• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    A power supply comprises a rectifier (101) for receiving input voltage (Vin), a boost converter (102) connected to an output of the rectifier and configured to form intermediate voltage (Vinm), and an output converter (103) connected to an output of the boost converter and configured to convert the intermediate voltage to output voltage (Vout). The power supply comprises a control system (104) configured to drive the boost converter in a critical conduction mode, to determine whether the input voltage is alternating or direct voltage, and to drive the boost converter as a power factor correction circuit when the input voltage is alternating voltage. The control system is configured to reduce the intermediate voltage in response to a change from alternating input voltage to direct input voltage in order to reduce switching frequency of the boost converter and thereby disturbances emitted by the boost converter on undesired frequency areas.
    公开号:FI20205428A1
    申请号:FI20205428
    申请日:2020-04-28
    公开日:2021-04-30
    发明作者:Hannu Vihinen；Markku Kuivalainen
    申请人:Helvar Oy Ab；
    IPC主号:
    专利说明:

    A power supply and a method for controlling the same Field of the disclosure The disclosure relates generally to control of electric energy. More particularly, the disclosure relates to a power supply for providing driving current to one or more light emitting diodes “LED”. Furthermore, the disclosure relates to a method for controlling a power supply and to a data processor program for controlling a power supply. Background Many power supplies such as e.g. ballasts or drivers, i.e. electronic control gears, for energizing light sources comprise a rectifier and a boost converter that is driven as a power factor corrector “PFC”. The boost converter is driven in a critical conduction mode in which inductor current ramps to twice a desired average value, ramps down to zero, then immediately ramps up again, and so on. Input current of the rectifier is typically filtered with capacitive and inductive filtering components at the alternating voltage side and/or the direct voltage side of the rectifier. Switching frequency of a boost converter that is driven in the above-described critical conduction mode is dependent on input voltage of the boost converter. The input voltage is substantially rectified sinusoid when a power supply of the kind mentioned above is supplied with sinusoidal alternating voltage. Thus, in conjunction with the < alternating voltage supply, the switching frequency of the boost converter varies. N The variation of the switching freguency, in turn, spreads a freguency spectrum of 3 disturbance voltage emitted by the boost converter.
    N =E In conjunction with many lighting systems, there is a requirement that power e 25 supplies for energizing light sources must be able to be supplied not only with > alternating voltage but with direct voltage, too. The direct voltage supply can be N activated for example in emergency situations and other exceptional situations in N which alternating voltage is not available from mains. In conjunction with the direct voltage supply, the input voltage of a boost converter is substantially constant and therefore the frequency spectrum of the disturbance voltage is not spread in the same way as in conjunction with the alternating voltage supply. Therefore, the frequency spectrum of the disturbance voltage may have peaks which violate criteria related to the disturbance voltage. Especially peaks at frequencies above 50 kHz can be harmful. Summary The following presents a simplified summary in order to provide a basic understanding of some aspects of various embodiments. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts in a simplified form as a prelude to a more detailed description of exemplifying embodiments. In accordance with the invention, there is provided a new power supply for providing driving current to one or more light emitting diodes “LED”. A power supply, i.e. an electronic control gear, according to the invention comprises: - a rectifier configured to receive input voltage, - a boost converter connected to an output of the rectifier and configured to form intermediate voltage, - an output converter connected to an output of the boost converter and configured to convert the intermediate voltage to output voltage of the power o 20 supply, and
    QA & + - a control system configured to control the boost converter to operate in the 2 critical conduction mode and to control the output converter.
    N E The control system is configured to determine whether the input voltage is @ alternating voltage or direct voltage, and to drive the boost converter as a power 3 25 factor correction “PFC” circuit in response to a situation which the input voltage is O alternating voltage. The control system is configured to reduce the intermediate voltage in response to a change from alternating input voltage to direct input voltage in order to lower switching freguency of the boost converter, e.g. to be below a predetermined frequency limit such as 50 kHz, and thereby to reduce disturbances emitted by the boost converter on undesired frequency areas. The reduction in the disturbances on the undesired frequency areas makes it possible to use smaller and/or less expensive filtering components in the power supply.
