DE102018110334A1 - Operating device for lamps with a resonant converter and a brightness control - Google Patents

Abstract

The present invention relates to an operating device comprising a resonant converter (8) for generating a voltage for the operation of a luminous means (4), a power factor correction circuit (7) for generating an operating voltage for the resonant converter (8) and a control device (9 ), which controls the switching frequency of the resonant converter (8) and reduces the operating voltage when the switching frequency exceeds a threshold (fs).

Description

The present invention relates to an operating device for lighting means, in which the operating voltage required for the lighting means or the operating current is generated by means of a resonant converter and in which the brightness of the light emitted from the light source can be controlled or regulated, and a method for controlling the operating device ,

Resonance converters with a series or parallel resonant circuit are often used in operating devices to enable energy-efficient operation with low switching losses.

Such an operating device, in which the resonant converter has a resonant circuit with two inductances and a capacitance (LLC) and a primary-side half-bridge, is known from US Pat DE 10 2012 007 450 A1 known. To cover a large load / dimming range and to allow precise control even in low load / dimming ranges, the DE 10 2012 007 450 A1 operate the LLC resonant converter at high dimming levels in a first mode of operation and switch at low dimming levels in a second mode of operation, wherein in the first mode of operation the desired brightness is adjusted by changing the switching frequency of the half-bridge and in the second mode of operation by repetitively suppressing turn-on operations of both switches of the half-bridge, a pulsed signal is generated at the output of the converter, so that the brightness can be adjusted by pulse width modulation.

However, the range of brightness control by the pulse width modulation is limited in particular when using light-emitting diodes (LEDs) as the light source, since the modulation at low dimming levels can be perceived by the human eye as a disturbing flicker. In addition, the control of the various operating modes and their change is complex.

The invention has for its object to provide devices and methods that reduce the problems described. In particular, it is an object to provide a lighting device driver with a resonant converter and a method of controlling a driver having a resonant converter that permit accurate control over a large load range with a simple and inexpensive construction.

This object is achieved according to the features of the independent claims. The invention is further developed by the features of the dependent claims.

According to the present invention, an operating device for operating one or more lighting means comprises a resonant converter for generating a voltage and a current for the operation of the lighting means, a power factor correction circuit for generating an operating voltage for the resonant converter and a control device which controls the switching frequency of the resonant converter and the Operating voltage reduced when the switching frequency would exceed a threshold for a non-changed operating voltage.

Thus, a brightness control or regulation in a known manner via a change in the switching frequency, wherein for a reduction in brightness increases the switching frequency and when reaching a maximum switching frequency, the operating voltage or input voltage of the resonant converter is reduced to the output power and / or the switching frequency to reduce.

The level of the maximum switching frequency or the threshold value may depend on the increase of the switching losses, the maximum frequency of the switching signals that can be generated by the control device, the maximum switching frequency of the switches of the resonance converter and / or frequencies at which unwanted oscillations due to parasitic effects occur.

The brightness of the light emitted by the light source can be controlled according to a dimming signal. Alternatively or additionally, when receiving a turn-off command, the operating device may reduce the brightness continuously or stepwise. To this end, the controller may be configured to receive a turn-off or dimming signal indicative of a decrease in power to be transmitted through the resonant converter and to increase the switching frequency for a reduction in power when the turn-off signal or the dimming signal is received ,

The current or set switching frequency can be detected and compared directly with the threshold. Alternatively, the current switching frequency and the threshold may be associated with a current dimming level and a dimming threshold, respectively, wherein the controller is configured to reduce the operating voltage when the dimming value indicated by the dimming signal falls below the dimming threshold ,

The power factor correction circuit may comprise an inverse converter or a boost converter, wherein the control device is designed to interrupt the clocking of the boost converter, to decrease the operating voltage when the switching frequency exceeds the threshold.

In addition, the controller may be configured to set the switching frequency to a lower value to compensate for the drop in power transmitted through the resonant converter due to the reduced operating voltage and to increase the switching frequency again to achieve a further reduction in power transmitted through the resonant converter.

Alternatively, the controller may be configured to increase the switching frequency only up to the threshold and gradually or continuously reduce the operating voltage to achieve a further reduction in the power transmitted through the resonant converter at a fixed switching frequency.

