(19)
(11)EP 3 806 302 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
26.01.2022 Bulletin 2022/04

(21)Application number: 19202150.9

(22)Date of filing:  09.10.2019
(51)International Patent Classification (IPC): 
H02M 1/42(2007.01)
(52)Cooperative Patent Classification (CPC):
H02M 1/4225; H02M 1/0009; H02M 1/0058; Y02B 70/10

(54)

POWER FACTOR CORRECTION CIRCUIT

LEISTUNGSFAKTORKORREKTURSCHALTUNG

CIRCUIT DE CORRECTION DE FACTEUR DE PUISSANCE


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(43)Date of publication of application:
14.04.2021 Bulletin 2021/15

(73)Proprietor: Tridonic GmbH & Co. KG
6851 Dornbirn (AT)

(72)Inventors:
  • Auer, Hans
    6850 Dornbirn (AT)
  • Marte, Patrick
    6840 Götzis (AT)

(74)Representative: Rupp, Christian 
Mitscherlich PartmbB Patent- und Rechtsanwälte Sonnenstraße 33
80331 München
80331 München (DE)


(56)References cited: : 
DE-U1-202014 106 015
US-A1- 2018 054 113
  
  • SANG HEE KANG ET AL: "Efficiency Optimization in Digitally Controlled Flyback DC DC Converters Over Wide Ranges of Operating Conditions", IEEE TRANSACTIONS ON POWER ELECTRONICS, INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS, USA, vol. 27, no. 8, 1 August 2012 (2012-08-01) , pages 3734-3748, XP011454760, ISSN: 0885-8993, DOI: 10.1109/TPEL.2012.2186590
  
Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


Description

TECHNICAL FIELD OF THE INVENTION



[0001] The invention relates in general to a power factor correction (PFC) circuit and to a method for power factor correction. The invention further relates to a control unit for implementing the method, and to a driver for light sources, such as LEDs.

BACKGROUND OF THE INVENTION



[0002] Power factor correction (PFC) circuits are known to convert a supplied DC or AC voltage to a higher level. At the same time, such circuits can be designed to guarantee a power factor of almost 1, in which, for example, the current drawn by this circuit has a sinusoidal time curve similar to the one of the mains voltage.

[0003] Boost PFC circuits are a special type of PFC circuits. In a boost PFC circuit an inductor, such as a charging coil, is connected in series with a boost diode, whereby the connection point between the boost diode and the charging coil can selectively be connected to ground via a switch. An AC or DC voltage can be applied to the charging coil, which charges the charging coil when the switch is closed. When the switch is open, a charging capacitor is charged via the boost diode. Typically, the switch is closed again as soon as the charging coil has completely discharged, i.e. as soon as the current through the charging coil has dropped to zero. This type of operation of the PFC circuit is called borderline mode.

[0004] At low loads, it is already known to operate the PFC circuit alternatively in the so-called discontinuous conduction mode (DCM) . Thereby, the switch is not switched on again immediately at the first local minimum of the voltage at the switch, respectively the first zero crossing of the corresponding current, but at a later point in time. To be more precise, the switch is not switched on again until the second or further local minimum, whereby these local minimums are caused by oscillation processes of the charging coil.

[0005] A problem now is that this particular clocking of the switch requires the detection of several zero crossings within a switch-off phase, i.e. while the switch is in an open position. However, the ringing, i.e. the oscillation, of the voltage decays over time such that after a view ringing circles it can become very difficult to properly determine the valleys in view of the decaying amplitude of the voltage.

[0006] In addition, the voltage oscillation at the charging coil is a damped oscillation, therefore the amplitude of the feedback signal detected via a secondary winding will also decrease towards a control unit following the damping. Thus, there is a risk that the maximum amplitude of the oscillation will drop below the discrimination threshold for zero crossing detection. This means that further zero crossings can no longer be detected. In extreme cases, the switch will not be switched on, i.e. closed, again.

[0007] In case no valley can be detected anymore, the PFC switch can be switched on again after a safety march in time period. However, as this safety march in time period is spaced substantially after the calculated switching on time, this leads to a fluctuation of the produced output voltage (Bus-voltage) of the PFC, which internally can lead to a visible relatively low frequency flicker in the light output of the lighting means.

[0008] The document DE 20 2014 106 015 U1 discloses a PFC circuit, comprising a switch which can be switched on and off by means of a control device for switching a coil current; and a signal output for detecting the current through the switch in time periods in which the switch is closed, and for detecting the zero crossing of the coil current in time periods in which the switch is open. Thereby, a bypass comprising at least one capacitor and coupled to the signal output is provided at the switch for detecting the zero crossing.

