WO2022233847A1

WO2022233847A1 - Driver circuit for photobiomodulation in led general lighting

Info

Publication number: WO2022233847A1
Application number: PCT/EP2022/061813
Authority: WO
Inventors: Shounak ROY
Original assignee: Silicon Hill B.V.
Priority date: 2021-05-03
Filing date: 2022-05-03
Publication date: 2022-11-10

Abstract

A driver circuit (12) for driving an LED general lighting apparatus, having a transformer with a primary winding (5) and two secondary windings (6, 7) for providing a first and second driving currents (101, 111) to an LED radiation source (10) and an LED light source (11), respectively; an energy storage circuit (23; 23a); a switching circuit (24; 24a; 24b); and a timer circuit (25) for generating one or more output signals which vary periodically over time. The switching circuit (24; 24a; 24b) is configured to switch the energy storage circuit (23; 23a) between a plurality of states during operation, including at least a charging state, a discharging state, and an idle state, in dependence on the one or more output signals of the timer circuit (25), such that the first driving current (101) is pulsed according to one or more duty cycles.

Description

DRIVER CIRCUIT FOR PHOTOBIOMODULATION IN LED GENERAL LIGHTING TECHNICAL FIELD

[0001] The invention relates generally to LED lighting, and more particularly to a driver circuit for LED lighting apparatus, an LED lighting apparatus, and a method for operating the LED lighting apparatus for delivering radiation in a non-visible spectrum sufficient to induce photobiomodulation (PBM) response.

BACKGROUND ART

LED driver circuits [0002] An LED driver circuit is an electrical circuit for powering an LED lamp. This driver circuit converts the current from a power source (e.g. AC current from the main power supply) to a regulated / rectified current suitable for LEDs. There are primarily two types of known LED driver circuits, namely isolated LED driver circuits and non-isolated LED driver circuits. [0003] In an isolated LED driver, the input (AC side) is separated from the output by a transformer which provides galvanic isolation, i.e. there is no direct electrical conduction path between the AC side and LED side, while it is still possible to exchange electrical energy between the windings of the transformer based on induction. This process enables the electrical energy to be transferred without direct electrical connection to the ground, thereby reducing the risk of electrical shock and increases the safety of application. A disadvantages of isolated driver is higher cost, and an additional energy storage circuit may be needed.

[0004] An isolated LED driver typically comprises a front end circuit for receiving a current power source (on the AC side) and a load end circuit for supplying a rectified current to LEDs (on the LED side). The front end circuit usually comprises various components, such as safety fuses, rectifiers, EMI filters, surge protection, etc. The load end circuit usually also comprises various components, such as rectifiers, energy storage capacitor, etc. [0005] In a non-isolated LED driver, the AC side and the LED side are electrically connected, e.g. via an inductor. Such non-isolated LED driver is typically cheaper (and typically does not require energy storage) but entails a higher safety risk.

[0006] A non-isolated LED driver also typically comprises a front end circuit for receiving a current power source (on the AC side) and a load end circuit for supplying a rectified current to LEDs (on the LED side). While exhibiting several differences, these circuits typically comprise similar components as those in isolated LED drivers.

Photobiomodulation (PBM)

[0007] Photobiomodulation (PBM) involves irradiating a living organism at certain energy/power levels to induce biological or biochemical responses. The irradiation may be in the visible spectrum, such as red light, or in the non-visible spectrum, such as infrared (IR). Research shows there are medical benefits of employing PBM therapy to treat physical and psychological symptoms.

[0008] In the prior art, the idea of incorporating PBM into general lighting has been proposed. A lighting apparatus for emitting stable visible light and additionally emitting pulsed (PBM) radiation is described in WO 2020/119965, herewith incorporated by reference in its entirety. By driving a radiation source with a pulse instead of a continuous wave (or nearly continuous wave) signal, it is possible to boost the peak power during the pulse to achieve a PBM response. This concept thus allows the general lighting apparatus to emit a sufficient amount of power to enable a certain power density at a certain distance that may induce PBM responses. The general lighting apparatus, such as a lamp or overhead lighting, is easy to use and commonly available, and therefore the need for medical specialists to administer PBM radiation is greatly reduced, which amounts to a significant saving of time and financial resources of the recipient of PBM radiation.