The resonant converter may be one of two inductors and a capacitance of existing LLC converters. Since a power factor correction circuit and a control device are included in many operating devices, no additional components need to be used. This is a very cost-effective implementation possible.

• - Erzeugen einer Betriebsspannung durch die Leistungsfaktorkorrekturschaltung für den Resonanzwandler;
• - Steuern der Schaltfrequenz des Resonanzwandlers zum Erzeugen einer Spannung und eines Stroms für den Betrieb der Leuchtmittel; und
• - Verringern der Betriebsspannung, wenn die Schaltfrequenz einen Schwellenwert übersteigt.

According to the present invention, a method for controlling a power device having a power factor correction circuit and a resonant converter for operating one or more lighting means comprises the following steps:

• - generating an operating voltage by the power factor correction circuit for the resonant converter;
• - controlling the switching frequency of the resonant converter to generate a voltage and a current for the operation of the lighting means; and
• - Reduce the operating voltage when the switching frequency exceeds a threshold.

• 1 ein Ausführungsbeispiel eines Betriebsgeräts gemäß der vorliegenden Erfindung,
• 2 eine Leistungsfaktorkorrekturschaltung des in 1 gezeigten Betriebsgeräts,
• 3 eine Schaltung des Resonanzwandlers des in 1 gezeigten Betriebsgeräts,
• 4 ein Diagramm mit dem Verlauf der frequenzabhängigen Verstärkung des Resonanzwandlers, und
• 5 ein vereinfachtes Ablaufdiagramm zur Darstellung des Verfahrens gemäß der vorliegenden Erfindung.

The invention will be explained in more detail with reference to the accompanying drawings. Show it:

• 1 An embodiment of an operating device according to the present invention,
• 2 a power factor correction circuit of in 1 shown operating device,
• 3 a circuit of the resonant converter of in 1 shown operating device,
• 4 a diagram with the course of the frequency-dependent amplification of the resonant converter, and
• 5 a simplified flow diagram for illustrating the method according to the present invention.

Components with the same functions are identified in the figures with the same reference numerals.

1 shows a simplified schematic representation of a control gear 1 according to an embodiment of the present invention. The operating device 1 is used to operate one at its output terminals 2 . 3 connected bulbs 4 which may comprise a light-emitting diode (LED, OLED) or a plurality of series-connected or parallel-connected LEDs, OLEDs.

At the two input terminals 5 . 6 of the illustrated operating device 1 a supply voltage is supplied, which may be a mains AC voltage of 230 volts. The operating device 1 has one with the input terminals 5 . 6 connected power factor correction circuit 7 , one with the output terminals 2 . 3 connected resonant converter 8th and a power factor correction circuit 7 and the resonant converter 8th controlling control device 9 on.

The power factor correction circuit 7 serves to provide the operating voltage for the resonant converter 8th , which may be a DC voltage of 400 volts, as well as for the correction of the power factor (so-called power factor correction), in which the switching times of the switched with a pulse width modulated control voltage switch of a DC-DC converter are selected so that the input current of the circuit a sinusoidal Course follows, which is in phase with the course of the AC line voltage. The provision of the operating voltage is achieved by the power factor correction circuit 7 from the mains voltage.

A simplified schematic of the power factor correction circuit 7 is in 2 shown. The shown power factor correction circuit 7 has a rectifier 10 with directly downstream boost converter (English boost converter) on. The boost converter consists of a coil 11 in series with a freewheeling diode 12 is switched, a charging capacitor 13 and a switch 14 that turns the coil against ground. The desk 14 by applying a turn-on signal to the terminal 15 from the controller 9 or a separate, for the power factor correction circuit 7 provided control device turned on.

For the determination of the switch 14 flowing current and the one above the switched off switch 14 oscillating voltage indicates the power factor correction circuit 7 one in series with the switch 14 switched measuring resistor 16 or one with the coil 11 inductively coupled auxiliary winding 17 on. The auxiliary winding 17 is with its one end to ground and with the other end over the diode 18 and a resistance 19 with a signal output 20 for the control device 9 (in 2 not shown). The signal output 20 is also about a resistance 21 with a node between the switch 14 and the measuring resistor 16 connected.