[0009] The document US 2018/0054113 A1 discloses a PFC circuit comprising an oscillator circuit. The oscillator circuit receives a valley detect signal indicating a zero current condition, determines a blanking time according to an operational cycle of the PFC circuit, and determines to initiate the operational cycle according to the valley detect signal and the blanking time. The PFC circuit may operate in a Boundary Conduction Mode or a Discontinuous Conduction Mode depending on whether a charge-discharge period is greater than the blanking time.

[0010] Thus, it is an objective to provide an improved PFC circuit and an improved method for performing a power factor correction, which avoid the above-mentioned disadvantages.

SUMMARY OF THE INVENTION



[0011] The object of the present invention is achieved by the solution provided in the enclosed independent claims. Advantageous implementations of the present invention are further defined in the dependent claims.

[0012] According to a first aspect of the invention, a power factor correction (PFC) circuit is provided. The PFC circuit comprises an inductor which is configured to provide a discharge current, a capacitor which is connected to the inductor via a connection point of a switch and which can be charged with said discharge current, a control unit which is configured to alternately switch the switch on and off based on a feedback control, wherein the control unit has an input interface for receiving a feedback signal (ZXCS) which represents a discharge voltage of the inductor being applied to the switch, wherein the control unit, in a DCM mode, is further configured to calculate a switch on time (Ton) of the switch which is after a first local minimum of the discharge voltage, and wherein, after switching off the switch, the control unit is configured to: either switch on the switch at a next or closest local minimum of the discharge voltage after Ton, in case Ton is less than a directly or indirectly set reference time (Tref), or close the switch at Ton, in case Ton is equal to or exceeds Tref. This provides the advantage that a light flicker can be prevented in case a local minimum of the discharge voltage cannot be detected.

[0013] In particular, the PFC circuit is a boost PFC circuit, in a drive for light sources, such as LEDs.

[0014] The discharge voltage refers to the voltage of the inductor at discharge. In particular, the discharge voltage refers to the discharge voltage of the inductor being applied to the switch.

[0015] The feedback signal (ZXCS) represents or corresponds to a discharge voltage and/or a discharge current being applied to the switch.

[0016] In the context of the invention, switching on the switch means making the switch conductive respectively closing the switch, and switching off the switch means making the switch nonconductive respectively opening the switch.

[0017] In an embodiment, if the switch is switched on, then a connection point between the boost diode and the inductor is connected to ground via the switch.

[0018] DCM mode refers to discontinuous conduction mode. In the DCM mode, the current through the inductor is allowed to fall to zero and to remain at zero without immediate control of the PFC switch to become conducting again. After the first zero crossing, respectively valley, of the inductor voltage, the inductor voltage is not immediately statically zero, rather there is an ongoing decaying ringing of the voltage.

[0019] In DCM mode, a local minimum of the discharge voltage generally coincides with a zero crossing, in particular a positive zero crossing, of the corresponding discharge current. In this context, the terms local minimum, or valley, of the discharge voltage and the term (positive) zero crossing of the discharge voltage can be used synonymously.

[0020] In a preferred embodiment, the PFC circuit further comprises a boost diode which is connected to the inductor in series.

[0021] In a preferred embodiment, the control unit is configured to determine the local minimum of the discharge voltage based on the feedback signal (ZXCS). This provides the advantage that the local minimum of the discharge voltage can be determined efficiently.

[0022] In particular, the control unit is configured to determine the local minimum of the discharge voltage when the feedback signal (ZXCS) falls below a threshold value.

[0023] In a preferred embodiment, the control unit is configured to detect the local minimum of the discharge voltage at a positive zero crossing of the discharge current. This provides the advantage that the local minimum of the discharge voltage can be determined efficiently.

[0024] In a preferred embodiment, the control unit is configured to calculate the switch on time (Ton) during a closing phase of the switch.

[0025] In a preferred embodiment, the control unit comprises a processing unit for analyzing the feedback signal (ZXCS) and/or calculating the switch on time (Ton). In particular, the switch on time (Ton) is calculated based on the feedback signal (ZXCS).

[0026] In a preferred embodiment, the control unit comprises an output interface for controlling the switch. This allows for an efficient control of the switch.

[0027] For instance, the output interface provides a voltage for switching the switch on or off, in particular if the switch is a transistor.

[0028] In a preferred embodiment, the control unit comprises a restart timer which is configured to switch on the switch at a set time limit after switching off the switch, wherein the reference time (Tref) is less than the time limit of the restart timer. This provides the advantage that light flicker can be prevented, since a switch on at Tref is always earlier than a switch on by the restart timer.