[0009] One possible approach of implementing this concept in an LED lamp is to use two separate drivers. A first driver can be used to power white LEDs to produce a substantially constant light for the general lighting purpose, and a second driver can be used to power infrared/red LEDs in a duty cycle to generate pulsed driving current in order to induce PBM responses. This implementation is simple, but it entails higher costs because of the use of two drivers. Leaving aside the need for additional circuits for generating pulsed PBM radiation, a double amount of components in the drivers (e.g. in the front end circuits and load end circuits) will be needed compared to a typical LED lamp, thereby basically doubling the costs.

SUMMARY OF THE INVENTION

[0010] It would be desirable to provide a single LED driver circuit that not only offers good general lighting experience (i.e. stable light with minimum disturbance) but also powers an additional LED radiation source (e.g. infrared) to provide PBM benefit.

[0011] The first aspect of the invention relates to a driver circuit for driving an LED general lighting apparatus according to claim 1.

[0012] The driver circuit comprises a transformer, comprising a primary winding, a first secondary winding and a second secondary winding (also known as tertiary winding). Preferably, each winding is galvanically isolated from other windings. The primary winding is arranged to transfer electrical energy from a power source to the first secondary winding and to the second secondary winding. The driver circuit further comprises: first terminals electrically connected (e.g. via a switch that can be opened or closed, etc) to the first secondary winding for providing a first driving current to an LED radiation source based on the energy transferred from the primary winding to the first secondary winding; second terminals electrically connected to the second secondary winding for providing a second driving current to an LED light source based on the energy transferred from the primary winding to the second secondary winding; an energy storage circuit for storing electrical energy; a switching circuit connected to control a first electrical connection between the first secondary winding and the energy storage circuit, and to control a second electrical connection between the energy storage circuit and at least one of the first terminals; and a timer circuit for generating one or more output signals which vary periodically over time. The switching circuit is configured to switch the energy storage circuit between a plurality of states during operation, including at least a charging state and a discharging state.

[0013] In the charging state, the energy storage circuit is electrically connected to receive a current from the first secondary winding (e.g. by using a first switch that is closed at least during a part of the duration of charging state, such closed during the entire duration of the charging state or switching between connection and disconnection with respect to the first secondary winding at a frequency, e.g. at or above 200 Hz, 500 Hz, 1 kHz, 5 kHz, 10 kHz, or 20 kHz) and is electrically disconnected from the at least one of the first terminals, so that the energy storage circuit is connected to receive electrical current via the first secondary winding. In the discharging state, the energy storage circuit is electrically disconnected from the first secondary winding, and is electrically connected to supply the first driving current from the energy storage circuit to the first terminals (e.g. by using a second switch that is closed at least during a part of the duration of discharging state, such as closed during the entire duration of the discharging state or switching between connection and disconnection with respect to at least one of the first terminals at a frequency, e.g. at or above 200 Hz, 500 Hz, 1 kHz, 5 kHz, 10 kHz, or 20 kHz), so that first driving current is supplied to LED radiation source (via the first terminals) by discharging the energy storage circuit. The switching circuit is configured to switch between the plurality of states in dependence on the one or more output signals of the timer circuit, such that the first driving current is pulsed according to one or more duty cycles.

[0014] In this way, electrical energy can be stored in the energy storage circuit during the charging state, and subsequently discharged to supply the first driving current in a discharging state. By switching at least between these states using the timer circuit, a pulsed first driving current suitable for PBM implementation can be generated. Moreover, by alternating the electrical connection and disconnection with respect to the first secondary winding and at least one of the first terminals respectively, the energy storage circuit can be quickly charged, thereby limiting the charging time that could otherwise entail a disturbance in the white LEDs (due to coupling of the windings in the transformer). The above measures regarding the charging state and discharging state make it possible to use one or more other non-charging states (e.g. such that the duration of the charging state is less than 10% during a few seconds of operation) when charging is not needed. For example, an idle state may be used during the majority of the operation, in which the energy storage circuit is electrically disconnected from both the first secondary winding and the at least one of the first terminals.

[0015] In an embodiment, the energy storage circuit comprises a capacitor connected across the first secondary winding, and the switching circuit comprises a first switch and a second switch, wherein the capacitor is disconnected from the transformer when the first switch is open, and is disconnected from the at least one of the first terminals when the second switch is open. [0016] In an embodiment, in the discharging state, the first driving current (101) is switched on and off at a frequency at or above 200 Hz, preferably at or above 500 Hz, 1 kHz, 5 kHz, or 10 kHz, and more preferably at or above 20 kHz (e.g. by closing and opening the second switch at said frequency); and/or in the charging state, a charging current is delivered to the energy storage circuit at a frequency at or above 200 Hz, preferably at or above 500 Hz, 1 kHz, 5 kHz, or 10 kHz, and more preferably at or above 20 kHz (e.g. by closing and opening the first switch at said frequency). By switching one or both of these switches at a high frequency, it is observed that the system performance is improved. [0017] The present invention also enables an integrated control system in e.g. a smart lamp. Thanks to the single driver and many shared electrical components in the driver, a control circuit (e.g. in an integrated circuit) may be used to monitor and control both the general lighting and the PBM radiation.

