaptive Abschaltschwelle Ipeak, und/oder
• – adaptive Einschaltzeitdauer Ton.

Any deviation, however, will lead to a deviation ERROR of the counter end of its initial state. This deviation signal ERROR is fed to a preferably digital regulator REGULATOR, which is also clocked by a timer of the control unit by a signal reg_clk. The REGULATOR controller implements a control strategy (eg PI controller) and controls a manipulated variable that influences the power of the LED depending on the input signal ERROR and the control strategy. This manipulated variable may, for example, be one or more of:

• - bus voltage,
• Adaptive switch-off threshold Ipeak, and / or
• - adaptive switch-on time tone.

The Manipulated variable (n) can in the current power up, in any subsequent power up or be changed in every nth turn-on, where n is a greater or greater integer is equal to 2.

In the example of 4 and 5 Either the on-time Ton is changed, or the regulator REGULATOR changes the reference value of another comparator K2 of the control unit, at whose non-inverted input the LED current I _LED is present.

The Output signal of the further comparator K2 controls the switching off gate_off of the switch.

at the converter for the LED can be, for example, a boost converter or a flyback converter.

Claims (33)

Method for controlling an LED by means of a converter with a switch, wherein the LED in the output circuit is interconnected and an inductance (L1) is magnetized when the switch (S1) is actively clocked, wherein as the feedback variable for the control on for the mean value of LED current (I _LED ) representative measured actual value, which is compared with a reference value (I _{AVG_SOLL} ). The method of claim 1, wherein the active clocked Switch (S1) is turned on at a time when the indirect or directly detected current has decayed to zero, preferably has reached its lower reversal point. The method of claim 1 or 2, wherein depending on a difference between the actual value and the desired value, the duty cycle of the current Switching of the active clocked switch and / or a subsequent switch-on is set. Method according to claim 3, wherein the duty cycle of the active clocked switch only every n-th switch-on changed becomes, with n larger or equal to 2. Method according to one of the preceding claims, in the duty cycle of the active clocked switch over the time of switching off the active clocked switch as Control variable is changed. Method according to one of the preceding claims, in the duty cycle by adaptive default a turn-off level of a measured representative of the LED current sizes is set, wherein when reaching the switch-off of the active clocked switch is turned off. Method according to one of the preceding claims, in as a control variable the power control alternatively or in addition to the timing of the active clocked switch the level of the DC bus voltage supplying the converter is used. Method according to Claim 7, in which the bus voltage by means of an active PFC circuit is generated, wherein the level of the generated bus voltage by changing the timing of a switch of the PFC circuit is executed. Method according to one of the preceding claims, in as one for the mean value of the LED current representative measured actual value a sample of the LED current, preferably measured at half of the Einschatzeitdauer the active clocked switch, is used. Method according to one of claims 1 to 7, wherein the for the mean of the LED power representative Actual value determined by a continuous measurement of the LED current becomes. The method of claim 10, wherein the continuous measured LED current is compared with a reference value and the for the Mean representative Actual value is the duty cycle of the comparative value is the on period of the active switch. The method of claim 11, wherein the duty cycle based a bidirectional digital counter is determined. Method according to claim 9 or 10, wherein the reference value from a predetermined dimming value and / or the measured LED voltage depends. Integrated circuit, in particular ASIC, used for execution a method is designed. control gear for one LED comprising an integrated circuit according to claim 14. Circuit for power control of an LED, including a converter with a switch, with the LED in the output circuit is interconnected, wherein a control unit is the magnetization an inductance (L1) controls by actively switching the switch (S1), in which the control unit for the mean value of the LED current is the representative measured actual value, which is compared with a reference value. The circuit of claim 16, wherein the control unit dependent from a difference between the actual value and the setpoint, the duty cycle of the current one Switching of the active clocked switch and / or a following power-up setting. A circuit according to claim 17, wherein the control unit the duty cycle of the active clocked switch only every n-th switch-on changed where n is greater or equal to 2. A circuit according to any one of claims 16 to 18, wherein the Control unit the duty cycle of the active clocked switch over changed the time of switching off the active clocked switch as a control variable. A circuit according to any one of claims 16 to 19, wherein the Control unit through the duty cycle adaptive default a turn-off level of a measured for the LED current representative sizes, wherein the control unit on reaching the switch-off of the active switched-off switch turns off. A circuit according to any one of claims 16 to 20, wherein the Control unit in addition to the regulation of the operation of the LED also a DC link circuit drives and of the DC link circuit Feedback signals gets wherein the DC link voltage, the DC bus voltage supplying the converter generated. Circuit according to one of claims 16 to 21, wherein the control unit as a control variable of the power control ver, alternatively or in addition to the timing of the active clocked switch ver the level of the DC bus voltage supplying the converter applies. The circuit of claim 22, wherein for generation the bus voltage is provided an active PFC circuit, wherein the control unit the level of the generated bus voltage by changing the Clocking a switch of the PFC circuit performs. A circuit according to any one of claims 16 to 23, wherein the Control unit as one for the mean value of the LED current representative measured actual value a sample of the LED current, preferably measured at half of the Einschatzeitdauer the active clocked switch, is returned. A circuit according to any one of claims 16 to 23, wherein the Control unit for determining the mean value of the LED current representative Actual value continuously measures the LED current. A circuit according to claim 25, wherein the control circuit a comparator, which supplies the continuously measured LED current with a reference value compares and the control circuit as representative of the mean Actual value is the duty cycle the output signal of the comparator used. The circuit of claim 26, wherein the output signal of the comparator to a bidirectional digital counter Control circuit is supplied. A circuit according to any one of claims 16 to 27, wherein the Control circuit the reference value depending on an external or internally specified dimming value and / or the measured and the control circuit supplied LED voltage depends. A circuit according to any one of claims 16 to 28, wherein the control circuit (IC) is designed as a digital circuit. A circuit according to any one of claims 16 to 29, wherein the control circuit (IC) as an integrated circuit, preferably designed as an ASIC is. control gear for LED, comprising a circuit according to one of claims 16 to 30. Luminaire comprising an LED and an operating device according to claim 31st Lighting system comprising a plurality of lights, including at least one according to Claim 32, wherein the lights preferably by one or more Bus lines with each other and / or with a central control unit are connected.