[0029] In a preferred embodiment, the reference time (Tref) is less than 300 µs, in particular less than 100 µs, more particular less than 50 µs, even more particular less than 25 µs.

[0030] In a preferred embodiment, the switch is a transistor, in particular a power transistor, a field effect transistor (FET) or a MOSFET. This provides the advantage that the switch can efficiently be controlled by the control unit.

[0031] According to a second aspect of the invention, a driver for light sources, in particular for LEDs, is proposed, which comprises a PFC circuit according to the first aspect of the invention. This provides the advantage that a light flicker can be prevented in case a local minimum of the discharge voltage cannot be detected.

[0032] According to a third aspect of the invention, a method for power factor correction (PFC) by means of a PFC circuit, in particular the PFC circuit according to the first aspect of the invention, is proposed, wherein the PFC circuit comprises an inductor which is configured to provide a discharge current, a capacitor which is connected to the inductor via a connection point of a switch and which can be charged with said discharge current, wherein the switch is alternately switched on and off. The method comprises the steps of:
receiving a feedback signal (ZXCS), wherein the feedback signal (ZXCS) represents a discharge voltage of the inductor, calculating a switch on time (Ton) of the switch which is after a first local minimum of the discharge voltage, and after switching off the switch, either switch on the switch at a next or closest local minimum of the discharge voltage after Ton, in case Ton is less than a directly or indirectly set reference time (Tref), or switch on the switch at Ton, in case Ton is equal to or exceeds Tref. This provides the advantage that a light flicker can be prevented in case a local minimum of the discharge voltage cannot be detected.

[0033] According to a fourth aspect of the invention, a control unit for implementing the method according to the third aspect of the invention is proposed.

[0034] In a preferred embodiment, the control unit has an input interface for receiving the feedback signal (ZXCS) and/or an output interface for controlling the switch.

[0035] In a preferred embodiment, the control unit is implemented as a micro controller, an ASIC or a hybrid solution.

[0036] It has to be noted that all devices, elements, units and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS



[0037] The invention will be explained in the followings together with the figures.
Fig. 1
shows a schematic diagram of a PFC circuit according to an embodiment of the invention;
Fig. 2
shows a schematic plot of a voltage signal occurring in the circuit according to an embodiment of the invention;
Fig. 3
shows a schematic diagram of a driver for light sources according to an embodiment of the invention; and
Fig. 4
shows a schematic diagram of a method for power factor correction according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS



[0038] Aspects of the present invention are described herein in the context of a PFC circuit.

[0039] The present invention is described more fully hereinafter with reference to the accompanying drawings, in which various aspects of the present invention are shown. This invention however may be embodied in many different forms and should not be construed as limited to the various aspects of the present invention presented through this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. The various aspects of the present invention illustrated in the drawings may not be drawn to scale. Rather, the dimensions of the various features may be expanded or reduced for clarity. In addition, some of the drawings may be simplified for clarity. Thus, the drawings may not depict all of the components of a given apparatus.

[0040] It is further understood that the aspect of the present invention might contain integrated circuits that are readily manufacturable using conventional semiconductor technologies, such as complementary metal-oxide semiconductor technology, short "CMOS". In addition, the aspects of the present invention may be implemented with other manufacturing processes for making optical as well as electrical devices. Reference will now be made in detail to implementations of the exemplary aspects as illustrated in the accompanying drawings. The same references signs will be used throughout the drawings and the following detailed descriptions to refer to the same or like parts.

[0041] Fig. 1 shows a power factor correction (PFC) circuit 20 according to an embodiment.

[0042] The PFC circuit 20 comprises an inductor 21 which is configured to provide a discharge current, a capacitor 23 which is connected to the inductor 21 via a switch 24 and which can be charged with said discharge current, a control unit 14 which is configured to alternately switch the switch 24 on and off based on a feedback control, wherein the control unit 14 has an input interface 42 for receiving a feedback signal (ZXCS) which represents a discharge voltage of the inductor being applied to the switch 24.

[0043] The control unit 14, in a DCM mode, can be configured to calculate a switch on time (Ton) of the switch 24 which is after a first local minimum of the discharge voltage.

[0044] After switching off the switch 24, the control unit can be configured to either switch on the switch 24 at a next or closest local minimum of the inductor voltage after Ton, in case Ton is less than a directly or indirectly set reference time (Tref), or close the switch 24 at Ton, in case Ton is equal to or exceeds Tref.

[0045] The discharge voltage refers to the voltage of the inductor at discharge. In particular, the discharge voltage refers to the discharge voltage of the inductor being applied to the switch 24.