[0018] In an embodiment, the driver circuit further comprises a control circuit (with which the timer circuit may be integrated) and one or more sensor circuits (which may also be integrated with the control circuit) and/or a memory, so as to monitor and control both the first driving current and the second driving current based on a sensed condition of the environment or user inputs. For example, in the winter the days are short and the Sun is low in the sky. This influences both the general lighting aspect and the PBM aspect. The control circuit may be used to adjust both aspects accordingly.

[0019] A second aspect of the invention relates to a lighting arrangement for general lighting, comprising, the driver circuit according to the embodiments in the first aspect of the invention, an LED radiation source connected across the first terminals, adapted to emit radiation in a predetermined spectrum in the range of e.g. 760-1400nm, and an LED light source adapted to emit visible light for general lighting.

[0020] A third aspect of the invention relates to a method for operating the light arrangement, such as the arrangement according to the second aspect. The method comprises switching between the plurality of states, including the charging state, the discharging state and the idle state (e.g. in accordance with a predetermined pattern based on the one or more outputs of the timer circuit), so that the first driving current is pulsed and has a duty cycle of not greater than 20%.

[0021] In an embodiment, the method further comprises: during start-up of the light arrangement (e.g. when a user turns on the lamp using the switch on the wall), operating at least in an start-up state, in which the first secondary winding is connected to supply current to both the energy storage circuit and to the first terminals, so that the energy storage circuit is being charged and the first driving current is supplied to the LED radiation source. [0022] In an embodiment, during the start-up of the light arrangement, the switching circuit switches between the start-up state and the charging state, so that the first driving current is pulsed and has a duty cycle of not greater than 20%.

[0023] It is to be noted that the meaning of the word "light" alone in the present disclosure is not limited to visible light. The word "light" in the present disclosure may include electromagnetic radiation outside the visible light spectrum. By the same token, it is also to be noted that terms such as "optical power" are not limited to power of visible light.

[0024] In the context of this document, "general lighting" means that it is not special- purpose illumination (e.g., killing bacteria, growing plants, detecting cracks, medical treatment, tanning) other than just illuminating to assist human vision. It means that when a space is too dark for people to work/live in, and its illumination level must be raised, the embodiments of this document can be used for the purpose of increasing the illumination level of that space such that it is convenient for people to live and work in that space. [0025] Visible light may refer to a color point in a CIE XYZ color space, which color point has a distance less than 10 Standard Deviation Color Matching (SDCM) to a black body line in said color space, preferably within 7 SDCM. Persons ordinarily skilled in the art understand that SDCM has the same meaning as a MacAdam ellipse. Visible light with a color point within 7 SDCM from a point on the blackbody line, preferably from a point between 1700K and 6500K, may still be considered by naked human eye as relatively white and may be suitable for general, task or accent lighting purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Fig. 1 shows an embodiment of the driver circuit 12 according to the present invention.

[0027] Fig. 2 shows a more detailed embodiment of the present invention, using a simple circuit with a capacitor 23 a and two switches 24a and 24b.

[0028] Fig. 3 shows an embodiment of a method for operating the driver circuit (and thereby the light arrangement) according to the present invention. [0029] Fig. 4 shows another embodiment of the present invention, which implements an integrated control system for both general lighting and PBM, e.g. in a smart lamp.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0030] Fig. 1 shows an embodiment of the driver circuit 12 according to the present invention, using a transformer comprising three windings 5, 6, 7, an energy storage circuit 13, a switching circuit 14, and a timer circuit 15.

[0031] The LED radiation source 10 may be adapted to emit radiation in a predetermined spectrum that includes a non-visible spectrum (e.g. in the range of 760- 1400nm) upon receiving or being energized by a driving signal, such as the first driving current 101.