The desk 14 is from the controller 9 so clocked that at medium to high dimming levels at the output terminals 22 . 23 an operating voltage for the resonant converter 8th of 400 volts is applied and at low dimming levels, this operating voltage is reduced, the operating voltage up to the value of the rectified AC line voltage with complete shutdown of the clocking of the switch 14 or the power factor correction circuit 7 may decrease.

3 shows a simplified circuit of the resonant converter 8th , which is a primary-side circuit 24 and a secondary side 25 comprising, by means of a primary coil 27 and a secondary coil 26 having transformer via a potential barrier 28 are coupled. The resonant converter 8th converts from the power factor correction circuit 7 Provided operating voltage (for example, a 400 volts DC) in a DC or DC for the bulb around. The DC voltage used for the bulb 4 is generated by the desired operating point of the bulb 4 certainly.

The primary-side circuit 24 includes an LLC resonant circuit configured as a series resonant circuit and a first inductor 29 , a second inductance 30 and a capacity 31 in a series circuit and a half-bridge with a first switch 32 and a second switch 33 , At the half-bridge is provided by the power factor correction circuit 7 operating voltage, wherein the first switch 32 with the output connector 22 and the second switch 33 about a resistance 35 with the output connector 23 the power correction circuit 7 connected is.

The resonant circuit is at the middle of the half-bridge between the two switches 32 and 33 connected and a first terminal of the first inductance 29 of the resonant circuit with the node between the first switch 32 and the second switch 33 the half-bridge circuit. A second terminal of the first inductance 29 is connected to a first terminal of the second inductance 30 of the resonant circuit and a second terminal of the second inductance 30 of the resonant circuit with a first terminal of the capacitance 31 ,

The secondary side 25 has one of the secondary coils 26 downstream and through a first diode 36 and a second diode 37 formed rectifier on. The middle of the secondary coil 26 is with the output connector 3 connected and the ends of the secondary coil 26 over the diodes 36 and 37 with the output connector 2 , A capacitor 38 is parallel to the output terminals 2 . 3 connected.

Other embodiments of the LLC resonant circuit are also possible. For example, the capacity 31 between the inductors 29 and 30 be switched.

In operation of the resonant converter 8th controls the controller 9 the first switch 32 and the second switch 33 so that only one of the two switches is turned on. In doing so, each of the switches 32 . 33 be switched with the same switching frequency, wherein changing the brightness of the output terminals 2 . 3 connected light source 4 (Dimming level) the switching frequency at which the switches 32 . 33 be switched clocked, is changed. A prescription for the assignment of a dimming level to a corresponding switching frequency may also be specified by the manufacturer or user for different light sources, which represent different loads, and stored, for example.

4 shows a characteristic course of the frequency-dependent transfer function (ratio of the voltage Uout at the output terminals 2 . 3 to the tension U _in at the output terminals 22 . 23 ) or the frequency-dependent amplification of the resonant converter 8th , Starting from an example selected operating point 38 of the resonant converter 8th at a switching frequency f ₀ the gain decreases with an increase in the switching frequency, which means a reduction in brightness, with the switching frequency f ₁ the new exemplary working point 39 and at the switching frequency f _s the further exemplary operating point 40 is present. As shown in the diagram, the curve levels off significantly with increasing switching frequency, so that the switching frequency must be increased disproportionately for a further reduction of the gain, and thus ultimately the brightness. With the aid of the invention, such a problematic increase in the frequency can be avoided to further reduce the output voltage.

In the 4 For the sake of clarity, only one curve is shown. In fact, however, the curve is load-dependent, with the curves for increasingly smaller loads progressively flatter for frequencies above a load-independent operating point.

According to the present invention, the switching frequency f _s or a dimming level assigned to it as a threshold value, wherein a dimming signal indicating the dimming level to be set is applied to the terminal 41 of in 1 shown operating device 1 the control device 9 can be fed.

If the operating frequency of 400V during normal operation reaches or exceeds the threshold value due to a required low dimming level, the switching frequency will reach or exceed the threshold value f _s , controls the controller 9 the power factor correction circuit 7 such that this reduces the operating voltage, resulting in a change in the gain or ratio U _out / U _in and to another operating point with a lower, below the threshold value f _s lying switching frequency leads.