[0046] The PFC circuit 20 can be supplied with an input voltage Vin e.g. in the form of an AC or DC voltage. The input voltage Vin can be a rectified mains voltage from a rectifier (not shown).

[0047] As output, the power factor correction circuit 20 can provide an output voltage which is a DC voltage. The output voltage Vout can be used to supply a load to which the power factor correction circuit 20 is connected. The load can, for example, be a component of a control gear for a light source such as a fluorescent lamp, a halogen lamp, a light-emitting diode (LED) arrangement, etc.

[0048] The input, respectively output, of the PFC circuit 20 can each be formed by an input terminal, respectively output terminal 27, and ground.

[0049] The input voltage Vin can be applied to a first terminal of the inductor 21 which can be a charging coil.

[0050] The PFC circuit 20 can further comprises a boost diode 22 which is connected to a second terminal of the inductor 21. The capacitor 23 can be connected between the anode of the boost diode 22 and ground, and can thus be charged by the discharge current of the inductor 21 via the diode 22.

[0051] The switch 24 can be a transistor, in particular a power transistor, a field effect transistor (FET) or a MOSFET.

[0052] In an embodiment, when the switch 24 is switched on, the inductor 21 is connected to ground via the switch 24, whereby the diode 22 is blocking, so that the inductor 21 is charged. If the switch 24 is switched off the diode 22 is conductive, so that the inductor 21 can be discharged via the diode 22 into the charging capacitor 23.

[0053] In Fig. 1, the inductor 21 is a charging coil that forms the primary winding of a transformer. A detection coil 31 forms the secondary winding of this transformer. The charging coil and the detection coil 31 are inductively coupled so that the current through the charging coil or the voltage at the charging coil can inductively be tapped by the control unit 14 at the input interface 42.

[0054] Accordingly, a resistor 33 and a diode 32 are provided. One terminal of the detection coil 31 is connected to ground, the other terminal of the detection coil 31 to the anode of the diode 32. The resistor 33 is connected between the cathode of the diode 32 and the input interface 42 of the control unit 14.

[0055] In an embodiment, while the switch 24 is switched off, the local minimum of the voltage via the inductor 21 or the (positive) zero crossing of the current (IL) flowing through the inductor 21 can be detected at the input interface 42. This detection of the voltage at the inductor 21 also indirectly detects the voltage at the switch 24.

[0056] In an embodiment, while the switch 24 is switched on, the current through the switch can be measured at the input interface 42 via a measuring resistor 26. This preferably low-impedance measuring resistor 26 is connected between ground and the switch 24, so that, when the switch 24 is switched on, a current flows through the inductor 21, the switch 24 and the measuring resistor 26.

[0057] In the exemplary embodiment of Fig. 1, another resistor 34 connects the input interface 42 and the connection point between the measuring resistor 26 and the switch 24.

[0058] A further capacitor 25 can be connected between inductor 21 and ground, which is connected in parallel to a series circuit consisting of the switch 24 and the resistor 26. The capacitor 25 can be connected to the same terminal of the diode 22 as the inductor 21.

[0059] The PFC circuit 20 further has an output interface 41 that is connected to the switch, in particular to a gate of the switch, for controlling the switch 24.

[0060] The control unit 14 can have a further input interface 43 for recording further variables. For example, the control unit 14 can detect the output voltage in form of a bus voltage Vbus via a voltage divider with resistors 36, 37.

[0061] Fig. 2 shows a schematic plot 50 of a voltage signal occurring in the circuit according to an embodiment.

[0062] The voltage in Fig. 2 is the fluctuating, or ringing, discharge voltage after switching off the switch 24 at time T0.

[0063] Fig. 2 shows the switching with two different calculated switch on times Ton_calc1 and Ton_calc2, wherein Ton_calc1 < Tref and Ton_calc2 > Tref, and wherein Tref is the directly or indirectly set reference time.

[0064] In a first time period region of the ringing voltage, which is before the reference time Tref, the so-called valley switching can be performed. This means, that if a calculated switch on time Ton_calc1 falls in this time period, then the switch 24 is not switched on at Ton_calc1. Instead, it is switched on at Ton_eff1, wherein Ton_eff1 is the time of the next or closest valley to Ton_calc1, and wherein often Ton_calc1 ≠ Ton_eff1.

[0065] In a second time period region of the ringing voltage, which is after Tref, the valley switching can be deactivated. A calculated switch on time Ton calc2, which falls in this time period, is directly applied to the actual switch on operation of the switch 24, i.e Ton_calc2 = Ton_eff2. The switching at Ton_calc2 is done if Ton_calc2 ≥ Tref, regardless of whether the discharge voltage at Ton_calc2 is in a valley or not.