[0032] In the embodiment shown, the primary winding 5 of the transformer is connected to transfer electrical energy from a power source (e.g. via a front end circuit 21) to the first secondary winding 6 and the second secondary winding 7 respectively. The first secondary winding 6 is used to supply a first driving current 101 to an LED radiation source 10 (comprising a plurality of LEDs 70 generating radiation in a predefined spectrum, e.g. red or infrared) via first terminals 8a, 8b, and the second secondary winding 7 is used to supply a second driving current 111 to an LED light source 11 (comprising a plurality of LEDs 71 for general lighting purpose) via a load end circuit 22 and second terminals 9a, 9b. The primary winding 5 is preferably galvanically isolated from the two secondary windings 6 and 7 to provide an isolated driver. In addition, the two secondary windings 6 and 7 are preferably also galvanically isolated from each other, to ensure that the first driving current 101 does not flow through the LED light source 11 and vice versa.

[0033] The energy storage circuit 23 is arranged to store electrical energy and may comprise one or more capacitors. The states of the energy storage circuit 23 are controlled by the switching circuit 24. The basic operation is as follows: electrical energy is being stored in the energy storage circuit during a charging state, so that the stored energy can be discharged to supply the first driving current 101 in a discharging state.

[0034] During the charging of the energy storage circuit 23, the coupling between the windings 5, 6, 7 of the transformer can cause disturbance in the second driving current 111 for the general lighting (LED light source 11). It is therefore desirable that the charging time is limited. This can be done by a proper configuration of the electrical connections in the charging state and discharging state. An example is shown in Fig. 2. [0035] Fig. 2 shows an embodiment of the present invention, in which the switching circuit 24 comprises a first switch 24a and a second switch 24b, and the energy storage circuit comprises a capacitor 23a connected across the LED radiation source 10.

[0036] The first switch 24a controls the electrical connection between the capacitor 23a and the transformer. When the first switch 24a is open, the capacitor 23a is electrically disconnected from the transformer. When the first switch 24a is closed, the capacitor 23a is electrically connected to the transformer. The second switch 24b controls the electrical connection between the capacitor 24a and one of the first terminals 8a. When the second switch 24b is open, the capacitor 23 a is electrically disconnected from the terminal 8a. When the second switch 24b is closed, the capacitor 23a is electrically connected to both terminals 8a and 8b. The combination of the first and second switches 24a and 24b define at least four states. When the first switch 24a is closed (or switching at a frequency at or above 200 Hz, more preferably at or above 500 Hz, 1 kHz, 5 kHz, 10 kHz, or 20 kHz) and the second switch 24b is open, the capacitor 23a is being charged (the charging state). When the first switch 24a is open and the second switch 24b is closed (or switching at a frequency at or above 200 Hz, preferably at or above 500 Hz, 1 kHz, 5 kHz, or 10 kHz, and more preferably at or above 20 kHz), the capacitor 23a is being discharged (the discharging state). When both switches are open, the energy storage circuit is in the idle state.

[0037] In some embodiments there can be a time in which both switches are closed (or switching at or above one of said frequencies), i.e. the energy storage circuit is (at least during part of this operation) electrically connected to both the first secondary winding and the first terminals (a fourth state). This mode may be used during start-up of the lamp (and may be referred to as a start-up state). In this way, electrical energy can be directly given to the capacitor 23a and the LED radiation source 11 in parallel. During start-ups users generally care less about disturbance in the light, so this period can be utilized to give the capacitor 23 a (or energy storage circuit 23 in general) sufficient charge. Once the energy storage circuit 23 is sufficiently charged, the normal operation described above can begin. This gives an advantage that the subsequent switching between the charging state and non charging states (e.g. discharging state) only needs to maintain the balance of the charge that the capacitor 23 a already holds, thereby minimizing the time needed for charging during normal operation of the lamp. In addition, by utilizing the start-up time to store sufficient charge in the capacitor, a capacitor with a larger capacitance may be used to enable a slower discharging. This makes it possible to control the first driving current 101 so that the pulse has a desired shape (e.g. substantially rectangular).

[0038] The first switch 24a and second switch 24b may each be implemented as an electromechanical relay or semiconductor switch such as a transistor or MOSFET or the like. In this disclosure the terms “open” and “close” encompass on/off switching such as produced by an electromechanical relay, or turning off and turning on of a transistor or MOSFET or the like, i.e. variation between an “on” or connected state with relatively low impedance equivalent to a closed switch, to an “off’ or disconnected state with relatively high impedance equivalent to an open switch.

[0039] In the embodiment where the first switch 23a and/or second switch 24b switch at high frequency (e.g. at or above 20kHz) as described above, a semiconductor switch is preferred, for example a GaN switch to reduce the size the losses in the switch.