    In accordance with the invention, there is provided also a new method for controlling a power supply of the kind described above. A method according to the invention comprises: - driving the boost converter of the power supply in the critical conduction mode, - determining whether the input voltage of the power supply is alternating voltage or direct voltage, the boost converter acting as a power factor correction circuit “PFC” in response to a situation which the input voltage is alternating voltage, and - reducing the intermediate voltage prevailing at an output of the boost converter in order to lower switching frequency of the boost converter in response to a change from alternating input voltage to direct input voltage. In accordance with the invention, there is provided also a new data processor program for controlling a power supply of the kind described above. A data processor program according to the invention comprises instructions for controlling a programmable data processor to:
    N S - control the boost converter of the power supply to operate in the critical 3 conduction mode,
    N - - determine whether the input voltage of the power supply is alternating voltage E or direct voltage, the boost converter acting as a power factor correction N 25 circuit “PFC” in response to a situation which the input voltage is alternating s voltage, and
    - reduce the intermediate voltage prevailing at an output of the boost converter in order to lower switching frequency of the boost converter in response to a change from alternating input voltage to direct input voltage. The above-mentioned data processor program can be called a computer program provided that a computer is understood in a broad sense so that e.g. a programmable controller or another programmable device is deemed to be a computer. In accordance with the invention, there is provided also a new data processor program product. The data processor program product comprises a non-volatile data processor readable medium encoded with a data processor program according to the invention. Exemplifying and non-limiting embodiments are described in accompanied dependent claims. Various exemplifying and non-limiting embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying and non-limiting embodiments when read in conjunction with the accompanying drawings. The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of unrecited features. The S features recited in dependent claims are mutually freely combinable unless
    O N otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or <+ <Q “an”, i.e. a singular form, throughout this document does not exclude a plurality.
    N =E Brief description of the figures a N 25 Exemplifying and non-limiting embodiments and their advantages are explained in
    LO S greater detail below in the sense of examples and with reference to the
    O N accompanying drawings, in which:
    figure 1 shows a schematic illustration of a power supply according to an exemplifying and non-limiting embodiment, figure 2 shows a flowchart of a method according to an exemplifying and non-limiting embodiment for controlling a power supply, and 5 figure 3 shows a flowchart of a method according to an exemplifying and non-limiting embodiment for controlling a power supply. Description of the exemplifying embodiments The specific examples provided in the description given below should not be construed as limiting the scope and/or the applicability of the appended claims. Lists and groups of examples provided in the description given below are not exhaustive unless otherwise explicitly stated. Figure 1 shows a schematic illustration of a power supply according to an exemplifying and non-limiting embodiment for supplying electric power to a load
    116. The load 116 can be e.g. a light source that may comprise one or more light emitting diodes “LED”. The power supply comprises a rectifier 101 configured to receive input voltage Vin. The power supply comprises a boost converter 102 that is connected to an output of the rectifier 101 and configured to form intermediate voltage Vinm. The power supply comprises an output converter 103 that is connected to an output of the boost converter 102 and configured to convert the intermediate voltage Vinm to output voltage Vout of the power supply. The output converter 103 S can be for example a buck converter, a fly-back converter, or some other suitable s converter for regulating the output voltage Vout.