The reduction of the operating voltage can be a particularly simple solution by switching off the power factor correction circuit 7 or the timing of the switch 14 respectively. After the reduction of the operating voltage, the controller changes 9 starting from the lower switching frequency then again the switching frequency to adjust the gain to a newly set dimming level. If the switching frequency falls below another lower threshold value when adjusting to higher dimming levels (eg the switching frequency f ₁ ), increases the controller 9 the operating voltage back to the original value ( 400 Volt). It is f ₁ preferably chosen so that after switching to the original operating voltage of here 400V again the frequency F _s is set.

Alternatively, the reduction and / or increase of the operating voltage can take place in several steps, to each of which different threshold values are assigned.

It is also possible with a down-dimming the switching frequency only up to the threshold f _s to increase and to reduce the operating voltage gradually or continuously in accordance with the dimming signal to achieve a further reduction in brightness at a fixed switching frequency. Alternatively, in a down-dimming, the switching frequency continuously increases and at the same time the operating voltage continuously from the controller 9 be reduced.

Instead of a dimming signal can be connected to the port 41 the control device 9 an on or off signal to be supplied, wherein the control device 9 on receipt of the switch-off signal, the brightness of the luminous means in the manner described above is lowered to zero. Upon receipt of the turn-on signal, the control device 9 lower or leave the operating voltage low and after falling below the threshold f _s increase the operating voltage.

Used in power factor correction circuit 7 Instead of the boost converter used an inverter, the operating voltage can be further reduced.

In the examples described, the controller controls 9 the switches 14 . 32 and 33 directly to. However, it is also possible that the power factor correction circuit 7 and / or the resonant converter 8th internal control devices for the control of the switch 14 or the switch 32 and 33 and the control device 9 only sends a control signal for the change of the operating voltage or the switching frequency to the internal control devices.

The control device 9 may be configured as a processor, a microprocessor, a controller, a microcontroller or an application specific integrated circuit (ASIC) or a combination of said units.

5 shows a simplified flow diagram of the method according to the present invention.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102012007450 A1 [0003]

Claims (10)

Operating device for operating one or more light sources (4), comprising: a resonant converter (8) for providing a voltage and a current for the operation of the lighting means (4), a power factor correction circuit (7) for providing an operating voltage for the resonant converter (8) and a control device (9) for controlling a switching frequency of the resonant converter (8), characterized in that the control device (9) is designed to control the power factor correction circuit (7) so that the operating voltage is reduced when the switching frequency at an unchanged operating voltage Threshold (f _s ). Operating device after Claim 1 wherein the control means (9) is adapted to receive a turn-off or dimming signal indicative of a decrease in the power to be transmitted through the resonant converter and to increase the switching frequency for a decrease in power when the turn-off signal Dimming signal is received. Operating device after Claim 2 , wherein the control device (9) is designed to reduce the operating voltage when a certain, the threshold value (f _s ) associated with dimming level is exceeded. Operating device according to one of Claims 1 to 3 wherein the power factor correction circuit (7) comprises an inverse converter. Operating device according to one of Claims 1 to 4 wherein the power factor correction circuit (7) comprises a boost converter. Operating device after Claim 5 wherein the control means (9) is arranged to interrupt the clocking of the boost converter to reduce the operating voltage if the switching frequency exceeded the threshold value (fs). Operating device after Claim 6 in that the control device (9) is designed to set the switching frequency to a lower value in order to compensate for the drop in the power transmitted by the resonant converter (8) due to the dropped operating voltage, and to achieve a further reduction of the voltage caused by the resonant converter (8 ) transmitted power to increase the switching frequency. Operating device according to one of Claims 1 to 5 in that the control device (9) is designed to increase the switching frequency only up to the threshold value and to reduce the operating voltage in order to achieve a further reduction of the power transmitted by the resonant converter (8) at a fixed switching frequency. Operating device according to one of Claims 1 to 8th wherein the resonant converter (8) is an LLC converter. Method for controlling an operating device (1) having a power factor correction circuit (7) and a resonant converter (8) for operating one or more light sources (4), comprising the steps of: generating an operating voltage by the power factor correction circuit (7) for the resonant converter (8), and controlling the switching frequency of the resonant converter (8) to produce a voltage or current for the operation of the luminous means (4), characterized by reducing the operating voltage if the switching frequency would exceed a threshold value with the operating voltage unchanged.

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