[0040] The shape of the pulse is not particularly limited. In an embodiment, the pulse may have a rectangular or triangular shape. Other shapes are also possible, such as sinusoids and sawtooth. A combination of pulses with different shapes are also possible. [0041] In an embodiment, the pulse duration of the first driving current 101 is in the range of about 0.05-500ms. In an embodiment, the pulse duration may be in the ranges of about 0.1-lOOms or about 0.5-20ms or about l-20ms or about 4-10ms. Other ranges for the pulse duration, such as 1-40 ms, 4-40 ms and 8-30 ms, are also possible. Depending on the types of PBM responses desired to be induced, other values or ranges of the pulse duration are also possible, such as 5 ms, 13.4 ms, 27.78 ms; 16 ms, 8 ms and 4 ms each having a respective pulse frequency of 50 Hz, 100 Hz and 200 Hz; and 8 ms and 40ms. These values and ranges may be particularly suitable for achieving certain types of medical benefits. [0042] The first driving current 101 is pulsed and may have a pulse frequency (inverse of pulse period) in the range of about 0.01-10000 Hz. In an embodiment, the pulse frequency may be in the ranges of about 0.1-2500 Hz or about 1-160 Hz. Other ranges for the pulse frequency are also possible.

[0043] A parameter related to pulse duration and pulse period (frequency) is duty cycle. The duty cycle describes the ratio between the period of a pulse and the period between pulses, and is usually expressed as a percentage. The duty cycle may be defined as the pulse duration divided by the pulse period. In an embodiment, the radiation 100 may have a duty cycle of not greater than 50%, 40% or 30%, and preferably has a duty cycle of not greater than 20%. Other maximum duty cycle values are also possible, such as 15%, 10%, 5%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05% and 0.01%. In an embodiment, more than one duty cycles may be used; they may also be used altematingly. Variable duty cycles directly allow different dosage over different times, especially if combined with variable frequencies. For certain types of radiation sources whose driving strength are related to the duty cycle (because of, e.g., thermal constraints), variable duty cycles may additionally allow different power densities over different time by providing different cooling periods. [0044] Fig. 3 shows an embodiment of the operation of the driver circuit (e.g. the circuit in Fig. 2) according to the present invention.

[0045] In the embodiment shown, Curve 30 represents the first driving current 101, and curve 32 represents the second driving current 111, which is basically a rectified AC current in this exemplified embodiment. As illustrated, the first driving current 101 represented as curve 30 is pulsed, while the second driving current 111 represented as curve 32 is not. The non-pulsed second driving current 111 may help the light source 11 to provide stable visible light suitable for general lighting. The rectified AC current may have a frequency of, e.g., 100 or 120Hz; such driving current may be suitable for visible light sources such as an incandescent lamp.

[0046] In the embodiment shown in Fig. 3, the first driving current 101 has a pulse duration of T_a and a pulse period T. The duty cycle is T_a divided by T. During the pulse, the energy storage circuit 23 is in the discharging state (switch 24a is open), such that the radiation source 10 is operated at peak emission. Switch 24b may be closed during this period, or switch at a high frequency during this period (which may be based on another duty cycle and may have a frequency of e.g. 20 kHz); in between the pulses, the energy storage circuit 23 is in other states, such that the LED radiation source 10 is turned off. During periods Tbi and Tb2, the energy storage circuit 23 is in the idle state (both switches 24a and 24b are open). During period T_c, the energy storage circuit 23 is in the charging state (switch 24b is open). As can be seen, during this period the charging only causes a small disturbance to the (white) LED light (shown in Arrows A). Switch 24a may operate based on at least one duty cycle T_c divided by T_a+ Tbi + Tb2 + T_c and may be closed during this period, or switches at a high frequency (which may be based on another duty cycle and may have a frequency of e.g. at or above 500 Hz). It is observed that such switching surprisingly not only further reduces the disturbance to the general lighting but also charges the energy storage circuit 23 faster.

[0047] Fig. 4 shows an embodiment of an integrated control system for both general lighting and PBM implementation. [0048] In the embodiment shown, the timer circuit is integrated in a control circuit

25a, which may be embodied in an integrated circuit (IC). In addition to the switching circuit 24 (e.g. the first and second switches), the control circuit 25a is further configured to control other parts of the driver circuit 12, such as the front end circuit 21 (for common functions of general lighting and PBM radiation) and the load end circuit 22 for controlling the LED (general) light source 11. The control circuit 25a may include a microprocessor, or may use one or more ASICs or FPGAs and may further include one or more sensor circuits and/or memory (not shown), so as to monitor and control one integrated system for both the first driving current 101 and the second driving current 102 based on one or more sensed conditions of the environment (e.g. time, season, sound, temperature, etc) and/or data stored in the memory and/or user inputs.