    O 2 The power supply comprises a control system 104 that is configured to control the z boost converter 102 to operate in the critical conduction mode. The control system N 25 104 is configured to control the output converter 103, too. The control system 104 s monitors output voltage Vor of the rectifier 101 and the intermediate voltage Vinm. N Using this information together with a reference value Vinmrer Of the intermediate N voltage, an error amplifier 118, and a multiplier 117, the control system 104 builds an envelope 113 for current of an inductor 111. When current of a controllable switch 105 of the boost converter 102 exceeds the envelope 113, a current comparator
    119 resets the PWM latch 120 and the controllable switch 105 turns off. Once the current of the of the inductor 111 has reached zero, a zero current detection block 121 sets the PWM latch 120 and a new conduction time of the controllable switch 105 starts. During each conduction time of the controllable switch 105, the current of the inductor 111 ramps up from zero to the envelope 113. When the current of the inductor 111 reaches the envelope 113, the controllable switch 105 turns off and subsequently the current of the inductor 111 ramps down to zero. Thereafter a new conduction time of the controllable switch 105 starts. The controllable switch 105 can be for example a metal oxide semiconductor field effect transistor “MOSFET”, a bipolar transistor, or an insulated gate bipolar transistor “IGBT”. Switching frequency fsw of the boost converter 102 is dependent on the output voltage Vor of the rectifier 101, the intermediate voltage Vinm, the inductance L of the inductor 111, and power P transferred by the boost converter 102. The switching frequency fsw can be estimated with the following equation: Vinm ViR-Vi fow = TE (1) The switching frequency fsw is 1/(Ton + Torr), where Ton is a conduction time of the controllable switch 105 and Tor is a non-conduction time of the controllable switch
    105. The above-mentioned power P is average power during a switching period whose duration is Ton + Torr. In a case where the input voltage Vin is alternating voltage, the output voltage Vor of the rectifier 101 has a pulsating waveform. The S envelope 113 has a pulsating waveform having substantially a same shape and a N same phase as those of the waveform of the output voltage Vor of the rectifier 101. S For filtering input current of the power supply, the rectifier 101 comprises a first filter N capacitor 107 between input poles of the rectifier 101, filter inductance on a path of E: 25 alternating current supplied to the rectifier 101, and a second filter capacitor 110 N between output poles of the rectifier 101. In this exemplifying case, the filter 2 inductance comprises leakage inductance of a common-mode choke 108 and O inductance of a differential coil 109. In many cases, the leakage inductance of a common-mode choke is enough and thus a differential coil is not needed.
    As the envelope 113 has the same waveform and the same phase as the output voltage Vor and the input current of the power supply is filtered, the boost converter 102 acts as a power factor correction “PFC” circuit. As illustrated by equation 1, the switching frequency fsw varies when the output voltage Vor of the rectifier 101 varies. The variation of the switching frequency fsw spreads a frequency spectrum of disturbance voltage emitted by the boost converter 102. In a case where the input voltage Vin is direct voltage, the output voltage Vor of the rectifier 101 is constant and the switching frequency fsw is constant if the power P and the intermediate voltage Vinm are constants. The constant switching frequency fsw tends to cause peaks in the frequency spectrum of the disturbance voltage. The control system 104 comprises a controller 115 that is configured to determine whether the input voltage Vin is alternating voltage or direct voltage. The determination can be based on the waveform of the output voltage Vor of the rectifier
    101. For example, the controller 115 can be configured to compare a lowpass filtered voltage Vor to unfiltered Vor to find out whether the input voltage Vin is alternating voltage or direct voltage. The control system 104 is configured to reduce the intermediate voltage Vinm in response to a change from alternating input voltage to direct input voltage in order to reduce the switching freguency fsw of the boost converter 102 and thereby disturbances emitted by the boost converter 102 on undesired frequency areas, such as e.g. above 50 kHz. As illustrated by equation 1, the switching frequency fsw is reduced when the intermediate voltage Vinm is reduced and the power P is constant. This relationship between the switching o frequency fsw and the intermediate voltage Vinm is illustrated also by the fact that the S slope of the current of the inductor 111 is reduced during non-conduction times of 3 25 the controllable switch 105 when the intermediate voltage Vinm is reduced. The & reduced slope increases the temporal lengths Tor of non-conduction times of the E controllable switch 105 and thereby increases the temporal length Ton + Tor = 1/fsw © of switching periods when the peak value of the current of the inductor 111 is 3 unchanged i.e. the power P is unchanged. Exemplifying ways to reduce the O 30 intermediate voltage Vinm are presented below.