[0066] This "adaptive valley switching" can prevent lost valley detection due to low signals. The PFC circuit 20 does no longer rely on a restart timer, that switches the PFC switch back on after a safety march in time period, which is much longer than the calculated switch on time Ton. The use of such a restart timer can lead to visible low frequency flicker in the light output of a lighting means supplied by a converter stage, which supplied by the output or bus voltage. However, a restart timer can still be implemented in the PFC circuit 20 as a safety measure.

[0067] The reference time can be less than 300 µs, 100 µs, 50 µs or 25 µs. In particular, the reference time, is less than the time limit of a restart timer.

[0068] The control unit 14 can calculate the switch on time (Ton), in particular during a closing phase of the switch 24. The control unit can comprise a processing unit for calculating Ton, e.g. based on the feedback signal (ZXCS).

[0069] Fig. 3 shows a schematic diagram of a driver 60 for light sources 61, such as LEDs, according to an embodiment.

[0070] The driver 60 comprises the PFC circuit 20, for instance the PFC circuit 20 as depicted in Fig. 1.

[0071] The driver can be an electrical ballast for an LED converter or for a fluorescent lamp.

[0072] Fig. 4 shows a schematic diagram of a method 70 for power factor correction according to an embodiment of the invention.

[0073] The method 70 can be performed by a PFC circuit 20, in particular the PFC circuit of Fig. 1, wherein the PFC circuit 20 comprises an inductor 21 which is configured to provide a discharge current, a capacitor 23 which is connected to the inductor 21 via a switch 24 and which can be charged with said discharge current, wherein the switch 24 is alternately switched on and off.

[0074] The method 70 comprises the steps of: receiving 71 a feedback signal (ZXCS), wherein the feedback signal (ZXCS) represents a discharge voltage of the inductor, calculating 72 a switch on time (Ton) of the switch 24, which is after a first local minimum of the discharge voltage, and after switching off 73 the switch 24, either switch on 74 the switch 24 at a next or closest local minimum of the discharge voltage after Ton, in case Ton is less than a directly or indirectly set reference time (Tref), or switch on 75 the switch 24 at Ton, in case Ton is equal to or exceeds Tref.

[0075] The step of calculating 72 Ton and/or the step of receiving 71 the feedback signal can be performed each before or after the switch off 73 of the switch 24.

[0076] The control unit 14 as shown in Fig. 1 can perform the method 70 shown in Fig. 4.

[0077] All features of all embodiments described, shown and/or claimed herein can be combined with each other. However, the scope of protection is only defined by the claims.

[0078] Although the invention has been illustrated and described with respect to one or more implementations, equivalent alternations and modifications will occur to those skilled in the art upon the reading of the understanding of the specification and the annexed drawings. In addition, while a particular feature of the invention may have been disclosed with respect to only one of the several implementations, such features may be combined with one or more other features of the other implementations as may be desired and if advantageous for any given or particular application. However, the scope of protection is only defined by the claims.


Claims

1. A power factor correction (PFC) circuit (20), comprising:

- an inductor (21) which is configured to provide a discharge current,

- a capacitor (23) which is connected to the inductor (21) via a connection point of a switch (24) and which can be charged with said discharge current,

- a control unit (14) which is configured to alternately switch the switch (24) on and off based on a feedback control,

- wherein the control unit (14) has an input interface (42) for receiving a feedback signal (ZXCS) which represents a discharge voltage of the inductor,

- wherein the control unit (14), in a DCM mode, is further configured to calculate a switch on time Ton of the switch (24) which is after a first local minimum of the discharge voltage, and

- wherein, after switching off the switch (24), the control unit is configured to:

a) either switch on the switch (24) at a next or closest local minimum of the discharge voltage after Ton, in case Ton is less than a directly or indirectly set reference time Tref,

b) or close the switch (24) at Ton, in case Ton is equal to or exceeds said directly or indirectly set reference time Tref.


 
2. The PFC circuit (20) according to claim 1, further comprising a boost diode (22) which is connected to the inductor (21) in series.
 
3. The PFC circuit (20) according to claim 1 or 2, wherein the control unit is configured to determine the local minimum of the discharge voltage based on the feedback signal (ZXCS).
 
4. The PFC circuit (20) according to claim 3, wherein the control unit is configured to detect the local minimum of the discharge voltage at a positive zero crossing of the discharge current.
 
5. The PFC circuit (20) according to any one of claims 1 to 4, wherein the control unit (14) is configured to calculate the switch on time (Ton) during a closing phase of the switch (24).
 
6. The PFC circuit (20) according to any one of claims 1 to 5, wherein the control unit (14) comprises a processing unit for analyzing the feedback signal (ZXCS) and/or calculating the switch on time (Ton).
 