[0049] Preferably, the driver circuit 12 further comprises an optional optocoupler 26 for receiving and relaying control signals between the control circuit 25 a and the front end circuit 21. In this way, a good isolation between the front end circuit 21 from the load ends can be maintained.

Claims

Claims:

1. A driver circuit (12) for driving an LED general lighting apparatus, comprising:

- a transformer, comprising a primary winding (5), a first secondary winding (6) and a second secondary winding (7), wherein the primary winding (5) is arranged to transfer electrical energy from a power source to the first secondary winding (6) and to the second secondary winding (7);

- first terminals (8a, 8b) electrically connected to the first secondary winding (6) for providing a first driving current (101) to an LED radiation source (10) based on the energy transferred from the primary winding (5) to the first secondary winding (6);

- second terminals (9a, 9b) electrically connected to the second secondary winding (7) for providing a second driving current (111) to an LED light source (11) based on the energy transferred from the primary winding (5) to the second secondary winding (7);

- an energy storage circuit (23; 23a) for storing electrical energy;

- a switching circuit (24; 24a; 24b) connected to control a first electrical connection between the first secondary winding (6) and the energy storage circuit (23; 23a), and to control a second electrical connection between the energy storage circuit (23; 23a) and at least one of the first terminals (8a, 8b); and

- a timer circuit (25) for generating one or more output signals which vary periodically over time, wherein the switching circuit (24; 24a; 24b) is configured to switch the energy storage circuit (23; 23a) between a plurality of states during operation, including at least:

- a charging state, in which the energy storage circuit is electrically connected to receive a current from the first secondary winding (6) and is electrically disconnected from the at least one first terminal (8a, 8b), so that the energy storage circuit is connected to receive electrical current via the first secondary winding (6);

- a discharging state, in which the energy storage circuit is electrically disconnected from the first secondary winding (6), and is electrically connected to supply the first driving current (101) from the energy storage circuit (23, 23a) to the first terminals (8a, 8b); and

- an idle state, in which the energy storage circuit is electrically disconnected from both the first secondary winding (6) and the at least one first terminal (8a, 8b), wherein the switching circuit (24; 24a; 24b) is configured to switch between the plurality of states, including the charging state, the discharging state and the idle state, in dependence on the one or more output signals of the timer circuit (25), such that the first driving current (101) is pulsed according to one or more duty cycles.

2. A driver circuit (12) according to claim 1, wherein the energy storage circuit (23) comprises a capacitor (13a) connected across the first secondary winding (6), and the switching circuit (24) comprises a first switch (24a) and a second switch (24b), wherein the capacitor is disconnected from the transformer when the first switch (24a) is open, and is disconnected from the at least one of the first terminals (8a, 8b) when the second switch (24b) is open.

3. A driver circuit (12) according to claim 1 or 2, wherein in the discharging state, the first driving current (101) is switched on and off at a frequency at or above 200 Hz, and/or in the charging state, a charging current is delivered to the energy storage circuit at a frequency at or above 200 Hz.

4. A driver circuit (12) according to any of the preceding claims, further comprising a control circuit (25a) and one or more sensor circuits and/or a memory, so as to monitor and control both the first driving current (101) and the second driving current (111) based on a sensed condition of the environment and/or data stored in the memory and/or user inputs.

5. A lighting arrangement for general lighting, comprising:

- the driver circuit (12) according to any of the preceding claims;

- an LED radiation source (10) connected across the first terminals (8a, 8b), adapted to emit radiation (100) in a predetermined spectrum; and

- an LED light source (11) adapted to emit visible light (110) for general lighting.

6. A method for operating the light arrangement according to claim 5, comprising:

- switching between the plurality of states, including the charging state, the discharging state and the idle state, so that the first driving current (101) is pulsed and has a duty cycle of not greater than 20%.

7. A method according to claim 6, further comprising:

- during start-up of the light arrangement, operating at least in an start-up state, in which the first secondary winding (6) is connected to supply current to both the energy storage circuit and to the first terminals (8a, 8b), so that the energy storage circuit (23) is being charged and the first driving current (101) is supplied to the LED radiation source (10).

8. A method according to claim 7, wherein, during the start-up of the light arrangement, the switching circuit switches between the start-up state and the charging state, so that the first driving current (101) is pulsed and has a duty cycle of not greater than 20%.