    In a power supply according to an exemplifying and non-limiting embodiment, the controller 115 is configured to keep the controllable switch 105 in a non-conductive state in response to a situation in which the input voltage Vin is direct voltage and greater than the output voltage Vout and a difference Vin — Vout between the input voltage and the output voltage exceeds a predetermined safety margin. In other words, the boost converter 102 is deactivated. This reduces the intermediate voltage —Vinm because the intermediate voltage Vinm Is greater than the input direct voltage Vin when the boost converter 102 is active, whereas deactivation of the boost converter 102 leads to a situation where the intermediate voltage Vinm is substantially the same as the input direct voltage Vin. In the exemplifying case illustrated in figure 1, the controller 115 is configured to deactivate the boost converter 102 via an enablement circuit 115. In a power supply according to an exemplifying and non-limiting embodiment, the controller 115 is configured to read a target value Vinmret for the intermediate voltage Vinm from a database that expresses the target value Vinm,rer as a function of the input voltage Vin with a boundary condition that the switching freguency of the boost converter 102 is below a predetermined frequency limit fswiim, and to control the boost converter 102 to drive the intermediate voltage Vinm to the target value Vinm rer. The above-mentioned database may contain for example a lookup table that returns the target value Vinm,rer When a value of the input voltage Vin is supplied as a lookup key. It is also possible that the database comprises a mathematical formula for obtaining the target value as the function of the input voltage Vin. The formula can be for example: v3 S Vinmref = TJT , (2)
    N 3 where q is a safety factor < 1.
    N I In many cases, the power P transferred by the boost converter 102 is substantially N 25 constant since the load 116 is unchanged and the output converter 103 is configured 3 to keep the output voltage Vout unchanged. The wording “substantially constant” N means that there can be a minor change in the power P because of changes in © losses when the input voltage is changed from alternating voltage to direct voltage and when the intermediate voltage is changed. It is however also possible that the controller 115 is configured to control the output converter 103 to change the above-
    mentioned power P in response to a change from alternating input voltage to direct input voltage. The power P can be e.g. reduced to enable batteries which supply the direct input voltage to operate longer. In a power supply according to an exemplifying and non-limiting embodiment, the controller 115 is configured to read the above-mentioned target value Vinmrer from a database expressing the target value Vinmrer Aas a function of i) the input voltage Vin and ii) the power P with the boundary condition that the switching frequency of the boost converter 102 is below the frequency limit fsw im The database may contain for example a lookup table that returns the target value Vinm ref when values of the input voltage Vin and the power P are supplied as a lookup key. It is also possible that the database comprises a mathematical formula, such as e.g. the formula presented in equation 2 above, for obtaining the target value Vinmyrer as the function of the input voltage Vin and the Power P. In a power supply according to an exemplifying and non-limiting embodiment, the control system 104 is configured to measure the switching frequency fsw of the boost converter 102 and to control the boost converter 102 to keep the intermediate voltage Vinm within a range where the switching frequency fsw is below the frequency limit swim, €.9. 50 kHz. For example, the controller 115 can be configured to reduce the target value Vinmrer Of the intermediate voltage Vinm as long as the switching frequency fsw is above the frequency limit fswim. In the exemplifying power supply illustrated in figure 1, the control system 104 comprises a counter 114 configured to count rising edges and/or falling edges of a control signal of the controllable switch o 105. The controller 115 is configured to estimate the switching freguency fsw based S on an output of the counter 114.