7. The PFC circuit (20) according to any one of claims 1 to 6, wherein the control unit (14) comprises an output interface for controlling the switch (24).
 
8. The PFC circuit (20) according to any one of claims 1 to 7, wherein the control unit (14) comprises a restart timer which is configured to switch on the switch (24) at a set time limit after switching off the switch (24), wherein the reference time (Tref) is less than the time limit of the restart timer.
 
9. The PFC circuit (20) according to any one of claims 1 to 8, wherein the reference time (Tref) is less than 300 µs, in particular less than 100 µs, more particular less than 50 µs, even more particular less than 25 µs.
 
10. The PFC circuit (20) according to any one of claims 1 to 9, wherein the switch (24) is a transistor, in particular a power transistor, a field effect transistor (FET) or a MOSFET.
 
11. Driver for light sources (61), in particular for LEDs, which comprises a PFC circuit (20) according to any one of claims 1 to 10.
 
12. Method (70) for power factor correction (PFC) by means of a PFC circuit, in particular the PFC circuit (20) according to any one of claims 1 to 10, wherein the PFC circuit (20) comprises an inductor (21) which is configured to provide a discharge current, a capacitor (23) which is connected to the inductor (21) via a connection point of a switch (24) and which can be charged with said discharge current, wherein the switch (24) is alternately switched on and off, the method comprising the steps of:

- receiving a feedback signal (ZXCS), wherein the feedback signal (ZXCS) represents a discharge voltage of the inductor,

- calculating a switch on time Ton of the switch (24) which is after a first local minimum of the discharge voltage, and

- after switching off the switch (24):

a) either switch on the switch (24) at a next or closest local minimum of the discharge voltage after Ton, in case Ton is less than a directly or indirectly set reference time Tref

b) or switch on the switch (24) at Ton, in case Ton is equal to or exceeds Tref.


 
13. Control unit (14) for implementing the method (70) according to claim 12.
 
14. Control unit (14) according to claim 13, wherein the control unit (14) has an input interface (42) for receiving the feedback signal (ZXCS) and/or an output interface (41) for controlling the switch (24).
 
15. Control unit (14) according to claim 13 or 14, wherein the control unit (14) is implemented as a micro controller, an ASIC or a hybrid solution.
 


Ansprüche

1. Leistungsfaktorkorrekturschaltung (PFC-Schaltung) (20), umfassend:

- einen Induktor (21), der dazu konfiguriert ist, einen Entladestrom bereitzustellen,

- einen Kondensator (23), der mit dem Induktor (21) über einen Verbindungspunkt eines Schalters (24) verbunden ist und der mit dem Entladestrom geladen werden kann,

- eine Steuereinheit (14), die dazu konfiguriert ist, den Schalter (24) basierend auf einer Rückkopplungsregelung abwechselnd ein- und auszuschalten,

- wobei die Steuereinheit (14) eine Eingangsschnittstelle (42) zum Empfangen eines Rückkopplungssignals (ZXCS) aufweist, das eine Entladespannung des Induktors darstellt,

- wobei die Steuereinheit (14) in einem DCM-Modus ferner dazu konfiguriert ist, eine Einschaltzeit Ton des Schalters (24) zu berechnen, die nach einem ersten lokalen Minimum der Entladespannung liegt, und

- wobei nach dem Ausschalten des Schalters (24) die Steuereinheit konfiguriert ist zum:

a) entweder Einschalten des Schalters (24) bei einem nächsten oder nächstliegenden lokalen Minimum der Entladespannung nach Ton, falls Ton kleiner ist als eine direkt oder indirekt eingestellte Referenzzeit Tref,

b) oder Schließen des Schalters (24) bei Ton, falls Ton gleich der direkt oder indirekt eingestellten Referenzzeit Tref ist oder diese überschreitet.


 
2. PFC-Schaltung (20) nach Anspruch 1, ferner umfassend eine Boost-Diode (22), die mit dem Induktor (21) in Reihe geschaltet ist.
 
3. PFC-Schaltung (20) nach Anspruch 1 oder 2, wobei die Steuereinheit dazu konfiguriert ist, das lokale Minimum der Entladespannung basierend auf dem Rückkopplungssignal (ZXCS) zu bestimmen.
 
4. PFC-Schaltung (20) nach Anspruch 3, wobei die Steuereinheit dazu konfiguriert ist, das lokale Minimum der Entladespannung bei einem positiven Nulldurchgang des Entladestroms zu erfassen.
 