    S 0 25 The intermediate voltage Vinm can be e.g. 400 V in an exemplifying case where the - input voltage Vin is 264 Vrms alternating voltage i.e. the peak voltage is 373 Vpk and E the power is 90 W. In a case in which the above-mentioned alternating input voltage S is replaced by 240 V direct input voltage, the intermediate voltage Vinm can be < lowered to be 308 V. According to equation 1 presented earlier in this document, N 30 the switching frequency fsw is about 47 kHz in an exemplifying case where the inductance of the inductor 111 is 1.5 mH, the direct input voltage is 240 V, the intermediate voltage is 308 V, and the power P is 90 W. If the intermediate voltage Vinm were kept at 400 V, the switching frequency fsw would be about 85 kHz. The implementation of the controller 115 can be based on one or more processor circuits, each of which can be a programmable processor circuit provided with appropriate software, a dedicated hardware processor such as for example an application specific integrated circuit “ASIC”, or a configurable hardware processor such as for example a field programmable gate array “FPGA”. Furthermore, the controller 115 may comprise one or more memory devices such as e.g. random- access memory “RAM” circuits. Figure 2 shows a flowchart of a method according to an exemplifying and non- limiting embodiment for controlling a power supply that comprises: - a rectifier configured to receive input voltage, - a boost converter connected to an output of the rectifier and configured to form intermediate voltage, and - an output converter connected to an output of the boost converter and configured to convert the intermediate voltage to output voltage of the power supply. The method comprises: - driving 201 the boost converter in the critical conduction mode,
    S N 20 - determining 202 whether the input voltage of the power supply is alternating S voltage or direct voltage, the boost converter acting 203 as a power factor N correction “PFC” circuit in response to a situation which the input voltage is E alternating voltage, and 00 S - reducing 204 the intermediate voltage in order to lower switching frequency
    LO N 25 of the boost converter in response to a change from alternating input voltage N to direct input voltage.
    Furthermore, the exemplifying method illustrated in figure 2 comprises increasing 206 the intermediate voltage in response to a change from the direct input voltage back to the alternating input voltage — the YES-branch of a decision block 205. Thus, the intermediate voltage is increased back to a value used in conjunction with the alternating input voltage. In a method according to an exemplifying and non-limiting embodiment, the reduction of the intermediate voltage and the lowering the switching frequency are carried out by keeping a controllable switch of the boost converter in a non- conductive state. In this exemplifying case, the switching frequency becomes zero. This approach is applicable when the input voltage is greater than the output voltage and a difference between the input voltage and the output voltage exceeds a predetermined safety margin. In a method according to an exemplifying and non-limiting embodiment, the reduction of the intermediate voltage and the lowering of the switching frequency are carried out by reading a target value for the intermediate voltage from a database expressing the target value as a function of the input voltage so that the switching frequency is below a predetermined frequency limit, and controlling the boost converter to drive the intermediate voltage to the target value. A method according to an exemplifying and non-limiting embodiment comprises reading the target value from the database configured to express the target value as a function of i) the input voltage and ii) power delivered by the power supply so that the switching frequency of the boost converter is below the predetermined frequency S limit. 3 In a method according to an exemplifying and non-limiting embodiment, the N 25 reduction of the intermediate voltage and the lowering the switching frequency are = carried out by measuring the switching freguency and controlling the boost converter v to keep the intermediate voltage within a range where the switching freguency is 3 below the predetermined frequency limit.