5. PFC-Schaltung (20) nach einem der Ansprüche 1 bis 4, wobei die Steuereinheit (14) dazu konfiguriert ist, die Einschaltzeit (Ton) während einer Schließphase des Schalters (24) zu berechnen.
 
6. PFC-Schaltung (20) nach einem der Ansprüche 1 bis 5, wobei die Steuereinheit (14) eine Verarbeitungseinheit zum Analysieren des Rückkopplungssignals (ZXCS) und/oder zum Berechnen der Einschaltzeit (Ton) umfasst.
 
7. PFC-Schaltung (20) nach einem der Ansprüche 1 bis 6, wobei die Steuereinheit (14) eine Ausgangsschnittstelle zum Steuern des Schalters (24) umfasst.
 
8. PFC-Schaltung (20) nach einem der Ansprüche 1 bis 7, wobei die Steuereinheit (14) einen Neustart-Timer umfasst, der dazu konfiguriert ist, den Schalter (24) bei einer eingestellten Zeitgrenze nach dem Ausschalten des Schalters (24) einzuschalten, wobei die Referenzzeit (Tref) kleiner ist als die Zeitgrenze des Neustart-Timers.
 
9. PFC-Schaltung (20) nach einem der Ansprüche 1 bis 8, wobei die Referenzzeit (Tref) weniger als 300 µs, insbesondere weniger als 100 µs, mehr insbesondere weniger als 50 µs, noch mehr insbesondere weniger als 25 µs beträgt.
 
10. PFC-Schaltung (20) nach einem der Ansprüche 1 bis 9, wobei der Schalter (24) ein Transistor, insbesondere ein Leistungstransistor, ein Feldeffekttransistor (FET) oder ein MOSFET ist.
 
11. Treiber für Lichtquellen (61), insbesondere für LEDs, der eine PFC-Schaltung (20) nach einem der Ansprüche 1 bis 10 umfasst.
 
12. Verfahren (70) zur Leistungsfaktorkorrektur (PFC) mittels einer PFC-Schaltung, insbesondere der PFC-Schaltung (20) nach einem der Ansprüche 1 bis 10, wobei die PFC-Schaltung (20) einen Induktor (21), der dazu konfiguriert ist, einen Entladestrom bereitzustellen, einen Kondensator (23), der mit dem Induktor (21) über einen Verbindungspunkt eines Schalters (24) verbunden ist und der mit dem Entladestrom geladen werden kann, umfasst, wobei der Schalter (24) abwechselnd ein- und ausgeschaltet wird, das Verfahren umfassend die Schritte:

- Empfangen eines Rückkopplungssignals (ZXCS), wobei das Rückkopplungssignal (ZXCS) eine Entladespannung des Induktors darstellt,

- Berechnen einer Einschaltzeit Ton des Schalters (24), die nach einem ersten lokalen Minimum der Entladespannung liegt, und

- nach dem Ausschalten des Schalters (24):

a) entweder Einschalten des Schalters (24) bei einem nächsten oder nächstliegenden lokalen Minimum der Entladespannung nach Ton, falls Ton kleiner ist als eine direkt oder indirekt eingestellte Referenzzeit Tref,

b) oder Einschalten des Schalters (24) bei Ton, falls Ton gleich Tref ist oder diese überschreitet.


 
13. Steuereinheit (14) zum Implementieren des Verfahrens (70) nach Anspruch 12.
 
14. Steuereinheit (14) nach Anspruch 13, wobei die Steuereinheit (14) eine Eingangsschnittstelle (42) zum Empfangen des Rückkopplungssignals (ZXCS) und/oder eine Ausgangsschnittstelle (41) zum Steuern des Schalters (24) aufweist.
 
15. Steuereinheit (14) nach Anspruch 13 oder 14, wobei die Steuereinheit (14) als ein Mikrocontroller, ein ASIC oder eine Hybridlösung implementiert ist.
 


Revendications

1. Circuit de correction de facteur de puissance (PFC) (20), comprenant :

- un inducteur (21) qui est configuré pour fournir un courant de décharge,

- un condensateur (23) qui est connecté à l'inducteur (21) par l'intermédiaire d'un point de connexion d'un commutateur (24) et qui peut être chargé avec ledit courant de décharge,

- une unité de commande (14) qui est configurée pour activer et désactiver alternativement le commutateur (24) sur la base d'une commande de rétroaction,

- dans lequel l'unité de commande (14) a une interface d'entrée (42) pour recevoir un signal de rétroaction (ZXCS) qui représente une tension de décharge de l'inducteur,

- dans lequel l'unité de commande (14), dans un mode DCM, est configurée en outre pour calculer un temps d'activation Ton du commutateur (24) qui est après un premier minimum local de la tension de décharge et

- dans lequel, après désactivation du commutateur (24), l'unité de commande est configurée pour :

a) soit activer le commutateur (24) à un minimum local, suivant ou le plus proche, de la tension de décharge après Ton, dans un cas où Ton est inférieur à un temps de référence Tref établi directement ou indirectement,

b) soit fermer le commutateur (24) à Ton, dans un cas où Ton est égal audit temps de référence Tref établi directement ou indirectement ou le dépasse.