    N Figure 3 shows a flowchart of a method according to an exemplifying and non- limiting embodiment for controlling an electric power supply of the kind described above. Initially, the input voltage of the power supply is alternating voltage and the boost converter is driven 301 in the critical conduction mode so that the boost converter acts 303 as a power factor correction “PFC” circuit. In response to a change from the alternating input voltage to direct input voltage — the YES-branch of a decision block 302, it is first checked in a decision block 307 whether power transferred by the power supply is below a given power limit. If the power is below the power limit — the YES-branch of the decision block 307, the disturbances are so low that there is no need for actions triggered by the change from the alternating input voltage to the direct input voltage. If the power is not below the power limit — the NO-branch of the decision block 307, it is checked in a decision block 308 — whether the direct input voltage exceeds the output voltage with at least a given safety margin. If yes — the YES-branch of the decision block 308, the boost converter is deactivated 303 by keeping the controllable switch of the boost converter in a non- conductive state. In response to a change from the direct input voltage back to the alternating input voltage — the YES-branch of a decision block 309, the boost converter is reactivated if it was deactivated, or the operation of the boost converter continues if it was not deactivated. If the direct input voltage does not exceed the output voltage with at least the given safety margin — the NO-branch of the decision block 308, the intermediate voltage prevailing at an output of the boost converter is reduced 304 in order to lower the switching frequency of the boost converter. In response to a change from the direct input voltage back to the alternating input voltage — the YES-branch of a decision block 305, the intermediate voltage is increased 306 back to a value used in conjunction with the alternating input voltage. o A data processor program according to an exemplifying and non-limiting S embodiment comprises data processor executable instructions for controlling a 3 25 programmable data processor to carry out actions related to a method according to & any of the above-described exemplifying embodiments.
    I E A data processor program according to an exemplifying and non-limiting N embodiment comprises software modules for controlling a power supply that S comprises:
    N - arectifier configured to receive input voltage,
    - a boost converter connected to an output of the rectifier and configured to form intermediate voltage, and - an output converter connected to an output of the boost converter and configured to convert the intermediate voltage to output voltage of the power supply. The above-mentioned software modules comprise data processor executable instructions for controlling a programmable data processor to: - control the boost converter to operate in the critical conduction mode, - determine whether the input voltage is alternating voltage or direct voltage, the boost converter acting as a power factor correction circuit “PFC” in response to a situation which the input voltage is alternating voltage, and - reduce the intermediate voltage prevailing at an output of the boost converter in order to lower switching frequency of the boost converter in response to a change from alternating input voltage to direct input voltage.
    The above-mentioned software modules can be e.g. subroutines or functions implemented with a programming language suitable for the programmable data processor.
    A data processor program product according to an exemplifying and non-limiting embodiment comprises a data processor readable medium encoded with a data N 20 processor program according to an embodiment of invention.
    N S A signal according to an exemplifying and non-limiting embodiment is encoded to Q carry information defining a data processor program according to an embodiment of E invention. 00 s The specific examples provided in the description given above should not be N 25 construed as limiting the applicability and/or the interpretation of the appended N claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.
    权利要求:
    Claims (15)
    [1] 1. A power supply for providing current to one or more light emitting diodes, the power supply comprising: - arectifier (101) configured to receive input voltage (Vin), - a boost converter (102) connected to an output of the rectifier and configured to form intermediate voltage (Vinm), - an output converter (103) connected to an output of the boost converter and configured to convert the intermediate voltage to output voltage (Vout) of the power supply, and - a control system (104) configured to control the boost converter to operate in a critical conduction mode and to control the output converter, wherein the control system is configured to determine whether the input voltage is alternating voltage or direct voltage, and to drive the boost converter as a power factor correction circuit in response to a situation which the input voltage is alternating voltage, characterized in that the control system is configured to reduce the intermediate voltage in order to lower switching freguency of the boost converter in response to a change from alternating input voltage to direct input voltage.
    [2] 2. Apower supply according to claim 1, wherein the control system is configured to keep a controllable switch (105) of the boost converter in a non-conductive state N 20 in response to a situation in which the input voltage is direct voltage and greater 5 than the output voltage and a difference between the input voltage and the output 2 voltage exceeds a predetermined safety margin.
    [3] N E 3. Apower supply according to claim 1, wherein the control system is configured @ to read a target value for the intermediate voltage from a database expressing the 3 25 target value as a function of the input voltage so that the switching frequency of the O boost converter is below a predetermined freguency limit, and to control the boost converter to drive the intermediate voltage to the target value.
    [4] 4. A power supply according to claim 3, wherein the control system is configured to read the target value from the database configured to express the target value as a function of i) the input voltage and ii) power delivered by the power supply so that the switching frequency of the boost converter is below the predetermined frequency — limit.
    [5] 5. Apower supply according to claim 1, wherein the control system is configured to measure the switching freguency of the boost converter and to control the boost converter to keep the intermediate voltage within a range where the switching freguency is below a predetermined freguency limit.
    [6] 6. Apower supply according to any one of claims 1-5, wherein the control system is configured to determine, based on a waveform of output voltage of the rectifier, whether the input voltage is alternating voltage or direct voltage.
    [7] 7. Apower supply according to any one of claims 1-6, wherein the rectifier (101) comprises a first filter capacitor (107) between input poles of the rectifier, filter inductance (108, 109) on a path of alternating current supplied to the rectifier, and a second filter capacitor (110) between output poles of the rectifier.
    [8] 8. A method for controlling a power supply for providing driving current to one or more light emitting diodes, the power supply comprising: - a rectifier configured to receive input voltage, o 20 - a boost converter connected to an output of the rectifier and configured to O form intermediate voltage, and
    S 0 - an output converter connected to an output of the boost converter and - configured to convert the intermediate voltage to output voltage of the power E supply,
    N 3 25 the method comprising driving (201, 301) the boost converter in a critical conduction O mode, and determining (202, 302) whether the input voltage is alternating voltage or direct voltage, the boost converter acting (203, 303) as a power factor correction circuit in response to a situation which the input voltage is alternating voltage,
    characterized in that the method comprises reducing (204, 304) the intermediate voltage in order to lower switching frequency of the boost converter in response to a change from alternating input voltage to direct input voltage.
    [9] 9. A method according to claim 8, wherein the method comprises keeping (303) acontrollable switch of the boost converter in a non-conductive state in response to a situation in which the input voltage is direct voltage and greater than the output voltage and a difference between the input voltage and the output voltage exceeds a predetermined safety margin.
    [10] 10. A method according to claim 8, wherein the method comprises reading a target value for the intermediate voltage from a database expressing the target value as a function of the input voltage so that the switching frequency of the boost converter is below a predetermined frequency limit, and controlling the boost converter to drive the intermediate voltage to the target value.
    [11] 11. A method according to claim 10, wherein the method comprises reading the target value from the database configured to express the target value as a function of i) the input voltage and ii) power delivered by the power supply so that the switching frequency of the boost converter is below the predetermined frequency limit.
    [12] 12. A method according to claim 8, wherein the method comprises measuring the switching frequency of the boost converter and controlling the boost converter to S keep the intermediate voltage within a range where the switching freguency is below O a predetermined freguency limit. 3 13. A method according to any one of claims 8-12, wherein the method comprises N determining, based on a waveform of output voltage of the rectifier, whether the E 25 input voltage is alternating voltage or direct voltage.
    [13] N 3 14. A data processor program for controlling a power supply for providing driving O current to one or more light emitting diodes, the power supply comprising: - arectifier configured to receive input voltage,
    [14] - a boost converter connected to an output of the rectifier and configured to form intermediate voltage, and - an output converter connected to an output of the boost converter and configured to convert the intermediate voltage to output voltage of the power supply, the data processor program comprising instructions for controlling a programmable data processor to: - control the boost converter to operate in a critical conduction mode, and - determine whether the input voltage is alternating voltage or direct voltage, the boost converter acting as a power factor correction circuit in response to a situation which the input voltage is alternating voltage, characterized in that the data processor program comprises instructions for controlling the programmable data processor to: - reduce the intermediate voltage in order to lower switching freguency of the boost converter in response to a change from alternating input voltage to direct input voltage.
    [15] 15. A data processor program product comprising a non-transitory processor readable medium encoded with a data processor program according to claim 16.
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    DE102010039154A1|2010-08-10|2012-02-16|Tridonic Gmbh & Co. Kg|Modulation of a PFC in DC mode|
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