 
2. Circuit PFC (20) selon la revendication 1, comprenant en outre une diode d'amplification (22) qui est connectée à l'inducteur (21) en série.
 
3. Circuit PFC (20) selon la revendication 1 ou 2, dans lequel l'unité de commande est configurée pour déterminer le minimum local de la tension de décharge sur la base du signal de rétroaction (ZXCS).
 
4. Circuit PFC (20) selon la revendication 3, dans lequel l'unité de commande est configurée pour détecter le minimum local de la tension de décharge à un passage par le point zéro positif du courant de décharge.
 
5. Circuit PFC (20) selon l'une quelconque des revendications 1 à 4, dans lequel l'unité de commande (14) est configurée pour calculer le temps d'activation (Ton) pendant une phase de fermeture du commutateur (24).
 
6. Circuit PFC (20) selon l'une quelconque des revendications 1 à 5, dans lequel l'unité de commande (14) comprend une unité de traitement pour analyser le signal de rétroaction (ZXCS) et/ou calculer le temps d'activation (Ton).
 
7. Circuit PFC (20) selon l'une quelconque des revendications 1 à 6, dans lequel l'unité de commande (14) comprend une interface de sortie pour commander le commutateur (24).
 
8. Circuit PFC (20) selon l'une quelconque des revendications 1 à 7, dans lequel l'unité de commande (14) comprend un temporisateur de redémarrage qui est configuré pour activer le commutateur (24) à une limite de temps établie après désactivation du commutateur (24), dans lequel le temps de référence (Tref) est inférieur à la limite de temps du temporisateur de redémarrage.
 
9. Circuit PFC (20) selon l'une quelconque des revendications 1 à 8, dans lequel le temps de référence (Tref) est inférieur à 300 µs, en particulier inférieur à 100 µs, plus particulièrement inférieur à 50 µs, encore plus particulièrement inférieur à 25 µs.
 
10. Circuit PFC (20) selon l'une quelconque des revendications 1 à 9, dans lequel le commutateur (24) est un transistor, en particulier un transistor de puissance, un transistor à effet de champ (FET) ou un MOSFET.
 
11. Circuit d'attaque pour sources de lumière (61), en particulier pour des DEL, qui comprend un circuit PFC (20) selon l'une quelconque des revendications 1 à 10.
 
12. Procédé (70) pour une correction de facteur de puissance (PFC) au moyen d'un circuit PFC, en particulier le circuit PFC (20) selon l'une quelconque des revendications 1 à 10, dans lequel le circuit PFC (20) comprend un inducteur (21) qui est configuré pour fournir un courant de décharge, un condensateur (23) qui est connecté à l'inducteur (21) par l'intermédiaire d'un point de connexion d'un commutateur (24) et qui peut être chargé avec ledit courant de décharge, dans lequel le commutateur (24) est activé et désactivé alternativement, le procédé comprenant les étapes consistant à :

- recevoir un signal de rétroaction (ZXCS), dans lequel le signal de rétroaction (ZXCS) représente une tension de décharge de l'inducteur,

- calculer un temps d'activation Ton du commutateur (24) qui est après un premier minimum local de la tension de décharge et

- après désactivation du commutateur (24) :

a) soit activer le commutateur (24) à un minimum local, suivant ou le plus proche, de la tension de décharge après Ton, dans un cas où Ton est inférieur à un temps de référence Tref établi directement ou indirectement,

b) soit activer le commutateur (24) à Ton, dans un cas où Ton est égal à ou dépasse Tref.


 
13. Unité de commande (14) pour mettre en œuvre le procédé (70) selon la revendication 12.
 
14. Unité de commande (14) selon la revendication 13, dans laquelle l'unité de commande (14) a une interface d'entrée (42) pour recevoir le signal de rétroaction (ZXCS) et/ou une interface de sortie (41) pour commander le commutateur (24).
 
15. Unité de commande (14) selon la revendication 13 ou 14, dans laquelle l'unité de commande (14) est mise en œuvre en tant que microcontrôleur, circuit intégré à application spécifique ASIC ou solution hybride.
 




Drawing

















Cited references

REFERENCES CITED IN THE DESCRIPTION



This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description